Concentric 900 series cut away.

[MrShifta]

Am I right in thinking that the amount of cutaway on a throttle slide is measured in 1/8" steps.  e.g. No. 3 cut away is 3/8" up from the bottom flat face ?

Amal reccommend a 3 1/2 cutaway so I need to machine a 1/16" more off my No. 3 slide. O.K. ?  It only comes off the top ( bottom when in the carb) and leaving the cutaway at the same place on the flat.  In other words a cheese shaped bit to be removed.

Amal have suggested a 200 main jet but I see on here many references to 250 mains.  It is a 1956 standard motor with a big fin iron head/barrels.  I don't want to seize it up as its all new inside.  Do I put 250 in to be safe ??

Thanks for any suggestions..

Barry



 

[muskrat]

G'day Barry.
The cut away is measured in 1/16th"
To increase the cut away the angle needs to be increased, so it's taken from the top of the cut away.
Always good to go rich and work down. A new motor likes it to be rich to start with.
Cheers

[Rex]

Slide are cheap enough, so rather than potentially destroy a good slide I'd  just buy another with the cut away needed. Always handy to have a selection of spare carb jets and slides anyway.

[Joolstacho]

"Slide are cheap enough"
Haha, try pricing a new TT carb slide!

No, I got the richest (lowest cutaway - a 3), then I can tune it by grinding the cutaway leaner without having to shell out for new slides.
The worst that can happen is that it's a bit lean in the low-medium throttle openings -just off the pilot jet.

[Triton Thrasher]

If they’re cheap enough, we can attack them with files if we want.

[MrShifta]

Thanks for pointing out my poor memory lads.  I have measured the No. 3 slide  and now accept 1/16" is right.  I am still unsure which size main jet to get.  I have a 150 which is clearly too small no matter who I ask, so having a good lathe and stock of drills I can afford to open it up to .200 which Burlem/Amal suggest. I could also buy a larger jet, so do I go for a 240 or 250 and once I get that big does it matter which ??

[Black Sheep]

Put in a 250 to start with. You really don't want to run lean. Also, just buy a few main jets. I have a great dislike for jets that someone has opened up. I like a main jet that's stamped 200 to actually be a 200, not a 250. Much the same with cutaways, if it says 3, I rather like it to be a 3, not a 3 1/2. Picky, me?   

[MrShifta]

Points taken,  Rex you are right about the cutaway for future owners, I would engrave it as 3 1/2 and as for drilling out jets I would only do it for testing to find what size to buy eventually.  If you take the corners off the drill so that they are rounded but still properly backed off they will cut dead size.  I was taught as a toolmaker and we used to have a selection of rounded drills to use for dowel holes, you can drive dowels in without reaming.

I will try  250 and keep my fingers crossed.

Thanks again all..

[Triton Thrasher]

You’ll never know the right size of main jet until you try one that’s too big.