PDA

View Full Version : Cold idle speed adjustment?


Kevin 89MC
08-25-2005, 12:48 PM
Ever since I've owned my boat ('89 Prostar 351 Indmar, Holley carb), it has never idled fast at cold start up. The electric choke works fine, and it idles warm fine, but I've always had to manually apply some throttle to keep it running upon cold startup. That can be hard if I'm the only one in the boat, if I need to paddle out, etc.
I dug into it last night, and looked on Holley's website, and have a few questions for the carb guru's here. It appears that there is a black plastic cam coming off the back of the choke that is supposed to interface with a brass lever on the rod that is connected to the throttle plate. I think the previous owner spun the brass lever out of the way so it never hits the choke cam. It is really hard to see under there! Holley's website does show a "fast idle speed screw" that I can't seem to find. It looks like I could get the brass lever to interface with the cam on the choke, but it seems like it would be a real PITA to get it calibrated correctly. :confused: Also it seems like a fair amount of force would be needed to make the throttle plate open, I can't do it with my fingers pushing on the brass lever.
I'll include a pic, to help this make some sense. The yellow circle is what I am calling the "brass lever" and the green circle is what I'm calling the "choke cam". I have the choke disconnected so I could get at these.
Thanks!
Kevin

Storm861triple
08-25-2005, 07:17 PM
Also it seems like a fair amount of force would be needed to make the throttle plate open, I can't do it with my fingers pushing on the brass lever.

That's because you're pushing against the whole throttle cable etc. The reason there is no fast idle is that if there were, you wouldn't be able to return the throttle to neutral and then shift into gear; the high idle linkage would prevent the throttle from returing all the way. They could have engineered a spring/slide mechanism in the throttle linkage to allow for this, but they didn't.

If you want a cold high idle, you need to pull the neutral pin on the throttle lever, and throttle the engine up. What is so hard about doing that on the trailer, and letting run at ~2000 RPM while you paddle out? (or sit on the trailer or what ever you do)

-Tom

87MC Dave
08-25-2005, 08:02 PM
Storm is right on the money....When I rebuilt my carb I had the same question you did. This model does not utilize that feature, for that specific reason.

I actually have my boat idle set to about 250RPMs at idle and it has been running like a champ ever since I rebuilt the carb. My question to you is when was the last time that carb was rebuit?

PeteS
08-26-2005, 09:25 AM
Storm is right on the money....When I rebuilt my carb I had the same question you did. This model does not utilize that feature, for that specific reason.

I actually have my boat idle set to about 250RPMs at idle and it has been running like a champ ever since I rebuilt the carb. My question to you is when was the last time that carb was rebuit?
Like Tom said, Holley assumed that the operator would manually advance the throttle to obtain higher RPM at start-up. Since a car has a much higher amount of constant pressure on the throttle return, than does a boat, I can understand the reasoning.

To Dave, I'm amazed your boat is even running at 250 RPM. The manual specifies 600 RPM in-gear for idle, and I wasn't aware that the ignition timing produces spark at even close to the right moment at 250. Could maybe your tac be reading a hair low?

Kevin 89MC
08-26-2005, 10:26 AM
Very interesting. I'm surprised nobody on here has a ~'89 351 Holley carb that idles fast on cold startup. A buddy I used to ski with bought the exact same boat as mine, but then moved ~1hr away. I was in his boat twice, and clearly remember noticing his idled fast on cold startup, then settled down when warm. I thought it was the same carb, but maybe not. I know it was the 351 Ford/Indmar. I will have to look him up and see how his is hooked up. Tom, you're right it's not a big deal, which is why I'm just now getting around to looking into it! The only time it's tough is if I'm launching by myself and have to paddle out or move the truck, I'd like it to be warming up. It seems like I have to manually advance the throttle past 2000 RPM to keep it from sliding back to idle and stalling, and it seems like I'm racing it too much for a cold engine (yes I know to pull the neutral pin). Maybe I can adjust the throttle lever. The other reason I've never really chased this down, is because I also thought it seemed tough on the trans to put it in gear at too high of an idle (like we did with my friend's). If I find out how his is hooked up, I'll let you all know.

I have never touched my carb in the 9 years I've owned the boat, because I've never had any issue with it at all. The boat runs great. Should I rebuild it anyways? It's got about 600 hours. I'm fairly good with engines, but figured if it isn't broke, don't fix it. Most of the vehicles I've owned have been EFI, so I don't have much experience with carbs, but I'm not afraid to learn & try it. I have thought that the idle has always been a bit "lumpy", but maybe that's because I'm used to inline 6 engines that usually idle super smooth. Do carb'd V8's tend to always be a little lumpy? Now that I have PP, I notice the rpm's go up & down 10 rpm or so. Is that normal?
Not to hijack my own thread, but I recently noticed that after a hard run, the idle is a bit high. If I proceed to run a bit longer at less than WOT, the idle will settle down. Any thoughts? The other recent carb thread has been a very interesting read, too. I want to say thanks to all for responding, and this is a GREAT board!
Thanks,
Kevin

MarkP
08-26-2005, 10:58 AM
Kevin,

Do you have a spring at the carb end of your throttle cable?? I did but removed it, mostly so I could let my boat warm up as I put the trailer away. I donít know if it is right or wrong to remove that spring but I removed mine.

Kevin 89MC
08-26-2005, 12:06 PM
I think I do have that spring. I'll pull it next time and see. Good idea!
Thanks,
Kevin

Storm861triple
08-26-2005, 02:14 PM
It seems like I have to manually advance the throttle past 2000 RPM to keep it from sliding back to idle and stalling, and it seems like I'm racing it too much for a cold engine (yes I know to pull the neutral pin).
You can adjust the friction of the throttle lever to you tastes. There should be a screw adjustment for that purpose. Slighty increase the friction, and then you should be able to set your hand throttle where ever you desire and it should stay. :)

-Tom

herevard
08-27-2005, 04:57 AM
Black plastic, you called "choke cam" opens choke, when you full throttle at cold engine.

Lance
08-27-2005, 08:01 AM
Rebuilding a carburetor is an enjoyable and learning experience but I wouldn't do it unless you have some specific issues other than a slow idle. If you use your boat regularly and do other PM (like clean fuel filters, drain water separator, fog engine in off season) you shouldn't have a need to rebuild the carburetor. I had to do mine after it sat unused for a couple of years and had several driveability issues.

Can't help though on the cold idle as I do it the manual way.

Lance

Kevin 89MC
08-29-2005, 09:59 AM
Thanks guys. Herevard I see what you're saying, that makes sense about how the choke opens when you open the throttle all the way. I looked a bit closer at my revs it's about 1500 rpm's when I can get the throttle to stay on it's own. I gonna leave well enough alone.
Kevin