Mercruiser 488 stalls at low RPM after running for half hour

[rob_bloozer]

Mercruiser 488 stalls at low RPM after running for half hour, it will then start again if I open the throttle and it will run at high RPM but stalls again when it drops down to 1800 rpm, eventually it won't start at all. If it sits for a day it starts fine and so does the whole process again. I am figuring that it is vapor lock but the engine bay is not that hot, also there is no misfiring or spluttering. I am going to check the vent on the fuel tank. my question is if it's not vapor lock what other things would create this problem?

 

[12Footer]

Re: Mercruiser 488 stalls at low RPM after running for half hour

Is it a quadrojet carb or injected?

 

[rob_bloozer]

Re: Mercruiser 488 stalls at low RPM after running for half hour

It's a 2 barell rochester

 

[rob_bloozer]

Re: Mercruiser 488 stalls at low RPM after running for half hour

no sorry, I checked, it is a quadra jet. I checked for the vapor lock thing and all seems to be okay. I think I will start to look at the carb, is there a chance that the choke could be it, the stall occurs after everything has reached usual operating temp for a few mins, I just bought this boat and both engines(mercruiser 488's) have a problem, the other is missing and running rough, I figure that may be carb or ignition, I will do a compression test first and then change the HT leads, I have already checked the timing and that seems okay. I will also try a different ignition coil. The ignition system is electronic. These problem occured after the engine overheated, so something must have been damaged, I hope it's not serious, I think the guy I bought it from definatly screwed me.

 

[blbj]

Re: Mercruiser 488 stalls at low RPM after running for half hour

it's relativly easy to eliminate vapor lock as a problem. take a small squirt bottle, the kind that is a plastic bottle with a spout on top that you sqeeze, and carefully squirt fuel down the carburator when the engine starts to run funny. if it picks up and goes it's a fuel problem, if it doesn't change it's probably an ignition problem.