I have fitted a Mikuni VM26-8074 to my MK2 MAR this  came with 190 main and 50 pilot I have now fitted a 150 main and 30 pilot and it is running ok but the throttle response at low to 1/4 throttle is still not right, as the main and pilot were to large I was wondering what the Air Jet size should be, the one fitted appears to be 0.5 but it is very hard to read

 

Not an expert on the MAR and I'm sure someone will come along soon who is but at small throttle openings I'd be suspecting the pilot jet or circuit. (30 sounds a bit small to me maybe 35?)

 

You don't say if a new or used carb and jet - irrespective,  I've found machining swarf in new carbs and styrene packing in new jets so probably not important.  

 

I'd be giving the pilot jet and circuit a good blow through with aerosol carb cleaner and air. But while you've got the carb off it doesn't take much more time the give all the jets and circuits a good blow out and check the float height. At least you then have all the bases covered before you experiment with jets.

 

Hope this helps Buddy.

 

Paul Mac

Hi Paul, Its a new carb and I have already cleaned it and checked the float height, I will try a larger pilot

I bought my 250cc MAR and someone had already fitted a VM26 Mikuni(from a well known supplier of twinshock parts) it never ran that cleanly low down.

My bike had the Romat reed conversion fitted, don't know if that made any difference.

I did get it very near to usable with similar jets you have fitted, around 30 pilot and 140/150 main.

But it was still quite fluffy when it started to pick up off the main jet.

I ended up with a 24mm VHST Dellorto in the end as I'd set a few up in the past, Mikunis aren't great as anyone that ever owned a Rev3 will tell you.

I've ridden one with a OKO that was miles better than one with a Mikuni.

I think Mid Atlantic Trials do a Mar kit.

I have an OKO on my 74 Explorer (same as MAR), on a 72 MAR I had and even on a 200 GasGas EC.

They work very well and great price.

The OSSA kits from MidAtlantic were complete and easy.

Sorry, can't help a lot on your Mikuni, just the usual. Figure if rich or lean, and adjust appropriate circuit to suit.

My last MAR 250, I fitted a new Mikuni VM26 and with many jet changes, I ended  up with 155 main / 35 pilot. And yes the air jet was 0.5.

and dropped the needle clip to 3rd notch down.

At the throttle opening you describe you are above the pilot jet region and well below main jet. This 1/8 to 1/4 area is controlled  by the needle, needle jet and throttle slide cut away.

you could try moving needle up or down depending if you think it is rich or weak. (you don't say which you think it is).

 

If you search Mikuni vm26, then click on vm "round slide" tuning manual, there is hours of fine reading!

 

cheers stan.

Thanks for all the info, unfortunately I wont be able to ride for a couple of weeks but will update when I have had a chance to try some new jets and settings