Ideas on Mercruiser 260, 1980 - Good idle under load, high in neutral, and shift prob

[flabum1017]

Well, first, I did not take the carb off to check the gasket, but I did tighten down the nuts/bolts a bit since they actually seemed a tad more loose than they likely should have been. Guess if I take it off to send out, I will def replace the gasket. I am thinking if I take it off to inspect gasket, it may tear and i'll have a bigger problem...? I did spray around the housing where I thought the buterfly shaft was... no change in rpm so I guess no leak there...?

Question: After unscrewing the idle to check contact on the butterflies, go ahead and then put idle screw back to position or am I looking to do something else at that point? With idle screw back, I guess the plates will be cracked open a tad? Is that going out of the idle circuit if they crack open? I am a bit confused about that part... Originally thought the idle circuit was limited to the two mixture screws. But after reading cliff's book a bit, it appears there are a LOT of areas that there may be some bad behavior. The whole choke/lever alignment/tuning part is a mystery to me as well, since i am not sure what the various symptoms are for each area that may need tweaking or re-building. just too many idiosyncracies in these things for me to wrap my brain around.

The choke adjustment becomes a moot point once the engine warms up and the choke is wide open. Idle adjustments are made with the butterflies closed as much as possible to keep the engine running during adjustment (in neutral). Basically your'e adjusting the air mixture screws to the highest obtainable idle speed, then enriching it by a quarter turn to keep it from going lean when the ambient temps change. Once that is set, put it in gear (not tied to the dock) and adjust the idle stop to obtain 700 rpm give or take 50.

[flabum1017]

Ya know, I read about that. Just today asked a newer shop about timing, but the guy said if it was far enough off to affect idle, it would also cause problems starting....? Will def check into that and I will check on the choke. Dumb ass question, but here goes: If the choke was partially stuck and not opening, would that adversly affect starting? And would that cause the high idle? Not being a mechanic, I would have suspected bogging...?

It would not necessarily affect starting if the timing were retarded by say 4 degrees. If it were advanced too much, the engine would give a hesitation while cranking.

[flabum1017]

A choke stuck closed or partially closed would create a rich condition. You would smell it coming from the exhaust. Best way to check the choke is by taking the air breather off and looking at it.

[Capt.Insane-o]

If it still has the original points distributor the mechanical advance in it is probably shot. You have to confirm stable timing advance and return before you can even touch the carb.

They aren't worth trying to fix. Throw it out and get a new hei conversion kit.

Get the lower shift cable replaced..

[flabum1017]

If it still has the original points distributor the mechanical advance in it is probably shot. You have to confirm stable timing advance and return before you can even touch the carb.

They aren't worth trying to fix. Throw it out and get a new hei conversion kit.

Get the lower shift cable replaced..

He said the ignition has been updated.

[flabum1017]

Set mixture by ear (which I am sure is not perfect... can't seem to find where I would hook up a vacuum gauge to do it better) at about 3.25 - 3.5 turns on either side. Set idle in the water, engine warmed up, in forward with no extra throttle... to 650-700 according to dash tach.

Attachment 372280

Going back to your original post here, you need to do the mixture in the water, not on muffs in driveway. Exhaust back pressure plays a big role in this too.

[Capt.Insane-o]

He said the ignition has been updated.

Yes..but how? All new unit or did a petronix pos get put in the old distributor?

[Dave Strong]

If it still has the original points distributor the mechanical advance in it is probably shot. You have to confirm stable timing advance and return before you can even touch the carb.

They aren't worth trying to fix. Throw it out and get a new hei conversion kit.

Get the lower shift cable replaced..

It's was converted to electronic. Still doubt it's a carb issue.

Dave

[Dave Strong]

Could be the power valve sticking and holding the metering rods up a hair. Seems funny he was trying to fix a bog by adjusting the mixture. If the accelerator pump was leaking should get richer when more vacuum is present like in neutral.

Dave

[CanyonDoug]

Yes..but how? All new unit or did a petronix pos get put in the old distributor?

Was done by previous owner... but was put in old disty.

[Dave Strong]

Was done by previous owner... but was put in old disty.

Doubt that's an issue, have an 80 260 that was done works just fine.

Dave

[Dave Strong]

Doubt that's an issue, have an 80 260 that was done works just fine.

Dave

It's possible if things are sticking guess a few hundred rpm could advance the timing enough to create the huge rpm gain. Could check with a timing light.

Dave

[Capt.Insane-o]

Was done by previous owner... but was put in old disty.

Start there. Pull the cap and rotor off and see how the weights and springs look and if the pins are worn out.

[Dave Strong]

Start there. Pull the cap and rotor off and see how the weights and springs look and if the pins are worn out.

All below the plate in those distributors, would need to pull the gear and shaft to see the weights.

Dave

[CanyonDoug]

Dave, to your question on why playing with mixture for cutting out. Basically trial and error on my part because of ignorance. I am not a mechanic, but I don't mind trying a few things to see if it helps or not. My thought was maybe the idle circuit was demanding more fuel under load. I actually tried adjusting in driveway and more importantly warmed up and under load while in the water... Each time yielded nothing noticeable to my untrained ear until I got close to one turn in and then it would slow down.

Just seems weird the problem is consistent and after warming up, and seemingly limited to idle speeds. I'll have to recruit some help in pulling the dusty and also checking timing. Think I read dwell needs to be set first, but is that applicable if no points? (See, told you I am no mechanic!)

You mentioned you doubt carb is the issue. That is encouraging since that would allow me to delay sending out for rebuild.... But it sure is a mystery. I'll check cables in addition to timing. And with dusty being an unknown age but showing signs of age with dust/dirt on top, maybe that is a starting point. Hour meter shows around 480 I believe....

What at is recommended replacement on disty if I need one? Electronic and marine specific I imagine...?