Engine Idle

[Split Shot]

New remanufactured Mercruiser v8 260 now (300hp. allegedly) because of hopped up cam. 2 hrs. run time. Rochester quadrajet carburater. I cannot get it to idle down to 600 rpm. Will not idle down from about 900-1000. Would it matter what cam you have or should it idle down no matter what type cam? Would it drop a little when put in the water from back pressure? Shifts in and out of gear ok. I have to use trolling bags even at 600 rpm. on the old motor, to slow down to trolling speed for Walleye fish'n. This high rpm will also make it hard to dock in the Marina. Thanks!

 

[mikel1291979]

Re: Engine Idle

idle adjustment screw on the carb.

 

[solar7647]

Re: Engine Idle

Sounds right to me, I believe the 600rpm is when in gear when it's out of gear the rpm will rise because there is no stress on the engine. Having a higher ratio cam simply opens your intake valves more to allow more fuel air mix into the cylinder you would still be able to bring your idle in using the needls on the carb.

You should try a happy troller it may be better then the bags.

 

[Brentathon]

Re: Engine Idle

Manuals usually say idle speed is checked/set when in forward gear in water.
Although, my 5.7 Alpha doesn't idle much slower at all, in that condition, as compared to Neutral and on muffs.

 

[Split Shot]

Re: Engine Idle

Thanks guy's!

Mikel (idle adjustment screw)please give me more credit than that!

My old motor with the same carb would idle at 600 on the muffs. I will check for vacuum leaks.

 

[dubs283]

Re: Engine Idle

so the engine dies below 900 rpm or you just can't get it to idle less than 900??

 

[wca_tim]

Re: Engine Idle

Shifting an alpha drive into gear at 900 rpms you will destroy it fairly soon. If you don't have a vacuum leak or fuel mixture issue, as in if it is too much cam duration, you've got bigger problems and will have reversion problems as well if you're running wet exhaust...

(reversion - water from the exhaust is sucked back up into the engine - not good)

 

[Split Shot]

Re: Engine Idle

so the engine dies below 900 rpm or you just can't get it to idle less than 900??

Run's good at 900, start backing off on the idle screw and rpm's drop but, it runs ruff and dies.

wca-tim, I will check vacumm leak like you and bubba had mentioned. I can't check it untill next week, when I go back to the boat. It is 135 miles away. Ya, I know about reversion, I hope that won't be an issue! I have run it on the Lake for about 2 hrs. and no water in oil as yet.

 

[81 Checkmate]

Re: Engine Idle

I would check the timming. May be advanced to much and that will bump up idle. Do not do by ear use a timming light to be sure.