++ PROBLEM SOLVED ++ OMC Power Problem at higher RPM

VonZipper

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Joined
Feb 27, 2009
Messages
10
First, before anyone goes there.......... I have used the SEARCH feature extensively, found lots of great info, but would like a fresh batch of input on my particular issue.......


Heres the rig: 1976 SeaRay 220 SRV with OMC 235 (Ford 351w)

Problem I have: Starts and idles smooth as a baby's bottom. Runs great up untill about 1800 rpm. Then starts to bog down, cough, sputter, and choke. Symptom is the same when in or out of water, doesnt matter. If I remove throttle cable, and try to baby it by hand at the carb, I still cant get it to rev past 2000 rpm. Looking into carb, I can see plenty of gas trying to make its way into there, but something just isnt right.

Previous owner (I just bought it) replaced plugs, wires, cap, rotor, points, all fluids, and installed new Holley carb (electric choke), in attempt to fix.

I took it out last weekend, and it still does the same thing.

Here's what I have looked at so far: Fuel separator/filter is clear, fuel pressure good, Mechanical advance in distributor appears to be working correctly.... no grime or rust, weights move freely, springs are intact. A timing light shows advance as RPM increases.

I was told it COULD be failed exhaust flappers getting stuck in the exhaust somewhere..... I pulled the elbows where they dump into the drive at the "Y", nothing in there. Nothing in drive unit blocking either. From all I can tell, looks like exhaust is clear.

I have gone over electrical system....... all connections and grounds appear to be tight and in good order.


I am thinking in my wee little mind that this is electrical, either coil not putting out enough juice, or advancer not advancing far enough at some point.


Any input or suggestions would be much appreciated!
 

WizeOne

Commander
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Mar 23, 2008
Messages
2,097
Re: OMC Power Problem at higher RPM

Re: OMC Power Problem at higher RPM

Your electric shift outdrive system did not use exhaust flappers so rule that out.

Have you checked the firing order? You could have it wired with two cylinders crossed and it would run at low RPM. Any smoke at any time? When you look down the carb is there any excessive wetness? Have you checked the fuel pressure at your maximum RPM? Have you pulled the fitting on the top of the tank and checked for any screens? Your '76 most likely did not have the anti-syphon fitting at the top of the tank, so that would not be an issue.
 

VonZipper

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Feb 27, 2009
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Re: OMC Power Problem at higher RPM

Re: OMC Power Problem at higher RPM

Thanks for the reply......I haven't checked firing order, will do that later today. No smoke of any kind at any time.

Would it really run that smooth at low RPM, then choke out at 1800+ with 2 crossed wires???


I have not checked fuel pressure at higher rpm, but am inclined to rule that out, because if I manually pump carb by hand, pumping fuel into intake with accellerator pumps (squirt squirt squirt) it doesnt want to go any faster.

Any other ideas?
 

KRH1326

Chief Petty Officer
Joined
Sep 22, 2007
Messages
491
Re: OMC Power Problem at higher RPM

Re: OMC Power Problem at higher RPM

Yeah Man,

From one 351W man to another, check and double check the plug wires.
I can look you square in the eye and guarantee that IF you have #2 and #4 crossed, it will idle, it will rev by hand, it will move the boat. It will make life miserable @ 2000 and above. It will also make the intake manifold get hot, and you will have a hard time cooling your exhaust. Trust me, I know. Been there, done that, moved on.
Seriously, check the plug wires. I would go after the coil, it may be breaking up as the rpms climb.

There is a chart in the appendix that shows the mechanical advance curve. ( for 351W it is more like two straight lines) page 489/572 appendix A-14

http://www.4shared.com/file/102988421/c4f26d54/OMC_64-86.html

Also great wiring diagram

http://www.4shared.com/file/102989243/c097b029/OMC_wiring_all.html

Don S. put alot of info together at
http://forums.iboats.com/showthread.php?t=288430
Good Luck
 
Last edited:

VonZipper

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Feb 27, 2009
Messages
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Re: OMC Power Problem at higher RPM

Re: OMC Power Problem at higher RPM

Yes, I am highly suspect of ignition system. Double checked firing order, plug wires are in proper order, but will go over them again. Just for reference, on the cap, where should #1 be?

Also, is it possible that I am getting arcing from wires to block at higher RPM?

Some of the plug wires are wrapped right tight to the engine block.

Just the fact that it cuts out when it gets close to 2000 baffles me.
 

futz

Banned
Joined
Jun 22, 2009
Messages
180
Re: OMC Power Problem at higher RPM

Re: OMC Power Problem at higher RPM

sounds like the carb needs to be rebuilt. After it being rebuilt, and the problem is not solved, then i would look to the valves to see if they are to tight.

You of course have performed a compression test, havn't you?

Another trick you can run the motor in pitch black to see if indeed you have arching anywhere.

And finally a vacuum test will tell you plenty.
 

56speedy

Recruit
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Aug 5, 2009
Messages
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Re: OMC Power Problem at higher RPM

Re: OMC Power Problem at higher RPM

Well I am new but I have about the same problem, I have a 1976 omc 302 175hp elec outdrive. I can get mine up to about 2000rpms then it falls on it face. i have done dwel and points and set timing, I also can get it to idle at or about 600rpms fine. once you hit it, it just falls on it face like not getting all the spark for it. I looked in the carb and it still has fuel going in at wot. i have checked fireing order it is right. please help SSG US Army
 

cooter2506

Senior Chief Petty Officer
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Apr 8, 2007
Messages
733
Re: OMC Power Problem at higher RPM

Re: OMC Power Problem at higher RPM

56speedy please start your own thread so we dont confuse you and the original poster. We cant confuse us we are already all confused!!
 

jtybt

Senior Chief Petty Officer
Joined
Aug 5, 2009
Messages
730
Re: OMC Power Problem at higher RPM

Re: OMC Power Problem at higher RPM

First suspects are timing and firing order.

One thing I've found, The advance weights have nylon sleeves on pins so the weights open evenly. The nylon sleeves go away after a time.
 

VonZipper

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Feb 27, 2009
Messages
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Re: OMC Power Problem at higher RPM

Re: OMC Power Problem at higher RPM

I found several older topics where the OP had a similar problem, and tracked it down, with the help of DON S., from OCEAN SHORES, WA.... to a missing spring on the points. Missing tension spring would allow points to "float" at 1500+ rpm.

I haven't checked, but I recall that earlier today, when adjusting my points, they moved around way too easy, seemed pretty floppy. If memory serves, shouldnt that spring (if it's there) hold them in pretty firmly?
 

futz

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Jun 22, 2009
Messages
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Re: OMC Power Problem at higher RPM

Re: OMC Power Problem at higher RPM

oh you didn't go thru the dizzy to check it was operating correctly. Being new here i would have thought you would have done that first.
 

VonZipper

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Feb 27, 2009
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Re: OMC Power Problem at higher RPM

Re: OMC Power Problem at higher RPM

FUTZ, that was a pretty useless comment. Thanks for all your help. :rolleyes:
 

futz

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Jun 22, 2009
Messages
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Re: OMC Power Problem at higher RPM

Re: OMC Power Problem at higher RPM

ok one has a problem such as yours. So you go thru the dizzy notice a problem with the points, and or weights. You run it on the water , and in the driveway and the problem is still there. Do you include the info in the original post? No.

So i posted what i would if the dizzy was working good and i tried everything else and it didn't fix the problem.

Good luck in finding your problem..
 

VonZipper

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Joined
Feb 27, 2009
Messages
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Re: OMC Power Problem at higher RPM

Re: OMC Power Problem at higher RPM

EUREKA !!!

PROBLEM SOLVED !!​

Well, just as suspected, previous owner, or somebody, when replacing points, left out the c-shaped spring that holds the points open.

Finally found a point set in town, replaced with all correct parts, and we're in business!


Gotta love the internet, more specifically the SEARCH button (and of course IBOATS), and lots of other fellas that post their problems and solutions. Thanks again to all, hope this post and responses helps someone out down the road!

Now if you'll excuse me, I need to go find my Pirate flag........ :D
 

bruceb58

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Mar 5, 2006
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30,454
Re: ++ PROBLEM SOLVED ++ OMC Power Problem at higher RPM

Curious...what was the dwell measuring at when you were testing before you found the piece missing? i would have thought the dwell would be all over the place.
 
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