Air Leak? How to investigate/solve

[adark248]

Honda Aero 50, 1984

So I've been having a tough time tuning my carb ever since I got the bike. I believe now that I have an air leak at the intake manifold.

I ran the bike, let it warm up and adjusted the idle as per the manual, but every once in a while it will catch and rev on the stand. I shot a spray of carb cleaner around the base of the intake manifold and the engine revved. I can tune it perfectly, then go out for a quick ride and when I return and put it on the stand, the back wheel will take off.

Is this symptomatic of a leak? If so, what could be the culprit? Are there seals or something that might be damaged/missing? Or is it probably more complicated?

[Bear45-70]

Just replace all the gaskets and "O"rings from the crankcase to the carb. Easier than trying to find a suspected leak.

[Dac]

Honda Aero 50, 1984

So I've been having a tough time tuning my carb ever since I got the bike. I believe now that I have an air leak at the intake manifold.

I ran the bike, let it warm up and adjusted the idle as per the manual, but every once in a while it will catch and rev on the stand. I shot a spray of carb cleaner around the base of the intake manifold and the engine revved. I can tune it perfectly, then go out for a quick ride and when I return and put it on the stand, the back wheel will take off.

Is this symptomatic of a leak? If so, what could be the culprit? Are there seals or something that might be damaged/missing? Or is it probably more complicated?

Air leak.

[adark248]

Air leak.

Lol, thanks Dac.

Makes sense, bear. Thanks.

[adark248]

Sooo, is there one particular place to start. A place that would be more likely to need replacing. I'm new to working on engines, so I'd like to start simple and work my way up. Perhaps a gasket near the manifold?

[Bear45-70]

Sooo, is there one particular place to start. A place that would be more likely to need replacing. I'm new to working on engines, so I'd like to start simple and work my way up. Perhaps a gasket near the manifold?

To truly check gaskets and "O" rings you need to disassemble. Since an air leak needs to be in the intake system or the case and the case will almost always show outward leakage too (Fuel and oil), then the intake system is the likely culprit. That's from the air filter box to the case. From the carb to the case is most likely a problem. The intake side of the carb, the spacer, intake manifold and reeds cage. So you have an "O"ring between the carb and spacer and between the spacer and the intake manifold. You have gaskets between the intake manifold and reed cage and the reed cage and the case. Any leak in front of the carb will be at the pipe from the carb to the air filter box and the box cover which has a gasket.

[noiseguy]

Like Bear said, replace the 2 gaskets around the reed block and the 2 o-rings at the carb at the same time is the best solution since you already know you have an air leak.

[zeolig]

I found that getting the carb tight enough is always a problemespecially the bplt and getting access to the nut on the inside ofside of the carb. Make sure that these two bolts are tight or you will never get the carb to tune. zeolig