Topic: jetting advice: 550 with topend mods

[flatlander]

i was wondering if anyone with a similar setup can give me some pointers for initial carb settings?

the bike's a cb550f (1976) with:

mike rieck stage 2+ porting
intake valves oversize +1mm
megacycle 126-00 cam
wiseco 59mm pistons

carbs
stock 069a
so far stock settings with 98 mains, 38 slow, needle in 2nd pos. - but that's the part the may need to change!

exhaust
stock 4-1

just looking for a good starting point as a base for further fine-tuning.

[flatlander]

should add:
stock airbox with unifilter inside.

[flatlander]

ignition is a boyer micro power. i'm gonna take it to a local shop to get it set with a strobe. i'm using a slotted cam sprocket.
as you say, my feeling is also that the stock setting for the carbs should be pretty close to the truth but wanted to get some informed opinions. my main goal is to be good enough for brake-in, later i'll take it to the dyno and see what comes out of it.

[Scott S]

 I have a very similar combo (turns out mine is also 1.00 mm over, not .50 as stated in my thread). My port job is probably milder, and so is the cam. No oversized valves, either. Why did everyone suggest richer jetting for mine? Because of the higher compression?
http://forums.sohc4.net/index.php/topic,146820.msg1671674.html#msg1671674

[flatlander]

thanks scott. what did you go with, in the end?

[Scott S]

 Still building the engine, so I'm still deciding myself.

[flatlander]

ah ok. i'm actually in the same situation, engine is not ready yet.
i think i'll start out with the stock setting, based it on the (maybe flawed) logic that airbox and exhaust have not been changed, and the engine itself is more efficient - so it should just use more of/make better use of the same air-fuel mix.

it may not get the absolute optimum mix like this but hope it's fine as a starting point, before i get it fine-tuned on the dyno.

[strynboen]

vhu not bay a set old karbs..and drill/machine them a bit aut...but only in the top halfe of the boring...so all in bottom stays stock..and all problems vith neddels fitting...and air mix are left aut..a end cutter 20 mm vill be fine to move sideverds in the top  to get it vident a bit up

[CBGhia]

I currently have a stock 550 with a CB650 cam, 4 into 1, and I use the stock plenum with a big K&N on the back.  I am running 110 mains with that setup.  I would think you would probably be pretty close to that, but maybe not if the stock airbox is very restrictive.

[Scott S]

I currently have a stock 550 with a CB650 cam, 4 into 1, and I use the stock plenum with a big K&N on the back.  I am running 110 mains with that setup.  I would think you would probably be pretty close to that, but maybe not if the stock airbox is very restrictive.

Needle position?

[CBGhia]

I currently have a stock 550 with a CB650 cam, 4 into 1, and I use the stock plenum with a big K&N on the back.  I am running 110 mains with that setup.  I would think you would probably be pretty close to that, but maybe not if the stock airbox is very restrictive.

Needle position?

I think I have it set dead center right now.  I moved it around a bit while I was trying to dial it in. I actually want to pull it again and go 1 notch up, so dropping the needle a bit.  I am slightly rich, but not much.  Down in the Texas heat, I figure it is better to be rich than lean.

[flatlander]

I currently have a stock 550 with a CB650 cam, 4 into 1, and I use the stock plenum with a big K&N on the back.  I am running 110 mains with that setup.  I would think you would probably be pretty close to that, but maybe not if the stock airbox is very restrictive.

if you mean a single big "pod" attached to the plenum then yes, i'm pretty sure the stock airbox is more restrictive.
your 4-1: what model is that? is it stock honda or something more open?

[flatlander]

vhu not bay a set old karbs..and drill/machine them a bit aut...but only in the top halfe of the boring...so all in bottom stays stock..and all problems vith neddels fitting...and air mix are left aut..a end cutter 20 mm vill be fine to move sideverds in the top  to get it vident a bit up

that's an interesting thought! for now i just want to get the bike running as it feels like summer is around the corner... this could be a winter project 

[CBGhia]

I currently have a stock 550 with a CB650 cam, 4 into 1, and I use the stock plenum with a big K&N on the back.  I am running 110 mains with that setup.  I would think you would probably be pretty close to that, but maybe not if the stock airbox is very restrictive.

if you mean a single big "pod" attached to the plenum then yes, i'm pretty sure the stock airbox is more restrictive.
your 4-1: what model is that? is it stock honda or something more open?

Yeah, like a big pod,  K&N made a kit for the cb550 back in the day.  I found one still in the package.

The header is the stock 4 model and I have a V&H megaphone with baffle.

[Scott S]

 I dont see how the stock plenum can be restrictive.  Someone's done the math on here before....probably on a pods thread somewhere. ...and they flow plenty.

[flatlander]

the plenum might be fine but to me, it seems like the stock filter box would restrict more than pods, or the K&N "single pod" that cbghia has. that's just conjecture though, not based on any comparison or math.

[Rgconner]

This is one option for getting pod flow, but not have the issues of individual pods:
http://www.steeldragonperformance.com/air_boxes_7.html

The stock airbox is slightly restrictive, Hondaman talks about drilling holes to increase flow.

[flatlander]

thanks for all the input guys. i won't drill holes in the airbox just yet as that would need more experimentation with jetting which i want to avoid during break-in.
... now if i burn a hole in my nice new pistons i'll be blaming y'all 

[CBGhia]

This is one option for getting pod flow, but not have the issues of individual pods:
http://www.steeldragonperformance.com/air_boxes_7.html

The stock airbox is slightly restrictive, Hondaman talks about drilling holes to increase flow.

Those are pretty nice.  Pricey, but nice!