[rayman]

Any experience with above combination. The thing is that we are running the RMC with the engine sealed of course, but also competing in a national class against other engines, and it is allowed to replace the VHSB34 with VHSH30 (used in ROK). We lack torque on the narrow curcuits and I assume a narrower venturi/choke would help. Any "converter" available for the VHSHcarb (Ø35mm) to the engine-connection ?

[DMmotorsport]

Hi!

You ar totally right! the VHSH is good Carb, we use it now for MANY years on KZ, and before ICC. and indeed the smaller venturi will bring you more torque.. smoother and a bit heavier acceleration in outcoming corners... but the inlettype of the Vortex Rok is different, so hard to explain at this point...
But for sure it wil word iff you use the right mainJets, Needles and polverizzatore (i do not know the englisch word, this is the house where you needle/timing for jetting goes in)
=> there are about 999 combinations for this... but i can help you out a bit iff you want to...
contact me if you need some inf!

Ciao, Kristof
www.DMmotorsport.be

[rayman]

Hi Kristof

I guess that setting up the VHSH30 (jetting, needles etc) for a KZ-engine is not the same as for the Rotax - but assume that a ROK-driver could help me out there, as the engines are much alike. I have a friend who drives ROK and will ask him for help - but thx anyway.

KR
povl

[DMmotorsport]

Okej no problemo...

We did this before on the Rotax...
And we do this A LOT, on the KF4 engines, this is de hobby-KF2, we build on this carb, cause its less hard to setup than the screws...

For you engine i should start with:

Needle K21 (on the 2nd stand, counting from the upper standing on the needle)
Polver. DQ270 or DP268
main jet: 175 (late betweest 172 and 180... to get it adjusted, but be care ful in the beginning...)
acc.Jet: 50

Ciao, Kristof

[rayman]

Thx vm Kristof - Will try that and keep an eye on the temp. Aprreciate ur help

kr
povl

[gp8]

Also try Tom Barth at Greeflag as he has some interesting information and kits for TAG type kart motors. See http://www.greenflag.net/dell/dellorto.html to get you started...

[rayman]

Thx will have a look at the page. We did some testing during raceweekend - which is obviously not the best time. We ended up running with atomizer 264DP, idle tube jet 45, Needle K28, floats 4,0gr and slide 50 and then went from main-jet 175 to end down 153 - This shd be standard ROK set-up. It really gave a lot of torque but had problems reaching more than 12,600rpm on the circuit which didnt have a very long strait. I am not shure whether engine got to much fuel and 4-stroke (its my son who is racing - I try to be the engineer ) In 2nd heat we went back to the 34mm VHSB carb and ended 3rd place after 6th in qualifying. I am sure the 30mm can do the job at the small twisting tracks. Will see if I can borrow the carb again and also a variable main jet. Will then put on a EGT to measure the exhaust temp and slowly go more lean in mixture

[DMmotorsport]

alsoo with the DP 'atomizer' you will run richer than with the DQ on same config....
But it's a lot of searchnig for sure... but you had a lot of torque now.. and less RPM's...
So now check out spark-plug or exhaust temp... and see if it runs to rich... probably it does..
exhasut temp for ROK, i do not know... probably 480 ... for sparkplug 87-88...
Don't know for sure for rok...never worked with ne for real... so..

Ciao, Kristof