Doesn't run while going downhill

[lemmy]

I had posted an earlier thread about my bike not running while warm. Well I have narrowed it down that it isn't a warm/cold issue but an uphill/downhill issue. When going downhill if I pull in the clutch it will die almost instantly and then be very hard to start. If I suddenly run up on a burm to make it pointed uphill it goes to a very high idle. The float level was at 17mm and I checked the fuel level with one of these (screw it in the bottom of the float bowl and bend the clear tube up to see the fuel level):



and the spec is 0 to 2mm above the mating surface and it was right at the mating surface. If I turn the fuel off 5-10 seconds before doing downhill, it runs ok. So I thought this proves it is a fuel level issue. I have made 2 adjustments to the level and it is now at 21.5mm and the fuel level is now at least 2mm below the mating surface. It is much better, but still will die if I ride up a small 7-8 foot hill in my back yard and then let it coast back down (it is a 15 degree hill). The only thing that fixes it is turning off the fuel 5-10 seconds before going downhill. I have thought of just buying a new PWK35 (should I get an airstriker, I don't even know what that does), but I hate to spend $230 and it work no better. Is there anything else that could cause this? When I had the carb off checking the fuel level with the gauge pictured above, I tilted the carb 45 degrees forward. After about 10 seconds some fuel started leaking out of the bore where the intake rubber boot would connect. But it was just maybe 1 drip every 4-5 seconds. When I moved the carb back to level, the fuel level was just a bit higher, but not much.

[canyncarvr]

Have you burnished the float needle seat?

Have you taken the floats OUT of the carb? Granted, the tube outside takes it into account, but I would want to know for sure I could give the floats a shake and not hear any sloshing noises from the inside of 'em.

My bike generally idles lower on steep downhills. Always has..three different carbs. It's a clutch issue on my bike..the same issue that makes the KDX hard to push in gear, engine off, clutch lever pulled. If you shift into neutral on a downhill, does the idle speed change? If it's hard to GET into neutral in that situation (wheel driving the transmission), it's a clutch issue.

The steeper the hill, the slower I'm going down it. I could say, 'On steep dowhills my idle speed drops' and relate it to the angle of the carb due to the slope of the descent. In my case, that would be incorrect.

[lemmy]

I have not burnished the float needle seat, but I have tested the float valve operation with air (blowing on a hose) and with fuel. It cuts off the fuel (or air) flow very abruptly when raising the float manually with my hand. In less than 1mm of float movement it goes from air or fuel flowing freely to not even a drop of fuel coming out and when using air, unable to blow any air through at all.

I have had the floats out and shaken them, and submerged them in water to see how they float and if they take on any water and they don't.

I have noticed the issue you are talking about with the clutch. That is why I did my experiment the other day coming down off of the mountain while in neutral. If I shift in to neutral it idles up maybe 200-300 RPMs. I was unable to test this until I lowered the float drastically (or I would have to turn the fuel off) otherwise the bike just dies on any downhill.

Also, after I get to the bottom of a descent and it levels out, I can put it in neutral and it still won't run well for a while. I have to keep revving it up. Then it is fine.

[canyncarvr]

Re: 'That is why I did my experiment the other day coming down off of the mountain while in neutral.'

I missed that you said that earlier.

Would the 2-300rpm (neutral) difference make this a non-problem? ..looking for a degree of state..what makes enough of a difference to BE different.

Re: 'Also, after I get to the bottom of a descent and it levels out, I can put it in neutral and it still won't run well for a while.'

That is a symptom of being too rich, or, put another way, if the bike is too rich on the bottom, it will do that. I'm not saying that is what's happening here, just that it does happen.

Are you still running the CEL needle?

Is this related to the 'Doesn't idle when warm'? A new issue or part of a larger issue?

Maybe your choke plunger leaks............

[lemmy]

You missed it because I didn't say it :) I left that out.

No, I am back to the 1173L clip in #2 position. I did have a 40 pilot but went to a 42 when I lowered the float so much yesterday. The "won't idle when warm" was a misdiagnosis of the problem. It has nothing to do with warm or cold. That is why I would let it warm up at home and ride around and not see the problem. Then ride up on the mountain and then start going down hills and see the problem. At first I thought it was a hot/cold issue, then an engine braking issue. Now, after doing the tests with bike in neutral and seeing it run on uphill and not on down and it being fixed with fuel being turned off and improved by lowering the float I am convinced it is somehow excess fuel getting in to the engine and making it rich. I can be stopped on a downhill while in neutral with the front brake on and it idling fine because I turned the fuel off 5-10 seconds before I got on the hill. Then kind of push down on the front to compress the the forks a few inches and it will start to sputter and almost die, then recover when the forks rebound.

The choke plunger leaking would make sense. How can I test that? I have looked at it and it looks fine, but I don't know the path the fuel takes to get up in to the choke plunger area. I see passage where the air comes around from the air breather side.

[lemmy]

I know that the FCR-MX carbs have a float chamber baffle for rough terrain. Why doesn't the PWK have something like this? Is there a carb that would work well with the 220 that has something like this?

[KarlP]

RB Designs does some work on your stock carb that is very nice for a 220.
It don't cost $235, either.

I can't say it will solve your particular problem, though....

It sure does sound like something is goofy in your carb.

[lemmy]

RB Designs does some work on your stock carb that is very nice for a 220.
It don't cost $235, either.

I can't say it will solve your particular problem, though....

It sure does sound like something is goofy in your carb.

I have contacted RB and asked if anything he does or looks at in the carb when doing his work might fix this. He seems to think it is all jetting related. I am not saying it isn't, but it just runs too good on flat and uphill. I am just afraid of spending $165 on the mod and still having this problem when I could spend $220-$240 and get a brand new carb.

[m0rie]

What main are you running?

[lemmy]

When I first got it there was a 165 in there. Now it is a 155. But I had a 152 in but the other day I was riding at 2000-2500 and it was 40 degrees. So I upped it to 155.

[KarlP]

This is a 220? OEM carb?
I think I was running 140/38 before RBD took over.

Sorry, nope, I see it is the 200 carb on a 220.

Ya know, your carb with a $165 modification is better than a brand new carb, assuming it takes care of your current strange problem.

If I understand correctly-
If you were to put this bike on a centerstand and tilt it forward it would load up and die. If you tilted it back it would go lean and the idle would come up? Hmmmm

[canyncarvr]

Re: 'You missed it because I didn't say it :) I left that out.'

I knew that. Thus the


The float level is now...what? You noted in an earlier thread (or earlier in this one?) that you didn't want to adjust it out of spec.

Do it. Spec is 16mm. Make it 19mm.


Does the 'C' sloped needle make any difference? It's leaner longer than the 'B'. Yeah..understood that doesn't fit with 'hit the brakes and it changes'. That does sound like something is shipping fuel that shouldn't be. Still..just a wondering...does the 'C' do the same thing?

And..what about the 40 pilot? You changed it when you changed the level..because it didn't run? Or just 'cuz you figured you should richen the A/F 'cuz you leaned everything by virtue of lowering the fuel level.


Regardless of what the float needle seat looks like..and what air pressure does as a test, I'd run a swab wrapped with a 600grit wet-n-dry loop around the seat (burnish it) anyway.

What about the needle itself? It's a viton needle, right? NO ridges, NO dents, NO marks?

Re: 'The choke plunger leaking would make sense. How can I test that?'

Buy a new one..find out that your problem is gone.


I'm drawing a blank on the choke fuel supply. I know where it is. Well, used to. I'm sure you could figger it out. I don't feel like taking mine apart just to look. Point being, you could block that fuel supply off to see if THAT made a difference.

RB knows. But, please...don't bother him with your carb/jetting problems. Even if he's got nothing to do, he's got better things to do than to try to diagnose a bunch of carb problems on the phone or via email.

Re: 'When I first got it there was a 165 in there. Now it is a 155. But I had a 152 in but the other day I was riding at 2000-2500 and it was 40 degrees. So I upped it to 155.'

A 155 main at 2000-2500' el, 40º sounds too rich to me.

[lemmy]

I went to 19mm and tried again with the 40 pilot. It made a slight improvement. I went to just over 21mm and went to the 42 just because I didn't want it running too lean and it got a bit better. I have not gone back to the C needle yet.

I will try burnishing the seat. It is a viton needle and it looks perfect. No marks, or dents. I think the owner before me might have replaced it because it looked much better than the other rubber in the carb.

This may be a stupid question, but how would I block the choke fuel supply off?

I was not bothering RB for carb/jetting problems. I just sent a short paragraph of what my bike is doing and said I had tried lots of jetting configurations and if he thought there was a possibility that his mod could fix my problem. I was not asking what he thought I should do to fix my carb. He just responded that he thought it sounded like jetting and that his work included jetting and so he thought it might. That is all.

I ordered a new choke plunger today just in case.

[canyncarvr]

Re: 'This may be a stupid question, but how would I block the choke fuel supply off?'

Man. That is a stupid question!!



Surely it is, 'cuz if'n it weren't, I should know the answer!

..kidding...

If I knew, I'd say. I don't. Like I said, I'm drawing a blank on where that fuel passage is. Yeah..you can get to it on the downstream bell, but I wouldn't want anything stuck in there that could come loose! You could block the air passage on the upstream side. Presumeably 'no air' would result in 'no fuel'. Maybe not, though.

How about try all of 'em? Together. 21mm level, 40 pilot, and a 'C' taper needle....and put the 152 back in while your there. Maybe even a 150.

A btw..but I'm currently running 38/148/DEK-4/#7TV 2k-3500'el with temps in the 40ºs (in places sometimes anyway).

[fuzzy]

Lemmy:

http://www.boyesen.com/cwo/OFFROAD/Products#sb

Can always run two fuel pumps ("pump-around") and ditch the needle/seat

[lemmy]

Will that bowl work on a PWK? When I click buy it now it asks for bike info and I put in KDX and it doesn't show up, like it isn't for that bike. Maybe I will call them.

[lemmy]

I found out that the superbowl is only for KDX200 up to 1994. Wasn't that a different carb?

[m0rie]

It was a slightly different carb in the 89-94 series but the float bowl end of it was identical.

[lemmy]

It was a slightly different carb in the 89-94 series but the float bowl end of it was identical.

I thought it was a Mikuni carb in those older ones? So the float bowls are the same? I might have to check this out.

[m0rie]

No you have to go back to the 87 and older bikes to get to the non Keihan carbs. You can check the part numbers but the float bowls should interchange.