Swapping Carburetors CB750F to CB750K Keihin | Carb Clean & Rebuild | Honda Project | Part 17
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- Опубликовано: 5 сен 2024
- 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.
Honda CB750 Carb repair kits I use: ebay.us/oF83mw
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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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 RUclips 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!
Thanks Joe, appreciate the recommendation of them. I'm sure from this point I should be able to get them running sweet, off to a good start with them!
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
Cheers Tony! My soldering repair on that wasn't the prettiest but it's still holding up well. Carbs can be a real pain in the backside to diagnose. Really glad you got your CB sorted, its likely it was the same issue thinking about it. :)
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.
Really! that sounds really interesting brother! I would love to see a picture of your work!
@@oilinmyblood3906 it’s a shame we can’t load photos on here, you can see them very briefly at the start of a video I posted a long time ago, just type “Marks CR dyno” into RUclips, it’s only the first second or two you can see it though, basically I cut the front out of the filter until it was a little smaller than the largest diameter of the velocity stack, then pushed the velocity stack about 15mm into the filter, then secured and sealed it with Sicoflex, then just attached to the carbs with the original clamps, hopefully that makes sense!
@@1234567marks yeah it does actually brother! that's pretty much what I was picturing in my head! But I would be cringing at the fact that I would have to tear apart that $50 K$N airpod × 4! That's a lot of money to be tearing it apart! But I guess in the pursuit of more power why not!
Planning to throw the matching air box and rubber stacks on with these new carbs for now. However sounds ingenious to combine the original stacks with individual filters. Cheers!
Very nice work. I need to clean the carbs on my k4. Might take me a bit longer than 11.55😀 what sort of filter will you use between the tank and carbs?
Excellent job mate. I have 1975 Honda 750k5 with the same carbs. :)
Put on a carb from Ebay for 26 dollars.Had to adjust the float. works great
👍😎👍
Thanks.
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.
Thanks for sharing, interesting that you had no issues with the later style carbs. Maybe a big part of my problem was that the later style carbs I had were problematic, despite my best efforts.
@@SPANNERRASH It very well could be. I had mine cleaned in ultrasonic bath and rebuilt with new parts. The one issue I had but found with the carbs hanging from the roof in the garage was that the accelerator pumps was not working. It was due to a just a fraction to big o-ring between the float bowl and the carb body for the acc.pump on number 2 carb that when squished didn’t let petrol pass. Once that was sorted and a squirt of petrol was sent, everything was golden.
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
Thanks Dave. You need to allow a fair amount of time to do a good job. I suggest a full day. The ultrasonic isn't an essential, you can find other ways to clean the metal. But I would recommend that compressed air to blow jets and airways in the casting is essential. And sometimes a set of jet files, or thin wire (guitar strings) to poke them through. I would try to keep the original jets and give them a good clean if possible. but change the float valve and gaskets. Make a tool for setting the float heights, see my other video. Usually, the main problems are with the pilot jets, so make sure they are really clean along with the airways to them. If you take your time and plenty of photos so that you put it back together correctly you should be fine. Good luck.
@@SPANNERRASH brilliant thanks a lot I ordered an E guitar string for the pilot jets and two cans of carb cleaner (spray) Winn's. Sorry no compressor. Thanks again for the advice much appreciated. Dave from Sheffield
@@kimsmith4409 No problem, hope it works out well for you mate!
Can you use 82’ cb750 DOHC carbs for a 1980 CB750F?
I think there are a number of issues, carb spacing, finding rubber manifolds etc. I suspect with patience it could be done but from various forum posts it doesn't look like plug and play. Good luck if you try it, and do let us all know how you go on.
That was amazing, did you have any problems we didn’t get to see, carbs are like a black art lol 😂
Cheers Mike, other than it taking a whole lot longer than it looked, it was a pretty successful swap. We'll see how we get on tuning them up properly.