mystery diagnosis- advice appreciated

[yankeeboy]

Had my ski out for the first time 2 weeks ago, and it ran amazing. Took it out yesterday and it ran like crap. It felt loaded up, with random throttle response and sounded like overall crap -with a lot of vibrating. Wasnt snappy at all like it should be and was prior to the ride. Checked the plugs and the rear cylinder was super lean ( two weeks ago both were perfect ), but tuning the carb had no effect, if not worsened the ride. Im stumped? The boat is a 785 riva flat top, dual 48 full specs - tuned per ed's advice, total loss, b pipe. Nothing was changed between rides, same gas ( fresh ), same battery etc. Help?

 

[WFO Speedracer]

Change the spark plugs and recheck it.

 

[SJBrit]

Super lean rear cylinder that got worse no matter what you did? I'm thinking rear crankshaft seal.

 

[yankeeboy]

I did change plugs with new ones, and i wasnt able to get a reading on the new ones ( maybe wasnt out long enough )??? I was thinking a seal too, but dont really want to rip the motor apart to be wrong lol.

 

[WFO Speedracer]

Super lean rear cylinder that got worse no matter what you did? I'm thinking rear crankshaft seal.

That is possible but I would rather take reading off of a new set of plugs to be sure, you could always fire it up and spray carb cleaner at the rear seal and see what happens, if it is leaking the engine will change pitch at the least when you douse it with the carb cleaner.

 

[yankeeboy]

could it be a possible fuel problem? Im not really sure what i should be looking for.

 

[Waternut]

Any chance that the temperatures got into freezing since you last rode?

I definitely sounds like an air leak. Maybe you got some water in your gas that is causing an issue now...unlikely but possible. Maybe the head pipe is loose causing an exhaust leak. It'll really feel like you've got no mojo if the head pipe is loose. You could've also blown an o-ring and you're sucking water into the cylinder now though I don't think that would really cause the symptoms you're describing. Either way, I'd pull the head just to see what things look like. If one of the pistons looks steam cleaned or much blacker than the other or you've got a mangled o-ring then you've got your answer in a matter of minutes. Plus if you were to replace the crank seals, you'd have to remove the head anyway.

 

[yankeeboy]

No, the water was actually a bit warmer, but the air was colder.

 

[Bobert540]

Nate after reading waternut's post I would def. pull the head off and check out the pistons. Esp. since they were steaming a bit when we checked the plugs.

 

[masterblaster]

run it longer with the new plugs till you get a reading,check comp for head gasket leak,fire ski at night and look for grounding coil,these are things that can change overnight

 

[munki63]

check your comp, when ever things go "funny" i 2nd you have a leak, what happens when you go WOT on the water?

 

[Waternut]

No, the water was actually a bit warmer, but the air was colder.

Well I didn't mean the water, I meant the air. Just trying to determine if maybe the water in the cylinder froze since your last ride causing a crack. Another unlikely case but thought I'd ask.

 

[yankeeboy]

comp was even at about 170-175ish. which is lower than it is suppose to be (200 i thought). Wide open throttle runs were rough. It would stumble on the bottom and clear up gradually until "full speed". I say "full speed" because it wasnt as fast as it normally is. frozen water is unlikely, it didnt freeze all winter.

 

[ger87410]

A long shot, but:

Have you looked at your ebox? Could there be water in it?

That was the solution to my problem with similar symptoms on a stock 650 motor.

 

[yankeeboy]

i'm running a total loss. I was hoping to eliminate most of the e-box woes i was having for the past 3 years, along with gaining some brap . But now my problem is i dont know how to trouble shoot the msd parts, or if they cause these problems.

 

[OCD Solutions]

2 things, Have you pulled your carbs and checked your jets? It could just be debris fouling the jets and
have you verified both cylinders are firing? If you were running on one cylinder you could have very similar symptoms.

 

[bllewis394]

there is also that internal filter in the carb.

 

[Philip Clemmons]

MSDs are famous for that......................If they dont fire the plug will look clean, as the fuel cleans it off.

Check wires and grounds on the ignition.

 

[masterblaster]

the salt water spay test at night tells the truth about a crapping out tl coil or wire or ground.........firework show

 

[munki63]

I had the EXACT problem but my compression was 40psi between so I had a bad cylinder, i'm going to guess your probaly going to have the same problem, Either pull your coupler off your pipe and check how wet and or oil is in your chamber, if you have lots it's probally blow by, or pull your head off and check your cylinder walls and how much play you have with your cylinders