Topic: Yet another carb jetting post

[AirCanuck]

I asked previously if anyone knew a decent jetting setup for my 78 cb550k with pods and a F model 4into1. 

I want to make sure I'm using this guide right, would anyone please back me up on this?  Reason I ask is I'm starting a rebuild on the carbs tonight.


Using these guidelines:


****************************************************
Jetting Recommendations
by Denny Zander

Here is a simple set of jetting guidelines that have worked for me. For those considering jet changes, this might help select a starting point.

1 jet size for custom 4 into 2 exhaust

2 jet sizes for 4 into 1 exhaust

1 jet size for K&N filter (single inside airbox)

1 jet size for drilling out the bottom of the airbox

2 jet sizes for both single K&N and drilled airbox

2 jet sizes for individual filters

2 jet sizes for no muffler (open header)

1 pilot jet size for every 3 main jet size increase

Add up all the jet size increases and subtract one. (Remember they go in steps of 2.5 for each jet size)

Under a mismatch condition, like individual filters and stock exhaust or 4 into 1 header with stock filter and air box, subtract an additional 1 jet size.

Check plug color often, sync carbs after each jet change, make sure the floats are set correctly, and seriously consider purchasing a Colour Tune. (See "Colortuning Carburetors" in the Maintenance Section).

Make sure your carbs are in perfect working order before making jet changes.

Example from my '79 XS1100 F:
Stock main jets: 137.5

Stock pilot jets: 42.5

2 sizes for 4:1 exhaust (Jardine)

1 size for single K&N

1 size for drilled air box

4 (main sizes) - 1 = 3 or 137.5 + (2.5 * 3) = 145.0
1 (pilot jet size) or 42.5 + (2.5 * 1) = 45.0

*******************************************************************


According to my shop manual, supplement to K3 (I believe has same setup as K4 for carbs?) stock is 90 mains, 38 slows.
so for me that's

2 sizes (for 4 into 1) + 2 sizes (individual pod filters) - 1 = 3 sizes
90 + 3 * 2.5 = 97.5

3 sizes main jet = 1 size increase pilot jet
38  + 2.5 = 40.5



Now, when I check this thread http://forums.sohc4.net/index.php?topic=124332.0

All I see is folks with similar setups (ctrl+f "pod") using main jets around 104-110. 

What am I missing?  I need to start somewhere and I know the stock jets won't be right... I also have to see what I find when I open it up as I know that the PO had it rejetted with bigger pilots only.

Halp.

[AirCanuck]

Am finding that the pilot is more likely to be 42 stock so switch out the 38 starting point for 42 and question remains the same as far as if I'm on the right track!

[calj737]

I would start with 105 Main jets and move the needle clip 1 slot richer. Then perform a WOT plug chop with clean, fresh plugs.

[AirCanuck]

I would start with 105 Main jets and move the needle clip 1 slot richer. Then perform a WOT plug chop with clean, fresh plugs.

WOT plug chop?

best source for purchasing jets?

[calj737]

Wide Open Throttle.

JetsRus or Sirius. Buy only Keihin brand jets.

[AirCanuck]

Wide Open Throttle.

JetsRus or Sirius. Buy only Keihin brand jets.

Perhaps a silly question..

Do I just need Keihin jets in x size, or do they somehow need to be specific for a CB550?

ie a Keihin 42 slow jet is the right one no matter what or I need to find a Keihin slow jet 42 for a CB550?

[calj737]

Jets are for the a specific carb model, and size. The jets for 022s don’t fit PDs.

Left side, original Keihin type is what you want:
https://jetsrus.com/a_jets_by_carburetor_type/jets_keihin_99101-357_main_Hex_25-xxx.htm

[AirCanuck]

Jets are for the a specific carb model, and size. The jets for 022s don’t fit PDs.

Left side, original Keihin type is what you want:
https://jetsrus.com/a_jets_by_carburetor_type/jets_keihin_99101-357_main_Hex_25-xxx.htm

So I had them apart. Going to bed now so I’ll give you some pics and details tomorrow but interestingly the mains were already 105s and the slows 42s. I had forgotten you said to move the needle but funny enough I already decided to do that as I had been told it was slugging in the first 1/4 throttle. Very excited! First bit of wrench turning for me and I loved it.

[PeWe]

An hour on a Dyno with air fuel ratio equipment will make everything much easier. Very important that the dyno guy will run the bike slowly from 2000-5000 rpm to verify the needles, not only WOT. Lean Pilot jets tricked me to run too rich needles when I jetted my Mikuni TMR carbs when I tried all needle settings.  Found pilot later but did not change needles until I saw the A/F on the graph.
A few Dyno runs made carb jetting complete. Soon time to change exhaust, I need to visit dyno again

[DaveBarbier]

I posted this last month in your other jetting post. Not satisfied with it?

“I had UNI pods and a 4-1 and my setup was stock slow jets, 110 mains, needle raised one notch. Worked well for me. I didn't feel that the 550 was particularly difficult or sensitive to changes. I even ran open mouthed carbs and velocity stacks and didn't notice a difference.

This should get you in a decent starting place, but you'll have to adjust the IMS (idle mixture screw) at idle to get nice tan plugs.

If you have a dyno near by I would highly recommend that for tuning. I have one near me and the guy charges...I forget...like $40 or $50 for three pulls. You'll obviously get HP and torque numbers but you'll want to watch what the fuel mixture is at a given throttle position.”

Your carbs should be PD46C if you have a K4 550K. The stock slow jet for those are 42.

[AirCanuck]

I posted this last month in your other jetting post. Not satisfied with it?

“I had UNI pods and a 4-1 and my setup was stock slow jets, 110 mains, needle raised one notch. Worked well for me. I didn't feel that the 550 was particularly difficult or sensitive to changes. I even ran open mouthed carbs and velocity stacks and didn't notice a difference.

This should get you in a decent starting place, but you'll have to adjust the IMS (idle mixture screw) at idle to get nice tan plugs.

If you have a dyno near by I would highly recommend that for tuning. I have one near me and the guy charges...I forget...like $40 or $50 for three pulls. You'll obviously get HP and torque numbers but you'll want to watch what the fuel mixture is at a given throttle position.”

Your carbs should be PD46C if you have a K4 550K. The stock slow jet for those are 42.

Hey my friend! I don't know how I forgot about that.  I remembered the bit about the dyno but not the jet sizes.

I opened up the carbs finally (it was nervewracking and exciting as a noob) and found 105 mains and stock 42 slows, needle at stock position.  PO mentioned it had good power throughout but was sluggish on the first 1/4, so I was considering raising the needle a notch.  hmm, 105s or 110s, what do you think?  I know the jets in it right now are not Keihin so I'm debating if I change those out or not.  What do you think?

Another question!  Cal mentioned this as well, that you have to go off of what carbs you have.  I do indeed have the PD46Cs.  So I noticed that none of the pictures in the shop manual exactly matched the carbs I seemed to have. 

The two options are either the main section which I believe applies to the 74 550, or the supplement to the K3, which was closer but still not exactly the same (a throttle return spring in one of the early steps being different).  It also quoted 38 as the stock slow jet, though I know it is supposed to be 42.  Is there a manual for exactly the carbs on the K4?

[AirCanuck]

Jets are for the a specific carb model, and size. The jets for 022s don’t fit PDs.

Left side, original Keihin type is what you want:
https://jetsrus.com/a_jets_by_carburetor_type/jets_keihin_99101-357_main_Hex_25-xxx.htm

Hi again Cal, thanks for your patience (I'm going to try it again!  )

Why only Keihin brand?  Currently apparently the jets are keystar (I think) although one of the mains has the numbers stamped differently than the others.  They look to be in good shape.

I was thinking of posting a carb post with some pictures of what I've found so far, pictures of the model number, and an interesting and different float bowl one of them has, along with the results of pulling them apart (solved the leak in number 1!) and a question or two I had regarding differences in my carbs from what I could find in the shop manual.  Should I make a new post for that, or just post here?

[calj737]

Keep all your carb building queries here. It will be easier for you and anyone else to track.

The big reason Keihin jets are recommended is the consistency of the orifice sizes. This is especially true with needles because the taper of the needle differs greatly from Keihin to Keyster. Jets, well, you could use Keysters if all 4 are the same. Then if you need to buy 110s, definitely get Keihins.

The jet that is in there now with a different stamping could be a jet from a different model of carb. This will haunt you endlessly. If you can, just replace all the slows and mains with new Keihins, set your float height with Clear Tube method for precision.

[DaveBarbier]

I have never seen a supplement or standalone manual for the PD46C carbs, but I don’t have those carbs anymore so I have no reason to look. If I were you I’d go to 110’s just because that’s what I used in mine and felt good power all through the range. But no bike is exactly the same, especially since you have a different exhaust than I had.

[AirCanuck]

Keep all your carb building queries here. It will be easier for you and anyone else to track.

The big reason Keihin jets are recommended is the consistency of the orifice sizes. This is especially true with needles because the taper of the needle differs greatly from Keihin to Keyster. Jets, well, you could use Keysters if all 4 are the same. Then if you need to buy 110s, definitely get Keihins.

The jet that is in there now with a different stamping could be a jet from a different model of carb. This will haunt you endlessly. If you can, just replace all the slows and mains with new Keihins, set your float height with Clear Tube method for precision.

Oh geeze.  I am using this kit http://4into1.com/ultimate-carburetor-rebuild-kit-honda-cb550k-1977-1978/

I am emailing them now to find out what brand the jet needle and jets are that came with it... I was going to swap in those pilots and keep the main jets.  Once I gather my info I'll make a call on buying jets and if so for sure a full set of Keihins.  When you say the taper varies, are you talking about the jet needle?  Right now I assume they are also keystar.

To make sure I am interpreting that diagram properly, you're saying you basically set your float heights and check it with a tube to make sure that the fuel is about 2-4mm is it?  I'm seeing different numbers... below the float bowl gasket (I assume basically the line where the carb and float bowl marry up).  Initial settings to get you close would be what, as per factory? 

And I assume all I have to do is connect the fuel lines and open the petcock to do this, with the bike standing level?

[calj737]

Yes, the needle tapers from stock to aftermarket vary hugely.

With your carb rack on a bench, set them up vertically. Use a donor tank of fuel (think medical IV stand) and flow some fuel to one carb by introducing into the drain screw hole. Determine the fuel height by measuring against the fuel line. They will equalize to each other. Adjust the float level so it stops the fuel inflow when the fuel is 3-4mm below the bowl seam. Repeat on other 3 carbs.

Do this after a bench synch for ease. When done, install on bike and ride away happy 

[AirCanuck]

Yes, the needle tapers from stock to aftermarket vary hugely.

With your carb rack on a bench, set them up vertically. Use a donor tank of fuel (think medical IV stand) and flow some fuel to one carb by introducing into the drain screw hole. Determine the fuel height by measuring against the fuel line. They will equalize to each other. Adjust the float level so it stops the fuel inflow when the fuel is 3-4mm below the bowl seam. Repeat on other 3 carbs.

Do this after a bench synch for ease. When done, install on bike and ride away happy 

When you say vertically... do you mean so the whole rack is sitting on the bench, 1,2,3,4 left to right idea or somehow up and down on it's side? 

You're describing the clear tube method, yes?  So when you say 'by measuring against the fuel line' you mean the clear tube?

[Gordo]

You want to have your carbs level as if fitted on the bike but actually on your work bench. Fit your clear tube and add fuel via temporary fuel tank. Then measure where the fuel reaches in the clear tube. You are looking for it to be approx 3mm below where the float bowl meets the carb body. Set all carbs to the same level.

[DaveBarbier]

I highly doubt any kit you buy online will have Keihin jets. Unless you specifically search them out. Keihin jets and needles all have a “K” stamp on them.

That being said, don’t replace your needles with the ones in the kit if you have Keihin needles in there already. Maybe that’s obvious but this needle swapping talk makes me second guessing that.

As for the clear tube method, the PD carbs are nice because you don’t have to drill out a float bowl screw. Just connect your clear tube to the overflow nipple and crack the drain screw open. Might have to flick the tube a bit to make sure there’s no trapped air bubble. Like a nurse removing air from a syringe.

You’re on the right track!

[AirCanuck]

ok this makes sense.  Thanks folks. 

Here is the work done so far with the state of the carbs, bowls, and the reason for the leak on #1.  Also a pic clearly showing model of carbs, and finally one that shows that #2 has a different bowl from the rest - anyone know what it is from?  Notice the overflow area is different, no brass tube, slightly different shape.  Fits perfectly to carb so I assume a different year of 550?

https://imgur.com/gallery/ZwYel

Dave, great to hear!  I saw many threads on that issue of how to connect it, and I was wondering if I could just use the overflow nipple. 

At this point I suspect none of the jets or needles are Keihin.  I just confirmed that 4into1's kits are generic needles and jets. I assume about $100 USD to replace all, so I may for now leave them since they are in good shape, ride it for next summer (keeping in mind I have never ridden this bike!) and see if I actually like the fit of it before I dump another $100 into the carbs (this kit already cost me $89 USD plus shipping!)

[DaveBarbier]

That’s an earlier bowl, maybe from the PD46A...? It acts the same though.

Yeah getting new jets and needles can be expensive. Might be an idea to get a cheap rack off eBay and use the brass. Maybe possible to get the seller to see if he sees K stamps on any needles or jets.

When you install the slides, remember to aim the cutaway towards the air filter, not the engine. There are no locating tabs so the slides are able to be installed wrong.

[AirCanuck]

That’s an earlier bowl, maybe from the PD46A...? It acts the same though.

Yeah getting new jets and needles can be expensive. Might be an idea to get a cheap rack off eBay and use the brass. Maybe possible to get the seller to see if he sees K stamps on any needles or jets.

When you install the slides, remember to aim the cutaway towards the air filter, not the engine. There are no locating tabs so the slides are able to be installed wrong.

Thanks for the tip.

I can't see getting a rack of carbs with the jetting I happen to need and Keihin needles for less than 100 USD, do you think? 

I'm still pricing things out but the go to for now may just be cleaning the carbs well, replacing all floats, gaskets, etc, keeping current jets (they are relatively new), properly bench synching/clear tube method for float heights and riding the **** out of it this summer to see if I want to put another $100 USD into it.

Anyone know how to even find the proper needle on Jets R Us?  I'm totally lost there.  The Jets you can find by bike model (Thanks Cal for showing me!) but the needles...

Also, despite Cal's best efforts I can't figure out what those specific jets are called in terms of a model number.  If I'm looking for other sources on parts, do I just search "Keihin PD carb jets"?  Do I use the SKU part number? ie (SKU- 99101-393 ) for the main jet, (SKU- 3L) for the slow jet?

[DaveBarbier]

Oh yeah, sorry. I mean maybe just for the needles and stock slows.

Might just be easier to email Mike at Jets R Us. He’s a good guy.

[AirCanuck]

Another question. Carbs are clean! Pics to follow. In process we removed a couple sort of soft paper o-rings from the carb body. Can these be replaced with rubber or do I need to order them?

[DaveBarbier]

Felt washers? I believe they should be replaced with new felt. I’ve never dismantled carbs before. Someone else will chime in with proper information.