Topic: what are stock jets for 77 cb550k and what exhaust do I have

[mitch5069]

Hi all, I've been digging around and cannot seem to find what is the stock set up for a 77 cb550k. When I got the bike I cleaned them and found that they had a 42 slow jet and 90 main jets. I have since started tuning them for pods and seem to be having some luck. Also I'm not sure what exhaust is on this either. From what I have read the 4 into 1 on my bike is not stock and may have come off a 550F model???

Thanks for the help!

[mitch5069]

forgot to post the pictures...

[TwoTired]

The exhaust system on your bike is not stock Honda.  Not even F model.
Stock mian and needle position wiil have to be enriched to compensate for induction and exhaust changes from stock.

Cheers,

[Deltarider]

First verify what carbs you have. If your bike is a CB550K3-A model, according to p.4 of the appropiate parts list http://www.honda4fun.com/pdf_parts_list/pdf_spac500-550/CB500-550_K3-K4.pdf stock carb was a PD46A-A - PD46A-D. See pic below for where to find number and suffix, the latter in the small rectangular. On p.178 of the Shop Manual CB500-CB550 http://www.classiccycles.org/media//DIR_1653304/DIR_1653404/DIR_1653507/ecc6759db0a214d5ffff8825ffffe41e.pdf Honda gives a Carburetor setting table suggesting main jet #90 and slow jet #38 for the CB550K3. However this setting may have changed corresponding with the suffix in your carb number, may. We're still in the process of finding out and all help is welcome. Also PO may have changed setting, may. Not much help, I'm afraid. What symptoms do you have?

[mitch5069]

Thanks for all the help!

I have a PD 46A then it has an "A" with a box around it and OH and a funky "Y" but I think it is safe to say I have a PD46A.

As far as symptoms go I'm not really sure. I had a lot of trouble when I first got the bike and had to replace some electrical components and then I was having some trouble getting the bike to run correctly. Once it would get warm and I would open the throttle it would hang pretty high, guessing around 3 or 4k (no tach hooked up currently). I started playing with the jets and such to attempt to fix this issue. The bike had a #42 slow jet and #90 main jets when I got it. Right now I am at #38 slow jet and #105 main with the idle screw at 1 turn out. I should mention that I have the cheap cone filters on (purchased form 4into1.com) Seems to idle good and come down after rev'ing the engine. I only got this running last weekend and took it for a short ride last night around the block after it was warmed up. Seemed to be pretty flat at higher RPMs but pull well through the lower RPMs. I will probably wait until this weekend to take it for a ride again to confirm that it is running ok and there is still a flat spot in the higher RPMs.

[cb_n00b]

Hey Mitch,

I'll give you my two cents since I have the same bike/carbs. I've had two sets of PD46A's now, the set that came on the bike and a set I picked up on eBay to learn how to take them apart and adjust them without screwing with a functioning motorcycle.

Interestingly enough, the set I purchased off of eBay had 42 pilots and a jet needle for a CB500 (which is a slightly richer needle)....Not sure which needle is in my installed carb bank; but I'll check in a month or so when I clean them up for the winter.

I changed out my stock pilot jets for 42s in my current installed carb bank (up from 38s) because the engine seems to like it a little better and it doesn't run so lean.

My only engine modification is a motogp werks 4-into-1 pipe, which is a pretty open pipe, that I'm running with the stock airbox and stock paper filter.

My jetting is 42 pilots, 95 main (up two from stock), and raised the needle clip from the 3rd clip from the top to the 2nd from the top, air screw turned out 1.5 turns, floats at 14.5mm. If it's helpful to anyone reading this later, I'm in Atlanta so at about 1,000 feet of elevation.

My bike runs perfect. Plug chops confirm I'm not lean or rich and the pulls hard at full-throttle with no flat spots...Based on this, your 105 mains sound really big for a regular 4-into-1 exhaust, even with pods, 6 sizes up from stock sounds like too big of a jump but I'm just speculating....I don't suppose you've looked at your spark plugs?

[Deltarider]

and raised the needle clip from the 3rd clip from the top to the 2nd from the top

so it lowered the needle one step (leaner), right?

[cb_n00b]

I think my dyslexia got the better of me - I "lowered the clip" by one which "raised the needle" thereby enriching the mix slightly in the mid-range.

[Bankerdanny]

The PD carbs were tuned lean from the factory (early days of emissions consciousness) the pipes alone might not have required bigger jets, but pipes and pods probably will.

[mitch5069]

Hey Mitch,

I'll give you my two cents since I have the same bike/carbs. I've had two sets of PD46A's now, the set that came on the bike and a set I picked up on eBay to learn how to take them apart and adjust them without screwing with a functioning motorcycle.

Interestingly enough, the set I purchased off of eBay had 42 pilots and a jet needle for a CB500 (which is a slightly richer needle)....Not sure which needle is in my installed carb bank; but I'll check in a month or so when I clean them up for the winter.

I changed out my stock pilot jets for 42s in my current installed carb bank (up from 38s) because the engine seems to like it a little better and it doesn't run so lean.

My only engine modification is a motogp werks 4-into-1 pipe, which is a pretty open pipe, that I'm running with the stock airbox and stock paper filter.

My jetting is 42 pilots, 95 main (up two from stock), and raised the needle clip from the 3rd clip from the top to the 2nd from the top, air screw turned out 1.5 turns, floats at 14.5mm. If it's helpful to anyone reading this later, I'm in Atlanta so at about 1,000 feet of elevation.

My bike runs perfect. Plug chops confirm I'm not lean or rich and the pulls hard at full-throttle with no flat spots...Based on this, your 105 mains sound really big for a regular 4-into-1 exhaust, even with pods, 6 sizes up from stock sounds like too big of a jump but I'm just speculating....I don't suppose you've looked at your spark plugs?

yeah so I checked the plugs when I set it up with the idle screw 2 turns out, I still had the idle problem so I tried the 1 (had it at 1.5 then went to 2). They were pretty sooty when I checked them after 2 turns which is why I went to 1. I might check them later tonight and post back. 105 might be too much and im bogging it out at a more open throttle position. I have some 100 jets I could try also. Unfortunately its starting to get cold in PA but I might be able to try some different combinations this weekend.

Also I dont think I mentioned it in my original post but I am on the 3 clip according to my notes... If I remember correctly there are only 5 clip positions??? original was 2 from the top I believe.

[mitch5069]

I went for a short ride today. Seemed to run ok. Once I got home I let it idle for a little before I pulled in the garage and pulled the plugs. Ill have to do some more riding to see where to go from here.

[754]

 If you let it idle for a bit , the only accurate reading you get from the plugs will be for idle circuit.

[mitch5069]

Ok, that's what I thought. I will have to warm it up and run it at half throttle or so then pull them again.

[TwoTired]

Be aware that engines under load have different fuel requirements than engines freewheeling at any RPM.  Making power needs more fuel.

Cheers,

[mitch5069]

Be aware that engines under load have different fuel requirements than engines freewheeling at any RPM.  Making power needs more fuel.

Cheers,

Funny you mentioned that because after it was warm I held it at half throttle for about 30 seconds (not under load) and the plugs looked pretty similar to at idle....

Still tinkering with it but I might try the 100 main jets and see what that results. I do have a question. Does anyone know what part of the fuel circuit these brass tubes are for? I noticed that my pod filters have a lip that seems to block them.


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[mitch5069]

See attached


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[TwoTired]

The two "tubes" at the entrance of the carb mouth are air jets.  One feeds the pilot circuit emulsion tube an the other feeds the mains emulsion tube.

They should not be blocked if you want the carbs to function correctly.

If your pods are blocking them, that is a good indication of the quality of pods you've chosen. (poor)

Cheers,

[mitch5069]

The two "tubes" at the entrance of the carb mouth are air jets.  One feeds the pilot circuit emulsion tube an the other feeds the mains emulsion tube.

They should not be blocked if you want the carbs to function correctly.

If your pods are blocking them, that is a good indication of the quality of pods you've chosen. (poor)

Cheers,

So do those air jets help fuel getting into the engine?

What symptoms would I see if those are blocked? Lean? Rich?

Thanks for all the good info


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[TwoTired]

The two "tubes" at the entrance of the carb mouth are air jets.  One feeds the pilot circuit emulsion tube an the other feeds the mains emulsion tube.

They should not be blocked if you want the carbs to function correctly.

If your pods are blocking them, that is a good indication of the quality of pods you've chosen. (poor)

Cheers,

So do those air jets help fuel getting into the engine?

Absolutely.  If you look or probe into those tubes, you will find a restricted orifice.  The shop manual supplements  show pictures with removable jets in those positions, no doubt used on the prototype to find best mixtures.

What symptoms would I see if those are blocked? Lean? Rich?

The emulsion tubes ,"froth" the fuel for easier draw into the carb throat and subsequent atomization.  If you block their supply of air , no froth and raw fuel is what is drawn. 
I would expect the circuits would supply over rich mixtures without the added air from blocked air jets.  I haven't tried it in practice, though.

Cheers,

[Spanner 1]

Oh I've seen it in practice.... blocked emulsion holes will cause raw fuel to well/dwell in the carb throat and cause an uncontrolled rpm rise enough to wreck the valves if the motor is not shut off in time  ! Throttle shut off hard at the grip has zero effect when the motor is sucking in the excess fuel and racing away ! Have to hit the kill switch FAST !