Good starting, but non-running Sachs

[John E]

I put my rebuilt 33-year-dead Motoplat back on and it fired on the second kick! But it still quits when I open the throttle. What am I missing? It seems like it's choked for gas, or getting air from a leak, but I can't find one. I've been through the carb twice, and have gone up to a 2.76 needle jet and raised the needle. The plug is not wet. I have the feeling I'm missing something simple and stupid.
Suggestions?

John

[slvrbrdfxr]

John,
The problem you are experiencing sounds like it could be ignition related but give us some more details please. I didn't understand your comment about the rebuilt 33 year dead Motoplat. Did you have a 33 year old Motoplat unit rewound ?? If so thats fine but has it been tested in another bike to ensure it's working properly ?? I think one of the first things to do is establish a good ground circuit on your bike. A faulty ground on a Motoplat or any ignition for that matter can really create headaches. I suggest displacing the engine to cleanup the mounting points on both the engine cases and frame especially if you painted the frame or engine as part of a restoration. Also remove the ignition coil and cleanup the frame and coil mating surfaces. Last but not least, remove the entire Motoplat stator and mounting plate to cleanup the mounting plate and engine case where the plate mounts including the threaded holes. Clean all the surfaces so that shiny metal is exposed and then reassemble everything using a coat of dielectric grease on all the mating surfaces. Once that is done it should create a good troubleshooting start by eliminating a bad ground as the source of the trouble. If cleaning the ground circuit doesn't help then I suggest swapping the coil and or Motoplat stator with a know good unit to see if the problem goes away. Hope this helps. Let us know.
Dave McCullough

[John E]

It is behaving exactly as it did with the Bosch points system I put on all those years ago. That is why I have discounted an electrical issue.

John

[Rain Man]

Sounds like its outta gas, Check your fuel screens, and see if it runs out of the tickler also.

Raymond
 Down East Pentons

[454MRW]

John,
Make sure that there is not a mouse nest or other obstruction in the exhaust pipe also. Once in a while I read a post about a rag left in the exhaust port flange or airbox boot that was forgotten when the pipe or carb was re-installed. On the bikes that I build to be ridden a lot, I like to run a separate substantial ground strap from the coil mount to the engine case boss where the rear engine support strap attaches for that extra measure of reliability. Motoplats really need good grounds to perform at their best. I don't trust frame to engine mounts as ground paths, because the engine mount bolts tend to loosen from vibration fairly often. Mike

Michael R. Winter
I enjoy rebuilding and appreciating Pentons!
1974 250 HS Pentons-1980 KTM 175-400'S

[John E]

It tickles just fine-even though one of the taps leaks a little, just for fun.
Would the ground issue cause it to start well, but not pick up revs?
I'll run a separate ground. I had to do that on my Husky but it would not start at all before I ran it.
Thanks, guys, I'll let you know what happens.

John

[linglewn]

Check to make sure that the pilot jet is not plugged. I had a non-Penton that exhibited similar traits and it ended up that the pilot jet was completely plugged. Cleaning it out allowed it to transition from idle to mid-range. Good luck.


Nelson Lingle
73 Jackpiner
71 DKW 125

[Doug Wilford]

Make sure your atomizer is not in backwards if it is a half moon type

[Big Mac]

Start with the easy...follow Mr. Lingle's suggestion and pull the pilot jet. Hold it up to a light, see if it looks clear. Try another one of same size if you have it, or use a copper strand from an electrical wire to gently clear it.

Twice I've had bikes that I was sure had electrical gremlins, only to find both times it was a clogged pilot from sitting too long/old fuel. On one, it would only run at 1/2 throttle and above, and only after bump starting. The other started and ran at low rpm or idle, but died just off the bottom as you describe.

Jon McLean
Lake Grove, OR

[John E]

Jon--I was certain it was clear, and it was.
Doug--Thought of that--because I did it on my 400 once!
I forgot about checking the exhaust and will do so tonight.

The only thing changed recently is plugging the the choke opening in the carb body. I checked that and it is sealed, still.

John

[Doug Wilford]

If the choke is sealed, did you also seal the small hole
at the intake spout?

[John E]

Doug:
At the mouth of the carb?

John

[Doug Wilford]

Yep that is the place. at about 5 o'clock position.

[John E]

As usual, you are correct Herr Wilford!
You've saved me twice now.
Thanks!

John