Grinding a carb slide cutaway...

[LPYYZ]

Would anyone have any tips on grinding/filing a carb slide cutaway?

I had a 2.0 slide installed on my VM34’s but I was getting the black plugs after 50 mile problem. Throttle response was great though.

I moved to a 2.5 slide to cure that problem but now my initial throttle response is poor due to the leanness.

Ive heard of people going a 1/4 size up or down by filing the slide cutaway.

Any tips or tricks would be appreciated...those slides aren’t cheap.

Thanks in advance,

Liam

 

[gggGary]

Following, Those slides are anodized. Would require some fixturing to get hold the right angle I suppose a real careful guy could mark the desired line with a sharpie and work to it on a sheet of sandpaper on a flat surface. So would you remove a pie shaped slice or would it be thin flat section that needs to go?

 

[XSLeo]

Wouldn't it be easier to put in a bit bigger idle jet? Possibly a richer needle?
Leo

 

[5twins]

I think where you sand/file would depend on what you're trying to do to that particular slide, make the cut-away taller or shorter. I'm pretty sure the 2.0 and 2.5 numbers refer to the height of the cut-away. To make a 2.5 into the "modded" 2.25, you would have to sand/file the flat bottom. To make a 2.0 into the "modded" 2.25, you would have to sand/file the angled cut-away.

 

[LPYYZ]

The number does refer to the size of the cutaway. A 2.5 slide is leaner than a 2.0 slide because it has a larger cutaway.

From what I understand I would have to file approximately .010” off of a 2.0 slide to turn it into a 2.25 slide.

I’m just trying to find a way to file both slides accurately so they are symetrical and retain their cutaway shape etc.

I don’t think I trust myself to do it with a hand file and set of calipers but right now I don’t see any other option.

 

[LPYYZ]

Unfortunately changing the pilot jet or needle won’t have much effect on the 1/4 throttle open fuel/air ratio. It’s mostly slide cutaway at that point and that’s where I seem to spend most of my time cruising around.

 

[5twins]

I think it would be easier to file/sand the flat bottom of the 2.5 than sanding the angled cut-away on a 2.0. Easier to do more accurately too.

 

[Jim]

Got a friend with a lathe?

 

[LPYYZ]

I don’t think sanding the flat top of the slide would have any effect as it’s the bottom cutaway bore that determines fuel/Air ratio.

 

[LPYYZ]

I might be able to find someone with a lathe...thanks for the idea.

 

[5twins]

No, not the flat top, the flat section on the bottom.

 

[LPYYZ]

Ahhhhh, I misunderstood.

It would be worth a try before getting into the cutaway curve. Definitely easier.

 

[Jim]

I might be able to find someone with a lathe...thanks for the idea.

And if you want to take down the cutaway..... find a fried with a lathe AND a mill...

 

[5twins]

I just found this VM slide pic on eBay. The bottom isn't solid like on the CV slides, it's just a ring of metal around the outside. Still, I think working the flat bottom would be easier than the angled cut-away .....

A piece of 320 or 400 taped to a flat surface like a plate of glass. Slide bottom worked against that in a circular or figure 8 pattern. Measure the total height first then sand a little, measure again, etc. From your research, it appears you don't have to remove very much.

 

[Signal]

Watching with interest. I think 2M has posted about doing this.
You have already worked out how much you need to remove.
I read that the number is the height of the cutaway in fractions of an inch. However I cant remember what the fraction is I think it may be 32nds but will need to check.

 

[5twins]

At first I thought it may be metric but MM's would be too small and CM's way too big. Fractions of an inch make more sense but a 32nd would be too small. That's not even 1mm. Maybe it's eighths.

 

[650Skull]

Can't find it at the moment.............I have seen an article on a spacer, (for the want of a better word), that fills the bottom of those sliders because they reckoned the area that is recessed causes to much disruption to the airflow/mixture..................makes sense to me but what do i know..............

Anyone heard or know about this???

 

[650Skull]

Found it...........Could be a snake oil product.................

any ideas on the theory and a practical application.........

 

[Jim]

Could be a snake oil product.................

That would be my guess. Claims a 1-2 hp increase per 100cc's means 6-13 hp increase for our motors..... just by cleaning up the airflow under the slide..... sounds like a pipe dream to me.

 

[650Skull]

Yes Jim the claims of all that horsepower could be the snake oil part ...............But......................what i am asking is the spacer going to make the fuel delivery more efficient due to less turbulence...........More than one part to that post............funny how people see what they want and not the content?????