Yamaha rd350 Road Racer Liquid Cooled!!

Re: Yamaha rd350 road racer

I always do, but on the stock parts (I assume you are talking about the upper case to cylinder match) it doesn't matter so much. If you place the base gasket on the cylinder you will see quite a mismatch, but when you place it on the case you will see it matters much less or not at all. If you bolt up the empty top case to the cylinders and match up and/or alter the transfer ports then the stock base gaskets will stick out quite a bit into the transfers but if all the parts are stock then in most cases it won't matter due to the factory mismatch. It is REALLY important that the base gasket surface on the two parts is really flat and unmarked. If some hack has got in there with a screwdriver or chisel to pry the cylinder up (I've seen this a fair bit on RD's) you can have a lot of trouble. RD's have very little real estate to seal the cylinder base, and even a tiny bit of damage can cause a leak. Air leaking into the transfers can be quite terminal and very hard to discover if between the cylinders. If you suspect trouble, machine the parts flat and use a thicker base gasket to make up for the difference. As far as the port matching benefits in general goes, every little bit helps, but as a single item I think it a pretty small gain (of course this depends rather a lot on how bad the mismatch is and where). It is however free, and very little trouble to do so why wouldn't you? If you already have your bottom end together, I would match the gaskets to the cylinders and carry on.
 
Re: Yamaha rd350 road racer

thanks Mobius!

I will have the engine apart soon and will have a look then to see how bad the match is. I think I was looking at it the same way you are, it wont cost me anything to do myself, so why not take that extra edge if its there to be had?

Talked to my local rd buddy. He is a young guy in the world of 2 strokes (25 or so id guess) but was brought up in the world of roadracing. His grandpa and great uncle were road racers in the glory days, and I still frequent his grandpas salvage yard, which is also where I got this project from. Here are a few pictures of it, just to make your mouth water =) They said I can post pics, but they don't want me to post pics and say where its at, they are a little finicky about not wanting the world to know. BTW these pics don't show the building/ outside where the other +- 700 bikes are =P

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all that to say, I was quizzing the kid about what carbs he has on his rd (rd250 with a 350 top end, tuned with chambers). He has 34 mm mikuni flat slides on them, but cautioned me that those will likely be overboard for my goad with this bike and said 32 max is what he recommended.

At the same time, he recommended BORING my stock 28's out to 30 and rejet. YES, bore them. Have any of you guys ever done this or tried it? I am a machinist and im not afraid to give it a shot, but I was wondering if its something you have done before successfully?

Side note: looking for a stock set of reed cages for the bike, ones I have are CRUSTY!
 
Re: Yamaha rd350 road racer

Sorry to report that I have NOT bored out the 28s, but do recall that being reported to be a proven good plan. Can't recall from what source though. I do have a pretty heavily altered 350 with 34s on it and it runs very well, so you can get them to work well on a street bike. I wouldn't claim that it is actually faster than with 30s on it though. Back when I put it together I had run the almost same engine with 30mm Lectron carbs and it seemed to run about as good. That is all just opinion - no evidence just riding impressions. For what its worth, the bike with the 34 Mikuni carbs (old style VMs, not flat slides) has very wide ports but comparatively mild port timing so it has pretty smooth power below the jump to hyperspace. The big carbs do seem to do well at high revs - the pipes are old Factory Pipe Products and it likes to run off the end of the tach which is very hard on cranks and the wide ports are pretty hard on the rings so consequently I take it pretty easy on it the rare times I drive it. It's great fun for 20 or 30 minutes and then it is sort of a bit much for a street bike. Only mentioning that because I have found it pretty easy to make your bike less fun over all even though it goes faster. I have an absolutely bone stock '74 Rd that I drive most of the time. It is very noticeably heavier and slower, but being a bit more balanced it is much easier and after a long day more fun. And while it may seem like no big deal, the bike with the 34s drinks an absolutely incredible volume of gasoline. If you think you put a lot in your stock bike, you'll be in for a shock with big carbs!
 
Re: Yamaha rd350 road racer

jpmobius said:
Sorry to report that I have NOT bored out the 28s, but do recall that being reported to be a proven good plan. Can't recall from what source though. I do have a pretty heavily altered 350 with 34s on it and it runs very well, so you can get them to work well on a street bike. I wouldn't claim that it is actually faster than with 30s on it though. Back when I put it together I had run the almost same engine with 30mm Lectron carbs and it seemed to run about as good. That is all just opinion - no evidence just riding impressions. For what its worth, the bike with the 34 Mikuni carbs (old style VMs, not flat slides) has very wide ports but comparatively mild port timing so it has pretty smooth power below the jump to hyperspace. The big carbs do seem to do well at high revs - the pipes are old Factory Pipe Products and it likes to run off the end of the tach which is very hard on cranks and the wide ports are pretty hard on the rings so consequently I take it pretty easy on it the rare times I drive it. It's great fun for 20 or 30 minutes and then it is sort of a bit much for a street bike. Only mentioning that because I have found it pretty easy to make your bike less fun over all even though it goes faster. I have an absolutely bone stock '74 Rd that I drive most of the time. It is very noticeably heavier and slower, but being a bit more balanced it is much easier and after a long day more fun. And while it may seem like no big deal, the bike with the 34s drinks an absolutely incredible volume of gasoline. If you think you put a lot in your stock bike, you'll be in for a shock with big carbs!

I think I may give it a shot, even if just for the heck of it. I guess its another one of those "free upgrade" things if it doesn't seem to be absolutely bonkers to you. Worse case, im out a set of stock carbs. I also have a pile of Various Mikunis off of snowmobiles that I could tinker with, but I don't know if that's a road I wanna go down, mostly because about every one of them will need a rebuild (at least bowl gaskets and float valves) and you start getting into a whole different headache when it comes to that.
The other nice idea to me about boring the 28's out to 30's is that im still stock rd. No need to mess with different or custom cables (besides shorter main throttle cable for the clip ons) and stock (or stock banshee) manifolds and all that jazz..
 
Re: Yamaha rd350 road racer

I know this isn't as wild but I have 28's on my DS7 that came with 26's. With the larger carbs it is very jet sensitive but we do have pretty good temp and humidity swings down here. I am actually looking for to putting the cylinders on that go with the carbs so hopefully I can put that to bed. It gets old rejetting so often.

Sent from my SAMSUNG-SM-G920A using DO THE TON mobile app
 
Re: Yamaha rd350 road racer

clem said:
I know this isn't as wild but I have 28's on my DS7 that came with 26's. With the larger carbs it is very jet sensitive but we do have pretty good temp and humidity swings down here. I am actually looking for to putting the cylinders on that go with the carbs so hopefully I can put that to bed. It gets old rejetting so often.

Sent from my SAMSUNG-SM-G920A using DO THE TON mobile app
Shot in the dark, but could some of that sensitivity be due to the piston port vs the reed motor of an rd?
 
Re: Yamaha rd350 road racer

Well, I guess that it could being that it inherently runs rich down low. Check out Klemmvintage.com he has a few good writeups that cover tuning and carbs. He also covers how the intake signal from the crankcase volume is weakened with larger bore carbs.

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Re: Yamaha rd350 road racer

IIRC 28s can be offset bored to 29.5 but take nothing off the floor of the carb and remember that the slide is nominally 30.0mm so if the boring is even slightly off center left to right, the slide will not shut off air supply.

Remember also that an RZ350 will make 60+ RWHP with 26mm carbs, so they are not the limiting factor here.

A.G.Bell had a set of dyno runs in his book on 2 stroke tuning with an RD400 running stock carbs compared to 34s and if I remember, the 28s were better at almost all useful revs.

I use 34 or 36s on a TZ350 but it has nothing below about 8,000 revs. For a race bike go with large carbs, on thr street keep costs and hassles down with stock 28s. Larger carbs have to opened up very slowly to avoid that big empty waaaaaagh sound as it falls flat on its face. If the throttle is opened too fast/far gas velocity drops precipitously and no fuel is pulled out of the float bowl. Bigger carbs tend to be more jet sensitive as a result.
 
Re: Yamaha rd350 road racer

I run TM28's on my RD. Pulls like a tractor down low (it's almost too grunty at times), wheelies like an RD at the power band, and continues on pulling right to around 9,500 where it goes flat pretty hard. The ID on my stingers is a little on the small side and kills me up high. I plan to make some new silencers internals soon to fix that. But a couple of times I ran without the silencers and 10k was no issue at all. The 28's are also super easy to tune. Very responsive to changes. Lot's of people told me I should have gone for 30's or 32's, but I'm glad I went with 28's. They work very well.
 
Re: Yamaha rd350 road racer

I prefer low end torque for street, personally. I like SavOr's suggestion on the TM28. Or what about a pumper carb?
 
Re: Yamaha rd350 road racer

teazer said:
Larger carbs have to opened up very slowly to avoid that big empty waaaaaagh sound as it falls flat on its face.

Right! Forgot all about that for some reason. Guess I must have adapted without realizing it!
 
Re: Yamaha rd350 road racer

I was actually planning to adapt pumper carbs to my RD but got too good of a deal on the TM28's to pass up ($120 for two unused carbs and a throttle cable). I have 5 billet pumper carbs similar to non-anodized carb pictured below. They however are only 24mm bores so they are perhaps a little small. I had a line on two Ibea 29mm flat slide pumper carbs but they were a little pricey at $350 a piece (used). I figured they would be the bee's knees, but I figured paying rent was more important than street bike carburetors.

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Re: Yamaha rd350 road racer

teazer said:
IIRC 28s can be offset bored to 29.5 but take nothing off the floor of the carb and remember that the slide is nominally 30.0mm so if the boring is even slightly off center left to right, the slide will not shut off air supply.

Remember also that an RZ350 will make 60+ RWHP with 26mm carbs, so they are not the limiting factor here.

A.G.Bell had a set of dyno runs in his book on 2 stroke tuning with an RD400 running stock carbs compared to 34s and if I remember, the 28s were better at almost all useful revs.

I use 34 or 36s on a TZ350 but it has nothing below about 8,000 revs. For a race bike go with large carbs, on thr street keep costs and hassles down with stock 28s. Larger carbs have to opened up very slowly to avoid that big empty waaaaaagh sound as it falls flat on its face. If the throttle is opened too fast/far gas velocity drops precipitously and no fuel is pulled out of the float bowl. Bigger carbs tend to be more jet sensitive as a result.

Sav0r said:
I run TM28's on my RD. Pulls like a tractor down low (it's almost too grunty at times), wheelies like an RD at the power band, and continues on pulling right to around 9,500 where it goes flat pretty hard. The ID on my stingers is a little on the small side and kills me up high. I plan to make some new silencers internals soon to fix that. But a couple of times I ran without the silencers and 10k was no issue at all. The 28's are also super easy to tune. Very responsive to changes. Lot's of people told me I should have gone for 30's or 32's, but I'm glad I went with 28's. They work very well.

well that's good to know. once again thanks guys. I will plan on sticking with the stock 28's for now and once I get it together, if there is a need, I will bore or go up a size on carbs. with the whole "roadracer" vibe, I still forget that this is going to be a sheep in wolves clothing so to speak. Look of a race bike, yet still streetable.
 
Re: Yamaha rd350 road racer

also, dumb question im sure, but does the k&n y boot mod still use a stock rd y boot, and you just clamp a k&n filter to it?
 
Re: Yamaha rd350 road racer

Something non engine related. Been wanting to build an alloy tank for a while, but I'm not much of a sheet metal guy. Saw a video on what a guy calls "flow forming" and decided to give it a shot. I got on the old south bend and started making the tooling.

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Basic idea would be to make the profile of the top of my tank in a piece of hardwood and start forming, but for a test I just used a piece of pipe. Turned out ok on 16 gauge steel.
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Re: Yamaha rd350 road racer

You can use the stock Y boot but the filter does not directly attach to it. You will need a short internal coupler to go inside both and two clamps. This is very easy to make as the most common size of canned beans, vegetables, etc is the exact diameter needed. Simply cut the length coupler needed and install! I use K&N part #RC-2600. That has the same base as Y-boot but the filter section is tapered. Fits a lot better on RD's than the straight section ones. You can see the coupler in first pic and how the filter fits in the second.
 

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Re: Yamaha rd350 road racer

Thanks moby! Anything sporting the weight of the filter or is it just hanging on the boot?
 
Re: Yamaha rd350 road racer

Nothing supports it, it is just cantilevered out from the carbs, which are themselves completely unsupported cantilevering out from the cyilnders. Does not seem to be a problem, but their is a frame cross brace directly under the boot and it is very close so if ever there was any sagging the boot would almost immediately rest on it. Does not seem to be an issue even after a long time though as I don't see the boots ever actually ending up resting on the frame.
 
Re: Yamaha rd350 road racer

Well, flow forming tool 1.0 already went out, very dishonorably at that. For the shank I just used a habbah freight chisel cut down. I knew it was high carbon steel and would probably crack. I hoped it wouldn't, but it did.
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So, I figured I'd start whittling away at a billet chunk of mystery steel that I snagged out of a scrap hopper. Guessing it's 1018 crs or similar, so I don't know how long it will hold up to the air chisel. May have to end up tig welding some hard face rod on the tip where it goes in the hammer, but we shall see.

Started out with a 1.125 " x 6" chunk
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And started making chips
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1st op done, time to flip it around (my 3 jaw Chuck has seen better days, so I'm getting pretty quick at indicating in a 4 jaw Chuck ha
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More turning
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Finished up besides turning the tube to be welded on the end that holds the wood insert. I'm really pretty impressed with the 1937 south bend. Still held a half thou tolerance on the od at 4" length of cut. Can't complain about that.

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