1977 Merc 140 hp Hesitation upon acceleration

I have a 1977 Bayliner with a Merc 140 hp that I have owned for 25 years. After years of taking it to a mechanic I decided to dive in and try to work on it myself(limited mechanical skills but a helpful neighbor) Recently I replaced the head(rusted through), cam(likely victim of a hydro lock), water circ pump, sea water pump and base(just old), etc.

Got it into the lake last weekend for a sea trial. Started great, stayed at 140 degrees, idled smoothly but hesitated upon acceleration. If I gradually eased it up it ran great on plane.

I just changed the canister fuel filter and it was water free. I was thinking my next step would be to change the fuel pump filter and carb filter and also hit it with carb cleaner and some seafoam in the tank.

Any other suggestions before I resort to rebuilding the carb.

I just tried to check what type of carb it is and I believe it is a Rochester, hard to read with a flash light.

Thanks as always for any advice you can offer.

Greg

Re: 1977 Merc 140 hp Hesitation upon acceleration

Sounds like an accelerator pump in the carb. Have you rebuilt it lately? An easy way to tell Rochester from Mercarb is that the Rochester has 2 mixture screws and the mercarb has one.

Re: 1977 Merc 140 hp Hesitation upon acceleration

thumpar said:

Sounds like an accelerator pump in the carb. Have you rebuilt it lately? An easy way to tell Rochester from Mercarb is that the Rochester has 2 mixture screws and the mercarb has one.

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It has two screws and I am pretty sure it say both GM and Rochester on the side of the carb. I have never rebuilt or had work done on the carb. Sounding like that may be the way to go.

Greg

Re: 1977 Merc 140 hp Hesitation upon acceleration

gpolkin said:

It has two screws and I am pretty sure it say both GM and Rochester on the side of the carb. I have never rebuilt or had work done on the carb. Sounding like that may be the way to go. Greg

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Rebuild kits are readily available...and the carbie itself is a relatively easy project.

A few of things to make things a little easier.

Start off with a CLEAN, well lit area. Don't be in a rush, and try and do it without interruption/distractions.

- I disassembled mine on the cover of a plastic storage bin turned upside down. Keeps things from falling into the abyss.

- Use compressed air to blow out all the little passages after it's had a good scrubbing/tanking.

- Buy a new brass float. The float will not be apart of the rebuild kit.

- Don't forget to give the entire throttle linkage a good soaking/lubrication also.

Give this http://www.youtube.com/watch?v=6RTf2yrGcA4 a look...it'll take you step by step through it!

Cheers!

Re: 1977 Merc 140 hp Hesitation upon acceleration

Last time I rebuilt the carb on my 1980 Mercruiser, it was a Rochester carb kit from a 1967 Chevy Impala with a 307 motor.

Tell me Mercury is not a progressive company.

There's little mechanical knowledge required to rebuild a carb. But a good service manual helps as a backup.

If you're uncomfortable, find an auto mechanic to rebuild the carb. Rebuilds just take a 1/2 hr. or so. But it's getting increasingly harder to find mechanics with carb experience any longer--believe it or not.