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Set squish and now won't start.

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I just had the head off my 2017 yz250 machined down to 0.055 thousands from 0.080 and I double checked the measurements and everything went back together smoothly except now the bike won't start. I tried a new spark plug so far and the air filter is clean and it was getting fuel as the old spark plug was completely soaked. I did run a compression check and it was releasing pressure from the reed area so that's the first thing I want to check but I don't know what else would be causing it. It has compression too.

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Did you use new head o rings? Did you check spark? What do mean it was releasing pressure from the reed area? Did you have anything apart other than the head?

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Took it all apart and it checked out and got it back together and I managed to get it to start up that time. It was definitely running very rich now off stock jetting and didn't want to idle more than 10 seconds.

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12 minutes ago, 2 STOKE YZ DOC said:

Your going to need to get out and ride it and check jetting. 

A stand never tells you nothing. 

Only reason I figured it was running rich was it went from barely smoking at all before to I hot boxed my garage in under a minute lol. 

I have a lectron coming by the end of the week so I'm just gonna throw that on and run it.

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4 minutes ago, mxchri5 said:

I have a lectron coming by the end of the week so I'm just gonna throw that on and run it.

Interested in selling the stock carb? 

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16 minutes ago, Bren Ledger said:

Interested in selling the stock carb? 

I don't think I will, rather keep it as a spare if something ever goes wrong

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11 hours ago, Bren Ledger said:

Interested in selling the stock carb? 

You can find them on eBay for 100-125 bucks all the time. 

I’ve bought a few because I like to have in stock if something messed. So, I have a rebuilt one ready to go. And I only deal in steel frame so 02-06 is same. 

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11 hours ago, mxchri5 said:

Only reason I figured it was running rich was it went from barely smoking at all before to I hot boxed my garage in under a minute lol. 

That makes sense.

Stock wide squish needs rich jetting (on all circuits), because there is not enough turbulence to get a consistent burn on every power stroke.

Correct squish gap doesn't need so much fuel, so the motor will response more consistently to throttle and load changes.

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You're going to have to lean out your jetting to account for the tighter squish and increased compression ratio.  Surprised it didnt' run anyway, sounds like you flooded it...

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After reducing the squish height by 0.25mm on my YZ125,

it now runs best on two sizes leaner pilot jet and a half clip leaner on the needle.

 

It also seems to run on a wider range of ambiant temperature swings on the same settings.

(jetting less finicky in the early and late season)

Edited by mlatour
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