I need help diagnosing a problem

[John_S]

I went riding for 4 hours this weekend and the idle was erratic. Sometimes 2200, sometimes had to blip the throttle. Adjusting the carb didn’t change anything. It would occasionally lean bog when getting on it quick. It idled high way more than it idled low.

I got home and took off the pipe, carb, and stator cover and did a leak down test. It held 7 pounds for 7 minutes. I don’t have the tools to do a bottom end vacuum test. The inside of the stator cover was dry.

Not knowing what to do I fired it up tonight and got it to full operating temp and was messing with it. I found a problem by chance. If the bike is standing straight up it could have a high or low idle after a quick rev. Leaning the bike left and I have to keep it running by blipping it. Leaning to the right it instantly gets a high 2200-2400 idle and won’t go down until I lean it back to the left. The handlebars were turned the same way the whole time to rule out the throttle cable.

Do you guys think this could be a stator side crank seal? Leaning to the right takes premix away from the seal and leaning left the premix blocks a vacuum leak? I believe my float valve and seat are in good shape.

[SS109]

If you did a leak down test, and it held pressure like you said, then it can't be a bad crank seal. That's exactly what a leak down test is for, finding leaking seals. I would lean towards something in the carb.

[doakley]

What carb is on the bike?

[John_S]

The bike has a 35 air striker that I got from jets r us a few years ago. Im glad you guys mentioned that. I have my stock 33 PWK up in the attic somewhere that I can try out. The other thing I noticed today was when it was leaning to the right idling high I could turn the air screw a whole turn richer or turn the idle down a couple turns and it kept its high idle. With the bike standing up if I turn the air screw all the way in it would die right away.

It’s frustrating because one rev of the bike and it comes to a low idle. Another rev and it stays high. I thought the slide was hanging up but it’s snapping shut. The leaning left low idle and leaning right high idle was very consistent.

SS something I forgot to mention is that the problem is much worse when the engine is up to temp. Warming up it’s not as bad. It made me think it had an air leak only when it was hot. I don’t know. I also thought a crank seal could pass leak down pressure but fail a vacuum test.

[bufftester]

Sounds like your fuel inlet needle is hanging up or your float is having issues possibly, or blockage in the petcock or pick up tubes causing erratic fuel flow. Anytime the bike starts doing something odd like yours I would look at the carb before anything else. Was it dusty on your ride? started with clean filter and fuel? any other work you did on the bike? Give the carb a thorough cleaning and blow out all the passages with compressed air, then set your float height and verify your float needle is working correctly and you have solid fuel flow through the petcock. Then ride it and see where you are

Bottom end vacuum test really isn't needed, the leakdown will tell you the same thing, although 7 psi is on the high side, you don't want to get much higher than that, 5psi at 5 mins is sufficient.

[John_S]

That’s why I love this site. Get back to the basics before I keep thinking I need to tear the whole thing apart. I also wasn’t looking forward to buying another tool and vacuum testing the engine. I usually do 6psi for 6 minutes and not sure why I did 7 this time. I’ll keep it at 5-6.

The fuel is fresh and the air filter was just serviced. It was surprisingly clean on the trails. Not dusty or muddy. The spark plug after 4 hours was tan all the way down but lighter in color than I expected to see. The float valve or float hanging up is a great starting point.

The only recent change on the bike is the addition of a fuel filter. I rode it once before two weeks ago with the filter and it seemed fine. After installing it and turning on the petcock it looked like it flowed the same. I run clear fuel line and was looking at it yesterday. There weren’t any telltale signs like air bubbles going through the line.

Before I go through my 35 I’ll ditch the fuel filter and see how that goes. If that doesn’t change anything I’ll get my 33 out of the attic and install it for a side by side comparison. Leaning the bike left and right since it’s so repeatable now and the idle changes are almost instantaneous. I installed a new jet block gasket, polished the seat and installed a new float valve on the 33 before I stored it, thinking I was going to sell it.

I’ll update once I try a few things. Thank you guys so much for the ideas.

[John_S]

I just removed the fuel filter and brought it up to temp. Everything was good warming up then once it gets up to about 150 degrees I could lean the bike left and right and get low/high idle.
I’ll try the other carb next

[John_S]

It seems to be good now. I grabbed my old 33 carb, checked that the float height was 18mm and installed it, keeping the same slide and needle that I’ve been using for years. I got it up to 180 degrees without any of the high and low idle symptoms while leaning the bike. I’m going to leave it on there for the next ride and fix up my 35 later.

Thank you guys again for the suggestions!

[SS109]

Cool. Glad you can ride!