Hard acceleration plus backfire

[jesse74]

Im trying to get a 75 shovel that I just bought on the road and there's a few problems I can't fix with the limited mech skills I have.
It starts fine. A bit hard but when it's warm it's acting up. First it goes, hesitates then it wants to die. I try to accelerate but I get the stuttering and the backfires. It won't even go in first without heavy clutch action.
The plugs are black so I'm guessing to rich and I've tested the charging system.
4 pin stator.
Wh to wh = 65V a/c
Bl to Rd = 105V a/c

Points are good.
Can't say about the condenser
Didn't test the coil.

Can someone help me out with troubleshooting.?

[Davestune]

i would 1st say make sure you dont have any manifold leaks to rule that out.
what color is your spark if its weak or yellow condenser. you need to perform a test on your coil allso ohms hot and cold
you also may possibly have a frayed wire coming out of the points/cone this sounds more like a short to ground on the back fire problem, possible coil issue
pop the cover and pull the points wire to be sure, this is what I would do but thats me as I have seen this and have had this problem.
do not rule out poor ground or power wire also. you need to go through all of your wiring

[ridgerunner1965]

sounds like my shovel with too small intermediate jet in the carb. whatcha got?

condensor will do that also.

[ridgerunner1965]

plugs may be black cuz stupid chinee condensor aint letting points fire all the time.jus saying.

tell us yur carb and jetting so we may help u?

[pantspisser]

If you're sure the problem only occurs when the motor is warm I'd put money on an intake mani leak. Get the motor warmed up and strategically spray individual intake mani flanges with starter fluid. If you get the motor to increase or decrease in speed as a result of spraying you found the problem. The guys above are spot on as well this could be the result of an ignition component/wiring failure.

[chopperbob1313]

All the previous answers are good ideas. Take your time and try all of them. A short somewhere can be the toughest thing to find. Just because a connector looks connected does not mean it did not break or come loose inside the shrink tube. When bike is running try to wiggle every connector you can touch and see if there is a reaction. Also, crazy too short pipes can cause problems too. Piece of gunk in carb should be considered too. Good luck.

[jesse74]

It doest leak at the manifold. But the front cylinder plug is weakened yellowed. I've changed the coil. It was in pretty bad shape. So it fixed the bad spark and back fires. I'm going to do the points wiring checkup. I think now I have a other problem I'll share below.

[jesse74]

It runs now. I've changed the coil. It was all cracked up. But when I ride it on highway speeds it just dies. I have to pull over and wait a bit the stars back up and I can go a little bit. Possible stator/regulator?

[Tattooo]

How is your battery???

[pantspisser]

If the battery checks good I'd suspect fuel starvation. Plenty of things will cause the carb bowl to not refill fast enough at sustained highway speeds. Easy check is to remove the bowl drain with bike off. If you can drain a gallon out of the bowl in a minute or less you got good flow which is an indication that the pet cock, fuel line, fuel filter, and float assembly are operating correctly. Obviously if your getting poor fuel flow these will be the areas to inspect for clogging or improper adjustment.

Once that you got that ironed out the next suspect is a vacuum error that isn't allowing fuel from the tank to replenish the bowl while the carb is actually moving air. Double check the integrity of all of the gaskets and O-rings.

My continued suspension of an induction issue is souley based on the intermittent-nes of the malfunction. It's been my experience that ignition and charging problems are constant if an issue does occur, the exceptions being an odd failure in the coil (got that box checked) and slow condenser degradation (cheap and easy box to check). Sorry to hear the fight continues man, keep posting what tests and trouble shooting you've completed. Also what carb are you running?

[jesse74]

If the battery checks good I'd suspect fuel starvation. Plenty of things will cause the carb bowl to not refill fast enough at sustained highway speeds. Easy check is to remove the bowl drain with bike off. If you can drain a gallon out of the bowl in a minute or less you got good flow which is an indication that the pet cock, fuel line, fuel filter, and float assembly are operating correctly. Obviously if your getting poor fuel flow these will be the areas to inspect for clogging or improper adjustment.

Once that you got that ironed out the next suspect is a vacuum error that isn't allowing fuel from the tank to replenish the bowl while the carb is actually moving air. Double check the integrity of all of the gaskets and O-rings.

My continued suspension of an induction issue is souley based on the intermittent-nes of the malfunction. It's been my experience that ignition and charging problems are constant if an issue does occur, the exceptions being an odd failure in the coil (got that box checked) and slow condenser degradation (cheap and easy box to check). Sorry to hear the fight continues man, keep posting what tests and trouble shooting you've completed. Also what carb are you running?

Thanks pantspisser. I sure hope you're right.
Since my oil seal bearing is leaking oil at the points it might be a issue. Fuel delivery is a good start with the explanation your giving. Seems obvious that no fuel would stop the bike and by waiting a bit it would start again.
The carb I'm running is the late keihin butterfly 1976 model. I have to go back at the books to see if there is a drain. I only see a vent line. Or this might be the overflows drain.