Bing Jets and Needles

[Bill Campbell]

I know I have posed this question before but i still don't have a solution to my problem. I have a wonderful 76 400 that is great to ride except for one problem. When I close the throttle the engine just wants to keep on running as though it is way too rich ( I think). I have a 324 needle jet,195 main a 45 pilot and a 230 slide but I have no idea what needle I am running. This is per the July 1976 KTM riders pamphlet.

Can any body out there provide me with the correct needle specs as I suspect my needle is too thin.

What set me thinking again was I have just rebuilt an 81 250 that has a 38 mm Bing. That carby has a 276 needle jet which is similiar to the needle jet in my 74 250.

Cheers Bill Campbell
ps 81 250 is an interesting bike

[t20sl]

Bill:  I would suspect a air leak more than too rich of needle.  My reasoning is that it won't run without air or fuel.  If you chop the throttle and the slide is closing then you have cut the air supply unless it is getting in from the mag seal or the manifold.  Have you taken some either and spayed both those areas to see if engine speeds up?  Will the engine idle eventually or does it just die? Ted

[tomale]

Ted is correct, regardless of what jets you have in then, either too rich or too lean, when you shut off the throttle it should idle right down, whether it stays running is another matter altogether. It sound to me like you are having a air leak problem,in addition to what Ted has listed there are a bunch of little things that can cause air leaks that alot of people over look too. Check the o ring on the air mixture screw, The o ring on top of the carb, and the rubber boot where the cable comes into the carb and the rubber gasket in the bowl. Check the float level too if it is too low and the gasket leaks it is possible that you are sucking air up through the bowl. In addition to that, It is possible that even though you have the right jets, needles and slide they could be so worn that they are giving you false readings. I was talking to the rep from the Bing agency and he suggested I replace the needle jet and the jet needle, They wear pretty fast and they need to be changed from time to time. Also the pilot jet could be suspect as well, if it has been in there for a long time it is a good idea to replace it. When he told me what I am telling you, I wanted to dismiss it because I could not see or feel anything that made me suspect that the needle was bad, I could not imagine that fuel could cause the jet to wear that much and I could not imagine that a little air leak could cause so much trouble, but I changed them and wham I was in business again. oh and don't over look the O rings, they may only cause a small air leak but if they are all bad then it can be accumitive. Bing also has a listing for what jets are correct for your bike. you can use this to double check the listing that you have.  Last year I was having some trouble with my Bing and I could not figure it out, It turned out to be a number of small problems that turned into one big one... hope this helps.

Thom Green,Still crazy after all these years!
76' 250 MC5 (orginal owner)
75' GS400 (project bike)
72'sixday (project bike)

[Rain Man]

Hi Bill and thanks Thom. I have the same  bike and had the same problem as you do Bill.  My 400's carbs been apart 4 times, the timings been checked and I tried all the little things Thomas mentioned as far as leaks go.  I knew I had a leak,, the carb was shut off so hard from air getiing in...
  Well low and behold I found the leak today.  While i was just getting started and the engine was revving to the moon after all the tinkering...  But I noticed the jug moved back when I cracked the throttle.  huh ?? wa ??
 The cylinder head bolts were loose allowing air to leak in around the cylinder base gasket... who would of ever thunk it.
 Anybody know the exact torque specs for this leg breaker 400 ??

 That bike now idles like a kitten  wow life is good again !!

Raymond
 Down East Pentons

[Knute]

Hey Raymond,

These big air-cooled cylinders and heads expand and contract a lot.  After a rebuild one year I had to retorque our 250 head/cylinder after 6 separate events until it settled down.  Torque them to 20 ft/lbs +/-.  I use an inch/lb wrench because most ft/lb wrenches aren't real accurate down that low.  Hopefully your head and base gaskets aren't damaged.  You should probably check them out if you could see the cylinder moving around.

Kent

[Bill Campbell]

Thanks for the tips guys.I have to go out and ride it again to check the theories and my memory. My description of the event was while riding the bike not just static revving. I have ridden the bike twice since a rebuild caused by the dreaded jug stomp. Blew the base gasket and let in heaps of crud. Pulled the motor down and cleaned everything. This time I checked the torques on the head and barrel after the first ride. Will now check for leaks etc after another torque setting. Here in Howards little hideaway I'm not sure where to chase Bing parts. Can you suggest a supplier in the States?

Cheers Bill

[Rain Man]

Hi Bill, On the POG groups  suppliers page, Bing International, in Kansas  
1 800 309 2464. They have the parts you need.
  BTW, what did you torque your head bolts to ?  I got a K/gm squared figure to work with

Raymond
 Down East Pentons

[Bill Campbell]

Thanks for the the address Rain Man. I will try that if all other avenues fail. I started the torque at 3 kpm (my 76 riders pamphlet)but I think I went to 4 kpm (the same as my81 250). Will check in the next few days or so. Cheers Bill