2003 4.3L mercarb high idle issue.

[Fishscales]

2003 4.3L Mercruiser with Mercarb idling high. The carb was rebuilt after accelerator pump failure. The mixture seems to be set perfect. It idles smooth, accelerates smoothly in all rpm ranges and runs smoothly at wot at 4800 rpm. I've adjusted the idle screw on the right side of the carb and tried to set it around 650 to 700rpm. The issue I continue to have is after I start it up and it's warmed up it will idle right at the 650 range but if I run down the lake and say come to a no wake zone and have to throttle down or go to neutral it wants to go to 1000 rpm. I can put it in gear, which is a slight jerk, and run it again for another mile or so then come to another bridge and have to go back to idle in gear or switch to neutral and same thing it wants to idle at 1000 rpm. Cut the engine off though and start it back up and it idles at 650 where I've set it at. So if I run it again and go to neutral and it goes to 1000 rpm I try to turn the idle screw till its down to say 700. Then it will come down to 700 rpm after coming of plain and going to neutral after that point. Then I feel like I've got it were I want it. Goes into gear without a jerk and runs perfectly until I cut it off. Because after I cut it off and re start it it then idles to low at say 500 rpm. Not sure what happens after I kill the engine but it's driving me crazy. I just want it to idle around 650 to 700 all the time. So while it's idling at 500 after I restart it I go turn the screw in a hair to get it back to idle at the 650 700 mark and go run it again but then once again after I run it down the lake and go back to neutral it goes back to 1000 rpm. Sometimes 1100. Let it idle there a minute....cut it off. Restart it and back to 650 she idles. What am I missing? Just don't want to mess up my gear case by jerking into gear each time at 1000 rpm. Any help would be greatly appreciated. Or is this normal?

 

[achris]

Throttle cable needs adjusting. It's in the manual on the correct procedure.

 

[Bondo]

Ayuh,..... The throttle cable has to put abit of tension against the linkages, so the idle screw can have an effect,.....

Boats don't use a throttle return spring, because they rely on the cable to push it closed,......

 

[Fishscales]

So I need to unhook the cable again as I did when adjusting the carb after the rebuild and try to set idle again and hook the cable up again and with slight pressure pushing it closed against the idle screw? I've looked to see if the idle screw is not seating completely down but it seems to be touching after coming of plane and idle going to the 1000 rpm mark. I will take your advice and try again Bondo......I must not be doing something exactly right with the throttle cable.

 

[Bondo]

So I need to unhook the cable again as I did when adjusting the carb after the rebuild and try to set idle again and hook the cable up again and with slight pressure pushing it closed against the idle screw? I've looked to see if the idle screw is not seating completely down but it seems to be touching after coming of plane and idle going to the 1000 rpm mark. I will take your advice and try again Bondo......I must not be doing something exactly right with the throttle cable.

Ayuh,..... A simple test,......

When it's idlin' at 1000, go back, 'n push the cable connection against the idle stop, 'n see if it idles down proper,....

 

[Fishscales]

It didnt. Although just to be safe I took the cable off....turned to barrel two turns to make sure and didn't help my issue. I tried messing with it for a couple hours today on the water. It either idles to high or to low and then boggs down. The weird part is the killing the motor and restarting it. If it's idling at only 600 rpm And you cut it off. When you restart it idles back at 1000 or 1100 rpm. It will do this every time. difficult to set the idle. I'm starting to suspect the shop didn't do something properly when rebuilding the carb. I'm fed up with it. Once in gear it runs perfect at all rpm ranges but when you go back to neutral the rpm just goes up. I tried quarter turns at a time up and down adjusting cable as needed and just can't get it. Just can't get that cutting off and restarting it makes it idle at 1000 or 1100 Everytime. As it sits now it's idling to low and bogging down until it finally does. It was to hot and I was frustrated so I just put it back on the trailer and came home. To the point of ordering a new carb and having it installed. A new carb out of the box would still need adjusting though wouldn't it?

 

[Fishscales]

I'm an outboard guy. Have owned several boats. Purchased this sterndrive to spend time with wife......I could just be an idiot and think it's suppose to idle at 700 rpm everytime I go to neutral if that's where it's set. I mean is this normal? Cause jerking into gear doesn't sound to healthy at 1100rpm. I just can't understand why I can have it idling at 650 rpm in neutral sitting still.....only simply cut it off and recrank the motor and boom...it's idling at 1000 rpm. Doesn't make sense to me.

 

[Fishscales]

Bondo....I think I found the problem. My electric choke is wide open. If it's staying open all the time and not adjusted so it's closed until engine warms up could it be causing my issue with the high idle?

 

[Bondo]

Ayuh,..... It's supposed to be open all the time, unless set, on a cold motor,.....

 

[Fishscales]

So when it's cold and sitting in the driveway it should be open? The choke was turned all the way back towards the console. I though it was to stay closed and once the motor warmed up it would open the choke?

 

[Fishscales]

Well I guess that's not the problem. Has anyone else not had this issue with it idling up after reving the motor or coming off plane? It doesn't matter where I set the idle or the cable it will come back to idle at 1000 rpm. Unless I back the idle screw way of till it barely runs and will just stall out. I guess back to the shop it goes.....was hoping a forum could give me a little more insight. I thought I was on to something with the choke being set at staying wide open all the time and never closing but apparently its supposed to stay open? After watching rebuild videos and Mike's carburetor videos is shows it's to be set closed and after 2 minutes the heat will all the auto choke to open. Regardless I don't think that could be the cause of my high idle issue. Can anybody give some advice on here?

 

[boatdude100]

you asked if anyone else had this problem. yes. Similar.
1995 3L digital ignition
Idles ok fine after starting but after running the boat coming off plane mine bogs out and stalls.
However, if I simply turn the boat off and on again it will idle fine
Why?

PLEASE if you ever find out what is wrong post it. I will do same

 

[Fishscales]

Mine goes to the shop in the morning.

 

[Fishscales]

Had the carb rebuilt today and had them go ahead and change out the cap and rotor. I thought the carb had been rebuilt but the accelerator pump was only replaced. Before the carb was rebuilt I was turning 4850 WOT with a 19 pitch 3 blade. Now she hits 5100 rpm then hit the Rev limiter shortly after. But best of all it idles right at 650 to 700 rpm...All the time. Like it should. Problem solved for those who are curious what can cause a similar issue.