Good morning everybody,
So I recently did a full tear down and rebuild on an rd350 motor that I locked up. And I'm having trouble getting it to go above 7,000 RPM, this was not an issue on the previous build, I had a four corner lock up and it was determined that the Piston to wall clearance wasn't set correctly.
After this rebuild was completed I put on a set of JL retro pipes and bounced up the jetting a bit it's been a few hundred miles now and I've just started to get higher in the RPMs on the motor and I've noticed that it cuts off around 7,000 RPM. The pressure test on the rebuild passed with flying colors and I'm a little bit confused on why the issue all of a sudden.
This motorcycle has a nutronic ignition system on it, vapor chamber crossover, k&n with y boot and the JL retro pipes.
My current carburetor settings seem to be kind of high and they were with the last motor too, I live at altitude and I'm assuming that's part of what's playing into this. Originally I got the bike to run fantastically before it locked up on the highway with the carburetors having 210 main Jets and 27.5 pilots center clip no aftermarket needle. The only thing added after the rebuild was the JL exhaust
Initially after the rebuild I just shoved some large jets in there since I didn't want to pin it to do a plug chop. what's currently and there's a 300 on the main and a 30 on the pilot, still in the center clip on the needle.
I'm going to pull out the dial indicator tonight and double check the timing, I hit it with a timing light this morning and had to move the old ignition settings to get the mark to even come close to the center. I was able to center up the timing marks setting the advance to 19.8° and adjusting the pickup. The bike does feel a bit more peppy but it sounds like it starts 4 cycling once you hit that 7K at full throttle if you back off a bit you can squeeze a bit more out of it. I initially thought that the Jets were too rich so I dropped down in size to a 280 then 250 and it just ended up getting worse, I'm trying to wrap my head around how much extra fuel this might need with the expansion Chambers on there but I'm also wondering if there's something else that I might be missing. It has the stock VM 28s on there the low top version. I have looked at the comparison chart with people's jetting settings or that PDF that's floating around online and I am significantly higher than everyone on it I think the only person close to me had some serious important polish work done.
I would appreciate any help and direction to get me going on the right path. Thank you in advance! I forgot to mention that I am still running the oil injection pump and not premix, I'm using Yamalube 2s and premium fuel
Here are a few pictures from The journey along the way
From your description, it sure sounds like it is way rich. So rich that 280 to 250 won't make any difference. Keep going down until really comes alive at 7000 and wants to go to 9000.
Quote from: 1976RD400C on July 22, 2025, 12:27:30 PMFrom your description, it sure sounds like it is way rich. So rich that 280 to 250 won't make any difference. Keep going down until really comes alive at 7000 and wants to go to 9000.
So I brought it back down to that 210 that it was at without the expansion Chambers and the problem still exists, any lower than that and it starts to sputter and spit or just completely cuts out at wide open throttle. I'm wondering if I need to jump up the pilots again to a 32.5, that made the largest difference the first time around was going from a 25 to a 27.5 and that bike came to life compared to what it was doing before. I did buy this bike non running so it's been a hassle the whole way.
I. running 270s on stock carbs w chambers (fpp) and a l&n w y boot. are the carb is internals stock or Dave f modded? how old is the Newtonics? from my experience, a lot of jetting issues...,are electrical.
If you're not sure if it's too rich or too lean flip the enrichener (choke) on. If it gets worse you are too rich, if it gets better you are too lean.
How good is your battery and what voltage do you get at 5k rpm?
Quote from: m in sc on July 22, 2025, 04:17:23 PMI. running 270s on stock carbs w chambers (fpp) and a l&n w y boot. are the carb is internals stock or Dave f modded? how old is the Newtonics? from my experience, a lot of jetting issues...,are electrical.
It's got to be ancient, it doesn't have the timing light adjustments on it that the new version has. I wouldn't mind picking up a new ignition system I'm just not trying to spend the extra $1,000 after I fully rebuilt the motor I'm still trying to recover from that financially. Carburetors are stock though, I was thinking about doing the Dave f mod but a lot of people seem to do just fine without it.
Quote from: Jspooner on July 22, 2025, 08:34:38 PMIf you're not sure if it's too rich or too lean flip the enrichener (choke) on. If it gets worse you are too rich, if it gets better you are too lean.
I'll take it out tonight and see how it does with that flipped!
Quote from: Brad-Man on July 22, 2025, 10:26:10 PMHow good is your battery and what voltage do you get at 5k rpm?
I will take a reading on it when I take it out tonight
hpi system well under 400.
I'll be honest, years ago i had a newtronics take a dump and went back to points briefly. (like 20). however, yambits sells the 'new' newtronics relatively cheap.
But IF you keep having to jet DOWN to get it to run right, that usually leads to weak spark as the cause. being as was touched on:
battery voltage, coils, or ign unit. def time to do some testing.
Quote from: m in sc on July 23, 2025, 08:09:51 AMhpi system well under 400.
I'll be honest, years ago i had a newtronics take a dump and went back to points briefly. (like 20). however, yambits sells the 'new' newtronics relatively cheap.
But IF you keep having to jet DOWN to get it to run right, that usually leads to weak spark as the cause. being as was touched on:
battery voltage, coils, or ign unit. def time to do some testing.
I remember I spoke with you briefly about timing with a timing light and I couldn't get that to come through at all. So I ended up doing it with the dial indicator and watching the spark. The right side was off a bit, but now both sides are set at 1.8 mm before top dead center.
I took the advice to wait for it to hit that point where it cuts off and flip on the enrichment switch and that seemed to make it worse. I'm starting to wonder if wide open throttle is too rich and maybe my pilot is too lean.
Either way I didn't get a running voltage but I'm always at 12.6 volts every time I start the bike that I've checked it.
I did notice that the spark seemed relatively strong although I was doing the timing at night just so I could make sure I could see the spark correctly but I am also wondering if that neutronic ignition is toasted. I don't necessarily like the way that it's set up with light beams.
So I didn't bring it up to 5,000 RPM to check the voltage today but on start with the lights off it immediately jumped to 14.8 once it was running.