OMC COBRA 4,3 L Knocking problem between 1500-2500.

[aov004]

Hello America!

My name is Andreas and I am writing from Norway. I hope You americans maybe can help me a litte bit with my engine.

I bought a boat with om OMC cobra 4,3 l 1987 model in it.
When I started it it worked fine. Everything is normal when it's not in gear. I can hear just a litte knoking noise the second its idles up.

When I drive the boat there is a knocking noise somewhere in the engine between 1500 rpm and 2500 rpm. After that I can't hear it og it disseapers.

The engine performance is good and it runds up to 4800 rpm.

I took off the manifolds and they are okey. I have adjusted the ignition an timing.
I adjusted the valves.

I found som water drops in the flame arrestor. I have checked the fueltank for water but there is non. ANyone know why there is water in the flamearrestor??

The oil is good and no metalparts or anything.

Can anyone help me with this?? On behalf of Norway. Thank you very much!

 

[Joshua Nichols]

Re: OMC COBRA 4,3 L Knocking problem between 1500-1500.

Re: OMC COBRA 4,3 L Knocking problem between 1500-1500.

Have ya had a good look at the rear motor mounts?

 

[aov004]

Re: OMC COBRA 4,3 L Knocking problem between 1500-2500.

Hey.

No I havent, but I will do that after you said it. The engine dos not move at all while driving. I will check it and come back..

Thank you!

 

[aov004]

Re: OMC COBRA 4,3 L Knocking problem between 1500-2500.

I have checked them and they are okey. The right one were a bitt losse, but thats is not the problem. Tanks anyway.

Anyone else have a good idea??

 

[CobiaXL]

Re: OMC COBRA 4,3 L Knocking problem between 1500-2500.

Cam bearings?try thicker oil.

 

[aov004]

Re: OMC COBRA 4,3 L Knocking problem between 1500-2500.

Cam bearings?try thicker oil.

I did a new experince today.

The knocking sound is still there, but I adjusted the ignition while driving and then the sound dissapeard.(it got away). But when I then returned to idle speed the ignition where on 8 deg. after tdc and it was not running very smoothly.

Any ideeas of how I know that the Ignitor is in the correct place??

Sorry for my bad english.

 

[Bondo]

Re: OMC COBRA 4,3 L Knocking problem between 1500-2500.

I did a new experince today.

The knocking sound is still there, but I adjusted the ignition while driving and then the sound dissapeard.(it got away). But when I then returned to idle speed the ignition where on 8 deg. after tdc and it was not running very smoothly.

Any ideeas of how I know that the Ignitor is in the correct place??

Sorry for my bad english.

Ayuh,... You need a Tune up, 'n include setting the timing, by Spec...

 

[aov004]

Re: OMC COBRA 4,3 L Knocking problem between 1500-2500.

Ayuh,... You need a Tune up, 'n include setting the timing, by Spec...

Okey...

Can you explain a bit more please`?? By spec.. U mean with the lamp??

 

[Joshua Nichols]

Re: OMC COBRA 4,3 L Knocking problem between 1500-2500.

Get a timing light and a dwell meter.. So you can set the timing and the dwell on the new point set..

 

[aov004]

Re: OMC COBRA 4,3 L Knocking problem between 1500-2500.

Get a timing light and a dwell meter.. So you can set the timing and the dwell on the new point set..

Okey. That I know how to do.

BUT I made some progress today. I drove on 1500 rpm and then adjusted the ignition while driving. Then the knocking disseaperd(it went away)

I took out the hole ignitor and cleaned it and fixed it up.

Anyone have any experience with that the weigths in the ignitor that are not working properly??

I belive it must be the springs that are too loose, because I get to much ignition before I get to 2500 rpm.

When I went back to idle speed the ignitin were 8 deg. after tdc. Way OFF.

When I was gonna test it today I was out of power.... typical...

 

[Joshua Nichols]

Re: OMC COBRA 4,3 L Knocking problem between 1500-2500.

how are they not working??? Spring broke or something?

 

[Lou C]

Re: OMC COBRA 4,3 L Knocking problem between 1500-2500.

It sound like you're saying that the springs were too loose and giving you full advance too early. If you remove the screws that hold down the plate in the distrubutor that the points are mounted to, and carefully lift it out (don't drop the screws in the dist!) you will see the springs and weights of the centrifugal advance unit. If you try to turn the mount for the point mounting plate, you should feel the tightness of the springs and when you let go they snap back. I lube the weights and springs with a tiny bit of motor oil to keep em moving easily when I change the points. The is also a felt wick in the center of the distributor shaft, I put a few drops on oil there too.

The standard setting at idle is 6* Before Top Dead Center. Full centrifugal advance which should not come in till about 3200 is 12*, so the total advance should not be more than 18* (6* base value + 12* advance). The right way to check this is to use an advance timing light. This light allows you to dial in the specified amount of advance with the dial, and then when you check the timing (if you put the dial on 18*) it should read zero on the pointer. I checked mine with the boat in the water because I did not want to run it at 3200 rpm on the water hose, not enough water volume. Mine checked out right on the nose.

look at this diagram, the weights and springs are on part #14...

http://www.dougrussell.com/partscat...8,499,500,501,502,503,504,505,506,509,507,508

Now as a matter of exprience, I had many cars with points and never had to replace the springs because of too much advance. If you get knocking when the timing is set right, I'd look at other causes. Like too much carbon build up (high compression, like over 175 lbs or so), and lean fuel mixture, and low octane gas. Those are actually more likely, than the springs stretching, unless somebody fiddled with em at some point. Check compression, spark plug heat range and fuel mixture. I always use high octane (93) gas because I'm sure my 23 year old engine has some carbon built up in it. They run cool, and rich, and those are factors that increase carbon build up in the cylinders.

 

[aov004]

Re: OMC COBRA 4,3 L Knocking problem between 1500-2500.

It sound like you're saying that the springs were too loose and giving you full advance too early. If you remove the screws that hold down the plate in the distrubutor that the points are mounted to, and carefully lift it out (don't drop the screws in the dist!) you will see the springs and weights of the centrifugal advance unit. If you try to turn the mount for the point mounting plate, you should feel the tightness of the springs and when you let go they snap back. I lube the weights and springs with a tiny bit of motor oil to keep em moving easily when I change the points. The is also a felt wick in the center of the distributor shaft, I put a few drops on oil there too.

The standard setting at idle is 6* Before Top Dead Center. Full centrifugal advance which should not come in till about 3200 is 12*, so the total advance should not be more than 18* (6* base value + 12* advance). The right way to check this is to use an advance timing light. This light allows you to dial in the specified amount of advance with the dial, and then when you check the timing (if you put the dial on 18*) it should read zero on the pointer. I checked mine with the boat in the water because I did not want to run it at 3200 rpm on the water hose, not enough water volume. Mine checked out right on the nose.

look at this diagram, the weights and springs are on part #14...

http://www.dougrussell.com/partscat...8,499,500,501,502,503,504,505,506,509,507,508

Now as a matter of exprience, I had many cars with points and never had to replace the springs because of too much advance. If you get knocking when the timing is set right, I'd look at other causes. Like too much carbon build up (high compression, like over 175 lbs or so), and lean fuel mixture, and low octane gas. Those are actually more likely, than the springs stretching, unless somebody fiddled with em at some point. Check compression, spark plug heat range and fuel mixture. I always use high octane (93) gas because I'm sure my 23 year old engine has some carbon built up in it. They run cool, and rich, and those are factors that increase carbon build up in the cylinders.

THank you vey much for allt he help. I will check this out soon as I can and wright back to you..

I also got a new problem today and that was that the the drive was stock in forward. Da....n all this problems- I cant get it out of gear and in newtral or reverse.

Anyway I hope I figer this out, THANKS so much for all your help so far..!!

I love america!!

 

[Lou C]

Re: OMC COBRA 4,3 L Knocking problem between 1500-2500.

Ah yes the old Cobra will not come out of gear issue, well do a search for the Stuart Hastings website on the Cobra, that tells it all. But for now, try getting the idle down to 550-600 in gear in the water, the lowest possible idle helps them shift better and check to see if the ESA is working, it is supposed to lower the engine idle to about 450 when you shift from in gear to neutral in the water (it won't engage on land on the water hose because there is not enough load on the prop). If the idle is too high and the ESA is not working you will have trouble shifting and may have to shut off the engine in gear, then shift to neutral and start it up. There is a lot of info on this site on Cobra shift problems.