85 carb motor major surge problem help!!

[dawsoncharles]

yes firing order is correct.the crazy thing is the boat ran fine when it was put last winter. Spring comes and here I am. Like I said I had a lot of trouble even getting it to run. It would fire on starting spray but wouldnt stay running I ended up pouring gas down the carb numerous times( i know that is dangerous) and then eventually would idle but could not rev it up. After continuous tries and nursing the throttle up I could get it to run at high rpm in idle. I just kept stabbing the throttle until it seemed to work it out. Put it in the water and now have the terrible surge under load. btw the boat will stall quickly if you just close the primary butterfly all the way but if you hold it just very slightly open it seems good

[thatsmrmastercraft]

I read through the post again. It sure does sound like a fuel volume issue. You might disconnect the fuel line at the carb, clamp a rubber fuel hose over the metal line and do a volume test. I don't remember the specs for volume and time cranking (again exercise caution here). Someone will probably know the specs, or check a manual.

[dawsoncharles]

well to let everyone know, because of the distance between me and the lake/boat, i ordered a fuel pump as possibility and a rebuild kit per most recommendations. I am planning on going ahead with the rebuild and bolting it on this weekend to see if that fixes it. if not i am installing the fuel pump and moving on from there. Thanks for all your input and will def post my results for hopefully somone elses benefit. Thanks again what a great resource this is.

[TMCNo1]

If it gets where it won't idle right and you get large amounts of black smoke out of the exhaust, it's the power valve that needs replacing. It has a hole in it and is flooding the engine.

I have an 88 Prostar 190 with a similar problem. It runs good cold at idle, but bogs down/cuts out once up to a certain speed. Then it doesn't want to start when hot and wants to die at idle. I rebuild the carb and I'm still having the same problem even after adjusting what appeared to be a bad float setting. Other than the carb cleaner spray suggestion, any thoughts? I think I also saw fuel pump mentioned. Thanks for any feedback!

[oldairboater]

You need to trouble shoot one problem at a time. Check the vent. Check the fuel line. Replace the fuel filter. Check the fuel pump. Check one thing at a time and make sure that everything you check is right---then move to the next possible problem.

[Alanb]

Fishing for a fix for mine as well, rebuilt the carb (4010) and replaced fuel filters. Runs very rich, it won't run at all if you plug in the crank case vent hose in the intake. Installed new plugs as well. Waiting for a cap and rotor from Ski dim, not sure what to look at next.

[thatsmrmastercraft]

Originally Posted by Alanb

Fishing for a fix for mine as well, rebuilt the carb (4010) and replaced fuel filters. Runs very rich, it won't run at all if you plug in the crank case vent hose in the intake. Installed new plugs as well. Waiting for a cap and rotor from Ski dim, not sure what to look at next.

That sounds like a blown power valve.

[oldairboater]

I am new to this web site and to Mastercraft boats. I am not new to boats. Vapor lock issue is a new one for me. I don't have that problem now and probably won't because of my set up. Just reading these post there are a lot of fuel problems on here and usually it is after storage from winter. With the big blocks and Holley's we run in the other boats we will have issues if they sit. We fight alcohol deterioration on fuel lines and it's affinity for moisture. We don't winterize--we use the boats year around but we also use fuel stabilizers. Sitting gas is a problem here due to humidity and fuel separation. I will partially winterize my Mastercraft this year in between use just in case we get to freezing temps but I will use fuel stabilizers all year around anyway. Seems some of this could be prevented. Glad this site is here. I appreciate the practical knowledge.

[Alanb]

Well, slapped in the new rotor and cap and life is good to go.. Thanks for the help!!