454 king cobra
 

Having a issue with a 94 fourwinns with a 454 omc king cobra fuel injected. Boat will fun fine up to 3200rmps after that if go full throttel it will start backfiring an spitting. Any ideas?

The first thing I would check for would be a fuel delivery issue, like a weak fuel pump. However, I had the same symptoms on my 454 several years ago, and the real problem was only revealed after a compression test. Turns out I had a 1/4" hole in an intake valve, that was put there when a chunk of piston departed the cylinder. Amazingly, that cylinder still registered about 90 PSI on the compression test, so the boat ran fine at idle and cruise - it just back fired and sputtered when I leaned hard on the throttle and the RPM's got above 3400 RPM. Hope your problem turns out to be something easier - and less expensive. :eek:

i would replace the plugs,cap&rotor and wires first,a weak ignition system cant fire the fuel under hard load.

Also check the timing. I had similar problems on my 1995 carbed OMC 454 with the spitfire ignition. Reset the timing & it ran like new.

Are you still using the coil packs from the spitfire ignition system. Most all of us have deleted that system at this point an converted over to a standard distributor since you can't find the parts.

Though it could very well be a fuel delivery system, and that ignition system isn't really fuel injected, it's "computer" controlled ignition with a standard carburator.

If you can still read the engine Model tag # on the port side valve cover that would help. Look below for a breakdown. Every 454 for 94 that I see here is a carburator. I had this issue and when I replaced the distributor to a standard system it cleared right up. Sometimes when this system goes nut's it detonates, backfires, and blows up pistons...

I used this:
MARINE 7000 DUI DISTRIBUTOR http://www.performancedistributors.com/marinedui.htm

1994 OMC breakdowns, yours will start with "74" as the size of the engine (7.4L). http://www.boats.net/parts/search/OM...994/parts.html

I would generally agree in most cases, but here I would change the entire distributor. See post above.

Checks the base timing and set it within spec like Itsallgood995 says (or that system will go haywire), if that doesn't help I'd just do the swap and check the carb at the same time.

The fuel pump is putting out 40psi which is enought fuel pressure. I'll look into the ingnition next thanks for the feed back.

Is it 40 PSI at idle? Check it in the RPM range that you are having an issue. Do a compression test as well, better would be a leak down test. I had a new to me customer, just purchased a used boat. It was a 4.3L Volvo, carb'ed with electric fuel pump. The carburetor and fuel pump were new and the old ones were in the boat. It ran at idle up to mid rang then started to crap out. I said I wanted to do a compression test. Low and behold one cylinder was low, the edge of the piston down to the ring land was broken and missing in a small area. Do a compression test first.

Ok now I'm confused, do you have a carburator????

With a carb you should have about 5psi??? Model # of your engine/drive package would help if you can get it. Did you/someone else put injection on it???

Yep, exactly what I had. Compression test is relatively cheap and easy compared to checking and replacing a lot of other components.