Topic: CR 29 carbs on CB750 SOHC

[Holty]

Hi All,
Looking for opinions on CR 29 carbs. I have the square top carbs with accelerator pump on my SOHC CB750 but just can't get them to work (and neither can my local bike mechanic) so thinking they are goosed. The bike is a hardtail chop so I'm not looking for performance - just good starting and driveability. Currently when (if) the bike starts it runs OK but is very difficult to start. Running slash cut drag pipes and stacks.
I'm happy to cough up £1000 if they are likely to work. Been looking at some used carbs on eBay but they all look to be in pretty poor condition.
Any comments appreciated.
Thanks.

[vik351]

Are the tops always off ...

Might be the problem...

vik...

[Holty]

Hi - no, tops are usually on.

[bear]

G'day Holty,
CR's  where originally designed  for competition or HP machines.
I could never understand why people where so keen to run them on their road bikes.
They have a very rudimentary low speed circuit and offer little for a daily rider.

Only my opinion of course, I can't claim to have much recent experience with these bikes in road going form.

Cheers,
Brian

[Holty]

Thanks Brian. That was my worry. Struggling to find a decent alternative at present.

[RAZZ]

Take a look here maybe a alternative : XJ650 Carbs on 750A question
 https://r.tapatalk.com/shareLink/topic?share_fid=13548&share_tid=180395&url=http%3A%2F%2Fforums%2Esohc4%2Enet%2Findex%2Ephp%3Ftopic%3D180395&share_type=t&link_source=app



Sent from my iPhone using Tapatalk

[Holty]

Thanks for the link.

I've been in touch with speedmotoco and for about $700 they'll ship a mikuni VM34 twin carb set up to the UK. I reckon for street riding and my wallet these are probably the best option. I'll post a write up on how they fit and run.

[paul_cb836]

Would not pay that much for them but have CR 29s on my 836 and like them. Only issue is you have to be a bit careful giving it WOT under about 3k but otherwise they are great. Don’t think I would bother with them on a standard engine.

[PeWe]

If the engine is stock or close to stock, standard CB750 carbs work fine. I had them with 836 ported head and cam replacing Mikuni smoothbore 29 that had poor rubber boots that cracked asap.
Bike had same top speed with stock carbs. Throttle response from lower rpm was a little bit better with the Mikuni 29 despite no acc pump.

It must be people with a good set of CB750 K2-K6 carbs for sale.  I guess 200-300USD.  If they are dirty, clean them as long as the aluminium has not corroded away inside due to a bad clean or similar.
I saw many good sets for around 100USD 5-8 years ago

My old ones that sat on my K6 in a barn between 1990 and 2009, finally cleaned 2017 work fine. Almost everything stock inside. I had to order new Keihin main jets since I have lost the old sets I had jetting carbs down to my stock K2. Needles stock that had done 100.000km with the carbs.  New rubber seals.
I think many replace the needles and other jets, replacing them with crap and make problems when stock is working.

[slikwilli420]

Im making 80hp with stock carbs on 760cc. CR carbs have wow factor but really not needed.

[HondaMan]

I have a bunch of rebuildable PD41 series carbs (for K7/8 and F2/3 bikes). You wouldn't need to send me 1000 [anything] for a set, but the postage might be close to $90 USD, I'd guess? Maybe that much again for the carbs?

[Lucho]

I have a bunch of rebuildable PD41 series carbs (for K7/8 and F2/3 bikes). You wouldn't need to send me 1000 [anything] for a set, but the postage might be close to $90 USD, I'd guess? Maybe that much again for the carbs?

Hi Mark, are these carbs usable on a K5? I would like a "plug and play" option that may run as new street ones. Any new sets as an option?

[bryanj]

PD carbs, which you have, are the nightmare child of the carb world. Unless you run a stock intake system the chances of getting them right are about the same as winning the lottery.
You can fit the earlier carbs with earier manifold rubbers and may have more luke

[newday777]

Thanks for the link.

I've been in touch with speedmotoco and for about $700 they'll ship a mikuni VM34 twin carb set up to the UK. I reckon for street riding and my wallet these are probably the best option. I'll post a write up on how they fit and run.

Did you order these?

[MauiK3]

I like stock carbs, predictable and reliable, no fiddling around.

[scottly]

Thanks for the link.

I've been in touch with speedmotoco and for about $700 they'll ship a mikuni VM34 twin carb set up to the UK. I reckon for street riding and my wallet these are probably the best option. I'll post a write up on how they fit and run.

Did you order these?

Look at the date, Stu. The OP hasn't been active since 2020.

[Don R]

 Man, I hope he didn't wait all this time for my opinion.

  Was everyone missing the fact that it's on a chopper with velocity stacks? Maybe the carb set he has with a breadbox style air cleaner would function better and look right also.   
  I wonder how the two carb setup ran?

[newday777]

Thanks for the link.

I've been in touch with speedmotoco and for about $700 they'll ship a mikuni VM34 twin carb set up to the UK. I reckon for street riding and my wallet these are probably the best option. I'll post a write up on how they fit and run.

Did you order these?

Look at the date, Stu. The OP hasn't been active since 2020.

Yes and he didn't update either.
Looks like Lucho is the one who did the drug up of the old post.