Port engine won't get full revs when trying to plane

[John bouy]

Having a little trouble with my port engine, just started this trip. When trying to get on a plane the engine won't rev up fully. It only revs to 3600 rpm at WOT instead of the usual 4500, while it is fighting to get on a plane it also sputters and backfires.
Only issue I've had in the past was several months back I got a crab trap line in the prop, could it be a spun prop hub just acting up now? Or does this sound like an ignition issue?

Engines are 2 barrel carb'd 4.3 litre mercruisers with alpha one gen 2's

thanks for any ideas

 

[Sous]

spark plug issue, maybe. Low RPM, backfires both sound like it could be a spark issue.

 

[dwna1a]

When was the last complete tune-up?

 

[src]

A spun prop would be the opposite, RPM's spiking with no increase (or with a decrease) of speed.

 

[John bouy]

Plugs and tune up done last season, but used all year long without issues.
I will do plugs again and a cap and rotor, hopefully that does the trick.

 

[SCORPIO]

Check the timing advance also.

 

[dwna1a]

When my ICM went it would run up to 2000rpm's but no further. The ICM controls the timing advance. It is an expensive part, try to see if there is another issue first.

 

[Captain Crispy]

It isnt caps/rotor/plugs. Clean the spark arrestor. Possible clogged fuel filter.

 

[John bouy]

So finally got back in town and was able to work on the boat/take it out. Did a new set of plugs and a new cap/rotor. Motor no longer pops and backfires but it still only revs to 3200 under load. Also put a new spark arrestor on. Any other thoughts?

 

[gtfireftr]

So finally got back in town and was able to work on the boat/take it out. Did a new set of plugs and a new cap/rotor. Motor no longer pops and backfires but it still only revs to 3200 under load. Also put a new spark arrestor on. Any other thoughts?[/QUOTE
Do a compression check.... Just to be sure....