mercury 115hp sputters when cover goes on

[trussmonkey]

I'm new here but read alot of previous posts

Got an '82' 115 6-cyl merc that had sit for about 5 years to replace an
85hp evinrude. Rebuilt fuel pump, and carbs, and replaced all fuel lines
checked compression 130-135psi on all, changed oil in lower unit, finally
went to start and it did! went to the river started idled but would not get up past about 2500 rpm, checked things out, replaced stator!

Back to river it staters good, good hole shoot, ran upto 6000 rpm (goining to change prop from 19" to 21")

Okay! now that i've giving my life's story here's the problem!:

I adjust the mixture (with the engine cover off) everythings great.
I put the cover back on and it starts choughing and sputters as if being choked out,

 

[AMD Rules]

Re: mercury 115hp sputters when cover goes on

Any chance you have an exhuast leak on the powerhead somewhere.... smothering itself with the cowl on?

 

[jimmbo]

Re: mercury 115hp sputters when cover goes on

Perhaps an ignition wire or any wire related to the ignition system is shorting to the cowl

 

[trussmonkey]

Re: mercury 115hp sputters when cover goes on

checked for an exhaust leak couldn't find any

all of the wiring is neatly tucked away not coming into contact with the cowl

it only sputters at idle or when backing down to idle it still has quick throttle response and full throttle with the cowl on

 

[Chris1956]

Re: mercury 115hp sputters when cover goes on

Truss, I had a stripped-out powerhead mounting stud on my '77 Inline six. The resultant exhaust leak into the cowling caused idle to really stink with the cowling on and be nice and smooth with the cowling off. I ran for a while with the lower cowl (where it said 150HP) off, and later caulked the stud and bolt to the block to seal it up.

 

[trussmonkey]

Re: mercury 115hp sputters when cover goes on

the exhaust leak theory sounds reasonable, would it only affect it at idle or throughout all rpm's
tried to find an exhaust leak, but can't, any ideas about areas pron to leaking or a good way to find a leak

 

[Chris1956]

Re: mercury 115hp sputters when cover goes on

The only two places it could leak is around the exhaust cover and around the powerhead base. The effect of a leak may not be noticeable at high speed

 

[trussmonkey]

Re: mercury 115hp sputters when cover goes on

run motor today,
I didn't find any exhaust leaks but I did find the top of the transfer port gasket for #1 CYL was blown out
no shops open today (that I know about) to get the gasket from.
I'll try to get one this week and get it changed

changed out prop today from 17in. to 19in. (hopefully brings my rpm's down from 6000)

 

[trussmonkey]

Re: mercury 115hp sputters when cover goes on

hey great news,

I got the transfer port gasket changed, motor runs great!

Saw a little carbon build up on the pistons, so I decided to run a can of
Sea Foam through, in the tank. It smoked for a little while, but it cleared up.

the prop change helped, but cavitates if I raise the rpm's too fast. WOT is 5800 rpm @ 45 mph. I've got a sting ray anti-cavitation fin I'm going to install maybe that will help

Of course there was one problem one time after taking it to idle it died, and wouldn't start, took the cover off and found that the enricher valve had opened completely, flooding the motor. I closed the valve and it started right way it's always something

 

[AMD Rules]

Re: mercury 115hp sputters when cover goes on

Thanks for the follow up. Glad to hear you got it sorted out.