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

[Krazymaan]

mine are 1980's as well. Does your look like this.
I have twin engines, so double the trouble.
I have both of these older carbs in my garage collecting dust.
I changed them out for newer with standard electric chokes. Much easier.

[Dave Strong]

Does your 260 have a marine quadrajunk 4bbl carb with electric choke? If ya lived closer, I'd let you use my UltraSonic Cleaning tank, those carbs would come out like N.O.S.

Probably a Q Jet with a choke stat on the intake. Nothing wrong with a Quadrajet if you know carbs.

Dave

[FMP]

That choke setup is great, not quite as good as the hot air tube jmo

[Dave Strong]

If someone had the intake off and did not put the correct crossover restrictor in the right place the choke will take longer than normal to fully open.

Dave

[flabum1017]

If it has a quadrabog carb, the secondaries could be hanging open a little giving you a "vacuum leak", seen this too many times to remember. I have seen the secondary butterflies catch the base gasket too. Also, make sure they used a "solid" base gasket when mounting the carb, not the one pictured:

[CanyonDoug]

Well, it starts and idles low for a little while until warm, and then shoots up to super high...... only because I had to dial the piss out of the idle adjustment screw to give it fuel under load. And then when off of load, it freaking soars to 1300 or so... about double. Helps keep it from stalling while shifting during docking maneuvers, (not completely, but did make the stalls less frequent). At forst i tought it was simmle, just raise the idle under load to spec. But that turned out to open a different can of undiagnosed worms. Guessing the choke is opening OK ( I think) because the high idle goes into effect when the engine is warm. Cold, it chugs along at 650-700... then gradually creeps up.

[CanyonDoug]

If it has a quadrabog carb, the secondaries could be hanging open a little giving you a "vacuum leak", seen this too many times to remember. I have seen the secondary butterflies catch the base gasket too. Also, make sure they used a "solid" base gasket when mounting the carb, not the one pictured:

"Quadrabog"! Take it you are not a fan...? Many thanks for the info. Seems like another great area to investigate... and I will gratefully take your advice on the gasket. guessing the one shown is automotive application? Cliff Ruggles would be the one to re-build I think, and he seems to be very versed even on the marine applications, so hoping he would supply the correct gasket but I going to make sure to inquire.

[CanyonDoug]

mine are 1980's as well. Does your look like this.
I have twin engines, so double the trouble.
I have both of these older carbs in my garage collecting dust.
I changed them out for newer with standard electric chokes. Much easier.

I hit the wrong "reply" button.... see below. But "Yes", mine is the same.

[Krazymaan]

I'm reaching for the moon here, but make sure your throttle plates are tight, with engine off, unscrew your idle and make sure both butterflies are touching the inside of the carb the exact same. You said you sprayed already. I remember in the old days, the throttle pin that the butterflies are mounted to could wiggle sideways and let air in through the carb body. They even made a sleeve to fix it. I'm sure that is no longer available.
While on land have you disconnected your throttle cable to see if your idle still creeps up, this is to eliminate throttle cable issues.
I'm assuming you made sure your base gasket was totally flat and gasket particle free.

[flabum1017]

Here in Florida, we tie the choke open, never need a choke here, LOL. Take your air breather off and verify the choke is fully open when warmed up. Make sure your idle timing is 8 degrees before top dead center. A lot of mechanics will set the distributor to full timing at full throttle. If the timing advance isn't working or not advancing as they think it is at full throttle, then the idle timing could be way off. SBC's usually are set at 8* BTC at idle.

[flabum1017]

"Quadrabog"! Take it you are not a fan...?

Goes back to the days of the big, heavy cars with them in them...... stomp the gas and wait 3 - 4 seconds for the launch.

[CanyonDoug]

I'm reaching for the moon here, but make sure your throttle plates are tight, with engine off, unscrew your idle and make sure both butterflies are touching the inside of the carb the exact same. You said you sprayed already. I remember in the old days, the throttle pin that the butterflies are mounted to could wiggle sideways and let air in through the carb body. They even made a sleeve to fix it. I'm sure that is no longer available.
While on land have you disconnected your throttle cable to see if your idle still creeps up, this is to eliminate throttle cable issues.
I'm assuming you made sure your base gasket was totally flat and gasket particle free.

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.

[CanyonDoug]

Goes back to the days of the big, heavy cars with them in them...... stomp the gas and wait 3 - 4 seconds for the launch.

Ouch...! Guess that's why my old vette had a Holley! Thinking that was a 750 or 850 double pumper on a 350 with decked heads... But what i read about the quadrajet is that it actually does well when dialed in right. Decent economy and the secondaries are huge, so they drop plenty in qickly... depending upon set up of the carb, but the marine one in general seems to be O.K. But I get it, chocolate vs. vanilla. I grew up in Ft. Laud... only moved out here ten years ago. Had an outboard and it def did not need any choking either.

[CanyonDoug]

Here in Florida, we tie the choke open, never need a choke here, LOL. Take your air breather off and verify the choke is fully open when warmed up. Make sure your idle timing is 8 degrees before top dead center. A lot of mechanics will set the distributor to full timing at full throttle. If the timing advance isn't working or not advancing as they think it is at full throttle, then the idle timing could be way off. SBC's usually are set at 8* BTC at idle.

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...?

[Dave Strong]

Well, it starts and idles low for a little while until warm, and then shoots up to super high...... only because I had to dial the piss out of the idle adjustment screw to give it fuel under load. And then when off of load, it freaking soars to 1300 or so... about double. Helps keep it from stalling while shifting during docking maneuvers, (not completely, but did make the stalls less frequent). At forst i tought it was simmle, just raise the idle under load to spec. But that turned out to open a different can of undiagnosed worms. Guessing the choke is opening OK ( I think) because the high idle goes into effect when the engine is warm. Cold, it chugs along at 650-700... then gradually creeps up.

If your adjusting the mixture screws to help under load chances are the power valve is hanging up. Once you move the throttle plates to the transfer circuit the idle should have next to nothing to do with things. You need a full understanding of all 7 circuits of a carb and when appart know what each passage in each piece of the carb goes to and how each have an effect on things. If not your just guessing and may get lucky and fix or not. Been rebuilding carbs for a living since 1976 and stuff people miss just comes 2nd nature to me. Wish I could help you more but without seeing, hearing, feeling, and smelling it's tough.

Dave