Hi all - I've been helping my dad get his 74 360 back in working order and a bit puzzled at the moment. It was running great but after sitting a while I noticed it won't run right. It will start, sometimes idle, sometimes not, and will rev a bit but when you go to ride it, it almost feels like the redline is 3k RPMs. It just hangs up there and falls flat, smokes, but if you cut back on the gas or try to put around at 1/4 throttle or so it runs more normal.

First thing I noticed was oily residue in the in-line fuel filter so we took off the tank, cleaned, and cleaned the petcock. Next, several times cleaned out the carb (I thought I must have missed somewhere so I ended up trying quite a few times). Changed the spark plug and checked the air filter. Still having these issues and a bit puzzled. Anything else to consider looking into? Appreciate any thoughts as I'm not so used to these older bikes but want to make sure we can get him going soon since spring is here. 

If it was running fine before sitting I'd try fresh gas. How long was it sitting? Were you using ethanol free gas or did you use fuel stabilizer before it was parked? 

If yer sure its getting fuel, here is a DT360 with a failed ignition for comparison.
Ive found almost all DT360 have failing ignition, the capacitors are simply well beyond their expiry date.
If it isnt bad now it has the potential to leave you stranded, good thing to try to replace even if it doesnt solve your issue.

My first thought is a lump of carbon has jumped up the spout from the inside & strangled it.
Easies way to eliminate that theory is remove the complete tail muffler & give it a rev.
That means the whole tail muffler not just then end cap.
Hope you get on well with your neighbors.

I bought a scrubcutting saw recently with that exact problem but luckily it was right at the outlet & visible.
Guy said he had tried everything--everything except the right thing.
Also i should've said, welcome from NZ.

Greetings from Tennessee  

My 360A had similar issues that I chased for along time. It was all resolved when I gave up on the CDI ignition and installed a stator and flywheel from a 250B which is the points and condenser ignition. Starts easy and runs great.

We completely drained the gas and put in some ethanol free. I also cleaned the carb a couple times so I don't think this is the issue.

Thanks! Greetings to you as well from New York State!

Interesting, we didn't think of this but not a bad idea for us to try and see. It's an old bike that sat for 40+ years in a dealer's basement so who knows. And thanks for the welcome, I'd love to visit NZ someday!

Thanks for this. I did notice that usually when I put the carb back on the bike and I release the fuel from the "stop" position, sometimes the fuel doesn't really trickle into the fuel line (I can see from the clear in-line fuel filter). Once I kick over once or twice it then starts to flow and fills the filter like I would expect. Maybe this is normal due to vacuum, but would gravity typically push down the fuel once the petcock is opened? I feel like I should know the answer to this but I'm wondering if this could be part of my issue.

The gas tank was filled with motor oil for 40 years and some residue/sludge got into the carb last summer and I spent a few times cleaning it (there is a chance that somewhere in the carb it's still a problem but I was pretty thorough in examining the jets/ports/etc. with carb cleaner and air to test.

I was thinking maybe CDI, although his bike isn't this bad. You can run it and up until about 3k RPM or so it sounds pretty normal. It's when you try to do anything beyond this that it just smokes and almost acts like there's a rev limiter on it. So in this sense it fools you - it may start, idle, rev a bit, then you ride it and lug seems fine, but any time you try to open it up when it's warm it just falls flat.