Sparks Plugs

Ollie88D

Member
Any recommendation for spark plugs on an Oliver 88 at 438 cid with 13.4:1 CR on Turbo Blue 110? Engine misses when it starts to load up; we are thinking the plugs are too hot causing pre-detonation. Current plugs are NGK AB6. I was thinking of trying one (AB7) or two (AB8) heat range cooler. Thanks in advance.
 
The miss isn't consistent. It misses/runs roughly when the load comes on, and after the RPM decreases, the miss goes away.
Turbo Blue 110 is good up to 14:1 CR. Thinking of trying 112 octane rated for excess of 15:1 CR.
 
Sounds like it's running lean to me. Carb not supplying enough fuel at the higher RPM and load. Once the RPM's drop it can keep up again.
 
Thanks for the replies. This is not a high RPM engine; it was only spinning 2700 RPM no load before hooking to the sled. Sounds like some load needle adjustment on the big Zenith will be in order, or changing the jet.
 
when it starts missing,pull the chock a little and richen the mixture. if that helps turn out the adjustment in the bottom of the bowl.
 
(quoted from post at 08:18:32 09/14/17) The miss isn't consistent. It misses/runs roughly when the load comes on, and after the RPM decreases, the miss goes away.
Turbo Blue 110 is good up to 14:1 CR. Thinking of trying 112 octane rated for excess of 15:1 CR.

Okay, you state the miss goes away after the RPM decreases. Why is the RPM decreasing; did you close the throttle or are you at WOT and the load is pulling the RPM down.

In the case of closing the throttle, it suggests a weak ignition or lean mixture. However, closing the throttle will also cure a detonation issue.

In the case of WOT; detonation tends to increase as RPM decreases, assuming the engine remains loaded. I would look for a weak ignition or lean fuel problem.

Turbo Blue 110 may be good for 14:1, CR but, those ratings are likely targeted for higher RPM engines as in race cars rather than tractors. I would be careful applying a rating to all engines and applications. However, I do not believe your engine has a detonation issue.
 
the higher the compression the harder it will be to spark reduce the spark gap to .025 , try the equivalent of 3116 autolite plugs or go to a high energy ignition like M.S.D.
 
Thank you all for the advice. The plugs were originally gapped to 0.025". We thought the high compression was "blowing out" the spark, so we reduced them to 0.020". The miss became more prominent, just by loading the engine using the brakes. Then the plugs were gapped to 0.030," and it made two blue ribbon passes on Saturday. This is the best the tractor has ran all year. Thanks again, everyone.
 

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