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Discussion Starter #1
I read a thread here about the little numbers stamped around the spark plug opening on ESR domes. It peaked my interest, I bought a 250r a few months ago and don't know too much about it. Just the word of the previous owner. So I called ESR this morning and they deciphered the numbers for me.. I learned I should be running race gas and i have stock stroke.

72DT7655RA
72 - Stroke length in mm (I guess 72 is stock)
DT - Dome Top
76 - Dome size : Basically the dome adds 76 cc's so 250+76=326
55 - Unsure what the number represents but ESR told me its a mid to top range setup
RA - Race Gas

I've been running pump fuel, I wonder if that has screwed with my piston or rings, compression is 170

Thougt I'd share this info.. post your numbers it might be interesting.
Fred
 

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You might need to call them back,, :blink: 76cc's, that dont sound right.
If a dome had 76cc's, that engine probably couldnt run.

76 could mean the bore size.
Neil
 

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Discussion Starter #3
i should have put a question mark after the cc's... I just guessed at that after he told me the 76 meant i had a 330 kit. My bad
 

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If you were riding on dirt, you probably didn't hurt you engine by running pump gas. ESR sets up their race gas domes on the low side (compression) because when you use your quad in sand with paddles, it puts a lot more load on the engine.
 

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Discussion Starter #5
Mostly the dunes.. racing the hill and touring the bowls.
 

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Discussion Starter #6
I pulled my dome to take a look at the piston.. it looks ok no pitting or holes.. but if you look at the right side of the piston there is a flat spot (exhaust side)... you can see the shinny piston ring, is that by design or is that piston damage?
Thanks
 

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That is definitely not by design. That is damage. You ought to put a new piston in there and check the bore for wear.
 

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Thank goodness you caught that in time, :eek: :( hopfully. Theres a few things you need to check after you get it fixed & before you run that engine hard.

Timming ??, use a timming light to check that properlly & check the flywheel key.
Compression amount.
Gas, octane.
Carb jets.
What you had was deff spark knock because it ate off the exhaust side edge of the piston from getting to hot.
If timming was retarded, that would mean it was firing late & blowing fire out the exhaust.
Neil
 

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Discussion Starter #9
uh oooh.. thanks for the heads up Neil and Mike.

Things i know to be true..

  • I'm in over my head
  • I've been running pump gas 93 octane which I now realize is much too low.
  • The previous owner had been running pump gas (or so he told me) since getting the 330 kit and porting from ESR.
  • It was running lean when i got it so i up jetted from 170 to 180 @2200 feet
  • Day 1 the compression was 170.. i haven't checked it since
  • I run it hard at the dunes and the hill
  • The piston I pulled is 75.94 mm so the Bore is 76?
I've pulled the jug/cylinder, but I'm struggling with piston clip removal.
Cylinder looks ok no major gouges, but some faint X patterns which i assume is from the last Bore

I'm trying to decide to take it to a local race shop in Tucson for the machining or send it off to ESR.. once I get a new piston i'll double check that timing

Fred



PS Good thing dunning season is over.
 

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What do you need to get machined? If the cylinder is in pretty decent shape with no crazy gouges then you shouldn't have to get it bored.
 

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Discussion Starter #11
What do you need to get machined? If the cylinder is in pretty decent shape with no crazy gouges then you shouldn't have to get it bored.

So i can just drop the same 75.94 piston?
 

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So i can just drop the same 75.94 piston?

Should be able to. And if you do get lost, look up Racer's Edge down there in Tucson. They have more than they're fair share of experience with the old R, and are willing to share thier knowledge.
 

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Discussion Starter #14
Thanks guys.. i guess i just don't have an eye for it.. I showed it to John at Racers edge as suggested, he's gonna bore it for me.
Thanks again
 

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wow seeing this makes me wanna see what my piston looks like!!
 

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Sent you a PM chief...
 

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Discussion Starter #17
Starting to wonder if my spark plug had anything to do with the melt down.. what do you guys run?
 
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