Topic: cb550k pilot jets #38 or #40

[orange550]

I'm about to rebuild my carbs. Stock for a 74 cb550k is #40 pilot jets. Most kits have #38s. I know the later 550s had #38. I wonder if this was to help with emissions?? I also wonder if the difference between 38 & 40 was made in the air screw and not some other setting?

I have heard that the #38s can run a little better then the 40s, but maybe it's too close to call. My bike bogs a bit when I grab a big fist full of throttle. It also sputters a bit when at cruising speed. It accelerates like a bullet and climbs the gears awesome. I vac syned the carbs but it didn't help the sputter or bog. The main jet orings are dried out, so I knew that I'd have to get that addressed before I tinkered with the sync....

Anyway, thoughts on 38 vs 40 on the pilots? Maybe I can try the #38s, and then keep the air screws a bit rich?

(BTW - everything else is stock)

[TwoTired]

According to Honda, the correct jet is #38.  But, some had #40 from the factory.  I think the air screw has enough adjustment range to compensate.  It does on mine.

You should NEVER be able to snap the throttle open at low RPM and expect it to pick up.  Physics won't allow it.  It's a carburetor with mechanical slides and no accelerator pump, not fuel injection with computer control, or CV carbs.
It should be able to respond cleanly with up to 1/2 total throttle travel and pick up smoothly and reliably.

As for "sputter".  Check/replace the air filter.  Look at the spark plugs for deposit pattern.  Leaky mains orings won't help, and neither will the slide needle in the wrong position, or the wrong size main jet.  The exhaust type can have an effect too, as well as the general tune up state, that should be corrected/adjusted every 3000 miles.

[orange550]

Thanks TwoTired.

My pilots are 40s. My Haynes manual says 40 pilot and 100 mains, throttle slide at 2.5, jet needle at 3rd groove. But I also have an old cb550 manual that says 38 & 90, jet needle at 3rd groove. My bike is in Canada, so maybe that explains the 40 in mine, but who knows really.

(Btw - what's the difference between throttle slide and jet needle groove?)

Good to know that the bog on a big throttle twist is expected. I don't need to ever do that anyway... but I am hoping to solve the sputter at cruising speed. My filter is a new foam replacement in the stock air box. I've also set the valves, timing, and points. The plugs read rich, but I suspect I can't really problem solve until the carbs are rehabbed and synced.


Thanks

[TwoTired]

My pilots are 40s. My Haynes manual says 40 pilot and 100 mains, throttle slide at 2.5, jet needle at 3rd groove.

My 74 CB550 with the 022A carbs were #40 from the factory, (I got the bike in 75)  However, ALL the Honda Documentation calls for #38 for the pilot jets.
All the N.A. continent 550s 74 to 76 used #100 Mains except the F model which used #98.  The 77-78 K models got different carbs (PD) and they used #90 mains to go along with the high pressure exhaust.

The 022A carb throttle valve needle, slide needle, or Jet needle (different terms for the same part) had the clip in position 4 from the top.
(You probably just found your stutter problem.)
btw, 2.5 is diameter of the slide needle at it's widest part.

But I also have an old cb550 manual that says 38 & 90, jet needle at 3rd groove. My bike is in Canada, so maybe that explains the 40 in mine, but who knows really.

The CB500 used #40, in the same carb type.  I figure early models of the CB550 got them 'cause that's what was in the parts bin during the production build, until they ran out.

Cheers,

[Duanob]

Which carbs are we talking about? I have a set of 22A and 087 and both have 38s.

[orange550]

Which carbs are we talking about? I have a set of 22A and 087 and both have 38s.

Mine are 022A carbs in a 74cb550k. I initially thought they all had 40s (my bike has 'em and the Haynes calls for 40s) but I now realize that the 40s were a bit of an anomaly in the early 74 550s. I feel better about using the #38s and plan to rebuild my carbs early next week.

I do have to figure out how to get the emulsions tubes out. I've read a bit here and there... so hopefully.

Thanks

[Duanob]

Are you talking about the needle jets? I took a short piece of coat hanger and bent the end about an 1/8" and reach in a push them down til they fall out the bottom of the carb (with the slide fully up of course)

[TwoTired]

Be careful pushing out those emulsion tubes, the end at the carb throat is actually a metering orifice.  Not a good idea to buggar those up.

[orange550]

Be careful pushing out those emulsion tubes, the end at the carb throat is actually a metering orifice.  Not a good idea to buggar those up.

so dumb question, where are they? above the pilots? and how do you get them out?

Thanks

[TwoTired]

Be careful pushing out those emulsion tubes, the end at the carb throat is actually a metering orifice.  Not a good idea to buggar those up.

so dumb question, where are they? above the pilots? and how do you get them out?

Thanks

For the 627b, 022a, o87a, and 069a carbs,  the main jet rests against them.  The opposite end you can just see in the carb bore.
If they are clean they can fall out or be blown out with compressed air.
If they are crusty or glued into place with fuel varnish, they need to be tapped out from the slide end.  As the slide needles poke inside them, stubborn emulsion tubes need be tapped out after the slides are removed.  I use a wooden or nylon dowel to dislodge them, along with a small tack hammer.

It's not hard, it just takes time and patience.

Cheers,