1980 F28 Merc 305 issue

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wetbuoy
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Posts: 17
Joined: Sun Jul 07, 2013 7:39 pm

1980 F28 Merc 305 issue

Post by wetbuoy »

Hi all, Managed to delete the long version of my question so here is the short. #2 engine will not go beyond 2500 rpm when under load. Neutral revs to 4000 easily. All new ignition and wires plugs etc, carb rebuilt, all cooling ok, vacuum lines, filters, timing checked. New fuel, switched tanks, control cables ok. 2 GOOD mechanics are stumped.
Anyone got any ideas? 18 months and counting, at least I had time to renovate the interior for my wife.
Thanks Wetbuoy
1980 F28 flybridge
2x 305 Mercruiser

mikeandanne
Moderate User
Posts: 614
Joined: Sun Sep 09, 2012 11:30 am

Re: 1980 F28 Merc 305 issue

Post by mikeandanne »

Here are a couple ideas....if that engine is running smooth and not popping when you accelerate then check to see that the secondary throttle plate is opening all the way, if the choke is not completely off it will block the secondary linkage from opening.......now if that is opening then it may be a timing issue where the advance curve is not correct and the engine will not spin up under load.Stuck advance plates in distributor will do it.

A question...was the engine ok before the tuneup, what changed....Mike

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captainmaniac
2021 Gold Support
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Posts: 1880
Joined: Sat Apr 30, 2005 10:26 pm
Location: Burlington, Ontario

Re: 1980 F28 Merc 305 issue

Post by captainmaniac »

At one point I had a problem with distributor not advancing as I accelerated. Only got a couple of degrees of advance. In neutral in the slip I could rev as I wanted to, but under load would not exceed 3000 RPM. Replaced distributor to resolve (and had old rebuilt as a spare).

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BarryL
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Joined: Thu Feb 24, 2011 2:53 pm
Location: Northern Illinois

Re: 1980 F28 Merc 305 issue

Post by BarryL »

You mention that you are not having any back fires so we all assume you have the plug wires hooked up per the firing order but I recently had some work done on a mercruiser 350 and plugs 7 and 8 were switched and out of the proper firing order. No back fires and it would run smooth and rev fine without a load. out on the water it was a weak and powerless slug that wouldnt get out of it's own way. A closer look at the plug wiring discovered that the two wires were swapped and now the engine runs as it should. Pull your plugs and make sure they all look like they have been firing. A chocolate brown is what you want.

Barry
I love my boat! It takes all of my money and doesn't bitch.

wetbuoy
Registered user
Posts: 17
Joined: Sun Jul 07, 2013 7:39 pm

Re: 1980 F28 Merc 305 issue

Post by wetbuoy »

Thanks for the suggestions, I will double check the plug wires. I have brand new distributors timed by a pro. Will also re-check the advance plates. I got a marina mechanic to suggest running up to the dead spot and spray a bit of fuel into the carb and see if there is acceleration; will also try that this weekend. Thanks everyone. Steve
1980 F28 flybridge
2x 305 Mercruiser

mikeandanne
Moderate User
Posts: 614
Joined: Sun Sep 09, 2012 11:30 am

Re: 1980 F28 Merc 305 issue

Post by mikeandanne »

wetbuoy wrote:Thanks for the suggestions, I will double check the plug wires. I have brand new distributors timed by a pro. Will also re-check the advance plates. I got a marina mechanic to suggest running up to the dead spot and spray a bit of fuel into the carb and see if there is acceleration; will also try that this weekend. Thanks everyone. Steve
Just make sure that the advance curves in those new distributors are marine versions and your total timing is the marine spec.......there can be considerable damage done if automotive specs are used.....you probably have but I felt I should mention it anyway.......Mike

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