Strange carb problem

[brian kirby]

The bike is a '77 MC5 400 with the stock Bing 38mm. If you stall the bike while riding it by locking up the rear wheel it acts just like if you tipped over and loaded the engine up with fuel. If you just ride back to the pits and stop, it restarts fine, but if you kill it while riding you have to turn off the fuel and kick it 73 times to clear it out so it will restart. I expect that to happen when you fall and dump all that fuel into the engine, but I can not figure out why it would happen just stalling the bike and keeping it upright. Its really a problem because I cant be aggressive while riding it for fear of stalling in the middle of a race. I dont believe its a float level problem because the bike will start and idle for 10 minutes without loading up, which a high float level or a bad float needle would flood it idling.

Any ideas? I am thinking about going with a Lectron instead of the Bing.

Brian

'72 Berkshire

[Dale Fisher]

I have a 125cc with a Mikuni.  Our wonderful Michigan E10 with ethanol ate the rubber off the end of the gas supply needle.  I have to be sure to shut off the petcock when I stop or I receive the same loaded up results.

[john durrill]

Brian,
 Does your Bing have the screen around the main jet? Its a baffle to keep fuel supply stable on rough ground. If it's missing , on a hard stop the fuel in the bowl could flood straight into the intake track. Just a  thought. If its the float needle ( one with the rubber tip leaking ) you could  order a new float needle and seat. Bing offers 2 kinds , one with the rubber tip and one that is just a polished metal tip.
 The Lectron will work a lot better than the Bing but its a good chunk of change. Get one that has the power jet option if you order one.
john d

[brian kirby]

John,

I was already leaning towards a Lectron after taking a spin on Speedy's bike at Combs, his bike ran almost like it had a reed valve, I was shocked. If a Lectron will make this 400 smooth out and run that clean down low, it is worth the extra dollars.

Brian

'72 Berkshire

[john durrill]

Brian,
 Give Speedy a nudge and see what size he thinks would work best.
We have the cable choke option on the 2 we have working. Its nice on cold starts to have every thing at your finger tips , especially when your short like me [8D]
 Pin floats , power jet with the short nozzle for piston port engines ,cable choke option . Get the cable adjuster that  bends over about 45 degs. Terry had some of the Penton style air boots to hook it to the air box. I can look around and find some pictures of one Larry V. has on his 75 250. He went a little different route that we did. May give you some ideas on how to get the intake , carb and air boot box to line up clean.
You will like it a lot when you get it jetted right.[]
John D.

[Ernie Phillips]

Hold on a minute Brian!  When you say that back in the pits it starts just fine – remember that "back in the pits" you use your step-stool to position your 5'-4" frame over the kicker.  In the woods, you have no such advantage.  So, just because your 140 pound bony butt is too puny to kick a 4 hundert with authority, don't go blamin' that dad-um Bing!  Remember, back at Ocala when you had to kick the ol' Maico several times ... and when I got a-hold of it, 1st kick?

Before you dump the Bing, spring for a compression release and some of those 4" high-rise boots.


Ernie P.
Chattanooga, TN

[firstturn]

Ernie,
  He could always have Christopher start it[B)].

Ron Carbaugh

[Ernie Phillips]

Good one Ron!  Maybe he should get Christopher to RIDE it for him.  You know, he had a '79 440 Maygo that "whipped him like a rag doll" last year.  I think he truly believes that the Mint will be easier to handle.  All joking aside, there aren't too many riders who can "handle" a large bore in woods ... certainly not me.  -EP

Ernie P.
Chattanooga, TN

[john durrill]

Brian,
 Ernie is just jealous chuckle chuckle. He is running a 40 lb weight
penalty on all his bikes.
But he did bring something to mind the could be a factor. What ignition are you running ? PVL with out weights or an internal rotor Motoplat would give you the stall / engine kill in a hard stop.
 We had an 86 XR 250 we modified some. One of the thing we did was lighten the ignition fly wheel 1/2 to 3/4 of a lb. after that the engine would stall / quit under had braking in a corner.
Anyway a heavier flywheel or the 78 weighted 400 crank would help that a lot.
 The Lectron will give you faster lap times for sure. You know how well they work from riding Speedys bike.
John D.

[firstturn]

Ernie,
  Good post...and Brian needs a flywheel off a Maytag gas engine(see haow many people know what this is...hint, it ran washing machines) and a 36mm Bing.  He would fly with as you say "140 pound bony butt".  I think Brian should run a 125 Penton in the open class.  Thanks for all you have done to understand and develop Sachs engines.  Keep those extraHorses in the barn.

Ron Carbaugh

[DKWRACER]

Hi all, being V-challenged at 135 lbs. I do run into similar issues....A comp. release on a 400 will help, finding one, might be an issue...I suppose one could de-tune with raising the X to .050 and a thicker head gasket. Didn't stock 400 already have heavier web fly-wheels, which should have helped as well....

Grip n Rip....


Adios,
Tom Brosius

[linglewn]

Ron,
I remember the Maytag motors. I put one on the first go kart that I built when I was about 11 years old. The exposed flywheel had a cast-in fan with a ring around the outside. It had such little power that the best was to stop it was to drag your foot on the flywheel. The best part was the built-in kickstarter. The power was so meager that I replaced it with a Reo lawnmower motor.

Nelson Lingle
73 Jackpiner
71 DKW 125

[Ernie Phillips]

Since we seem to be drifting off-topic, check out this week's handiwork: Kerrville Special (RC4).   Should be plenty zippy with 6B crank, PVL and high flowing Bing.  Of course since I'm +40lbs, I need all the zip I can get.



Ernie P.
Chattanooga, TN

[firstturn]

Ernie,
  This is a R rated picture[:0].  Looking good.

Nelson,
  Nice post and I should have know you would have know this engine.



Ron Carbaugh

[brian kirby]

I see you fellas have been having a little fun at my expense. Thats fine, I'm a (figuratively) big boy, I can handle it.

I do need to clear up a couple of things for the record though:

1. I am not 5'4" I am 5'7". That might not seem like a big difference, but from where I stand it is. I am around 145lbs, which can be a serious issue kicking a big bore.

2. Christopher could not start the bike either the first time this happened, we had to pull the bike off with a Japanese bike, which had neither a Motoplat nor a Bing.

3. Cold starting is not a problem (and thus the bony butt issue is eliminated from the troubleshooting flow chart). It starts first or most often second kick cold or hot in the pits, its hot re-starting on a stall that is the problem.

Now, for the serious stuff.

John, the bike has the stock Motoplat with an external rotor which I assume is lighter than the GS? I'd really like to have even more flywheel weight than it has now, and I would not consider any internal rotor ignition. I rode Chicago Jerry's 250 with a PVL and its flywheel was too light, they are ideal for the Sachs or smaller KTM, but my opinion is the 250-up KTM engines need more flywheel than the PVL has, at lest for trail/CC use.

I also think you may be onto something with the screen/baffle on the main jet John. I know the screen is not on there, but I didnt really consider that as possibly being an issue. Now that you mentioned it, I noticed that the carb is mounted at such an angle that under hard braking fuel could indeed flood through the main jet with the throttle shut. If the engine keeps running you probably never notice it, but if you happen to stall it floods.

Brian

'72 Berkshire