Need help again (i just want to ride)

[HERTENSTEIN83]

95 xp 720 when i go to start it now i have to hold it wide open and then it wont even move it self under wot it just boggs. If i mess with it long enough it will take off and run perfect as long as i dont shut it off. Sense this problem i have cleaned entire fuel system 3 times and still no luck so i completely rebuilt carbs replaced plugs and checked rotary valve timing, checked compression 150 ea. once i get it off idle it will run great but like i say on start or restart it wont idle and when the throttle is fully wide open it will just idle no rev. The only other thing i have noticed is that it sounds loud out of the air box and i have never noticed that before

 

[I WOULD RATHER STAND]

I rebuilt a 580 last year with very similiar symptoms, everything was good fuel system wize, I discovered the crank bearings and seals were right out of it. You can still get a good compression test if the crank is bad.

 

[HERTENSTEIN83]

I installed a new crank kit & pistons, honed cylinders bypassed oil injection system and only have about 15-20 hrs on it. This problem occurred from one day to the next this season. Its been out 2-3 times so far this year and now having this problem

 

[Dr Honda]

IF... once you get it to clear out, it will run perfect. Full throttle, mid, and will idle... then it's easy... your carbs are leaking.

When you did your rebuild, did you check your pop-off pressure, and leak down? Those are 2 of the most critical things.


Right now, there are issues with the aftermarket diaphragms. The first problem is that the pin is too long, and it messes up your pop-off pressure. The other issue is that the diaphragms are to stiff, and when you tighten down the cover screws, it opens your needle and seat, allowing the fuel in the pump to drain into your engine, making it VERY hard to restart.

Go buy 2 new OEM Mikuni diaphragms, double check your pop-off pressure, and I bet your problem will go away.


Just an FYI... Mikuni diaphragms have a red tit. (easy to identify)

 

[HERTENSTEIN83]

This problem was occurring before the carb rebuild. I thought it was an fuel issue so thats why i rebuilt them after the third cleaning that day. I did use new oem mikuni diaphragms (red tit). Still after four cleanings of entire fuel system and carbs plus rebuild i have the same results. I just dont understand also the constant bogging sound coming the carb filter housing even at idle.

 

[Dr Honda]

Well... if you have good compression, and you know for a fact that the carbs are right... then your rotary valve isn't timed right. (or the clearance is too high)


But if that was the problem... it would not clear up, and run.

 

[Dr Honda]

I was just thinking about it... and nothing, other than fuel, will give you a "Bog" and then clear up.


If it was an ignition issue... you would feel a miss.

If it was a plugged up exhaust, it would choke at higher RPMs.

If it was a RV... it would just run poorly all the time. (along with high clearance)



YEP.... when you shut it off... fuel is dribbling down into the engine.


OR... oil can do the same thing. I know you say that you just rebuilt the crank, but one of the center seals could have been nicked... or the RV seals are bad.


Do this: Go out and run it until it's running clean. Shut it off for what ever time it needs to have the problem happen again. Pull one of the spark plugs, and put a clean white towel over the hole(s) and crank it.

If it's mostly clear, and smells like fuel... it's fuel. If it's gray, or what ever color your oil is... its crank and/or RV seals.



Just because you put in new seals, doesn't mean your case was seamed properly. You could have a leak between the 2 halves.

Let us know what you find. (I got to get back to work)

 

[HERTENSTEIN83]

I will try that. It will be a couple days before i can get out again. Just a few more clues or answers to your thoughts i did switch to premix when i rebuilt the engine and i have about a 1/4 tank in the oil inj reservoir and used a marker and made a line on the tank and the level has never changed. You say the case might not be seamed properly would i have noticed that last year and at the beginning of this year? This was an over night problem that just happened at once there was no warning signs it ran great and sense then i have put about 3 hrs on it just hoping it would clear up or something and it has not. thanks

 

[Dr Honda]

Well...... if the oil in the tank hasn't changed... then its probably not oil getting past the seals.

BUT... it can still be fuel.

 

[HERTENSTEIN83]

Just anthor question could an exhaust leak cause any of my problems i have noticed a little extra water in my hull than usual. Maybe after an hour or two of riding there is about there is about 3-4 quarts of water in the hull and it is pretty warm water?

 

[voodoo]

Me thinks you have an air leak in the fuel system, anytime air comes in fuel does not and you will spoil that repair work with a leanout overheating, the motor lubrication comes from the OEM injection system that has spray nozzles running from a pump driven by a shaft inside the rotary vavle cover - great picture by phough, but sometimes what happens in a boat transfer is so much exictement the type of oil is overlooked entirely and mixing 2stroke oil is a big gamble - many times it forms a gel that the pump can no longer spray inside the motor either blocked nozzles or the small oil lines get plugged with the gel product - it is like when you smear jelly on the outside of the jar, flush it all with kerosene to restore the pumping action and then choose and stay with oil from a reputable supplier, when you run your first bottle empty cut off the front and leave it in the glove box so you can always get the same type.type.

 

[HERTENSTEIN83]

I have cleaned the entire fuel system from top to bottom at least four diffrent times and the same results. I have always stuck with the same brand of oil from day one (premix) sense the motor rebuild. I have switched to all automotive fuel lines and clamps and on each cleaning making sure everything is tight.

 

[HERTENSTEIN83]

Never did get a response from any body about if an exhaust leak would cause any of the problems that i am having thanks ?

 

[HERTENSTEIN83]

Did some more testing and did what someone suggested about waiting till it did it and use a white towel to see if fuel or oil came out of the cylinders while cranking with out the plugs in it and it was a fine mist not enough to even wet the rag at all. I put inline spark testers in while idling and noticed it look like the rear cylinder had a weak spark and the front cylinder looked like it was weak too but at times it looked like it had no spark any suggestions? Is there a way to test the coil

 

[Dr Honda]

Yes, if your exhaust is leaking... you can have water coming in. Also... if you have an exhaust leak... it could make your engine run poorly.


As fare as your coil... the have a weak spark, but they are hard to test since the 720's coil has the CDI built into it.

 

[Rotor13B]

Maybe try running without the seat on? You could also check for leaks while it's off also. Just a thought.

 

[HERTENSTEIN83]

Well i hooked it up to the hose yesterday and left the air filter housing off. While running i sprayed the base of the carbs down with carb cleaner and the idle picked up real high so i replace the carb base plate gasket and the rotory valve o-ring and i still have the same results. My question is can where the pump bolts to the rotory valve cover can it draw a vacuum from there? It is converted over to premix but the pump is still there with no drive gear to the pump. I do have all the old oil inlets capped off with vacuum caps.

 

[HERTENSTEIN83]

Confirmed fix. While i stated that the ski had a new crank kit and seals that didn"t mean any thing. I finally found out what the problem was. On the pto side the rear crank seal spring had came off from around the seal and it was sucking air replaced rear crank seal and all is good. Runs like a new machine. thanks for every ones help