Carb Overflow with All New Parts

[Newell33]

I would like to apologize for continuing this saga. Sometimes something small can trigger a reaction, and Steve's comments triggered an uncharacteristic reaction from me. Yes, there are plenty of message boards with ego issues. www.fiatspiders.com was started due to a similar problem at www.fiatspider.com. Check out any A/C thread at www.pelicanparts.com and you'll see the same. I don't typically speak out like I did, but I wasn't in the right mood at the time, and then I pushed ahead. Again, my apologies to the board.

I spent about an hour tonight playing with the carbs. I took the seats back out, made sure all the o-rings were not pinched, made sure that the needle springs were ok, and checked all four floats to see how they actually float in fuel, not water. Everything looked good and moved freely. I then hooked the fuel up with the bowls off, and with the fuel flowing I pressed up lightly on each float. The fuel flow shut off for each carb as it should. I then put the bowls back on and hooked up the fuel. As soon as the bowls filled up, the vent tube in between 1 and 2 started leaking fuel.

At this point in time I decide to check the board some more for ideas. BigD's post got me thinking about the gaskets (sometimes a different perspective helps). Looking more closely, it appears that my aftermarket gaskets are much wider on the sides than they need to be. When the bowls are tightened down I could see where they might actually contact the sides of the floats. I decided to trim the sides and see if that fixes the problem. I was excited that this may be the fix, but unfortunately it wasn't. The good news is that before trimming the gaskets the carbs would leak regardless of me banging or tapping on the bowls. Now I can get the fuel to stop by banging / tapping the carbs on the bench. What's weird is I can hear all four floats moving up and down when I tip the carburetors with the bowls intact. I then swapped fuel bowls and floats around to see if maybe the floats were rubbing on the side of the bowls. Still no change.

Although I ran out of time for tonight, I plan to take another look this weekend. Obviously, something has to be keeping the float(s) from moving as freely as they should with the bowls in place. I had previously set the float heights a little lower in the bowls (more than 22.4mm) to try to see if that would fix the problem. I'm wondering if that maybe one of the floats is rubbing on the bottom of the bowl since the height is slightly more than it should be right now. It still shouldn't touch, but who knows. There's nothing else left to check unless I'm missing something.

One question that I have is if the floats are rubbing on the bottom outer edge, could they be trimmed ever so slightly? Are they solid internally, or do they have cavities inside? If solid, I may put some sort of marking material on the edges, see where they may be rubbing, and do a little trimming.

 

[tatu]

Steve is a precise, mega helpful and all round good person.

Have you tried, Bowls off, blowing down the fuel inlet with a tube and operating the float manually to see if they are actually shutting off and roughly at what point? Are the seats and needles exactly the same as the ones you took out.

 

[Newell33]

Steve is a precise, mega helpful and all round good person.

Have you tried, Bowls off, blowing down the fuel inlet with a tube and operating the float manually to see if they are actually shutting off and roughly at what point? Are the seats and needles exactly the same as the ones you took out.

I didn't used compressed air, but I did hook up a small fuel tank to the fuel inlet while the bowls were off. The fuel shut off as it should when I lifted the floats for each carburetor. It seemed to shut off just when the floats just start to depress the needle spring mechanism. Below is a photo of the carb kits that I ordered. The needles and seats appear to be the same as what was removed. I'm pretty sure the floats have to be making slight contact with the bowls, or they're barely getting hung up somehow.

 

[chewbacca5000]

If tapping stops the overflow then maybe it is an air bubble? I'd suggest at this point to screw in a clear tube to the bottom of the float bowl and check the actual fuel height, and maybe sure they are the same across all 4 carbs. Should be the same with new kits and proper adjustment of floats.

I am going to strip my completely and put each body 1 at a time in my ultrasonic. The dip bucket probably works best though with compressed air after. I just hate that nasty stuff though.

 

[Larry D]

Attach the vacuum line as well.

 

[Guest]

I didn't used compressed air, but I did hook up a small fuel tank to the fuel inlet while the bowls were off. The fuel shut off as it should when I lifted the floats for each carburetor. It seemed to shut off just when the floats just start to depress the needle spring mechanism. Below is a photo of the carb kits that I ordered. The needles and seats appear to be the same as what was removed. I'm pretty sure the floats have to be making slight contact with the bowls, or they're barely getting hung up somehow.

You just spent a lot money you didn't need too. EgoSteve, that's funny. Anything but.

 

[BigD_83]

One question that I have is if the floats are rubbing on the bottom outer edge, could they be trimmed ever so slightly? Are they solid internally, or do they have cavities inside? If solid, I may put some sort of marking material on the edges, see where they may be rubbing, and do a little trimming.

I think it will depend on what floats you have. The brass one's are definitely hollow. I believe the rubber ones are, too, although I have never cut one open to have a look. IMHO, this is a less than desirable way to go about things as it will change the mass/density of the float, and may lead to you chasing your tail. Still, marking them and checking for rub might be an informative exercise.

 

[tatu]

I didn't used compressed air, but I did hook up a small fuel tank to the fuel inlet while the bowls were off. The fuel shut off as it should when I lifted the floats for each carburetor. It seemed to shut off just when the floats just start to depress the needle spring mechanism. Below is a photo of the carb kits that I ordered. The needles and seats appear to be the same as what was removed. I'm pretty sure the floats have to be making slight contact with the bowls, or they're barely getting hung up somehow.

I wouldn't use a compressor, just a length of tube and blow with your mouth and push the floats up until you find the point at which the air ceases to flow you will then have an idea of what you have and where to look re, sticking floats if at all, are the needles and seats exactly the same as the ones you took out? If not it will be another indication where to look.

 

[BigD_83]

Hi guys. I have a 1980 GS750 that I've been working on. I installed all new needles and seats, as well as all new stock jets and gaskets. Josh

Going back to the original question, why did you go with the new needles and seats in the first place? Were the carbs flooding before the rebuild?

 

[Newell33]

Going back to the original question, why did you go with the new needles and seats in the first place? Were the carbs flooding before the rebuild?

I actually purchased the bike in non-running condition. It had been setting for the last 3-4 years. When I opened up the carbs two of the original seats were so gummed / crudded that I didn't think they'd ever come clean. The needles also had a ring around them where they rested against the seats. The rubbers that were installed over the pilot jets had turned into a stringy gooey mess, and the jets were plugged with this goo and fuel residue. Since I needed the rubbers, and I was concerned about the pilot jets and needles / seats, I decided to go with the kit as shown. Based on the condition of the parts I was happy to spend the money on new pieces. I haven't had any problems in the past with aftermarket kits, so quality wasn't a concern.

 

[Newell33]

Problem solved!

I had a chance to take another look at the carbs the other night. I decided to take the bowls off again and check things out once more. I thought I had the aftermarket gaskets trimmed enough, but evidently I didn't. I ended up trimming them a bit more, and that solved the overflow problem. A good lesson here is aftermarket parts can be suspect. I had the original gaskets removed for a period of time before installing the new gaskets. I didn't even thing about them being wider than the originals until another member mentioned it.

Thanks for the help and suggestions.