Carburettor Jets

[Wayne1960]

Ok

So I kept everything the same and put in the 120 main, Rich as was expected!!!!!! anyway it proves some of the theories.

So carbs stripped and im going to check everything again.

Im going for the 117 main as suggested.

I cant find anything here for setting up the throttle slide and going to stick with the A4 spec of 1.5mm however, and theres always another questoin?

Do i have to have the throttle stop wound in as in all the literature, think 10mm gap or simply let the slides bottom out and adjust to the 1.5mm gap.

My slides on the VM26s do not have a cut away which i keep rading so i guess its measured fro the availble gap created.

[zed1015]

Easy way to bench sync without mucking about with bits of metal bar under the slides etc is to set all your slide adjusters midway on their travel and level the slides to the top of the carb bores with the throttle open.
Once done you need to vac balance to get all the cylinders working equally.
Once vac'd all the slides are not forced to be level as you are balancing the work each cylinder is producing with its neighbors so a weaker, less efficient cylinder will have its slide slightly higher than the others.
Your slides do have a cutaway and it is the raised curve on the bottom face of the slide facing the airbox.
The size is stamped on the under side of the slide 1.5 or 2.0 etc.
The higher the number the bigger the cutaway and the weaker the signal to the pilot and needle jet.
Bigger cutaway equals weaker mix and smaller equals richer.
It affects fueling between 1/8th and half throttle.

[johny brando]

Easy way to bench sync without mucking about with bits of metal bar under the slides etc is to set all your slide adjusters midway on their travel and level the slides to the top of the carb bores with the throttle open.
Once done you need to vac balance to get all the cylinders working equally.
Once vac'd all the slides are not forced to be level as you are balancing the work each cylinder is producing with its neighbors so a weaker, less efficient cylinder will have its slide slightly higher than the others.
Your slides do have a cutaway and it is the raised curve on the bottom face of the slide facing the airbox.
The size is stamped on the under side of the slide 1.5 or 2.0 etc.
The higher the number the bigger the cutaway and the weaker the signal to the pilot and needle jet.
Bigger cutaway equals weaker mix and smaller equals richer.
It affects fueling between 1/8th and half throttle.

I HEAR & FEEL YOUR FRUSTRATION ROB ! ........I can't for the life of me understand why your carb set up directions are not just being followed !!!! Why make it so hard & try to reinvent the Wheel ? This bloke ( Rob ) has forgotten more than the rest of us know ! ........why question or doubt his sincerity .....when we already know that he know's way more than us ?
This forum is very fortunate to have that level of expertise combined with that level of willingness to share that very hard earn't experience based knowledge , which has taken years & years to gather & retain .
I'm not saying for one minute that there are not other well meaning & versed contributors on the forum but really .......please give him a break aye !

[Kwackman]

Easy way to bench sync without mucking about with bits of metal bar under the slides etc is to set all your slide adjusters midway on their travel and level the slides to the top of the carb bores with the throttle open.

Damn that's clever, I wish I'd read that a few months ago!

[moizeau]

Easy way to bench sync without mucking about with bits of metal bar under the slides etc is to set all your slide adjusters midway on their travel and level the slides to the top of the carb bores with the throttle open.

Damn that's clever, I wish I'd read that a few months ago!

Absolutely +1, when you think about it the wire is just a reference point so why not use the carb itself. So simple it's ingenious.

[Wayne1960]

OK this is what i have received from someone in the know and i have just completed the set up.

In every case start off setting the gap between push pull cable butterfly and tin cable bracket.
Think it's about 1.5 mm to 2,00mm. Absolutely critical this gap and you do it by simply turning in the
tick over screw until you get that gap… Do not touch it again.
At this point hold the carbs up towards a bright ceiling light and make sure you can see light through
the bottom of the slide and bottom of carb bore.

Just a word of warning, if the gap mentioned above is already at that distance something could be wrong.
It may be that one or two slides are completely bottomed already. No visible light through slide and bottom of bore.
If so, undo the locking nuts and turn the lifter arm adjuster screw one way or the other until you can see light.
The push pull butterfly may have moved so check the distance again and ensure it is 1.5mm

With the butterfly gap at 1,5mm or 2.00mm turn the adjuster of each carb so that the slide moves down.
The distance between bottom of slide and bottom of carb body should be 0.60mm
I used to use pin gauges for this because they are rigid. You may have to find a piece of wire 0.60 mm thick.
If the adjuster screw becomes tight to turn then release the tension in the lifter arm by backing off
the clamping bolt next to the adjuster. Repeat for remaining three carbs.

To conclude, push pull butterfly gap at 1.5 mm, slide to bottom of carb body 0.60mm

If the slide height is greater than 0.60 mm the engine may be slow to shut down…

All being well you have correctly set slides. When the engine is warm and tick over
to high or low that 1.50 mm gap I keep harping on about gives you the facility to increase
or decrease. It only takes a bit of a turn when everything else is right.

[Wayne1960]

For those that are still interested.

Carbs back on and I'm satisfied I have the set up right.


Started first time and for the first time I have the ability to use the idle jets to adjust carbs.

However I need to be a good 2 x's out to get mixture right so I'm guessing the 117.5 main jet needs changing.

I also checked the balance and they were very close but will need adjusting which I will do when I sort the idle.


I'm still a little concerned that I get a very slight fluctuation that definitely gets better when I pull in the clutch.

It feels like its missing and I'm now wandering if its electrical.