What happened to 2800 RPM and more?

[quinnutah]

Got my 4.3 OMC Mark Twain out this summer to find it would not rev over 2800 RPM. So after reading several of the forums here. I rebuilt the carborator, put in new points, condensor and rotor. Changed the inline filter at the carb intake. Replaced the fuel seperator with a new one. All of this realy help the idle but it is still missing or running rough at 2800 rpm and faster. So I check the cable set ups, to make sure that the interrupt and overstroke swithches were set right. Still not any improvement. I then unplug the E.S.A. module without an improvement. I even went back to the old condensor and rotor still the same. I did a quick check on the fuel pump, ( disconnected it from the carb and check flow as I cranked the motor) it looked good. So now I am thinking coil but I am unsure of how to check it. So would someone give me some input to how to check the coil and what ever else would be suspect causing the problem. By the way my tach is also not working, I am wondering if this could be common to the problems.

 

[quinnutah]

Re: What happened to 2800 RPM and more?

I just thought of some detail that I left out. This is a 1987 OMC cobra drive. Thanks

 

[quinnutah]

Re: What happened to 2800 RPM and more?

Can I run a jumper to the coil from the battery as a troubleshooting step for the coil without damaging the coil or the points?

 

[olbuddyjack]

Re: What happened to 2800 RPM and more?

Hows the distributor cap? Maybe a carbon track taking out a cylinder. Double check all your secondary ignition(cap, wires, plugs)and do a compression test.

 

[novicetech]

Re: What happened to 2800 RPM and more?

if you have a mechanical pump, there may be a fuel filter in that.

 

[quinnutah]

Re: What happened to 2800 RPM and more?

I'll check the cap tonight and I read an early post about the anti-syphon valve. These are the next items I am checking. Thanks for your inputs

 

[searay3]

Re: What happened to 2800 RPM and more?

I have a 4.3 as well (1987). Had the same issues. Anything above approx 2500 rpm, it would backfire thru the carb and die. Extensive fuel system checking showed no obvious issues. Changed the coil and it runs good again. Since you say the tach quit working, look around the coil connections. The tach runs off the neg terminal on the coil. No easy way to check the coil. In my case, whenever the spark was checked after it died, it would spark. Only under load did it fail. Coil is fairly cheap anyway. 10 to 15 bucks stock, about 30 for a performance. I chose accel super stock. about 25 bucks. (IMHO)

 

[quinnutah]

Re: What happened to 2800 RPM and more?

Is the coil the same as a 4.3 automotive? And where did you find one for near $15 ? I would lke to get this one replaced this week end.

 

[SILTHUNDER77]

Re: What happened to 2800 RPM and more?

I recently replaced the coil on my gm 2.5L for 9.95 at oreiily's auto parts, it works fine, also if you are concerned about marine issues, you could place a couple drops of epoxy or use a hot glue gun to waterproof the contacts so as to reduce the likelyhood of a flashover..etc..

 

[Don S]

Re: What happened to 2800 RPM and more?

Originally posted by SILTHUNDER77:<br /> I recently replaced the coil on my gm 2.5L for 9.95 at oreiily's auto parts, it works fine, also if you are concerned about marine issues, you could place a couple drops of epoxy or use a hot glue gun to waterproof the contacts so as to reduce the likelyhood of a flashover..etc..

Where in the He11 did you hear that a few drops of a hot glue gun or epoxy will make an automotive coil turn into a marine coil. The difference, if there is any for a particular coil is how it works inside. The output and the voltages it is designed to be used with. Rather it's internal resistor or not.<br />Don't go thinking a bit of epoxy and does anything. It absolutley doesn't.

 

[quinnutah]

Re: What happened to 2800 RPM and more?

Ok, then what is the differences between an auto ignition coil and a Marine ignition coil? I sure would like to know

 

[tommays]

Re: What happened to 2800 RPM and more?

different systems are matched to work together<br /><br />different coils have different OHMS which will give a different output<br /><br />it will give spark but it might be different enough to cause a problem and your chaseing a ghost<br /><br /><br />tommays

 

[quinnutah]

Re: What happened to 2800 RPM and more?

Here is the conclusion to my motor problems. I did replace the coil but without an improvment. I put the old coil back on and still not any better. It still continued to miss at anything over 2800 RPMs. AS a last resort I opened the distributor again to check the gap on the points. But this time I noticed the spring tension on the point swing arm very light. Early on I suspected floating points but didn't check deep enough. So at this point I removed the new points and reinstalled the old points. A miracle the motor revs right up to where it should be. A closer look at the points showed that the points tensioning arm material is copper and it is also the conductive path for the oneside of the points. This material doesn't have enough tensile strength to provide the spring needed. A quick trip to the dealer and I found out the new points are suppose to come with and additional spring loop to apply the tension. My tune up kit was missing this item. Now I have a fine running motor with the right point set up but I am still missing a month of work and troubleshooting. But thanks to all who attempted to quide me.

 

[Don S]

Re: What happened to 2800 RPM and more?

I've seen this happen before, but never seen one go past 1500 rpm without floating.