Author Topic: help jetting this rd400g got it almost perfect  (Read 217 times)

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Offline joseimport

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help jetting this rd400g got it almost perfect
« on: October 08, 2021, 05:36:29 PM »
hey guys i need a little help here on my pilot jetting.

this is my rd400g

https://www.youtube.com/watch?v=_fpOQJUjanM

she's on her  final stages of tuning after a complete rebuild that took almost 5 years.

info on the bike:
-altitude 5250 feet
-2r9 carbs
  • 27.5 pilot jet
  • 150 main jat
  • keyster 5j6 needle (i have the original 5j6 needles but one has lost the anodizing, had to order the closest thing which was a rebuild kit from keyster that has the 5j6 needles from yambits, but they are a little different from the original mikuni, so had to change them both.
-2r9 exhaust
-stock airbox
-squish band on 3j7 heads fixed by chuck quenzler
-crank rebuild by chuck quenzler

the bike starts first kick with the "choke" from cold.

i synched  the carbs as per the manual suggests.

set the idle at 1400ish rpm.

i have been learning about this mikuni carbs, but still learning.
i have been fiddling with the airscrew:
When i close the airscrew totally once warm the bike does not die (should it die?). and it seems to be working better at 0.5 turns out than the 1.5 out its supposed to run.
when i open the screw 3.5 turns out, there is a change and the bike seems to get worse when out, but the difference is only noticed when I give her some throttle, not idleing.
On all positions of the airscrew (0.5 , 1.5 and 3.5 turns out) the bike returns to idle in the same manner.  not faster not slower once revved. probably better when 0.5 out like the video.
in the video the airscrew is set at 0.5 turns out from fully closed which is the one i think works better.
When i quickly open the throttle, there is a little hesitation on the bike to get from 1400 rpms to 2000 rpms. what i try to say is it does not feel linear.



my main question here is following what I have read on other posts..... should i go from 27.5 pilot to a 30 pilot?

or this means i should try  a 25 pilot?


1975 cb750k2: ongoing restoration project. http://forums.sohc4.net/index.php/topic,183427.msg2122966.html#msg2122966
1979 rd400g daytona special: started putting it back together. http://www.2strokeworld.net/forum/index.php?topic=71.0
1987 tr200 fatcat: running.

Offline Striker1423

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Re: help jetting this rd400g got it almost perfect
« Reply #1 on: October 08, 2021, 06:47:47 PM »
Yes bigger on the pilot.

Offline 1976RD400C

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Re: help jetting this rd400g got it almost perfect
« Reply #2 on: October 09, 2021, 05:45:55 AM »
2 votes for bigger
'76 RD400 green  '76 RD400 red   '84 RZ350

Offline Hawaii-Mike

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Re: help jetting this rd400g got it almost perfect
« Reply #3 on: October 09, 2021, 06:35:17 PM »
Two thoughts:

- Keyster brass parts are known to be inaccurate compared to original Mikuni.

- Daytona carbs are known to be difficult to work with.  I had a Daytona years ago, talked to the local 2-stroke mechanic, he said to ditch them and go with earlier RD400 carbs.  I did that and jetting was much easier.

Offline SoCal250

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Re: help jetting this rd400g got it almost perfect
« Reply #4 on: October 09, 2021, 07:05:15 PM »
Two thoughts:

- Keyster brass parts are known to be inaccurate compared to original Mikuni.

- Daytona carbs are known to be difficult to work with.  I had a Daytona years ago, talked to the local 2-stroke mechanic, he said to ditch them and go with earlier RD400 carbs.  I did that and jetting was much easier.

True, I stay away from Keyster brass.

He has 2R9 carbs (which are basically the same as 1A1), not 2V0.

79 Yamaha RD400F     77 Yamaha RD400D     
75 Yamaha RD250B     75 Yamaha RD200B (project)
75 Yamaha RD125B     75 Yamaha RD125B (project)
89 Yamaha FZR400      05 Yamaha FZ6
91 Yamaha TZR250R    02 Aprilia RS250 Cup (sold)

Offline Milan

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Re: help jetting this rd400g got it almost perfect
« Reply #5 on: October 12, 2021, 11:23:50 AM »
When I put a K & N in my Canadian Daytona, 2R9 carbs,
I had to go with a 160 Main, & #30 Pilot.

So try a #30 pilot.

I may end up with some extra 5J6 needles.
If they ever get here from Ebay purchase.

M

Offline joseimport

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Re: help jetting this rd400g got it almost perfect
« Reply #6 on: October 12, 2021, 12:14:52 PM »
When I put a K & N in my Canadian Daytona, 2R9 carbs,
I had to go with a 160 Main, & #30 Pilot.

So try a #30 pilot.

I may end up with some extra 5J6 needles.
If they ever get here from Ebay purchase.

M


i ordered a set of mikuni pilots 30 and 32.5 just in case

plus 155 and 160 jets

if you can sell me either a set or just one of the 5j6 needles let me know, i would appreciate that.


« Last Edit: October 12, 2021, 12:22:46 PM by joseimport »
1975 cb750k2: ongoing restoration project. http://forums.sohc4.net/index.php/topic,183427.msg2122966.html#msg2122966
1979 rd400g daytona special: started putting it back together. http://www.2strokeworld.net/forum/index.php?topic=71.0
1987 tr200 fatcat: running.

Offline joseimport

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Re: help jetting this rd400g got it almost perfect
« Reply #7 on: October 12, 2021, 12:19:59 PM »
Two thoughts:

- Keyster brass parts are known to be inaccurate compared to original Mikuni.

- Daytona carbs are known to be difficult to work with.  I had a Daytona years ago, talked to the local 2-stroke mechanic, he said to ditch them and go with earlier RD400 carbs.  I did that and jetting was much easier.

-that's what I have heard from everybody, but the original 5j6 needles are not made anymore and impossible to find, so what are my options? will see how the bike behaves with the keyster ones, only used the needles, all the jets are mikuni.

-its 2r9 carbs not 2vo the g models do not have the emissions stuff of the daytona plus have cdi ignition.
1975 cb750k2: ongoing restoration project. http://forums.sohc4.net/index.php/topic,183427.msg2122966.html#msg2122966
1979 rd400g daytona special: started putting it back together. http://www.2strokeworld.net/forum/index.php?topic=71.0
1987 tr200 fatcat: running.

Offline joseimport

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Re: help jetting this rd400g got it almost perfect
« Reply #8 on: October 12, 2021, 12:21:29 PM »
Two thoughts:

- Keyster brass parts are known to be inaccurate compared to original Mikuni.

- Daytona carbs are known to be difficult to work with.  I had a Daytona years ago, talked to the local 2-stroke mechanic, he said to ditch them and go with earlier RD400 carbs.  I did that and jetting was much easier.

True, I stay away from Keyster brass.

He has 2R9 carbs (which are basically the same as 1A1), not 2V0.

its impossible to find 5j6 needles.....  what are my options besides the keyster ones, which are diferently sized.
1975 cb750k2: ongoing restoration project. http://forums.sohc4.net/index.php/topic,183427.msg2122966.html#msg2122966
1979 rd400g daytona special: started putting it back together. http://www.2strokeworld.net/forum/index.php?topic=71.0
1987 tr200 fatcat: running.

Offline m in sc

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Re: help jetting this rd400g got it almost perfect
« Reply #9 on: October 12, 2021, 01:22:53 PM »
... flatslides.   :whistle:

Offline teazer

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Re: help jetting this rd400g got it almost perfect
« Reply #10 on: October 12, 2021, 03:13:08 PM »
fJ6 were used in RD400E and F in Australia and I think Canada, so you could check the parts list and see if your dealer can get a pair or see if they are available in either of those countries as a Yamaha part.

They are leaner than say 5L1 used in C/D models and richer that 5I4 used in RD350s.  The closest Mikuni needle I found is 5DP7 which is a little leaner and may require larger needle jets or different air jets to get the fuel slope right.

You could measure your OEM needles every 5mm and compare the dimensions to keyster to see how close they are. To do that you can use an optical comparitor or just take a piece of paper and mark a line every 5mm.  Then make sure to tart at the very top in the same place and measure the diameters.

A simpler but less numeric way is to use a set of vernier/digital calipers and close them most of the way up on a needle and then slip the other needle in beside it. If the second needle is smaller diameter it will slide further through the jaws and if it's fatter it will sit higher.  It's fiddly but easy to see if one needle is thicker or thinner than another at any point along its length.