1979 CBX Project

[RobbieAU]

Hi All,

I have been restoring a 1979 CBX1000 for the last few years with heaps of help from all the advice on this site. Today was the first longer ride (60 KMs) after finally getting my CRS31 Carbs dialled in pretty nicely. All the effort was worth it just hearing this beast rev out to 9000RPM today.

Bike is a 1979 USA model, with an SC engine from a pro-link model.

I will post some before and after photos when I figure out how this works...

Thanks everyone and happy riding

Cheers,

Rob

[RobbieAU]

Before

[RobbieAU]

After

[RobbieAU]

Heaps of fun to be had tuning these CRS31 carbs too

[steve murdoch icoa #5322]

Congrats on finishing off the restoration, Rob.
Great looking bike.

Now i know why there is no DR8ES-L plugs at my local shop. Cheaper by the case?

[NobleHops]

Great job, Robbie! The bike looks amazing!

[RobbieAU]

Thanks guys, the plugs are cheaper by the 100, but optimistic me thought I would get away with 60 initially...and here we are 126 used plugs later! .

I purchased the CRS carburetors from JB Power in Japan and they came with the following settings

240 Air Jet
120 main jet
62 pilot
Air screws at 3/4 turns out
YY8 Needle highest setting 7
Size 25 slides

I now have the carbs set up like this (leaner almost everywhere)

240 Air Jet
120 main jet
60 pilot
Air screws at 1 3/4 - 1 7/8 turns out
YY9 Needle highest setting 7
Size 30 slides

I messed around for a long time with different needles and clip positions before biting the bullet and forking out about $500 AUD to purchase 6 size 30 slides. Turns out that was the key to success as the size 25 slides were just fouling the plugs after 15 minutes riding at low speed.

After yesterday's 60KM ride at speeds mainly at 60 and 100 KMPH the electrode insulators are white and the bike is running well. I will check again after a few 100 more KMs to see if the plugs turn a tan colour and report back.

I also haven't done too much riding above 3/4 throttle, so the main Jet could see some changes. It did scream out to 9000RPM a few times quite nicely so I suspect it is close.

I hope this info saves others time (and plugs) tuning their Keihin CR31 carbs for the CBX1000. I know it would have saved me 50+ hours if there was any info about tuning these carbs to the CBX out there. I had to go down this route as the cheap bike I picked up had damage to one of the original carbs and I could not find a replacement.

I am running Pipemasters exhaust, velocity stacks with metal screens and premium unleaded fuel (without ethanol) with sta-bil fuel stabilizer added. I also changed the fuel tap to a Pingel unit.

Cheers,

Rob

[NobleHops]

Thanks guys, the plugs are cheaper by the 100, but optimistic me thought I would get away with 60 initially...and here we are 126 used plugs later! .

I purchased the CRS carburetors from JB Power in Japan and they came with the following settings

240 Air Jet
120 main jet
62 pilot
Air screws at 3/4 turns out
YY8 Needle highest setting 7
Size 25 slides

I now have the carbs set up like this (leaner almost everywhere)

240 Air Jet
120 main jet
60 pilot
Air screws at 1 3/4 - 1 7/8 turns out
YY9 Needle highest setting 7
Size 30 slides

I messed around for a long time with different needles and clip positions before biting the bullet and forking out about $500 AUD to purchase 6 size 30 slides. Turns out that was the key to success as the size 25 slides were just fouling the plugs after 15 minutes riding at low speed.

After yesterday's 60KM ride at speeds mainly at 60 and 100 KMPH the electrode insulators are white and the bike is running well. I will check again after a few 100 more KMs to see if the plugs turn a tan colour and report back.

I also haven't done too much riding above 3/4 throttle, so the main Jet could see some changes. It did scream out to 9000RPM a few times quite nicely so I suspect it is close.

I hope this info saves others time (and plugs) tuning their Keihin CR31 carbs for the CBX1000. I know it would have saved me 50+ hours if there was any info about tuning these carbs to the CBX out there. I had to go down this route as the cheap bike I picked up had damage to one of the original carbs and I could not find a replacement.

I am running Pipemasters exhaust, velocity stacks with metal screens and premium unleaded fuel (without ethanol) with sta-bil fuel stabilizer added. I also changed the fuel tap to a Pingel unit.

Cheers,

Rob

Great data, Rob, a nice contribution to the knowledge base.

N.

[bobcat]

Hi Rob,
When you are talking about slide size, are you referring to the "cutaway angle "
at the bottom of the slide ?

[Michael Vidovic]

wow
well done! Looks great.

[RobbieAU]

Hi Rob,
When you are talking about slide size, are you referring to the "cutaway angle "
at the bottom of the slide ?

Yes sorry, it is the cutaway angle. 30 has a larger cutaway than 25 so it runs a little leaner.

[RobbieAU]

The sun came out today, and the network went down at work so it gave me a perfect opportunity to get the CBX out for another ride.

After 15KMs, one of the headlight bolts came out so I turned around and went home to replace it. When I got back home I could smell fuel and noticed that the number 3 carb was leaking. So I took them off and gave them a good clean. All the jets were still totally fine and not gummed up, but there was a bit of sediment in the bowls due to not running a filter.

I put in an inline fuel filter and replaced the plug on that cylinder and went out for another 100KM ride. The bike rides perfectly now. Plugs are turning a tan colour and I couldn't be happier with the CBX1000.

I have read 100s of threads on here and couldn't have done it without you all!

Happy Friday

[RobbieAU]

Plugs after 200KM riding (number 3 only has about 70KM on it)

[bobcat]

The plugs look pretty good but it looks like carbs could use a vacuum sync.
I don't believe those CRs have any vacuum ports for the sync adaptors but
I bet there is a way to fashion some depending on the wall thickness of the
carb to port tubes (front of the carbs).

Bike looks great ! Nice job.

[bikeymikey748]

And another SIX brought back from the edge!
Great save