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Old     (patrick)      Join Date: Apr 2003       05-12-2003, 12:38 PM Reply   
A friend's got a 89 sport nautique with a Ford PCM 351 engine with Holly carb.
While trying to accelerate the boat starts slipping and reducing speed, cutting out and acts inconsistent, he's tried different gas stations, using gas cleaner &/or water removal from the gas tank to try and troubleshoot, but nothing's helping. Also he replaced all of the spark plugs still cutting out and some backfiring type noises persist. We think it might be the carb. but not sure... Anyone have similar problems? Any suggestions?
Old    byerly03            05-12-2003, 1:02 PM Reply   
have you had the timming checked? I had a 94 sport nautique that was doing that and it was just the timing. hope it works out
Old     (ndh2o)      Join Date: Oct 2001       05-12-2003, 1:19 PM Reply   
Do you smell gas strongly, it sounds kind of like it is burning very rich. Maybe there is trash in the carb, and is letting too much gas in. Timing could be off as well.
Old     (sandbag)      Join Date: May 2002       05-12-2003, 1:48 PM Reply   
Holley's can't take backfiring too well.
They have a proportioning valve that
has a tendancy to blow out if it backfires
thru the carb.
Was the backfire out the carb or exhaust?
If you end up replacing the carb
stay away from Holley. Ask any gearhead.
Old     (csquared)      Join Date: Jan 2002       05-12-2003, 1:56 PM Reply   
Friend with the exact boat/motor was having similar problems. Problems were all electrical. Redid the grounds and cleaned up/redid all the connections at the ignition switch. Seems to have solved all the problems.
Old     (tlb)      Join Date: Feb 2003       05-12-2003, 6:34 PM Reply   
I had a '90 prostar 190 with same engine. I was having the same problem you're describing. It was almost like the boat was running out of gas. My mechanic replaced the power valve and the problem was solved. He suggested doing this before rebuilding or replacing the carb. It was the best 30 bucks I ever spent on that boat.
Old     (h20jnky)      Join Date: Mar 2003       05-12-2003, 7:17 PM Reply   
Sounds electrical? Check all the connections under dash......If boat starts to hesitate under way you definitely want to get the timing gun on the drive belts. Also, check all connections to ignition and distributor points(wire brush will clean nicely)....
Good luck and let us know.....
Old     (bcoppinger)      Join Date: Sep 2002       05-12-2003, 7:51 PM Reply   
Sounds like Timing
Old     (sandbag)      Join Date: May 2002       05-13-2003, 6:02 AM Reply   
Power valve. Thats what I meant instead of proportioning valve.

OK, you have way too much advise here.
Best to cover all the basics as any mechanic would do to diagnose you problem.

1.Check compression to make sure there are no internal engine problems.
2. Check for spark and see that plugs are clean and unfouled. Run the motor in pitch darkness
to see if plug wires are arc-ing. And see that
you have sufficient voltage to the distributor.
Check for loose or cracked cap and look at the rotor.
If everything checks-out, measure timing.

3. Try a "known good" carb. For me this is easiest
because I have multiple Chevy 350's with tons
of spare parts. If you have to, buy a carb
(most are ready to run out of the box.) Knowing
full-well you will return it if it doesn't help.
Old     (peter_c)      Join Date: Sep 2001       05-13-2003, 9:04 PM Reply   
Sandy is onto something here. I would definetly look at the ignition system, but take it one step farther and scope or at the least ohm the ignition wires. Take a good hard look at the distributor cap if it has one. Any kind of carbon tracking is an idication of a missfire. If it has old school points replace them and the condenser. Is this a DIS motor? Distributerless that is.

As Sandy also said the Holley carbs are prone to destroy power valves when a motor backfires. Please do not change the carb or you will cause all kinds of problems. If it has a problem fix the problem or rebuild it, but fuel mixture is too important on a boat motor. The carb is most likely not the problem as you said it was intermitant. Fuel problems are usually more consistant under load.
Old     (patrick)      Join Date: Apr 2003       05-14-2003, 7:14 AM Reply   
He has a appt. with an inboard mechanic today to troubleshoot the problem. I'll let you know what happens. Thanks for the information.
The engine does have a distributer as well.
Old     (patrick)      Join Date: Apr 2003       05-14-2003, 10:59 AM Reply   
The mechanic adjusted the timing a little, but more importantly the distributer points looked bad, so he replaced those and everything tested 100%.


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