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460 OMC King Cobra Cold Start Problem

T

tmakows

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I have a 1991 23.5' Chris Craft Concept that has a 460 King Cobra engine in it. I am a relatively newer boater, and not very mechanically inclined. I'm trying to see if anyone might be able to help shed some light on a problem that I noticed last boating season. Here's the issue I'm having:

On a cold start, the engine stalls out alot. Basically, my starting process is as follows: I pump the throttle back and forth a couple of times, and then push the neutral button in and move the throttle open about a 1/4 of the way. I then turn the key to start the engine. This always starts the engine. However, as soon as I put the throttle back into the neutral position to just let it idle, it always stalls out. My fix to this last year was to just the let the boat idle high for 3-5 minutes prior to putting it into neutral. This allowed the engine to warm up and then it was good to go. Once the engine was warmed up, it allowed me to start the boat in neutral without giving it any gas and it never stalls out.

Does anyone know what could be causing this problem? I have had a few people tell me that it could be my choke needs to be adjusted. Someone told me it sounds like the choke is running too lean?

Again, I don't know very much about this type of thing, so any feedback/experience would be greatly appreciated!
 
Does sound like the choke is either not setting right or is coming off too soon since it runs fine when warmed up. Next time before you start it, pump the throttle and then take the flame arrestor (air cleaner looking thing) off and check if the choke plate is closed.
 
the way you are doing it bye letting it warm up is the correct method for starting a carbed motor. 3-5 minutes is perfect.

I bet you have a electric choke plate the old style took a little less time to warm up.
 
This pic shows the choke closed

choke_closed.jpg
 
Thanks again Bob. That helps alot. So if I do what you are saying, should the choke plate be closed or open?

My only concern with letting the engine idle high for 3-5 minutes is that I wouldn't think that it is very good for the engine. It has to idle pretty fast for it to not stall out.
 
When it's cold it should be closed just like the pic above, as it warms up the plate should slowly open until it's vertical. I have a pair of 460's in my boat (1989's) and I generally let them run for a few minutes to warm up around 1000 RPM's, if you listen to them you can tell the choke is opening as the RPM's start to increase. Then I pull the throttles back and she idles nice and smooth around 650 in neutral.
 
Cool....thanks again for all your help Bob. So based on what I'm telling you, are you guessing that the choke plate is not opening up (vertical) or something? What is the remedy for this? Is there some kind of adjustment I can make to the choke?
 
The Choke Plate could be sticking, or even wired open by the previous owner.

The best way to check the operation of the Choke is before you touch anything to do with starting the engine, remove the Flame Arrestor and observe the top of the Carby. Isd the Choke open, or closed?

When the engine is cold, after sitting for a long period, like a half a day, the Choke should be fully open, because the engine was hot when you shut it down. As soon as you open the throttle, the Choke Plate should snap closed on its' own accord, as it should be spring-loaded.

When starting the engine, the Bi-metallic Spring that controls the Choke is heated up, and the Choke Plate will gradually open up, and when the engine is warmed up, the Choke will be fully open.

It is the same as in a Carburettored Car engine when you start it. Hit the Gas Pedal to operate the Choke, and squirt a bit of gas into the engine via the Accelerator Pump, and hit the Starter.

Hope this helps.

Bruce.
 
The pic below shows a carb with the spring adjustment on the side, yours will be somewhat similar. I suspect your choke is not closing all the way or is opening too soon. The adjustment either puts more tension on the spring or takes some off. Before you even touch the adjustment by loosing the 3 clamp screws scribe a mark across so you can always return to the position you started from.

IMG_3131.jpg
 
Thanks for the feedback guys. Do you feel with my starting procedure that I am reving the engine too fast and for too long? I have to keep it above 2000 RPM's for 3-5 minutes to get it to warm up. I'm just afraid that is possibly bad for the engine.
 
I will do that Bob. I am hoping to gte the boat in the water this weekend, but the weather is supposed to be really crappy here in Ohio, so we'll see what happens. Thanks for all your help man!
 
Just pulled a pair of 460s out for replacement and had the same issue. When cold they just don't want to idle. Played with the chokes and idle mixtures for years and just gave up (had Q-Jets). When cold, let them run at 1500 rpm. Within a minute or two you will hear them pick up speed, At that point, you can bring them back to idle without a problem. No harm at all to the engines.

Gene
 
Just pulled a pair of 460s out for replacement and had the same issue. When cold they just don't want to idle. Played with the chokes and idle mixtures for years and just gave up (had Q-Jets). When cold, let them run at 1500 rpm. Within a minute or two you will hear them pick up speed, At that point, you can bring them back to idle without a problem. No harm at all to the engines.

Gene
 
Comogene is 100 percent correct:

Young people do not know carbed motors they just don't.

It's the nature of the beast.

pump the throttle in neutral 3-4 times and then leave it 1/4 of the way down and start the motor it will rev 1200-1500 i like 1200 if it will run there cold till you hear the revs come up and then slowly pull back the throttle it should idle in the water around 650.

Youngins, we old farts still have a little we can learn ya.
 
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