Bike Dies While Idling

[cmckeeman]

So i will get my 77 Bonne started and she will ride fine for twenty minutes or so and then all the sudden when i am stopped the idle will dip real low and the bike will shut off, it will kick back up, but it will die again unless if i feather the throttle. The bike will be like this for another 10 to twenty minutes and then the problem will go away. This problem also happens occasionally when starting the bike after it has been of for a short period of time, it will start then sputter off before i get a chance to give it gas.


Any ideas?

 

[DaveM]

Have you checked to make sure your fuel lines are all clear as this sounds like it is being staved of fuel

 

[Rocky]

I agree, it sounds like fuel or carb related.
This is usually a symptom of worn Amal carbs letting in too much air.
I had this problem with both of my old bikes when I got them, but new carbs cured that immediately.

 

[grandpaul]

A total overhaul of the carbs, and thorough check of the fuel delivery system to ensure it is completely free flowing and properly vented, is the way to eliminate fuel-related issues. Fuel can flow easily for 10 minutes run time with a blocked fuel cap vent. When it gets to that much vacuum in the tank, it might be releasing the pressure against the clog, then it just "resets".

 

[cmckeeman]

I agree, it sounds like fuel or carb related.
This is usually a symptom of worn Amal carbs letting in too much air.
I had this problem with both of my old bikes when I got them, but new carbs cured that immediately.

The carbs are kind of old...

A total overhaul of the carbs, and thorough check of the fuel delivery system to ensure it is completely free flowing and properly vented, is the way to eliminate fuel-related issues. Fuel can flow easily for 10 minutes run time with a blocked fuel cap vent. When it gets to that much vacuum in the tank, it might be releasing the pressure against the clog, then it just "resets".

What would be the best step to cleaning the lines and checking the venting?

 

[CarlS]

To check the gas cap venting. When the bike starts to stall, loosen the cap and see if you hear air going in.

 

[The Seeker]

Running the bike with the furl cap off should stop the stalling if the venting is the problem.

Then either get a new cap or try to clear the blockage with some fine wire into the vent holes on top and underneath.

-- Posted with TapaTalk

 

[cmckeeman]

Well while riding and experiencing the problem at a long light i took the cap off and the problem remained so it doesn't seem like there is a vacuum issue. haven't had to time or money to replace the carbs yet though, any way to tune them up in the meantime?

 

[Rocky]

If the carbs are worn out there is no way to compensate for that.
If you tune them very rich to try and compensate for too much air getting in you will be blowing black smoke and there will be a lot of carbon buildup in the engine.
Generally, the bike will run terribly.
If you decide to get new Amal carbs the new ones have either a brass or chrome slide and don't wear out like in the days of old.

 

[Paul Mojo]

I have essentially the same issue on my 78 TR7. It will occasionally stall when rolling to a stop. It will start back up fine and otherwise runs well. Might happen once or twice on a ride, or not at all. I have replaced gas cap, bought a new Amal Premiere carb, replaced the coils, battery, plugs, wires, and cleaned up the positive grounding on the bike yet the issue remains. Must be a classic veteran out there who knows what's going on here. Because the bike runs well 99% of the time! it is difficult to resolve.

 

[gumpt1oo]

I had the same problem with my T140. I tried everything to cure it but nothing seemed to help.
Then I noticed that the carbs were getting hot when I was riding and found that the previous owner had mounted the carbs using a gasket instead of the correct O rings. This meant the heat from the head was transferring to the carbs. So I removed the carbs and mounted them using the correct O ring and the problem was gone! When the carbs are correctly mounted there is a 25 thou air gap between the carb and the inlet manifold on the head.
I'm not sure if the fuel was evaporating when it was hot, but the heat was the problem on my bike.
Might be worth a try.

 

[grandpaul]

There are also thin insulating spacers available.

 

[Keith Phillips]

I had a similar problem with my T-140 when I first got it. It turned out to be electrical. I changed the ignition found a few wires loose here and there after spending the day on it I was rewarded with a sweet motor and no more problems. Thank the lord for Lucas aftermarket parts. Hope this helps because (no spark no fire)

 

[grandpaul]

As they say: "90% of all carburation problems are electrical"

...and 90% of all electrical problems are carburation!

 

[cmckeeman]

As they say: "90% of all carburation problems are electrical"

...and 90% of all electrical problems are carburation!

I am beginning to think it is electrical since i discovered the fuse from the battery has some intermittent connectivity issues. i am going to try and see if i can get it more solidly connected or replace the holder and see if that gets rid of the problem.

 

[CarlS]

Let us know how it works out.