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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?
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