Jump to content
Sign in to follow this  

Yz250f only wants to start with hot start, cold?

Recommended Posts

My bike was running great until yesterday just before a ride. It fired up first kick I was letting it warm up and it died after about 2 minutes. Went to restart it nothing,. Choke pulled kicked and kicked tell I wore my self out. Got off for a breather and noticed a small puddle of gas under the bike. So pulled the plug and it was fowled out. Gapped a new one and tried again same results. Tonight I pulled the carb and blew it all out, pulled the plug and cleaned it up got on and started kicking again choke pulled and nothing, this time no gas dumping out of the bottom. Decided to try pulling the hot start and bam fired up, but as soon as I let off the hot start it died again.

What could be going on bike was running great before this little issue. Any help would be greatly appreciated!

Share this post


Link to post
Share on other sites

Could be the valves causing the starting issue. When were they checked last. Also, if you are twisting the throttle while you try to start, it will flood. These have accelerator pumps which squirt a small stream of gas every time you twist the throttle and kick

Share this post


Link to post
Share on other sites

Also, the hot start leans out the air fuel ratio so if it runs with the hot start pulled in, sounds like it's running rich too. The combo of a fouled plug on a 4 stroke(rare), puddle of gas in floor and the hot start tells me we have a rich situation or you are activating the AP. You can do a little test by pulling to air filter out and see if it runs. If you are too rich, it will run with the filter out telling you that you need to look at jetting. It shouldn't run or really even start without the filter in since it would be REAL lean on a correctly jetted bike

Share this post


Link to post
Share on other sites

Thank you for the reply. My concern is that the bike has been running awesome with the current jetting and always fired first kick. I'm running the JD jet kit in the current configuration:

Main- 175

Pilot- 42

Needle- red second to the bottom

Leak jet- 40

Screw-1 1/2 out

Alt-5000- and up

Location colorado

Usually when I first start it, I cycle the cylinder a couple times to TDC then crack the throttle once with choke on and kick she fires every time until the other day.

Share this post


Link to post
Share on other sites

thanks for finally putting your jetting info in the post.

 

imho, your 42PJ is way fat.  try a 40 or maybe even a 38 for that elevation

175MJ (while not in use for starting) seems pretty fat for the fsw as well.  try 170.

you clip pos seems fat as well.  i would move it up 1 notch.

 

make these changes 1 at a time.

1) open the screw just a hair...maybe 1.6 to 1.7 turns out

2) pj to 40

once those 2 are done....then move onto

3) clip up 1

4) mj to 170

 

also you should almost never *need* go gap a new sparkplug...check yes, but reset the gap is almost a never.

 

since you didnt put what year your bike is i have no idea if its coil on cap or not.  could be a cap/wire issue as well.

Share this post


Link to post
Share on other sites

Thanks SUnrah, the bike is an 04. When I went to swap the plugs out the new one was out of spec per the manual. Not enough gap.

I will try the new jetting recommendations thanks for the help. This forum has helped me out a ton. Since I am newly back into dirt bikes and carbs. Coming from racing sport bikes I really miss my fuel injection but am enjoying learning about it.

Zack

Share this post


Link to post
Share on other sites

Highly suggest checking valve clearence too. It will take about 30 mins to check and will keeping you from chasing your tail. If the valves are too tight, it will be real hard to start. Figured that out the hard way when I came from the XR side of Hondas

Share this post


Link to post
Share on other sites

I will re- check my valves tonight but they were done less then 5 hours ago by a local shop after I bought it.

Were they shimmed at that time? I shimmed mine and about 5-6 hours later they moved again. Sold the bike at that point. It was a first gen CRF so it ate valves for lunch

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:

Sign in to follow this  

×