I do the same as Loose Chain (probably because I got his advice). I can't remember what mine are at, but they are around 2.5 turns. FWIW, no manual will use 'half turns'.
Keep us updated.
Keep us updated.
Carb Rebuild kit advice requested
- Thread starter Sprinter
- Start date
gustav129
CB750 New member
I think I have the same PDF. I started out at 3 turns per the PDF, but I always was fighting a higher idle, and it would just stop accelerating at about 6k rpm. I then watched a video about pilot screw adjustments, and they said that if you are at 3 or higher, your pilot jets need to go up one size. So I was all confused as to what do I adjust for the idle (How do I know to adjust the knob or the pilot screw?)
Lurking and searching on this forum has helped a lot (I'm an old forum user since 2002, and not a fan of FB groups or Reddit). I now have them all at 2 turns and it runs so much nicer. Idle is still a little off, as I know the idle adjustment knob is all out of whack per the PDF. So now I have to take the carbs off again and reset it to the PDF base line. Oh well, practice, practice, practice.
Thanks for all of the advice, for a carb newbie that has always shied away from carbs it has been very helpful, and i think i will drop the Pilot screws back to 2.5 turns.
I have added a couple of pictures of the choke spring locations primarily for my own future reference as i couldnt find anything that clearly showed where to put them.
Carbs are back in the bank and bench synced, i will go and get some new fuel later and leak test them on the bench before i put them back on the bike and see if they work.
Tag: Carb 2 Setup, Carb 2 choke mechanism (so i can search for it later)
I have added a couple of pictures of the choke spring locations primarily for my own future reference as i couldnt find anything that clearly showed where to put them.
Carbs are back in the bank and bench synced, i will go and get some new fuel later and leak test them on the bench before i put them back on the bike and see if they work.
Tag: Carb 2 Setup, Carb 2 choke mechanism (so i can search for it later)
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kirky
CB750 Addict
i had mine set at 2 and half full turns and found it a bit rich and choky on set off . i set them at 1 and a half and it ticks over and picks up a lot better
Biebs
CB750 Addict
2 full turns out will be a good starting point.
fitted the carbs back last night (a job i will now avoid doing again if at all possible), couldn't get the throttles to close quickly which after a search on the forums was identifued as being not enough slack in the cables, and poor cable routing, so went for a startup this morning, i was very surprised that it started instantly and sounded good.
However it is leaking from the float bowl on carb 4, swapped the bowl with that of carb 1 and carb 4 was still leaking (not the o ring on the drain screw), tapped the bowl, wriggled the float around and its still doing it, turned the fuel on with the bowl off and it poured fuel, pushed the float up and it sealed and stopped the fuel flow, so its sealing fine, i am now tweaking the float height to try to get it right
But as a carb newbie I'm very happy (will be even happier if i can fix it without taking the carbs out again
)
However it is leaking from the float bowl on carb 4, swapped the bowl with that of carb 1 and carb 4 was still leaking (not the o ring on the drain screw), tapped the bowl, wriggled the float around and its still doing it, turned the fuel on with the bowl off and it poured fuel, pushed the float up and it sealed and stopped the fuel flow, so its sealing fine, i am now tweaking the float height to try to get it right
But as a carb newbie I'm very happy (will be even happier if i can fix it without taking the carbs out again
)Be careful with carb height adjustments. In an effort to force the float needle up, some people will adjust too much and reduce the fuel height and affect idle and pilot jet performance. Your issue could be as simple as needing a new float valve on the the float. I would try that first.
It may not be the bowl leaking. It could be one of the fuel tubes leaking and running down off the bowl making it look like the bowl leaking. Did you replace the o-rings on the fuel tubes?
When I clean or rebuild carbs......maybe 33% of them will have a float/float needle issue right at the beginning. Don't be too hasty to call it a fail. Bang both sides of the bank where the bowl meets the carb body with a rubber mallet, ALWAYS works for me. It may not work if the seats and float needles were not good to start with.
Off topic but, often I will push a bike around that has sat for some time (years even) and the fork seals will leak. I do the seal-mate thing, cleaning the seal lips, one little piece of dirt is all it takes to make those seals leak. Tried and true, many times over on different bikes. The seals with the double lips are a bit harder to do. No disassembly and usually not much oil lost, but hey nothing wrong with draining and new oil.
Off topic
but, often I will push a bike around that has sat for some time (years even) and the fork seals will leak. I do the seal-mate thing, cleaning the seal lips, one little piece of dirt is all it takes to make those seals leak. Tried and true, many times over on different bikes. The seals with the double lips are a bit harder to do. No disassembly and usually not much oil lost, but hey nothing wrong with draining and new oil.Well it wasn't so difficult to fix, I tried knocking the float bowl but that didn't work, so I took the bowl off, pushed the float up and turned the fuel on, no leaks, showed me that the needle was sealing correctly and after a tweak of the float height everything seemed to work and the leak had stopped, though i am aware that if could have over adjusted it and it may not be able to supply enough fuel on the move, will deal with that one at the time.
As it only had a small amount of fuel in the tank, I decided to empty it and filter it through a piece of white cotton so that I could see ow clean the tank was, "not clean" was the answer, whilst it wasn't terrible, I didn't want to risk putting that through the carbs i have just spent two weeks cleaning, so tank cleaning next, but i think it will just be a good rinse so that I can ride it, then a good clean over winter.
As it only had a small amount of fuel in the tank, I decided to empty it and filter it through a piece of white cotton so that I could see ow clean the tank was, "not clean" was the answer, whilst it wasn't terrible, I didn't want to risk putting that through the carbs i have just spent two weeks cleaning, so tank cleaning next, but i think it will just be a good rinse so that I can ride it, then a good clean over winter.
kirky
CB750 Addict
as regards the tank get some apple cider vinegar i did my tank over a week period in the winter with it and it shifts loads of crud, keep it in for a couple of days and drain and filter it then keep repeating , finish off with steel nuts or large washers and keep shaking it. then rinse with paraffin or petrol.
Quick update,
thanks for all of your advice, carbs need some final tweaking with the fuel mix, but are running pretty well, I was not convinced that i had done as good a job as i had hoped with the cleaning as the idle was still a bit eratic but this turned out to be a secondary issue with the ignition system that i am working on currently (weak advance and retard springs, new plugs, new caps, HT leads, coils and now new CDI units).
I am going to get this thing running properly, and then tackle the valves
thanks for all of your advice, carbs need some final tweaking with the fuel mix, but are running pretty well, I was not convinced that i had done as good a job as i had hoped with the cleaning as the idle was still a bit eratic but this turned out to be a secondary issue with the ignition system that i am working on currently (weak advance and retard springs, new plugs, new caps, HT leads, coils and now new CDI units).
I am going to get this thing running properly, and then tackle the valves
danadalis
CB750 Member
I'm a bit late to this thread, but did you have the MacGregor Carb Rebuilding Manual to guide you?
I'll attach it just in case.
I'll attach it just in case.
Yes I did, and watched the YT video, plus many other videos, I admit that I didn't follow the guide as carefully as maybe I should have which is why I striped the bank down further than I needed too, and then struggled to get them back together. I guess we live and learn
Welder Dave678580
CB750 New member
As a reader and owner of 80 750 f hoping for info for jet size running 4 into 1 Yoshimura header and k&n air pods.sent carb rail out for rebuild and either I failed to mention performance upgrades or mechanic didn't listen. He used stock jets.Do those manuals cover such info?
