Topic: Carb cleaning--Getting away with liquid carb cleaner-Other Carb questions

[Honda_Dan]

I have a 76 CB750F. When I put on full choke I can get the bike to start almost immediately. It runs and revs for about a minute and the engine sounds good, but when when I  would normally start easing off the choke as the bike warms up, it dies. (it does this regardless of whether I ease off the choke.)

I bought some carb cleaner additiive, which I added to a couple gallons of new gas. Do you think that running this tank of gas through the bike willl help the carb problem or will it require taking off and indiviually cleaning the carbs. I'm trying to avoid that, as I have never done it before and have heard it is difficult, and I will likely have to retune the carbs after cleaning.

Any thoughts? If I do take off the carbs, do I need to soak them, or can I get away with spraying carb and choke all over them.


Dan

[Harry]

Seems to me the problem is getting enough fuel to carbs, not carbs themselves. When engine dies, open gas tank, if you hear air sucking in you have a vacuum = blocked tank cap vent. If not check tank filter in petcock and fuel lines for blockage. D'you have an inline filter - replace this.

[Honda_Dan]

Would it also work to try to drain the carbs immediately after the bike dies? Or would a fuel flow problem not necessarily mean that they are empty. What about measuriing how much fuel comes out of each carb?

What about blowing in the tank cap vent?

Also, how do not know if I have an inline filter? How do I check this? Would it be in the petcock somewhere? 


Really appreciate your help.


Dan

[Honda_Dan]

Also, I don't think this bike has a tank cap vent. It looks like it has another hose coming out the back of the tank and this is how air circulates.

Danh

[Harry]

You need to be sure the flow of fuel into the carbs is sufficient to replenish the consumption of fuel by the motor.

When bike "dies" do the described gas cap test to hear if a vacuum in the gas tank is the cause.

If ok, close petcock, open drain screws under each carb (after placing a bottle under the drain tubes) and empty carbs. Open petcock and confirm you have a decent flow of fuel from each carb.

You have now identified/eliminated fuel flow to the carbs as your problem.

Report back here, and someone will take you through the next step.

[Honda_Dan]

Harry,

Thanks a lot for your help. I'm pretty sure it is a gas flow problem because 1) It made that sucking noise when I opened the tank and 2) the flow bowls were pretty much empty right after it died.

I took off the petcock and inspected the fuel filter. It looks like it has some rust dust on it, and also the membrane is ruptured near the top. I will replace the fuell filter. I also inspected the air intake hole on top of the bike, and sprayed a little bit of carb cleaner in there. Is there a better way to make sure that hole is not clogged? I'm suspecting that is the problem.

I tried running the bike with the gas tank open. Gas started to flow out of one of the carb overflow valves (those nipple like things on the bottom of the flow bowl) and the pod filters also got wet with gas.

Thanks for your help! I also started a new thread under "gas flow problems."



-Dan from New Hampshire-