Dead spot off idle

[danny9696]

Hi all I have a 85 200hp merc that seams to have a dead spot just off idle, just off neutral or just befor neutral it dies, I have timed and sync, and rebuilt carbs, fuel pump replaced primer bulb and put in new plugs. runs great past that point but if you just are trying to ldle around to the dock or load the boat it dies, it idles in neutral fine, I turned up the idle and still the same problem. I am running the boat at 650' elevation, and did not have this problem when running at 2000' elevation, so I changed the jets to try to solve the issue and still no luck, the jets that were in it 76's & 78's were rated for 0'-2500' elevation and I just put in 80's & 82's that are for -2500'-0' elevation. I am stumped and I live about 9 hours from the closest shop can anyone give me a clue what I should do now?

Thank you all very much

Danny

 

[CharlieB]

Re: Dead spot off idle

The 76 and 78's should be fine for your elevation, main jets are not the issue.

Idle mixture should be readjusted 'in gear' and 'on the water' to best idle speed PLUS about an eighth turn. Any off-idle bog, hesitation or stumble is a sign the idle mixture is still just a bit too lean.

 

[danny9696]

Re: Dead spot off idle

Thank you charli I will try it, I have to order the jets to change it because its a fixed jet carb, WH-28

 

[CharlieB]

Re: Dead spot off idle

When you came down in elevation the air is denser and the engine needs more fuel.

The original main jets should have been enough, but you needed to readjust the idle screws out about another 1/4 turn.

Readjust the idle now, adding fuel until there is no bog or hesitation on a hole shot.

Then do a WOT run and try to shut it off as clean as possible without a following wave swamping your boat.

Pull the plugs and see how they burn with those main jets, also look at the piston domes to see if you are wet black aluminum, dry black or an accumulation of wet soot building up.

Your engine may like those mains, run it, look and repost your findings.

 

[danny9696]

Re: Dead spot off idle

Charlie are you meaning idle mixture screws? this carb does not have any mixture adjustment screws it has fixed jets for idle, main and vent, all adjustments have to be made by replacing jets