Combat Wombat trouble

[Bill123]

Hello,

I have a 1973 Model 95 Combat Wombat with an intermittent problem that has me stumped. The bike has had a recent rebuild from the crank up. I built it with the intention of riding in vintage hare scrambles events in New England. I have had 2 dnf's in my last two races due to the following symptoms:

At the beginning of the race the bike is running fine and after about 20 minutes, the engine starts to cut out and die.
I pull over to the side of the trail and am able to get it restarted, it will run and I can rev the engine at a stand still but it will not run under load.
If I let the bike cool a little bit it sometimes will let me get a little further down the trail then it starts to spit and pop and stall again.

By the time I get home and try the bike, it will start up and seems OK while riding for a few minutes around my yard.

My thoughts are that something in the ignition system is failing when it gets hot and then healing itself when it cools down.

I took the flywheel off and I can't see anything obviously wrong with the coil or wiring and the points are not burned or pitted.

Has anybody experienced similar symptoms?
Any suggestions would be appreciated.

Thanks,

Bill

[hodakamax]

Hey Bill, a bunch of us are going to say "Condenser" first. Try changing that.

Max

[thrownchain]

Condenser, fuel flow and tank vent should all be checked .

[Bill123]

OK, Thanks for the quick replies. I can see thru the hole in the gas cap so I know the vent is OK, the petcocks and needle and seat in the carb are new, so it looks like I should try the condenser. I'll get one on order. Bill

[Bill123]

P.S. I just saw the recent post about the Road Toad and someone mentioned mounting the condenser under the tank with the coil to keep it cooler. Sounds like a "cool" idea. I may do that too. Bill

[matt glascock]

There are other possibilities that can be temperature-sensitive. Temperature-induced exciting or high-tension coil failure or a temperature-induced air leak come to mind. Leak down and coil testing AT operating temperature could sort it out. That said, I'm throwing in with the condenser fault crowd. Get a Wombat Shop Manual if you don't have one. It has allowed a schmoe like me to feel like a real dirt bike mechanic and there are secret pictures of The Captain to boot.