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Hi guys, i'm having problems with my 350 (wc) scrambler and I'd appreciate any thoughts ….it doesn't want to run when revved up past 1/4 or 3/8th throttle and it starts to miss and backfire as it looses all its power. As soon as I cut the RPM's back a bit it runs great. It really seems to me like the timing is just not advancing or off.

Long story, but here's the short version:
It has a complete Electrex World Digital CDI ignition kit with the alternator. (STK-164)
It has a brand new Amal carb on it.

I had the whole bike running well with this set up but had to take the motor all apart to fix an issue with a missing transmission shim from the previous owner. When I put it back together I had it at TDC and aligned all timing dots up top and dots down below.

Question 1:
I read somewhere about the 450 Ducati having a special mark on the timing gear (off its dot?) that needs to be used. In another post a guy with a 350 said he has to use this same mark/alignment procedure to make his 350 happy. Am I doing something wrong when I align all the dots and then put my degree wheel on my 350 to set the pickup at its total advance setting?

Question2:
I know CDI's can fail, but short of contacting the company who sold me this..... is there anyway to test it? All I've tried so far is I ran a separate (additional) ground wire from the coil, to the CDI and back to a good ground. This didn't seem to make a difference.


Like I said, this setup worked really good before I tore it all apart and I haven't changed the carb settings or anything, I've convinced myself this is timing related. In true fashion, … I didn't align everything and take note of things before I tore it apart…..just figured it shouldn't be that hard to put back together. (I blame the beer, the dog or my wife )

Appreciate any thoughts, (….other than stop drinking beer lol)

-jeff

If it was running fine before the teardown, then I would think that the problem is to do with something not put back right. Is it a Mototrans engine? Jon Pegler on here points out that the Mototrans bottom crank bevel has two timing dots, which changes the timing by one tooth.

What about the earth wires? I have known something like this happen when an earth wire has come loose - the engine will run fine at low revs, but die when given any throttle.

Other suggestions will be forthcoming!

Hi Duccount, thanks for the reply.

"What about the earth wires?" That was also my first thought too. What I didn't mention in my post is that when I tore down the motor to get into the tranny, i also painted the frame. So the other day before I ran that separate ground wire (to the coil ground and the CDI bolt) I used my meter and did a wack of continuity checks from my main ground on Neg battery terminal to the coil, engine, etc etc. I also unplugged my bikes wiring so the there was no keyed loads or kill switch hooked up to the main ignition components. (their system will run without a battery) In my mind I think I'm grounded properly and don't have a kill switch or ignition switch shorting my CDI or coil.

As for being a Mototrans motor I have no idea. I don't how to tell. I'm also at work right now

Thanks for suggestions, I still suspect this thing should run..... and that I did something wrong with the timing marks.

-jeff

AMyquestion: what is a "transmission shim"?

Your question 1):
It does not matter if you aligned the timing shaft gear on a dot or a line (which is indeed meant for the 450), as long as the spark appears with the correct timing. This can be basically checked by a visual inspection, as the Electrex PU rotor and stator have the necessary timing marks (I suppose). A indispensable requirement is, that you afore have turned the crankshaft into T.D.C. position when you try to statically align the markings on the PU stator and rotor (for your 350 to 38°). If you realize the slot holes not being long enough to get the correct position, you might reposition the timing shaft gear by one tooth, forwards or backwards as needed.
For a precise check/alignment, you should use a timing light/stroboscope, https://www.amazon.co.uk/s?k=timing+light&i=automotive&rh=n%3A248877031%2Cn%3A5136307031&s=price-asc-rank&dc&qid=1586103509&rnid=1642204031&ref=sr_st_price-asc-rank.
I use this one: https://de-jbtools.glopalstore.com/equus-3568-digital-timing-light/?gclid=EAIaIQobChMI66zkhdrR6AIVj4KyCh2GOQz-EAkYAiABEgLpOPD_BwE

Question2):
Your grounding wire is OK, but obviously does not solve the issue.
The CDI seems to work in principle, otherwise the engine would not start. Again: get a stroboscope light anf check the action of the electronic AAU. This can be done with the bike on the stand, at no load. You need about 5000/min to see if your "FA" mark on the PU stator is reached by the line on the rotor.

Good luck ;o)

Hans

Hi Hans.
Makes perfect sense now...

I'll hunt down a strobe and give you guys a update later this week.

thanks
jeff

You will also need a pointer that screws into the end of the crankshaft, to use with a stroboscope.
The pointer has a tongue that engages with slot on crankshaft. When it spins its pointer indicates, so it needs to be accurately and rigidly made.
Just mention it in case you have a go at making one yourself.

After they started making 450s, two marks were cast into the clutch cover - a dot for 250 & 350, and a line for the 450.

I suspect Hans has put you on the right track; but just for reference:

Ducati350ontario wrote:As for being a Mototrans motor I have no idea. I don't how to tell.

Check the engine number: Bologna engines start DM. Barcelona engines, MD.

Come on now, Craig keep up.
We've been here before.
All widecase engine numbers start DM whether they are from Bologna or Barcelona.
I would suggest you look on your Vento motor but...

That said, they engine number would probably indicate where it was from.

Jon

Jon Pegler wrote:Come on now, Craig keep up.
We've been here before.
All widecase engine numbers start DM whether they are from Bologna or Barcelona.
I would suggest you look on your Vento motor but...

That said, they engine number would probably indicate where it was from.

Jon

. Allow me a little brain fade now and then ...

(DM350 74349. See? I haven't entirely forgotten ...)

The engine number is DM350 07211

The guy I bought it off of said he thought its a wide case scrambler and likely a 1969. He didn't have the registration so I manged to get a new registration and called it a 1969. It has "made in Italy" on both sides of the motor and also on top of the bevel housing .

I'm assuming its not a moto-trans?