Question on plugs for 77' Johnson 140

[RamAirZ]

Hey guys, last time out I overprimed the fuel system and fouled out my plugs (it cleared up after some WOT but time for replacement anyways). It's a 1977 Johnson 140hp V4 and currently has Autolite 2892 airgap style plugs in it currently and I have read that the UL77V are originally recommended for this. After some further reading seems that there is some debate between this airgap style plug and say a conventional version like QL77JC4. My main worry is wil the conventional plug contact the piston. I really don't want to run into any clearance issues. The motor runs great, has 132-135psi on all cylinders and I'd hate to throw a set of plugs in it and have the piston slam into it. I'm not always WOT but spend alot of time say between 4-5K rpm running across the bay and across the lake I'm at WOT until I get to the creek sections and then I run along at slower speeds, I also like to pull skiers etc. Any suggestions would be great, I haven't had a problem with my current plugs until this last trip but that was all me. It has been a little cold natured as for getting it started after sitting but nothing insanely irritating.

 

[Haffiman]

Re: Question on plugs for 77' Johnson 140

It is another alternative: QL16V

 

[Daviet]

Re: Question on plugs for 77' Johnson 140

I replace UL77V plugs with the QL77JC4 plugs all the time. Take a small screw driver and measure the distsnce between the piston at TDC and the bottom of the plug threads, I think you find that there is ample room for the QL77JC4 plugs.

 

[RamAirZ]

Re: Question on plugs for 77' Johnson 140

I'll check it in a bit, on my boat I have zero electronic equipment except for the gauges, think an L77JC4 plug would work fine? And from what I read a .030 gapping should be about perfect for what I do?

 

[Daviet]

Re: Question on plugs for 77' Johnson 140

Sounds like a plan to me.

 

[RamAirZ]

Re: Question on plugs for 77' Johnson 140

Just checked the piston clearance and from my not super precise measurements it's going to be close (I used a standard plug I had lying around and measured the overall increase in length in the chamber compared to the airgap style, then measured with a screwdriver the distance from the piston to the threads). I know the spark plug chart here: http://www.docstoc.com/docs/4877037/Spark-Plug-Application-Chart-for-Evinrude-Johnson-Outboards-thru and a few others only list the UL77V and the QL16V for my engine.

 

[Daviet]

Re: Question on plugs for 77' Johnson 140

You could always screw in a plug and rotate the engine by hand and see if it hits the piston.

 

[Haffiman]

Re: Question on plugs for 77' Johnson 140

Surface gap plugs gives a better performance and longevity on those engines. You may loose some idling with the UL77 plugs, but quite an improvement on the QL16 plugs. The (Q)L77 plugs will 'work', but rather short lived if running hard. If used, 'index' them so the side electrode is pointing either up or down.

 

[boobie]

Re: Question on plugs for 77' Johnson 140

I'd go with the QL16V as that mtr orginally required surface gap plugs.