72 JD 400 WILL NOT IDLE

flacker36 · Post by **flacker36** » Tue Jan 01, 2008 12:46 pm

NEW OUTCOME!!!!

I adjusted the high speed needle all the way closed or open just slightly & the machine idles good. I was able to adjust the idle to 2300 - 2400 RPM.

New problem - when you throttle up to move the sled, it bogs. I adjusted the HSN to get it to move & ran it for 15 minutes at various speeds. Came back to shop & it would not idle anymore. So I ajusted the HSN back to closed & it idles again. It appears in order to move the machine the HSN needs to be open about 1 turn, but this setting will not let it idle.

Any idea what could be going on now???

Post by **Matt** » Tue Jan 01, 2008 11:54 pm

We have the same problem - I was working on a carb today doing the same thing. If I figure it out first, you'll be the first to know.

flacker36 · Post by **flacker36** » Wed Jan 02, 2008 1:15 am

Thanks - I hope one of us figures it out.

One thing I did notice with the HSN closed is that it will not start very easy. I know the solution is not to run the machine with this setting. I was thinking I had weak mags, but know I'm back to the carb.

400brian · Post by **400brian** » Wed Jan 02, 2008 3:21 am

At idle, no fuel should be flowing from the HS needle, it's position should have no effect. The throttle plate uncovers the idle ports in sequence as it is opened.
The HS has no role until intermediate throttle position, when the air bleed in front of the needle mixes air with fuel to supply the intermediate ports.

Check your air bleed, it is a very small hole in the bottom of the bore, between the choke and needle.

The Walbro is different from many carbs, in that the idle circuit remains functional as the throttle opens and the vacuum signal drops. At WOT, EVERYTHING is flowing fuel.

On Start up, with the choke closed, again, EVERYTHING is flowing. So the HS setting would effect that.

flacker36 · Post by **flacker36** » Wed Jan 02, 2008 1:50 pm

Thanks - I will take it apart agian & check for any passages I may have missed.

Are there any you can't see that I may be missing?

Also - Should the throttle plate have the hole in it or not?

If in fact I need a needle valve, where would I get them?

400brian · Post by **400brian** » Wed Jan 02, 2008 5:33 pm

Look on pages 30 / 10-2 and 30 / 10-3 to see what I am talking about. It shows the location of the air bleed on 10-3. ( SM2100 )

I dug out a '72 Walbro and took a look, it appears to have two dimples and one small hole. Photo attached. This carb is off a '72 400 that has been in our possession since '73, don't think it has ever been touched.

I was thinking a needle comes in the full ( genuine ) Walbro kit.

flacker36 · Post by **flacker36** » Thu Jan 03, 2008 12:16 pm

Sounds great I will check it out. Also thanks for the pic of the throttle flap - I will drill out the JB weld I closed it up with.

I did buy the genuine walbro total rebuild kit & no HS or LS needles came with it.

Hope this new info works out!!

400brian · Post by **400brian** » Thu Jan 03, 2008 4:41 pm

Oh, THAT needle!

I never throw anything away, If I could find the remains of that full kit I might find out for sure.

flacker36 · Post by **flacker36** » Thu Jan 03, 2008 11:28 pm

Well - not so good of news. I removed my JB weld & openned up the small hole on the throttle plate. I also found the air bleed hole which is wide open. I still think it is something in the carb instead of weak mags. I adjusted nothing, & it now will not idle with the HSN all the way closed.

Does John Deere still even work on their own machines? or are we it for figuring this thing out? I do have a small engine repair shop around & many polaris dealers around.

400brian · Post by **400brian** » Fri Jan 04, 2008 4:23 am

The full kit I have apparently came with no mixture needles.

I doubt you can find a Deere dealer who has a mechanic that has ever seen a JD sled.

Danzig · Post by **Danzig** » Fri Jan 04, 2008 2:04 pm

The JD sleds.com admin. dept is rebuidling carbs, testing them and ..... I will let them take over from here....

HoosierDeereMan · Post by **HoosierDeereMan** » Fri Jan 04, 2008 4:35 pm

I know you said that you had rebuilt this carburetor, what did the throttle shaft look like where it works in the main body of the carburetor? I've had some of the same idle issues that you guys have been talking about. I had sprayed ether around the crank case halves, crank seals (Flywheel side is next to impossible) and around the intake. One place I never thought of was to spray around the throttle shaft bores. Sure enough if I turned the shaft about 1/4 turn I could wiggle it up and down in the bore. I tore the carb apart and found the shaft to be worn very badly. The book states to set the throttle cable with I believe 1/8" play before the throttle opens. I'm guessing this is to compensate for any engine vibration and handle bar flexing. This one wasn't set with any play so I'm assuming that is what caused most of the wear. I did try a good throttle shaft in this body and it was also loose. So I assumed that the bores were worn as well. If these are worn alot it could allow air to leak into the carb and cause a lean condition at idle.

flacker36 · Post by **flacker36** » Sat Jan 05, 2008 9:25 pm

I'm in luck, my local JD dealer has a mechanic that use to work on JD sleds. Though he does not anymore, he is a wealth of information. He recommended eliminating vacum leaks by submerging the entire engine in water & pressure testing with 7 - 10 lbs. of compressed air. If any leaks, you would see the bubbles. I just got done, no leaks what so ever - I now know it is not a leaking seal, head gasket, base gasket or mating surface problem. While I have it open, I will put in new condensers (points are new) assemble, set points & time. I also will put 2 new external coils on.

Great point on the throttle shaft! I did not pull the shaft out of the body. I will do so & see if worn.

flacker36 · Post by **flacker36** » Sun Jan 06, 2008 1:19 pm

I may have stumbled on to something. When I recieved my new points & condensers, I new they looked different from what was in the machine. I figured after 30 years or so design most likely would have changed some. I used the points, but the condensers were not the right ones - so I didn't use them.

The points I ordered were part # 025 & condenser # 043.

I know I have condenser # 045 & according to Central, the points to match are part # 027.

My machine is a KEC 340, but not an E & G (which designates the year 1976 & 1977) mine is an A which is 1972.

I am going to buy a set of 027 points along with a set of 045 condensers (being that they are somewhat cheap) to see if the points resemble the old points. Only one major problem, I throught the old points out - but I think I can remember what they looked like if I see them.

I don't know if this could have anything with the non-Idle issue, but one step at a time.

Joe

400brian · Post by **400brian** » Sun Jan 06, 2008 7:40 pm

Yes, as I recall, the points are different.

The '72-75 400s used a Kukosan ign., but the part numbers for the points are different.