Topic: Round top carb slides - help!

[bomorr]

I have been in and out of this carb and after about the 100th time trying to fix the 1/4 throttle hesitation and I think I just found out what may be causing my issue. I noticed that at some point PO must have taken the slides and took a grinder to them.  If you take a look at the pictures you can see some notches in the slide where the A/F mixture flows by. And it also looks like it was ground down a bit, the inside of the slide has some lipping that wouldn't occur from the factory. My question is does anyone have a set of these out of their bike that they can do some measurements to see if my suspicions are correct?
Let me know what you guys think.

Full top to bottom measurement


Top to bottom measurement in the cutout


Lipping

[pjlogue]

The notches are from the factory.  Not sure of the reason/function for them but they are on my slides on original carbs and a second set I purchased.

-P.

[BPellerine]

some do mod the slides,when running pods or similar,they grind them a bit ,in hopes of making them work better,dont know if that is the case with yours.bill

[bomorr]

some do mod the slides,when running pods or similar,they grind them a bit ,in hopes of making them work better,dont know if that is the case with yours.bill

I did recieve the bike with pods on it... That's my thoughts as well

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[DH]

Not to open a can of worms, but have you considered worn "needle jets" and
"jet needles"? A worn spot on the needle(s) can occur if the bike has a lot of
city miles, where the throttle is in and out of that 1/4 range frequently, and when
the engine is shifted a lot. The needles are in nearly constant contact with their
jets. Just throwin that out there as a suggestion. I went thru this before, but replacing the needles and jets was done as my last resort. Have you tried raising
or lowering the needle position? that can put the worn spot of the needle (if present) higher or lower in the jet. Grinding throttle valves will definately affect tuning if it has been done tho. A "Don't try this at home" kind of thing

[flybox1]

Not to open a can of worms, but have you considered worn "needle jets" and
"jet needles"? A worn spot on the needle(s) can occur if the bike has a lot of
city miles, where the throttle is in and out of that 1/4 range frequently, and when
the engine is shifted a lot. The needles are in nearly constant contact with their
jets. Just throwin that out there as a suggestion. I went thru this before, but replacing the needles and jets was done as my last resort. Have you tried raising
or lowering the needle position? that can put the worn spot of the needle (if present) higher or lower in the jet. Grinding throttle valves will definately affect tuning if it has been done tho. A "Don't try this at home" kind of thing

[pjlogue]

Don't mean to hijack a thread but does anybody know what the "nicks" in the face of the cutaway are for?  The area of the nick is miniscule compared to the cutaway area on the slide.  To introduce turbulence perhaps?  Anybody?

-P.

[bomorr]

Not to open a can of worms, but have you considered worn "needle jets" and
"jet needles"? A worn spot on the needle(s) can occur if the bike has a lot of
city miles, where the throttle is in and out of that 1/4 range frequently, and when
the engine is shifted a lot. The needles are in nearly constant contact with their
jets. Just throwin that out there as a suggestion. I went thru this before, but replacing the needles and jets was done as my last resort. Have you tried raising
or lowering the needle position? that can put the worn spot of the needle (if present) higher or lower in the jet. Grinding throttle valves will definately affect tuning if it has been done tho. A "Don't try this at home" kind of thing

I haven't checked them out just yet but I was looking at carb rebuild kits that had all that in it. I have moved the needles up and down to see what works best and I always go back to the middle clip giving me the best midrange.

[bomorr]

Following up on that last post, here are some pictures of the needle valves,  I think they may have some slight wear (arrows)  pointing to them. It's really hard to tell. Let me know what you guys think

[DH]

 Hard to tell, but are those the emulsion tubes or the needle jets?

[bomorr]

Hard to tell, but are those the emulsion tubes or the needle jets?

Aren't they one and the same?

[david 750f]

Nope.. Main jets screw into the emulsion tubes. The needle jet is in the body of the carb that the needle passes through. Any parts fiche will show you better than my description 😉

[bomorr]

Nope.. Main jets screw into the emulsion tubes. The needle jet is in the body of the carb that the needle passes through. Any parts fiche will show you better than my description 😉

Gotcha,  I see it now. How the hell do you get those out? Do they just tap out?

[DH]

Thru top of carb body and downward with a correctly sized wooden dowl and
light tapping so as not to distort them. If you need to replace them,(jet and needle) be suspicious
of the replacement NEEDLES that come in carb kits as they are very often the wrong ones. Very
common to have the wrong taper. O.E. will have a number stamped on them.

[sinister902]

if necessary I have a broken down set of parts carbs I would let go cheap to help get your working again. have all 4 slides and stock needles and carb bodies.....my parts set is missing all the racking brackets and throttle linkage arms and rods, but the individual carbs are all there.

[bomorr]

if necessary I have a broken down set of parts carbs I would let go cheap to help get your working again. have all 4 slides and stock needles and carb bodies.....my parts set is missing all the racking brackets and throttle linkage arms and rods, but the individual carbs are all there.

Thanks unfortunately I already got a decent set of slides off some guy on ebay for a good price

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[bomorr]

I took a shot down one of the carbs,  it looks good to me,  no excessive wear. I'm going to try out these new slides once I get them in to see how that works.

[bomorr]

Ok now I'm confused, just got the used slides in and they are legit keihin slides 102's with 2.5 pitch but they look different. They have the same pitch when I put a caliper on both but they have different lip on the front. If I remember correctly the one with the more pronounced lip will make the mixture slightly leaner right?

[harisuluv]

I'm just walking in here but I don't see any of the basics covered here at all.

Carb settings, (jets, needles, mixture, etc.)
Bike mods, bike year, etc.

[bomorr]

I'm just walking in here but I don't see any of the basics covered here at all.

Carb settings, (jets, needles, mixture, etc.)
Bike mods, bike year, etc.

76 - cb750
Slow jet - 45
Main jet - 137
Needles - middle notch (D54)
Mixture screws -  1.25 to 1.50 turns out
Uni black foam pods
Dyna-s Ignition
5ohm & dyna coils and wires
DCPR8E NGK plugs

[harisuluv]

Odd settings.

I would recommend:

Slow jet:  40 (stock)
Main jet: 120
Needle jet:  5th position (stock is 4th position, so it's been adjusted LEANER)

Pretty common for pods to give hesitation in that range, and many times it's because people don't adjust the needles.

[bomorr]

Tried that combo already, I have done plug chops at idle and the 45 gives a good color to the plugs. the original issue I was having was @ WOT It was cutting out so I moved from 125 to 130 to 137 and finally I got some relief @ 137 where it didn't fall on its face.
All that being said I think I need to start fresh due to the new slides. I started it up tonight and ran it around for about 20 min and idle seems a little smoother so the new slides are affecting the mixtures. So back to idle chop then main jet chop,  then back to the needle clip adjustment. I just have to find the best combo.
If I don't, I did just pick up a stock Airbox and I have the old jets 40/115 so I can always revert if I get too frustrated.

[harisuluv]

ok, keep in mind that changing the needle position which is what needs to be adjusted to address your problem will affect everything else.  which means, you'll have to just retune again anyways.

[Vin750]

ok, keep in mind that changing the needle position which is what needs to be adjusted to address your problem will affect everything else.  which means, you'll have to just retune again anyways.

Does the needle position affect the idle as well? If so by how much?

I was having hesitation issues with my bike and I moved the needle clip to the 4th position from the top and it's much better but cylinders 3 and 4 are rich in idle and putting out back smoke. Not sure if it was related to the chance I made or I have some overflow there.

The air screws are 1 turn out.


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[sinister902]

Does the needle position affect the idle as well? If so by how much?