Checking Timing

[Tim Frank]

Sorry the jc4s are what im running

???
What plug are you running?
In post #33 you said

Im running j4cs

Correct gapped-plug is L77JC4

Per your question, most HS orifices have the number etched in....but some do not.

 

[atengnr]

jc4 it is.

 

[atengnr]

New set of plug wires are installed. Now just need some warmer weather to take this for a run on the lake.

 

[atengnr]

Question for you all - So this motor was rebuilt with the newer flat top pistons, and rods (mid 1970s style I believe). I dont want to be second guessing the builder, but did this change require a different cylinder head?


I havent run it yet with the new plug wires, and coil wire boot, and despite the issues I found here, I actually am not hopeful that the miss issue will be gone. Its been there 10 years, back to a time when I am quite confident that the plug wires were still good.

 

[racerone]

The 1968 55 HP was the first big loop charged engine by OMC------They had flat pistons in 1968 model year !!----That engine style ( 3 cylinder 70 HP )had flat pistons in 2001.-----So review your information on the " newer flat top pistons " that were installed.-----There were lots of issues with thin skirts breaking off.----Newer pistons were much more robust in the skirt !!

 

[atengnr]

Understood. My recollection is that the 68 55hp piston had a slight dome and was not completely flat. Just wanted to be sure that any reduction in compression ratio from the newer flat top piston is not an issue.

 

[Tim Frank]

I notice that in the description of the rebuild you say "newer carb". I went back to check because I have seen a recurring theme in here that someone picks up a motor "foer a steal" and then has problems because the PO went rogue on a
repair and plug-and-played some component that just does not work in practice.

If you do not have OEM carbs, anything could be going on, and the 1-1/2 turns on slow speed jets could be a hint that there is an incompatibility.

Did you ever establish what size the HS jets are?
Do you know which cylinder is missing?