1986 Maxim 750 Fuel Leak

I'm a bit stumped. I've taken apart and cleaned and inspected my carbs recently due to a gas leak out the overflow tubes. I found lots of corrosion and varnish and spent a bit of time cleaning an freeing everything up. I then bench tested the fuel flow and there were no more leaks. I figure that the problem was resolved. However, after reinstalling them and starting the bike...fuel started to pour out again. I can only assume the needle valves are stuck or not functioning but if that's the case, why would it not leak on the bench? I attached my portable test fuel tank and let them sit overnight. I tipped and shook the carbs to be sure and nothing leaked. Verified carb bowls were full of fuel. The minute the carbs went on the bike...leaking like crazy. Did i miss something? I've worked on hundreds of carbs and can't see why this happened. Only thing I can think of is the float valves are toast but why would it not leak on the bench? Any ideas?

Thanks!

 

Just to understand, you have not rebuilt the carbs with new parts, you have just disassembled, cleaned, and reassembled with the old parts and wet set the carbs on the bench, right? And when you mount the carbs back on the bike and start the bike, you have fuel leaking, just exactly where is the fuel leaking from?

 

Thanks for the reply. Actually, i did replace the main jets as one broke off when removing it. All other parts I kept as they were not worn or damaged only gummed up. The float valves and seats were quite bad and attributed the leak to this but as I said, when I run the bike, the fuel pours out the overflows but not when wet tested on a bench.

 

I think you got lucky when you tested it on the bench. My bet is that the float needles are cockeyed in their bores, or the ends are swollen from having contact with carb cleaner.
Regardless, you need to visit The Church of Clean. Three decades takes its toll on carbs. A quick flushing simply will not do.

 

I'm with k-moe. But it is strange that you couldn't get them to leak off the bike. In any case, I recommend the solid brass needles instead of the "rubber" tipped ones. Buy them from Chacal with the matching seats and you won't have any problems. I have to admit to being a little nervous about the solid needles but Chacal convinced me to try them and I'll never go back to the others.

 

I like my viton tiped needle valves just fine. The brass ones are good too.

 

I suppose you got a point. it's the first time this has ever happened to me though so I wasn't completely convinced it's the float needles and/or bores. I've done at least a hundred or more carbs over the past few years as I know a lot of people who own vintage/older bikes and this never happened. Just did a set off a 1979 GS750 and they were in worse shape. Bike runs like a mint. But I digress. I will pop them off again and replace the needles and seats and try it again. Thanks for the tips. Much appreciated.