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04 yz250f hard starting and engine tapping.

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I just do not understand why this bike starts so easy when it is cold (1 kick) and hard as heck to start when it is warm (6 to 8 kicks). I bought this thing and it needed work done to the top end and I did that, new timing chain, all new chain guides, and adjusted all the valves into spec, I even went as far as putting a micromater on the cams to make sure they were in spec. Before I did all of that it would hardly start, I meen you had to pull it to start it, not fun. I also thought that the engine tapping would stop but no luck their either. This bike is all stock, stock bore, stock jets with stock exhaust.Any suggestions? Also when you are at an idle and you gun it, it boggs down.

Edited by peprice
adding info.

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I am in mid missouri I am pretty sure my alt is around 850 to 910. And no changes, all stock. And without sounding like a moron what is a EKR clip?

After I sit back and think about it the bike has a whole mess of problems.

1. The idle is erratic, sitting at an idle at first it idles perfect, take off and run it for five minutes and then let it idle, it is super high, gun it and it goes back down. It does this over and over agian.

2. The engine ticks. I change the oil every 3 rides with good filters and use syn oil.

3.Hard to start when it is warm.

4. 1st gear at idle doing about 3 miles per hour you gun it and it boggs down, if i was to keep on it it would die and I am sure of it.Anyway, as it is bogging down and you let off get back on it two times in a row it will take off like a bat out of hell.Weird....

Edited by peprice
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Have you checked valve clearance again? If so, what were they? Generally, if the valves are too tight they are harder to start when cold. What condition is the piston, camchain, and camchain adjuster? If the engine is mechanically sound it sounds like your idle mixture is a bit rich.

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I checked the valve clearance about two weeks ago and they are right where I put them, all of them are in spec right in the middle of the board. Piston was in good shape when I had the head off along with the jug, I even cleaned off the piston, and the cam chain is 1 month old from yamaha. And as far as the tensioner goes it is in good working order. I talked directly to yamaha on operation of the tensioner.

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I'd say that you either have the float level set too high or the idle mixture screw is too far out (or maybe both).

If you can't get the starting issue resolved by leaning out the idle mixture then you might want to check the float level and/or replace the pilot jet with one leaner (in that order).

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I will check that out tonight, thanks. Any suggestions on the piolet jet size as far as bigger or smaller. And float level I will have to do some checking on as far as how to do so. 6 Months now in the dirtbike world and so much to learn.

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Have you ever cleaned the carb thoroughly? Checked the accelerator pump for proper operation and timing? That might be all it takes is a good cleaning and replace the pilot jet. Accelerator pump problems can cause a bog when accelerating.

Check for vacuum leaks as well.

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Sounds like good advice, everybody keeps pointing out the carb, I think I will give it a good once over, thanks for the advice, very helpful...

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It was harder to start prior to the top end being done, trust me it is alot easier now but not easy enough, I see all of these guys starting their yz and it seems much easier for them.

My starting technique is the same as cold, find the hard spot and kick the hell out of it.lol

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My starting technique is the same as cold, find the hard spot and kick the hell out of it.lol

Not to doubt your smarts or be a master of the obvious, but when the bike is hot you are using the hot start lever, right? If not, that will surely make things easier. Also, I'm leaning toward the carb needing a good cleaning - especially the pilot jet since that is a usual suspect with its tiny holes that clog easily.

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Its cool, and yeah I am useing the hot start, and you are the third person to mention pilot jet, so I am going after that, thanks for the info. I actually put a new hot start plunger in it about 3 weeks ago.

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Allright, took it completly apart last night found that the piolet jet was half clogged, cleaned it out, then I took the needle clip off and moved it up one space put it all back toghter, fired it up and it was one ticked off machine, would not idle spitting popping backfiring, it ran better before, guess I should of left that needle clip alone. I checked the float height also, it was in spec,Will be putting it back to stock setting and starting from scratch tonight.

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