I'm stuck rebuilding a DT-1B magneto. My biggest problem seems to be new parts.

This bike won't have lights so I removed the two light stators, installed new points and condenser, assembled the plate, and mounted it back on the case. When I installed the rotor and set up a dial gage to fine tune the points adjustment I found the points stayed closed no matter how much adjustment I made. I also had some continuity problems. Hmmm....

I pulled the rotor off and found the top of the new condenser with the soldered wires had parted from the body... that solved the electrical problem. I chalked that up to cheap counterfeit parts. I slipped the rotor back on to work on the issue with the points and found they were not contacting the cam at all. I took the rotor back off again, took a close look at the new points, and compared them to the old points that I had tossed in a box. The height of the phenolic cam riser on the old points (which were badly worn) was .214". The new points are .185" - a gap of about .030" - that's about twice the rated gap when open.

The points came in a Diachi box stamped "218-81321-20"; when I checked the fiche for a -1B motor I got "1M1-81321-20". Am I a victim of a badly made or counterfeit part, or are there different points for the early 1B motors with a longer riser? The height of that riser is a critical dimension and these measurements looks way out.

I'm also confused about the gap. There's no mechanical adjustment for the points gap, only the time of opening - so I don't understand why I read about the proper gap being .015". The amount the points open is fixed by the geometry of the cam and the points. Once you adjust the points to start opening at the required BTDC distance (in this case 3.1-3.3mm) the gap is what it is. Or am I completely missing something.

Jumping straight to where you say there's no adjustment on the points--there has to be!! or something strange is going on like wrong points. Lets have a pic of what's going on if possible please. i can't think of any points that can't be adjusted unless the type which have a threaded base point on some twin cylinder bikes. Hope you get it sorted.

point gap should fall into the 012-015 range when properly timed. I recently bought one of these condensors and they are good ones, they are made to work with the Mitsubishi magnetos the early points mags use.

this one is for a set of points and should be the right ones.

the 250 and 360 use the same breaker points.

Holly molly $71.99 on Babbits bugger that. Says RH at the top. What's that mean? are they for a twin & the right side works on DT1's, i dunno, goota be wrong if non adjustable. www.babbittsonline.com/oemparts/p/yamaha...ontact-brkr-assembly www.babbittsonline.com/oemparts/a/yam/50...fd8/flywheel-magneto

here's the points you have 'i think' & look adjustable but do you mean you can't adjust enough by far.

No need to remove lighting coils, just don't connect them to anything. Some models have lighting coils tied to ignition coil so could be an issue.

Removing coils must also mess with something because on some MX bikes that used "Enduro"-type ignitions, Yamaha either left the lighting coils intact or used a dummy lighting coil core on most.

If rubbing block is wrong and it does happen, you might have misboxed or wrong points. Part numbers have been superseded over the years.

To answer what I think your questions are...

YES. You set the timing by adjusting the point gap.

YES. You don't adjust the point gap.

What you do is MEASURE the maximum point gap after setting timing. It should be within the specified RANGE... usually 0.012" to 0.015 or something like that. If say gap was too tight... like 0.008"... then you need new points.

Complication to this is the bigger bikes have slotted stator plates. You can mess with the rotation of the plates to get everything back in spec with worn points sometimes... the problem is that the you're also messing with the relationship of the coils to the magnets when the points open which could result in a weak spark.

Best to leave the stator where it came from the factory (usually about centered in the slots) and set timing by adjusting points.

I purchased the condenser that broke from Niche Cycles... in addition to it coming apart, the mounting tab is not placed in the same location as the Mitsubishi which places the wires too close to the edge risking contact with the rotor.

There's certainly an adjustment on the points - what I meant to say is that the adjustment is there to set the opening of the points... after that geometry determines the ultimate gap between the points.

I still can't understand why the riser on the new points is shorter that the old set... these can't be correct for this -1B motor... or they're mis-manufactured.

Yeah, no amount of adjustment will put the points in contact with the cam.

Just looking at this picture - I can see that the riser portion (the part that rides on the cam) is bigger on these points vs. the ones I have.

MarkT - super cool... that makes a lot of sense and captures what I was trying to say. Set the timing and then check to see the gap is sufficient. These points have to be wrong because they're simply not contacting the cam. I double-checked my order and these were supposed to be for the -1B motor but not joy. Since points ain't cheap these days I'm going to have to really watch what I'm ordering.

MarkT - By the way, I might have goofed and it was a long time back, but in racing these early DT motors we pulled the lighting coils, unwrapped them, and put the bare frames back in. I did the same on this motor since the lighting coils were in really bad shape. There was something about keeping the field unchanged or something that generated the recommendation to leave the frames in. As you said, on an MX bikes just leaving them hanging doesn't effect anything.