Topic: bike stalls when throttled hard.

[asom]

Hey everyone.  Just finished syncing my carbs with a vacuum guage they are even across all four, starts right up sounds great, BUT when I hit the throttle it dies.  If I slowly throttle up it's fine but if I hit just a little hard it stalls.  Also, when I do rev it up the RPM's stay where ever I stop (i.e. rev'd to 3k stay at 3k)?

any ideas?

Thanks.

[manjisann]

Air leaks on the engine side boots. An easy way to confirm this is to start the bike and then hose the boots down with something (I use start fluid but some people worry that if it hits a hot engine, KABOOM). If you idle changes significantly then you've found your leak.

Brandon

[mlinder]

Box and filter on?

Which carbs?

You can't whack open mechanical slide piston carbs.

[asom]

this might help....1978 Honda CB750

box and filter on.  synced all four carbs

not sure what whack open mechanical piston carbs means....sorry

[mlinder]

Opening more than half throttle quickly.

As Manji said, check for airleaks.

[asom]

got it.  I'll check and get back soon...

[asom]

boots between airbox and carbs, between carbs and head, or both?

[mlinder]

Both.

[manjisann]

Mlinders more of an expert than me, but my guess is it's the boots between the carbs and engine. If I win will Hush send me a chocolate fish?? 

Brandon

[mlinder]

The leak between carb and head is more serious, but the leak between carb and box will still lean out the mix.

Hardy an expert, manji, I have just posted a lot. But thanks for the ego boost!

[BobbyR]

You have an accel pump on those carbs, that pump can gum up quickly, if you have not cleaned it out that may be your problem. 

[asom]

haven't been able to locate any air leaks in the boots on either side.  i was thinking about liquid electrical tape just to se if I'm missing the leak.  If that fixes it then get new boots?  bad or good idea?

I'm assuming the accel pump would relate to the throttle sticking, right?  Is that the rubber plunger with the spring on the 2nd from right carb?

[lrutt]

I'd be willing to bet the accel pump diaphram is not working at all. Mine wasn't. There wasn't even a hole in it to xfer the fuel up the squirter circuit. I punched a hole in there and voila, now I have squirters. I also bent the actuator tab so that whenever you twist the throttle you get accel pumps, Before it would take almost a 1/4 turn before it did anything. Runs WAY better now.

[BobbyR]

haven't been able to locate any air leaks in the boots on either side.  i was thinking about liquid electrical tape just to se if I'm missing the leak.  If that fixes it then get new boots?  bad or good idea?

I'm assuming the accel pump would relate to the throttle sticking, right?  Is that the rubber plunger with the spring on the 2nd from right carb?

No it would not stick. there is like a 1/2 thimble full of fuel in there and it spoils quickly since it is such a small amount.

[eurban]

Pull off your air filter and visually check the operation of the accelerator pump.  Fuel must be available.  Whack the throttle open quickly and look for fuel squirting from the pump's brass nozzles located at the bottom of the carb bore next to the choke plates.  You will notice a notch in the choke plates to clear the nozzles.  Got fuel squirting?  These carbs need the pump working to function properly . . .

[asom]

I'll remove the box today and look for fuel squirting.  In the mean while, can anyone recommend  where to purchase all 8 replacement boots?  I'm guessing I'll replace them either way.

Thanks