Topic: Mikuni TMR32 Needle jet removal - setup pilot circuit solved by correct Pilot Air Jet June 2022

[PeWe]

I need to take out the needle jets, replace them with smaller.

How to get them out?
No problem to remove the main jet holder that is a fuel pipe up to the needle jet (red arrow) where the needle pass thru.

I tried one, it sit hard if it should be pressed out from inside when the main jet holder is out. Not to much force to  be used either since it look fragile.
I need to try again with a wooden stick with needle out I guess.

Anyone that has done this before?
Internet is not overflowed with TMR service guidelines.

[1976cb750f836]

White viniger might loosen them, not sure what it will do to the alum though.
Heat might help,  doesn't alum expand more than brass?

[PeWe]

I could get it out. The brass sticking up in the venturi should not be touched. The jet sit under.
I got a hint from a carburetor specialist here in Sweden to stick a piece if thin wood inside and press it down. He  recommend size (O-8). TMR32 stock size P1 is too rich the first 5mm throttle lift, not possible to adjust with needle. No other available needles that match the need.

I made a thin stick and hammered it from above with an allen head tool I had sticked thru the slide without needle.
Pling! Out it came.
I hope I can do all other 3 carbs without taking them out.

[MRieck]

 Good info Per. Maybe you could get me a set or possibly 2 sets as I have TMR-36's too....please PM me. TMR stuff is impossible to get here.

[PeWe]

Hi Mike,
Yes TMR parts are not that easy to find.
I found float bowl gaskets on eBay Holland, Frank! MX parts.
An extra set a must when changing pilot jets when all bowls must go off, together.
The gasket swell by fuel so replace all gaskets with dry ones.
The other set will work next time when dried up. This will avoid pinching them as I did the first times.

Other small parts available at Webike Japan.
They have also these needle jets. The total price for me will be almost the same if order here 210SEK/each. We have high customs fee and VAT.

I'll go for 2 sizes smaller, O-6.

P1 is almost working with needles at the very bottom, highest clip notch + 1mm thinner washer under the clip making 1 notch further. One size smaller would probably fix it.

But, this setting however, cause too lean at higher throttle lift. Hesitation around 90-100mph where it earlier accelerated very well, like a fright train passing the 200kmh mark

Needles must go back to 2:6 notch for the higher lift , needle jet reduce the fuel on low lift where engine runs very rich. Pilot jet does not help there.

Email sent Mike...

[MRieck]

Hi Mike,
Yes TMR parts are not that easy to find.
I found float bowl gaskets on eBay Holland, Frank! MX parts.
An extra set a must when changi ng pilot jets when all bowls must go off, together.
The gasket swell by fuel so replace all gaskets with dry ones.
The other set will work next time when dried up. This will avoid pinching them as I did the first times.

Other small parts available at Webike Japan.
They have also these needle jets. The total price for me will be almost the same if order here 210SEK/each. We have high customs fee and VAT.

I'll go for 2 sizes smaller, O-6.

P1 is almost working with needles at the very bottom, highest clip notch + 1mm thinner washer under the clip making 1 notch further. One size smaller would probably fix it.

But, this setting however, cause too lean at higher throttle lift. Hesitation around 90-100mph where it earlier accelerated very well, like a fright train passing the 200kmh mark

Needles must go back to 2:6 notch for the higher lift , needle jet reduce the fuel on low lift where engine runs very rich. Pilot jet does not help there.

Email sent Mike...

Thanks for the email Per. I forgot about Webike....I do have carb rebuild kits etc for the TMR's that I purchased from them. I'll look it up.

[PeWe]

It is good to know alternatives, if there is a part urgency and Webike is out of stock.
http://www.braigasen.se 
info@braigasen.com

Swedish website, but the automatic webpage translate will fix that. Order outside EU will remove the VAT.

The guy I have been in contact know what he sells and what that might be needed if a perfect explanation about the carb -engine behaviour and throttle position etc. is written for him.

There is no general guideline for a specific bike. The carbs needs to be changed drastically when I mounted the Hindle 4-2-1, earlier Lotus Root 4-4 that has been checked on dyno.

I guess the breathing is improved and affect the idle and low lift by the engine that suck harder. Main jet was not a surprise, 2 steps up. Needle jet must be leaner, plugs sooted at idle-low throttle lifts.

I have read somewhere that larger displacement also can cause higher underpressure, need of leaner jets when engine sucks harder. My engine same setup as before, only exhaust.
I hope I'll get the right setup before season is off, it need a dyno run to verify the power.

[PeWe]

Smaller needle jets in today,
O-6. (Before P-1)
Used an allen tool with rounded end to slam the old out.
Easy to mount with carbs on bike, only drain plugs out.
Needles removed.
Used a thin allen tool sticked thru main jet holder and needle jet on top. In the drain hole and pressed inside until holder without main jet found threads.

Now good idle with needles in correct position for 1/3-3/4 lift that earlier was really rich from idle to less than 1/4 throttle lift (around 5mm throttle lift was richest).

Allen tool inside throttle hole for needle has just punched out the jet.



Ready to go in thru the drain hole, allen pin keep the jet in place.


Update:
Road test today after work.
Too lean
 Size up to O-8 will arrive next week. Hopefully correct jetted carbs before winter.

[PeWe]

Changed needle jets today. From O-6 to O-8 (richer).
A quick job when knowing how to do.
Here the allen tools used for pressing out the jet thru the needle hole in throttle, 3mm, guide for needle jet assembly, 2mm.

Next is road test up to 4000 rpm with transition to 5000 rpm to verify not too lean.
Roads too wet today.

Engine idles nice and even so assembly is OK.



Next size up (P-0) is ongoing from Webike just for sure. I need the complete series up to stock P-1. It take too long time to get these parts uf urgently needed.

Even Webike had to order which will take 1+ month extra.

Strange,  old Mikuni smoothbore jets available almost everywhere. Modern Mikuni TMR  has only a few that sells jets.

[MRieck]

Thanks for all the testing Per.

[PeWe]

I like to contribute by sharing my experiences on this forum. I have got many ideas and answers here.
Nice people that are very helpful, like you Mike!

Difficult to find TMR32 jetting for CB750/1000

Settings now: Updated Oct 24
Pilot jets: 30 (27.5 at delivery)
Fuel screws 2 1/8   Had to increase to 1 3/4 from 1 1/2. Misfires at throttle off decelerations.
Needle setting 4:6 (4:th from top as carbs had at delivery)
Needle model: 9E11-52  (as delivered with carbs)

Needle jets: O-8 
(earlier much richer P1 since carb delivery, compensated with less needle height (leaner) and too much fuel screws)
(This jet work from very low throttle lift in combination with needle. I thought that pilot covered 1-3mm throttle lift)

Main jets: 140 (150 at delivery, probably for vel stacks)

KN pods filter (recently cleaned)
1005 cc
Cam: RC295 profile
Hindle 4-2-1 (long muffler)

I'll update the complete good jetting when verified on dyno. I can not book a future day this year when that day might be rainy or frosty.

Update:
Test ride with needles at 4:6 is not good enough either. Plugs do not indicate rich setting after the test ride mostly in needle area. (light grey to almost white on ground strap.)
Richened up needles 1 notch to 5:6.
If this will not work fine with too rich at the middle-top needle area, next size up on needle jet, P-0.

I have got the impression of these carbs that needles and needle jet have the same interaction as fuel/air screws and pilot jet.
If needle need to sit in the extreme position change the needle jet. Rich needle can indicate too small needle jet and vice versa.
If fuel screw must sit very rich, step up the pilot.  I do not know where the limits are, maybe 2- 2 1/2 turn out larger pilot:
I think these carbs can have a working range of fuel screws between 1- 2 1/2 turn out.
Sometimes difficult to feel and hear the difference between rich or too lean when engine runs uneven on low throttle lifts.

Mikuni carb chart below show it rather well. Needle jet comes into the picture very early.
October 28:
I tested more to find out while I still have the feeling about how the jets works in these carbs, I must know before winter. The jets are rather separated with their own working range.
- Fuel screws must be set to get good idle and no banging exhaust at decelerations with closed throttles or idle when warm.
- Pilot jet can be increased to cover up for the low area of needle jet. BUT, the idle will suffer at red light choking sooting at take off almost killing the engine if not playing with clutch and twist throttle.
- Needle jet must be correct to cover from 2-3mm lift and together with needles that continue.
- Needles can be set in extreme position to cover up for the needle jet but it will not be enough as I have seen. Before very closed position with rich needle jet (P1), now at the other end very high with a little bit lean needle jets (O-8).

It ran rather OK with fuel screws 1 3/4, Pilots 35, needle jets O-8, needles 5:6, main jets 140.
Oversized pilot to cover up the first 1-2 mm lift for lean needle jet gave sooting idle at red light when taking off.

Next setup I'll do this winter when Needle jets arrive
Needle jets: need to be richer, P-0  (today O-8)
Pilot jets:30
Fuel screws: around 2 turns out
Needles height: I'll start with 4:6
Main jets: 140   The ride today felt like 142.5 would improve. But it was cold weather, 3*C, felt cooler at 160km/h. This is easy to change and I have sizes in steps by 2.5 up and down.
[/i]

[PeWe]

I add more info about these carbs.
Changing pilot jets is easy to do with carbs still on.
- All 4 bowls goes off and back on at the same time hooked into each other by acc pumo fuel hoses.
Rubber band strapped under them from carb 1-4 at removal. Fuel drained before.
4x3 allen screws holds them.

I do not use rubber band at reassembly. Just put all 4 in correct position under so acc pump will find its place, can't move sideways. Raise all 4 with one arm, quickly attach 2-3 screws on carb 3-4, still holding them lean yourself over bike and fasten carb 1. (Possible ti start from 1-2 side too)
 Check that no gaskets have popped out before tighten them all. It can sometime help to use minimal amount of vaseline under the gasket to glue it in place.

An extra set of gaskets is a must. They swell by fuel so they will pinch if reused if not dried up for a few days
I have an extra set, the old saved to next time.

Small screwdriver needed for the pilot jet. I have one with cut handle. Another cut one for main jets.

Cheap screw driver kit with small ones that has a thicker handle to extend them.

Photos with swelled gasket and with fresh dry.
Gasket pop out of the curved groove around fuel screw.

Update December 18:
I finally got the ordered needle jets, size P-0. They were out of stock when ordered.
Will change this weekend
Needle jets:P-0  (today O-8, stock was P-1)
Pilot jets:30 (Stock was 27.5)
Fuel screws: around 2 turns out
Needles height: I'll start with 4:6 (stock was 4:6)
Main jets: 140  (stock was 150)  TMR stock setting probably for velocity stacks

Update December 21:
Needle jets P-0 installed with needles changed to 4:6 as planned.
Waiting for spring and road tests. Only 3 months if lucky

[PeWe]

Update after initial test ride a few days ago and further jet change test idled today:

Needle jets: P-0
Pilot jets: 27.5 (leaner, no test ride jet, idles better)
Fuel screws: around 2 1/4 turns out
Needles height: 4:6
Main jets: 145  (142.5 tested before, 145 better response at >100mph.
Max main jet not double checked yet. I have 147.5 to test and see.

It runs better at low throttle lift, before too rich with P-1. It stuttered just a little at a few mm over idle that the leaner pilot might have fixed.

No reason to lower the needles and loose power where mostly needed. The fright train feeling when twisting the throttle.

More cc make carbs to work different I guess.
2015 with 836cc:
I solved a pinging problem at take offs, the very first mm after idle by going richer on Pilot to 30 from 27.5.
Now is 27.5 back and it idles better. I have to check my notes if I had needles at the leanest back then. One thing is clear, I have learned the carbs, fuel screws must be over 2 turns out. A few years back 1 1/4- 1 3/4.

I had a nice thrilling moment when passing cars in a long left curve on a country road this weekend when testing the jetting
 A long curve with 5-6 cars in front  of me, just twisted,  leaned bike rather much, had to release the throttle a little since 100mph was closing, bumpy road released a low frequency wobble I had to fix by twisting more throttle, straighten bike up and threw it to the right in front of the first car and bend it back again avoiding the ditch and to avoid meeting cars.

It was a guy on a plastic rocket that twisted before that which the old Honda could hang on a few km. He stopped behind the cars.

I gave him a few sec to think and let him hear the Hindle maxing out on 3:rd gear passing him and the curve arrived on 4:th.
Maybe I could have done it without the embarrasing high speed low frequency frame wobble. Less throttle maybe when I slammed in the gear and no need releasing too heavy..

After that I had to continue to ride hard in high speed to not get any psychic obstacles for future rides.

I know that it must have looked scary for whitnesses, but this is how to ride a CB750, a very stable one 

Good news the needles and main jets feels OK.

[seanbarney41]

God damn right PeWe...avoid those psychic obstacles!

[PeWe]

YES, fight fire with fire
That can give a nice thrill in your stomach in scary moments when you want to brake, just twist more

Too cold here for a ride today verifying the low throttle lifts.

[PeWe]

One overseen jet, Pilot Air Jet (PAJ)

This jet is special for these carbs, Mikuni TMR. How it interact with the pilot circuit.

PAJ feeds the Pilot jet with air.
Remove PAJ and Pilot jet, blow with compressed air into Pilot jet hole and feel the flow at the rear. Or use carb cleaner only I sprayed mine to clear them from dirt.

This Pilot Air Jet, PAJ has been not filtered, a design flaw by Mikuni. The filter adapter available with the TMR32 carbs does not cover the PAJ.

Yoshimura has seen this problem and designed an adapter covering the Pilot air jet too. Even the Main Air jet sitting beside that is pugged, not used. 
It fits Yoshimura TMR MJN and Mikuni TMR which the Yoshimura version is based on.
Same for the other sizes.
https://shop.yoshimura-jp.com/en/product/syousai.php?id=20069
Webike has too or had.
https://www.japan-webike.se/products/24600898.html#specification

Latest setup.
Pilot Air Jet: 130
Pilot jet: 27.5
Fuel screws: 3/4 turn out +1/8*
Needle jet: P1
Needle height:  4:6
Needle model:  9D3-52   (aka 9D03-52/ J8-9D03-52)

Wrong needles delivered with carbs, 9E11-52 too rich and not possible to get it right with. Has tried too many combinations.
9D3-52 according to jetting chart found on Internet, Webike.

Main jet: 145*


*With the shorter Hindle muffler

I made my own filtering of the PAJ with 90* fittings found at a model racing website, 300mm PVC hoses ID 4mm and a small KN filter for breathers.
It work fine, not choking the engine. 
Before clogging up affecting air supply.

Nipples M4 thread and 4mm ID hose. 45 SEK each (around 5 USD)
http://shop.miniracingteknik.se/index.php?route=product/product&product_id=2470&search=nippel%2090

My project page with photos
http://forums.sohc4.net/index.php/topic,180468.msg2211515.html#msg2211515

Yoshimura adapters use 50mm pods, Mikuni adapters 54mm.

If ordering Mikuni TMR with adapters for pods, make sure to get the Yoshimura model.

Or fix the filtering as I did. Run without not good, dirt will block.

Engine data:
970cc running on Shell V-Power fuel.
Ported K2 head 34/28mm valves. 
(Aug 2022: Changed back to restored ported 392 head 33.5/28.5mm valves)
Megacycle 125-75 cam
107.5 whp Oct 2022

Cam worked best when In open 27* at 1mm lift, 0 lash.
Tested 30* with power loss,  around 8whp less. 24* also less.

These carbs were also used with 836cc and 4-1 from the beginning
Same jetting can most likely be used except for smaller main jet.

Hindle 4-2-1, short baffle. Good flow.