Can't get it running

[Andreas Piepke]

Hi All,

I put my 1973 Hare Scrambler together but just can't get it started.

1) The Motoplat ignition has been load tested, the magnet re-magnetized. There is spark when watching the removed spark plug.
2) I am using a Champion L78C spark plug which should be the equivalent of the NGK B8SV. I couldn't find the NGK.
3) I re-checked the ignition timing, it is set at 2.55 mm BTDC (I rotate the rear wheel back after reaching TDC and measured with a dial indicator).
4) I tested the engine's (freshly rebuilt) compression and measure 165 psi. I think this should be sufficient, I didn't mess up when setting the deck height I conclude.
5) There is gas in the engine. After kicking the engine over a number of times (>30) the spark plug is wet. I cleaned it a number of times in the process. I use 98 octane ethanol-free leaded gasoline (mixed from 112 octane race gas and ethanol-free 90 octane pump gas). I am using a 1:32 pre-mix ratio (Maxima Super M synthetic race 2-stroke oil).
6) I installed all new jets in the Bing 54 carburetor: new float needle and seat (I measured the fuel volume to be about 40 ml when the float valve is blocking, the floats are adjusted parallel as described in the instructions), a 46-281-01 jet needle (set to second notch from top), a 290 needle jet, a 165 main jet, and a size 40 pilot jet. This is as close to the manual as I could get.
7) I am using a foam air filter.
I have checked all air ways (inlet and outlet) and found no obstructions in there (rags or debris).

There is spark, gas, and compression! I also tried push starting but that doesn't work either, the engine has good compression and the rear wheel blocks at the kind of hill we have here. I am kind of at my wit's end at this point. Any ideas what else I could try?

Cheers

Andreas

[Paul Danik]

Have you changed plugs trying another, possibly one from a running motorcycle that is for sure not fouled, or another brand new one?

Good luck...

Paul

[Andreas Piepke]

Hi Paul, I am using a brand new spark plug. The only thing I could think of plug wise is to get an NGK, but I can't find one here.

Thanks for your input!

Andreas

[Richard Toghill]

Have you changed the plug cap? As I recently discovered, Motoplat ignitions will only work with a non-resistor type plug cap.

[454MRW]

A new plug does not guarantee good. Change plugs & squirt some gas/oil into plug hole & try it. It takes a great deal of gas to fire a dead cold KTM engine. Try to find a NGK B8HS plug. Mike

Michael R. Winter
I enjoy rebuilding and appreciating Pentons!
1974 250 HS Pentons-1980 KTM 175-400'S
1975 Can Am 175 TNT & 77 250 Black Widow
1979 Husqvarna OR390
1976-78 RM & 77-79 PE Suzuki's
1974 CR250M 07 CR125R 79 CR250R

[Andreas Piepke]

Thanks for the ideas! Actually I do use a new, non-resistor cap. I think I'll try Michael's suggestions, both of them!

Cheers

Andreas

[SouthRider]

Make sure that the air filter is not over oiled. Try starting with no filter.

Is the jet needle seat facing the correct direction?

_____________________________________________________________________________________

"We the willing, led by the unknowing, are doing the impossible, for the ungrateful. We have done so much, for so long, with so little, that we are now qualified to do almost anything, with nothing."

1972 Penton Berkshire 100
1983 Husqvarna 250 XC
2011 Jayco 31.5 RLDS
2009 Chevy 2500 HD Duramax

[Andreas Piepke]

I haven't oiled the air filter yet, so this ain't it either. Which part is the jet needle seat?

Thanks!

Andreas

[dennis brown]

sounds silly but check the pipe.i have seen plugged pipes before

dennis l.brown

[Andreas Piepke]

Actually a clogged connection sounds quite plausible. No gas flow=stalled engine. I've checked some time back:



I can put the plumbing implement seen in the picture above through the pipe until it reaches the spark arrestor. I was worried to find some residue from "biological activity" in there. However, nothing was found. I even fashioned a little mouth piece and verified that I can blow air through the pipe.

Cheers

Andreas

[slvrbrdfxr]

After looking at the picture of your bike it appears to have a freshly painted frame. Did you remove the paint on the engine to frame contact points and apply dielectric grease to ensure a good ground path ?? The motoplat ignition must have a very good ground path to work correctly. Let us know what you find.
Dave McCullough

[Richard Toghill]

If you cant get it running, I'll have it! [][][]

[rob w]

Andreas wrote -> 3) I re-checked the ignition timing, it is set at 2.55 mm BTDC (I rotate the rear wheel back after reaching TDC and measured with a dial indicator).

Andreas, When timing, it's easier just removing the right hand side cover, and turning the flywheel with your hand. I would think more accurate also.

Bob

[454MRW]

On all my Motoplat ignition bikes, I run a separate ground wire from the coil mount to the engine or stator mount plate to insure a good ground, so I don't need to remove paint from the frame or worry about loosing ground due to corrosion or bolts loosening from vibration. Mike

Michael R. Winter
I enjoy rebuilding and appreciating Pentons!
1974 250 HS Pentons-1980 KTM 175-400'S
1975 Can Am 175 TNT & 77 250 Black Widow
1979 Husqvarna OR390
1976-78 RM & 77-79 PE Suzuki's
1974 CR250M 07 CR125R 79 CR250R

[SouthRider]

What I called the "seat" is actually the atomizer or vaporizer.

It has a half moon cutout on the top where the needle "seats" into it.

The open side should face the engine so that as the needle is raised by the slide that fuel can be drawn from the float bowl.

If inserted the wrong way the incoming air flow would not allow fuel to into the engine.

_____________________________________________________________________________________

"We the willing, led by the unknowing, are doing the impossible, for the ungrateful. We have done so much, for so long, with so little, that we are now qualified to do almost anything, with nothing."

1972 Penton Berkshire 100
1983 Husqvarna 250 XC
2011 Jayco 31.5 RLDS
2009 Chevy 2500 HD Duramax