Carb Issue

[Gangly]

Holley 4175

I rebuilt the carb and the engine is running as smoothe as a sewing machine. However, I cant get the idle to stay down, it hovers around 1100 rpms. I adjusted the idle screw one way and the idle increased, so i turned the screw the other way and the idle went back down but never got below 1100 rpms. I kept turning and nothing. It took me a second but I realized that the idle screw was working properly, but the throttle lever arm wasnt moving in response unless I was adjusting the idle screw to increase rpms. After manually operating the throttle, I noticed it got somewhat spongy right as it was about to close causing the blades to remain slightly open. I manually operated the throttle lever a few times and was able to set the idle adjust screw to have the boat idle right at 750 rpms and it ran there for 10 minutes. As soon as I gave it throttle and then let off, it would idle back around 1100 rpms. I again manually operated the throttle lever to close the throttle and then it settled down perfectly to 750 rpms.

Basically, if I want it to idle at 750 rpms, I have to close the throttle lever by hand because it will stick around 1100 rpms if I dont. The actuation of the throttle lever by hand to get it down from 1100 to 750 seems to have some very very very slight resistance, like vacuum or something is keeping the throttle from closing, but I cleaned it meticulously. Is this an indication of a stuck choke or should I tear the hole thing down again to clean it? Any Ideas?

 

[Silvertip]

Re: Carb Issue

If you removed the throttle blades during the rebuild you likely did not seat them properly or you inserted them backwards during reassembly. If you look at the blades carefully, the edges have a bevel on them. That bevel is to allow the blades to make a full seal against the throttle bores. During assembly, you leave the two screws in each blade loose. You then snap the throttle so seat the blades. Then tighten the screws. And be sure you use loctite on the screws. You don 't want the engine to swallow them should they come loose. If you didn't remove the blades, then something is binding preventing the throttle from closing. We must also assume you are adjusting the idle "speed" screw and not the idle "mixture". Idle speed should be adjusted with the throttle cable disconnected. When speed is proper, you then adjust the cable to the new carb setting.

 

[Gangly]

Re: Carb Issue

I am adjusting the idle speed screw, not the mixture screw. I did not adjust it with the cable disconnected though so that could easily be the culprit, will check it out to see.

That makes sense now that I think about it, thanks for the heads up. I will adjust the idle screw with the throttle cable off, adjust the cable, then repost my findings.

 

[Bondo]

Re: Carb Issue

That makes sense now that I think about it, thanks for the heads up. I will adjust the idle screw with the throttle cable off, adjust the cable, then repost my findings.

Ayuh,... There should be a slight tension of the cable, against the idle screw stop, just in case there's slop in the cable...

 

[Gangly]

Re: Carb Issue

I adjusted the throttle cable and the engine is running great now, thanks for the advice guys, I appreciate it. New problem though, posted in new thread.