82 atc250r engine trouble.

[82atc250rkart]

HI everyone, I've read and read forums trying to find a definite answer to my problem but haven't found a solution to my exact issue. My atc250r engine is in a grass kart. Plug chops suggest it's running rich as porcelain is black and there is slight moist look around ring of plug. I've left it this way because I'm having trouble with the engine building heat then starts to detonate (from what I can tell i get loud knock from head area) if I back off throttle the knock gets worse and if I give it more gas it lessons but of course eventually I have to back off and it seizes. It's seizing on each side of Gudgeon pin. I can get 3 800m laps out of it before I get any of these issues what else can I do to run it colder? It measured .006" clearance on piston, standard timing, slightly higher compression, running av gas (100+octane) 24:1 oil mix. I was short shifting a bit causing a bit of load on engine as it was muddy if this could have caused it? Engine is out to side and has good air flow. Hopefully I've put enough info in here cheers.

[Shawn Powell]

Unless your at real high elevation I'd quit running AV gas. Could be the reason your over heating. AV gas is designed to run with limited oxygen. Plus 10,000 feet. I'd switch to maybe an unleaded 100 octane. I like the VP MS109 blended with a good premium 91octane pump gas 50/50. Just my initial thought.


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[barnett468]

What is your compression?

Did you do a leak test?

What oil are you using?

Do you have a stock ignition?

Has your head been modified?

What plug are you using?

How fast was it going?

How long has it been doing this?


Post a large photo of the end of the plug and of the cart that shows the engine.

Race gas will definitely help it run cooler because of some of the things it is made of.



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[barnett468]

What piston are you using?

Have you ever driven it casually for a while to see if it still does the same thing?

Something is obviously very wrong if you are seizing up a 250 with .006" of clearance.



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[barnett468]

I also see you are new here and this is your first post so welcome to the forum. You will find it has some of the most knowledgeable people on 3 wheelers anywhere and that it is also quite entertaining on occasion. :)



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[82atc250rkart]

HI guys I'll get some things together for you to answer some questions. I bought the kart all built the way it is so quite a few things are unknown. It has been toyed around with lots of grinding on inside of ports etc and the piston is apparently not a atc250r piston but has been made to fit .I have compared it to a atc piston and it's slightly higher in crown etc so most likely higher compression hence why I ran race gas to prevent pinking. It has thicker walls than the atc piston I am wondering if this could be my problem? I am running fully synthetic castrol tts race oil at 24:1. I have checked timing and it looks to behave as it should starts on one mark at idle then move's to other mark with revs. I'm running a 10 cold plug where standard is said to be 8 I'll get some pics up when I'm back home.

[Shawn Powell]

I have compared it to a atc piston and it's slightly higher in crown etc so most likely higher compression hence why I ran race gas to prevent pinking.

AV gas ( I assume you saying aviation fuel) isn't the same as race gas. It's designed to run with limited oxygen at plus 10k foot altitudes. I would recommend actual race gas. Like VP ms109 (unleaded 109) mixed with pump or VP even has one called street blaze 101. With AV gas at low elevation it has too much oxygen and burns WAY hotter. I've seen it burn motors up at glamis. Might be a easy check off.


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[barnett468]

what brand is the spark plug?

sounds like a cast piston.

measure the bore and post the size.

you should also check the piston to quench/squish ring clearance and also the angle of the piston dome compared to the angle of the quench/squish ring in the head. it is possible that these angles are incorrect and possibly even reversed which could cause a problem but most likely would not be the only problem.


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[82atc250rkart]

You could be right with this unfortunately it's all I can get over 100 octane here in nz. I tried 98 octane pump gas 24:1 full synthetic and had same problem after about 5min of riding nothing too hard and no wot for long periods.

[82atc250rkart]

Plug is ngk B10EGV pics coming and a link to video where you can here the (what I think is) detonation knock and then seize.

[82atc250rkart]

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[82atc250rkart]

https://youtu.be/KxFdEP6e1eE

[82atc250rkart]

right before it locked up it seemed to go very well almost like it leaned out where the first 3 laps it was quite boggy and running rich as shown by the plug colour or is this a spin off effect of overheating the ol light burns brighter before it blows kinda thing

[82atc250rkart]

bore size is 71.5mm, i do have another barrel and piston ready to go that is 70.5mm and uses a wossner piston meant for 1981-84 cr250r would i be best to just swap to that for now and get a 71.5mm atc250r piston for the other barrel instead of usuing this custom made piston (i was told is a husqvarna piston brand wiseco)

[atc300r]

Your cylinder to piston clearance is to big. Should be around .002-.003. That piston looks hacked and could be causing the knock. Your best bet is using the other cylinder and wossner piston. The early cr piston is same as 81-84 atc and I think 250 odyssey.

[barnett468]

Unfortunately I can not see your photos in the format you posted them because the owner of the site doesn't like me so he blocked me from viewing photos that are posted in some formats for what he thinks is some type of punishment that is supposed to hurt my feelings or something :lol: which certainly is a big help to people like you that need help and post photos to show a problem. :crazy:

If you can figure out another way to post photos, you can try that and I will tell you if I can see them.

If the head looks heavily pitted, the pits and/or any sharp edges on the pits can contribute to detonation. If it looks unmodified and you use a stock piston, the quench/squish angle between the head and piston will be factory correct, however, this does not mean it will be ideal and it might be able to be improved but the angles in stock form are good enough that they will not cause the problem you are having IF the bike is properly tuned.


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[barnett468]

Your spark plug is likely colder than it needs to be but we need the compression numbers to tell.


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[barnett468]

You could be right with this unfortunately it's all I can get over 100 octane here in nz. I tried 98 octane pump gas 24:1 full synthetic and had same problem after about 5min of riding nothing too hard and no wot for long periods.


You can not buy race gas in NZ?



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[barnett468]

I bought the kart all built the way it is so quite a few things are unknown.

Why don't you call the builder and ask him or her if they know why it keeps seizing? It's not likely that it ran fine for them and then suddenly instantly seizes on you unless all they did was build it and fire it up to make sure it ran then sold it.


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[barnett468]

I couldn't hear any detonation in the video. What time in the video do you think you hear it?

It's hard to say for certain without actually driving it but if anything, it seems to me that it is geared a little too numerically low causing the engine to work harder than it otherwise could and not be in the ideal rpm range as often as it could. Working the engine hard will generate heat.

If you never get very close to top speed in top gear, you might consider increasing the size of the axle sprocket by 2 or 3 teeth but it would help to know what the tooth count is on both drive gears first. My guess from what I can tell is that going 1 tooth smaller on the counter shaft gear would be way too much which is whay I would do a small change with the axle gear.



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[82atc250rkart]

I'm imagining that the previous owner went out to .006 because of this seizing issue. The knock is only coming along after a few laps so as the piston is getting too hot I did wonder if the knock was actually the piston starting to stick as I lose alot of power when it starts to happen going by plug and head and top of piston there is plenty of fuel in there. Is there a reason my head has comE out looking so clean has oil film but no soot or carbon

[82atc250rkart]

I was shot shifting alot that day due to mud so I may have been loading it up myself maybe I'll change it all over to the other piston and cylinder run it in and try not short shift so much I only do it because we it gets on the pipe pretty much all traction is out the window lol. What I think is detonation is about 4:30 in video I pull off briefly when I think it's about to lock then go back on youl here a more profound rattle than earlier in video

[barnett468]

going by plug and head and top of piston there is plenty of fuel in there.

You can't go solely on that . When you are uncertain about jetting, it is safest to start so rich that it burbles and then jet down from there.

The new cylinder combo will need to be jetted.

It would not be wise to run it without doing a pressure test first.

If the compression is around 190 or less, I would not use a plug as cold as 10.

Irregardless of short shifting, it still seems like the gearing may be slightly off.

You did not answer my question regarding race gas.



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[barnett468]

I was shot shifting alot that day due to mud so I may have been loading it up myself maybe I'll change it all over to the other piston and cylinder run it in and try not short shift so much I only do it because we it gets on the pipe pretty much all traction is out the window lol. What I think is detonation is about 4:30 in video I pull off briefly when I think it's about to lock then go back on youl here a more profound rattle than earlier in video

You do not want a "pipey" engine on a muddy track but if the other cylinder is unported or not ported very much, you won't have that big of a problem, however, your compression will likely be fairly low which I would correct.



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[yaegerb]

Help is abound in this thread.....

Unfortunately without you providing baseline numbers we can't magically tell you what's wrong. Don't assume that you should be running race gas, you need a UCCR test to accurately tell you what octane you should be running.

1. Reassemble your top end and as 300R already stated, use your freshly bored jug and wossner piston
2. Post assembly and as Barnett suggested, do a pressure test to confirm your seals aren't leaking and causing a lean condition.
3. Perform a UCCR on the engine to determine exactly what octane you should be running in that engine. I have a spreadsheet with directions I can send you to accurately perform this process and corresponding calculation. Without the UCCR number you are truly guessing.
4. Use an NGK B8ES gapped at .028-.031"
5. Before starting the motor take a baseline compression test

[82atc250rkart]

Ok cool thanks guys I'll reassemble using the other bits and get some figures, like I said I've just bought it the guy that owned it was an engine builder so that's probably a dangerous thing and hence why all this strange stuff has been done to it. Race gas is very hard to come by and very expensive so av gas seemed like the next best thing I'll go back to 98 if it suits the new build. The old owner seems very vague on it didn't want to tell me much and said he freshly built it rode it once. Please do send me instruction to do uccr test thanks.

[yaegerb]

Ok cool thanks guys I'll reassemble using the other bits and get some figures, like I said I've just bought it the guy that owned it was an engine builder so that's probably a dangerous thing and hence why all this strange stuff has been done to it. Race gas is very hard to come by and very expensive so av gas seemed like the next best thing I'll go back to 98 if it suits the new build. The old owner seems very vague on it didn't want to tell me much and said he freshly built it rode it once. Please do send me instruction to do uccr test thanks.

Send me your email via private message

[barnett468]

You could also fabricate some type of shroud to force more air through the fins on the cylinder head if you want . This shouldn't be absolutely "necessary" in your case, and it definitely won't cure your current big problem, however, it will lower engine temps a little which won't be a bad thing, especially when it is hot outside.

It would also add a cool "works" type look which imo is always a good thing.

From vintageklemm.com

.....................http://www.klemmvintage.com/h1%201st%20assy%20006.jpg

.....................http://www.klemmvintage.com/h1%201st%20assy%20008.jpg



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[barnett468]

...the guy that owned it was an engine builder... ...seems very vague on it didn't want to tell me much and said he freshly built it rode it once.

Well without being able to see the photos it's difficult to comment on the "builders" skill level, but imo, it certainly seems questionable at the very least based on the info, especially if he purposely ran .006" clearance on a new piston and bore along with the fact that he was "vague" and not fully forthcoming with info which right there suggests to me he has very little idea about performance engine modification and very little skill at assembling it. :rolleyes:




Race gas is very hard to come by and very expensive so av gas seemed like the next best thing I'll go back to 98 if it suits the new build.

Av gas was not the sole contributing factor to your engines demise and you can run 2 strokes on av gas if properly tuned for it, but as was suggested, it is not ideal.

Your 98 octane will be sufficient for a stock or near stock engine, which also means that the head has not been heavily machined to increase the compression by a big margin.

To put it in more simple terms, you can run at least 170 psi cranking compression with your 98 octane if it is properly jetted. Do the compression test with the gas off and throttle wide open and kick it fairly hard. There are other ways to do it but in your case, this should suffice. Use a high dollar gauge. The cheap ones can be off by as much as 15%. A short hose will give you a more accurate reading than a long hose.



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[82atc250rkart]

http://i517.photobucket.com/albums/u333/lewishorrell/20170717_190416.jpg (http://s517.photobucket.com/user/lewishorrell/media/20170717_190416.jpg.html) http://i517.photobucket.com/albums/u333/lewishorrell/20170717_190658.jpg (http://s517.photobucket.com/user/lewishorrell/media/20170717_190658.jpg.html) http://i517.photobucket.com/albums/u333/lewishorrell/20170717_181821.jpg (http://s517.photobucket.com/user/lewishorrell/media/20170717_181821.jpg.html) http://i517.photobucket.com/albums/u333/lewishorrell/20170720_182137.jpg (http://s517.photobucket.com/user/lewishorrell/media/20170720_182137.jpg.html)
http://i517.photobucket.com/albums/u333/lewishorrell/20170717_181812.jpg (http://s517.photobucket.com/user/lewishorrell/media/20170717_181812.jpg.html) http://i517.photobucket.com/albums/u333/lewishorrell/20170716_212634.jpg (http://s517.photobucket.com/user/lewishorrell/media/20170716_212634.jpg.html) http://i517.photobucket.com/albums/u333/lewishorrell/20170720_182121.jpg (http://s517.photobucket.com/user/lewishorrell/media/20170720_182121.jpg.html)

[barnett468]

Unfortunately I can't see a single one of those photos either but I think that may be a problem with photo bucket as they have recently changed their system, however, if you can see them them then I can't see them cuz this sites owner doesn't like me. :lol:



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[82atc250rkart]

Unfortunately I can't see a single one of those photos either but I think that may be a problem with photo bucket as they have recently changed their system, however, if you can see them them then I can't see them cuz this sites owner doesn't like me. :lol:



PREVIOUS KAWASAKI INTERNATIONAL R & D PROJECT ENGINEER AND ATV DEPARTMENT SUPERVISOR AND THE ONLY PERSON ON 3WW WITHOUT AN EDIT BUTTON OR A STAR :lol:

That could be the case haha

[82atc250rkart]

Actually nope since putting them up photobucket has changed and now wants to charge me haha that won't be happening. I could link to Facebook album perhaps.