Checking Timing

atengnr

Chief Petty Officer
Joined
Sep 18, 2006
Messages
482
New set of plug wires are installed. Now just need some warmer weather to take this for a run on the lake.
 

atengnr

Chief Petty Officer
Joined
Sep 18, 2006
Messages
482
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

Supreme Mariner
Joined
Dec 28, 2013
Messages
36,043
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

Chief Petty Officer
Joined
Sep 18, 2006
Messages
482
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

Vice Admiral
Joined
Jul 29, 2008
Messages
5,333
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?
 
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