750 Maxim Project

Well I don't know how or why but I guess persistance pays off. I just kept trying and it seems to idle and rev ok. I messed with my pilot mixtures and it seems to load up a bit, it is a pain taking the seat on and off everytime to adjust slightly. Oh well thats what has to be done. My popping from the exhaust I guess was a lean condition? Seems to be gone now. The bike seems to cut out a bit at high rpms, I have the smaller stage 3 dyno jets in now gonna step up to the bigger see if it helps.

 

The Pilot Mixture is regulated by AIR.
The AIR allowed to be pulled into the Cylinder "Picks-up and brings-along" Fuel from the Pilot FUEL Jet.

Increasing the Size of the Pilot FUEL Jet won't have the complete effect of adding Enrichment to a Critically LEAN Engine without Increasing the Size of the Pilot AIR Jet, too.

You need an increased AIR Flow to pull-up FUEL from the Pilot FUEL Jet's Supply.

The MAIN AIR Supply is exactly the SAME.
Shimming Needles and Increasing Main FUEL Jet Size to help alleviate running Lean also needs Increasing the Main AIR Flow to the Emulsion Tube.

The Problem which arises for getting enough FUEL to an Engine with Air Pods is:

The supply for Main AIR is regulated by the Main AIR Jet ... and ... The --> Maximum Amount of AIR allowed to be drawn to the Emulsion Tubes surrounding cavity by the INSIDE DIAMETER of the Main AIR Passage.

To satisfy the NEED for more FUEL for Top-End Performance it may be necessary to remove the Main Air Passages External Plugs and INCREASE the Diameter of the Main AIR Passages along with Incrementally INCREASING the AIR PORTS drilled in the Emulsion Tube to Increase the amount of FUEL Flow at Wide Open Throttle Conditions.

Until such time as someone solves the Pilot AIR and Main AIR capability; fumbling-around changing FUEL Jets up and down ain't going to get the job done.

 

wwwwwwhhhhhhhhhooooooooooooosssssssshhhhhhhhh.........

What the hell was that that just went flying over my head???

 

Thank you rick I really appreciate your help. I am going to have to study your recommendations to fully understand, it is a lot to take in right now. The plugs read a dark tan/brown when I pull them after idleing a while. When I drive it normal and just up to speed no hot rodding and come back the plugs are a nice even tan. I have not done plug chops yet I plan to, I have shimmed the needles up a click (dynojet adjustable) It pulls with power from low rpm no bog or cut out even if I should shift down to get power but don't it pulls up smooth. I think maybe I will do a plug chop tomorrow at the point where it cuts out to see what they look like.

I have drilled the diaphram piston as per dynojet recommendation with supplied bit, this would allow faster needle rise and air intake? Where are the external plugs for the air passages located, would that be figure 7.10b on page 124 of the haynes manual? air compensator jet it says on the air intake side of the carb.

 

the emulsion tube is referred to as a needle jet (main nozzle) in the haynes manual? The piece that the needle goes up and down in basically

 

Hey Rick I just had a revelation about the whole carb air/fuel passages/jets. I always thought that the stoichiometric fuel/air ratio came from the air drawing up enough fuel from the venturi to make the proper mix. That would be too easy. I followed what you say, and looking at the diagram I finally get that the Main Air and Pilot Air go through the Main and Pilot passages, and pick up air due to the venturi effect. This fuel/air ratio is MUCH higher than stoichiometric, and *should* reach a stoichiometric ratio when mixed with the air in the venturi.

I offer this hypothesis for why pods cause problems:
The slide and diaphragm in the venturi are supposed to make keep the velocity in the venturi constant (i.e. CV). Simple fluid dynamics here...if the mass flow of a fluid (air) increases through a tube with a constant area, conservation of mass dictates that the velocity must increase proportionally. The CV nature of the carbs allow them to conserve mass flow by increasing the area of the venturi proportionally with the increase in mass flow to keep the velocity *relatively* constant. So why does an increase in mass flow cause lean issues? I propose that the increase in mass flow will open up the slide too quickly, pegging it to the top of the carb, when the butterfly valves are not fully open. Opening up the butterflies further then increases the mass flow further and therefore increases the velocity proportionally - rendering the "CV" portion of the carbs ineffective.

Just as Rick points out, the air flowing through the main air jet, though passages, through the holes (14 on mine) of the emulsion tube is getting pulled by the "constant" velocity in the venturi (due to the venturi effect of course). That same effect is what causes the negative pressure in the emulsion tube to "pick up" the fuel. However there is a limit to the speed that air can flow through a certain area hole, and that is dictated by the speed of sound. You cannot get air to move faster than Mach 1.

So with the throttle full open, the slide is pegged, the velocity in the venturi is higher than it's supposed to be, and the smallest holes in the main air passages restrict the air flow that is supposed to draw up the fuel. I propose that the "choke" point would be the emulsion tube, as those holes seem smaller than any other in the system (even if you sum them). Whatever the choke point is...it's area would have to be enlarged...but you'd still have a non-CV situation. Perhaps if the spring in the slide were stiffer, or the slide was heavier, or the holes "transmitting" the vacuum to the top of the slide were smaller...anything to keep the slide from opening too quickly (*edit* - opening the slide slower would increase the velocity). If only there were some way to test this.....Again this is all my hypothesis...and maybe it should be in a new thread.

 

Well yay or nay rick? BTW I put the larger jet in and it might of helped but as you said didn't fix it.

 

I've had my say about this more than a few times, in the past, ...

Search:

Turbulence, CFM, Velocity Stacks, ... and you'll get my take on trying to make Pods work.

Essentially, and with my tongue planted firmly against my cheek, I see this discussion as a work in progress. The discussion started sometime in the early 1980's and continues, now, going-on 30-odd years.

All things considered; it boils down to: "Pods or Airbox"???

I pick: Airbox.

 

but pods look sexier.... that's the most important quality of our bikes, right?

 

I meant about what manbot said. I have that pvc intake on there. So it should get restriction, I have read most of posts and never heard you say aboout the slide pegging to the top.

 

another way to increase the air supply to the emulsion tube or needle jet would be to drill a hole in the bottom of the float bowl

 

Slide pegging to the top is MY theory...I could be completely wrong. It's the only reason why I could see a CV carb failing. Don't go drilling holes in anything.

As for the pods being sexier, I think I can assemble an airbox boot clamp with a pleated paper filter glued on that wraps around the boot, giving that sexy pod look to a proper airbox set up :wink: :lol:

 

I'll give that a try and if doesn't work I'll put hole in my forehead and see if that helps.

Manbot, I know that was your theory just getting some more input, you titled it to Rick. I didn't mean to offend just trying to learn about the functions, I read Chacals write up about carburator physics, just trying to gain more insight on how it all comes together to make the bike run.

Form without function is worthless.

 

The Diaphragm Pistons don't open any faster with the Pods on the Bike.
Jet Kit Suppliers used to send a Drill with the Kit and have you Drill an additional hole at the base of the Diaphragm Piston to make the Piston rise more swiftly.

But, the Air Stream entering the Intake Horn is Turbulent and without shape.
Without a Velocity Stack the Air Stream has:
Too much volume
Insufficient shape and speed to lower the pressure above the Emulsion Tube to draw-in enough Fuel from the Main FUEL Jet Supply.
So ... People Increase the Size of the Main FUEL Jet.
They Shim the Needle ...
They alter the Length of the Needle
They reduce the Diameter of the Needle

Non of which:
Provides Speed to a Condensed Air-flow above the Emulsion Tube.

You can hold a Coke Bottle out of the window of a speeding car and not make it whistle.
Purse you lips and blow across the opening and its a different story.

Look at all them light bulbs that just started glowing above all those heads.

 

That intake is nasty! I love it.

 

...I'd steal the idea if I had not already spent $130 on KN pods...

 

Thanks rick I got a glowing light now, I appreciate the help. This is my first time actually trying to tune carburators this in depth.

Thanks Barzu, I can't take credit for the intake idea however I designed mine a bit different than the one I ripped off

 

Here is the spacer on the shock mount koolaid

 

Put 220 miles on yesterday, went on the flood run, through Wabasha up the Wisconsin side to Bay City across to Red Wing and back down to Wabasha and home. No problems whatsoever. Ran really smooth. Saw thousands and thousands of bikes. I have never seen anything like that before. And it was a beautiful day!

 

Thanks for the pic. I'm glad you got to get out and enjoy the bike. I spend the day working in our flower beds