Hi again. Got part throttle fluffyness on 75 MAR250. Amal carb. Had it apart, done all needle heights, all possible air screw combinations, never right. Air screw fully in gives nice no throttle type torque. At full throttle all OK, just on part futtt splutter. Never stalls, always starts first time. No air leaks, although compression when kick starting seems a little easy.

50 to 1 synthetic.  Thinking of a Mikuni carb from Inmotion. Any input appreciated.

 Thanks

Nicky, I have no patience with Amals , for me Mikuni , the only problem is jetting.

The carbs we get from the largest supplier come std. with a 60 pilot / 190 main

on the 26mm , this is very safe as I have yet to see that combination work ( way rich=safe).

Hopefully Inmotion has a good jet combination.

Good Luck

Larry

Thanks, they do say, "jettet for model", so here goes.

 

 

Just for talking purposes only 40 or 50 pilot, 100 main is what we have found

for the Bultacos'.

Maybe a starting place, I am sure there are those closer to you with more expertise.

I'm running an OKO on my 74 Explorer and MAR with. Pioneer engine.

So,far they have been great. Pretty easy to setup and work well- plus the price is right.

If you are working with a VM26 an ideal starting point is 155 main and 35-40 pilot from sea level to around 4000' then come down 5-10 on both.

Tony

Thanks all

I've similar issues with my 74 MAR, starts fine but once it's warmed up part throttle is fluffy. The old Amal thottle slide is worn out and I'd be interested to know how you get on with Mikuni carb from Inmotion as I'm thinking of getting one as well. It looks like the only way to cure it.

 

Its a shame as I really like the bike but the engine bogging down when I just want to lift the front a bit over a log is a real pain.

 

Cheers

Carb improved it, 150/55 too high a no. though, 135 better it seems.

Wasn't right though, had an aftermarket rear silencer and let someones son have a go. He fell off (full front brake in the mud, REALLY) and snapped the exhaust off. Ran perfect from then on! So it's so much more than just the carb. Pulled the barrell, bore looks fine but small end play and too much big end float IMO. Engine now with Steve Sell for a full rebuild and re-shim of the gearbox.

 Mikuni worth doing? Yes, although my Amal seemed in good nick there was an improvment.

 

 Not sure where Inmotion get their carbs, but also check out

http://www.allensperformance.co.uk/

Get some jets while you are there, and you will need to convert the airbox hose

 

Edited August 13, 201511 yr by nickyburnell

Thanks I'm going shopping for a new carb

I've had my MAR running on quite a few different carbs.

 

The Amals I find a bit soft, whatever they are made of seems to wear and go out of shape after a few years, so an old one will more than likely be unservicable in my opinion.

 

The Mikuni VM26 isn't a bad carb, it's cheap and easy to tune.

It seems they are fairly robust and don't tend to have some issues associated with other carbs.

The drawback is they do meter out fuel a bit rougher and aren't as smooth as some.

The settings and jets required are out on this forum somewhere, so you could save a few quid over the one mentioned.

One (used) off a Rev3 pretty much runs right.

 

I've also tried a couple of Dellorto VHST's. (flatslides) Both 24mm and 26mm.

These are a little more fussy to tune and considerably more expensive (though can be snapped up on scooter sites reasonable).

But once sorted are far smoother and responsive, so much my bike feels totally different.

They do seem to suffer from the slightest spec of dirt and can suffer blocking of the pilot circuit very easily.

 

With the 24mm, the air speed through it is increased, so feels tighter and zippier.

The 26mm tends to give it more of a wallop.

Again, the settings and jetting are pretty close the the Rev3 (for the 26mm) and are on this forum somewhere.

 

Not tried the OKO yet, though I here they are very similar to other flatsides but easier to tune than most.