4.3 OMC struggles on acceleration

[Doral90]

My 90 OMC 4.3 cobra has had the same issue going on a year now. Boat started fine today but leaving the marina it hesitated, backfired and would not accelerate. Engine started to die but once I got off the throttle it would idle fine as long as it was near idle speed. Had the boat in the shop for the same issue a few times. Most recently they replaced the coil saying that was the issue. Clearly that wasn’t the case. New plugs and wires and same thing happens.

an ideas?

 

[Scott Danforth]

Its never the coil

Fire your mechanic

Rebuild your carb

 

[Doral90]

He is fired! Thanks for the heads up. They said it was a tough diagnosis but it was the coil. First trip out proved that wasn’t the case

 

[Lou C]

Does this have the points ignition or electronic?

 

[Doral90]

Points. And they’ve been done and didn’t improve.

 

[Scott Danforth]

did you just swap the points, or did you properly service the points by filing the points, gap the points (0.014"), verify the dwell is 37 to 39 degrees, then set timing to 6 BTDC,

 

[Lou C]

If you can, get a tach dwell meter and check it. Its a simple system. Points, condenser and mechanical spark advance.
You should also get an advance timing light and check the total timing advance at the specified RPM....
1st you rule out any ignition system issues, the move on to the carb. Is it a 2bbl or 4bbl? I think by then (1990) they had switched over to Holley carbs from Rochesters….

 

[Doral90]

4 BBl carb. I’m going to look into all these suggestions.

 

[Lou C]

Probably a Holley 4160...

 

[Doral90]

Anyone have the part number for the 4.3 HO 4 BBL carb?? Is that it above?

 

[Doral90]

did you just swap the points, or did you properly service the points by filing the points, gap the points (0.014"), verify the dwell is 37 to 39 degrees, then set timing to 6 BTDC,

going to check with the mechanic. Time for me to learn how to do this stuff myself. Can’t afford paying someone to not fix things anymore. Bloody pandemic here lol

 

[Scott Danforth]

there is a very detailed sticky at the top of the forum that also has a very detailed write up on points type ignitions.

 

[Lou C]

4160 is the model # you can look for the build # on the air horn. Go over to Holley.com and start reading

 

[Star64]

Almost sounds like an accelerator pump to me