Carb Overflowing, fuel coming out of overflow

1265 Views 10 Replies 6 Participants Last post by reclinedrelic, May 5, 2022

tom3157

Discussion Starter · May 4, 2022

I have a 1981 Honda cx500c, I’ve rebuilt the carbs multiple times trying to chase this problem down. After rebuilding them the first time it was fine for a few months but then started. Fuel comes out of the bowl overflow tube. It comes out pretty fast. I cleaned the carbs and it has all new parts. There’s no cracks in the overflow tube. If I drain the carbs then it will be fine for a few days but comes back when it sits for atleast a day. I’ve been thinking it could be the pet cock as it is the vacuum operated one. I have a gravity petcock that I’m going to try. I don’t normally turn the fuel off but I drained the bowls yesterday, rode it around for a little bit and then parked it and turned the fuel off and will see if the problem comes back once I start it up again. Is there anything else that could cause this? I’ve gotten pretty good at taking the carbs off and can have them off in a few minutes. So it’s not a problem to me to have to take the carb off to check something. If yoy have any idea let me know. Also should point out that this bike sat for 15 years and that was the original reason for rebuilding the carb.

thanks, Tom.

Save

1 - 11 of 11 Posts

The lost Dane

· #2 · May 4, 2022

Hi
Did you replace the float needle
The needle from the rebuild kits are wrong and will give you problems
All ways replace the needle with a OEM needle from HONDA
Also all the brass that comes in the kit's are mostly wrong
ALL ways re use the brass from the old carburetors

TLD 🇨🇦 🇩🇰

Save

Randall-in-Mpls

· #3 · May 4, 2022

It could be grit slipping through the peacock screen and fouling the float valve. Do you have an inline fuel filter?

Save

tom3157

Discussion Starter · #4 · May 4, 2022

The lost Dane said:
Hi
Did you replace the float needle
The needle from the rebuild kits are wrong and will give you problems
All ways replace the needle with a OEM needle from HONDA
Also all the brass that comes in the kit's are mostly wrong
ALL ways re use the brass from the old carburetors

TLD 🇨🇦 🇩🇰

I did not use oem needles. That was another thought and I was going to buy a new set of needles and floats but I didn’t. I’ll have to get some coming in the mail then. I did buy a fairly cheap rebuild kit on Amazon as I couldn’t find a decent one for sale. Thanks for the reply

Save

tom3157

Discussion Starter · #5 · May 4, 2022

Randall-in-Mpls said:
It could be grit slipping through the peacock screen and fouling the float valve. Do you have an inline fuel filter?

I do not have one but I should and I’ll add it to the list. The petcock does have a screen. But I also had the carbs out a lot of times and cleaned them and it still did it. Although I never thoroughly flushed and cleaned the tank. Which I should also do and I will if I replace the Petcock. The tank did looks clean tho, no rust or anything that I could see

Save

reclinedrelic

· #6 · May 4, 2022

Are you sure that the float bowl drain screws are sealing properly? Did you replace them as part of the carb refresh?

Save

richnct

· #7 · May 4, 2022

Since you said it “overflows” it would seem the float needle/seat is the cause. As said, debris or bad aftermarket needle. Vac petcock may be leaking too, but the float needle should still prevent overflow, just as a non vac petcock is often left on and no overflow should occur.

Save

tom3157

Discussion Starter · #8 · May 5, 2022

reclinedrelic said:
Are you sure that the float bowl drain screws are sealing properly? Did you replace them as part of the carb refresh?

From what I can see they are seating properly, but then again it has to be perfect and I don't know if I can see that with the naked eye.

Save

tom3157

Discussion Starter · #9 · May 5, 2022

richnct said:
Since you said it “overflows” it would seem the float needle/seat is the cause. As said, debris or bad aftermarket needle. Vac petcock may be leaking too, but the float needle should still prevent overflow, just as a non vac petcock is often left on and no overflow should occur.

They are new floats and needles, it could very well be the seat. I was going to see if I can find some oem needles because someone said the aftermarket ones are bad. I also never actually soaked the carbs in anything to really clean them, but there not that dirty. I did clean them pretty well by hand. Ill get some oem needles and swap those in, and then if that doesn't work ill buy another rebuild kit and re-do it again and make sure to really clean everything by soaking it in some fluids for a bit. I appreciate the responses and hoping to get this thing running good!

Save

nolimitz

· #10 · May 5, 2022

first thing you need to buy is a carb book. see my sig line. Do you still have the OEM parts?

Save

reclinedrelic

· #11 · May 5, 2022

Get a length of clear tubing, 4mm IIRC, and attach to the overflow barb on the bottom of the float bowl. Run the tube up beside the carb. If the drain screw is leaking the tube will fill with fuel to a level equal to the fuel in the bowl. If fuel does not enter the tube then crack open the drains screw. Fuel should now rise up in the tube until the fuel level is at the joint between bowl and carb body or slightly below. If the level rises higher than that then there may be a problem with the float and needle valve.

Save

Reactions: 1

1 - 11 of 11 Posts

This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.

Top Contributors this Month