Need Help. L20b dies when filter is on the carb

[69dimez]

I was working on my 510 the other day (it has an L20 swapped into it) and I was able to turn it over just fine. This engine has been a runner for months, close to a year.  I let the car idle for about 10 minutes so it could warm up, but the moment I backed out of the driveway the engine died, almost as if the car stalled. I attempted to turn it over but it wouldn't start. I got the car back into the garage and started to investigate the problem. My fuel pump works and is providing gas to the Carb(Weber downdraft 32/36). None of the jets are clogged either. The car will run and idle completely fine WITHOUT the air filter or the lid that fits on top of the carb, but once they are on the car doesn't want to start. I have had the car running and then put the filter on and it dies. Lack of air flow? Need some help to find a solution.

[Stoffregen Motorsports]

Look for a problem. This shouldn't happen, so there's something else going on.

 

Is the carb tight to the manifold? If you're using a two piece carb adapter, those allen screws in the middle come loose (I use red loctite). Same goes for the rest of the carb nuts. Those are known to come loose.

 

Is the air cleaner physically hitting something? Like a linkage piece or a choke butterfly? Or is it grounding out on the fuel cut solenoid?

 

I just went through this reverse problem on my Polaris 700 quad. It was a broken rubber intake manifold. The manifold looked fine, but had a massive slit on the bottom allowing for more air than the engine wanted. It would only run with the air filter installed. Acted like a clogged jet, but I knew it wasn't, since the carb had previously been cleaned.

[banzai510(hainz)]

do as mentioned above.tighten all bolts and nuts.

clean out the idle jet.

I would also check or redo the mixture screw at the base of the carb