Carb trottle.issue mercury 5.0

[sk7499]

I have a mercury 5.0 carb motor after 2 carbs now my 3rd rebuild finally go it started. Here is the issue on cold start chock closed boat starts but idles 1500 rpm then goes to 2k rpm. When warms up I engage throttle not in gear and rpm drops to 1k ..not sure what the issue is ..preload on cable..cable appears to be good and was good on my previous carbs. Is 2k to high on high idle..how do I get this to when I hit trottle I come to 650 rpm not 1k or over. Do I have vacume leak I sprayed carb cleaner around carb and no change in rpm..I did notice the vacume line on carb was little loose would that cause issue? I sprayed carb cleaner in that area and no change in rpm

 

[sk7499]

any ideas anyone

 

[Levinz11]

So you have installed three carbs in your boat? Or rebuilt your carb three times?

I'd disconnect the throttle cable from the carb and see what happens.

 

[Scott Danforth]

boats dont have vacuum lines.

post a picture of the carb you have.

 

[sk7499]

I ordered the carb from a carb rebuilder. The first two seemed off. The third which is on the motor seems better.its a Rochester 2 bbl. If I remove throttle cable and hit accelerator on carb it appears normal however if i start from cold motor it's real high rpm. If I push on throttle I can lower rpm after motor heats up. I think I either have cable preload issue or somehow the lever on carb keeps sticking should I bend the linkage on throttel

there is pcv valve and rubber tube that connects to base of carb I thought this is vacume line

 

[Bt Doctur]

do all you adjusting with the throttle cable removed, then adjust the throttle cable for some preload downward

 

[sk7499]

I do all adjustment on warmed up motor as that's what I'm doing now

 

[Bt Doctur]

with the throttle cable disconected

 

[ltklein]

Ran into a similar issue 2 weeks ago on my 1985 140 Mercruiser. Short story long....I rebuilt the carb, set it all up in the driveway and it was hummin' fine. Dropped it in the lake and set the idle in gear and all of that. Ran for 5 hours and but couldn't get the idle to stay consistent.

Pulled the engine cover again and disconnected the throttle cable. Working the carb I noted the accelerator pump wasn't retracting fully every time. It was very stiff. Even with throttle cable preload it wasn't always going all the way back.

On the bench at home I found the brand new aftermarket plunger was just too stiff in the bore to let the spring reliably retract it.

Bought an OEM replacement and it totally solved the issue. Perfect idle each time and excellent hole shot (for that size engine anyway).

Won't mention the aftermarket company as they are one of the bigger ones and I've used lots of their parts. But this one part didn't measure up.

Like Bt Doctur sez...take the throttle cable off the carb and manipulate the throttle. Make sure the springs can bring it fully to the stop without binding.

Just one thing to try...

Good luck!

 

[QBhoy]

How is the choke for function?

 

[sk7499]

Chock seems to work closed when cold and slowly opens

 

[sk7499]

So on a cold boat chock closed the rpm is 1500 . Then I need to let it warm up and hit trottel in netural then idles fine at about 650. The issue is the idle is a1500 rpm and only way for me to come off of high idle to low idle is petting trottel. Does this seem normal my old carb didn't work like this. Almost like it's stuck on high idle dial