Idle dies when hot

[drake900]

I apologize if there has been previous threads regarding this...I haven't been able to find them.

My '76 bike has XS Pod filters, straight pipes, 135 mains, 27 pilots, points and PMA.

I've been trying to dial in the jetting and it is not perfect yet. It hesitates mid range 2nd gear, almost as if there is not enough fuel. Im going to install 137 mains and 30 pilots to see if it fixes the issue.

My other issue is that the bike starts and idles with one kick but after riding for a while and being fully warm the idle will drop at stop lights to the point of stalling. It will start back up fine and run as long as I stay on the throttle.

Then, when it's colder, it will idle fine again!

I'm just looking for suggestions! I thought it would be the idle circuit, but i've cleaned the carbs like 4 times!

 

[5twins]

You don't have the vent ports on the inner sides of the carbs connected together, do you? Also, you might have a slow leaking float needle seat. Slow enough that the extra fuel gets used while running at faster speeds but floods the carb out at idle.

 

[Belle]

I hear of problems w/ the coil whenever they get hot

 

[Detale]

Do you have a vented gas cap? Could be clogged and creating a vacuum and not letting gas out.

 

[drake900]

5 Twins: How can I confirm this? And if so, how can I fix this? I installed new needle previously. I believe the ring is in the stock position still.

Belle: My coils are contained in a vented container, but I'm not sure why there would be a problem only once the engine is hot at idle.

Detale: I do have a vented cap on a sporty tank, although the issue isn't gas flow, as I have clear lines and can see if there are air bubbles.

I guess when I install new jets I'll take the carbs off AGAIN and clean them completely AGAIN.

 

[5twins]

I wasn't speaking about the needle in the slide. I meant the float needle and seat assembly, the parts that the float acts against to stop the flow of fuel into the carb from the gas tank. On the bike I had problems with, if parked for a few days, gas off, all the fuel in the lines would slowly leak into that carb with the bad seat and it would start dripping gas. It was over-filling and leaking out the overflow tube. When I would come to a stop, the bike would idle normally for a few seconds, then begin to slow down and eventually die if I didn't keep blipping the throttle.

The reason yours may idle cold is that a motor needs a richer mix when cold. Maybe it can handle the richer mix caused by the float bowl over-filling when cold but not when hot.

If you've re-jetted but not leaned your needles a step, that might also be contributing to your too rich mix. You say the midrange in 2nd hesitates like it's too lean but that may be a rich symptom in this case.

 

[drake900]

5twins: That makes sense because I turned the bike off today, and gas started pouring out of the overflow tube on the right side carb. I was also at a stop light and the bike idles good for a while, then the idle drops right down. Same thing, if I blip the throttle then it keeps idling well.

I was unaware that the float needle is a part that wears out. I suppose I will have to order new ones. I will also lower the needle a step...

Thanks for the help once again.

 

[5twins]

The float needle and seat are a matched set or pair. Either one or both can wear out. Usually you just replace them as a set.

 

[drake900]

I finally got the float needle and seat installed. I also lowered the needle and put in 140 mains.

The bike runs way better especially up in the rev range, which is awesome.

I do still have an issue though...I had to set the floats to 26.5mm due to overflow and still when the bike is idling and on the kickstand I get a large amount of overflow out of one of the carbs.

I'm wondering if the issue is float height still...or the brand new needle and seat I just installed...?