Swapping Carburetors CB750F to CB750K Keihin | Carb Clean & Rebuild | Honda Project | Part 17

Swapping Carburetors From CB750F to CB750K Keihin | Carb Clean & Rebuild | Honda Project | Part 17

In this episode, I cleaned and installed a set of round top carburetors to try on my CB750 project bike. These are the earlier style Keihin carbs from a CB750K, I'm replacing the CB750F carburettors that came with this bike in the hope to get it to run better. I am building this bike to be a road-going runner, not a full restoration.

I have a set of PD carbs on the bike, but they are off a later model. It was suggested in the comments by Joe (Jose) that I might try a set of the correct round top carbs, due to possible differences between the earlier and later Honda CB750 engines in terms of compression ratio etc, so I decided to give it a go.

The carbs that I found were pretty gummed up. But once I started cleaning them they turned out not to be too bad. Apart from the seals, float valves and the pilot jets I used all of the original parts. I wanted them in working condition, so that was the focus of my efforts.

I set the floats to the standard 26mm, but despite this and the new float valves and seats and fuel filters, the bike does sometimes leak a little when you first switch the fuel on. Not always and not much, maybe it’s a normal thing, but I don’t remember it from the first time around with these bikes!

When I fitted the carbs I realised that the inlet rubbers are wrong, in that they are too short. Obviously, they are for the later carbs. The knock-on of this is that where the throttle cable is clamped is very close to the heads, and when I fitted the airbox, the rubber horns don’t seal into the box, they nearly an inch short. If I decide to keep these carbs on the bike I will buy the correct ones.

I also had to adjust the nipple on the pull cable, and the outer sheaf on the push cable. This happens every time for me. Maybe I am buying cables that are too cheap, or just using mismatched parts. There is another video on soldering the nipple to come so I can show you how that adjustment is done.

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[oilinmyblood]

Right on brother! This is Jose by the way, my actual legal name is Joe but Jose is my name in Spanish, I changed my name for YouTube also, Glad to see you took my advice on picking up some original carbs, sounds like she just needs the air and fuel mixture tuned and airbox fitted and she should run way better, looking forward to seeing a video of her being tuned and running, good luck brother!

[anthonypickering]

Just like to say a big thanks for sharing your carb problems .

When you found that cab overflow pipe cracked that was a real eye-opener for me.
I own a CB 350/4 and had problems with the carbs for ages, I could not get it to run right whatever I did .

I must’ve had the carbs off six or seven times, but it still kept leaking out of the overflow pipes.
This baffled me to the point that I managed to source a really nice set of recondition cars from a chap in Holland.
I fitted these to the bike, and I’ve never had another problem since.

Thanks for sharing
Tony

[rider]

Excellent job mate. I have 1975 Honda 750k5 with the same carbs. :)

[marks]

You’ll find these bikes much prefer having the original air box fitted, the rubber velocity stacks in the original air box are there for a reason, when I fitted K&N style pods to mine it ran ok but had a stumble when snapping the throttle open, I took the rubber velocity stacks out of the original air box and grafted them onto to K&N’s, it completely fixed the stumble and the engine ran better in every respect.

[mikemanfredonio]

Put on a carb from Ebay for 26 dollars.Had to adjust the float. works great

[petrolated]

I have a K2 with a set of K7 carbs and wide open inlets (3d-printed trumpets). The bike runs sweet and pulls hard to the red line. I can’t see the advantage in the old style carbs, with the lack of accelerator pumps and all.

[jayrico]

Can you use 82’ cb750 DOHC carbs for a 1980 CB750F?

[mikeymike]

That was amazing, did you have any problems we didn’t get to see, carbs are like a black art lol 😂

[kimsmith]

Wow excellent job How long did it take to overhaul the carbs. I only ask because I can't set my cb750k 1981 carbs to run properly it splutters and cuts out. So this weekend I removed them and that was a pig. I have 4 carbs overhaul kits and wonder how long I need to put aside to sort these out never done this before so your videos have been a godsend to me and has given me the confidence to have a go. I did have them done at a garage but same problems reoccurring. Cheers Dave from Sheffield