All 4 carbs overflowing

[stevelknievel]

I apologize if this is a dumb question I’ve been searching and looking at every resource I can find and I’m still somewhat stumped. It’s been a good 12 years since I’ve messed with a bike / carb. I recently was given a 81 750c that had been sitting, I’ve pulled the carbs and replaced the floats and needles as well as cleaned everything out but I am still getting all 4 carbs overflowing as soon as I put gas to them. Float level is in spec according to the service manual, there appears to be no real wear on the seats either. I have checked the overflow tubes and they’re all fine and I’ve made sure it wasn’t coming from the o rings on the fuel rail as well. I’m sure I’m missing something but I cannot for the life of me figure out what it is. Thank you in advance for any advice

 

[brettp]

If your float valves are good then perhaps you're overflow tubes are cracked. Which is odd considering it's all 4

 

[stevelknievel]

I’ve taken the bowls off and filled them with fuel and none leaked, I’ve visually inspected all of them as well and didn’t see any cracks

 

[brettp]

If those are good, then either your floats are seating the valve well enough or your fuel rail orings have deteriorated and failed. I had an oring between carb 1 and 2 fail and when the fuel ran out it would drip along the body of carb 2 and down to the drain. I didn't realize the leak started above because I couldn't trace it easily.
So, since the bowls are off clean the valve seats (where the fuel comes in the carb bowl) with some brasso to polish it up. When that is done, bench test the carbs by feeding the inlet (I put a tube on it with a small funnel or use a bottle feeder) and you'll be able to more easily see where the leak is coming from.

 

[Davidson750]

Floats or needles.

 

[loxley007]

Make sure you have the correct floats. I ordered replacement ones and they were no adjustable. I had overflow issues so bought more expensive adjustable ones - problem solved for me.

 

[Davidson750]

Floats or needles.

 

[Davidson750]

I always give them a slight little tap when I first put fuel to them.. it can help seat but if you have all four overflowing that's a bit of a problem

 

[Capt Dave]

I apologize if this is a dumb question I’ve been searching and looking at every resource I can find and I’m still somewhat stumped. It’s been a good 12 years since I’ve messed with a bike / carb. I recently was given a 81 750c that had been sitting, I’ve pulled the carbs and replaced the floats and needles as well as cleaned everything out but I am still getting all 4 carbs overflowing as soon as I put gas to them. Float level is in spec according to the service manual, there appears to be no real wear on the seats either. I have checked the overflow tubes and they’re all fine and I’ve made sure it wasn’t coming from the o rings on the fuel rail as well. I’m sure I’m missing something but I cannot for the life of me figure out what it is. Thank you in advance for any advice

I'm having the exact same problem. I have checked everything. The needles are new and do not leak when the bowls are off, but when I put the float bowls back on the carbuerators and put fuel to them, they all leak! It does the same thing with new floats and the original ones. Help!

 

[Davidson750]

I'm having the exact same problem. I have checked everything. The needles are new and do not leak when the bowls are off, but when I put the float bowls back on the carbuerators and put fuel to them, they all leak! It does the same thing with new floats and the original ones. Help!

Are you using aftermarket bowl gaskets?..where is the fuel coming from?. unfortunately some aftermarket rebuild kits are not that good,... Is it coming from the overflow, or is it coming from the float bowls themselves?

 

[Davidson750]

Are you using aftermarket bowl gaskets?..where is the fuel coming from?(Overflow )unfortunately some aftermarket rebuild kits are not that good.

 

[mrtwowheel]

Where do the carbs leak from?

 

[plantguy]

Make sure you have the correct floats. I ordered replacement ones and they were no adjustable. I had overflow issues so bought more expensive adjustable ones - problem solved for me.

I have found some of the aftermarket parts for these bikes to be junk, even some parts from a reputable source like 4 into 1. Check https://www.ronayers.com/ and https://www.sudco.com/carburetors.html also tuning help http://www.shiny-red.net/guides/keihin-carburetor-jetting/