1975 Yamaha RD350(LC) Preservation-mod Hellride

canyoncarver

'hacking is learning'
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I promised to have this thing running by the end of 2021. So, with it being New Years Eve I had to hit the kick start. I have done zero tuning on the carbs. They are as you get them from Mikuni. No idle adjustment. No plumbing on the cooling system, so I don't want to run it very long or very often. Just a quick hitter to make the new year.


I LOVE first start videos. Nice work man.
 

irk miller

You've been mostly-dead all day.
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I’ve been spending a lot of time behind the counter at my local auto parts store looking at hoses to figure out the best combo. Here’s where I’ve landed so far:
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I’m going to replace the plastic elbow with a section of hose that makes that angle, otherwise this is about as clean as I’ve been able to get. The RamAir sock came in too. Not sure this is something you couldn’t make myself with sheets of foam from Uni.
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teazer

Over 10,000 Posts
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Couple of thoughts. I usually cut that lower hose connector off LC radiators and re-weld it pointing down at about 45 degrees. It makes for a shorter, simpler hose run. I have done that to a few to fit that radiator on a TZ motor/pump.

For the hose that sticks straight out, is it possible to use the 90 degree angle at the outlet and then take that hose straight up and under the right side reed box?

Or how about fitting a Banshee right side cover? It would need a small amount of welding and machining to the right side of the crankcase to take the waterpump shaft and for the feed tube, but that can wait until the next time the motor is out.
 

teazer

Over 10,000 Posts
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Getting better all the time.

BYW, which direction does that pump pump ie which is the outlet and which side is the inlet? The reason I ask is that on a mechanical TZ pump, the equivalent of the pipe coming out of that side cover would be the inlet. I'm sure you already checked but I was looking at a TZ pump and had to ask.
 

irk miller

You've been mostly-dead all day.
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Getting better all the time.

BYW, which direction does that pump pump ie which is the outlet and which side is the inlet? The reason I ask is that on a mechanical TZ pump, the equivalent of the pipe coming out of that side cover would be the inlet. I'm sure you already checked but I was looking at a TZ pump and had to ask.
This pump is the same direction. The pipe coming from the back of the head goes to the inlet on the pump. The outlet to the bottom of the rad, then the cooled water to the top of the head. You have to really zoom in on the diagram to see the arrows, but they show the pump with the inlet facing vertical and the outlet horizental.

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irk miller

You've been mostly-dead all day.
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Going with a Trail Tech. Cool thing about it is the thermostat threads into the LC head.

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irk miller

You've been mostly-dead all day.
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The build is mostly done (minus paint and body), so I took it for test rides. This is the part where I get really inexperienced. It rides nothing like I expected, so I need to find the tune. It shows little power in the lower gears. The power band comes on way up in the rpm’s. Very little low end torque. It shows the ability to get up in speed, though I never took it above 4th gear. Any advice on stuff to go through is much appreciated. I can't remember the jetting in these carbs, in fact the jetting may be as they come still. I need to go back and check. So much to learn about 2 strokes and how to discern tune on the carbs.

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pidjones

Over 1,000 Posts
Here is one way to find out - get it started off and into 2nd gear, then wind it out full throttle. When the front end heads skyward, you have found the bottom of the power band. Be ready to shift fast as the band is pretty brief on a 2T.
 

teazer

Over 10,000 Posts
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Close to TZ350 pipes and ports. Hmm that's what we would expect. It should start to pull quite low - say 6,000 and should start to really scoot along above about 7,000 and should pull like a rocket up to the red line at say 10,500.

The best way to get jetting close is idle, just off-idle to get moving, then main jet and then see if it needs something different for midrange. Try to avoid the temptation to jet for mid throttle before you have the right main jet in there.

That plug is wet but not much sign of color. I am guessing that wasn't a hard run plug chop so it's hard to draw much in the way of conclusions. What are the plugs and where is ignition timing set?
 

Rider52

Over 1,000 Posts
I didn't ride our TZ250s much but you almost perfectly described their manners. Not much low end but when the power hits, it hits hard. I did an 80 mph wheelie coming out of a turn at Mid Ohio because I wasn't use to the power band. It may take a bit of fiddling to get it where you want it. I'd start by following Teazer's advice. He knows way more about 2 smokes than I do.
 

irk miller

You've been mostly-dead all day.
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I watched some YouTube videos, including this one from Spike Edwards :


I learned a lot watching where he revved for startup, how he shifts and where he keeps it. The video is race 2. Race 1, he struggles on the start where his revs remained pretty low and it really took a while for him to get going.

I did some more small runs last night. My headlight/power is cutting out when I rev high, so I am nervous about venturing too far. The ignition continues to have power, so I think it might be somewhere between the magneto, the relay and the NUUT. I kept it above 6k most of the time, and it's really starting to make sense to me now. I did a hard 1/8 mile pull on my side street to the stop sign, took a right, then right up the parallel street over and just floated at 5k up that street cruising at 25mph to the next stop. Turned right again and another hard pull through 5 gears on the main highway to loop back around to the shop. The plug still looks the same, so I'm still not doing enough for tuning I suspect, but at least I am starting to understand the engine. The Trailtech doesn't seem to offer accurate rpms, however, unless I really am getting into 12k. It doesn't sound at all like 12k though, as I expect it to be really screaming and it's not.
 

Maritime

Over 10,000 Posts
Yep. 2 strokes are soooo different. I bairly can keep the 50cc scooter happy LOL. Go na be fun. Ask Brad how fun his RD was to try and tune. It was nothing, nothing, Holy Shit! Shift repeat
 

pidjones

Over 1,000 Posts
One of the reasons I like the RD400c - much broader (and lower) power band. But, since my first 2T was an RD250, it actually seemed quite calm to me. Now, going from GoldWings back to the RD400c, it is still a bit "busy". Going straight to a performance 2T has to be a BIG change. You are going to have great fun tuning and riding it.

Already have track days booked?
 

irk miller

You've been mostly-dead all day.
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I do love how quick and easy the shifting is. When I drag raced VWs, we set the shifter at 1/2" throw and you shot through the gears in quick succession in under 2 seconds. This bike reminds of that. Just flicks between gears and hardly a clutch pull.
 

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