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#91

Turning Wrenches / Re: FZR Bits on RD

Last post by teazer - June 13, 2026, 05:02:30 PM

Did someone mention TZ top ends on air cooled cases? Back in the day, TZ cases used to wear out and replacements were not always available, so racers took to modifying RD cases to take the TZ crank arrangement. Others bougt TZ top ends and fitted them to RD bottom ends.

This is a set of RD cases with a TZ crank and water pump with RD400 transmission and 40900 (64mm bore) top end with bigger reeds. 40970/40971 66.25 TZ750 C/D/E top ends also drop straight an to an Air cooled bottom end.


I forgot how to insert and image.  I'll be right back as soon as I work that out.

#92

Show Off / Re: Whats in my garage

Last post by busa1300 - June 13, 2026, 03:12:01 PM

Took the RGV VJ21SP and the RS250 to dyno today...
The RGV is now using stock carbs and airbox, as the 38mm powerjet Lectron experiment did not work for a street bike.
Pulled ok, but seems to die off too early at 10,500... should pull past 11,000. Not sure what's up with that yet.

65HP...

Sadly all the work I did with ignition on the RS250 was a waste, as it ran like total shit.... Have to go through the whole thing again to see if I can find the issue 

#93

Turning Wrenches / Re: Livening up my top end

Last post by m in sc - June 13, 2026, 07:44:40 AM

yes, anything tighter will be better. you may not feel it but the motor will/should run a bit cooler

#94

Turning Wrenches / Re: Livening up my top end

Last post by Vintagewannabe - June 12, 2026, 11:21:20 PM

youre going to need to machine the top of the cyl to fit a 400 head gasket. once you do that you  cant go back. so... will it probably work? sure. but just guessing is risky

I think the recess for the headgasket was about .025 to .03 in, so I will take that off and re measure.
My question was more is there a benefit to getting the squish tighter without hitting that .030 that I have read people use for pump gas

#95

Turning Wrenches / 1975 RD350 - Right Cylinder No...

Last post by KONOW - June 12, 2026, 10:47:06 PM

I recently acquired a non-running 1975 RD350 that hadn't been started in three years. The previous owner noted weak spark as the reason it was not running well and believed it needed a new ignition system. I received the bike mostly assembled except for the rotor and ignition system, which I installed and set the timing to 1.8mm before top dead center. I confirmed strong spark on both cylinders and got the bike to fire up, but it's only running on the left cylinder at idle. Right cylinder is dead at idle.



Initial Troubleshooting:

1. Confirmed strong spark present on both cylinders

2. When I cover the right carb inlet (with the air boot removed), I can draw fuel in manually, the right cylinder fires and maintains idle. Once I remove my hand and normal airflow resumes, the cylinder goes dead.

3. Swapped the left and right carburetors

    3.1 With the left carb installed on the right side, the right cylinder fires normally

    3.2 With the original right carb installed on the left side, the left cylinder does not fire

4. Swapped the throttle slides between the two carb bodies (keeping each carb body in its original location on the bike)

    4.1 With the left throttle slide installed in the right carb body, the right cylinder came alive

    4.2 With the right throttle slide installed in the left carb body, the left cylinder went dead

    4.3 I understand that these slides are asymmetric and this test might not prove that the issue follows the slide. With the slides installed on the incorrect carbs the fuel/air circuitry is likely not acting as intended.

5. Swapped the threaded throttle slide caps between carburetors — no effect

6. Swapped jet needles between carburetors — no effect

7. I have cleaned both carbs but I have not drilled/removed the brass ball on either carbs



Carburetor Observations:

1. The left carb (with choke lever) has a float bowl with an orifice jet

2. The right carb (no choke lever) has a float bowl without an orifice jet

3. The right carb has a hollow brass tube attached to the carb body positioned near the pilot jet; I cannot pass music wire through it or blow air through it to determine how it relates to the carb circuit (photos attached)

    3.1 This is confusing because I would expect this brass tube to be present on the left carb w/ choke, not the right carb. To be clear the left carb does not have this brass tube.

4. Air screws on both carbs are set to 1.75 turns out

5. Float height on the right carb (the non-firing side) measures 15.5mm



My questions are:



1. What is the purpose of the hollow brass tube on the right side carb body and if it is functional which circuit is it connected to?

2. Are my float bowls installed in the correct location?

3. What additional troubleshooting steps can I perform to identify the issue?

4. Is it likely I need to drill out the brass ball and clean that portion of the circuit?

5. For the choke lever which position is on/off?
   

Thanks!

#96

Turning Wrenches / Re: FZR Bits on RD

Last post by SmokeAddicted - June 12, 2026, 06:52:11 PM

I look forward to pulling it apart. It's an SRX 600 swing arm. Rough measurements between the stock pivot tube with bronze bushings, and the SRX pivot tube, it's so damn close.  Hopefully digging in within the next few days.

#97

General Chatter / Re: MotoLanna Swing arm substi...

Last post by m in sc - June 12, 2026, 05:28:01 PM

nice.  here we go!       

#98

Turning Wrenches / Re: FZR Bits on RD

Last post by m in sc - June 12, 2026, 05:26:26 PM

you'll just need to mill in the sides, an thrn countersink the bearing in the arm a bit. i dont remember the actual dimensions but 6mm rings a bell...?

#99

General Chatter / Re: MotoLanna Swing arm substi...

Last post by SmokeAddicted - June 12, 2026, 03:04:46 PM

Holy crap,
this company I search for since a while. I had contacted them a few years ago and due to a computer crash I lost the conversation and I forgot the name of these guys.
They are the manufacturers of the Motolanna swingarm.......
I have a teammate who has emigrated to Thailand and is in the Thai racing scene. I will call him and he should contact them.
Regards Uwe

I went digging for them when I read your post from years ago! You made a similar comment about loosing the conversation bc of a computer crash.

That post is the ONLY reason I went digging around to try and find them. Pretty cool 

#100

Turning Wrenches / Re: FZR Bits on RD

Last post by SmokeAddicted - June 12, 2026, 03:01:18 PM

Thanks guys. I appreciate the feedback/pictures. In my mind, I envision the finished product looking like the second picture. I have a left clip on, just need to source the throttle side.

I have a spare RD stem. As Mark suggested, I'm going to have the FZR stem press out of the triple, and the RD stem pressed into the FZR triple.

I believe all I need is new set of RD tapered bearings and it should be plug and play with the RD stem pressed into the FZR triple. Swing arm is next on the hit list