97 Challenger 1800 - Left Engine Bogging When Warm

[97ChallengerJake1800]

Just bought this 97 Challenger 1800 and put it on the water for the first time last night. Twin 787 Rotax's. Dropped it in the water and took it a few hundred yards up and down the river to make sure everything was going to run okay. Picked up the family from the dock and helped friends load their boat. Followed them about a half mile up river where we dropped anchors and tied off and swam and hung out for a while. After probably 45 minutes of cool-down my wife wanted to go out on the tube. Ran great and cruised up to WOT with no problems at all. Traded off the tube to friend's boat and took the Challenger down river for a ride. After a minute or two, the left engine started bogging down and wouldn't rev above ~5000rpms. Right engine ran WOT fine. Left Engine would cruise ~4500rpms but slowly dropped when I tried to give it more throttle. Stopped the boat and checked/changed plugs. Didn't make a difference. Friend pulled up and tied off on us and we BS'd for about a half hour about it. Decided to load it up on the trailer and head home. Fired it back up and it ran like it did at the start of the day. Both engines ran WOT for about 2-3 minutes and then the left one started bogging again.
Fuel lines have been replaced with black rubber, had new fresh oil, about half a tank of old gas and half a tank of new gas with a full bottle of Stabil Marine additive. Any ideas or help where to start??

 

[97ChallengerJake1800]

Tore into the RAVE valves since they were an easy place to start. The top diaphragm was melted where the cap screws on in the rearmost RAVE valve. I don't know if this would cause my problem but it needs fixed regardless.

 

[Lumps]

I wonder if you engine is overheating and is the cause of both the bogging down and melted rave valve? Does your buzzer work?

 

[97ChallengerJake1800]

I wonder if you engine is overheating and is the cause of both the bogging down and melted rave valve? Does your buzzer work?

The buzzer never went off, however I have no idea if it works. Is there a good way to test it?

 

[Lumps]

When you put the dess thingy on the post does it beep a couple of times? I don't have this boat anymore so I could be wrong how many beeps but it should chirp at least once. It is really common for these to fail

 

[97ChallengerJake1800]

When you put the dess thingy on the post does it beep a couple of times? I don't have this boat anymore so I could be wrong how many beeps but it should chirp at least once. It is really common for these to fail

Negative. It doesn't beep at all.

 

[Lumps]

The buzzer is under the helm by you knees. There is a collar that unscrews. It may be hard to turn at first. The connector for the wiring is just a water resistant plug that has a catch on one side. Take out the buzzer and test it with a battery. Even a 9v will work. I think the specs are 5 to 15v

I don't know your problem with your engine but the buzzer is east to fix. And is availed from Floyd bell or something like that

 

[97ChallengerJake1800]

The buzzer is under the helm by you knees. There is a collar that unscrews. It may be hard to turn at first. The connector for the wiring is just a water resistant plug that has a catch on one side. Take out the buzzer and test it with a battery. Even a 9v will work. I think the specs are 5 to 15v

I don't know your problem with your engine but the buzzer is east to fix. And is availed from Floyd bell or something like that

I jumped 12v to the buzzer and got nothing. I'll add a new one to the list along with a rave valve.

 

[dieselndoo]

Clean all the raves. Poor choice in oil causing them to stick. Yes, that's your problem. IF, it persist, inspect the ones on the muffler. Good job at diving into ur

 

[dieselndoo]

Also, no worry on buzzer, if she's pissing out the back, and head/exhaust are warm to touch, .. Your good

 

[97ChallengerJake1800]

It may be a while until I get the new valve and get it back on the water to try it out, but when I do I'll be sure to check back in.

 

[97ChallengerJake1800]

Threw the new rave valve in last night. Taking it out on the river tonight to test it out. I'll check back in later with an update.

 

[97ChallengerJake1800]

Still had the same problem as before after the new RAVE valve. Although I spent more time playing around with the throttle. The left engine's throttle lever is much looser and will fall to idle if you let go of it. If moving at low speed with a load, the left engine will only rev to about 5000rpms. Once the right engine is at full speed and the boat gets to a nice plane, the load lightens up on the left motor and if you play around with the throttle it'll eventually rev to about 6500rpms at full throttle and run great (the right engine will rev to about 6800-7000rpms). So I'm assuming this lies in the carb tuning, as once it's at full throttle it runs great.

 

[steve on the water]

I had this issue with my challenger 1800 in the past. I melted a few rave valve diaphrams before I realized the rave valve body was worn and I was getting blowby up the shaft. A new valve body fixed that. A carb rebuild fixed my mid RPM bogging issue. It never seems to end with these boats. Luckily the parts are cheap and the engines are easy to repair.