Engine died. Restarts only @ high RPMs.

[lekmedm]

Hi all. This afternoon I had my boat out and all was well for over an hour when the engine mysteriously died. It wouldn't restart in neutral. If I gave it throttle in neutral it would start, but it would die at about 1200 or so as I was dropping down the RPMs.

So 2 things I will mention. One is that the engine has a new Holley 4 barrel marine carb on it that is factory tuned for my 460 Cobra engine. Two is that I put in fuel stabilizer in the tank today before leaving the dock.

Oh, this old boat is new to me, but I believe the distributor was upgraded to a Pertronix.

Any ideas what to look for or what to check? I'm going out to work on this tomorrow (Sunday).

TIA

 

[Maclin]

Re: Engine died. Restarts only @ high RPMs.

Sounds like a carb problem, and with a new-to-this-boat carb that is where I would start.

Might be flooding, if so you should be able to smell a strong odor of gasoline from the carb, also should notice vapor in the carb bores. If it is flooding then it will not start without the throttle open to near WOT and will not want to idle well at all.

Possible causes are needle and seat needing adjusted, or debris keeping the needle from seating. If the fuel bowl is too full then you should be able to watch gasoline leaking and dripping into the bores from the venturi boosters or the fuel bowl vents.

On a Holley also could be an internal problem with the powervalve, it is rubber and if it leaks the fuel will run right from the bowl into the intake manifold. Powervalves on some Holley models can get torn by just a simple backfire thru the carb.

It could also be the opposite problem, too lean from a large vacuum leak somewhere. In this case you should be able to hear a whistling around the carb just before it dies as the rpms drop to the 1200 mark.

 

[chiefalen]

Re: Engine died. Restarts only @ high RPMs.

Yep carb got to be cleaned dirty.

After you do that check all the fuel filters.

I would also suck all the gas out of the tank and replace with fresh gas.

Or suck out the garbage bye lifting the bow of the boat and sucking all the garbage out of the bottom till you see clean gas.

 

[wca_tim]

Re: Engine died. Restarts only @ high RPMs.

since some things have been upgraded, and assuming that it's flooding, Check the needle valves for dirt, etc... ie clean the carb, check your fuel filter in front of the crab. If yoiu don't have one, get one). If you have an aftermarket fuel pump, check the fuel pressure (too high will push gas past the needle valves). my two cents, may be worht what you paid for it...

 

[chiefalen]

Re: Engine died. Restarts only @ high RPMs.

Fuel pump should give between 4-6 pounds. For a carbed motor that is.

After you do clean the carb you can try running it on a external tank with fresh gas.

 

[lekmedm]

Re: Engine died. Restarts only @ high RPMs.

OK, so here's today's continuing saga...

Since yesterday's circumstances were rather strange as to why the engine should die in this way, today the first thing I did was just to start the engine. The only thing I did was reajust the idle screw since I fooled with it yesterday. So today with one pump of the throttle the engine fired right up, and I adjusted the idle to the 600 - 700 rpm range. Everything seemed fine, although perhaps the idle was a tad rough. (One thing I should clarify about the carb is that I was the one who installed it.) It died once or twice pulling away from the dock, but it started up again, and I was able to pilot it away from our marina at about 900 - 1000 rpms.

When we got into open waters, I brought it up to 2000rpms - no problems, 3000rpms - no problems, 4000rpms - no problems, back down to 1500 to 2000rpms - no problems. On our way back while doing approx. 3300rpms the rpms started slowly dropping. This , I believe, is what happened yesterday while my wife was piloting. This time, I took the wheel, pulled back on the throttle a bit to bring it to abour 2700rpms where it seemingly stabilized. In fact, it even creeped up a bit to almost 3000rpms on its own.

As we approached the marina I reduced to 2000rpms - no problems, 1500rpms - no problems, 1100rpms - no problems, 900rpms - sputters and dies! I can only get it to start with quite a bit of throttle, and when I reduce it, at about 1100rpms it sputters and dies.

So here are a couple of things to mention. The oil is pretty fresh, full, and pressure was in the 60 to 80 range during the day. Perhaps unrelated, at some point there were what I would term some drivelive vibrations that went away on their own. When going at about 2700rpms the water temp was at about 160, but when I brought it up to about 3000rpms, the temp jumped right up to about 200. Someone mentioned a whistling sound when the engine dies. I did hear a whistle sound as described but couldn't find a source for a vacuum leak. I have replaced the PCV valve.

A lot to read, I know, but I'm trying to give the most clear picture I possible can so the iboats gurus may lay some wisdom on me. I have a factory service manual and can post or send some pages, if it's helpful.

 

[lekmedm]

Re: Engine died. Restarts only @ high RPMs.

I was just wondering if the choke setting might have anything to do with my problem. The previous carb had it set running leaner (I guess. It was rotated clockwise.), and this new one was set in the middle from the factory.

 

[Bondo]

Re: Engine died. Restarts only @ high RPMs.

Ayuh,....

It sounds like you need to Rebuild the Carb,+ install a New Impeller....

 

[lekmedm]

Re: Engine died. Restarts only @ high RPMs.

Do you guys really think that I need to rebuld a brand new carb that barely has 2 hours on it? If I do need to rebuild it, do I need a rebuild kit for it, or can I take it apart and just clean it out? Why would it idle fine when cold but not at all when hot?

 

[drrm123]

Re: Engine died. Restarts only @ high RPMs.

I'd check all the basic stuff first, like plugs see how they are burning, wires-with a multi meter, timing, you can check carb for plugs on any vacuum fittings that may not be used or manifold for the same. check dist. cap and rotor. then after that you can do compression test or leakdown maybe adjust valves. i dont think your new carb needs to be rebuilt.

 

[lekmedm]

Re: Engine died. Restarts only @ high RPMs.

Well, the plugs and wires were installed last year by the previous owner. The plugs look OK - just normal grey coloring. I have new plugs to replace anyway. There's nothing to check at the distributor since it was converted to electronic ignition with a Pertronix kit.

I was wondering if the vacuum line from the carb to the PCV valve should be replaced. Could a leak there be causing this kind of problem, especially on a hot engine?

If I have to break down and open up the carb for cleaning, do I need a kit to replace all the gaskets and what-nots, or can I reuse what's there since it really is a new carb?

 

[imported_TheMan]

Re: Engine died. Restarts only @ high RPMs.

Have you checked all the fuel filters as was suggested?

 

[chiefalen]

Re: Engine died. Restarts only @ high RPMs.

I bet the little holes in the carb are blocked with junk.

Just take it apart and with carb cleaner and compressed air clean every hole.

And reassemble with the existing gaskets if your careful that is.

The smallest holes are blocked not giving you idle.

 

[abj87]

Re: Engine died. Restarts only @ high RPMs.

If you just installed a new carb i would suspect a vacuum leak or a poorly tuned carb. You cant just bolt on a carb and expect it to run right, you have to spend the time tune it. What was wrong with the carb that came with the boat?

 

[lekmedm]

Re: Engine died. Restarts only @ high RPMs.

If you just installed a new carb i would suspect a vacuum leak or a poorly tuned carb. You cant just bolt on a carb and expect it to run right, you have to spend the time tune it. What was wrong with the carb that came with the boat?

Yeah, I was wondering about whether the carb needs tuning. Wouldn't that mean adjusting the idle mixture screws? I saw a Holley video on YouTube about tuning these screws that seems to cover my problem. I just need to get a vacuum guage.

The original carb was busted at the idle adjustment thingamajig.

 

[lekmedm]

Re: Engine died. Restarts only @ high RPMs.

Yesterday I spent the say tinkering on the engine again. First off, I did 3 things:

1. New fuel filter. I have the screw on type filter that looks like an oil filter, so I do not know how it looked inside. I didn't bother saving it to cut it open. When I poured out the fuel that was inside, I did not see any contaminants or water.

2. New spark plugs all around. The old ones weren't bad, but it's easy enough to do and eleiminates one issue.

3. Adjusted the electric choke.


So the last thing I did was to try to tune the carb the way the Holley videos show. This meant adjusting the idle mixing screws. I bought a vacuum guage and hooked it up to where the PCV line goes to the carb. This means that the PCV line was disconnected. With this setup I was getting low vacuum readings. There was also exhaust smoke coming up from under the oil cap. So I got myself a piece of hose and a plastic T so that the PCV line was hooked up along with the guage. No smoking, but no pressure readings either. I have the carb set at the point suggested by Holley, and the engine run better, idles well both in neutral and in gear.

What is the best way to tune this optimally? How should I hook up the vacuum guage? I think my original problem was the engine being starved for fuel after it was hot.

 

[abj87]

Re: Engine died. Restarts only @ high RPMs.

The original carb was busted at the idle adjustment thingamajig.

Return the holly and get the org. carb from mercruiser. no need to go reinventing the wheel. It seems like you don't know enough about carbs to start swapping them around.

 

[lekmedm]

Re: Engine died. Restarts only @ high RPMs.

Return the holly and get the org. carb from mercruiser. no need to go reinventing the wheel. It seems like you don't know enough about carbs to start swapping them around.

I appreciate your suggestion to keep things simple. That's always what I try to do as well.

However, I'll point out as is in my signature that my engine is OMC and not Mercruiser, and the original carb WAS a Holley, so I am working with a direct replacement.

Also, the fact that I am not extremely experienced with carbs does not mean I am not willing to learn. It is thanks to forums like this one that I have amassed a great deal of knowledge and experience on computers, cars, homecare, landscaping, and now boats. This forum is awesome, and I have searched and read many threads before posting my own questions. I even read threads that are not related to my own problem, just to see what others are going through. You never know when you might end up with the same situation. Knowledge is power!

 

[abj87]

Re: Engine died. Restarts only @ high RPMs.

Oops my bad i thought you were switching to a aftermarket carb from a factory carb. I have had friends do that and it was a disaster! You had it the vacumme gage hooked up right. With the pvc disconnected a little smoke out of the breather is normal. Any vacume leaks? at the carb base, or disconnected vacumme likes. What was the reading on the gage? It should be a "higher" reading at idle. Whats the idle speed, have you adjusted the idle mixture yet?

 

[lekmedm]

Re: Engine died. Restarts only @ high RPMs.

Well, the vacuum is at about 15-16 in Hg (~40 mm Hg) at 700rpm idle. At this setting when I put it in forward gear I'm going at about 650rpms. I checked in my factory manual, but it doesn't say what the proper vacuum should be. Shouldn't vacuum increase as rpms increase? I don't think there were any leaks around the carb, at least I couldn't hear any.