3.0 OMC ignition problem

[Chuckyd973]

Re: 3.0 OMC ignition problem

What is your timing set at? I have an 04' 3.0 HO motor with points and im 8 degrees ATDC. Also verify compression. I had a blown head gasket that was sperated under the intake/exhaust manifold. It was blown on the exhaust side of the head only so it confused the hell out of me that it wasnt just an exhaust leak. Also have you done any manifold gaskets lately? The wrong gasket can cause fuel to pool in the intake. One more thing. While its running try removing the PCV valve hose away from the carb. See if that makes it run better.

CHUCK

 

[Darringer]

Re: 3.0 OMC ignition problem

Unless I have missed something in this thread, it would appear your cam timing is off (as stated by {obc}patch). Spin the crank until number one has both valves closed and at tdc. See where the timing marks of the cam and crank are. If they are not next to each other at 12 and 6 o'clock, as they are apparently supposed to be, move the cam. You've pretty much eliminated everything else. I think all cylinders are getting spark, fuel, and air. Just not in correct time.

 

[Jessfly1]

Re: 3.0 OMC ignition problem

Unless I have missed something in this thread, it would appear your cam timing is off (as stated by {obc}patch). Spin the crank until number one has both valves closed and at tdc. See where the timing marks of the cam and crank are. If they are not next to each other at 12 and 6 o'clock, as they are apparently supposed to be, move the cam. You've pretty much eliminated everything else. I think all cylinders are getting spark, fuel, and air. Just not in correct time.

Thanks for your input but this is why I elected not to change the cam orientation....

After much debate I elected to put the timing cover back on without changing the cam orientation. This is why... I wanted to make 100% sure #1 was at TDC compression stroke so with the valve cover and timing covers off I conducted a few tests. First I took the shrader valve out of my compression tester and just put the hose in the plug hole. With about 30psi of air supplied to the cylinder I rotated the motor by hand and when a valve opened I could hear air either escaping out of the carb (intake) or transom (exauhst) I then labled the valve respectively with a marker. FYI, my clymers manual had the valve orientation wrong!! I did this for all 8 valves. Once i knew without a doubt which vavle was what i rotated the motor again until #1 intake valve started to open. Once it was on its way shut I put a screw driver in the plug hole to gauge where the piston was. At the top of the stroke the intake valve is closed as well as the exauhst valve AKA TDC compression stroke! I verified they were closed by putting air in the cylinder and It was escaping past the rings not intake or exauhst. This proves the cam to crank orientation is correct! Timing marks orientation also wrong in my manual! I did this for all four cylinders.

 

[Jessfly1]

Re: 3.0 OMC ignition problem

Thanks for all the inputs.

I think I have narrowed it down. I got it running on muffs and It was still not firing on 1 and 2. I would give it a little gas and #1 would fire. I know this because after letting it just idle I pulled plugs and 1 and 2 did not look like they were firing. After running it on a fast idle (a little gas) I pulled the plugs and 1 look as if it was firing but 2 still nothing. So I figured what the heck and took it to the local pond to see if it had WOT power. Once on the lake I let it warm up and taxied out of the no wake zone. Once we were in the clear i opened her up and she had no problem getting on plane. WOT seems to be adequate with speed and power. While cruising around the lake I would stop occasionally, let it idle and pull #1 or #2 plug wires and lo and behold a change in idle! This is pointing me directly to the carb! I think there is something wrong with the idle circuit.

 

[Jessfly1]

Re: 3.0 OMC ignition problem

Thank you everybody who commented on my post. With your help i was able to narrow the problem down to the carb. Once i leaned the carb out it was running on all four. I am in the process of serchng for a new carb because this one has been giving me problems since i bought the boat. I figure spending almost 500 unnecissary dollars is enough for me to purchase a new one. I have been mechanically inclined for years but this problem baffled me. It all started by replacing the plugs then s#&! hit the fan. I still dont understand how a carb would make two cylinders not fire but it did. I guess this is a hard lesson to learn but i will never overlook the carb again.
Happy boating
Thanks again

 

[6meter]

Re: 3.0 OMC ignition problem

Remanufactured carbs are usually junk. Rebuild yours! With a good kit. Glad you figured it out.

 

[Fish-a-Palooza]

Re: 3.0 OMC ignition problem

Did it turn out to be the carb?

 

[Jessfly1]

Re: 3.0 OMC ignition problem

Im almost 100% sure it was the carb but wont know for sure until I take it out this year.