1998 Challenger 1800 Starboard Engine Bogs After 4000rpm-SOLVED!! Collapsed exhaust hose!

[Jet Slicker]

**SOLVED 06/21/2024** Details in post #6!

Hey everyone! Really looking for some guidance with my 1998 Challenger 1800 with the twin 787’s. I am fairly well versed working on engines, but less knowledgeable on 2 strokes.

The boat has been sitting for 3 years and I purchased it. The starboard engine had oil in the cylinders (Presumed crank seals) so I got all the oil out, put a ¼ turn valve on, and got it running. I have about 30 minutes driving the boat and the port engine runs perfectly and I’m super happy with it. The starboard engine starts and idles fine, and has great throttle response. However, it would hardly go above 3500rpm in gear (Not rev limiter). Removed the intake screen and it ran better, but now it won’t go about 4000~4500rpm.. It runs great until it gets to that RPM and then it bogs. The more throttle I give, the worse it bogs. At WOT it will drop at least 300rpm and sounds the worst out of any throttle position. I pulled the plugs and they look a bit funky after just 20 minutes of run time. Neither of them smell like gas. The engine revs to 7k out of the water, but not in the water.

Things I’ve tried:
-Disassembled, cleaned, and reassembled both carbs. No notable problems and both pretty clean.
-Replaced line that goes from fuel pump to the crankcase (It didn’t seem cracked, but it was old
-Replaced fuel filters and oil filters for both engines
-Unplugged rectifier with no change
-Tried 2 sets of plugs
-When the engine is bogging, choke makes it worse
-Connections going to coil are tight and not corroded. Coil could be bad?
-Engine does not produce an abnormal amount of smoke, even when bogging.

I understand that I should probably do a compression test, but I won’t be able to grab my tester for another week almost. I’m not fully convinced the problem is bad compression, but who knows. The engine is original to the boat to my knowledge. Not super high hours, but the boat has been used. The port side engine was replaced 12 years ago.

Does anybody have any other leads? I was hoping to enjoy my week off without having to work on the boat all week but that’s not happening. I was hoping that somebody more knowledgeable and experience would have a lead. Any help is appreciated!

 

[Jet Slicker]

No thoughts from anybody? I did check spark and it seemed equal to the other engine, and equal between cylinders. I found a broken valve on the PTO side rave valve. I swapped the valve with a good one from the other engine with no change. Looks like I really need to do a compression test.. Any other thoughts?

 

[mikidymac]

Where did the broken piece end up?

Did you do all the pop-off and leak down tests on the carbs?
Typically just inspecting and checking is not the same as a full rebuild with Genuine Mikuni parts.
The Seadoo Carb Rebuild Thread

 

[bsbracing]

check your compression, but I have seen a clogged or melted exhaust exit do that.

 

[Jet Slicker]

I did a compression test and found 140psi on the mag cylinder and 135psi on the PTO cylinder.. So, everything looks pretty decent there. I should do the pop-off test and probably rebuild the carbs. The carbs really did look good though. Any other thoughts of what could be going on?

 

[Jet Slicker]

PROBLEM SOLVED!! COLLAPSED EXHAUST HOSE.

Stored the boat over the winter and just revisited the problem in hopes to get it ready for 4th of July week like I tried to do last year.. Was looking over the boat more and realized the starboard side rubber exhaust hose that goes from the (muffler?) to the exhaust exit at the back of the boat was oblong, and not round. I squeezed the hose and it was very easy to collapse it. I removed the hose, and found it had collapsed/delaminated, and had around a 50% blockage of exhaust flow!! I've read that exhaust flow problems can cause significant power and RPM issues in 2 strokes. It kind of goes without saying I suppose.

A few other threads indicate that sometimes these hoses can get too hot, which causes them to collapse/delaminate. I cleaned and adjusted the water regulator valve to ensure the exhaust was getting enough water/cooling. I'll need to make sure the engine isn't running too lean as well.

Anyways, the part number for the starboard exhaust hose on the Challenger/Sportster 1800 is 204340028. That is for the 1998 model, and I don't know if it works for other years. The part is no longer being manufactured, and thankfully there was ONE used hose on eBay. If you need this part, good luck. There's a good chance you can recreate the hose with marine exhaust hose, but you will need some elbows or bends to make it work.

The boat is finally running great!

**PSA** If you have power issues and cannot get past a certain RPM, make sure the boat is not in neutral, check your rectifier, and check for collapsed or delaminated exhaust hoses!! If none of those work, check your RAVE valves, your water regulator valve on your exhaust, and your entire fuel system.