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03 250f won't start hot

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I just bought a 2003 yz 250f, it has a thumper 280cc kit installed and runs very well. The only problem I am haveing is it will NOT start when it is still hot. After it cools down it starts fine.

I have limited experience with 4 strokes, and this is my first yzf.

Could someone please give me some hints on how to start it hot.

thanks , stevenrees1@yahoo.com

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typical intake valves need shimming issue.

or if valves are in adjustment, the pilot jet may be too fat.

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or fuel screw set too fat.

or idle set to low

or float stuck closed

or fuel boiling

or.....

well the list has many variables. but the obvious ones are well, pretty darn obvious.

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+2 on the pilot jet/fuel screw setting.

Valves typically (when too tight) cause cold start issues. As the engine heats up, the clearances widen.

Dont you have that backwards? When metal gets hot, it expands, and thats why engines have clearances, to account for the expansion when heated. So I would think valves being to tight would cause more issues when hot, not allowing the valves to close all the way. Maybe I am missing something.👍

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Aluminum expands more than most of the other metals used in the head. So for argument sake, the vlave stem grows .001", the aluminum grows .002" So the valve ends up with a tad more preload and the cam also moves a little further from the bucket.

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you have it backwards william.

if it wont start cold because of valves it will NEVER start hot because of the valves. in one harescramble i was at, crf250 had to be pull started before the race. during the race his bike stopped running at about the 1 hr 30min mark. he was being towed back to camp by a quad.

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Aluminum expands more than most of the other metals used in the head. So for argument sake, the vlave stem grows .001", the aluminum grows .002" So the valve ends up with a tad more preload and the cam also moves a little further from the bucket.

True for the same change in temperature, however the valves are much hotter than the head, as aluminum has excellent heat dispersing qualities, is open to the air, and is cooled by water flowing through it. The valves are much hotter, and thus expand more. The whore reason for valve clearance cold is that it tightens up when the engine gets hot. Idealy you want close to zero clearance when the engine is hot to maximize valve lift. Any less than this and the valve will not close all the way.

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As I said earlier, I am new to 4 strokes. I raced Rm250 and Maico 250 for 11 years and quit riding in 1983 due to injury. I am now riding again with my twin boys (kx-85's). But I am BRAND new to the 4 stroke. I appreciate all the reply's and any more that will come in. I ordered a clymer manual, but do not have it yet. Is there any "must have" books or manual for beginners ? For example what exactly is a hot start? Is it the small lever next to the clutch lever? (I thought it was a compression release) Any help on ANY aspect of my yz-250f will be greatly appreciated

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I could of sworn Eddie told me otherwise. Being I respect both SUnruh and KJ790 I respectfully request my previous posting to be ignored and t4reated as the rantings of a madman.

But I can blame my error in posting on old age, yeah, that's it. Gotta go, time for shuffle board.....

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As I said earlier, I am new to 4 strokes. I raced Rm250 and Maico 250 for 11 years and quit riding in 1983 due to injury. I am now riding again with my twin boys (kx-85's). But I am BRAND new to the 4 stroke. I appreciate all the reply's and any more that will come in. I ordered a clymer manual, but do not have it yet. Is there any "must have" books or manual for beginners ? For example what exactly is a hot start? Is it the small lever next to the clutch lever? (I thought it was a compression release) Any help on ANY aspect of my yz-250f will be greatly appreciated

The hot start button or lever is either the big red button above the choke on the carb or it could be a small lever near the clutch. When the bike it hot you need to pull the hot start until you get it going then turn it off.

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