Refreshing Carburetors For My SOHC Honda CB750 Cafe Racer Project Bike | 23

Refreshing Carburetors For My SOHC Honda CB750 Cafe Racer Project Bike | 23

In this video I refresh the carburettors of my CB750 SOHC Cafe Racer project bike. Overall the carburettors look in quite good condition. It appears that they have been refurbished, but then left for 5 or more years, so that there is some corrosion, especially on the steel parts.

I know that they did work to start the bike, as I have had it running for a short time. But as I found that I needed to strip the engine because of an oil leak, which led on to a full top end rebuild they haven’t been used for a while.

I started by removing the float bowls and checking and cleaning all of the jets. I found that they were in pretty good shape, I think that the only petrol that they had seen was from when I test started the engine.

After I used some carb cleaner through the jets and all of the little vents in the carb body, I blew them through with some compressed air.

I then checked and reset the float heights. In my first rough check I thought that they were set a little too low at 28mm. But when I got out the gauge I had made to set the carbs on my K0 project I found that they were mostly OK, and that I only had to reset one of them.

When I came to strip the mechanism that opens and closes the carbs so that I could address the surface rust, I realised that I had never stripped that part of the carbs before. This made it a bit of a struggle, especially as a bit of corrosion made them a little harder to get apart.

I made sure that I took some good photos when I stripped them. The mechanisms on carbs always seem to be very complicated, with lots of fiddly parts. The hardest part of putting them back together is the spring that goes between the plate that the throttle cables connect to, and the part that opens the slides. I think it is some kind of damper, because it is so stiff I can’t see it allowing the parts to move very easily.

The longer spring that actually closes the carbs is quite strong. I know that some people replace this with a lighter spring to make the throttle action lighter. I will see how it goes before thinking about changing it though.

I also adjusted the slides so that they all open at the same time. This is quite easy once the rubber boots, that have really perished, have been removed.

Overall the job was pretty straightforward, and the carbs should be OK when I get them back on the bike. They will need the idle setting and balancing with gauges. But I think the initial setting should be OK.

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[H-M-]

Great job and video. This is a real 50 years old Superbike

[daveco]

Can't wait to see the next video to see how they work on the bike. I have a 1975 CB750. It has the stiffest throttle spring of any bike I've ridden. I may try a lighter spring next time I have the carbs off the bike.

When I was cleaning my carbs a couple years ago I had the same worry about missing a tiny brass piece on the two end carb vent holes. I had to go look at a bunch of photos on-line to realize they're not meant to have that brass piece there.

[robbateman]

Good video Les. Have not done the early 750 carbs but done many a 400/4 set. Did you notice the slot on the shaft with the woodruff keys? This is a "gotcha" there is a pin in the alloy body to stop the linkage moving side to side. you have to drill out the pin or you bust the brass bush/sleeve in the link casting. and the shaft will now move a bit. Also that bit where the cables go round do not clean it in acid before you plate it. it is rivited with metal that dissolves in the acid and you have to rerivit or bolt it together (ask me ho i know) look forward to teh running video.

[johncollins]

Looked very fiddly but you got them back together 😊

[CBK]

...got this same set of carbs. Mine were left in a dishpan, all in pieces for...20 years? Hahahhaah. It's so sad, all I can do is laugh.

[CBK]

I have an off-topic question that any of you motorcycle loving Brits could help me with.
Does anyone in the UK still say "Goes like the clappers" "Bitsa" (for a Frankenbike) or "Bodger"? Would you call your gauges "Clocks"? Outdated? Any others you care to share?
Apparently, here in the US I'm an "Atgatt". All the gear, all the time. Squids are the guys who wear Crocs and shorts on their crotchrockets...