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Discussion Starter · #1 ·
I was out yesterday on a real mild day ( 50F) , sled has 330 MJ, needle at #3, low octane head,91 Gas ,32:1 premix. Had my young son riding on the sled with me for trail ride so the throttle is running at 1/4 positon for most of the ride. Rode for about 40 minutes untill the engine lost power ( no high temp light) and stated running on one cylinder. I figured since I am jetted so rich for the temp that I just fouled a plug. Pulled the PTO plug and it is white, the mag side is a nice tan. Instaled new plug and the engine still ran the same. Towed sled home. Have not done a compression check yet. When I see white, I am thinking something terminal has happened.

I don't want to pull the engine apart if I don't have to. Lot's of spark on both sides. Could I have a carb problem.?

There are times when I am out riding with my sons and that means I am not running the sled hard. Could engine have stated running lean in the 0-1/4 throotle position at position 3 on the needle? Do I need to drop the needles if that is the case?
 

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I hate to be the one to tell you, but white means lean and there's a good chance the piston has a hole in it. Put your finger over the plug hole and pull it over slow to do a quick compression check
 

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Discussion Starter · #3 ·
I hate to be the one to tell you, but white means lean and there's a good chance the piston has a hole in it. Put your finger over the plug hole and pull it over slow to do a quick compression check[/b]

Did the compression check and the piston is holed. No pressure buildup when I plug the hole with my thumb.

How do I prevent this in the future? Drop the needles.
 

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Did the compression check and the piston is holed. No pressure buildup when I plug the hole with my thumb.

How do I prevent this in the future? Drop the needles.[/b]
Dropping the needles will lean out the mid range even more.
 

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Discussion Starter · #5 ·
Dropping the needles will lean out the mid range even more.[/b]
Thats right, I want to move the clip down one notch to #4. But is that goiing to solve the problem of running too lean at less than 1/2 throttle. As you can tell I am really pissed here. This was a brand new sled.

What are the chances the cylinder is damaged?

Why would the PTO side run burn down and not the mag side? Same carb setup
 

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Race motors, detuned or not, aren't designed to ride around at 1/4 throttle as you have unfortunately found out. They tend to run lean in the midrange and need the throttle to be constantly varied, just like on the Sno-X track.

Your cylinder might be damaged and that depends on how hot everything got. It's about 50/50 if it's damaged or not. I cannot tell you why it was the PTO that went down. Maybe someone else can chime in on that.

SK.
 

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trail needle would be the best bet. from a 01 440.


the race needle was still lean on the 4th clip. at -5 Celsius or so



just experience ive have had
 

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I would look for more reasons than needle settings. Nice & brown on one side and holed on the other is sending up flags to me.

My understanding is that a hole on top of the piston is the sign of a sudden & violent burn down, while simply running a little too lean usually detonates and erodes the top of the piston on the exhaust side.

Either way, one good side, and one bad side would make me start looking at more than needle settings and jetting. Did you loose a crankshaft seal? Suck in a base gasket? Or maybe plug the pto side main jet?

I do buy the partial throttle idea, but just wonder wht one side would be fine, and one not.

Good luck, Get the wrenches out.
 

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Discussion Starter · #9 ·
I would look for more reasons than needle settings. Nice & brown on one side and holed on the other is sending up flags to me.

My understanding is that a hole on top of the piston is the sign of a sudden & violent burn down, while simply running a little too lean usually detonates and erodes the top of the piston on the exhaust side.

Either way, one good side, and one bad side would make me start looking at more than needle settings and jetting. Did you loose a crankshaft seal? Suck in a base gasket? Or maybe plug the pto side main jet?

I do buy the partial throttle idea, but just wonder wht one side would be fine, and one not.

Good luck, Get the wrenches out.[/b]

What cylinder pressure should I be reading wiht low octane head?
 

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I would look for more reasons than needle settings. Nice & brown on one side and holed on the other is sending up flags to me.

My understanding is that a hole on top of the piston is the sign of a sudden & violent burn down, while simply running a little too lean usually detonates and erodes the top of the piston on the exhaust side.

Either way, one good side, and one bad side would make me start looking at more than needle settings and jetting. Did you loose a crankshaft seal? Suck in a base gasket? Or maybe plug the pto side main jet?

I do buy the partial throttle idea, but just wonder wht one side would be fine, and one not.

Good luck, Get the wrenches out.[/b]
Water in gas from condensation maybe? It has happened to me before, just seems strange on side runs good at the same settings an one side burns down just my 2 cents
 

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do you have the timing selector on it? if so make sure its on E. if your lucky the jug could be fine. most likely its screwed but there is that chance.
 

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Maybe check the airscrews, if one is set with alot more air that could do it I think. also i would give the carbs a good cleaning and check the carb boots for cracks, that could burn down one side. good luck!
 

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Discussion Starter · #14 ·
Ok I have the engne apart and on the intake side of the piston between the transfer port and booster port the piston has a hole the size of a dime burned through it. The top of the piston on the intake side alsois melted enough that ou can see the rings. The exhaust side of the piston is good. The cylinder may be ok, it has some aluminum stuck to the wall that may come off with acid.

I don't think these engines have a booster port in the piston on the back side to keep the piston cool do they?
 

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The clip on the needle needs to be dropped therefore this will raise the needle allowing more gas in this area of the throttle. It is too lean with the clip in the third position.
 

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How does the other oiston look? I personaly have burnt several pistons from jetting to lean, to much timming temp drop etc. But i have never lost two at the same time. One has to go first. If it was a lean condition for both you should be able to see some signs on the other piston. Keep in mind that your piston is kind of like solder. It holds it shape all the way up to its melting point and then ssppluuee. It is gone. No real warrning untill to late.
 

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Discussion Starter · #17 ·
How does the other oiston look? I personaly have burnt several pistons from jetting to lean, to much timming temp drop etc. But i have never lost two at the same time. One has to go first. If it was a lean condition for both you should be able to see some signs on the other piston. Keep in mind that your piston is kind of like solder. It holds it shape all the way up to its melting point and then ssppluuee. It is gone. No real warrning untill to late.[/b]
The mag side piston top is brown. If anything it looks like at 32:1 ratio the engine is running too rich. If I knew how to add photo on here I would take a pic of the piston that is cooked so ou could see it. Anyone know how to add a picture?
 

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Just click on reply then click on browse and find the photo you want to add then click up load and it will be on here!!!
 

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this was a result of running 110 head 50/50 gas timming set on a and it was 0* outside. If i remember it was 230 mains. With this combination a should have just put a grande in it and been done. My son was riding it just some ditch banging it should have been ok. But we came to a large field i told him just brap brap brap acrossed it. Bad plan.
first is pto head
second pto
third mag head
forth mag piston
 

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If you click on the mag picture you can see it was starting to get aluminum flecks. It would have melted but the other one went first.
 
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