Intake Manifolds

[Lance Gothard]

Hey .. I have a 1985 .. new to the site and have a question .. polished my intake manifolds and have had trouble ever since getting it to run sweet .. should I go back to stock?? Or can I reject the carburetors ??

 

[Lance Gothard]

Hey .. I have a 1985 .. new to the site and have a question .. polished my intake manifolds and have had trouble ever since getting it to run sweet .. should I go back to stock?? Or can I reject the carburetors ??

Rekey .. lol

 

[Lance Gothard]

Rejet .. lol

 

[MaxMidnight]

Hey .. I have a 1985 .. new to the site and have a question .. polished my intake manifolds and have had trouble ever since getting it to run sweet .. should I go back to stock?? Or can I reject the carburetors ??

When you say 'polished' was that inside or out?

If it was running OK before your efforts then I doubt that just polishing them would have any significant effect on the fueling.

You need to go back over your re-assembly as it is more likely that you haven't put something back correctly i.e. manifold sealing rings missing or displaced or carbs not correctly seating in their rubbers.

I don't think there is any need to reject the carbs just yet.

 

[sdt354]

There is one manifold bolt that needs a dab of sealer or a possible vacuum leak can happen . I smear some high temp sealer around the O-rings too. Did you use new O-rings? I always go back to what I touched, when things don't go well. Carb mounting, like are they fully seated, carbs resynced? Like Steve mentioned, just polishing them shouldn't be an issue.

 

[Fire-medic]

Yeah I bet you have a torn or misplaced o ring on the manifold of one or more cylinders. I use a smear of water-soluble gel like KY to hold o rings and gaskets in place. Try spraying some starter fluid around the manifold base to cyl head to see if the rpms increase & if so you found one. Check all & all around.

 

[Lance Gothard]

Thanks everyone for your response after reassembly carefully with new o rings first start up idle was 1000 rpm higher than normal carbs were never touched only on and off after manifolds were polished internally could only back down with idle adjustment result was extremely rich fuel mixture

 

[Fire-medic]

Yeah, if they're off they need to be reset for synch and idle, and possibly the air bleed screws below the CV carburetor covers, to maximize results. You might think, "hey I shouldn't need-to mess with that, it was set-up OK before I removed the carburetors." But for some Curse of Bernoulli reason, you need to do it.

I think I'd now check a wet-set level for the carburetor floats.

 

[MaxMidnight]

I agree with Mr Medic that you would need to re balance and adjust the idle after removing the carbs.
However, as I have said previously, if it was running OK before disassembly then I don' t see how the idle mixture or float level would change so IMO are not an issue here.
If it is running as rich as you say (how have you established this?) then I would check that the choke plungers are returning to the closed position.

 

[Fire-medic]

I agree with Mr Medic that you would need to re balance and adjust the idle after removing the carbs.
However, as I have said previously, if it was running OK before disassembly then I don' t see how the idle mixture or float level would change so IMO are not an issue here.
If it is running as rich as you say (how have you established this?) then I would check that the choke plungers are returning to the closed position.

Yes that's another one, a shot of WD-40 or CRC 5-56 will free 'em-up. Work the lever a few times, and see that they fully-open and fully-close. I've tweaked the movement by slightly-bending the forked 'fingers' on the enrichener piston shaft, to allow more opening travel. It doesn't take much. You might also want to ensure that the set screws for the forked 'fingers' are snug on the shaft. There's a detent on the shaft that the forked 'fingers' brackets ride-upon, for the set-screw to hold its position better.

Should you encounter difficulty in seeing the required enrichener piston movement, from fully-open to fully-closed, you may need to remove them, to see if you need to remove any corrosion/oxidation on the brass piston, or in the bore into-which it fits. A small rolled-up 'pencil' of wet-or-dry 120-180 grit sandpaper should clear-out any oxidation, be-sure to rinse it thoroughly with whatever spray solvent you prefer.

 

[Lance Gothard]

Thanks for the input guys it’s all valuable information I have another question with manifolds polished the air flow should be improved or increased . Less restriction inside the manifold I would think increased flow would result in higher rpm and also removing the rough surface inside the manifold would result in less tumbling or should I say mixing of the air fuel ratio it would be an extremely small factor but a factor just the same. The carbs have been completely rebuilt top to bottom spared no expense reassembled and I backed the pilot screws to roughly 2.75 to 3 turns from seat running better still curious about jetting don’t know that much about it thanks again take care and be safe

 

[Fire-medic]

Please add your location below your screen name, as someone may be local to you, and it also helps us to answer questions.

The jetting can often be lowered from the stock setting one or two sizes to lean it out a bit. What jetting did you find when you had the carbs apart (assuming you did notice the #'s)? Stock in most of the USA is 152.5 Mikuni. There may be a difference for someplace like 1 mile high elevation Denver CO. I do not know that to-be the case, just surmising that may have been done, perhaps by a dealer there.

 

[Lance Gothard]

Did not pay attention to the jets had the Yamaha dealer do the carbs but going smaller makes sense but to tell you the truth that was a while ago since then found one cylinder with only 90 compression decided screw it it’s now completely apart found a crack in one crank journal same one with bad compression cylinder had a wear spot as well guess I’m committed now had the bike since 85 so it’s my second love wish me luck I’ll be buying my parts from Sean even though I’m in chilliwack bc thanks again for the chat I’ll have it back together in a couple of years can’t tell my wife how much I’m spending so have to go slow bye

 

[MaxMidnight]

Thanks for the input guys it’s all valuable information I have another question with manifolds polished the air flow should be improved or increased . Less restriction inside the manifold I would think increased flow would result in higher rpm and also removing the rough surface inside the manifold would result in less tumbling or should I say mixing of the air fuel ratio it would be an extremely small factor but a factor just the same. The carbs have been completely rebuilt top to bottom spared no expense reassembled and I backed the pilot screws to roughly 2.75 to 3 turns from seat running better still curious about jetting don’t know that much about it thanks again take care and be safe

Not necessarily; whereas you would have a smooth exhaust you leave the inlets with a rough(ish) surface.
If you have a highly polished surface that will encourage laminar flow and this can lead to the fuel dropping out onto the surface of the manifold.

Conversely, a rougher finish will cause a small amount of turbulence which will help mix the atomised fuel with the air.
What you are aiming for is a smooth flow through to the inlet port i.e. any lumps and bumps have been removed.
The Max inlets are not too bad in that respect.
What you do need to concentrate is removing any steps between the manifold and inlet port as this is far more likely to cause unwanted turbulence.

If the inlets are polished the I suggest to take them off and roughen them up with some emery and ensure that the aren't any steps at the port.
If you were wanting to be particularly pedantic you would also measure and adjust all inlets and ports so they are the same shape and size.

 

[Lance Gothard]

Thanks for the reply I’m going to get a set of stock ones used there not expensive problem solved

 

[MaxMidnight]

Thanks for the reply I’m going to get a set of stock ones used there not expensive problem solved

But note my comment on checking the matching of the manifolds to the ports.
Apply a light smear of engineers blue on the face of the inlet and offer it up to the inlet port (without the O ring) and fit the screws; carefully remove and the parts of the mating faces that are sans blue is where there is a step.
You may decide that you want to eliminate the step.

You probably won't notice any significant difference in performance but you will have the satisfaction that your ports are matched better than the majority of other Maxii.

 

[Lance Gothard]

Very true I also have a weight advantage I’m only 140 lbs lol

 

[Fire-medic]

Pee Wee!

 

[Lance Gothard]

Ya but a fast one

 

[Lance Gothard]

Fire medic have a question about my fly wheel after removing it I inspected it and found a circular mark at one end of one of a projection also a small scratch I can’t help thinking this is a problem I know nothing of how the projection actually works in relation to the pickups thought about polishing them out but I have a feeling you can’t do anything to the surface do a need to find a new one