Messages

 I continued my conversation with AI...
I asked about the YL1. "The YL1 is the stock UK jet needle for the 75 RD350?"
<<No, the stock jet needle for a 1975 UK-specification RD350B is actually the 5L1.
The YL1 label is an aftermarket part code quirk. It stems from modern pattern part manufacturers (like Keyster) using the stamp "YL1" or "YL2" on the brass components inside their European/UK market rebuild kits to denote their exact replica profiles of the factory 5L1 needle.
The difference between the two specifications highlights the distinct setups used:

UK/Euro vs. US 1975 RD350 Specs

The 1975 UK market RD350B utilized a different carburetor internal setup than its American counterpart to comply with local noise, fuel, and emissions standards:
• UK/Euro Spec (1975 RD350B): Features the 5L1 jet needle paired with a significantly smaller 105 or 110 main jet because the European models used a heavily baffled, restrictive intake air filter box.
• US Spec (1975 RD350B): Retained the 5I4 jet needle paired with a much larger 140 main jet because it drew air through the standard open-element foam filter box.
If you are sourcing an aftermarket rebuild kit labeled with a YL1 needle, it is designed to mimic the leaner European/UK factory 5L1 sweep profile.>>

 I'm not claiming that this is right or wrong. Just pasting what AI said. I haven't learned to trust AI yet even though we are experimenting with it at my company in a regulated environment. Not even at "trust but verify yet". It does make creating SOP's easy without having to look up a lot of specs. ...At least until the "verify" point. I've caught it out on a few things but it usually admits to being wrong when challenged.

So what happens if you use the 5L1 with a 110 main jet in an engine without restrictive filter? <<(Paraphrasing): too Lean>>. How about 5L1 with a larger main?:
<<Running a 5L1 needle with a larger main jet in an open airbox configuration is a proven, highly effective tuning strategy. It is precisely how many vintage racers and performance tuners configure their RD350s to clear up mid-range bogging while maintaining massive top-end fuel delivery>>

IR8D8R

[AI response is interesting:]

5I4 are stock for the 73 RD350 but they discontinued them. That sounds unlikely but here we are. Chuck was looking for some for my 350. We both were, but they do seem to be scarce. I will probably never know how well they would have worked.

AI response is interesting:
<<Because the 5I4 jet needle was custom-engineered by Mikuni specifically for Yamaha's OEM production lines, it does not have a direct, universal aftermarket counterpart in standard Mikuni part catalogs. If you need a replacement, you cannot simply order a standard Mikuni 5-series catalog needle without altering the bike's mid-range performance profile.
 If you are struggling with the notorious mid-range "burble" or rich stutter common to the stock RD350 jetting profile, the most highly recommended swap within the vintage two-stroke community is to switch to TR-1 specification needles (?? Never heard that before). Historically, vintage enthusiasts discovered that a shorter, more aggressively tapered needle from early 1970s Yamaha "TR" series trail/enduro bikes (like the TR1 or early DT/RT models) could be fitted into the RD350's Mikuni bodies.>>
 Then it goes on to contradict this as a misread and suggests the notorious Keyster needle is an exact copy of the 5I4 and says to use 5DP7 or the still available 5L1 which were allegedly used in UK/EU area RD350's(?).

 Anyone heard of the "TR-1 needle mod"? I found references to that elsewhere. That does give some reasoning for a shorter needle. But the Dave F mod seems to add tune-ability and 5DP7 needles are common. How about 5L1 needles?

 The VM-28-419 flat slides were a better solution in the end and basically a direct swap for me using stock cables and manifolds. After trying 3 different sets of RD carbs. Dave and no Dave without any notable difference in midrange behavior it was welcome. Obviously a more costly option than finding needles but they run better than Dave F. modded carbs on my RD.

IR8D8R

None whatsoever. Internet searches are like that.

Someone pulled a 5I14?

https://streetdrivenperformance.com/products/athena-derbi-2t-gpr-75-complete-gasket-kit-excl-oil-seal.

The 100/90 fits. There is adequate clearance between the inward curve of the stock RD350 fender's fork brace using stock rims. Wider rim? It needs to be perfectly true. The wide rim lets the tire open up right where the brace is narrow and the tire is it's widest. There will be about 1.5mm on either side where the little ripple is on the 350 fender mount.

The stainless RD400 front fenders don't have that issue. They look pretty close to stock and you don't need stays.
If you don't run the stock front fender you need a brace. It's built-in to the stock fenders.

Turn in is supposed to be faster with a 90/90 front. I've run 100/90 front on both a stock and a 2.15" wide rim.

Rear 110/80 is better than a 110/90 IMO.

IR8D8R

You really need gaskets on both sides of the reed block. The rubber manifold doesn't reliably seal the connection.

IR8D8R

Of course,

https://rswracing.com/collections/rd350-400/products/yamaha-rd-350-400-and-daytona-400?srsltid=AU7gw4WDaVcJqtMtpG8Gcalq0h3pdrr9Nq32IvvQO1typcfl7ekjB4DV&variant=7808385515572

https://www.ebay.com/itm/327322451982?

Similar to the late TZ fender but without holes.

My favorite version:
https://www.ebay.com/itm/198627238991?_

BIN/BO $25k

Not mine. Not likely to be mine but I wish...

Apparently has been street registered? Not sure.

IR8D8R

Chuck did a topic about rod bearings and using Suzuki RM125 small end bearings a while back. Economy Cycle had some at one point I think.

https://www.2strokeworld.net/forum/index.php?topic=1672.0

 Someone just needs to go to China with a 400 crank and commission a lot of them. A factory drawing set would be helpful too. They are surprisingly accommodating and business is down. The unit price is lower with economy of scale.

 The question is, how many would people buy one right away to recoup the investment? Setup costs are much lower than you'd expect and they have low profit expectations compared to the West. You really have to go over there to get the best deal. But then they'll never stop calling you...

IR8D8R

I have a later version of a TZ350 fender on my RD350. It's a fiberglass replica. Probably Airtech?
This one:
https://gpcycleworks.com/products/tz125h3

It does fit an RD350 even though the fork spacing is different. Installation was super easy.

There are a few that would probably fit there:
https://gpcycleworks.com/pages/search-results-page?q=Yamaha%20fenders

Airtech is now owned/manufactured by GP Cycleworks.

IR8D8R

Nevermind the rust stains and water damage. It was only underwater for 5 hours 3 years ago.

If you want to sell a piece like this wouldn't you take 5 minutes with a rag and some WD40? ...Or does that remove the "patina." Maybe that's why it's $7500 with no title.

IR8D8R

Definitely better than oil dripping from your chest pocket.

...shifting with your right foot!