News:

Mat Oxley 1986 IOM TT


click above to read more about Mat.

Main Menu

Step by Step Guide on RD350 Carburetor Tuning VM28

Started by Pravin, June 17, 2021, 11:16:05 AM

Previous topic - Next topic

0 Members and 1 Guest are viewing this topic.

Pravin

Hi All ,

I know this is there somewhere but do we have any link or topic explaining how to set and tune RD350 VM28 carburetors ?

Like once installed , setting up the slides which I know using candy sticks but then I get confused on Idling and air screw setting which one to set first and how to do it for independent cylinder...

Any  step by step writeup or link will help :)

Cheers,
Pravin

m in sc


SoCal250

In addition to what Mark posted I think this is a great reference: "Carb tune aid" (see attached PDF)

More info:
http://www.iwt.com.au/mikunicarb.htm
"Beginners Guide to Two Stroke Jetting" from advrider.com (see attached PDF)
75 Yamaha RD125B   75 Yamaha RD125B (project)
75 Yamaha RD250B   75 Yamaha RD200B (project)
73 Yamaha RD350     77 Yamaha RD400D   79 Yamaha RD400F  
91 Yamaha TZR250R  89 Yamaha FZR400   05 Yamaha FZ6   
05 Yamaha XT225TC  82 Honda MB5  02 Aprilia RS250 Cup (sold)

Pravin

Thanks For the links , I do understood the functioning of the carbs  with this ,

Now on the Specific Tuning part ,

1) I clean the carbs , pilot circuit , main jets , pilot jets , all brass basically.
2) Assemble the carbs , needle in center notch
3) 140 mains 25 pilot .. standard set up..
4) I put Air Screw 1.5 turn on both
5) Start the bike and adjust the idle..

DO we take out the idle screws while adjusting the slide levels ?
DO we adjust the air screw of one cylinder at a time ? and we need to raise the RPM of that cylinder by turning the Idle Screw in ?
At what point the air screw to be adjusted ? how do we make out the air fuel mixture is ideal ? by listening to the engine revs?
And ones Air Screw is set we bring down the idle to around 1200 rpm and doesn't that affect the air screw tuning we did ?

Cheers.
Pravin Dalvi


m in sc

#4
dont forget to pull the jet tube out and clean as well, and the air jet orifice at bottom of bellmouth on filter side of carb.

get slide screws where they just touch the slide then go in maybe 3/4 turn as a starting point.

air screws should always be even. IF not, something else is requiring them to be different from each other.

you should view tuning a twin or triple as 2 (or 3) single cyl motors linked together and synchronized.

set pilot screw settings 1st.  you want the highest idle obtainable, and smooth, with the air screw.  IF the air screw doesnt affect it, either the pilot is too large or small, or you have the bike idling on the needle(slide too high) a method i use it to get bike warmed up, and let idle. then, very gently just crack the throttle up to 1/16th and see if the rpms hold. IF it revs high, its lean. if it burbles, its too rich, you can get this really close before you ever ride it. aim for a target of 1.25 to 1.75 turns out. yes, they should be evenly adjusted together.


start with needle on middle if not stock. 

set those 2 1st.


you should be able to get it really close if the bike is stock by just setting it up to factory specs.  as far as carb synchronizing, i always set the slides even at the top of the bore using a mirror.

this has worked for me for 20+ years