72 JD 400 WILL NOT IDLE

flacker36 · Post by **flacker36** » Sun Dec 30, 2007 1:48 pm

I have a 72 JD 400 that will start & run, but will not idle. The engine will stay running if I feather the throttle or am going at high speed. I am at wits end & am looking for some help. Here is what I have done:

- rebuilt engine from ground up (new crank, pistons, rings, gaskets, seals etc..)
- pressure tested the engine, ether & soap/water tested all seals & mating surfaces all = no leaks at all.
- new points, plugs & plug wires.
- Timed the ignition.
- rebuilt walbro carb with walbro rebuild kit.
- replaced all gas line & am running premium gas.
- I have adjusted the carb a billion different ways including the metering lever & it still will not idle.

I HAVE NOT DONE THE FOLLOWING:

- replace the two ignition coils.
- replace the two ignition generating coils.
- replace the two condensors.
(would replacing any of these help?)

The engine will start (not the easiest) but seems to want to bog out unless you feather the throttle. I have had it out & while running it seems fine. The minute you stop & want it to idle, it starts to bog down & then dies.

Any ideas out there!!!!

Joe

400brian · Post by **400brian** » Sun Dec 30, 2007 4:59 pm

Sounds like you have been through things pretty well.

It sounds like it is not getting enough fuel at idle. After you attempt to idle it, are the plugs dry?

Vacuum leak at the intake to jugs, or carb? You've probably thought of that.

Does turning the idle screw have any effect at all?

flacker36 · Post by **flacker36** » Sun Dec 30, 2007 5:55 pm

The only time the plugs have been dry, is right after I took it out & ran if for 10 or 15 minutes. Most of the time the plugs are wet to very wet. I have changed plugs multiple times with no improvement. I have checked for leaks around the intake & found none. If anything, I think the carb is pumping too much fuel. I have adjusted the metering lever to both ends of the specs with not much improvement. Turning the idle screw in all the way dies it out. Turning it all the way out, hardly does anything.

I have not adjusted the metering lever beyond the specs, maybe I should try that.

I start out with the idle screw set open one turn & the high speed screw open 7/8 to one turn. It does seem to run better with the high speed screw at the 7/8 open.

Are these carbs WR7-5 really that tricky to set?

What about the coils & condensor? I did not replace them due to the fact I have spark & it does run.

The service manual mentions a "Spark retarding mechanism" any idea what it is & where located?

Joe

Danzig · Post by **Danzig** » Sun Dec 30, 2007 8:29 pm

Have you taken torch tip cleaners or similar objects to the small holes in the idle circuit? If not , do so. How clean is the fuel filter? How is the fuel filter positioned on the sled? Positioned vertically or horizontally? If horizontal, how much fuel is in the filter at idle, half full or completely full?

YOU WILL BE AMAZED WHAT A SMALL CLOG IN A FUEL FILTER WILL DO, IT MAKES YOU BRAKE THINGS WITH LARGE HAMMERS AND DRINK COLD ALCOHOLIC BEVERAGES UNTIL YOU CANT SEE STRAIGHT......

:blink:

This sounds like my X8 problem last year before the Hall of Fame ride. It ran better with the high speed needle almost closed off.

The problem............microscopic rust in the fuel filter,you can barely see it.

400brian · Post by **400brian** » Sun Dec 30, 2007 9:20 pm

Are you bending the metering lever in the correct place?

And NO, it should not be that difficult.

flacker36 · Post by **flacker36** » Sun Dec 30, 2007 11:30 pm

Yes - I have cleaned out all the small idle ports with cleaner, compressed air & a torch tip cleaner.

I have two new inline filters, one in the tank with a check valve, & another about 10 inches from the tank. The inline filter lays semi horizontal & seems to be half full or less. I have only run about 2 gal through the machine so far.

As for bending the metering lever, I hold down the bumper ( the part the touches the diaphragm) & bend the other end that holds the needle valve.

Are the coils (ignition & ignition generating) prone to going bad on this engine???

MARK · Post by **MARK** » Mon Dec 31, 2007 12:03 am

Are the clutches set correct???? correct belt?? easy check,remove drive belt and start,does it start easy? DONT' REV MOTOR UP!! "bad for clutches"if all works fine then check clutches or make sure you have the right belt on it

Mark.

JDFanPa · Post by **JDFanPa** » Mon Dec 31, 2007 12:33 am

you are bending the wrong end of the metering lever and keeping the needle from seating most likely and its flooding the motor

400brian · Post by **400brian** » Mon Dec 31, 2007 2:29 am

send an email to: < ca-2@centurytel.net >

And I will send you the page from the manual that shows this.
I'll let you decide if you have been doing it correctly.
Then we'll go from there.

JDFanPa · Post by **JDFanPa** » Mon Dec 31, 2007 3:05 am

BrIAN i SENT YOU AN EMAIL THEN i REALISED i READ YOUR LAST POST WRONG MUST BE TIRED HERE BUT SEND ME THE PAGE ALSO

flacker36 · Post by **flacker36** » Mon Dec 31, 2007 12:06 pm

I do have the service manual SM2100 from JD. I have the diagram of how to adjust the metering lever - so I believe I am going about it right.

As for the spark plugs, I have Champion L-82c (the L-82 replaced the L-81)gapped at 0.020 in. I have not tried any other plug, but the previous owner ran the AC S-42F.

I am using 1/4 ID fuel line, should I be using 3/16 ID?

I am going to adjust the carb again, & see what happens. With the amount of adjusting I am doing, you would think I would get it right once. These carbs shouldn't be this touchy to adjust. My attention is starting to go back to air leak or weak mags.

flacker36 · Post by **flacker36** » Mon Dec 31, 2007 1:53 pm

Ok - I just adjusted the carb for the umpteenth millionth time with the same outcome.

The carb can not be so difficult to set just to keep the machine running.

I also just did another starting fluid check at every place air coud be sucked in & no increase in RPM.

I really think I have a couple or one weak mag.

Any thoughts?

400brian · Post by **400brian** » Mon Dec 31, 2007 4:01 pm

Did the engine run before the rebuild?

If you have SM2100, you have the proceedure to check the ignition system.

We rarely see bad coils and such here. But, back in the day, I had a coil ( not sure if it was primary or secondary ) go bad. As I remember, the sled was hard to start, would idle, but would not make power.

JDFanPa · Post by **JDFanPa** » Mon Dec 31, 2007 5:52 pm

after seeing the manual page from Brian I stand corrected on where to bend the tab.

flacker36 · Post by **flacker36** » Tue Jan 01, 2008 11:05 am

When I got the machine, it had been sitting for around 8 - 9 years outside under a cover in N. Wis. The rest of the sled is in really great shape for the age. The engine had blown a connecting rod bearing. I replace with a new crank, seals, bearings & connecting rods. The cylinder walls were honed, pistons were ok so I reused them. I put on new needle bearings, wristpin, c clips & rings. I rebuilt the engine word by word from the service manual.

I checked the compression & it is right on the money.

I ran it yesterday, & it did seem to idle somewhat when I had the high speed needle all the way closed or slightly open. When I took it out though, it would bog when asked to go WOT.

ONE LAST THING, WHEN I GOT IT A SMALL HOLE HAD BEEN DRILLED IN THE BOTTOM PORTION OF THE THOTTLE FLAP (THE ROUND DISK). THE ENGINE STILL BOGGED THEN, BUT I DID JB WELDED IT SHUT.

SHOULD THAT HOLE BE THERE? IF SO, OPEN OR SHUT?