CB550 Carb Boring Services- "Almost Free"

Rick has finished boring the 550 carb sets and these babies are on the way back to moi. Here are a few pictures he sent. Notice we are getting close to the "Edge" with a 28mm bore. I believe our wall thickness is 1.3mm at thinnest point!
 

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I received my carbs back from Rick earlier in the week.

Let me begin by saying that Rick is a professional. His communication throughout the process was great and his work is top-notch.

As you can see from the pics, both mine and those posted by Kemp, there is a considerable amount of material removed on the engine-side of the bodies. Pictured along with the ones that have been bored is a standard, unmodified body.

Bored
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Standard
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I just got the entire rack reassembled this afternoon and am waiting for my jets to arrive. I'm planning on trying the carbs out with the stock airbox and with pod filters.

The bike I'll be testing on has a stock engine with a MAC 4-1 exhaust with a modified baffle (I cut the inner half of it off). As I get some riding time with these carbs I'll post up my observations and jetting info. Hopefully testing will begin in the next week or two - whenever my jets arrive and it decides to stop snowing.
 
The horizontal breather tube doesn't get touched. The vertical needle jet air tubes get pulled out of the carbs before the machining begins.

Rick Denoon
 
Ah, yeah PJ for some reason my brain was seeing a before-and-after, when it really was front and back! One of those days I guess! Thanks for clarifying Rick.
 
Finally got around to doing some testing, albeit not much.

I got the carbs swapped into my bike and i'm doing my initial tests with the stock airbox. The carbs are currently just bench sync'd, but i will have them vacuum sync'd in the next week or so.

The fist set of main jets i swapped in are #125's. The pilots are #40's. The bike will hold an idle but as soon as i roll on the throttle it bogs down and dies. Seems way too rich to me. I'm going to swap in a set of #115 main jets and see where that gets me. May also bump down to #38 pilots, but i'm going to first work on getting the main jets set.
 
Also, does anyone have any tips for installing/removing the carbs?

Currently i'm having to remove the battery box, air box, and plenum in order to get enough wiggle room to actually pull the carbs from the intake. It's a real pain and takes me the better part of an hour to remove then install the carbs.
 
I haven't got my carbs from Rick assembled yet but I have finished building the 591 engine they will go on. Just getting it to run right with stock carbs has been an issue. I have a Dyna S ignition and 5 Ohm coils and the plugs are black! Using a 110main, #40 pilot, needle on 2nd clip. Have tried a #38 pilot but 4o seems better and probably needs bigger yet. Stumbles and hesitates off idle low speed running while higher rpm under load seems fine. I think you will need a big main with Rick's carbs #115 seems a good bet and maybe raise the needle and a bigger pilot. I try to do one change at a time to see the effect and not confuse myself. Can't wait to get Ricks carbs on the 591!!
 
I've got a set of #115's that i'll be swapping in next. When i talked with Rick, he said that on the cb400 he goes up by as much as 28% on the main jet size depending on how built the engine is. I took a stab in the dark and confirmed what i thought - #125's are going to be way too much for how much engine i've got.

With the pilot jets he also said that he runs #38's instead of #40's to help keep throttle response as the engine warms up.

I'm fascinated with all the engine builds people are doing with the 550's and i'm hoping to attempt one at some point. ffjmoore, do you have a build on the soh4 forum too?
 
I swapped in the #115 mains a few days ago and have been dealing with random fuel leaks but finally got it all buttoned up and went out for a ride today.

The current specs:

Mains: #115
Pilot: #40
Needle: 3rd clip (middle position)
Idle Screw: 1/2 turn out

Below 4000rpm with the engine under load i get a really bad surge then drop off in power. The surge/drop off happens at a frequency of about 4 times per second until the bike gets over 4000rpm. It's really noticable and rocks the bike pretty good. Kind of frightening when this happens going at any speed.

Once i get into the higher rev range this thing really comes to life. Throttle response is excellent and acceleration is huge. Between 4000rpm and 8000rpm it's a total joy to ride.

After i get the low rpm surging issue sorted out i'll be excited to see if these carbs will pull as hard through the entire rev range as they do in the top end.

With that said - does anyone have any idea what might be causing the surging and what i migth do to remedy it? I have a feeling like it'll involve moving the clip on the needle up or down, but i'm not sure if the surging is a symptom of running rich or lean.
 
You need to do a plug chop to determine where your a/f ratio is. Below 4000 rpm (and above about 1/4 throttle), it will be needle clip position. Main jet sizes are affected by the upper throttle position to full open. The lower part of the throttle is affected by the slow speed jets. Surging could also be float height.
 
I just bought a new set of plugs today, so i'll be doing a plug chop asap.

All float levels are set to 22mm at the moment.

I found this chart to be a great help for visualizing which circut is doing what at a given throttle position:
technical_carburetor_tuning-guide.jpg


I also got a few tips from Rick for diagnosing issues:

"Here is a few more tips.
1. If the bike is stumbling or missing at a certain rpm, put the choke on a bit. Does is make it worse ( you are too rich) or does it make it better (you are too lean)
2. Does the bike run better when cold, then get worst as it warms up (You are too rich) Or, does it run rough when cold, and get better as it warms up (too lean)"

I went for another ride last night and put a bit of choke on around the 4000rpm stumble. As soon as the choke went on all power from the engine left and i would lose acceleration and torque. I'll consider that "making it worse" and assume that i'm running too rich at that given throttle position. I'm going to swap in some #38 pilot jets and see if that will help the issue at all. If not, i think my next move is going to be dropping the needle down a clip.
 
Where are your air screws set at? In is rich, out is lean. Also, lean increases the idle speed and rich slows it down. Better to err on the rich side slightly. So, while it is idling, turn the screw out a few turns and then in until the idle speed drops. That is the point where it goes from lean to rich. The manual setting should get you in the ball park. This is if everything else is in good tune (ignition timing, spark gap, points gap, valves adjusted, etc.).

I was going to post that same chart but didn't have it handy.
 
I've pretty much got the 592 hot rod motor jetted with the stock carbs. I'm getting miles on the bike now and will re-torque the head and degree the cam (hopefully). Then next step is put in the carb set that Rick Denoon has bored to 28mm, get the jetting close and then go to the Dyno with stock carbs and the Denoon overbored carbs. Here are my findings currently with the stock carbs.

Engine - Fully modified CB550 for street use:
Dynoman 592 piston kit 10.5 compression ratio, Webcam 58B, ported head, Kipplewhite racing valve springs, Dyna 2 Ignition and coils, Mac Exhaust, Barnett Clutch kit, Carbs are 75-77 CB550F which are labelled 069A, plugs are NGK DR-7ES, Uniflow Pod air filters.

Carb 069A final settings

Main Jet #120
Needle - Stock in stock clip position (2nd from top)
Pilot Jet - #38 (stock)
Air Screw - 2 turns out

The bike runs quite well, a little burble and hesitation at 2000rpm but pretty clean thereafter, steady 1200 rpm idle. Very strong from about 6500 rpm to 11000 rpm. When I say very strong I mean an absolute rocket ship!! I might try raising float level to clean up the bottom end a bit more. Currently I'm at 22mm float level which is stock and others have gone as far as 27mm to get good results at bottom and mid range response.

I agree that you must get main jet sorted first, forget everything else and get some wide open throttle plug chops to set the size of main. Everything else will fall into line IF you do the main jet properly and do it FIRST. Otherwise, everything is a guess and super frustrating.
 
I should have read through the posts before responding as I've repeated myself and not really answered the mid range jetting question, my apologies! Anyway these observations are just my experience but I hope it helps>

I tried raising the needle to richen up the midrange but it made the bike too rich down low. It would burble, buck and wouldn't rev when I tried a downshift, just hesitated and felt like it was trying to clear it's throat. Went back to the stock setting and problem went away.

I tried a #40 pilot jet also and it was a bit too rich, response low down improved when I went back to a #38

All that said, I was jetting the stock carbs and not the big bore jobbies. I was also using pods which make low speed jetting more difficult because they affect (reduce) the pressure differential that actually makes our carbs work. We must go bigger on the main jet just because we need to supply more fuel everywhere with pods or they won't work at all properly. It seems that the bleed over with a bigger main jet when you are running pods helps the carbs work better from low rpm right up to the top. You will never get the super response back that you have with a stock airbox throughout the rev range but you can get close and on the top end it sure feels a lot stronger (even if the bike has a stock engine).
 
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