Carburetor Question

[CoralReefer]

Well I fixed my idle issue with a new carb bought off eBay. Runs like a champ now. However, the Rochester carb that I bought had a vaccum port on the rear that my mechanic said should have been plugged. Anybody know what this is for?

 

[fc3]

Depends. Above or below the throttle plate? Large or small diameter port? Could be for a choke pull-off or PCV hose. Are you 100% positive that you have a marine carb? Marine carburetors usually don't have vacuum ports. You have to be 100% positive. You're betting your life and the lives of everyone on and near your boat.

Best regards,
Frank

 

[douglee25]

It sounds like it's a vehicle carb. If it's a large port on the rear of the carb below the throttle plate, more than likely it was for a brake booster. If that's the case, it should be plugged. There should be a large port on the front side of the carb below the throttle plate (3/8" nipple) for the PCV valve. There should also be small 1/8" ports that are for ported and full vacuum. The ported vacuum (above the throttle plate) signal goes to the vacuum advance on the distributor and the full vacuum port can be plugged. You can test for ported or full vacuum with a gauge or your finger by feeling the ports at idle. Ported vacuum has little to no vacuum at idle and the vacuum increases with engine rpm. Full vacuum has just that, full vacuum no matter what rpm.

Doug

 

[Cap10Pat]

I'm with Frank, if this is not a marine carb your only choice is to remove it. Any advice about how you're going to fix it to become a marine carb without knowing what it is or what your skills are is equally reckless. Just take it off. If it was misrepresented you should get your money back. The proper carb will probably run better anyway.

 

[CoralReefer]

My mechanic plugged it (he's very reputable in the area). What am I risking by not pulling this one and return it? The boat is running great.

 

[douglee25]

If in fact it's a non-marine carb, it lacks provisions to contain fuel leakage or fuel vapors as compared to a marine version. They all start out as non-marine carb bodies but they they go through a series of modifications to suit the marine environment.

See this thread for Holley carbs.

Doug

http://www.cpperformance.com/products/Fuel_Systems/carb-selection.htm

 

[CoralReefer]

The inverted vent tube on the carb is correct. I need to check the throttle plates tomorrow to see if they are grooved. Could they have used an automotive base and a marine top portion on their rebuild? My marine mechanic is one of the best in the area and he didn't act like the open port was any big deal and that they forgot to plug the port on the rebuild. He actually got the plug (I forgot the actual techical name for it) from a marine rebuild kit at his shop or so he says. I'll check tomorrow and post my findings on the throttle plates. Thanks again!

 

[GREGNLIZ]

Our resto on our 78 SRV 240 includes switching out auto carb and fuel pump to marine so we know what you're going through! YIKES. First - dangerous to be even starting the boat in the driveway, let alone on the lake. Could burn down everything in proximity. We just bought an Edelbrock Coast Guard approved marine carb and have a Carter marine fuel pump on the way. Have to have the vent port on the carb returning to the pump or else. Insurance is Void! Wish us luck and hope your set up works great too once your done,
Cheers!

 

[CoralReefer]

Yep. It was done some time ago and works perfect. It was the correct carb. They forgot to plug the vacuum port that was designed to power the brake booster (auto application...they sometimes use auto carb parts during rebuilts) It's coast guard approved with the J tube and only cost me $160 on eBay.

Good luck on your deal!!