Rejeting carbs

Hey all. I am very new here and sorry if this topic has been covered before. I have a 1971 Honda cb500 four and am modifying the hell outa it( pics to come soon). I have a question however about my carbs. I wanna put cone filters on the carbs and eliminate the giant clunky air box. However I've been told by a few that I will never get the same performance out of it if I do this. I know many people who said they have been trying to do this for years and no luck. I also see many bikes out there with the cones and run fine. Anyone have any advice or experience with this?? Thanks

J

Hi J, I have the same problem my friend, mine are off my CB750, haven't been run in 26 years and I'm mating them to these


They are from Steel Dragon Performance in Deer River, Minnesota http://www.steeldragonperformance.com/

I don't believe dropping the air box means you'll never get the same performance, all race bikes have stacks so that gives lie to the concept, but I do believe Honda 'fours' are a b*tch to set up!

I suggest you look for some help here http://www.sohc.co.uk a site dedicated to sohc Hondas and with a wealth of advice freely shared. Good luck with the build and let's see some pictures!

Jetting shouldn’t be a major headache on the 550, the engine will run weak when you put the filters on to compensate this go up 2 sizes on your main jets and that will allow more fuelling to the engine
If you are running standard exhaust then that should be enough ,but if you are changing the pipes to a more free flowing type you may have a issue with back pressure or the lack of causing backfiring or popping on deceleration and this will require a even larger main jet and pilot jet
Here’s a cb550 I did many years ago not cafe style the two outside ones had to be put outside as there was no room

Hey Miffa-
I am currently running 4 into 2. So I should start with going up to jet sizes? What else should I be doing? Thanks man in advance....!!!

Unless you are changing the silencer (muffler) to allow greater air flow i.e. removing the baffles, a 4:2 won't make a lot of difference, it's the air going in without the restriction of the original air-box that will necessitate changing your jets.

paul-- did you get those on your 750? how did the rejetting go? I guess the first thing I should invest in is the gauge to read my mixtures??

Hank you start with changing nothing
Pop on the filters and run the bike you really need the bike on the road as the engine will react differently under load and the main jets won’t kick in till higher up the rev range you might be lucky and it will run fine, if not at least you have a starting point for reference
You already have a gauge for reading the mixture they are called spark plugs and of course all the symptoms of either running to weak or to rich after a good old blast and getting the engine hot remove the plugs and check there condition sooty or black in colour to rich light or even whitish is to lean a nice mid brown is what you’re looking for
Lower/smaller jet number = weaker mixture..... Higher/larger jet number =richer
there’s a mixture screw on your carbs for fine tuning i think that about 1 1/4 turns out from seated should be a good starting point you will need some carb balancing gauges to make sure they are all opening from the same point and time as each other
The site Paul recommended http://www.sohc.co.uk is a great source of information by guys who specialize in that particular engine

Thanks milfa. I'm Gunna do just that. One more question. Whats your opinion on a good sync gauge when I get to that point?? Not a cheap one but nothing to crazy. Thanks

J

anything along these lines
uk ebay
Seller assumes all responsibility for this listing.Item number: 120857194768

or just lend some off a mate thats the cheapest option

Ok Paul-
The pod filters did not fit as miffa showed us above on a prior project. I could go the route he once did and put the pods on the outside but don't think I want the look. Now I'm looking into stacks. Just wanted to ask about yours paul and how they function vs. the pods? From my understanding the velocity stacks were made to increase performance by allowing more air intake into the engine but still room for adjustment. So I checked out the website you got yours on Paul and seems like they got some nice products for reasonable prices. I just wanted to ask what about all the junk in the air thats not protected from the air filters? Seems like the screen is a minimal protection from anything in the air. OR does it mean you just gotta clean the carbs more often? Any info would be awesome. thanks again. getting close to finishing btw minus the carbs.

J

The screens inside the carbs aren't a patch on a proper filter for stopping teh lightweight stuff i.e. dust, they are really there to prevent bigger items, flies, leaves, small children etc. being ingested. It's not that the carbs themselves get dirty, excess dust and grit can cause premature bore wear. You might want to give the boys at Steel Dragon a call and ask their advice, but in the end it's a case of you pays your money and takes your choice!

Having said that, why don't the pods fit? I looked at those originally and I've seen a lot of CB4s with the K&N individual pods on, you just remove the old airbox and connectors and they should slip straight onto the inlets of the carbs. Perhaps some photos of what you are trying to do would help?

The other place you might want to look at is Steve Carpenter's website http://www.cb750cafe.com/carpy.php he does lots of interesting things to CBs, mainly 750s but there's not that much difference in principal.