Carb Differences

[simonuk]

Hi
I have a cb550K and it feels a little slower than the 550f2 I had a few years ago. The current bike does have a 4:1 system on it but I think its a bit slow to rev. I have been told the carbs are smaller on the K model to the F2, is that true and if so can you fit them without messing with jet sizes?

Thanks
Simon

[SteveD CB500K0]

If you mean the CB550K3 (four piper), it was actually faster than the Fs in all the road tests at the time. The carbs are completely different from the Fs.

However, if it has a restrictive 4-1 then it is possible that the mixture is screwed and it is making less power.

[Bryanj]

Also if a K3 not easy to fit the F carbs as you would need everthing from the head backwards due to different spacing and i don't think there is room on the K3 frame

[simonuk]

Hmm, it has a 'JAMA' 4:1 system on it, possibly does need rejetting. Has anyone experience of fitting a similar system on a K model and what the jetting changes were?

Thanks for help
Simon

[z1100r]

Slow to rev is extremely unlikely to be the carbs....assuming they are clean and funtioning properly.

It is also very rare that you need to rejet  for an exhaust pipe. There is an awful lot of crap about changing pipes and having to re-jet - even on 2-strokes.

Your jetting is far more sensitive to airbox changes/leaks and I would start there. If K&N type filters are fitted then a complete rejet from scratch of the whole carb is required - and is an unbelievable pain in the arse aswell as requiring special equipment. Refit an airbox - makes the bike so much nicer.

I agree K3's are faster and more economical, they are also smoother and a lot nicer to ride. Its all down to a much better carburettor and exhaust system. The original 4 pipes were the best I've ever fitted to a honda 4 and worked great on all of the many capacity changes my bike went through. I fitted loads of 4-1 pipes and nearly every single one of them made more noise and was slower.

No matter what you do you wont beat Honda. They cast new manifolds and rubbers, swapped the carbs, and finely tuned the whole system making the K3 a much more refined bike. IMO

Which is why my 500-4 600cc bike has a K3 motor with K3 carbs and a std airbox...shame about the pipes, but I cant get K3 pipes anymore.

[z1100r]

I said NEARLY every single one. The Yoshimura pipe was slightly better  but not much. I raced one of these things early eighties and spent ages trying to find an exhaust pipe that was better than stock. (Stock K3 not the 500 ones like I've got - they are terrible). The Yoshi one worked very well with a R&T cam and screaming at 10,000+...not so good pulling out of a 30mph corner in top.

The Piper was awful. Loadsa noise and no go. That was the one with a 2ft long dead straight tube 2.5" silencer if I remember right.

[SteveD CB500K0]

The Piper was awful. Loadsa noise and no go. That was the one with a 2ft long dead straight tube 2.5" silencer if I remember right.

Like the one in my avatar.

My engine was so knackered in those days that I never noticed any power difference between pipes...

It was loud though, and to an 18 year old that was what really mattered 

[matthewmosse]

Best setup I ever had was a bsm 4 into 1 with a triumph rocket3 (old 70's one not modern) 'raygun' silencer welded on. Chrome was very good, sound awesome. It was linked up to k&n filter utilising standard mixing chamber and 500/4 carbs that I think would have been rejetted by previous owner. I heard it comming 6 miles away the day it was delivered and was able to pull power slides round town at the whim of a twist of the throttle, even with 2 victims in the sidecar. In the end the noise meant I removed it, but it is all still in the barn. Fuel economy wasn't bad either. My Laser 4 into 1 system was almost as loud. Motad Neta was the most civilised but didn't feel as fast though that may have just been the inpression created by the din on the other systems. I definately found power slides harder to pull with motads and standard airbox over the K&N single filter behind a stock mixer chamber and found individual S&B custom filters to be awfull to get running acceptably and consistently though I didnt really try that hard. Good mod to my bmw but a pain to get right on the 550 or 500.

[z1100r]

It was loud though, and to an 18 year old that was what really mattered 

OF course, we were all the same. When I first got mine it was fited with an unknown set of header pipes welded to an upswept single pipe and an old Brit 'pea shooter' style silencer. I thought it sounded great.

[florence]

I have a laser 4-1 from the eighties on my bike which is more or less an open pipe.  I also have larger than standard jets and KN style individual filters.  I can't compare to standard set up but it seems to go really well and noticeably better than when it had a motad.

[matthewmosse]

I had the same laser system fitted at one point, it was loud. Sometime I'll dig it and the K&n's out and see if I can get it running right. What size jets are you running? And what carbs, I could choose for mine, 550k3 or 500/4, likewise I can play with bits to try 500/550/650 cc engines, it's a 'one day' project to use up my spares and unfinished projects. I quite fancy going back to my 550 solo bike days.

[Yoshi823]

I've had numerous CB550s over the years...Fs & a K3. My commuter F1 was the most fun though as it had a piper 4-1 fitted



I had also fitted a standard replacement K&N air filter which I also fitted to my later K3, neither of which I rejetted for



The Motad on the K3 was nice & quiet & with the K&N fitted gave me 62 mpg around town & was fun on a rideout as the carburation was clean with no bumps or jumps