I have 350 chev in boat, Holly 4 barrel carb running great now wont starves for juice under 1800 rpm no idle?

Question

Had the carby off blewn it all out nothing seems out of the ordinary gaskets all good, running great then two days later just will not cooperate I bet it's something really simple I don't have a lot of experience with holly's but if you do please can you offer me advice, cheers steve.

Answer 1

Runs good at higher RPM? Did it backfire? Is it a new carb, or an older one? You might have a vaccume leak at the carb gasket, or elsewhere on the intake. You might have a blown power valve in the carb, plugged air bleeds, or even cracked metering block. only the newer Hollys have blowout protection. Do you have a marine carb, and do you use it in salt water? If you have an automotive carb and use it around alot of salt water, then you should step up and get a marine carb. Check for vaccume leaks first, spray some carb cleaner lightly around the base of the carb and around the intake while its running, if the RPM suddenly increases, then you got a leak. If not then rebuild the carb, If you dont have the knowlege to do it yourself, then check around for a carb rebuilder and have it rebuilt. You might be happier with an Edelbrock marine 650, no power valve to blow, and much easier to tune.

Answer 2

If you blew the carb out with compressed air you probably lodged a piece of debris into your metering circuit or downleg booster. Take your carb apart, front and rear bowls or front bowl if it's a single pumper, and thoroughly clean the entire thing. Holley carbs are easy to fiddle with, there are no small parts that will fly out or get lost. Take your time and pay attention and you'll be ok.

Answer 3

1.  did you adjust the idle (throttle position?)

2. did you adjust the idle circuit s***w?

3.  if it ever backfired, you may have ruptured the diaphragm in the accelerator pump. or you could have ruptured it when  you "blew it out".  (dont do that ever again....we'll let it slide this time, cuz this is probably our first carb)

4. did you change cams?  did you go to a more agressive cam? like 500 lift /220duration intake? if so then you will naturally have a much higher idle speed.  it just wont "lope" at low RPM.

5. do you have an intake plenum with your new carb.  if you are using 650cfm or such then  you will likely need at least a small plenum (chamber that helps mix the air/fuel mixture prior todistribution.