CR carbs

[Rozabikes Tim]

Should be renamed PMT carbs perhaps?

Sorry to any girls amongst us!

[ST1100]

Sorry to any girls amongst us!

Methinks you're fine as long as you don't name any parts PMS... 

...hon' I swear that this stands for Parked Motorcycle Syndrome, really!!...  

[MarkCR750]

Hi, I'm thinking of fitting a set of 29mm CR carbs to my 78 cb750, 
Can anyone advise me if it's a good idea or not... Cheers

I look into this a couple of years ago before building my CB 750 K6 café racer, so I agree with Bryanj stick with the stock carbs especially if its a standard engine [not tuned]
CR carbs can even cause unreliability for race tuned engines, they are also difficult to ajust in situe.
I finished up putting K&N filters on mine [stock motor] along with re-jetting which took a bit of sorting, but it goes like stink now....

I put 135's in my k7 carbs, cheap cone filters, new diaphragm in the accelerator pump, needles on middle slots, I expected loads of messing about but it runs great, also a home made 4 into 1 (well a drastically altered piper 4into1 I should say) no flat spots, I was very surprised tbh, might go up to 138's then!, I don't know where the timing is cos it's fitted with an old piranha gizmo, I just built a new she's so now have space to complete the build at last!.

[Greebo]

MarkCR750

I forgot to mention that I also fitted a electronic ignition [ Dave Silver] & iridium spark plugs.

I would also like to add that when trying to set up the carbs it wasn't easy initially, & with the stock jets it ran like a pig, we tried different main jets & needle settings before we finished up with the set up mentioned previously.

[Greebo]

MarkCR750

I forgot to mention that I also fitted a electronic ignition [ Dave Silver] & iridium spark plugs.

I would also like to add that when trying to set up the carbs it wasn't easy initially, & with the stock jets it ran like a pig, we tried different main jets & needle settings before we finished up with the set up mentioned previously.

PS... when we tried the needle on the middle slot it was still lacking fuel ,even with the 138 jets,so we gradually moved it down & to get the correct fuelling the needle finished up on the bottom slot

[onethumb]

MarkCR750

I forgot to mention that I also fitted a electronic ignition [ Dave Silver] & iridium spark plugs.

I would also like to add that when trying to set up the carbs it wasn't easy initially, & with the stock jets it ran like a pig, we tried different main jets & needle settings before we finished up with the set up mentioned previously.

PS... when we tried the needle on the middle slot it was still lacking fuel ,even with the 138 jets,so
we gradually moved it down & to get the correct fuelling the needle finished up on the bottom slot

Hi Greebo and Mark CR750 do you think the 138 jets would be OK on my PD carbs I've read somewhere on the USA site about using 110 jets when fitting cone filters to pd carbs, anyone tried this size and what was the outcome?

[Greebo]

Onethumb

Its trial and error mate, it took us a few weeks of trying different jets & needle positions before we cracked it.

I have 4 into 2 open pipes bought from CycleX USA & K&N pods, our main issue at first with the stock jets & stock needle position was the bike wasn't getting enough fuel, when we finished up with the 138 main jet it was still lacking fuel from 2000rpm, it was like riding a kangaroo , so we then concentrated on the needle position, it was only when we dropped it on to the last notch that it solved the fuelling problem, all we had to then was set the air / fuel mixture.

Don't forget that the main jet only really comes into its own on full or near full throttle.

[bladeboy]

Thanks for yr input guys, think I'll keep standard carbs but just re jet them, I will be fitting new electronic ignition so this will all help....

[westfieldandy]

I have sold several sets of cr29's to several sohc bike owners now, mainly F2 owners with blocked up throttle pump jets and rough running bikes. and the new ones with idle circuit can be made to run really well, as long as they are set up correctly on a dyno.  I currently have an 812cc K engine running on them with a mild cam and standard unmodified K head, the bike is really tractable and pulls really clean all the way through the revrange. but it was set up on an dyno properly.  I would really recomend.

If the bike were to be used for touring long distance and in all weathers then I would probably point you back towards standard carbs because they work better with air filters. and CR's have open bellmouths, so road grime and dirt dont agree with your engine.

[onethumb]

Hi greebo, Is there a quicker way to change needle position than to split the banks of carbs?
I've got the f2 with the pd carbs.


Sent from my iPhone using Tapatalk

[Greebo]

Sorry for the late reply, only just noticed your post question.

I am not really sure how your carbs differ from mine ,ive not had my honda that long so I am not an expert , with mine you have to remove the carbs, obviously, take the tops off each carb to get to needles,its a fiddly job, the guy who built my bike did all this while I watched & Learned, we had the carbs on & off about 5 times before we got everything right.

have you tried searching youtube  for info.

Lets us all know how you go on

Cheers
Greebo

[Johnwebley]

  try this video,

  https://www.youtube.com/watch?v=nMFxF-DAJmQ

  I recently re-built my CB500 carbs,and to do the needles only needed the top caps removed,

[yozzer74]

No good that video for the PD carbs totally different .I've tried to find a link & video how to strip rebuild these carbs can't find one .

[Greebo]

Hi, I'm thinking of fitting a set of 29mm CR carbs to my 78 cb750, 
Can anyone advise me if it's a good idea or not... Cheers

I look into this a couple of years ago before building my CB 750 K6 café racer, so I agree with Bryanj stick with the stock carbs especially if its a standard engine [not tuned]
CR carbs can even cause unreliability for race tuned engines, they are also difficult to ajust in situe.
I finished up putting K&N filters on mine [stock motor] along with re-jetting which took a bit of sorting, but it goes like stink now....

I put 135's in my k7 carbs, cheap cone filters, new diaphragm in the accelerator pump, needles on middle slots, I expected loads of messing about but it runs great, also a home made 4 into 1 (well a drastically altered piper 4into1 I should say) no flat spots, I was very surprised tbh, might go up to 138's then!, I don't know where the timing is cos it's fitted with an old piranha gizmo, I just built a new she's so now have space to complete the build at last!.

Mark

where did you get the New Diaphragm from ?, also sent the question in a personal post

cheers
Greebo

[MarkCR750]

Greebo sorry at the moment I can't remember!, I think it could have been eBay but I've had a look in my purchase history and can't see it, I seem to remember it was only about £15 , I'll keep thinking, I'm sure it will come back to me.