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.



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

[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.



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

[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.



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

[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.


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

[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]

[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.