I think the slides are in the wrong bodies

[Eldrick]

Is that possible that my carbs are having an out of body experience?

I removed the carbs a few months ago after the bike choked to a halt, out on a run. After that I removed the carbs from the block, checked and set the float heights and specifically replaced the Carburettor float valves in all four carbs as they were stuck solid.
I then followed Bryanjs’ ‘Basic bench carb balance guide', replaced the gaskets (top and bottom) on the carbs and mounted them on the bike again. The bike runs now, however I have an issue getting the bike to idle at anything near 1200rpm, it is more like a minimum of 2000rpm.
I removed the carb block again to bench sync again, mainly because I messed with the slide adjusters too much. I decided I got it benched properly and mounted the carbs on the block again. I also used a vacuum carbtune kit, the perfectionist in me insisted, I still cannot get the idle down to 1200rpm.
I have also checked and set each air pilot screw, could be naming those wrong, to 2 plus one half turn open. On the carb tune I can only match the carbs to within 10-8cmHg. So, carb 3 may be at 16cmHg and carb 4 would be at 24-26cmHg.

The main observation I had and the reason for the question:
Bryanjs’ ‘Basic bench carb balance guide‘ says about the slides; ‘Engine side, it has the flat bottom not the cutaway.' During my observations whilst doing this bench sync I could really tell there was a cut away on the slide so I proceeded working on the engine side, my brain is now convinced that there was a different shape to the slides on the air box side. Too late for that thought, the carbs are now on the bike again and I don’t mind removing them again to check.

Questions are;

1. Could the slides be on back to front?
2. Can the slides be extracted from all four bodies without removing the bodies’ from the block?
3. If 1 and 2 are possible and I fix the issue can I just use the vacuum sync and be confident that the carbs are performing optimally if I then get 1200rpm tick over and a balance of around 16-24 cmHg and all four within 3cmHg of each other?


ThanksKenny m

[McCabe-Thiele (Ted)]

The slides will only fit one way round as there is a groove down one side and a notch it slides down.

As a starting point I set my air screws at one and a half turns - it idles nicely at 1200 when up to temperature.

I assume you did not mix up the parts of each carb so the same slider goes in it's original carb. On these old bikes I also use an in-line filter due to the risk of debris from the petrol tank.

[Sesman]

Blocked pilot jets and/or pilot jet carb drillings is my guess.

[Eldrick]

 I did not remove the slides from the bodies at any point during my inspection/cleaning. That does not exclude some other owner having done that in the past. The question remains tho, could they be in the wrong body and therefore reversed?
 
 I know about the grove on the slide, technical question; is that grove on the right hand side for all four slides? If so, then I guess they cannot be reversed. If, on the other hand, for example, they are on the right hand side for 1 and 2 and the left hand side for 3 and 4, that is to say the groves all face into the centre line of the carb bank, then the wrong slide could be in the body. Having never took one apart I can’t be sure if that is possible.
 
 Don't know about blocked pilot jet, I did blast all Needle and Slow jets with compressed air (is the slow jet the pilot?), before re-assembly and air passed through those quite well in my amateur opinion.
 
 

[Sesman]

Hi, Eldrick. Unfortunately air blasting is no guarantee of a clear passage. I’ve discovered that much.

As for the slides, I’d whip the carbs off an have a peak. I cannot recall if the ‘pips’ are handed, thus allowing the slides to be incorrectly installed. Eg no1 in no 4. Sounds like you need to take them off to satisfy yourself. Could be 30 mins well invested?

[kevski]

The amount of vacuum is not important as long as they are even, with regards to the slides adjust the height adjusters to the middle of their travel, then back off the tickover screw until iit s out of contact with operating lever, then check to see if slides are bottomed out, if bottomed out raise them using the tick over screw then bench set the heights evenly, then back off tickover screw until you can just about see light through carb throats, upon start up if tickover is racing back off idle screw, if this fails there is another problem , ie  choke plates not fully open, ignition timing, air leak on engine side.

[Bryanj]

Something lurking in my adled brain tells me that the carbs are "handed" so if you have a total box of bits(still got the 400 ones to do comfy, need felts) and you mix the slides up it is possible to get them in wrong. I may well be wrong on that myself, would be glad for confirmation

[Eldrick]

Something lurking in my adled brain tells me that the carbs are "handed" so if you have a total box of bits(still got the 400 ones to do comfy, need felts) and you mix the slides up it is possible to get them in wrong. I may well be wrong on that myself, would be glad for confirmation

Then I am just going to remove the carbs from the block and look. The education alone from removing and replacing them gives me more confidence in doing my own maintenance

[McCabe-Thiele (Ted)]

There are two part numbers for the actual slider bodies so I'm guessing two on the left & two for the right.

If you look into the carb body from the air cleaner side you should see the raised curve of the rear skirt of the sliders if the air intake is off - you might need a small mirror or use a phone to photo it.
 
The front skirt is flat on the engine side.

[Cappodimonte]

Currently stripped down and rebuilding all four of my Carbs.
No 1 and 2 carbs have guide pin for slides on the LEFT
No 3 and 4 carbs have guide pin for slides on the RIGHT.

This Carb numbering is as you look down from the riding position on the seat facing forwards, the slides as you look at them have a flat front and a slight curve at the rear,
When attached to the engine by the carb attachment bar, the curve of the slides are what you should see looking out at you, NOT the flat side.
When setting them up on a bench the distance from the FLAT side of the slide to the inlet Venturi should be 1.5 mm.
Is the emulsion tube where the needle jet fits and slides up and down fitted the right way up ? It should protrude into the Venturi a small way,looking like a small ‘cup’ if fitted upside down it will not be seen.
When dealing with multi cards ALWAYS keep them in separate labelled boxes to prevent them being fitted from one carb to another.
See how it goes.

[Eldrick]

Is the emulsion tube where the needle jet fits and slides up and down fitted the right way up ? It should protrude into the Venturi a small way,looking like a small ‘cup’ if fitted upside down it will not be seen.

I will find out tomorrow when I take the carbs off the bike and I will have 4 boxes set aside for each individual carb should I deem it necessary to swap those slides.

[McCabe-Thiele (Ted)]

I would be surprised if the sliders are wrongly fitted as this would also cause problems on the top levered plungers unless they have been removed & put on back to front as well.

It will be interesting to see what you find.

[Eldrick]

I would be surprised if the sliders are wrongly fitted as this would also cause problems on the top levered plungers unless they have been removed & put on back to front as well.

It will be interesting to see what you find.

I will photo-document it and if it proves to be 'an out of body experience' I will post the photos.If it is not the case, I may well get the idle and fast idle set knowing that it is me that needed expierience.

[McCabe-Thiele (Ted)]

Is the emulsion tube where the needle jet fits and slides up and down fitted the right way up ? It should protrude into the Venturi a small way,looking like a small ‘cup’ if fitted upside down it will not be seen.

I will find out tomorrow when I take the carbs off the bike and I will have 4 boxes set aside for each individual carb should I deem it necessary to swap those slides.

You do not need to take the carbs off to check - a mirror or phone will do the trick. You will see the curved part of the sliders - or not as the case maybe.

[Eldrick]

Well, they are back to front so looks like I willl be learning a new task today, removing and replacing slides.

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