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  #1  
Old 09-24-2016, 03:45 AM
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Default KTM 360 will not rev up after top end rebuild

     

I have rebuilded the top end of an KTM 360 with the year 96. The cylinder was restored and a new one ringed piston has gone in, it used to have a two ring piston.


It will not rev up, even in neutral gear and it is also smoking pretty much. It idles also only around one minute and then it dies, I do not know, if the exhaust valve is 100% correctly adjusted, but I think, that it would still rev up to the top in neutral? The carb adjustment does not affect anything, tried to adjust the air screw, idle screw and also the needle, but these did not make any change to anything. Before the disassembly it had some idle problems but it revved up pretty good. What can cause that kind of problem, what should be the next steps what to check??
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Old 09-24-2016, 04:47 PM
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I need more info to try and help.
1. What year is the bike?
2. How long have you owned it?
3. How long did the bike set while the rebuild was being done?
4. Did you do this rebuild?
5. Have you done rebuilds before?
6. Are you using fresh fuel mix?
7. What is your fuel mix ratio?

Paw Paw
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Old 09-25-2016, 12:06 AM
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1. What year is the bike? - 1996
2. How long have you owned it? - it is my friends bike, he has purchased it this year spring.
3. How long did the bike set while the rebuild was being done? - It sat from the spring until now in a garage.
4. Did you do this rebuild? - The owner has done it
5. Have you done rebuilds before? - The owner has not done a dirt bike 2 stroke rebuild, but he is working everyday as a car mechanic and also I have supported him as much as I know, I have done one rebuild for my 94 year CR250.
6. Are you using fresh fuel mix? - The fuel has sat there from the spring I think
7. What is your fuel mix ratio? - Need to clarify with the owner.
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Old 09-25-2016, 07:36 AM
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Ok with that info I would suggest there are several issues at hand.
1. The fuel mix is very old and needs to be replaced with a fresh batch.
2. The fuel vent lines need to be cleaned as pest love to make homes in them.
3. You will need to do a compression test.
4. The carb must be removed and cleaned. I suspect you have some trash or dried fuel in the carb passages and jets. The carb needs to be cleaned by doing a good soaking and not just sprayed with carb cleaner and blowing air.
5. The fuel tank needs to be removed and cleaned and the fuel pet cock filter removed and cleaned.
6. The air filter needs to be removed, cleaned and re-oiled.

A bike can't set with old fuel in it without there being issues developing and they have to be addressed prior to it running correctly.

Paw Paw
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Old 09-26-2016, 11:44 AM
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1. The fuel mix is very old and needs to be replaced with a fresh batch. - No change.

2. The fuel vent lines need to be cleaned as pest love to make homes in them. - All clean.

3. You will need to do a compression test. - For sure it is not any compression related issue.

4. The carb must be removed and cleaned. I suspect you have some trash or dried fuel in the carb passages and jets. The carb needs to be cleaned by doing a good soaking and not just sprayed with carb cleaner and blowing air. - Cleaned several times.

5. The fuel tank needs to be removed and cleaned and the fuel pet cock filter removed and cleaned. - No change.

6. The air filter needs to be removed, cleaned and re-oiled. - No change.

It runs now on idle when cold, when it runs warmer, then it does not idle anymore. It seems that it runs rich, with the choke applied it runs more worse. What else? Can it be the crank seals? Ignition coil?
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Old 09-26-2016, 01:05 PM
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Crank seal, float height setting, rich jetting or worn cylinder will do all of the things stated. I still think a compression test is needed as well as a leak test.
Just making the statement that the compression is good does not mean it is in fact good.
You can check the coil ohms readings on the primary and secondary sides, but that just does not sound like the problem.
Did you remove, soak and clean each part of the carb?

Paw Paw
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Old 09-27-2016, 08:05 AM
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Yes, the carb is soaked and cleaned properly.
float height setting - It ran good before the rebuild with the current float height setting, will try to adjust.
rich jetting - ran good before rebuilding it, is there any difference in jetting when it has a single or dual ring piston?
cylinder - the cylinder is re-plated and looked like a new one.

Last edited by raksike; 09-27-2016 at 08:14 AM.
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Old 09-27-2016, 09:55 AM
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OK, what I see is that there are things you have elected to ignore and not check. These are some of the very things that will cause the issues you have ask for help with.
Float levels do change.
Compression may not be good as you think.
Things looking good without checking sizing or fit will not get this fixed.
You have to be willing to check and test things to find the problem or be ready to spend a lot of money to have a pro look at it and fix the problem.
With you not wanting to do these things , I can't help you.

Paw Paw
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Old 09-27-2016, 11:33 AM
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I currently do not have any tool available, to measure the compression, but I am 100% sure, that the problem is not there.

Today I have noticed one thing, when I lean the bike to the left side, then it idles good, when I lean it to the right side then it will start to sputter and wont idle.
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Old 09-27-2016, 02:05 PM
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PawPaw is right about the checks and you should do them, but after noticing this then probably it is the right crank oil seal or the carb float level, or even worse... worn right crank bearing which makes oil go through the oil seal but that would add some engine ticking noise for sure.
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