All of a sudden my Tyler Crockett built 502 has become very hard to start. I believe it is getting too much fuel and flooding out. I am more of an automotive fuel injection guy... I see there are some adjustment areas on this carb, but I have no idea what each does. It is a marine 850 Mighty Demon carb, I believe the part # is 5563010GM? I bought boat with the engine already done by Tyler.


I have NGK TR8 plugs with MSD igntion gapped at .040

My fuel pressure regulator is reading 9 PSI with key on. The regulator seems to be making more noise than it has before.

I can see the carb squirt fuel


If anybody can please give me directions for how to adjust this carb (I cannot find the directions on the internet), that would be AWESOME!

Or maybe even some help diagnosing why it is very hard to start now all of a sudden


Thanks!!!!!!!

Turn your fuel pressure down to 6-7 lbs. Sounds like too much pressure pushing past your float needles .

Agree fuel pressure needs to be 6-7. Lower the pressure then adjust the floats while on the water, not trailer. Floats are adjusted by removing the sight plugs on the side of the fuel bowls and you adjust the floats by loosening the top jamb screw on the fuel bowl and turning the nut below the jamb screw to raise or lower the float. Adjust to where fuel is just below the sight hole. You might also try adjusting the idle fuel circuit on the side of the metering plates. These adjustments are a small needle screw that accepts a small straight screw driver. Turn the screws in until they stop and count the turns. Should not be more then 1 1/2 turns in. Then screw the needle screw out 1 turn and start the motor, once motor is at operating temperature turn each screw in and out and adjust to maximum RPM, or maximum vacuum if you have a vacuum gauge handy. Once done you can adjust the final idle speed with the straight screw on the throttle shaft. These are your basic outside adjustments. If this does not resolve the issue you probably need to service the carb, take apart and throw a rebuild kit in it.

The 9 PSI pressure is with the key on and engine OFF. Is it ok to adjust the pressure with the key on and engine OFF???

Yes then recheck with engine running .

I got the boat running and starting good. Adjusted the fuel PSI and lowered the float bowls... What would have caused the fuel pressure to jump to 9 PSI?

Also, I was looking at my Dyno sheets from Tyler Crockett and it shows the fuel pressure to be set at 7.5 PSI.... Should I use the 7.5 PSI he used to dyno it, or lower it to the 6-7 PSI range?

Thanks again for the insite guys!!!!!!!!!!!!!!!

7 lbs and you will be good to go.