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Can wrong plugs and large gap cause bogging…?

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bigtime_mcalpine

Regular Contributor
Went out on the water last night to test an engine and had some issues. Engine started beautifully and idles nicely but taking it past 1/3 throttle was a bit of an adventure. At first it might be fine but then power would go down to almost idle then maybe come back up but then come right back down again. If throttle was up too high for too long it would stall. I swapped out the fuel pump before going out on the water but it made zero difference. Did this a few times and then the engine became hard to start unless I let it sit. Felt like I was flooding it. Didn’t seem to really respond to bulb being pumped but the rev’ing up and down was so erratic that it might have, not sure.

So…brought it home and pulled the carb apart (again!) and inspected the high speed jet closely. Clean as a whistle. Entire carb looks perfect. Gaskets are in good condition, needle is fine, etc. Fuel hoses are all new, fuel pump mesh is clean.

I then went right back to basics and pulled the plugs. Well…a) they were NKG 7HS which is not spec for the 35hp 1987 engine AND the gap was .04. The 7HS are spec on some more recent 10’s and 15’s. So my question is this, would incorrect plugs and large gap cause the issues I’ve been experiencing? I’d really like to just take this back on the water and test it out but it takes a bit of time/set-up to get to the river so would prefer for the next trip to be a full success.

Fuel is new, tank has been run with other motors without issues. Compression is 105 in each cyl.
 
Wrong plugs can cause detonation and ruin your engine if too much hotter than spec and may foul if too cold of a plug is used too much gap can cause spark to fail under compression but doubt .04 will be an issue
 
Well that was wishful thinking. I got back on the water at lunch and there was no behaviour change at all. I also swapped the coils with known good ones and that did nothing as well.

Buuuuut, if I gave it 1/2 throttle and let it bog a bit if I shot fuel out of the primer pump, the engine did come to life albeit briefly. However, if I squeezed pump it did not. Im thinking that means a carb restriction. So…for the third time the carb will come off and this time I’ll remove all lead shots to see if anything is clogging….not hopeful.
 
bigtime_mcalpine said:
I then went right back to basics and pulled the plugs. Well…a) they were NKG 7HS which is not spec for the 35hp 1987 engine AND the gap was .04. The 7HS are spec on some more recent 10’s and 15’s. So my question is this, would incorrect plugs and large gap cause the issues I’ve been experiencing? I’d really like to just take this back on the water and test it out but it takes a bit of time/set-up to get to the river so would prefer for the next trip to be a full success.
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The recommended plugs are Champion QL77JC4 gapped at 0.030"

NGK B7HS ( or B7HS-10 ) would be an acceptable alternative although the closest equivalent is BZ7HS-10

-10 on an NGK plug merely denotes that it is supplied gaped at 1.0mm
Q in the Champion number and Z in the NGK number indicate that the plugs are inductively suppressed.

Being gapped at 0.040" would not be an issue. It was the standard gap for Evinrude and Johnson engines until the late 1980s
 
vics said:
The recommended plugs are Champion QL77JC4 gapped at 0.030"

NGK B7HS ( or B7HS-10 ) would be an acceptable alternative although the closest equivalent is BZ7HS-10

-10 on an NGK plug merely denotes that it is supplied gaped at 1.0mm
Q in the Champion number and Z in the NGK number indicate that the plugs are inductively suppressed.

Being gapped at 0.040" would not be an issue. It was the standard gap for Evinrude and Johnson engines until the late 1980s
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Darn. Well, I gave it a try and as expected same behaviour. I pulled
 
Thanks guys.
flyingscott said:
Sounds like your motor is running lean.
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yeah, I’m thinking same. I’ve got streaks of black coming down left side of lower cowling which I figured was a leaking exhaust gasket so will probably tackle that AND the lower crank seal for good measure. Do the lower seals go on these bad boys or am I reaching?
 
Have seen a few with bad lower seals from day 1 at the factory.----Must be really good motors if factory / dealer / first owner could not detect the issue.
 
Update: pulled the powerhead over lunch…lower seal is a mess. There is light brown goo (likely a mix of water, exhaust and oil) on the outside of the seal housing and there is some strange blue silicon gunk that has totally disintegrated that was presumably applied to help seal the crank. It’s unclear to me whether that’s an OMC part of whether someone went in there and did some MacGyver’ing. Looks like I’m definitely in need of a seal, and an o-ring for the seal housing and of course a base gasket But I don’t think I need anything else. Below is a short video of what I found. The seal within the seal enclosure fits VERY loosely against crank. I can push it on with very minimal force and it slides almost effortlessly up the crank. there is no way that was providing any kind of seal.

 
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