raise idle?

[Chaparralboater]

1991 chap, 3.0 lx mercruiser...I just had a new carb installed. The guy said it ran great on the hose. I put it in the water and noticed my idle is a bit low like 300 rpms of something, hard to read my gauge. And just past idle forward it bogs down a bit until I give it more gas then it runs GREAT..what could be the problem. I made sure the plug wires and plugs were good to go and tight. What else could I do? HOW DO I RAISE IDLE?

 

[dubs283]

Re: raise idle?

HOW DO I RAISE IDLE?

no need to yell, idle speed is controlled by the idle speed screw on the carburator, flat head/3/8" head screw at the throttle linkage on the back side of the carb

there may or may not be an idle speed spec on the flame arrestor cover, either in gear or neutral - if not, roughly 650 +/- in gear should be sufficient, 300 is too low

 

[Chaparralboater]

Re: raise idle?

clock wise I take it? I capitalized because I asked about 4 questions and thats the one I needed answered for sure. Thanks

 

[dubs283]

Re: raise idle?

yes clockwise, it will be obvious when you turn it

 

[a70eliminator]

Re: raise idle?

Idle speed on the hose vs idle with drive submerged will vary 2-300RPM higher. Some specify idle with drive submerged and in gear.

 

[Aloysius]

Re: raise idle?

the idle MIXTURE should be adjusted at the same time.

 

[Chaparralboater]

Re: raise idle?

wow I have no clue about idle mixture either.

 

[dubs283]

Re: raise idle?

the "guy" who said it ran great on the hose probably adjusted the mixture screw(s) - there may be one or two depending on the carb

if the engine idles smooth, the idle mixture is set properly

to verify, with the engine idling, turn the screw(s) at the base of the carb in the front in until the engine stumbles, then back out counting the turns until it stumbles again, turn back in half the amount of turns and it is set

 

[cr2k]

Re: raise idle?

That is correct for a Holley but others are a little more precise then that.

 

[Aloysius]

Re: raise idle?

Time for someone to get a manual on that engine.

 

[dubs283]

Re: raise idle?

That is correct for a Holley but others are a little more precise then that.

yep, on four stroke outboards

but this is a 2 bbl carb on a sterndrive, not a swiss watch

 

[fat fanny]

Re: raise idle?

Alrught here goes if the cab only has one screw on the base of the carb it's a mercarb if it has 2 it's most likely a rochester but first off set the base idle in water if possible to between 650 to 700 rpms and that's accomplished by turning the afore said screww on the carb linkage (transom side of carb) until the rpms are achieved then adjust the screw and or screws on the base of the carb (air idle mixture screws) until the idle stubles and then back out until it smoths out this may need to be done a few times until optimum setting is achieved a good start on these screws would be to turn the screws all the way in and back them or it out 11/4 turns out and then start adjusting. One more ? for you is is this a brand new carb or rebuilt the issues could ly within the carb it's self also if that carb was only idleing @ 300 rpm's it almost had to be stumbling that is extremely low

 

[Chaparralboater]

Re: raise idle?

well the guy said he needs t rebuild the carb so I am thinking it was a kit. But i looked at the carb today and its super shiny on the outside. all black so I dunno? And the problems I have now that I didnt before : I start it and I have to start it with 1/4 quarter throttle forward. Then after about 30 seconds of that back off intill neutral, then it shakes the boat pretty good and will hold at a low +- 300 rpm. My tack is hard to read but is deff not 700 rpm. looks to be around 300-400..I will sit at the docks and mess around with it. Thanks for all the heads up. I had gas powered RC cars that I constantly had to be tuning them so I can mess with a carb just don't know where the screws were. Thanks !!

 

[nola mike]

Re: raise idle?

no one mentioned it, but check your dwell first (if your boat has points) and timing (not sure of the ignition system). that can affect idle speed.