1990 chaparral with 4.3 OMC Cobra that is running rough & driving me insane !!!!!

[chrish99]

I have a 1990 Chaparral 1900SL (19ft bow rider) with an OMC Cobra 4.3 I/O. Have owned it for years , have always kept up with routine maintenance and it has never giving me any major problems..until now

I had it out on the water 2 weekends ago , started driving the usually 20 minute commute up the C&D Canal to the Chesapeake Inn..about 10 minutes in she slightly started miss firing and progressively got worse and worse so I shut it down to take a look. Everything seemed normal , nothing obvious or out of the ordinary. Went to start it back up and wouldn't fire. Sat for a few minutes and finally got it to run again (missing badly) I was limping it back to the dock and all of the sudden it started running perfectly normal again? I figured maybe it got a little water in the fuel so I turned around and had some drinks and the Inn. Well long story short and $500 later I had it towed back to the dock and on the trailer she went ( wouldn't start at all).

Since being towed back I can get it to run , but it runs horribly , miss firing and sputtering. So far I have :
- drained entire fuel tank, changed fuel filter and replaced with fresh 93 octane gas
- replaced ignition coil , distributor cap, rotor, points and condenser
- adjusted timing - is set to 6* BTDC ; also checked gap on points and set to .019"
- replaced all spark plugs
- compression test
- removed carb and cleaned ( everything seemed OK on the inside; float worked, no blockages, etc)
- made sure all plug wires are in correct firing order

I used to be able to put the boat in the water, turn the key and it would fire up instantly. To get it running now I have to have the throttle wide open, start it , and quickly ease back on the throttle until its idling. after it warms up I can shut it off and it will fire right back up, but that only if I restart in within a few minutes. Also I can get it to idle damn near perfect while adjusting the idle mixture screws, but after shutting it off and restarting it later , it idles horribly again like I never adjusted anything?

I'm thinking it may be fuel related but I'm not sure. Have been throwing lots of time and money at this and its driving me nuts! Just want to be back out on the water.

Thanks for any input in advance !!

 

[southkogs]

Welcome aboard Chris ... plug wires? Are you sure you're getting spark consistently at every plug?

 

[Lou C]

A few more things I'd check:
Wiring that goes to the ignition coil, make sure its not grounding anywhere. There is a purple/black stripe wire that goes from the + terminal on the coil over the back of the engine down to one of the small terminals on the starter solenoid. These small terminals can easily get corroded. The other wire (red/purple) on the + terminal goes to a connector and then to the E terminal on the alternator. On the neg terminal, there is one wire (grey) that goes into the engine harness connector and also to the connector for the ESA system. You might try disconnecting that big engine harness connector and make sure there is no corrosion on the pins inside.
Look at the fuse for the ignition system at the fuse box under the dash, I had a problem with oxidation on the glass/metal fuses and had no power to the ignition sys at all. New fuse fixed it.
Fuel pressure & volume, measure what the fuel pump is putting out (but be careful!!!)
When you took out the old spark plugs, how did they look?
White as in a lean condition (more fuel related) or black as in rich/fouled (possible ignition cutting out)???
You're sure the float is not sticking and there are no vaccum leaks right?
What carb, 2 bbl or 4 bbl?

 

[Bondo]

I'm thinking it may be fuel related but I'm not sure.

Ayuh,.... Welcome Aboard,.... Yer last paragraph says fuel issue, probably the carb,....

Runnin' it on a remote tank to the fuel pump will eliminate the boat's fuel system,....

 

[chrish99]

thanks for all the input.

I went back and double checked all my wiring at the coil , starter, battery and distributor. Everything was tight and I read continuity at every wire. I checked spark at every cylinder and each one has good spark, so I'm thinking it is definitely either fuel delivery and or carb related.

Since I can get it to run I decided to take it to the canal after work and see what happened. After managing to get it to finally start and idle (somewhat) I left the dock and idled out to the no wake zone (misfiring badly the whole time). But once I got into the no wake zone I had it cruising at 3000 rpm like it was brand new. It does miss slightly and sputter at WOT (which is about 4500rpm) but I'm happy that it didn't fall on its face. I shut it off a few times and it would fire back up and idled perfectly.

Trailered it home and hooked muffs on it to flush it out (about 30 mins after I shut it off at the ramp). Turned the key hoping it would fire up and idle like new but no luck. Had to hold throttle at WOT and feather it back to get it to idle.

So it definitely runs a lot better when it's warmed up, just puzzled on why it acts completely different after sitting for 5 minutes or so ? Does this sound like a possible carb rebuild or maybe anti syphon valve issue ? I am familiar with carbs but new to anti syphon valves but from reading on here a lot of people have had issues with them.

 

[Bondo]

Does this sound like a possible carb rebuild or maybe anti syphon valve issue ? I am familiar with carbs but new to anti syphon valves

Ayuh,.... Diagnose the issue, by isolatin' the components,....

The anti-siphon valve, aka; a check valve is at the tank's outlet,....

By runnin' yer motor on a remote fuel can, you take the valve outa the picture,....

Still got a problem on a remote tank, that leaves the fuel pump, or carb,....
Test the pump,....