slow carb flat slide

Hi all hope to try start the vfr very soon,carbs cleaned but i noticed 3 flat slides pop up and down loveley but one is a little slow not so easy to lift and drops slow? when top off moves freely diaphram in all 4 are good no holes or splits nothing catching springs all good is it to do with vacuum or somthing sounds like an air issue and maybe when engine running its ok ? any thoughts

Have you tried swapping the springs around?

No but i,ve put carbs back on and blow through a hose that goes to airbox 3 work easy together but the lazy one takes longer to operate... strange when you lift plunger there is more resistance compared to other 3...have to investigate further

Probably needs some cleaning done on the slide and bore. Gas residue can gum them up.

There's multiple areas that can cause this. So there's two tests that needs to be done to confirm which is causing problem:

1. mechanical fit and friction. Remove cap on back of diaphragms. Push slide up and down with fingers on each side. Slide should move smoothly with no friction or binding.

2. Vacuum operation. Re-assemble cap making sure diaphragm is sealed. Push up on slide and feel how much force it takes to open. Let go and notice time it takes to close.

ANALYSIS: If #1 is same for all slides, we can conclude that all slides are clean and straight. And their bores are smooth with no obstructions. Then go on to #2

If #1 test passes, but #2 doesn't, we can conclude there's no mechanical issue with slides. Difference in force of opening and speed of closing is due to clog in vacuum circuit.

Does slow slide sound different opening & closing? Most likely vacuum circuit is clogged. This will cause that slide to not open as fast and not as fully as the others.

Its not mechanical got good idear now from joe at V4 dreams and yourself its a vacuum issue on slide also no fuel going into cylinders although float bowls got fuel so apart again more cleaning also chock tubes i never thought of them.

 suspect that slide's diaphragm is pinched and not correctly seated in its groove.

Leaky diaphragm wouldn't cause difficulty lifting and slow drop of slide though?

29 minutes ago, DannoXYZ

Leaky diaphragm wouldn't cause difficulty lifting and slow drop of slide though?

maybe, maybe not. gotta pull it apart to check. make sure all 4 springs are the same lengths.

A leak would cause a slow rise, but have no effect on the fall. Thats why I feel it's gummed up or something causing friction in both directions.

got a wet weekend coming up so plenty of time to get to the bottom of it all got new jets too as now i know my slow jets are blocked up

DannoXYZ, 5/20/2021 at 12:31 AM

Leaky diaphragm wouldn't cause difficulty lifting and slow drop of slide though?

i was chasing a slide problem on a set of recently-worked-on '86 carbs and discovered that the spring had bent over when cap was replaced carelessly and symptoms were just as you describe.

3 hours ago, squirrelman

i was chasing a slide problem on a set of recently-worked-on '86 carbs and discovered that the spring had bent over when cap was replaced carelessly and symptoms were just as you describe.

So would bent-over spring increase or decrease spring-preload pressure on slide?