Topic: KO Carb sync....can of worms.

[Old Moe Toe]

Lucky enough to have a reasonably low mileage (almost 13K miles) KO that has spent most of it's life in air conditioned comfort. It is almost like a brand new (46 year old) bike to ride. However I have noticed when your riding along at say 60mph/100kms and want to overtake or just accelerate hard for fun there seems to be a lag where nothing really happens for a while then all of a sudden it will pick up and start accelerating and not want to stop.
After checking the points,timing and valve clearances I decided to try and sync the carbs. I do have another 750/4 a K2 with a later F2 motor in it and find those carbs pretty simple to sync with vacuum gauges and have been pleased with the results. So after reading up about the earlier type carbs felt half confident about the task at hand.
Got a few workshop manuals and the old Clymer one I've got seemed to be the most promising as it only dealt with the KO,K1,K2 type carbs.
First step is to take off the airbox and set the throttle stop screws (the ones that look like a mini pizza) see pic 1. The T mark has to align with the mark on the carb body. As I understand it you watch the carby slide,slide lower as you turn this screw counterclockwise and when the slide stops lowering the T mark SHOULD align with the mark on the carby body. Therefore when you turn the mini pizza clockwise you know the slide is going up. However I found that the moment when the slides stopped going down the T mark did not align with the mark on the carbs. So what are you meant to do? Wait till the slide is in the lowest position then turn the pizza wheel clockwise till the marks align raising the slide a wee bit,or back off the pizza wheel till the marks align creating slack in the cable?.
Best leave the questions there for now as there are more to come and if I got that bit wrong the rest are irrelevant.

[greenjeans]

The throttle stop is kinda like the idle screw on the later models.  It's been a while since I've messed with the K0 carbs.  If you haven't had the carbs off in a while, it never hurts to go through them and really clean things out.   If you are cruising at very low rpms (around idle), the slow jets come into play a bit.  That could cause your low rpm stumble when opening things up.   As I recall, I would set the throttle stops when the carbs were off the bike where I could see them bottom out together.   Back the screw out and then turn them in until you can just feel the screw hittling the slide.  Then turn it 1 turn.  When I had my K0, I didn't notice that there was a mark  That should get them pretty darn close.  It's easier to see this and feel it when the carbs are not on the bike.   When the carbs are back on, then, I'd set the cables.  Basically, you want them to pull the slides at exactly the same time.  Turn each cable adjustment (4 of them) until the ferrule (the silver metal on the end of the cable housing) of all 4 cables lift equally.  I like to get all 4 cables "just taut" then back them in a hair so all 4 cables have the same amount of slack in them - 1mm would be fine, you don't want much.  That way when the main cable pulls, all 4 go at the exactly same time.   Don't forget the air screws.  Back them out, trun them in until they just bottom out, and turn them all back out per the manual - around 1 full turn.   Then, you can hook up the vaccum gauges.  First you have to balance the idle with the 4 throttle stop screws until even.  Then, adjust the individual slides with the cable adjusters at 2500-3000 or so until you are even.

   

[Stev-o]

I dont believe throttle lag would be a sync issue, it may be time to pull and clean your carbs.
Worst thing for these bikes is to let them set unused, and if you only have 13K miles, that may well be the issue.
My K4 suffered the same....

[Johnie]

Having gone through a couple KO carbs and noting your acceration issue first thing I would do is remove them and clean them up. They are do. The bike will only perform as good as those carbs are. Keep in mind if that bike still has the brass floats they are prone to leak and suck in gas which will make your float level wrong. My KO carbs had sat on the bike for 20+ years. I did not even try to run it until they were clean along with the new points, new condensers, timing and valve adjustment. You don't need to change out the brass jets or needle just clean them good. Those slow jets have such a small hole they probably are part of the problem. Check the emulsifier tube that the needle slides into to be sure all holes are clear. The cool part about these 750 carbs is you can get the jets out by just removing the float bowl. Regarding the sync, I agree with green jeans...I never paid attention to any T, but just watched when the slide began to move by the pizza screw. A word of caution...don't get to frustrated with the sync. It can drive you crazy because when you adjust one carb cable or pizza screw the sync will change on the other carbs too. It takes time and patience for sure. And to clarify you do need to sink the low idle by the pizza screws and then the high speed by the carb cable adjustment which I do at 3,000 RPM. You have a good start that she runs pretty good now. If you do happen to remove the carbs to clean them I would suggest changing out the o-rings which are located on the fuel T between carbs 1&2 and carbs 3&4. Those o-rings are old and are ready to start leaking on you. Good luck with your project and let us know how you come out.

[Spanner 1]

^ Johnie for the win

[Old Moe Toe]

Great advice you guys! It was the pizza screw to set the low revs by that fixed the problem. My Haynes manual says to make sure the T mark aligns with the pointer on the carb body on all carbs then use the cables to sync with vacuum gauges......seems like bad advice. Nearly drove me round the bend trying it that way.
I have also decided to completely strip and clean them but will do that later when I have all the gaskets and O rings etc.
Now as promised in my first post I do have a few questions about these early carbs.
Question 1.... is about the airscrew (pic 2).Before syncing I turned them in until they seated then backed em out 1 turn or 360 degrees. Is that it? Is there any finer adjustment? Bike was idling about 1100rpm after sync. however I did notice they were all about 3/4 of a turn out from seated before.
On to more pressing issues. This bike leaks fuel. Original airbox was rotten due to this. When I synced the carbs I put the tank up on a bench with longer makeshift fuel lines. I noticed before fitting the lines that the petcock was leaking out of one of the outlet pipes with the tap in the off position. Question 2.....do you reckon a petcock kit with new washers is all that is needed for the fix?. I see you can buy new petcocks wholus bolus but if the gaskets are all that is needed that'll do.
Today after syncing the carbs I went for a test ride and am happy to say the lag had gone and all seemed good. Dropped in to a shop to buy a liter of milk and when I came out there was a pool of fuel under the bike!. Once home I took the bowls off the carbys to see what was going on. First step was to check float height. My CLYMER MANUAL says the floats should sit 26mm down from the surface of where the bowl attaches to. Mine were all pretty close to 35mm (first picture). That seems like a long way out. Question 2......Is Clymer right about the float height? Most other carb float height specs I have seen you measure the carb when it is upside down not in situ.
I could tell from the fuel leakage that carb 2 &3 were the culprits as it was their overflow tubes the river was coming from. Had a really good look at the floats and realised what one of the big problems was. The floats are pinned into 2 posts which suddenly reduce in diameter below the pin holes. This reduced diameter bit of the posts is where the float stops contact. However when the float rises these stops can get caught on the bit where it goes from a smaller diameter to a larger one. Therefore the float wont rise if it gets stuck (which it can) and fuel will endlessly flow. Question 3.....Anyone else noticed this?

[Johnie]

You are not measuring the float height correctly. That OEM measurement is with the carbs out and almost upside down. You tilt them until the needle valve is lightly seated. That is where you get the 26mm measurement. On occasion floats can get stuck on the outside of the carb body. You just bend them in a bit. And since you have not had those brass floats out do you know if any of them are leaking? Might be a good idea to check it. Once they leak they get heavy with fuel and then the float height is really off and you will get overflow. OEM specs for the air screw is 1 turn out and then adjust it a little if you think it makes a difference. Jet needle spec is in the 3rd position.