[mdot]

Hey everyone, I'm new to motorcycles (but not new to fixing vehicles). I picked up this bike a little while ago and haven't had the pleasure of ridding it much yet. I had a series of problems and once I fixed them, I seem to have a bigger problem--the bike won't turn over. Can you give me some advice?

The other week I didn't let it warm up long enough and it kept stalling while riding... it didn't take long before starting it killed the battery. A friendly biker stopped and tried to help me push-start it. While doing that, the throttle cable pulled out of it's connection to the clutch (or the clutch return mechanism, I think it's called). He was nice enough to give me a ride home. I fixed the clutch connection and re-adjusted the clutch cable to the best of my ability: so that with the clutch pulled, I could push the bike in 1st, but with the clutch released, I couldn't budge it. I also replaced the battery. Then I saw my fuses was blown (single fuse, right on the hot line), so I replaced that, too.

With all that taken care of, I let it warm up a good, long while and took it for a ride. I barely had any throttle, and couldn't break 30mph. I rode it for about 30 minutes to see if it would work it's self out, but it didn't. Then I left town for work for a few weeks, and when I got home, the bike wouldn't turn over at all. Power is good, starter is working, but the engine isn't catching. I've got gas in the tank, starting with choke on.

Only other thing to note is that I had filled it up with gas and a cap-fuel of engine stabilizer on a buddy's advice.

What do I do? What do I look at next? It ran great before I ran it dead. Thanks to whoever read all this!!

 

[cmonSTART]

Hi there! My assumption is that the starter is turning the engine but it's not starting.

It SOUNDS like a lean condition. First thing I would check is whether your petcock is letting fuel flow TO the carbs in sufficient quantity. I think you have a vacuum operated petcock, so there should be a fuel line going to the carbs, and one vacuum line going to the back. If it's disconnected or has a hole fuel won't flow as well (or at all.) Try switching to the "pri" setting and starting it then - this bypasses the vacuum on/off feature.

If it still doesn't start I would pull the tank and let the petcock drain into a jar - visually check if fuel is flowing on the "pri" setting. Don't spill the gas! If it's not there may be a screen inside the tank around the carb, or you might have an inline fuel filter that's clogged.

Those are a couple good first steps. If fuel is flowing well and it's still not starting I would suspect the carbs next - they might need to be pulled and cleaned.

Just an afterthought - check to see whether you have points on that bike. If you do you should probably tune those up first.

 

[mdot]

Thanks for that! I set the petcock to PRI and it started up like it was nothing. I gave it a test ride and I'm still not getting any kind of power though. What do you think my next steps are? Swap out the fuel filter and check the fuel flow on PRI?

This bike doesn't have points.

 

[cmonSTART]

The Prime setting just bypasses the vacuum shutoff feature of the petcock. Next I would remove the tank and hook up hoses to the fuel and vacuum ports on the petcock. Run the fuel hose into a jar, then suck on the vacuum hose a bit (use your mouth). Suction should trigger a good amount of fuel flow from the petcock and it should stop when you remove your mouth from the vacuum hose. (Note that if you get a mouth full of gas the diaphragm in the petcock is bad.) If it doesn't perform as above it will need to be rebuilt or replaced. Perform this test on the 'reserve' setting with the tank level.

Next, since you have the tank off I would drain it and remove the petcock to make sure any screens on it are clear and the tank is free of rust and dirt.

Good suggestion on the fuel filter - if you have an inline filter you should change it.

Since you have the tank off you can either pull the carbs now and check them, or make the above repairs and try it again - that's up to you.

 

[mdot]

Welp, I pulled the tank: PRI has flow, and ON has 2x the flow of PRI when the sucking the vacuum tube. I'm not sure how much flow I was looking for. Pulled the petcock and it's intake-filter was clean. Fuel filter was very clean.

Still only starts while on PRI, though-- I'm thinking that means the carbs aren't making a vacuum? It just occured to me that I should start it on PRI and then switch to ON and see how it runs.

Also I should note, when I do try to ride it as is, I get a lot of backfiring with WOT, which is what I need to make it go over 15mph.

Soooo carbs, huh? I've never dealt with a carburetor before. How can I tell the difference between a set that needs cleaning and a set that is shot?

THANK YOU!

 

[cmonSTART]

Out of curiosity where is it backfiring from when you try to ride it - intake or exhaust?

Do try to start it on prime and switch to on while it's running - curious if that will make a difference.

Diagnosing dirty carbs is usually done by the behavior off the bike. If you know gas is getting TO the carbs in sufficient quantity and lean symptoms still exist, it's usually the carbs. They don't have to look physically dirty inside to be dirty - the jets within the carbs are generally pretty small and can clog easily without much visible contamination. Sometimes though it's obvious when you open up the float bowl......

I think this is probably the next thing to check if you don't have any obviously bad rubber parts - such as carb boots or vacuum hose.

 

[mdot]

Yes, I can start it up in PRI and switch to ON. It doesn't die but it doesn't run any better, either.

The misfire is in the carb.

 

[Dodsfall]

Misfire or backfire? Those are two very different things.

Backfiring into the carb is a sign that there may be valve issues. The adjustment should be checked.

 

[mdot]

Oops, I meant backfiring into the carb. It's my truck that's got a misfire--whole nother story.

Can you explain what you mean: value issues, and what adjustment? The air/fuel ratio?

 

[cmonSTART]

Intake backfiring can also be a symptom of a lean condition, though I do agree on checking the valve clearance adjustment. Always good to start with that within spec.