Stumble on hard Acceleration Mercruiser 140 HP

[ejnichol]

I have 700 hours on a 1980 model Mercruiser 140 hp sterndrive. Engine tuned up about 20 hours ago starts and runs good in most rpm transitions. <br /><br />Starts well, accelerate well during moderate throttle transition, but when pulling a skier up or just doing a hole shot with operator and no one else on board the engine stumbles during the transition from idling in the water to just past planing out. Engine smoothes out past this initial high load/lugging zone and accelerates smoothly from 2750 - 4200(red line). Acts as if it has weak spark. Engine has been been well maintained,.... but still has original spark plug wires and coil.<br /><br />I don't know why this is happening. <br /><br />Thanks for you input.

 

[Trent]

Re: Stumble on hard Acceleration Mercruiser 140 HP

Look down the throat of the carb and have someone pump the throttle. You should have a good stream of fuel pumping out when you do this. The accelerator pump sound weak.

 

[ejnichol]

Re: Stumble on hard Acceleration Mercruiser 140 HP

I'll check out this out. Their was a vacuum type line running from the base of the engine mounted fuel pump to the notch between the two carb throats that no longer was open, ie the metal nipple on the carb was all clogged up. I cleaned it out with a needle and put a new hose on nut this didn't change this stumble. Do you have any idea what this line was for.<br /><br />Thanks for your feedback

 

[ejnichol]

Re: Stumble on hard Acceleration Mercruiser 140 HP

I checked out the fuel flow in the carburator while someone pumped throttle and got good flow from two seperate streams, for each barrell. The stumble comes once the engine has throttled up and the maximum load is on the engine. Once boat gets up on plane and rpms really start climbing this stumble goes away.

 

[D. Engstrom]

Re: Stumble on hard Acceleration Mercruiser 140 HP

It sounds like the accelerator pump in the carb. I have a 1986 140hp Mercruiser and had the same problem but was also backfiring through carb. I rebuilt the carb and this took away the hestitation under load as well as the backfiring.

 

[Yepblaze]

Re: Stumble on hard Acceleration Mercruiser 140 HP

If it has one check out the centrifical advance mechanism. Make sure it is free to advance as required.

 

[ejnichol]

Re: Stumble on hard Acceleration Mercruiser 140 HP

I'm going to get a kit for the carb and see if rebuilding doesn't straighten out the problem. I'll also do a visual check on the dist. timing advance as see if it appears ok. Thanks for the feedback

 

[mountainmariner]

Re: Stumble on hard Acceleration Mercruiser 140 HP

I am having the same problem, 140 hp 1985 sylvan 17' i/o, gm 3.0 litre motor.
Runs and starts ok( the idle had to be set high to stay running), but when accelerating from idle to "wot" quickly it completely fails, and will stall unless " feathering" the gas.
All the dealers I have spoken with have indicated this carb can not be re-built, yet many persons have mentioned accelerator pump replacement ( where can I find this, or compatable part).
Now, this boat sat for 6 years, and " over-winterized" itself, so bad gas is possible.
Any resolutions to this problem? carb linkage schematics would be great if available also,as the choke appears to be not working properly.
Thanks to all the Sea Dogs that are able to help, and all that may have some insight.
By The Way,
Hope Everyone Enjoyed the Season "kick-off" Today.
My Family and I sure did.

 

[srrwood]

Re: Stumble on hard Acceleration Mercruiser 140 HP

That clear tube running from bottom of fuel pump to top of carb is a sight tube to indicate failure of the diapragm. If there is any fuel in it, time to rebuild pump. Serves no other purpose. I found this out by searching through shop manual.

 

[JB]

Re: Stumble on hard Acceleration Mercruiser 140 HP

You have replied to a 8 year old thread, srrwood.

 

[elkhunter338]

Re: Stumble on hard Acceleration Mercruiser 140 HP

I would say gas might be a problem, fill it with non eth fuel and try it out.
you could connect it to an outboard can with fresh fuel and give it a test run to make sure it is not fuel related.

 

[ejnichol]

Re: Stumble on hard Acceleration Mercruiser 140 HP

I checked out the fuel flow in the carburator while someone pumped throttle and got good flow from two seperate streams, for each barrell. The stumble comes once the engine has throttled up and the maximum load is on the engine. Once boat gets up on plane and rpms really start climbing this stumble goes away.

Fix was to replace distributor cap and button and wires. Problem went away.