Motor Performance Question

[SHickey]

Hello

I finally got my StarCraft '76 American 20 with the 165 HP straight six and the MC-1 OD on the water and it performed pretty well for sitting 8 months. It ran well in all RPM until I got to @ 4,200. At 4,200 it ran strong for @ 10 sec and then it stuttered. I immediately throttled down and it ran fine after that. I did not attempt to go beyond 4,000 RPM during that maiden outing.

I was wondering if it may be running too rich and maybe a carb needle adjustment might be in order.

This is the same boat that I had problems diagnosing a ticking sound coming from the motor. I cleaned the lifters, adjusted the valves, replaced the shuttle but to no avail The ticking is still there and most annoying to me but the motor starts and runs fine except at that high RPM.

Any thoughts or advice would be most appreciated!!

SH

 

[Bondo]

I was wondering if it may be running too rich and maybe a carb needle adjustment might be in order.

Ayuh,.... It's more likely goin' Lean, from crud in the filters or carb,......

 

[SHickey]

Thanks for the reply.

When I winterize the boat I run the carb dry so there is no old gas sitting in the carb. The filters and gas is new and clean.

Would you suggest I spray the carb with some carb cleaner and flush it out and see how it runs?

I believe the operating max for that motor is 4,500 RPM.

 

[Bondo]

Would you suggest I spray the carb with some carb cleaner and flush it out and see how it runs?

Ayuh,..... So long as ya understand that all the important places to shoot the stuff,.... ya can't see til the carb is disassembled,......

 

[SHickey]

Thanks for the reply,

I rebuilt the carb in the winter of 2014 and have been very careful with the fuel that goes into it. (premium w/ lead additive and a can of dry gas with every 18 gal fill up) I will remove the carb filter and see if there is any debris in it. The fuel also goes through a water separator.

If all looks clean, would you suggest a 1/4 turn counter clock wise on the 2 carb screws for starters? The timing is set to specs and the spark plugs are new this year.

 

[Howard Sterndrive]

could be a weak fuel pump or a restriction, but it sounds like the fuel supply isn't keeping up with the demand.

 

[SHickey]

Thanks for the response!!

The fuel pump is @ 3 years old and it is a mechanical pump attached to the side of the motor. Is there an easy way to test the volume of fuel being pumped to the carb or test the pressure of the fuel line while the pump is working? I have a compression gauge I could use but I would need to make some modifications on it to test the fuel flow.

I am not sure how much fuel or pressure the pump creates while it is working

 

[Howard Sterndrive]

the test is generally to tee a gauge into the fuel supply at the carb. Pump should maintain 5 psi or so on plane.
requires an accurate low pressure gauge and some plumbing, but that pressure means the fuel pump is delivering more than the engine is drinking.
Is the clear yellow hose from pump to carb clear of fuel? (or does a 76 have a glass bowl?)

has the anti-siphon fitting at the fuel tank pickup been mentioned? not sure all 1976 boats had one, but they can get crud in them and restrict fuel . also some tanks do have a mesh screen on the pickup.
you also might try a run with the fuel cap off in case the tank vent is restricted - can check for mud wasp packing of the vent

any carb pop or backfire with the "stutter"? you might let it die and see if it lets out a big lean pop verifying it ran out of gas. then you could pump the throttle and see if the accel pump is shooting gas to verify fuel in the bowl.

of course that's a hard way to shut off an engine and you will get a big transom wash so not something you want to do repeatedly or if exhaust water shutter is not known to be healthy.

 

[SHickey]

Thanks for the response,

I will see if I can borrow or but a low pressure gauge from Harbor Freight and check the fuel pump pressure. I was also curious if guys have installed electric fuel pumps on these motors for reliability? I am also thinking of installing an electronic ignition and eliminating the points for a more reliable ignition system, I just have not gotten around to it this summer.

Any thoughts??

 

[Rick Stephens]

Thanks for the reply,

I rebuilt the carb in the winter of 2014 and have been very careful with the fuel that goes into it. (premium w/ lead additive and a can of dry gas with every 18 gal fill up) I will remove the carb filter and see if there is any debris in it. The fuel also goes through a water separator.

If all looks clean, would you suggest a 1/4 turn counter clock wise on the 2 carb screws for starters? The timing is set to specs and the spark plugs are new this year.

Sounds like carb needs cleaning again. It sounds lean, not rich, All that takes is a plugged passageway in the carb. Generally speaking any crud in a carburetor will make it run leaner.

The idle mixture screws will do nothing to change any carburetor problem except at idle. They play no part in higher fuel and airflow operation.

Rick

 

[SHickey]

Thanks for the response.

I wont touch the idle mix settings because it runs great at idle and all speeds below 4200 rpm. I will spray some gumout into the carb after I look at the carb fuel filter and see if it is dirty.

Any thoughts on the electric fuel pump and the electronic ignition on that old beast of a motor??