So I picked up a sweet little RD 400 a while back. Anyway, the day I bought it it seemed to run pretty well, but I did not really want to go killing it in someones neighborhood. Though it did seem it needed a carb cleaning, so I figured no big deal. It has 13,000 miles, about 1k on new pistons. Got it home, cleaned it up some, found a slight air leak in the carb to head boots. replace them and the gaskets, also the carb to airbox boots. clean all the carb out, and new needles with viton seats and fresh carb bowl gasket. reset all the carbs per the manual, and test ride it. at the bottom it runs good, a little flat spot around 3k, but that seems normal for an RD (from looking online) The problem I am having is it will not rev past about 6500 RPM; it is load dependant, if I go slowly I can sneak it to about 8k I have tried coils, noticed the petcock was a little slow, so replaced that, and cleaned out the tank and sealed it. cleaned and reset point gap and have checked my carb work. Also found the jets were not matching side to side, and matched both of them at 130's the coils and tank cleaning didn't do much, but the jetting seemed to make it a little better, but now its like 6500-7k it starts slowing down. so the thing has pissed me off, and I have stuffed it in the corner. I really wanted a cool little 2-stroke street bike, and have always heard the old RD's were pretty quick for what they were. Anyway, I'm over a year of ownership, and at 10 miles of around the neighborhood. Summer is coming, and I want to be able to ride the thing, with it running correctly. any suggestions from the all knowing? I know there are a few old Yamaha guys around here.
I'd keep looking at jetting to start. How do the plugs look ? It might be lean on top end, to check that ride it to the trouble rpm then give it some choke. Does it get better or worse? Nice bike btw. :up:
Yep, sounds like too small on the big jet. That thing should pull like a freight train at the RPM's you mentioned. Lot's of great two stroke guys here but also a wealth of information at 2strokeworld.com. They have sticky's that probably addresses your exact issue. I'm going totally by memory but I think I have 165 mains, but I've been ported/polished etc. Oh, and beautiful machine you have there. Mine looked exactly like that before I transformed it to a race bike.
Also I love that you've kept the bike totally stock, but if you really want to wake that thing up you have to put a set of chambers on it. It will make it a completely different machine. I'm a big fan of Spec2's... http://www.spec2.com/chambers.html
I always thought I would modify one, and make it a real screamer, but this one came up. It is so nice, I want to keep it all stock. Its more of just a neat piece, I want to keep it that way, but I know it should be just waking up about 6500, and its falling on its face.
When it hits that limit and stops pulling, reach down and loosen the fuel cap. If that solves the problem, the tank vent is not working correctly.
heres where I saw some jet numbers, hence going with the 130's (it had a 130 in it, though I do not have the Y-boot) I did try to do as close to a plug chop as I could, It wasn't bad, it didn't look way rich, it was kindof tan like I would think it should be. http://www.hvccycle.com/carburetor-jetting.html
If I remember right 115's were stock,130's if you cut the air box lid and flip over the air cleaner. Just going from memory.I'm old and it may be faulty.Still I'm 99% sure on this.
I'd do that then the same thing with the choke. Nice simple things to check before you dive into it again.
I will definitely try this, I hope its something that stupid and easy. I believe you are correct. 115 is stock, I was advised they are known to be lean stock, and I should go up on jet size anyway. Also, the stock oil pump is still on and working. Lyn looks to be about 1.5 hour drive. I usually work on my own stuff, but after a year on this one, I'm not against that in the near future.
I was the same way when I got my first RD. And had similar problems as you. Knew a guy that was a local RD guru and within about 30 minutes he had mine running perfect. That's probably 20 more minutes than it will take Lyn
Is there a mouse's nest in the airbox?? Exhaust baffles clogged?? Remove the rubber air horn thing and see if it picks up any.... :up: And that thing is BEAUTIFUL!!
+1 And if it was lugged around for 13K on godnosewhut kind of oil, it may even have the top of the exhaust ports coked up.
I have a 76 RD 250 and my buddy has the same bike as you but in green. All OEM. Had mine going last year and let it sit and Carbs went poop. Hope to have her back out this summer. Your bike looks very nice.
It's not to check if the choke is working, it's a rough and dirty way of determining a direction to look towards. Full throttle, part throttle, turn choke on. Does it slow down, pick up or do nothing? Just gives you some more data to go on. If you want to mess with it of course, with all the established RD data out there there should be a good recipe to go to right out of the gate
