Iv got a 96 gti I just bought. Engine was rebuilt 3-4 years ago and has run fine up until recently. The guy I bought it from has replaced one piston three times for melting the center of the piston. I bought it cheap and want to fix it but want to figure out why it keeps melting only that one piston. I ordered carb kits to rebuild them. I really hate to pull the cases apart to reseal them and check the crank seals but I don't want to burn a piston again. Any other suggestions of things to check.
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96 720 leaning out on one cylinder only?
- Thread starter Tims1957
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Sportster-2001-951C-Stock
Well-Known Member
If one of these carbs is too lean or there is an air leak somewhere, the cylinder will run hot and thus prone to detonation or even more destructive, pre-ignition.
You can pressure check the crankcase to find air leaks, and you can replace the outer crankshaft seals in case they are worn and leaking:
Items #7 and #11 on this drawing:
http://partsfinder.onlinemicrofiche...wc&a=302&b=5&c=0&d=-CRANKSHAFT,-PISTONS-(717)
Edit: Also make certain the spark plug is the correct heat range. If the plug electrodes are overheating they can cause pre-ignition.
Here are some ideas on what types of failures can occur, and what to look for as the root cause:
http://www.off-road.com/dirtbike/tech/dirt-bike-tech-twostroke-seizure-52428.html
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I joined this forum last year and I'm remembering why I never returned after I originally joined. I ask a pretty straightforward question and I get one answer. And he tells me the same things i stated could be the problem in my post. Then a link to piston diagnosing that has nothing to do with my lean condition. And no one else has any ideas or is willing to help out? Guess I need to find a different sea doo forum
Sportster pretty much gave you the correct info and you had asked for, you were already on the RIGHT track. When you opened up your carbs you would see stuff in the filters and possibly else where clogging or restricting the fuel flow, thus LEANING OUT that cylinder. He also mentioned pressure testing the engine, again another step in the trouble shooting process.
Are the fuel lines gray? If so they break down and clog the filters in the carbs and need to be replaced with black ethanol safe fuel line available at your local parts store. Did you clean the fuel separator? Which piston keep burning down? Have you checked the small oil lines coming from the oil pump? If one broke or is leaking you're not getting oil or the correct amount, they should also be replaced. Did you check the oil injection cable is functioning?
But if it were me, I would rebuild the carbs and fuel system, and check the oil injection system, typically an air leak won't melt a hole in the crown of the piston.
Jetskigoodies
Well-Known Member
X2 on that :agree:
I don't know what kind of answer he is looking for. As there is not a magical answer. Also if he looks at pictures of piston damage and the root cause of the issue, and then compares his he can use that to his advantage. Someone has already done the work for him. If he still has grey fuel lines and original oil lines then he has not done any research. The first thing I did when joining this forum is read, read, and then read some more. This forum has mountains of information, you just need to do the leg work.
It is sad when people come in ask a question and a valued member takes time out of his day and responds with a reasonable answer just to get disrespectful reply.
And good luck in another forum getting SEADOO knowledge.
That kind of responce will not make anyone else want to try to help you out.
I bet it is the pto piston.
I don't know what kind of answer he is looking for. As there is not a magical answer. Also if he looks at pictures of piston damage and the root cause of the issue, and then compares his he can use that to his advantage. Someone has already done the work for him. If he still has grey fuel lines and original oil lines then he has not done any research. The first thing I did when joining this forum is read, read, and then read some more. This forum has mountains of information, you just need to do the leg work.
It is sad when people come in ask a question and a valued member takes time out of his day and responds with a reasonable answer just to get disrespectful reply.
And good luck in another forum getting SEADOO knowledge.
That kind of responce will not make anyone else want to try to help you out.
I bet it is the pto piston.
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Jetskigoodies
Well-Known Member
Sportster I also gave you a helpfull post since I felt the no you received was not deserved.
RodInEscondido
Well-Known Member
Wow guys, I think you are being poor sports about this. I think someone needs to jump on a plane, fly to NY, diagnose and fix his problem ... for free. And as long as you are there, maybe toss in a few free reading lessons.
It has been a long time since I have seen this type of attitude towards people trying to help. I will stop here.
Rod
It has been a long time since I have seen this type of attitude towards people trying to help. I will stop here.
Rod
LOL, So did you! :lols:
Sportster-2001-951C-Stock
Well-Known Member
Or perhaps another planet.
Sportster-2001-951C-Stock
Well-Known Member
Good call, I bet you're right.
First off let me apologize if I came off rude. It's just that I am frustrated with why this engine has melted three pistons and I turned to this forum for advice and after a week I had one answer it most of it was ideas I mentioned I already checked.
I'm not going to respond to all the posts making fun of me as I guess I had it coming,lol.
However if anyone is at all willing to still lend an opinion here's some follow up info.
Gray lines have been replaced by previous owner,however carbs were not rebuilt after he changed lines...they were cleaned he said. Not sure exactly what cleaned means,but rebuild kits came today so I will be pulling them apart shortly. Fuel separator o ring has been checked and looks good. Little oil lines while not replaced are in good shape. I will replace them when I reassemble though. Brass oil fittings are tight. It is the pto side piston that is melting. I have pulled the motor apart and separated the cases. The rotary valve cover has maybe a .050 deep 1/8 wide groove in it from the intake port of the bad cylinder about halfway around the dia of the cover.could that allow too much air in? I'm thinking not cuz at that point it would be air and fuel together. Am I ok with the groove? The rotary valve itself has some minor pitting in it. Again I don't see how this could cause my problem but maybe? In the posts where I was getting made fun of :facepalm: I noticed a few guys said they bet it's the pto piston and it is.......is there an issue with the pto side of those engines?
I'm not going to respond to all the posts making fun of me as I guess I had it coming,lol.
However if anyone is at all willing to still lend an opinion here's some follow up info.
Gray lines have been replaced by previous owner,however carbs were not rebuilt after he changed lines...they were cleaned he said. Not sure exactly what cleaned means,but rebuild kits came today so I will be pulling them apart shortly. Fuel separator o ring has been checked and looks good. Little oil lines while not replaced are in good shape. I will replace them when I reassemble though. Brass oil fittings are tight. It is the pto side piston that is melting. I have pulled the motor apart and separated the cases. The rotary valve cover has maybe a .050 deep 1/8 wide groove in it from the intake port of the bad cylinder about halfway around the dia of the cover.could that allow too much air in? I'm thinking not cuz at that point it would be air and fuel together. Am I ok with the groove? The rotary valve itself has some minor pitting in it. Again I don't see how this could cause my problem but maybe? In the posts where I was getting made fun of :facepalm: I noticed a few guys said they bet it's the pto piston and it is.......is there an issue with the pto side of those engines?
And again I wasnt trying to be disrespectful but the link that was posted for me to look at originally was about piston seizure. There is a lot of helpful info on why pistons seize and how to read the piston that has seized but mine didn't seize ...it melted a hole in the center and would still run...sorta.
Yes.
The pto flywheel rust's near the seal and cuts the seal. That leads to the pto cylinder running lean and then detonation occurs which leads to the hole you see there.
So what does the seal look like ?
AdamXP800
Well-Known Member
That is probably the most dbag comment I've seen from a newby on here.
I'm actually shocked you got a response after that or get another answer on any post
Sportster-2001-951C-Stock
Well-Known Member
I forgive him, he's a NY'er and they're rude.
I thought he was asking about the things he listed, it sounded like he has limited experience and wanted confirmation.
Will I try to help him further? No, he doesn't need my help.
I thought he was asking about the things he listed, it sounded like he has limited experience and wanted confirmation.
Will I try to help him further? No, he doesn't need my help.
Jetskigoodies
Well-Known Member
The pto piston usually goes because it leans out due to the internal filter gumming up with the green goo from the fuel lines. The rear filter tends to be full, at least in my experience. I have not seen too many bad rear seals, yes maybe a few but the majority of the time it is a clogged filter. If you are going to be rebuilding the carbs you will probably see it is clogged. Also if you pressure test the cases you will see if you have a leak anywhere. The manual shows the steps for testing. Yours was probably fuel related. Also check the low and high speed screws, people tend to play with them.
Jetskigoodies
Well-Known Member
1996
GTI
717
270500278
270500279
BN-38I (SB)
Jets should be MAIN-130 PILOT-67.5
Needle 1.2
Pop off 36 - 60
Screws should be set to LOW- 1-1/4 turns HIGH- 0
Also when rebuilding your carbs use your stock springs, do not match up the new springs by size, just because they are the same length does not mean it is the correct spring.
GTI
717
270500278
270500279
BN-38I (SB)
Jets should be MAIN-130 PILOT-67.5
Needle 1.2
Pop off 36 - 60
Screws should be set to LOW- 1-1/4 turns HIGH- 0
Also when rebuilding your carbs use your stock springs, do not match up the new springs by size, just because they are the same length does not mean it is the correct spring.
Sportster-2001-951C-Stock
Well-Known Member
Yeah, I guess you didn't even read the article or your reading comprehension is poor. F-
Jetskigoodies
Well-Known Member
In the link sportster sent you this info was there. It was not just seizures
Hole in piston: This is not technically a seizure, because you can hole a piston without it ever really seizing to the cylinder walls. It is caused by detonation, as a result of the timing being too far advanced, a spark plug that’s too hot, or far too much carbon on the head and piston. This can be accompanied by a ridge eaten out of the combustion chamber, and parts of the head gasket eaten away. Bore it and replace the piston; then check the timing and the heat range of the plug. Clean carbon off the piston and head more often.
Hole in piston: This is not technically a seizure, because you can hole a piston without it ever really seizing to the cylinder walls. It is caused by detonation, as a result of the timing being too far advanced, a spark plug that’s too hot, or far too much carbon on the head and piston. This can be accompanied by a ridge eaten out of the combustion chamber, and parts of the head gasket eaten away. Bore it and replace the piston; then check the timing and the heat range of the plug. Clean carbon off the piston and head more often.
RodInEscondido
Well-Known Member
proper oil
new gas
new gas
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