140 87 Looper surge at WOT & Uneven burn/Plugs

[Riley C]

Hi All,

I hope all you fellow boaters are enjoying great times on the water, engine free.

On my 87 140 Looper:

I’m having a little issue with plugs at present. Mainly with plugs fouling. See pics below.


I have just swapped them from NGK BR9HS10 to Champion QL77JC4 today. Hopefully this will make them burn better. But I’m really curious about the uneven burn on them.

The port cylinders are the same, but different to startboard, with its half clean half brown?

The big thing I notice is after warming up I get a power surging at WOT. This surge is at 6k rpm, it does go after running for an hour.

Could the spark advance be to much?

Just recently completed:

Running SST 13.5x19 prop
coils are cdi in port side, Omc on starboard
power pack replaced in 02, has done 200hrs since
carbs cleaned, vro replaced with vacuum pump
new thermostats, water pump
New fuel lines throughout even to carbs, with new fuel filters
flushed fuel tank
Reed valves cleaned and fitted new gasket
Head gaskets replaced

Compression at 115 on three and 125 in the other.

I have learnt the loopers don’t like idle revs at all.

Any advice would be a big help.

 

[Faztbullet]

I am going to say a fuel pressure/supply problem. The carbs that feed the starboard side are a tad higher than the ones that feeds port side. This is a X intake motor..so looking at carbs, the ones on left feed port and one on right feed starboard. That fuel pump may not deliver enough GPM at WOT.

 

[Riley C]

Thanks Fazt,

So the new fuel pump could be the issue? Maybe a bigger one?

wish I didn’t throw the VRO pump out.

 

[Riley C]

I completed a lync an sync again. The valve plates were slightly different. When the cam roller hit the cam, port plates was a little delayed in turning to the stbd side.

Found a slight kink on the lower stbd fuel line from manifold. So maybe at WOT this explains the surging?

I still would like to know why the plugs burn on even on half the plug, but the other is half is clean. Does anyone else experience this?

 

[cfauvel]

That's the oddest thing.

I think you found your issue...it doesn't take much in kinking lines to feed the carbs a little different.

I had a similar issue (near wot), and it was a pinched hose from the air silencer...glad I didn't ruin my 33 year old engine.