mercruiser 120 engine backfire

[scottishgold]

Hi there,<br /><br />After a lengthy rebuild on a merc 120 we took her out for some trials. Engine runs sweet, but when we shut the trottle off as we come into the harbour slow zone, she backfires through the carb. If we don't keep the revs up, she'd conk out on us. Once we're tied up and the engine is idling, she runs fine. This backfire through the carb is very worrying. Anyone any suggestions?<br /><br />Cheers<br /><br />Terry

 

[Bondo]

Re: mercruiser 120 engine backfire

That's Unusual,... That's For Sure,........<br /><br />I Wonder if you have an Intake Valve wound alittle too Tight,...?????....<br /><br />Or,.. Maybe an Intake Manifold Vacuum Leak,.???...

 

[scottishgold]

Re: mercruiser 120 engine backfire

Hi there, could be. Can anyone give me some advise on how to expertly do the valve clearance on the mercruiser 120, 153ci chevy? The SELOC manual says start with cyl 1 at TDC then gives you the valves to adjust, but I read some guys just do TDC for each cylinder and adjust those valves? Is there a correct procedure and what is it?<br /><br />Cheers