1975 400 Hard to start when warm.

[markzrt1]

Starts great cold. After riding if you let it sit for 5 -10 minutes it will not want to start. It will pop a little but it will not build rpms. Throttle is all the way open when trying to start. Has great spark so that isn't an issue. Give me some ideas on what to look for. Has a Walbro carb.

[Steven Rempel]

After you have it warmed up, and wont restart, will it start up if you give it a prime shot of fuel? This might rule out a fuel delivery problem. My last time I had a problem like this it was a poorly seated needle rubber tip was not seating, causing a flood issue "like" symptoms. It would stutter and start hard, prime would just flood it. Readjusted needle and reset spark plug gap.

Also I have been told that this can be a sign of worn seals, even new seals can have a defect. I would try a leak down test to check.

Are you saying you are trying to start it with the throttle wide open? Not sure why.

[markzrt1]

Yes, Throttle wide open. if I don't have it wide open it won't pop at all. If I give it a prime when warm it makes the issue worse. Where can I get a carb rebuild kit?

[Steven Rempel]

http://www.psep.biz/store/walbro_carburetor_parts.htm

I have had good luck with these guys. check them out also go to there home page lots of stuff

[Steven Rempel]

http://www.mfgsupply.com/snowmobile/sno ... epair.html

but have better luck with this one PATS seams to not have what I thought anymore.

[Steven Rempel]

http://www.newbreedparts.com/newbreed/i ... duct_id=93

and of course best place is...

[markzrt1]

Hmmm, maybe I should put a mikuni carb on it. Saw the first link has a kit.

[400brian]

You may just be suffering simple vapor lock.

Re-insulate your firewall and fuel lines, and route them away from the exhaust.

Read through this: http://www.jdsleds.com/community/viewto ... ock#p81743

[markzrt1]

Did they have insulation on the firewall from the factory?

[400brian]

LOL! YES, and the fuel lines. This was a HUGE deal in '73, that just about put Deere out of the sled biz.

[markzrt1]

I'll have to pick up some insulation like you did. My fuel line run through the tunnel, not under the motor like yours do.

[Steven Rempel]

question, does this happen even if you start cold let warm up, shutdown and then try to restart?
Do you have the same symptoms?
ei warm up good and warm with hood open and access panel on top off.

This is a way I would try to rule out vapour lock, but pls chime in anyone if I am wrong in the process. Still learning.

I have only experienced this once after a long and slow ride, but I did not even have the heat shield installed at the time.
After I got it going again we continued on but with the top access panel removed to let more heat out.

[daisydukers]

Hows the compression...

Mine acted like that....bad head gasket.... Checked everything else but that....

It would start fine cold....but if I ran it for a while, and then shut it down.....It would be dead till she was cold again....

All it would do when it was hot was almost like it was backfiring a bit...Pop...Pop...sorta deal.

I doubt the issue is the same...but something to check if you haven't already.