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Bog on startup only

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Bike is a 2006 YZ250. 2 weeks ago the bike started and ran fine. Last weekend the bike did not start well when it was cold. After it wormed up it sounded good. We started out ride and the bike ran great like always, but every time we stopped for a little brake the bike would fire right up  but bog really bad then rev and run fine. If I turned the bike off and started it up right away it was fine. So I rode the rest of the day and only had problems at startup, the bike ran normally all day. So today I checked compression 245PSI (fairly new top end). Pulled the carb and cleaned it and did not fine anything stuck in a jet and the float level was good (7MM that's what I had it set to) so I changed it to 6.5MM. The only think I found that was not right was the little boot on the chock was pushed up a little. Put carb back on and still same think. I did notice that after I reinstalled the chock boot and installed it into the carb I could see a little bit of the brass above the boot. I never noticed if it is supposed to be like that or if something holding it up. I always remember the chock knob touching the boot. I was playing with the air screw. I could have it 1/2 turn out or 3 1/2 out and it did not make a difference. My next step is to check the reeds and ignition. I did try another spark plug and it made no difference. I posted a video of how it sounds and a pic of the chock. NOTE: The bike did not stall in the video. I turned it off so you can see it will start up fine after the first start.

 

Carb settings are:

168 Main

45 Pilot

50 Power

JD Red Needle second clip from top

Air Screw 1 to 1 1/2 out

32:1 premix.

 

https://youtu.be/KdVONVY2BmQ

 

WP_20160124_002_zpsf3olxtrl.jpg

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It won't let me open your video but your saying it only bogs on start up? Which is completely normal as far as I've seen with my yz125 as long as the bike runs perfects after you warm it up but it wouldn't be a bad idea to check your spark plug reeds maybe clogged over flow tubes

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It won't let me open your video but your saying it only bogs on start up? Which is completely normal as far as I've seen with my yz125 as long as the bike runs perfects after you warm it up but it wouldn't be a bad idea to check your spark plug reeds maybe clogged over flow tubes

Try the video now.  It is not completely normal. Maybe for a bike that sat over night but not 5 minutes after it was running for 30 minutes or more. As I posted above I tried a different plug and cleaned the carb completely including the over flow tubes. I was going to check the reeds and ignition today but was really busy with work.

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It would also be a good idea to check out the crank shaft seals to it could be air or oil be sucked in

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But ignition timing or the spark plug could also be causing it's always hard to say a lot of things can cause the same thing...

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Start it up with the gas off and see if it makes a difference. Then shut the gas off a little before you stop the engine. Let it sit long as you normally do when it bogs on start up, then start it with the gas off again and see if it does it.

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Since it is cold outside I have noticed my bikes loose a lot of heat very quickly. You need to warm it up every time after it sits, even for 5 minutes.

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Well the problem was the spark plug cap. When I checked the Primary & Secondary Coil resistance they were fine. When I removed the spark plug cap I was getting very erratic readings. So I took it apart very carefully and there was a little rust on the spring and what appears to be a fuse. So I cleaned it all and put it back together. Now the resistance was in spec. The bike fired right up and after sitting it fired right up again. So thx for the ideas.

It would also be a good idea to check out the crank shaft seals to it could be air or oil be sucked in

good suggestion but normally if they were bad the bike would not run well.

 

Start it up with the gas off and see if it makes a difference. Then shut the gas off a little before you stop the engine. Let it sit long as you normally do when it bogs on start up, then start it with the gas off again and see if it does it.

Im assuming you were looking for a float or float valve not sealing properly. Good way of checking.

 

Could your power valve possibly be sticking? Not sure if it would cause what you are describing, just throwing out another idea.

Normally if the power valve is stuck open it would start fine but have no low end power. I should know, I broke 2 valves and they were stuck open,LOL

 

If it's a bog when snapping the throttle, I'd start with a simple air mixture adjustment.

Thx for the reply but if you read my hole post you would of seen I tried that.

 

Since it is cold outside I have noticed my bikes loose a lot of heat very quickly. You need to warm it up every time after it sits, even for 5 minutes.

Well I have had this bike for 9 years and it never did that and plus its not that cold here in AZ. Yes you should still warm it up but it should not start like crap. If it does something is wrong.

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Good find. Good to hear you got it.

 

Yes, I was thinking needle / float not seating.

 

So, what took you to the coil / plug wire?

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Good find. Good to hear you got it.

 

Yes, I was thinking needle / float not seating.

 

So, what took you to the coil / plug wire?

Well since I checked all fuel/air related stuff my next step would be ignition. Checking coil resistance is easy and when I got to the cap I new there was a problem.

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