The Stovebolt Site Forums The Shop Area Engine Shop 250 Chev Engine Question

My father has a 250 chev (1976 maybe) in a boat with electronic ignition and a single barrel rochester. The motor runs good and starts right up but if you bring the rpm's up too fast, it bogs and sometimes stalls (mostly just bogs then catches itself). If you bring the revs up relatively slowly, it revs up without issue, no missing etc.

It can be a pain, when trying to dock the boat, when you have to make quick corrections.. The plugs are new, and the carb has had the fuel filter changed. We have adjusted the air/fuel mixture in until it started to stumble, then backed it out 3/4 of a turn until it idled smoothly- didn't help- still bogs if you get on the gas too fast. Any ideas?

Hy shawnmd, welcome, it sounds like the accelerator pump is not working up to capacity. Remove the air cleaner and work the throttle with the engine off, you should see a shot of fuel being injected into the carb each time you work the throttle. If you don't see that then the carb should be rebuilt, hope that helps.

Take the flame arrestor off the carb and look down into the carb throat (Engine not running) and have someone work the throttle lever. There should be a squirt of gasoline anytime the throttle lever is moved toward the open position. (Accelerator pump). Chances are the pump is bad, or isn't providing enough of a squirt to prevent stalling unless the throttle is moved very slowly. It sounds like it's time for a carburetor rebuild.
Jerry

Thanks guys...I thought it muight be the accelerator pump. Something I noticed tonight, it seems like there is a second port for the gas line on this carb towards the top (we have the line connected at the bottom port), and it is wide open- no plug. Is this a fuel line port and should it be plugged?

scratch that, i think that is a vacuum port just above fuel line, , on an angle downwards. If that is wide open, that would be a vacuum leak and cause the same issue?

That one is probably a float chamber vent line, intended to go to a charcoal canister on a car engine, not a boat. Leaving it open might allow gas fumes to accumulate under the engine cover and present an explosion hazard. Marine carbs have a different vent system to prevent vapor buildup in bilges or under engine covers.
Jerry

Hy shanmd, any vacuum leak can effect performance, leaning out the mixture, cap that open port and see how she runs then, you can check the accelerator pump function at the same time, hope that helps.

In addition to the accelerator pump, and depending if its a mercruiser or OMC unit, there may also be an issue with the advance on the distributor. the Marine guys did their own ignition systems.

They use centrifugal-only distributors, with a slightly different advance curve. There are also flame-arrestor vents on the distributor to prevent an arc from the points from igniting bilge vapors. Lots of boats have blown up while starting from a stray spark getting together with a few gas fumes trapped below decks. ALWAYS run the bilge vent fans for a while before starting an inboard boat!
Jerry

Thanks guys, but the motor is mortly made up of car parts- including the distributer.

I checked for the squirt of fuel and pumping it before starting and even after its warmed up, produces no squirt of fuel in the carb.

So it must be the accelerator pump. Where is it located in this carb? Can you buy just the accelerator pump assembly?

Do it the right way, and get the carb rebuilt by a qualified professional. While you're at it, if the engine is enclosed in any sort of a housing, buy yourself a flak jacket and a good life insurance policy. Running car parts without flame arrestors on inboard boats is asking for a disaster, sooner or later.
Jerry

It does have flame arrestors etc, bige fans, etc. , I meant that it is using auto type distributer, like every other fising boat in the maritimes.

OK, just concerned, as I've run the salvage barge at a few accidents at marinas here in middle Tennessee, and it's not pretty cleaning up after a bilge explosion that burns a couple of sections of the dock as a result. If a distributor has conventional points, all it takes is a little vapor accumulated under the cap to cause real problems. HEI distributors with good-condition wires aren't quite as dangerous.
Jerry

Finally figured it out, took carb apart, and found the accelerator pump in upside down......yep, don't know who did that ... Anyway, put it back together, runs perfectly now.