Bust out the tow strap!

mdscott... curious if your DT360 had the light throttle cruising pinging issue?

When engine was warm, hot day worse. Worse at about 1/8-1/4 throttle, while moving the throttle between those points at about the middle of the RPM range. At low rpm or lugging it would not. Above 1/4 under a load accelerating none.

Could probably be fixed with a richer needle diameter it's easier than finding a slide with less cutaway or if you had a spare needle and some emery paper and a drill you could take the top needle diameter down a touch by hand to richen the 1/8th to 1/4 throttle range

Thanks for the video share mdscott. I'll be trying a 10 heat range spark plug as an inexpensive and simple test. A bit cold for riding now but that will change.

I have tried opening the starter circuit (aka choke) while the pinging was present. I could not notice an improvement. I have not tried a smaller diameter needle but did try to locate a new one to no avail. From my recollection the needle jet was available. If so, that could open up the possibility of honing the outlet orifice slightly larger.

I haven't studied the jet needle and needle jet charts enough to know if there would be something avalable worth subbing. I'm not experienced with these two parts so the learning curve would be steep.

Turbodan had indicated he had jetting issues with both the Mikuni and with a Keihin PKW.

If there's a way to improve or resolve the pinging with a simple change that would ideal

I've tried so many jetting combinations it would make your head spin. Bigger pilot, needle clip adjustments and air screw adjustment with the stock carb. When I installed the PWK I now had a whole box of needles and jets to try. Started with the NIAL, went to the N2EJ, tried an NECJ and NECK, ran the NOZG for a while. Tried my single taper EGQ. I had an extra slide for the PWK35 so I tried modifying the notch and cutaway. Tried leaner needles and richer pilots and vice versa. These days I've settled on the NECJ needle, 42 pilot, 145 main and larger slide cutaway. The other cylinder with even less case volume likes a 135 main and N2EJ needle.

With the original motor, no matter what you do, you will run lean at a cruise. Surging and pinging. You can richen the same circuits that are in operation during cruising which causes problems at lower revs and idle and yet still run lean at cruising RPM.

One thing I did think of the other day was to epoxy over the small holes in the stator cover, behind the stator plate. Some other engines like the KX65 can leak air here between the aluminum casting and the sleeve the main bearing presses into. Couldn't hurt to rule that out.

I tried a zillion combos, now I am just committed to riding between 4 and 7k rpm and no ping.

I think the truth of the performance of these bikes is "somewhere in the middle" ive ridden RT1, DT360, and DT400 early and later bikes all side by side and the performance difference between them is not that much.

I think the later 23bhp power rating is more "honest", if the RT1 made 32hp and weighs only 275lbs, it should be able to do well over 100mph and perform as well as an RD350 with the right gearing, which is not the case! My Yamaha CS5e makes 22whp on a dynometer and does 85mph, similar to an RT1 in weight and performance.

The 360 model came out strong and then was strangled to death by emissions and noise requirements...

Yamaha RT360 - less restrictive exhaust, different airbox, 32mm carb, 240 main jet
DT360 - baffle plated muffler with spark arrestor, more restrictive airbox, 30mm carb, 180 main jet
DT400, same but back up to 32mm carb and different crankcase volume

Lets compare portmaps..
the RT came out as a strong performer and then yamaha went to more conservative exhaust and transfer port timing, and on the DT360 the secondary transfer port is 10mm narrower..
Ive personally had a 75 DT400 cylinder next to a DT360a cylinder and they have the same portmap.

Its a combination of all these factors and a change in how SAE power ratings were reported in the 70s in my opinion, lets compare some graphs.


I think the small port sizes in the motor a problem, they make the same power and have the same port area as a 250cc engine.
For the RT2 yamaha added a boost port but didnt narrow the secondary transfer yet like the DT360, so it has the most port area of the 3, and makes the most power!
I thought It was funny Mark should mention the TS400, I own a TS400 1975 model.
After building a pipe, port work, and bigger carb on my DT360, my very first impression after I was done with the first ride was "wow! it feels like my TS400 now!" Though to be honest..my TS400 is smoother running engine still than the dt360...
Just for fun, we can compare the power

very similar!
I've managed to solve the deto issues on my bikes with shaving the head and jetting, but my next step to solve it was to try this head Mod to make the squishband a bit smaller, I own a 1981 IT465 that this helped on , maybe a DT360 owner could try something similar.

Great post akara1.