89 EVINRUDE 88 SPL Rough running

[pennyanman]

I've been pretty happy with this motor so far but I'm experiencing a nuisence problem. At all throttle settings above say 2000 rpm the motor has a "rumble" kind of like it has a cold. It isn't really a miss or stumble, it is like it is having trouble "clearing it's throat". When I first rebuilt the carbs it ran perfect at all speeds. It is also worth mentioning that I still get full RPMS. (5300 at WOT with average load). I'm using the NGK plug specified as the OEM replacement for the Champions. I've seen a couple of posts where folks mention a different plug for some years of 88SPL V-4s. Anyone know about a Tech Bulletin or other publication that might have changed the plug recommendation?

 

[rickdb1boat]

Re: 89 EVINRUDE 88 SPL Rough running

Are you using BR7HS NGK Plugs?

 

[rickdb1boat]

Re: 89 EVINRUDE 88 SPL Rough running

I would stay with the Champion Plugs, as they tend to do better in these Motors. Ql77JC4 come to mind!

 

[rickdb1boat]

Re: 89 EVINRUDE 88 SPL Rough running

RL77J=NGK BR7HS <br />RL78= NGK BR7HS <br />RL78C=NGK BR7HS <br />RL4J= NGK BR7HS <br /><br />Not sure about this one!!

 

[Jack Shellac]

Re: 89 EVINRUDE 88 SPL Rough running

I think you'll find that the factory recommended Champion QL77JC4 gapped at .030 will give the best performance in this motor. Has for me.

 

[pennyanman]

Re: 89 EVINRUDE 88 SPL Rough running

Thanks for the response guys! The gap mentioned is .030 I believe I was told .040 by the parts guy at the place I bought the NGKs (BR7HS). I need to inform him if this was in error. Do you all think the "rumble" is due to plugs, then, and not carb related?

 

[rickdb1boat]

Re: 89 EVINRUDE 88 SPL Rough running

Some time ago OMC decided to lower the Gap to .030. I have stuck with .040 and always have with no problems. Try both and see with does better for you!

 

[ob]

Re: 89 EVINRUDE 88 SPL Rough running

As rick suggests, your best bet is using the applied champion plug in your motor.The good thing about spark plug applications is that even after running a short distance with plugs they can be used as an excellent visual barometer of cylinder combustion.Remove plugs and inspect electrodes and insulators.Too cold a plug will show signs of excessive oil residue and soot as too hot of one will show electrode pitting and a dry conditon.All plugs vary slightly in the length of electrode placing them in deeper or shallower location in top of cylinder.This is why it is important to use the specific plug for your motors intended use and even geographical elevation for optimal firing.Also ,bare in mind that the plug itself is not always the culprit as fuel mix and carburation will also effect the visual condition of plugs.Stick with the proper champion plug gapped corectly and any adverse plug condition will be an indication of incorrect fuel mix,carburation,compression,or any combination thereof.

 

[pennyanman]

Re: 89 EVINRUDE 88 SPL Rough running

Again I really appreciate the feedback! I'm still getting used to this engine. I've had OMC cross charged V-4s for more than 20 years and they each have had their quirks. I will try the Champions!<br />It is odd, though, that each motor had a "preferrence" for specific plugs. My '78 85 hp ran best with Autolites, My '76 115 seemed to run best with the NGKs, and this one...we'll see!<br /><br />I'll keep you posted!