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Old    Nacho (denverd1)      Join Date: May 2004       07-31-2006, 12:30 PM Reply   
A little history on my boat: 1986 MC Tristar 220 w/ 677 hours on 351W. First trip out with new plugs and oil change. Running the best ever since i've had it. Put weight in it less than 10 times this year. Last year and the year before we had about 1000 lbs of sand in it. No problems.

Found a new cove to ride over the weekend. Drove to the new cove, pulled the girls. Two fairly short sets, no probs. Begin filling ballast...

Ballast full, my buddy hops in. Getting up on plane we hit something. Running gear not affected. We stop, check everything, trans fluid level, and start to tow again. At about 2000 RPMs its backfiring through the carb and just won't for crap.

In neutral, the engine runs fine. Feels like the trans is going... Maybe its old and not used to the weight...

Saw another thread where the guy was waiting for a trans rebuild and then realized the firing order was off. Not logical, but any chance its fuel/air related? All this began when we hit something...
Old    Rod McInnis (rodmcinnis)      Join Date: Sep 2002       07-31-2006, 5:25 PM Reply   
What kind of something did you hit?
How do you know you hit something?

I would not expect the transmission to cause backfiring.

It is possible that the engine could get messed up when you hit something and the engine goes from 3000 RPM to zero in an instant. But I would expect the prop and shaft to suffer more than the engine would. What can happen in such a situation is that the timing chain (which is not visible, buried in the engine) can jump a tooth or two. Normally the crank is driving the camshaft, and pulls all the slack in the chain one direction. If the crank suddenly stops the momentum in the camshaft pulls up all the slack and then can jump a tooth. The result would be very poor running and backfiring through the carburetor.

It is also possible that you didn't hit anything at all, it was the timing chain or similar breakdown that made such a loud THUMP noise that you thought you hit something. Timing chains do wear out so it is possible that its time was up.

A quick test would be to check the ignition timing. If the timing chain jumped the ignition timing will be off. Note that readjusting the timing might improve its running a little bit but it won't make the valve timing correct so it will never run right.

Assuming that the ignition timing was off, and also assuming that the distributor wasn't loose, then I would assume that the cam shaft is off. I am not aware of any easy way to verify the camshaft timing short of disassembling the front part of the engine to get to the timing chain.

If it is the timing chain then it shouldn't be too difficult to tear down to it with the engine in the boat. The timing chain is basically behind the water pump. But then, you might want to consider that it is a 20 year old motor with 677 hours on it. It might be time for a complete rebuild.
Old    Todd (snyper1d)      Join Date: Mar 2005       07-31-2006, 9:02 PM Reply   
Will the boat get on plane or drive at all? Any funny noises besides the backfiring?

If the boat will not drive, it is possible that the engine coupler (also called dampener plate) has given out. When you hit something, did you hear a loud pop? Possibly a sound like a crushing aluminum can? It is not uncommon for older boats that have quite a bit of wear on them to have this part go out.
Old    Nacho (denverd1)      Join Date: May 2004       08-01-2006, 11:11 AM Reply   
we're in the middle of our 2nd drought season in a row. this should help explain things:

i know we hit something because the boat rocked to the starboard side and then leveled out once we came off of it.

Rod - while what you're describing sounds possible, wouldn't it run like crap when in neutral?

Todd - the boat will run, just not above 2000 rpms. and when not in gear, it runs perfectly, up to 5000 RPMS
Old    Rod McInnis (rodmcinnis)      Join Date: Sep 2002       08-01-2006, 12:33 PM Reply   
The valve timing effects how well the engine breaths. Without a load on it the engine doesn't need to breath much.

The backfiring through the carb is telling me that there is something wrong in the timing and/or ignition area.

I can imagin a number of things that could cause a major loss of power. If the prop shaft was bent, or the strut that holds the shaft was bent (and it wouldn't take much) then it could require an major amount of power to turn the prop. I would expect this to have an effect at idle speeds and I wouldn't expect it to cause backfiring.

If the transmission shifts into forward and reverse and will idle in neutral then I doubt that it is causing such a problem. I have had transmissions start to slip, and also had the forward clutches warp and not release to the point that I had no neutral and it would stall the engine when I tried reverse. I just can't think of anything in the transmission that would rob power at higher RPMs.

Buy, beg or borrow a timing light and see if the timing is off.
Old    Nacho (denverd1)      Join Date: May 2004       08-01-2006, 12:43 PM Reply   
will do. just got back from the house and I tried to spin the prop by hand to see if the shaft was binding anywhere. nothing. it spun freely, same as before. Sounds to me like the timing too. Just surprised it was caused by a minor impact. Thanks Rod
Old    Alessandro Garabaghi (pimp131)      Join Date: Aug 2003       08-02-2006, 4:45 AM Reply   
Could the boat be in limp mode? I know our prostar had a problem where it would not go past 2,000 rpms replaced a sensor near the ECU and all was good


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