Topic: CB 750 K2 carbs

[emlupi]

Good evening all and Merry Christmas,

I removed the carbs from my '72 CB 750K2 tonight in preparation for cleaning and adjusting. Upon  disassembly I found a couple of peculiar things inside. The main jets are all 110 in the four carburetors and they are supposed to be 120's. Also, the #4 carb had a #38 pilot jet and #1-3 had #40 pilots. The bike has a stock air box, stock coils,  and stock 4-4 exhausts.

I would like to put this bike back to stock specs so what is the best source for jets for this bike? I know there are many aftermarket jet kits of questionable quality which I would like to avoid. Let me know your thoughts. Thanks.

[Davez134]

Plenty of suppliers sell genuine Keihin 120 mains. As far as pilot jets (#40), I've had the best luck with the wanted section on here, or eBay. Make sure they have the logo stamped on them. Every supplier I've seen so far only has reproduction pilot jets. You might take a look at David silver spares though.

[b52bombardier1]

My local Honda dealer could order those for you, most likely.  This would guarantee OEM Honda Keihin quality.

Rick

Sent from my SAMSUNG-SM-N900A using Tapatalk

[emlupi]

 I see that Partzilla has the 40 pilots and 120 mains. So far, everything I have gotten from them has been genuine Honda.

I'm at a loss as to why there were mix and match jets in these carbs in the first place. Kinda odd.

Thanks for the replies.

[Davez134]

I'm at a loss as to why there were mix and match jets in these carbs in the first place. Kinda odd.

Thanks for the replies.

Every time I'm at loss as to why someone did something weird or stupid to a bike/car, I look at the general public around me and I'm no longer surprised.

[ekpent]

 Since the K2 had HM341's exhaust instead of 300's and your running stock airbox I would maybe try running it with the 110's first and see if somebody here can sell you a couple of #40 Kehin slow jets. Main jets are pretty easy to change after carbs are mounted.
  I do see this dealer in my area does show they should be 120 and they are around $4.69 each. Do you have a Honda dealer nearby to give the part number to ?  http://shop.pawpawcycle.com/fiche_select.asp?mfg=Honda&partnumber=Part%20Number&bigSubmit=Search

[millla03]

Jetsrus.com is a good source for OEM Keihin brand jets.

For what it's worth, I believe the K2 left the factory with 105 mains, and that's what mine had in it when I first got the bike. If someone more knowledgeable can confirm this it would be appreciated. Needle clip position was one down (richer) from stock, though I'm unsure if that was the factory setting. Stock pilot jet size is 40.

I also might have a 2 #40 pilot jets in my spare carb parts box if you need them. Please PM if you do as I don't get on the forums all that often. I'd send them for the price of shipping.

[MikeSimon]

Honda shows all main jet sizes listed. There is no #105 listed. #140 is marked "STD" on all engines and is p/n  99114-246-1400
#120 is p/n 99114-246-1200. #110 (smallest) is 99114-246-1100.
#40 slow is marked "STD" and is p/n 99124-300-0400

[754]

I had stock jets in my K2 ran good with hooker 4-1..
 My buddy could always pull away just a bit with his 74 with a Jardine 4-1..
 Then one day i put 120,s in and I could beat him..it ran so freaking sweet..
 About 3 days later we had an accident, with both bikes...totalled both of them...
 

[emlupi]

After doing a lot of researching today through several publications and internet searches it seems that the CB750K2 did come from the factory with 110 main jets during it's production run. So, the 110 mains are probably the correct items for this bike. That does not explain why the #4 carb has a #38 pilot jet. By all accounts, that should be a #40 as with the rest.

I did notice something when looking at the casting #'s on these carbs. The #1-3 carbs are stamped "657A" followed by the letters "KA". The #4 carb is stamped "657A" followed by the letters "JL". Perhaps the #4 carb, with the oddball jet size, was replaced at one time in this bike's history? I dunno.

I will keep the 110 mains in these carbs as is but will swap out the #38 pilot for a #40. Thanks again for all the input.

[ekpent]

Probably be some disagreement but from what I have seen is this
K0-K1- #120
K2-K3 and most K4- #110 (there is a specific serial number where they switched to #105 for the K4)
K5-K6- #105
And never found anything less than a #40 slow.
Brass floats in K0-K1

[emlupi]

Sorry, I need to amend my previous post about the casting marks. The #1 and #3 carbs are marked "657A  KA' and the #2 and #4 carbs are marked "657A  JL". So, my theory is debunked. I guess for some unknown reason a #38 pilot jet was installed in the #4 carb along the way.

[jcarthel]

Hi guys. Question, how many of you factor in elevation when dialing in carbs and jetting. It stands to reason 120's would work well at 700 or 1000ft. At my elevation 3200 ft, 110's in a 750 would seem a wiser choice. Input, anybody? Justin

[emlupi]

I see that a set of overflow drain tubes is not available for these carbs. Can anyone tell me the tubing size used for these so that perhaps I can fabricate some for my bike? There is OEM 3.5mm fuel line available but I am not certain that this is the correct size. Also, is this the same size as the short rubber tubes that connect the float bowl vents between carbs? Looking to refurbish all the old dried out rubber tubing and need some help. Thanks,

[ekpent]

 Some guys have used automotive windshield wiper line I have read. Were your hoses missing or are they old and hard and you want something new.

[scottly]

Hi guys. Question, how many of you factor in elevation when dialing in carbs and jetting. It stands to reason 120's would work well at 700 or 1000ft. At my elevation 3200 ft, 110's in a 750 would seem a wiser choice. Input, anybody? Justin

Hey Justin, 3200 ft isn't much of a factor regarding jetting, IMHO, and even if it were, 117's or 115's would be a wiser choice.

[emlupi]

My overflow tubes were missing. The short rubber vent tubes are old and hardened.

[emlupi]

Some guys have used automotive windshield wiper line I have read. Were your hoses missing or are they old and hard and you want something new.

Will the windshield wiper line hold up to being exposed to gasoline? Any other solutions to replace carb overflow tubes?

[b52bombardier1]

Some narrow diameter fuel line from an auto parts store should work.  Maybe 3/16th inch line?  Try a short length first before buying a bunch of it.

Rick

[jonda500]

I used vacuum tube on mine (automotive distributor vacuum advance or carb vacuum line)
John