Posts
94
Joined
11/24/2019
Location
Lake Stevens, WA, USA
Edited Date/Time
3/13/2023 6:24pm
Hi first time doing a top on for the first time and was wondering what kind of condition this piston and jug is in? I have no idea how many hours. a while back I asked about an odd sputter and took some pics with the pipe off and every one said time for a top end. also while it's apart is it worth having the head shaved at all? I ride this bike as pit bike with a few buddy's and also with my small kids so reliable is most important 
Also I should mention I never got the sputter to go away and it's sent me over the bars a few times so I'd like to get that figure out as well. I plan on doing a full carb rebuild and jetting it back to what the manual says for my elevation and average temps
Also not to keep adding stuff but should I drill the two small holes in intake side of the piston or just keep it the way it is? I'm looking at wisco pistons
I forgot but when I was running 32 to 1 it was half 110 leaded race fuel and have 92 non ethanol not sure if that changes anything
When it was spluttering was it running the 110 fuel but not on 92? If so then that would make sense as it will make your bike run a lot richer, running race fuel for on an engine that is not designed for it is a waste of money and you will loose performance although you won't necessarily damage anything just run pump fuel
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No it sputter worse on just 36 to 1 and pure 92 non ethanol. It got a little better on the half and half 110 and 92 at 32 to 1. I was running it cause thats what my father runs in his 85 and I was completely out of fuel I think I ran my 2 or 3 tank fulls threw it. Wasnt sure if maybe that's why it looks rich
Thats really strange, the only thing I can think of is that from where your jettings lean and you ran 110 fuel it essentially richened it up and which might be why it ran better? Im not convinced this is right. Seems like the way you have "diagnosed" the problem by doing the opposite of what it should have done lol
Well I got the bike all back together and ran it threw 2 heat cycles with slight blips of the gas and then putted it around a little bit feels a lot better I am waiting for the new jets to show up and swap them before I go and beat on it hard but seems mint so far. Thank you alot for the insite on stuff the new oil smells better too ha
Your top end was in pretty tough shape in my experience. The coking on the power valve linkage indicates you have a leak on the orings that control the power valve, the power valve case points should be extremely clean with just some oil in them, no coking/carbon. Only the valve itself should have any coking on it.
Pics above are from on an 85 with 40 hours on the top end and 80 on the crank total. I have run 50:1 Maxima K2 for most of that 40hr but changed to the Motorex at the tail end just to consolidate on one premix for every 2T bike I've got. The piston has some carbon but the piston dome i just wiped with a microfiber cloth and took that pic, that wasn't -after- cleaning it, it was as it came off the bike and just a 5 second wipe. The first cylinder pic is as it came off the bike with just a degrease - still had visible cross hatching but had some vertical glazing you could see in the right light, the last pic was after ball honing it for like 10 seconds tops.
There is no reason to run anything less than 40:1 which is what the manual specs, so you've got too much oil in there to start regardless of brand you're using. If your kid isn't on the pipe all the time it also helps to drop the main, clip, and pilot all down a size so it runs a bit leaner. My son when he first started was getting a bunch of plug build up from not holding it wide open much and that really helped, but you can see on this top end its not as bad as yours.
BTW - I run a ball hone on my nikasil jugs and you can see the after honing picture above too. It removes the glazing (straight lines you're seeing in your jug) to restore the cross hatching that helps with lubrication/sealing on the single ring design. I've never had it change the dimensions of the jug even after 1/2 a dozen top ends, but the point is that you're just removing the glazing, you're not trying to "fix" any flaws.
Hope that helps some - I've got other pictures if you need more.
Thats great to hear! Well done on the rebuild, like VetStuff said run 40:1 with the recommended jetting because your 32/36:1 fuel to oil ratio will change what jets you need and wont be accurate to what the manual recommends. Also if your riding it like a pitbike as you said then the little less oil wont hurt.
I came to the conclusion that the reason the bike ran better on 32:1 with 92/110 octane is that with the lean jetting it was allowing less fuel/oil through because of the thicker fuel as appose to 36:1 which done your bike a favour as it could not burn the extra oil because your riding it as a "pitbike" also your higher fuel octane could have slightly compensated for the lean jetting. So really when you ran the extra oil the bike may not of been getting as much oil when you ran less oil because of the smaller jets, also on 92 octane the bike could have been detonating. Sounds a bit backwards I know lol
Alright update I finally was able to take the bike and and beat it and it still has a sputter I have 122 jet main I couldn't find I pilot so still have a 45. Its hard to describe but it rails hard perfect but if I I hammer it in first it cuts out 2 times before just singing the way it should I'm guessing I need the pilot? Idk also it only does it in first gear
Also I'm running vp 110 with amsoil dominator. I ran that fuel cause my little cousin has it ready to go
https://www.ktmworld.com/oemparts/p/ktm/54531607048/idle-jet-48-keihin
That's the pilot jet part number you need, what fuel/oil ratio are you running? Amsoil dominator will be fine as its a lower flash point oil but unless your head has been cut you really don't need the vp 110 and you will always have a sputter. If your head has not been cut then run 40:1 amsoil dominator with pump fuel then test it again. Just out of curiosity did you check your needle and clip position also where is your air screw set at?
Needle is at clip 3 it's was 60 degrees today and roughly 500 feet elevation. I didn't have any 92 non ethanol on hand so just ran what was available. My head hasn't been cut and my piston vs jug was maybe a few thousandths off the timing tool and the timing was perfect. Maybe tomorrow I'll go get some 92 and try it and I got jets coming but the local shop only had the mains I need. I'll report back when I swap to 92
Someone is not doing their air filters!
All that crud in the top end its from sucking dirt!
I think the poeple who had it before me didn't take great care of it I do mine as soon as it starts getting dirty
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