running lean

[kazoom]

I ordered some new diaphragms for my carb, (could see through the old ones) its the ones where u reuse your slides and put the new diaphragm over the slide it fits and looks like a good product, while i was waiting for the diaphragms i cleaned my carb at work in an ultrasound cleaner just to do something while waiting, now i have put i all back together and the bike runs super lean on both cylinders the only two changes are the diaphragms and an inline fuel filter. before the carb clean and changes it ran great.
i have never messed with carbs before so if anyone could give me hint on where to start my trouble shooting.

all is stock, yamaha 400 xs se from 81 4g5
mainjet 125
pilotjet 42,5
float 21mm
airfilter stock
exhaust is not stock but is the same as before

best regards from denmark

 

[JARichmond]

How do your carb boots look? Are you sure that the entire assembly (from air filter to intake manifold) are tightened down and there are no loose spots?

 

[kazoom]

well the boots look fine i, think they have been changed by po they have that new rubber look and seem flexible, about the carb its the first time i have taking a carb apart but i am pretty sure everything is put back together correct, took it apart again last night and it "looks" clean.
1: could that inline filter reduce the flow enough to cause this condition both sparks have the exact same gray colour and it looks like the float houses fill up nicely.
2: when the carb was cleaned in that ultra sound thingy i didnt take the choke lever off, i read somewhere that its pretty tough on all non metallic surfaces.
3: can i check the slides travel with the engine running if i take the air filter of, to check if they work with the new diaphragms.

 

[JARichmond]

The in-line filter will absolutely not affect your fuel flow rate enough to starve your engine. You can prove this by checking the flow rate into a bucket and figuring if your engine could use this much fuel over your given time.
I believe your float measurement is actually way too low. The readings are "floating" around somewhere on the forum as the Haynes measurements are actually incorrect.

 

[kazoom]

ok read that somewhere too, but the thing is i havent done anything to the float hight, while cleaning it, what throws me off a bit is that its both cylinders that run lean, indicating either insufficient fuel or an airleak that effects both carbs.

 

[JARichmond]

Float height should be set to 26mm. See if that clears up your problem. It's easily possible that a PO set them both wrong during a previous tear down.

 

[xschris]

I would put at least a 135 main in it.

 

[cutlass400]

Ya 125 main jet is tiny I'm runnin a 150 right now because of my pod filters but I've heard 145 is a very common size for these bikes to run well

 

[kazoom]

hi cutlass
yeah its tiny, but its stock size for my bike, will change it once i go with the kn filter, but need to get the carb tuned in stock before i start to fiddle around with jetting.
Cleaned the carb out again last night after i found the gas filter from the petcock on the buttom of my gastank.
also i think my float height is right at 21mm i saw that drewpy`s tracker had that height i have the plastic floats.
please correct me if iam wrong.

 

[JARichmond]

I've also got plastic floats on mine and run fine at 25mm +/- 1mm. I'm not sure if it's related, but I believe he is running DOHC carbs on his tracker.

 

[DanMach]

It could very well be the new rubber diaphragms(sp? Chrome says its right...) .. if they have issues the slide wouldn't rise properly and thus it would be lean. I would do the standard carb cleaner test on the boots(lightly spray carb cleaner around the boot seals and see if the rpm's change, if so, they leak.). If they aren't leaking then its going to be your new rubber in the carb.

There is a test for them.. but I can't recall what it is.

 

[JARichmond]

To test your diaphragms (if Chrome says it's right, it's probably right) you can lift the slider inside of the main chamber until your diaphragm sits like a bubble. If it slides down slowly, they're ok and are holding positive pressure. If it slides down quickly, you likely have a leak in the rubber and it must be replaced. Of course, you can also visually inspect the rubber for cracks and wear.

 

[kazoom]

Thanks for all the input, i cleaned the carb again last night (and yes i do have other things to do in my life ) and reajusted the float height with just 2mm so its now around 22mm
and it runs better now it seems to not get so hot i messured 110 degres where spark plug sits on the engine after a small 4 km trip. the spark plugs are stil grey but not white.
about the the float height it seems i had to bend the metalthing quite alot just to reach those ekstra mm so if i need 25 mm its alot of bending is that usual, i mean where it was flat on the head of the float needle its now only some of the metal touching the needle.
Jar my diaphragms move down slowly when you push the slide up and cover the top slide hole on the intake side of carb.

best regards from denmark

 

[kazoom]

doubblepost

 

[JARichmond]

Good stuff. I'm not too sure about how far you have to bend the tang for your float as mine were within about 1mm of spec. From the way I see it, if you want a perfect mix you will have to adjust your floats higher but I figure you're probably losing your patience by now (I would be) and just wanna get out and ride. Now you know what has to change, and are able to go from there at your own pace

 

[kazoom]

Forgot to say i still have a fair amount of popping from my left exhaust on decel and idle iam guessing it could be one of two things 1: bad plug/ignition 2: airleak on left carb.
can a lean condition cause popping in the exhaust.
jar when you say float height, is it the one where you meassure from the bowl edge to the actual float top or the one where you meassure with a tube from the assembled carb, just to make sure we are talking about the same thing. i have used the edge of the bowl to the top of the floater.
also i have been wondering how can raising the float height increase the amount of gas in the lower float chamber.