1997 Challenger 787 Slow-To-Plane NOT Cav....Where to start?

[Sandman251]

So I'm having this ongoing problem with my 97' Challenger single. NOT cavitation. Boat bites fine. No over revving. As I start to advance the throttle everything comes up fine...to a point. Then It plows water at around 4K for 5 to 15 seconds before it jumps up and makes full throttle. This doesn't happen every time. I almost think the problem is more frequent with a heavier load and/or when warm. Making some quick erratic movements on the throttle seems to help. It never misses and runs smoothly. Once on plane, everything is great. It goes down to slow cruise and back to WOT without a problem. Throttle response is fine.

My current WOT is around 6500 with an average load. Engine has 40 hours since rebuild and 145 PSI on each side this spring. Running XPS and midgrade fuel. Tickling the choke during this condition causes the engine to puke out. Switching to RES line does nothing.

Been told to start with a RAVE service which I will do this week. Been told to change out the plugs, too. Other than that, I'd like to pinpoint my efforts a little. Ive never really heard of filters being a problem on these boats. Maybe carbs? What to you think.

 

[Dr Honda]

So... if you push it up to full throttle, does it...


A) Just hang out at 4500 rpm?

OR

b) Rev's up... but just doesn't build speed?

 

[Sandman251]

[ sorry if I wasn't clear. when I go to full throttle from idle, the boat spools smoothly to around 4.5K and remains there in sort of a plowing no-plane attitude for 5 to 15 seconds at which time the engine " kicks in" with normal full throttle power. RPMS build quickly to 6.5K and the boat planes right off and performs perfectly. After that, throttle response in the upper range is fine and so long as you stay on plane the boat performs as it should. You can run at lower power settings and go back to full throttle anytime you like.



QUOTE=Dr Honda;483848]So... if you push it up to full throttle, does it...

A) Just hang out at 4500 rpm?

OR

b) Rev's up... but just doesn't build speed?[/QUOTE]

 

[IDoSeaDoo]

sounds like your raves aren't opening. Once they open, you get a noticeable boost in power as your exhaust port opens up. Have you checked your plugs to make sure you're running a good mixture in the carbs? They shouldn't be too black and def. not too light. You want them in the middle somewhere, like a chocolate brown.

 

[Murph_13]

I would definitely look at the water regulator valve on your water box/muffler (same housing/looks like your RAVE valves, but it's on the muffler)...the condition you describe is often caused by a water regulator problem...look for evidence of it leaking, but keep in mind the problem could be internal...it provides the cooling water to your tuned pipe...

 

[Tudorc]

I had this issue where my 97 Challenger would just stick at 4800 rpm and take forever to plane. I adjusted the low speed and high speed screws on the carbs to run a little richer and then adjusted the RAVE valves by turning the red screws downward significantly. Now it jumps past the 4800rpm and accelerates onto a plane nicely. I think my problem was the RAVEs were opening too early (?).

 

[CadeZ]

Did you ever find the solution to your problem? I am having a similar symptom with my Challenger as well.

 

[Tudorc]

I found a solution (maybe not the right one for you): RAVE valves need to be screwed ALL THE WAY DOWN on 1997 787 Challengers. Once the RAVES were cleaned and screwed all the way down (not flush with the cap but completely down), I adjusted the idle to 1800 RPM, adjusted the low speed screws slightly to get the right mixture sub-5000 RPMs, and then adjusted the high speed screws to get the right mixture over 5000 RPMs. It was a lot of trial and error to get the right screw settings but I ended up adjusting both sets less than a 1/4 turn from the factory settings.
Once the motor sounded better after the initial screw adjustments and the hesitations, bogs and surges were gone, I used the choke to determine if the engine was running too lean (if you pull the choke and it runs better or revs up, you're running too lean); and then pulling the plugs to determine if they were chocolate brown (no unburned fuel, not white, not jet black) - which indicates the mixture is right.
Don't profess to be an expert... lots of trial and error. But cleaning the RAVE valves, making sure the RAVE screws were all the way down and making sure TOP written on each valve was pointing to spark plugs made most of the difference... the carb screw adjustments topped it off and mine runs 100% now.

 

[CadeZ]

Thanks very much for info! I’m hoping this will help fix my problem very similar to yours. Fingers crossed. Will come back with an update most likely.
Thanks again!