RT 450 carb replacement

[nigmar]

Hi All

During the lock down I have time to work on the RT and am looking for advice on what carb to replace the VHB with.

Thanks in advance
Nigel

[graeme]

Hello Nigel

A phf 32 dellorto worked well enough on my RT
Same jetting etc as a Darmah but change the 265 atomiser to 262
Or mikuni but I have no personal experience on a 450

Graeme

[tobydmv]

I went the Mikuni route and ordered a prefab'd unit from Sudco in the states. I had to increase the idle jet and drop the needle a slot or two and i'm now spot on. I used a bolt on intake manifold from Guzzino http://guzzino.com/duinma250350.html and a rubber coupling from somewhere, maybe treatland to connect it all. It was quite an adventure figuring out whether I had carb or ignition problems. It ended up being ignition and my bike is now somewhat sorted.

[Dan C]

I had to increase the idle jet and drop the needle a slot or two and i'm now spot on

Hi Toby,
I'm assuming you have a Mikuni VM carb. I'd be interested to know:
a. What size
b. Pilot jet
c. Needle jet
d. Needle
e. Main jet

Reason being I am trying to find jettings for VM30 Mikunis for 450, 350 and 250. I am replacing the VHB's with Mikunis.

Cheers
Dan

[tobydmv]

Hi Toby,
I'm assuming you have a Mikuni VM carb. I'd be interested to know:
a. What size
b. Pilot jet
c. Needle jet
d. Needle
e. Main jet

Reason being I am trying to find jettings for VM30 Mikunis for 450, 350 and 250. I am replacing the VHB's with Mikunis.

Cheers
Dan

Hi Dan, heres the spec list i've worked out. Note that I run ethanol free premium gas. I was not happy with this needle taper until I increased the pilot jet and then it seems ok, it has an on/off feeling when you finally get on the taper. I tried a diff needles but it was much worse.

a. Mikuni VM 28, part # 001.112, from Sudco in USA
b. Pilot jet 35(up from original 30)
c. 169 0-2 needle jet
d. 5DP7 Needle on 2nd to lowest/richest clip
e. 140 main
f. 0.5 air jet

[Dan C]

Hi Toby,
You're a dead set legend - that's really helpful. Thank you very much!!
I assume its on a 450RT? should have asked first time......
Cheers
Dan

[tobydmv]

Hi Toby,
You're a dead set legend - that's really helpful. Thank you very much!!
I assume its on a 450RT? should have asked first time......
Cheers
Dan

250 NC Scrambler 5 speed

[Dan C]

Thanks Toby, I have one of those without a carb so now i know what to get!

[HMBAtrail]

I'm kind of in the same situation. I am looking to swap out my VHB 29 on the RT 450. I simply could never get it right. Particularly up on the top end. On my 350 race bike I have a 38mm Mikuni and I have an extra one of those on the bench. I also have a VHB 30 with a little bit of a sloppy slide. I have jets upon jets as well as several needles for a VM or a VHB.

I know a VM38 sounds huge but it's the cat's pajamas on the race bike but I'm trying to figure what route to go. I don't want to go through a ton of jet swaps only to pull the carb and go a different route. Mind you, I'm racing the RT and it isn't for the street. It's motocross race only.