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mitchq

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I have a 1982 chris craft scorpion with a 305 898 mercruiser in it. When I got it I put on a new Rochester two barrel, changed the oil, all new filters. It started out running great at full speed and then would start to die quickly like it ran out of fuel. Took a minutes to get it restarted like it needed to refill the fuel bowl, once it started again it would run up to full speed and die out again and the engine would completely stop. So I decided to replace the fuel pump cause I thought it wasn't able to keep up. The last two times I have had it on the lake it will not pick up past 1500 rpm and chugs alone at full throttle. I have messed with the screws but doesn't seem to make any difference. The engine runs great on the hose, idles great and revs up nice, sounds good just under load it will not run with any kind of power. Could this be some kind if ignition issue? Or maybe have the wrong jets?
 
Check fuel pick in tank and anti siphon valve, sounds like it has a fuel volume problem. Need to do fuel psi test and volume test. The screws you were "messed with" are more than likely idle mixture screws and only effect low speed and idle. Also try unscrewing fuel cap and run it to see if it still dies, could have a plugged tank vent. Check fuel lines for obstructions and when was last time fuel filter was changed. Does it have a water separator? change that also. As for running on hose, not a true test, no load.
 
Thanks man. I understand there is no load on the hose. I have checked the fuel pick up and it's clean. It has fresh ethanol free 88 octane. New fuel filter/ water separator. And I did actually take the cap off with it in the water and tried that, did not help unfortunately. Later I made sure the vent was not plugged. All my fuel lines are in good order as well. BUT the anti-siphon valve is something I need to look at.... It just looks like a brass nipple so I didn't realize that's what that was so I was figuring I just didn't have one of those . (I just looked it up) so thank you again. I hope it's that easy. I have not tested the fuel pressure but i had a new pump on hand so I just replaced it hoping it would do something and I know I have good compression because like I said before I have seen it run very well briefly. Anti siphon valve. 10-4. Now that I think back when I had the fuel pick up out inspecting it I did blow thru the fuel line and had no restriction. Right off the pickup in the tank is a ball valve just to shut the fuel off and that's it I'm pretty sure. I'll double check next days off.
 
The new carb I put on it also has a smaller float inside the bowl to provide for more readily available fuel, or is this what's screwing me?
 
mitchq said:
The new carb I put on it also has a smaller float inside the bowl to provide for more readily available fuel, or is this what's screwing me?
Click to expand...
Is that smaller float a standard feature of the carb? In any event, I think that smaller float/more available fuel theory (given the physics of modern carbs and fuel pumps) is a "urban legend"...especially on a plain vanilla marine engine.
 
Yeah I know it's just what's in it. Bought it that way. Just more room inside that bowl doesn't mean the flow is increased or anything
 
If you have an electric fuel pump, temporarily disconnect the plug from the no oil pressure sensor switch, short out the pins in the connector ( a paper clip is about the right size) and see how it runs.
 
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