Need help diagnosing a problem

[SilverTalon]

Hey guys, here's a new one.

Yesterday the bike had trouble running, like I'd open throttle and it would barely accelerate, and it sounded like it was struggling to increase RPMs. It would be on and off like that, and it stalled once. So I figured I was low on gas, since I couldn't see the level just by eye. I filled the tank and it seemed like the problem resolved.
This morning I had the same issue again. It started no problem, and idled between 1k and 1.5k. After going for a short bit, it started having the same trouble. I would try to throttle, and it wouldn't go . After getting up to speed on highway it was fine for a bit, but once I got off the highway, and got to a stop, it stalled. Then I turned it around.
Going home it had the same issue, every so often it would act fine, but others it would struggle to accelerate.

I can't figure out where to start looking for issues. The carbs were cleaned over the winter, I replaced the air filters, the fuel lines, spark plugs.

 

[Lepttack]

When I first got my bike it was real sluggish, turns out one of the spark plug wires was loose and was only running on 1 cylinder a lot of the time...maybe you are dropping a cylinder at some point?

 

[drewpy]

sounds like a gas issue, give it an Italian service and If that don't cure it check for air leaks, fuel flow etc

 

[SilverTalon]

Is there a better fuel filter I could be using?

I don't know if the one I bought is working well, if it clogged already, or if need to make sure I get one that works with gravity fed systems (even though I'm using the vacuum feed).

 

[lhaolpa]

Is there a better fuel filter I could be using?

I don't know if the one I bought is working well, if it clogged already, or if need to make sure I get one that works with gravity fed systems (even though I'm using the vacuum feed).

Even though the vacuum line opens the petcock,it's still gravity fed,as in no fuel pump. lha

 

[SilverTalon]

Even though the vacuum line opens the petcock,it's still gravity fed,as in no fuel pump. lha

Yeah I ended up getting one of the clear mr gasket filters and come clear pvc tubing.

Will just re-run the fuel line

 

[lhaolpa]

The filters made of glass tube with screw-on ends,with a cleanable plastic filter work well also.I use one on my Dt400 dirt bike,my Toyota truck[with Weber carb]and my '41 Ford tractor with good results.The tractor is the only one that's collected any trash,cleaned it with the garden hose and W-D 40.Seventy-one years have done a job on the tank,so it releases a little junk every so often. lha

 

[SilverTalon]

Heres the before and after.

I made sure on the new filter and tubing that the fuel could get through to the carb on gravity feed alone. I ended up using PVC. This was the quote, which i'm hoping means it should be fine:

A general purpose, clear, and flexible PVC plastic tubing for transmission of fluids, gases, and some solids. Especially useful when light weight is necessary and rough handling could be encountered. Superior resistance to strong oxidizing and reducing acids, gasoline, oils in general, alcohol, and hydrocarbons. Durometer hardness of 68A.

Also tested the vacuum tube, to make sure it worked out.

 

[lhaolpa]

Both of those pics look good,especially the bottom one with the Glass/plastic filter.This type of filter will hold a lot of trash before giving you trouble,as you'd see it through the glass. lha

 

[SilverTalon]

So I took the bike to work again. It seemed to run better, then I got near the same spot as last time. It started having the same trouble. This time I was intent on getting to work. I kept going at what seemed like half power. After about 5 minutes, I started to rev the engine, and full power returned. I went about the same distance as when i started, same thing happened, with same result after driving for a bit and reving it a little.

Fuel was flowing no problem.
When running was close to 13v, between 11-12 when idling/braking.

 

[lhaolpa]

Have you checked the tank cap for vent? Since it's happening at about the same spot in your trip[same distance/time] you might have a situation where the gas flows,then slows due to a vacuum in the tank.This will happen if the tiny opening gets clogged with gunk. Also check carefully for air leaks,as they will allow the slide to fall,creating a problem. lha

 

[SilverTalon]

Have you checked the tank cap for vent? Since it's happening at about the same spot in your trip[same distance/time] you might have a situation where the gas flows,then slows due to a vacuum in the tank.This will happen if the tiny opening gets clogged with gunk. Also check carefully for air leaks,as they will allow the slide to fall,creating a problem. lha

Would coating the tank with chrome spray paint cause this, someone may have done that over the winter...

 

[Drewcifer]

Mine acted up like that when I had poorly gapped points.

I might check your points if you have them. Mine sometimes misfire with vibration if I've set them too far apart. I can wear a leather glove and press on the side of one, tightening it slightly and it evens out. that's my verification of when my points are too loose.

Clean the points up with contact cleaner and ultra fine sandpaper, like 200 or 600. Never hurts. It will idle smoother/better and usually start on a first kick too.

 

[SilverTalon]

So we are closer to figuring out the problem. It started happening again. We stopped riding and took a look. We took the right plug cap off, engine turns off. We took the left one off, engine stayed running.

The wire still sparked when touched near metal. I didn't have a spark plug ratchet on me, so i couldn't switch them around to see if it was the plug itself.

We started riding again, and aftger riding fora bit it started working again...

sigh.

Also, fuel was leaking out the air filter case.

Edit - Switched plugs and went for a ride no issue. I know my buddy stripped the wire a little. Think maybe those needs to be replaced?

 

[SilverTalon]

So I replaced the coils, and took it out for a ride today. At first it ran great, and the voltmeter was reading close to 14v. Then all of a sudden the left side kicked out again, and I'm back to square one.

I'm going back to carbs on this one, they were cleaned over the winter, and now im having issues, on the left side only.I also have fuel coming out of the left air filter sometimes (when sitting idle for length of time, not after running).

I will also check the points out too, but I don't think they will be the issue. (Have the day off tomorrow)

 

[Drewcifer]

Fuel out could be poorly fitting exhaust valves, poorly timed spark ignition. Clean plugs of corrosion. Check for sooty condition ie poor rings burning oil fouling plugs.

 

[SilverTalon]

So I took the bike out again today. I went 50 ft, took a left turn, got maybe another 150/200ft, then the left side went again.

I limped back to the garage, pulled the carbs off. There was a good amount of fuel in them.

Both coils are brand new, and getting power.

I'm back to the left side plug off works fine, right side off won't work at all.

Pulled the left plug out, tip still pointed, but blackened.

I'm at my whits end here. Guy at work thinks it might be the cylander itself, but if that was the case, wouldn't that happen from the beginning?

 

[jmd_forest]

Since the bike seems to work fine for a while I would discount compression or valve problems or other mechanical breakage. Most likely cause is electrical and/or fuel.
1) Spray starting fluid around all the air joints /plumbing of the carburetor, including the throttle shafts, and listen for changes in the idle. If idle changes you probably have an air leak.
2) Set the timing using a timing light
3) Since you have already replaced the coils, replace the wires, wire caps, and plugs. These are cheap and the most likely source of problems.
4) Pull the carbs and CLEAN, CLEAN, CLEAN. The carbs on these bikes are very susceptible to dirt.

 

[XSLeo]

If you have fuel leaking out the left air filter your float is sticking open or is adjusted wrong or fuel soaked.
The only way gas leak out of a carb is through the float valve. Pull your carbs, clean them check the floats for fuel soaked and ajustments.
Leo

 

[SilverTalon]

I guess I should rephrase. Would it be worth it to replace the floats themselves? I bought a rebuilt kit for everything else.