1975 rd350 tm28 flat slide mikunis, stock cylinder, pro x pistons, yz85 reed conversion, y boot with k & n filter, boost bottle, hvc expansion chambers , dyna s electronic ignition, btdc 2mm
Anyone know approximately what my jetting should be? The list that is available here is not super helpful.
Currently :
Main jet : 310
Pilot : 30
Needle jet (bleed style) : 175 p8
Needle : 5 dp 175
Middle clip position
Should I run a 169 series p0 or p2 needle jet? Should I run a 5 dp 7?
Any specific set ups?
I think my confusion with the list on here is stock round slides are vm series mikunis. The flat slide mikunis are referred to as tm or tmx except for the 28 flatslide. It is listed as a vm28. The list does not specify flat or round slide.
I don't know anything about the TM28s as far as about what the jetting will be for an RD but what you have listed out seems like it will be way rich, hopefully someone that has experinence with these will chime in for you. As for your other question, VM28s are roundslide, I would guess they are referring to the stock carbs in the thread you talked about
(http://scoot.net/gallery/bbs/20190317_142607.jpg)
(http://scoot.net/gallery/bbs/20190317_142529.jpg)
any and all vms are roundslide. when referred to as 'stock28s' or the such, it means VM
310? that seems crazy rich. im running 330's ona super modified rd with VM34's.
IF indeed you are running a carb that requires a 300 series main, make sure your needle and seats can flow as much as the main.
so, you are sure you have TM28s? whats the air jet size? that want listed.
I need to clarify. The carbs are not yet installed on my bike. I am trying to jet them prior to installation so they are close to correct. I have changed the mains to 220. Yes they are absolutely 28 mikuni flatslides. I have been building, riding and racing vintage two stroke singles for many years. I have owned my rd for a number of years so not entirely a mystery. Just mostly a mystery hence my many questions on the new and old site.
As listed by the mikuni catalog tuning manual not all vm are round slides. The vm28 418 catalog number 001 023 is the flatslide 28 mikuni. It is commonly called/referred to as a tm, but it's not, if the mikuni catalog is to be believed. The vm28 49 catalog number 001 022 is the round slide. That's why.I posted the pictures directly from the catalog. Feel free to crrect me explaine.
Anyone running 28 mikuni flatslides want to chime in?
My TDR250 and my old TZR250 run TM28SS carbs stock.
I don't know the difference between a tm28ss and a vm28 418. I'm really just concerned about jetting for a 28mm mikuni flatslide.
well, the bike will tell you what it wants. Wasn't trying to step on toes but you weren't really clear as to what you knew and didn't.
again, no mention of the air jet size. its critical for main jet sizing. is it open, or is there one in there? i've seen them run both ways. friend of mine has an rz with the tm28s and is battling this right now. i'm pretty sure the catalog has a typo btw. :patriot:
Fun fact: TM28SS do not have adjustable airscrews.
...and there is no way a TM28 is really a VM28 418. That's just too confusing and weird to be true.
Thanks for trying, and giving a few tips all who replied. I'll get it the old fashioned way, trial and error.
It's true, vm28 418 is the 28 flat. There is no air jet. Please refer to the pages in the mikuni manual or just look at the two pages from the mikuni manual I posted. On the tm chart, the 28 is listed as vm 418. I agree, weird and probably unnecessary to make that one carb have an odd prefix.
From British supply company:
Standard Jetting Specifications
Carburetor # Venturi Size Main jet (VM4/042) Pilot Jet (VM22/210) Needle Jet Jet Needle Throttle Valve Air Jet
VM28-418 28 180 15 P-8 5DP39 2.5 None
TM Series Carburetors provide significant performance improvements over older design round slide carburetors. Air flows faster and smoother through the TM Series venturi due to the flat slide configuration and the jet blocks which help create a smoothbore effect. The high velocity of the air flow means a stronger vacuum at the needle jet, providing more precise metering and better throttle response.
While the sku of this part is VM28-418, it shares the typical characteristics of the TM series flat slides. Many people call this the TM28, but the sku is not a mistake.
http://www.mapcycle.com/categories/carburation-intake/carburetors-tuning/carburetors/mikuni-carbs/vm28-418-mikuni-vm28-tm28-flat-slide-28mm-carburetor.html
When you say Boost Bottle are you referring to one of mine TSR/Barlow designed or a aluminum aftermarket for a Banshee?
The Banshee's work very poor and in general don't work well on the air cooled RD cylinders.
Start tuning with just a standard crossover tube, then try the boost bottle.
Chuck
https://www.jetsrus.com/carburetor/carb_mikuni_TM_series.html
calls out a 1.8 air jet. from everything ive read, they usually don't have one installed particularly in stock applications, but aftermarket, yes.
that part numbering is super weird.
In the TM34's, they come with no air jet and is how I do run them.
Starting jetting for TM34 on my stg2 RD400's with VF YZ85 reeds, aftermarket intake manifolds, pipes, porting, uni foam filters, using my TSR/Barlow designed boost bottle:
310 main
Q0 needle jet
42.5 pilot
needle clip on 4 or 5 position
1 - 1/2 air screw
Chuck
.. for clarification, i was referring specifically to the 28's. there a bunch of variants on them, including some that had factory installed power jets. :twocents:
I think I have 180 or 200 mains, P6, 32.5 pilot, and clip in the middle on standard needle with TM28's.
I also adapted the outlet spigot up to the right size for the RD intake rubbers, but am running YZ125 reeds, modified DG's, a tiny bit of porting, and uni's. It runs good but my stingers are tad small and it doesn't rev quite as far as I'd like it to as a result. It is tractable and easy to ride around the city and it starts first kick 90% of the time.
If you use the needle and needle jet provided you will end up at the 380 range. Start with a 32.5 pilot as well. I have set these carbs up on several rd350s and my Rz at one point. The Rz ended up at 420 on the main.
And yes the spigot should be cut off and a new one machined and pressed on. Run uni filters as well. And Rz 350 intake manifolds with a cross over tube or the Barlow bottle chuck makes and use tdr yz125 reed petals. Machined heads for proper squish will be one of your biggest improvements you can do as well.
Garrett
i'm currently in a fistfight with mine, on the main, but everything else seems to be good. the mid range pulls like a monster truck. sudco gave me the following as a baseline. note the need for new needle jets. This is also for an 88 RZ, so i'm sure there will be some minor differences. hope this helps. they told me that with the stock needle jets i'd never get it running right. when i finally get the top jet figured out, i'll let you know
250 mains (i'm at 230)
35 pilots
169-O-0 needle jets
sdp39 needles (second from the top slot best so far, but this and main are changing )
2.5 slides
open air jet
i'm at about 1.75 turns out right now
Ok......I have it narrowed down to 230 mains. One clip lean of centre on the needles. 220 was pretty all right on the plug chops (pictured), but was stuttering a little bit under really hard acceleration. I put the 230 mains on it and I think it's running pretty well. I haven't done a chop from the 230s yet but even the 220s looked pretty good.
Figured out a trick last week that saves you from having to cut apart almost new plugs. Take a picture with your phone, flash on and it will get a clear picture all the way down the insulator. Zoom in to the base and theres your ring.
Quote from: sav0r on March 18, 2019, 07:49:48 PM
I think I have 180 or 200 mains, P6, 32.5 pilot, and clip in the middle on standard needle with TM28's.
I also adapted the outlet spigot up to the right size for the RD intake rubbers, but am running YZ125 reeds, modified DG's, a tiny bit of porting, and uni's. It runs good but my stingers are tad small and it doesn't rev quite as far as I'd like it to as a result. It is tractable and easy to ride around the city and it starts first kick 90% of the time.
I am using RG250 GJ Mikuni TM28SS carbs on my RD350AC. Bike has a Dyna S ignition and UNI pod filters and Banshee reeds. Present set up is MJ-190 , PJ- 25, slide cutaway-2.0 , float valve-2.5 , Needle- 5DP39 , Needle jet-P-0 ( is this 175 P-0?) . What is the ball park jetting for such a bike ? Bike shows some hesitation after 85km/hr. Plug is black oil fouled looks. Compression is around 125 psi in the left and 120 psi in the right cylinder. Thanks