Another 400 question...

[Friesen400]

Well I tried to search past topics to see if anyone else has had this problem but I couldn't find an answer, so here goes...
My '73 400 would sometimes stall while idling because the linkage that the throttle cable attaches to was loose on the throttle shaft and would slip behind the idle screw, allowing the throttle plate to close too far. I took the carb off and (as a temporary fix) bent the tab on the linkage so that it can't slip past the screw. I was hoping to pull the whole shaft out and make fix it properly, so initially I had pulled the throttle plate out from the throttle shaft and took off the snap ring on the opposite side, but I wasn't sure how to get the rest out and since I didn't have a lot of time I put that back together.
I'm pretty sure that I put everything back exactly the way it was, and everything worked the way it was supposed to. However, when I started the sled it immediately revved up and almost started to drive away. I checked to see that the throttle plate was closed and it was, and tried again. Same thing. I'm baffled.
Its a Walbro carb, by the way, and if anyone has any ideas I'd love to hear 'em.
Thanks in advance guys.

[JDT]

Possibly a bad air leak is causing the high idle.

[400brian]

That was my first thought as well. From what's being described, I don't know what else could cause that.

[JD600]

I had one do this to me on a 76 400 one time. Take the throttle butterfly out, turn it over, and put it back in. It sounds like the first fuel inlet in the venturi is open just a little bit. Over time, the butterfly seemed to wear itself to the carb. Also, an air leak is possible. I would advice you to change your crank seals and make sure your carb gaskets are in good order.

DE

[Friesen400]

Thanks again for the help guys. I will try flipping the butterfly around first and then go from there.
I had checked the crank seals the last time that I had the sled running (about a week before this happened) by spraying a bit of ether around them to see if the RPMs would go up and there was no change. Do you think the seals would still need to be replaced now?

[JD600]

I would still recommend replacement of the seals. The problem is that these seals are 40 years old and brittle. While they may not be leaking now, it is quite possible that once they reach operating temperature, they may crack open and cause all sorts of issues, the worst being metled pistons. They best thing about a mid-enigne sled like your 400 is that it is super easy to change the seals without pulling the engine. And, the seals are avalible from www.newbreedparts.com for around $10. If you have any more questions, feel free to ask them on here or send me a PM.

DE

P.S., let us know how the carb works out.

[Friesen400]

Thanks DE, you make it sound so easy! Do I need any special tools to get the clutch or flywheel off of the shaft?
I just ordered the whole Walbro pump rebuild kit along with the 73-75 JD 400 seal kit from newbreedparts... I had taken the four screws out of the bottom to take a look inside and now that it's back together it leaks fuel by the pump.
I flipped the butterfly valve around and it does look like it fits better now, so hopefully when I can get everything together it will work...

[400brian]

A good cleaning of the carb is in order. Don't scrape the sealing ridges off the plates, and reassemble with new gaskets. Carefully remove the big screen in the bottom, as you'll be re-using it. Check the metering lever setting,
It's in the FAQs. The biggest pucker point for me is when I'm removing the screws that hold the metering plate.
If they strip, the carb is junk. On my own carbs they've always come out OK, but on parts carbs I've bought, not so much.

[DLDeere]

They best thing about a mid-enigne sled like your 400 is that it is super easy to change the seals without pulling the engine. And, the seals are avalible from http://www.newbreedparts.com for around $10. If you have any more questions, feel free to ask them on here or send me a PM.

DE

Hi Dustin,
Can explain how you replace the seals without pulling the motor and opening the case? Thanks.
Howard

[JD600]

Howard,

In there mid mount sleds, its fairly easy to get to the engine once the cowlings are removed. Things that will need to be removed from the engine: The primary clutch, recoil, fan tower, flywheel, and stator. Once the seals are accessable, a screw driver can be driven through the old seals so that they may be prted out of the case. The next thing i do is inspect the outer bearings to make sure they look ok. Once the old seals are removed, the new seals can be driven back into the case. I usually use a 4X4 with a hole bored in the end so i can drive them on evenly. I lube the seals with 2 stroke oil as well. It is also important to mark a stribe line on the stator before you remove it so that you can install it back in the same location. I've done this a few times in the sled and can now do it start yo finish in under 2 hours. If you have any more questions, feel free to ask.

DE

P.S., Its a lot harder to do this on engines that have ribbed seals, but i've done it. The key is to use a seal that doesn't have a rib in it.