1979 70 hp mercury stalls when putting in forward or reverse from neutral

[bnbad11]

My motor stalls when i go from neutral to forward or reverse. starts right back up but does it repeatetly. it has run fine until now. won't idle at low rpm idles great at higher rpm .it goes in forward when on trailer hooked up to the hose! but not in water under load. I recently replaced switch box,stator, fuel diaphram,all fuel lines. also when trimmed all the way dowm boat seems to slow down alot, even rpms go down almost like i throttled down runs faster and sounds better with tilt up alot, but when i turn it winds up and i have to trim down.????? HELP!!!

 

[timmathis]

Re: 1979 70 hp mercury stalls when putting in forward or reverse from neutral

It sounds like it could the carb float adjustment. I'm Not sure on that year model though. Maybe a pro on that one will help.<br />Good Luck, Tim

 

[bnbad11]

Re: 1979 70 hp mercury stalls when putting in forward or reverse from neutral

Thanks. I am trying to figure it out with out taking her to the shop but it looks like i might have to.

 

[Texasmark]

Re: 1979 70 hp mercury stalls when putting in forward or reverse from neutral

You are suffering from fuel starvation. Everything you said points to that. Cause? just have to chase her down.<br /><br />On the trimming down part, you are "plowing" your boat which is increasing the load on the engine, which takes more fuel to maintain the status quo and you aren't getting it so she boggs down.<br /><br />Sounds like low speed jets are clogged (or adjusted too lean if adjustable) if the float is not part of the problem. Might read up on the "decarb" thing. May have your answer there.<br /><br />Mark

 

[Boatwizard]

Re: 1979 70 hp mercury stalls when putting in forward or reverse from neutral

Have you checked the compression, spark and fuel? Have you pumped the ball and see if it hold tight or leaks down? Do the basic checks first, never overlook the obvious.

 

[bnbad11]

Re: 1979 70 hp mercury stalls when putting in forward or reverse from neutral

have not checked compression. spark is good. i just replaced all fuel line from the tank to the motor. ball stays hard now. did not before. still stalls when shifting into forward or reverse. ???? driving me nuts!!!

 

[Silvertip]

Re: 1979 70 hp mercury stalls when putting in forward or reverse from neutral

The engine will idle differently running on muffs than in the water due to back pressure when in the water. You need to set idle mixture and idle speed in the water. sounds like all that's necessary is better adjustments. Its idling too slow in the water. Set mixture first, then idle speed.

 

[bnbad11]

Re: 1979 70 hp mercury stalls when putting in forward or reverse from neutral

i was just told from the marine shop that there is a hole in the exhaust plate? and water is actually comming in the motor??? never heard of an exhaust plate. Does that sound right?

 

[Texasmark]

Re: 1979 70 hp mercury stalls when putting in forward or reverse from neutral

Over my head. I know we have exhausts, tuned exhausts, with tubes and sound revibrators and all that tech stuff, with sound absorbing water surrounding it and all, but an exhaust plate?<br /><br />Now I do understand that in salt water, you can corrode thru the cylinder wall and thus get water in the combustion chamber. BTDT<br /><br />Mark

 

[Silvertip]

Re: 1979 70 hp mercury stalls when putting in forward or reverse from neutral

That's an exhaust cover on the side of the engine. If you are getting water into the cylinders it certainly will idle and run poorly and it needs to be fixed. Run the engine, pull the plugs and check to see if one or more are pure white while others are tan colored which is an indication of water ingestion. If you intend to work on this problem yourself -- do yourself a big favor and buy a service manual specific to your engine.

 

[bnbad11]

Re: 1979 70 hp mercury stalls when putting in forward or reverse from neutral

I just got back from the shop. he showed me the hole it's about an inch long on the side of the plate,corroded.(cover) (don't remember if it was in the inner or the out plate) with this plate removed i could see the cylinders from the side. he told me that the water under pressure was leaking into the cylinders and killing the spark. Hopefully around a $200 job he said. let's see if that works!! thanks for all the responses.

 

[Silvertip]

Re: 1979 70 hp mercury stalls when putting in forward or reverse from neutral

Yes -- water getting into the engine will definitely put out the fire. Good luck on the repair.