1997 Challenger 1800 engine issues

[ericauch]

1997 challenger 1800 just rebuilt left top end and right whole engine. Carbs were gummed from previous owner using sealant so I bought 4 OEM carbs. Runs good at idle while cold adjusted low speed screws and plugs look good although I feel like there is a misfire here and there on both engines. High speed runs horrid it misfires on the right engine and will hold a 4K rpm for about 1 minute then start dying off if I try to go over 5k roms it just does. Left engine will Go 7k rpm if I jam the throttle for about 10 seconds then die. It also has bad misfire and if I try to slowly increase throttle it does. I tried new plugs pulled them out and it’s carbon fouled bad so I turned out the HS adjusters 3 hole turns it seemed to make a slight difference at around 2 turns out but pulled the plugs and still carbon fouled and still runs bad.
Any ideas?

 

[Theguyinmi]

1997 challenger 1800 just rebuilt left top end and right whole engine. Carbs were gummed from previous owner using sealant so I bought 4 OEM carbs. Runs good at idle while cold adjusted low speed screws and plugs look good although I feel like there is a misfire here and there on both engines. High speed runs horrid it misfires on the right engine and will hold a 4K rpm for about 1 minute then start dying off if I try to go over 5k roms it just does. Left engine will Go 7k rpm if I jam the throttle for about 10 seconds then die. It also has bad misfire and if I try to slowly increase throttle it does. I tried new plugs pulled them out and it’s carbon fouled bad so I turned out the HS adjusters 3 hole turns it seemed to make a slight difference at around 2 turns out but pulled the plugs and still carbon fouled and still runs bad.
Any ideas?

Lots of directions to go here but possibly fuel related check your tank vent. Did you replace lines and filters? What are the adjustments set at on your carbs? LS should be 1.5 HS should be closed. Couple of ideas to start.

 

[DaveFournier]

I have the same jet boat. Since you have new carbs and, replaced 1 engine completely and the top end on the other I'm going to rule those out as potential problem areas. After all, both engines start and idle well which indicates you have good fuel. At the high RPM I believe the voltage regulators can breakdown and cause problems with RPM's. Typically you will have trouble getting above 55 - 5500 RPM's. You should consider swapping the regulators and see if the trouble follows from the RIGHT engine to the LEFT engine. If it does, I would get a new regulator. If the trouble does not follow to the LEFT engine then swap the regulators back to their original position.

I would next check the engine gounding. In another thread I posted how one on my engines would stall after a few seconds because the engine ground was loose. Make sure you have grounded both engines to the battery. The right engine (on my 97 Challenger) got it's ground daisy-chained from the left engine. I would consider running a separate ground from the battery to the right engine.

 

[ericauch]

Lots of directions to go here but possibly fuel related check your tank vent. Did you replace lines and filters? What are the adjustments set at on your carbs? LS should be 1.5 HS should be closed. Couple of ideas to start.

replaced all fuel lines and oil lines along with filters. LS is 1.75 turns out. After low speed adjustments and when in low speed has great combustion. Also to note all cylinders have around 150 psi pressure. I have not checked the tank vent. My fuel sending unit is original though that and the fuel shut off valves are about the only part of the fuel system not brand new.

 

[ericauch]

I have the same jet boat. Since you have new carbs and, replaced 1 engine completely and the top end on the other I'm going to rule those out as potential problem areas. After all, both engines start and idle well which indicates you have good fuel. At the high RPM I believe the voltage regulators can breakdown and cause problems with RPM's. Typically you will have trouble getting above 55 - 5500 RPM's. You should consider swapping the regulators and see if the trouble follows from the RIGHT engine to the LEFT engine. If it does, I would get a new regulator. If the trouble does not follow to the LEFT engine then swap the regulators back to their original position.

I would next check the engine gounding. In another thread I posted how one on my engines would stall after a few seconds because the engine ground was loose. Make sure you have grounded both engines to the battery. The right engine (on my 97 Challenger) got it's ground daisy-chained from the left engine. I would consider running a separate ground from the battery to the right engine.

interesting thought. I will try this hopefully find an issue in the spark.