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XP 800 won't run
- Thread starter Adzy110
- Start date
- Status
andrewterri
Active Member
Are you sure the clunk is coming from the engine and not the starter? Can you turn it over with your hand on the starter to feel if it coming from the starter
andrewterri
Active Member
Can you post the video on youtube then but the link up here? That might help people to hear it
This is very common on the 97’ XP because the cables are so long. I would bet it is either a bad battery or crap starter or a combination of the two. Cables would be next.
My friend had the exact same symptoms on a 97’ XP with a brand new engine and Walmart NeverStart battery. As soon as he borrowed my Yuasa it fired immediately.
My friend had the exact same symptoms on a 97’ XP with a brand new engine and Walmart NeverStart battery. As soon as he borrowed my Yuasa it fired immediately.
andrewterri
Active Member
That ski had the 720 right? Are you sure You got the engine aligned correctly?
96’ SPX has the 720 not a 787.
I still think it’s the starter.
If you can turn the engine over by hand and with the plugs out it isn’t something mechanical.
If it will crank with the plugs in but the plug wires not connected then it is a timing or sparking at the wrong time issue.
If it won’t crank with the spark plugs in but not connected it is either the starter, battery cables, solenoid or battery.
Connect the jumper cables directly from the car battery with the negative to the ground/earth and the positive to the positive post on the starter. DO NOT have the car running! If it doesn’t crank it’s the starter. If it does it’s the battery, cables or solenoid.
The RFI crank has a different taper on the front so the carb flywheel won’t work.
The DI is a 951 so no the cranks aren’t even close.
I still think it’s the starter.
If you can turn the engine over by hand and with the plugs out it isn’t something mechanical.
If it will crank with the plugs in but the plug wires not connected then it is a timing or sparking at the wrong time issue.
If it won’t crank with the spark plugs in but not connected it is either the starter, battery cables, solenoid or battery.
Connect the jumper cables directly from the car battery with the negative to the ground/earth and the positive to the positive post on the starter. DO NOT have the car running! If it doesn’t crank it’s the starter. If it does it’s the battery, cables or solenoid.
The RFI crank has a different taper on the front so the carb flywheel won’t work.
The DI is a 951 so no the cranks aren’t even close.
IDoSeaDoo
Well-Known Member
What size pistons are you using? If it's more than .25, then you need to clearance the Rave Valves. If you're running .50 pistons and didn't shave the raves, chances are the two probably made some intimate contact.
What was the nature of the "bang"? Was it an explosion, like a backfire? If so, backfires are caused by a lean condition. You might not be getting enough fuel. If it was of the metallic/contact variety, then you might have a physical problem, like parts making contact, or a hydrolock condition. I trust you're trying to fire it up before turning on the water, so I doubt it's the latter.
SBT starters aren't as bad as people say. I had one reliably work for years. Is it spinning over pretty fast when you crank it with plugs in? Does it sound like it's at least trying to start? If you squirt some fuel into the carbs, does it fire up?
As for squish gap, that's a pretty important characteristic. I'd get some solder and measure that before running that motor. It's a quick death if that gap is too tight. You can pull the head and check the pistons for contact signs, and that the arrows are pointing the right way (toward the exhaust ports).
What was the nature of the "bang"? Was it an explosion, like a backfire? If so, backfires are caused by a lean condition. You might not be getting enough fuel. If it was of the metallic/contact variety, then you might have a physical problem, like parts making contact, or a hydrolock condition. I trust you're trying to fire it up before turning on the water, so I doubt it's the latter.
SBT starters aren't as bad as people say. I had one reliably work for years. Is it spinning over pretty fast when you crank it with plugs in? Does it sound like it's at least trying to start? If you squirt some fuel into the carbs, does it fire up?
As for squish gap, that's a pretty important characteristic. I'd get some solder and measure that before running that motor. It's a quick death if that gap is too tight. You can pull the head and check the pistons for contact signs, and that the arrows are pointing the right way (toward the exhaust ports).
Have been thinking about getting an oem starter and might soon.
Pistons are STD size and are the ones that were in it when it was running.
I have the jet pump out so I'm not putting any water through the engine.
The bang happens weather or not the spark plug caps are on so it's not spark related.
I had a new rotary valve sitting around that was never used so it has a bit of surface rust on it. I decided to put it in just to see what happens. With that one it seems it will crank longer before the bang happens and if I squirt fuel down the carbs it will fire but not start. I'm starting to think the rotary valve area is worn down causing the valve to not seal correctly.
Have had the head off and no contact points are visual. The pistons don't go past the top of the cylinder so they won't be hitting anything
Pistons are STD size and are the ones that were in it when it was running.
I have the jet pump out so I'm not putting any water through the engine.
The bang happens weather or not the spark plug caps are on so it's not spark related.
I had a new rotary valve sitting around that was never used so it has a bit of surface rust on it. I decided to put it in just to see what happens. With that one it seems it will crank longer before the bang happens and if I squirt fuel down the carbs it will fire but not start. I'm starting to think the rotary valve area is worn down causing the valve to not seal correctly.
Have had the head off and no contact points are visual. The pistons don't go past the top of the cylinder so they won't be hitting anything
IDoSeaDoo
Well-Known Member
If the rotary surface is worn, it will make it hard to start, as one port will suck excess air from the other port. This becomes especially prevalent once the ski is hot. You can check this with a bit of solder on the RV valve, and both it back on to squish it. Measure with micrometer.
I'm still curious about that bang though, can't imagine what it could be. Does it happen at a pretty predictable time since you start cranking, or it is random?
I'm still curious about that bang though, can't imagine what it could be. Does it happen at a pretty predictable time since you start cranking, or it is random?
Okay well I think you guys will be surprised to know that I sanded the surface of the rotory valve cover put it back on and it has stoped banging completely. But it still won't start. I have checked the squish and it was about .40 mm. I have just sanded the edges down and it is just above .3 mm. I'm just about to put it in and try it
IDoSeaDoo
Well-Known Member
When you sand the face of the RV, you're creating more space for the RV disk to flap around. What you really have to sand down is the mating surface of the RV to the block, but that is something I've not heard of anyone else besides me doing. It's extremely tedious. The way I did it was dab valve grinding compound all round the mating surface and rotate the RV cover back/forth, grinding away the aluminum. I did this on an old 587 and succeeded at reducing the RV clearance. I think it's supposed to be .30mm. Refer to the manual for the correct spec.
IDoSeaDoo
Well-Known Member
Also, try measuring the RV squish with the O-ring installed. There are two different O-rings, one for the 787, and one for the earlier engines. They both fit, but one is thin, one is thick. I was using the thick one and couldn't get my ski to start until I realized my problem. Could be someone installed the wrong o-ring there.
What i did was sand the scratches out of the cover as they were pretty bad, put it back on and my problem was gone, but now it wouldn't start. I measured the squish clearance and it was .40mm. I then sanded the mating surfaces to get the squish down to .30mm (factory spec). Now its backfiring
IDoSeaDoo
Well-Known Member
You sanded that mating surface down pretty fast... how did you do that?
Backfiring could be an indicator of a lean condition. You could be sucking air somewhere. I had a rotary valve crack at the bottom right bolt hole because I didn't have the carbs supported (Aftermarket F/A). It was a tiny hairline crack that I barely noticed, but it was enough to suck some air).
Backfiring could be an indicator of a lean condition. You could be sucking air somewhere. I had a rotary valve crack at the bottom right bolt hole because I didn't have the carbs supported (Aftermarket F/A). It was a tiny hairline crack that I barely noticed, but it was enough to suck some air).
Okay. After messing around with the squish clearance on the RV it stoped banging and I was able to turn the engine over enough to try and start it. It kept backfiring. Turns out the the mag cup wasn't timed correctly. Set that all up and she runs like a dream (for now). Just wanted to say a big thank you to everyone who commented trying to help me. It's much appreciated!!
andrewterri
Active Member
We are glad you got it running plus you gained a little bit of knowledge that you can use to help someone in the future. Happy riding 
Good to hear.- Status
