Idle Mixture Theory, Adjustment Screws, and Bypass Holes

Warning! Hornets nest about to be kicked... 8O

I claim that if the carbs are working properly, the setting of the idle mixture screw should have virtually no impact on the air-fuel ratios at any throttle position other than almost dead closed idle.

If you look very closely into the butterfly end of the carbs, you'll see that there is more than one tiny hole in the roof of the carbs. My Mikunis have a total of four and here's what they look like with the butterfly held open.



The literature refers to hole closest to the engine as the "pilot outlet" and refers to the other three collectively as the "bypass" hole. Note that all four of those holes connect internally to the pilot circuit, but the pilot outlet is the only one metered by the idle mixture screw. The bypass hole(s) connect directly to the pilot air and fuel jets with no metering by the pilot screw.



Why is this so important? Because when the butterfly is closed (like it should be at idle) the only hole exposed to intake vacuum is the pilot outlet hole. The bypass holes don't do anything because they are blocked off by the butterfly and do not see any vacuum.



Hence, at idle with the butterflies closed, the pilot screw can be used to control the fuel ratio. However, as you open the butterfly and transition away from idle, you progressively expose the bypass holes:



First one, then two, and eventually all three of the bypass holes are exposed and supplying fuel. And since the pilot outlet is metered by the mixture screw while these three holes are NOT, the pilot hole will get virtually no fuel. Once the butterfly is cracked open enough to expose the bypass holes to the same vacuum as the pilot outlet, there's no differential pressure to pull fuel past the restriction presented by the pilot screw. Remember... they're all connected to the exact same place upstream.

And since I've already kicked the nest... I also claim that the bypass holes, not the pilot outlet, are responsible for supplying off idle fuel transitioning to the main jet. And since they are not metered by the pilot screw, no adjustment is possible.

If you find that you need to use the idle mixture screws to get your bike to run right at any place other than idle, then you've got problems elsewhere. Clogged bypass holes... clogged emulsion tube air inlets... leaking throttle shaft seals... something else.

Also, if you find that you've got to have the butterflies open far enough to expose the bypass holes (edit: not screws) just to get your bike to idle, then again, you've got problems elsewhere.

OK... I'm ready... Let the stinging begin? :lol:

Burnarr

 

Wow.
Instant sticky.
Great pics.
I hope you are right, because it makes sense to me.

 

Hmm I love a good debate and I see your points but have a couple of questions:

1) If Idle is full closed butterflys how come the idle adjust screw exists at all? Seems to me it would not make any sense to have it in that case. I contend Idle is actually the butterflys open - very slightly but not fully closed - therefore the idle adjust is able to adjust the idle up and down by controlling that gap.

2) If the contribution controlled by the mixture screw is negligible at off idle speeds how come the color of the plugs change when you adjust the mixture screws showing a fuel mix change at those RPMs? While it may be minor I agree, I don't see how we can say negligible when it causes a demonstrable difference in the fuel mix.

Great pics by the way and well stated position. I hope to learn a lot from the discourse that I'm sure will follow....

 

As Rick stated in my thread (compression verification):

The pilot mixture is the supplemental fuel source to the main, off idle.

Without it - the bike will always run lean off idle, with too much in the pilot screw, you run rich. Hence Bill's need for an answer as to why the plugs change color.

I myself must have some really clogged passages, but none of which are CLOGGED fully.

 

I mostly agree with you, with the following points:

The pilot mixture screw controls 1 of the four orifices supplied by the pilot system. When the other 3 come on line they reduce the impact of the screw setting, but they do not eliminate it. Hence opening that screw will effect the mixture off idle, but very little as the throttle goes ahead and opens. I will agree though that once the rpms climb off idle it doesn't do much.

You do bring up a good point though: If the butterfly isn't darn near closed that pilot screw will have very little discernible effect on the mixture. This means that if one or more cylinders isn't pulling it's share of the load the butterflies will be so far open that colortuning is impossible. Also, will be the same problem if out of sync.

So, for those of you colortuning and not seeing the screw have any effect you need to make sure that you are at 1000RPM or less and all 4 are firing.

Oh, also if the plugs don't read right at high rpm and load twiddling the mixture screws is a waste of time. Better to look at the passages, jets and float levels.

 

Yeah, bad choice of words on my part... Sorry about that. I should have said almost dead closed using the idle speed knob to position the butterflies juuuussst the tiniest smidge off dead closed. Just enough contact that I could see a tiny bit of light getting around the butterflies in some areas, but not enough to expose any of the bypass holes.

I just put my carbs back on my bike and I set the big idle knob to no more than a half turn after it just contacted the linkage and my idle is rock solid at 1100 RPM. All four cylinders are firing and idle is smooth and strong.

I do wonder though... I wonder if I could crank my idle knob all the way off and have the bike still run. The butterflies aren't an absolute perfect seal in the carb bores and even with them aligned as well as possible, there's still some leakage around the edges in spots. I wonder if that leakage combined with what the engine can suck through the pilot air jet would be enough? :?:

If the bypass holes are clogged then the pilot screw adjustment would have an affect at any throttle position.

Also, with no load on the engine, running while sitting still in neutral, I bet you can reach 2000 or 3000 RPM and you're probably not into the throttle far enough to even expose the third bypass hole. In that case, yes, you're still running off the pilot circuit, including some measurable contribution from the pilot hole.

Because of engine loading considerations, RPM isn't a very good descriptive parameter for this discussion though. A better parameter is "throttle plate angle" or "throttle shaft rotation". Why? Because I don't know what RPM my bike will reach with five degrees of throttle shaft rotation under no load conditions, and I also don't know how close yours would be to mine. So the RPMs aren't what's important here. The throttle position beyond which the bypass holes are exposed is the important parameter. The "RPMs that throttle position will cause" is highly dependant on load conditions, engine quality, temperature, gas quality, air density, phase of the moon......... Does that make sense?

Under load while riding is a completely different situation though. If you come back to the garage after a 20 mile bike ride and pull your plugs, only to find that they are all white from running hot and lean... There's no amount of idle mixture screw adjustment that's going to fix that. You've got problems elsewhere. 8O

Burnarr

 

I just edited my original post to "almost" dead closed idle....

 

The reason I chose RPM is that these are constant velocity carburetors. The slide acts like a second throttle. You can see on the bench that with the butterfly wide open there is very little opening to the throat at 0 rpm.

So, the instant you snap the throttle wide open all the fuel still comes from the pilot circuit. The needle jet doesn't really come on until the engine starts pumping enough air to lift the slide.

The snapping open of the throttle tends to make the mixture lean. If the idle is already too lean this can cause the engine to stumble until the needle jet starts to come on. That's why the focus on the pilot mixture screw for stumble coming off idle.

 

I contend that if the vacuum seen by all of those holes is the same, then there will be NO flow out the pilot hole.

Let me put it another way... All four of those holes are connected together at the supply side. The only difference between them is where they are located and the fact that one of them has a restriction between it and it's supply.

If you put the same vacuum on the downstream side of all four of them, physics dictates that the one with the restriction will not be able to steal any flow from the ones that to not have a restriction. There's no force for the fuel to "climb the hill" past the metering restriction.

I guess the question is... "How far must you open the throttle before the innermost bypass hole sees the same vacuum as the pilot hole?"

Burnarr

 

AHH the plot thickens. This is a great discussion.

I agree about the WHITE lean but I know from experience that with a plug chop under load I can adjust my mix to dial it in. Granted it will be a minor contribution but not negligible as it does have an effect.

You can not tune out critically lean with the mix screws - we agree there.

 

Wow, I was going to write almost the exact same thing (but nowhere near as pleasantly) late last night, even typed it all out, and then thought to myself, "why bother"? Let those who choose to "believe" believe what they want, and what comforts them, or makes them feel proud; after all, who cares about science, facts, and reality....that's not meaningful in today's world anyway.

Doug, I'll point this out one last time and then shut up:

a) If you require 6 turns out on your idle screws, then there is something fundamentally wrong, somewhere else, in your carbs or engines or ???? that no amount of manipulation of the idle screws, nor plug chops, are going to detect nor fix.

b) you're going down the wrong path of inquiry and exploration in trying to fix your problem, and that path will make things worse.

The main fuel circuit supplies up to 12 times more fuel under high rpm, high engine load coditions than the pilot circuit provides or even could provide. That a basic fact of math, physics, and geometry. And the amount of air that either the pilot or the main fuel circuits "use" or contribute to the overall volume of air used by the engine (via the "air jets") is so negligible in relation to how much air the engine passes through the throats as to not even being worth counting.

How and where some people develop their theories is beyond me, but as Kurt Vonnegaut used to say, some people's motto seems to be "In Nonsense Is Strength".


To all others, I realize that perfection in the basics of blocking and tackling isn't real sexy, but it's actually how the really successful people operate and produce positive results.

 

the holes don't have to be on the engine side of the butterfly valve to see vacuum as the air comes to the opening it picks up speed and looses pressure
so they may be passing fuel before the valve gets to them
the hole closest to the valve would have the most effect on the mixture since it has the lowest pressure but just because the first hole has a restriction doesn't mean it passes no fuel , it just passes less

 

That's what I suspect. :lol:

My Mikunis are surgically clean inside.
I've got new seals and O-rings everywhere.
My float levels are right on spec.
My pilot screws are 2 1/2 turns out from fully seated.
And my idle speed knob is one RCH into contacting the #3 linkage.

My carbs work flawlessly. Go figure. :wink:

 

All four of those holes are in a smooth non-diametrically changing part of the carb bore.

I can guarantee you that with the throttle opening at 90 degrees they will all be seeing the exact same vacuum to within a level of accuracy that neither you or I possibly care about.

The only thing that can cause a pressure differential in that area of the carb is the butterfly plate. The slider venturi is well before this area.

 

I have new seals o rings etc everywhere as well, even silicon greased them.

The bodies got soaked in dip, but I don't think I much through the ports.

So that is probably my issue. That's why I think the seafoam in my gas started giving me slightly more positive results.

 

Hey I'll freely admit I don't KNOW the right answer - I have been asking this question for a while myself and trying to learn.

What I do know is I can effect the plug coloration under load so how come?

This is a great discussion, some ideas will be proven wrong some right and some folks will never be convinced one way or the other.

BUT none the less I think it's a discussion worth having.

 

agreed.

 

The Mikuni's are totally different from Hitachi's.

The Hitachi Carbs are Cast differently and Drilled differently.
The Mikuni's draw Pilot and Main AIR from External Ports on the Outside Ring of the Intake Venturi.
The Hitachi Carbs draw Pilot and Main AIR from Internally drilled Ports (Some under a limiting cover.)
Some of those holes you show on the Mikuni Carbs do not exist on the Hitachi's.

The discussion of Supplemental RICHNESS and the CONSTANT Supply of Fuel through the Pilot Mixture Screw Ports is limited to Hitachi Carbs.

The Supplemental Richness of the Pilot Mixture Settings determines the GROSS Air~Fuel Mixture and whether or not you are Rich or Lean.

I cannot say from looking at the photographs if those Mikuni Carbs are the so-called "Racing Carbs" or the ones that were used on "California" Bikes which have an additional vacuum and intake Ports to allow auxiliary Exhaust Recirculation to reduce emissions.

 

Haha!! No... Those pics are from your run-of-the mill stock Pennsylvania grade Mikunis. No Cali racing carbs in my stable. :lol: If you're questioning the existence of the bypass hole(s), then just take a look at the 550 service manual. The holes are clearly shown and labeled on the cutaway in the carb section.

As for the Hitachi's being so totally different, I disagree. The basic castings of the Hitachi's are clearly different, but the operational concepts look absolutely identical to me.

That's not quite right...

The Mikunis do NOT draw pilot air from the venturi ring. The Mikuni pilot air jet is up under the slider piston diaphragm just like the Hitachi's. In fact, the only difference between the two is that the Mikuni's have the main air jet out there on the venturi ring while the Hitachi's put both the main air jet and the pilot air jet up under the slider diaphragm. That side of the diaphragm is at atmospheric, so there shouldn't be any functional difference though.

I don't have a set of Hitachi's here for good photos of the are in question, but again, I believe they operate exactly the same. From the pic heavy Hitachi thread (http://www.xjbikes.com/Forums/viewtopic/t=3649.html) here's a cutaway diagram of the Hitachi's. Note the location of the Hitachi's bypass hole on the diagram and also note that the bypass hole is upstream of the pilot screw just like the Mikunis:



From the same thread, here's a shot down the outlet of the Hitachi's:



Hard to tell with all the dirt specs in there and the butterflies closed, but I think I can see the pilot outlet and just a tiny sliver of a bypass hole that isn't quite completely covered by the almost completely closed butterfly.

Looks functionally identical to me... You got a better pic of the pilot area on a clean Hitachi so we can tell for sure?

Burnarr

 

That's easy... Because all carbs are open loop compromises.

The human race is yet to create a carb that can supply the exact perfect correct mixture for all varying operating conditions. You can tune great for one RPM and one set of loading conditions, but you cannot tune perfect across the entire range from 1K to 10K RPM with conditions from no load idle to big highway hill with two heavy riders sitting on the saddle. And that's not even considering all the variable ambient conditions like temp, humidity and 02 density.

So you do the best you can for what you expect to see most of the time. If you want better, use a computer controlled closed loop fuel injection system. We've got no oxygen sensor, no incoming air temp sensor, no manifold pressure sensor, no finely controlled pulse width modulated fuel supply, and no computer to close the loop and put it all together.

It's an open loop compromise. One that works surprisingly well, but not perfect!!

 

For discussion sake, here's a shot of the intake end of the Mikunis:



Sure wish I had a Hitachi here...

 

I have some that are completely disassembled in my basement. I will try to get some close-up shots of them form different angles, sides, etc.. tonight and post them up here

 

I was poking around a little more looking for pics and I realized that there are a couple different versions of the Mikunis and some of them have the pilot air jet out on the intake venturi just like you said. Sorry about that. I gotta be more careful about blanket claims when there are different versions...

From this thread: http://www.xjbikes.com/Forums/viewtopic/t=3633.html you can see both the main and idle air jets on the intake throat. However, in all the configurations and locations of the air jets, they are all pulling air from atmosphere, just from different physical locations. Functionally identical however:



Also interesting to note from that same thread the presence of three bypass holes:

Thanks! That would add a lot to the discussion.

Burnarr

 

If the Pilot Mixture is bypassed during Wide Open Throttles, ...

Why does Tweaking them during Plug Chops and Dyno-runs have an effect on BOTH the Sparkplug's Center Electrode Ceramic coloration AND the RPM & Power capabilities of the Engine during the Dyno-run?

I can Tweak BOTH Mikuni's and Hitachi's to provide a different Performance Factor by adjusting the Pilot Mixture Screws.

The Performance changes from Heavy Acceleration / Engine Braking -to-
Smooth Acceleration / Engine Coasting by Dialing-In the Supplemental Mixture.

I have often shown this graphic which pertains to Hitachi Carbs.



On Mikuni Carbs -- The Fine Tuning Window is LESS

 

I would like to add that the bypass holes are supplying air to the mixture screw as long as the butterfly is closed past them as they are seeing less vacuum on the other side,,,

great post by the way,,,I can turn my mix screws an keep my sync in a fairly wide window an greatly affect the way the bike runs,,an even shifts,,,they do more than 1 would think if they are truly in the game,,,but if plugged up an not working well their out of the game,,,,keep going I would really like somebody to get this all out,,,,

I'm going to repeat my bike holds a sync up to about 70mph or better,,,I've got a handle on it but it needs proved,,,an I'm on another inline 4 because of it,,,the truth is out there,,,

the ability to tune an inline 4,,,I believe you guys can do it,,,alls I can say is keep digen,,,,there's some out there that don't believe the mix affects the sync but it all starts getting off idle an if you can't get off idle cleanly an onto the mains your sync is going to go way off,,,,this ain't for the faint of heart guys this is only paid for with sweat,,,

great post I applaud good people here who can have an intelligent discussion

 

Hitachi's also do have the bypass holes, only two of them on the HSC32 series, haven't had a chance to check the HSC33 series.......

 

+1 for that. It's refreshing to see people of drastically differing opinions hold an intelligent debate using facts and solid theory instead of getting personal and taking digs at each other's credibility.

 

Gonna throw in here what I just wrote in my other thread, see if it makes sense to you guys.

Now here is how this applies to this thread...

My pilot circuits could very well be clogged. And my IDLE screw might just be far enough in that I am drawing fuel from somewhere other than the pilot circuit - is that possible?

If the butterfly opens enough because the pilot circuit is clogged I can get it to idle with a higher, idle... so this would explain why my COLORTUNES are nearly not affected at all by my mixtures! Wow! Epiphany! I think I might have solved my problem... we shall see Saturday when I go through the carbs again.

 

If your IDLE SPEED screw is opening the butterfly valves far enough to expose the "bypass holes", then yes, you are going to draw fuel through them (and probably have a very high idle! and if you DON'T have a very high idle, well, that means more problems somewhere else....as the larger throttle valve openings should produce a much higher idle, and if not, then it's "masking" some other problem. )

And yes, if your pilot circuit is clogged enough, then that is why fiddling with the mixture screw will not produce any color (mixture) change visible with the Colortune plug.

Of course, if your pilot circuit is realy, REALLY clogged, then the carbs won't be drawing any fuel through either the idle mixture screw port OR the by-pass ports, since they all feed FROM A COMMON (perhaps clogged) SUPPLY ROUTE.


Epiphanies. They're like a nice bunsen-burner blue colored light going off in yer head......

 

I'll buy you can only tune for the moment and the rest is a best compromise but that is true of any tuned system. You still have not address my basic question/premise.

You stated the Idle mixture contribution is negligible past idle RPMS. I am contending (and others above appear to be too) that you can effect the mixture at higher RPM with the idle mix screws (which I know from experience to be true). If we take that to be true then by definition the contribution is not negligible (small yes but still has an effect).

 

All I have to say Bill, is, SHIZZAGGUM! Dead on.

 

:lol: what the heck is SHIZZAGGUM?

It did get me LMAO

 

It's a method of expressing extreme happiness. Say it LOUD, yell it!

Just do it, it'll feel GOOOOOODDDD...


SHIZZAGGUMMMMM!!!

 

The position of the Throttle Plates determines how well you'll be able to adjust IDLE and MIXTURE ... After you have done a BENCH Sync and determined that you DO NOT have ANY Air Leaks to contend with that will throw-off the ability to Fine Tune the hole.

Bench Sync with the THINNEST Material Possible.
Set the Carbs to where you can Actually CLOSE the Throttle Plates and Depend ONLY on the Pilot Mixture to Supply Air~Fuel Mixture to "The Holes"
3 X 5 Card Strips 1/2 Inch or less work perfectly.

Benched this way allows you to CLOSE the Throttles all the way.
Closed Throttles when the Engine is Turned-over hooked-up to Vacuum Gauges will suffice to test for any serious Air Leak.
A "Dead", Low, well-below others reading means there is a Leak to find and cure.

With Throttles Closed you adjust the Pilot Mixture Screws to get the Bike to Idle.
As Idle is achieved you raise the RPM's to 16~18 Hundred and perform a Vacuum Sync.
Once the Carbs are Vacuum Synchronized the YICS Tool is removed and the Bike Tuned the way it will be run.

The IDLE Mixture MUST support a STEADY Idle >> AND Include enough Supplemental Richness to add enough Fuel to the Front End of the on-rushing fresh air allowed to pass when the Throttles are opened Off-Idle.

The Supplemental Richness is variable.
Just barely enough will keep the Ignition of Air~Fuel constant and allow the Engine to accelerate without a hesitation and provide a GROSS Mixture that is LEAN and Explosive for exceptionally fast acceleration and harsh Engine Braking.

As the amount of Supplemental Richness is INCREASED ... The Bike begins to Idle without a miss and the Gross Mixture made more Rich which will not be as Explosive as the Leaner Mixture and result in Velvety Smooth Acceleration with a less severe Braking and slowing upon closing the Throttles.

A Deliberately Rich Mixture will allow the Engine to be Tuned to run Quietly and Smoothly with the additional factor of running "Cool" as the Mixture burns less explosively and much cooler. Perfect for the occasion when you will be riding for hours on-end. Although deliberately Rich, the Mixture is not that far from being Lean. The Fuel economy is only marginally effected.

The Instant the Mixture is made to be too Rich the Cylinder will begin to misfire.

 

Some of this stuff is definitely hard to test and I'll admit that I've not run my pilot screws all the way to the bottom and then taken my bike on a long "never-needing-to-idle" ride to see what if anything can be discerned by plug color. I doubt that's even possible in my neighborhood! :lol:

The biggest problem is that the concepts under question needs to be examined at measurable throttle shaft rotation, and under no load sitting still conditions, that results in unreasonable RPMs.

A dyno and an EGA would be trick...

Park the bike on a dyno and run it with the throttle shaft at like 12 degrees off idle and twiddle the pilot screw while you watch an EGA stuffed up the tailpipe. You could pinpoint the throttle rotation at which the contribution from the pilot outlet is negligible, if that point even truly exists.

I'm certainly not going to tell you guys that you aren't seeing what you say you're seeing. I will gladly admit that there are times where reality differs from theory due to real world influences or subtle nuances and details which may be difficult to explain.

Maybe this is one of those times?

Anyone near Phila, PA area have a dyno and an are as curious as I am? :wink:

 

You don't need a Dyno.
Find a closed Industrial Park with a loop road that has a decent straightaway.

Crank it open.
Hit the Kill Switch and coast to a stop.
Check the Plugs.
Note the colorization of the Center Ceramic.
Tweak.
Do another run.
Check to see if the condition changed and by how much.

A second set of Plugs helps speed-up the process because you don't have to handle hot plugs.

 

So... What's considered a decent straightaway?

In other words, how long would you expect it's necessary to hold steady test conditions in order to get meaningful results on a plug exam?

Ballpark here... One second, ten seconds, hundred seconds? Hours?

 

Rick's previous description of his "playground" I mean, "proving ground" was an industrial park a few city blocks long. Multiple runs at different loads and shift points.

My idea for testing mostly the pilot circuit would be to drive up a slight hill holding only the slightest twist of throttle, like 1/8 inch of twist at a steady 2,000 RPM for as long as possible, like 2 minutes. This would be hard to do in traffic, but would give the idle/ just off idle plug reading.

 

I'm baaaaack..... :lol:

Question So why is it that the pilot screw adjustment seems to affect mixture conditions under real world driving conditions and not just at idle?

Answer Because under normal driving conditions a significant contribution of the total fuel still comes from the pilot outlet.

What's that you say??? Are you saying you were wrong with the claims about the setting of the idle mixture screw should have virtually no impact on the air-fuel ratios at any throttle position other than almost dead closed idle??? No, I'm not saying that at all... I'm saying that there's enough room on the island for all of us and here's why.

Before I run pilot mixture test runs on my bike I thought it would be prudent to understand the throttle and butterfly positions during different driving conditions and with that in mind, I rigged up this VERY fancy throttle position gauge and a corresponding throttle shaft angle measurement device on my carbs (pat pending):





I spent a few hours on the bike paying attention to the throttle gauge and making notes of the position under different conditions and here's what I found.

Throttle position 1-2 - Maintain 35 MPH on flat and level secondary roads

Throttle position 2-3 - Maintain 45 MPH on flat and level secondary roads

Throttle position 4-6 - Maintain 65 MPH on flat and level highway.

Throttle position 7 - Maintain 65 MPH up long highway hill. Not mountain pass quality grade, but for subjective normalization, it's traditionally a place where most cars absentmindedly drop their speed by approx 10 mph.

I also made note of the RPMs that my engine would attain at a few throttle position settings while sitting still under no load conditions.

Throttle position 0-1 - Idle at 1100 RPM
Throttle position 2 - 3000 RPM
Throttle position 3 - 6500 RPM

Keep in mind that there's a lot of subjective verbiage in this analysis. I'm trying to provide as objective analysis as possible about somewhat subjective subjects. Also note that your results for all of the above may be different due to your weight, wind profile, engine conditions, carb conditions, temp, humidity, etc, etc, etc.

I annotated copies of the pics with my test results and the conclusions that can be drawn should explain the potential impact of pilot screw settings





1) I still contend that the pilot mixture screws do nothing above a certain throttle position, but that position may be higher than what's used during normal driving.

2) The amount of throttle required for lightweight casual driving is astonishingly small. The percentage of the bikes available power which is actually USED under non-race conditions is a small fraction of what's really tucked away in there.

3) Under what can be considered normal driving conditions for some people, it's completely plausible to take an entire trip... from the house to the supermarket and back again... and never require enough throttle to even uncover all three of the pilot holes.

4) Below highway speeds, by the time I'm far enough into the throttle to expose all of the bypass holes, I am accelerating. Briskly.

5) Results obtained during no load testing is questionable because even at 6500 RPM you haven't exposed more than one bypass hole.

6) My butterflies never even reach 90 degrees fully open. With the non-linear response of that type of valve, however, I'm not sure I care. It's not like I'm really missing the power!! :lol:

I did try to do some plug color testing, but my plugs are mottled and choppy colored and very difficult to read. I suspect the past three years of riding with dirty carbs are to blame there. I'm going to replace the plugs and start fresh, but in the meantime....

Burnarr

 

Makes you wonder about the guys doing plug chops at WOT at 35mph. Are they really at WOT?

 

Now that is something even I could understand. I have noticed I use very little throttle when not accelerating. So most of my driving is under low throttle.

I'll have to think this over but it does make sense.

 

I need a bike with more power hahahah i'm usually running position 6-7 doin 90km/h on a flat surface

Nice presentation tho! TY!

 

All of which is exactly why the "idle" circuit matters so much; cruising at 1/4 throttle, you ARE running on the idle circuits as well.

Personally, I use VERY LITTLE throttle opening in almost all day-to-day riding OR driving; WOT is only for rare occasions.

 

I gotta get the revs up to around 7k to get my 300 pound but moving sometimes. Of course ppl around here drive 110km/h on 80km/h roads. So sometimes it's an oh @#$% get goin reflex.

 

I didn't say 1/4 REV RANGE, just 1/4 throttle. I LIKE 7K-9K, but don't need WOT for more than a few split seconds to get there.

 

I have an air fuel ratio gauge, maybe i should try to get some video footage of the gauges operation while moving, my mains are too big so you can see exactly where they come in.

Anything under 1/4 throttle is fully controlled by the pilots, theres no question about it on my maxim's hitachis thats for sure.

 

all good info , but what is sea foam :?:

 

Sea Foam is a strong solvent.

 

My motorcycle has a good idle but no power at even one degree beyond an idle! I think you proved what it is on this site!!! Does this mean I can pretty much just clean the bypass holes in the carb, with wire or some such and the acceleration will return? 1982 Honda 450 size, CB . I have been confused about this ever since I cleaned it out thoroughly and got the idle to work perfectly at about 1200 RPM. I did it with one float bowl gasket and a gallon of carb cleaner that I soaked the carb in for 20 minutes. I got it from Napa for $20.00. My acceleration is so bad, I think I could do a max of 5 mph in first, or second and that is it. I have no upper end!!!!!
Rick, you do seem quite expert I must say. Perhaps you can help me with this problem. It is a real stumper.

 

You have to go WAY beyond just making sure the Bypass Holes are clear.

You have to disassemble the Carbs. Leave the body's on the rack.
Remove the Bowls
Remove the Floats
Remove the Jets
Remove the Float Seats
Clean everything spotless

Remove the Top Lid.
Remove the Spring and Diaphragm
From the Bottom ... Tap-out the Center Nozzle (Emulsion Tube)
Clean the Tube
Scrub the Diaphragm Bore with ScotchBrite Gray
Flush the Passageways

Remove the Pilot Mix Screws and small parts.
Flush ALL the Passages Top-down and Down-up.

Every little Jet or Metering Port that Fuel passes through needs to be done.

You can't leave one stone unturned.