Carb tune issue?

I think my next thing to try was someone else's suggestion of trying one of the tubes from the carb tune and trying it on each cylinder..? I really done think thats the issue though, but who knows.

 

It won't hurt, and it will be obvious if the problem is with the carbtune.

 

Will give that a shot when I get some time.

 

Hi wingnut , I think you,re confusing the colour tune with the Morgan carbtune

 

Oh, neat! Never fiddled with one of those.

 

Murray you are right I was using the wrong names for those tools. Sorry for the confusion.

 

Are you using a yics blanking rod when balancing ?

 

Not a yics engine... And from what I've been hearing, even if it was, that's not essential

 

So tried that... same results, nothing wring with the carbtune. Figured that would be unlikely anyhow.
here's a new vid at idle.

idles bit high... hangs a bit on throttle blips... so vac leak and lean..? starts great from dead cold. I have sprayed the heck out of the engine to carb boots and throttle shafts... has no effect.
I have no idea what else to do here. could try the color tune again i suppose... but i felt that was adequate when i previously did it...

 

I have an educated WAG. Pop the tops, and check that the air jets are in the correct places.
This is the correct positioning. The photo in the manuals are all incorrect.



It might also be worth removing the throttle cable and making sure that it's not keeping the throttle plates open.

 

Will look into these things... Pretty sure it's all put together correctly, but who knows

 

One of the carb tops may be a bit loose

Edit: hum I think i'm wrong with that, the vacuum leak test would have told you...

 

still worth going over again... I'll try about anything at this point

 

Just for giggles, open your pilot screws another half turn or so. If they are at 2.5 out now, open them to 3 and then 3.5 and note the difference. I know everyone screams "IF THEY ARE MORE THAN 2.5 TURNS OPEN EVERYTHING IS WRONG, GO TO CHURCH, MAKE THINGS ZESTFULLY CLEAN!!!!!!!!!!!" but that is an overreaction. Every motor is different. 2.5 is a baseline, but anywhere within one turn of that would be acceptable if it makes the bike run right. Isn't that the end goal here, making the bike run and getting some saddle time in?

 

I'd agree with you Drew, except for two things

Yamaha set the pilots at 2 turns out form the factory and then sealed the adjustment off. Very few XJs have enough miles on them to warrant increasing the richness of the pilot circuits by much, and those that do need that much extra enrichment are just compensating for some other problem.

There are over a decades worth of real-world observations on this forum that back up the need to go to church and set the idle mixture at somewhere between 2 and 3 turns out, and have all the cylinders in synch.

 

I wont argue that the adjustment being outside of the 2-3 turn range is compensating for something. The question ultimately becomes- how much compensation is too much, before you decide to go further down the rabbit hole instead of just riding? Or, from the other direction, time spent removing the carbs or performing further diagnostics VS tuning the bike a little richer and just enjoying it.

Case in point? My bike has leaky throttle shaft seals. I have the pilots set at 4.5 -4.75 turns out. That is why the bike stumbles below 2500 RPM and wont idle when it is cold- because in those circumstances, its too rich. But it idles once it warms up (and the air leak increases and leans it out), and I just downshift sooner to avoid the low RPM lull. Its nice out and I want to ride haha, and I'll do the throttle shafts next winter. The bike runs fine besides the aforementioned low RPM issue, and it isn't harming anything.

With two strokes, the rule of thumb for the pilot AIR screw (different than the fuel mixture screw on thumpers) is that if you are more than a turn away from the standard 1.5, then you need once size larger or smaller pilot jet. I could theoretically get the next size smaller pilot air jet for my XJ carbs (or maybe two sizes smaller really), and then set my fuel screws at 2.5, and it may run even better than it does now. Again- it is certainly compensating, but swapping some air jets out and going riding beats doing throttle shaft seals any day.

 

The idle circuit can only compensate so much. If you have a vacuum leak, at the minimum you'll be lean during some portion of the RPM range. At some point there will be a hole in a piston. If you're running so rich at idle as to compensate for leanness throughout the RPM range, you will be washing oil off of the cylinder walls with the excess fuel. In either case you're trading a few seasons of fun for an engine that will die a premature death.

Four stroke engines are not two stroke engines. They do not have the safety factor that can be given to a two-stroke by changing the pre-mix ratio (though you can fudge a little by using a top-end lube like MMO), and they do not respond to jetting changes in the same way.

EDIT: I don't; think it's a bad idea to "fudge" and ride for a few months if the rider in question is diligent about frequently inspecting the plugs for signs of detonation, and understands the potential risks of running lean, and also understands how to limit those risks by altering riding habits.

 

* 1980-81 XJ650 Maxim and Midnight Maxim, and XJ650RJ Seca Hitachi carbs with the coarse-threaded idle mixture screws: 1-3/4 to 2 full turns out from their fully closed (their fully seated, or "gently bottomed") position.

* All Hitachi carbs (other than the above) which will have the fine-threaded idle mixture screws: 2-1/2 to 3 full turns out from their fully closed (their fully seated, or "gently bottomed") position.

* All Mikuni carbs: 2-1/2 to 3 full turns out from their fully closed (their fully seated, or "gently bottomed") position.

 

Can we all just color tune and get a long!

Hanging idles can be a bunch of things. The easiest and most practical test right now is to color tune and then sync the carbs then color tune again. Yes there can be other issues at play bad compression, gasket leak, intake issues, etc... No one is saying not to check that stuff. Its just sometimes the issues is a lot simpler. After the carbs are balanced/sync'd throw the color tune on and make sure Carb 3 is cap'd or a tube with a screw to block the port from getting air. The extra air will force you to run #3 rich.

To make everyone feel better and see if the issue was the sync. Turn the mixture screws so they are back to factory spec and then see how the bike runs. Its just a test... wont cost ya anything, wont hurt anything, but it will help cancel out a few possibilities.

Also what color are you trying to match when you tune it?

• blue with a hint of orange on a rev
• blue with orange and just fire on rev
• blue with a touch of white
• green with poke dots
  
• papa smurf? (blue with a touch of white and red orange on rev)

 

And the brain-fart strikes mid-day. Pre YICS. Look at Hogfiddles' post. You're rich at 2 1/2 turns out, which probably explains the too-high of an idle and why you are having trouble synching. The fine-thread screws are sensitive, but the coarse thread screws mean that each turn makes quite a big difference in the A/F ratio.
I've been thinking vacuum leak because of the high idle, and because of not noticing that you do not have a YICS engine.

 

have any pictures for reference? it is a seca650, but who knows for sure if these are the original carbs. But I am def going to try this

 

have tried the colortune and I thought things looked good but still ran into issues... Going to try as hogfiddles says above and see how it goes.

 

makes sense... I've been thinking it's gotta be something stupid I've missed. I cant find a vac leak for the life of me but it's behaving similarly. also tried the throttle cable disconnect as you mentioned previously with no effect.

 

You have the original Hitachi Carbs.

 

I would think so yes. That is assuming they are the ones that came with the bike.

 

Never mind, mine are different as the bike is an '82.

 

Read Hogfiddles post. The 80-81 carbs fitted to the 650 engine have a different pitch to the idle air screws.

 

I looked at the vid. Unless someone swapped in a set of later Hitachi's, they are the original.

 

It's possible that the wrong jets are in there........

 

i am just getting the impression from looking at a carb tune pic then a colortune then a carb tune photo, so I have to ask.

are you trying to balance the carb tune readings by using the color tune? or to put it another way are you using your Idle mixture screws to sync the carbs?

 

This thread reminds me of my issue where I had what I thought a smooth idle but giving it throttle, rpm would just go up and hang there etc.
My issue got resolved after the float height was in spec. Are yours? Didn't see this point mentioned anywhere and thought I'd mention it.

 

no. Trying to use the sync screws

 

I did wet set the levels. Have checked it like 3 times... Suppose I could again.

 

what settings do you have with the wetset ?

 

3mm

 

Measured from where?

 

bottom of where bowl connects to carb body.

 

Then you're good.

 

so

so set the screws at 1.5 out... maybe a slight difference in idle, slightly lower. Color tune plug in on each cylinder, bunsen blue, no difference. Tried again to sync.. same results. Going to tear carbs out again.... re bench synch.... set the screws at 1.5 out again, recheck wet set... carb hats are tight, will take those off and check the jets are right, pretty sure they are but hey why not. I really dont know what else to do.

 

something additional i'd never even thought of that I will check when I take the carbs out..
http://www.xjbikes.com/forums/threa...s-clean-and-gasket-replace.84498/#post-509757
butterflies possibly binding???

 

Finally had some time to get back into it today. Some interesting findings... Firstly, carbs and motor were completely flooded with gas despite petcock rebuild and being left in the on position, not prime... Carbs also have been fully rebuilt and wet set multiple times... so Im not sure what to make of that. Anyhow... Drained out, changed oil and filter... tore carbs out...
Took hats off to be sure those jets were correct... they are

So put that back together.
Next took all bowls off

Took floats off too... nothing funny.

so was putting back together, and while putting the pieces for the "choke" back together noticed that on carb #1 when I would tighten the set screw for that fork, it would ever to slightly pull on on that plunger. So pulled that fork... bent it slightly so when put back together that not longer occurs.

next... re-evaluated my mixture screws...
here are mine...

from reading and searching, here is comparison btw fine and coarse

Based on this... Pretty sure I have the "fine" variety.
So these should be at 2.5 turns out.

Next... Re-did wet set

hard to see, but mark at 3mm... all 4 dead on.

Next... re-bench sync.

back on bike... started... set idle... seems to be OK now for most part.... Now time to try color tune and running sync.

 

you may want to put a on off petcock in the line until you figure out your petcock problem

 

Where's the valve clip that hooks on the float tang?

Gary H.

 

Good eye Rocs!

 

Replaced needle valves with all brass sets from Len. Don't need that clip for them

 

Agreed

 

Ok, Hopefully solved...
Hooked everything back up, mix screws 2.5 out.
warmed up
pretune:


post tune:


Then color tuned... all seemed to look good at 2.5 turns out.

Idles much better, no longer hanging up and not out of control

 

Sounds sweet to me

 

that wasn't hard, was it