Topic: I don't know what I'm doing. Specifically about CR tuning.

[q2418130103p]

Background on the bike:

• 1974 CB550
• DR8EA
• Web Cam 58A (the following was confirmed with a dial indicator)
     Cylinder 1
       Exhaust 40.5bbdc, 7atdc, 106.75LC
       Intake 42abdc, 8.5btdc, 106.75LC
       0.311 lift
  
     Cylinder 4
       Exhaust 40.5bbdc, 7atdc, 106.75LC
       Intake 40.5abdc, 7btdc, 106.75LC
       0.309 lift
  
• Dynoman/JE Pistons 592cc 61mm 10.5:1
• Ported Head
• Dyna S electronic ignition + 3 ohm coils + 1.5ohm resistors.  Confirmed dynamic timing with a light.
• 4 into 2 exhaust from BCR
• CR29 carbs w/ factory velocity stacks and sock style filters

What works well / what I've done:

• Starts after 1-2 kicks, but I have to turn the idle up about 3/4 turn and I don't use the choke.  As it gets warm the idle will rise, so I have to keep dropping the idle back down over the first 10 minutes of riding.
• Drives around town fine
• Accelerates smoothly in most throttle positions as long as I don't twist really fast.  I haven't really tested full WOT much.
• I set the air screw by starting all the way rich and backing it off until the idle maxed, then I richened that a hair.  Its about 1 turn out, which I think is a healthy position.
• Synced cards

What doesn't work well:

• I think it should accelerate faster, maybe I'm picky
• Bogs if I go from cruise to 3/4 throttle in one quick motion. Eventually it catches up.
• Plugs are black.
• As it gets warm I have to keep dropping the idle.  I usually set it 1500rpm.  Sometimes when I come to a stop it goes up to 2000rpm, then sometimes I stop and its back at 1500rpm
• If I have to come to a quick stop after being around 1/2 throttle then the idle will drop lower than I like

Not that I questions my abilities but uh... Does anyone know a good dyno/tuning place in the RI/MA area that will have CR jets and stuff?

[DaveBarbier]

Call up Rick Stetson at Harry’s Machined Parts in Northborough, Mass. (508) 366-1455. Great guy, and recommended by MRieck. I got my 674cc build tuned there and I have CR26’s. CR29’s honestly seem large for a 550.

He doesn’t have a full selection of jets so I recommend bringing a bunch, needles too.

[calj737]

What Dave said. 29s don't have an idle circuit, are very large for a 550 motor, and without getting on a dyno, you're in for some hard times.

Also, despite the CRs, "whacking" the throttle isn't going to respond like a modern EFI motor. Mechanical carbs, Baby... Learn to "roll" on the throttle and downshift first for more aggressive response. (I hope you're running the motor +6k for cruising.)

[MRieck]

Less is more in this case....29's are to large. You can drop the needle, go down on the main and turn the air screw out a 1/4 turn. The plugs should be tan.

[q2418130103p]

Call up Rick Stetson at Harry’s Machined Parts in Northborough, Mass. (508) 366-1455. Great guy, and recommended by MRieck. I got my 674cc build tuned there and I have CR26’s. CR29’s honestly seem large for a 550.

He doesn’t have a full selection of jets so I recommend bringing a bunch, needles too.

Thanks

What Dave said. 29s don't have an idle circuit, are very large for a 550 motor, and without getting on a dyno, you're in for some hard times.

Also, despite the CRs, "whacking" the throttle isn't going to respond like a modern EFI motor. Mechanical carbs, Baby... Learn to "roll" on the throttle and downshift first for more aggressive response. (I hope you're running the motor +6k for cruising.)

What are the implications of not having an idle circuit?  I'm generally pleased with the driveability, I just know it can be better.  Why do you say 6k?  I'm usually between 4k-5k depending on city/highway, but I could make some changes there.

Less is more in this case....29's are to large. You can drop the needle, go down on the main and turn the air screw out a 1/4 turn. The plugs should be tan.

I'll give that a shot.  I have a full set of smaller main jets.  There are just so many settings, I really wasn't sure which would be most effective.  But I suppose now that I'm looking at the adjustment chart the clip and main jet cover a lot of the range.

[Bankerdanny]

The stock carbs have a separate jet and air bypass that provide fuel and air at idle when the slides are mostly closed. I would assume what he is saying is that the CR's don't have this and so slide and main jet provide all the fuel and air during idle.

[bochnak]

I have spent some time trying to tune these carbs. Total PITA.

Some issues I was dealing with:

1. Only liked to idle at 1500-1800

2. Off idle bog when you hammer the throttle unless you go with large pilot jets. This of course caused a rich cruise condition.

List all your jetting and I can dig through my notes and we can compare.

[DaveBarbier]

I see a higher idle, especially with 29’s, as not something easy to eliminate. I mean, these are race carbs and are designed to be run at WOT or at least designed to best perform at WOT. Just keep that in mind. That’s why MRieck suggested 26’s for me so they’d be a little more tame around town. I believe my bike idles at like 1200 rpm smoothly.

[MRieck]

I see a higher idle, especially with 29’s, as not something easy to eliminate. I mean, these are race carbs and are designed to be run at WOT or at least designed to best perform at WOT. Just keep that in mind. That’s why MRieck suggested 26’s for me so they’d be a little more tame around town. I believe my bike idles at like 1200 rpm smoothly.

The idle problem are more baed on the amount of vacuum generated. The small bore combined with longer duration cam kills vacuum....that's why you have to crank up the idle.

[q2418130103p]

I haven't modified the jetting, so it should be whats in the manual (attached):
Main Jet 120
Air Jet 250
Throttle Valve 2.5
Needle YY8
Clip position 4
Slow jet 60
Valve seat 3.2
Starter jet 45

I can set the idle to 1200 rpm and it still sounds ok, not great. I haven't tried driving around like that though.

[bochnak]

I haven't modified the jetting, so it should be whats in the manual (attached):
Main Jet 120
Air Jet 250
Throttle Valve 2.5
Needle YY8
Clip position 4
Slow jet 60
Valve seat 3.2
Starter jet 45

I can set the idle to 1200 rpm and it still sounds ok, not great. I haven't tried driving around like that though.

I haven't been able to find my notes, since it was about 3-4yrs ago since I worked on that bike.

What is your air screw setting? Should be about 1-1.5 with those pilot jets.

Don't bother messing around with starter jets. I installed the smallest ones and would not lean out choke. The design is flawed, since the starter jet feeds a small reservoir and ultimately does not reduce amount of fuel supplied to choke tube. The jet should be in the pickup tube IMHO.

In tuning, I was unable to satisfy the following:

1. Bog when accelerating quickly from idle

2. Rich cruise

For example, 65 pilots with AS 1.5 out yielded no off idle bog, however 1/8 throttle cruise was super rich, black plugs, etc.

If I had more time and money back then, I would have liked to try smaller pilots (like 55 or so) and richer slides (from 2.5 to 2). Slides are expensive.

I also wondered what would happen if I increased initial timing to possibly increase engine vacuum? (of course you have to do something about total timing)
 

[PeWe]

Tuning carbs is PITA, completely normal
Important to change in correct order when there are no guidelines of others with same carbs and setup.

I tried all needle settings and still problem. Found that pilot needed to be larger so needles still wrong when I had them in delivered position. Found correct needle setting later after a some dyno visits. Last was fuel screws that must be richer to avoid choke too much and too long when not completely warm.
If having intermittent ignition problems (due to a HT lead) will make it worse since that can feel like too lean, or too rich....

After problems like this, you will hopefully know better for next time

I had too sensitive and high idle when fuel screws were lean. Your carbs have air screws, work similar adjusting air to the pilot circuit

[DaveBarbier]

All Rick requests is that the bike starts up and runs. The rest he can deal with.

[q2418130103p]

All Rick requests is that the bike starts up and runs. The rest he can deal with.

lol, well it does that very well actually.

Thanks for all the input so far everyone.  I will probably start with the main jet and clip position, as MRieck suggested.  Those seem like good candidates, plus I have the mains already.

[q2418130103p]

I changed the air screw, main jet, and clip position as follows:
Main Jet         120 -> 115
Air Jet            250
Throttle Valve 2.5
Needle           YY8
Clip position   4 -> 3
Slow jet         60
Valve seat      3.2
Starter jet      45
Air Screw        ~1 -> ~1.25

I didn't totaly work out the details but it seems that the 1/2->3/4 throttle acceleration is excellent, even better than I excepted it would be.  Below half isn't great, a bit boggy.  I don't know for sure because I now see that I have to fix, or replace, my tach before I can really do any more troubleshooting.  The tach is clearly not working well beyond ~6k.

[q2418130103p]

After an exhaustive search for just the right digital tach I finally settled on literally the cheapest mechanical unit I could find...

Anyway, that works now, so I'm back to troubleshooting.

Seems that 3/4 to full throttle is excellent, right through redline. But around 1/2 throttle is very poor, seemingly through the whole rpm range.

I realize that my test method isn't scientific, so I'm open to advice.

[calj737]

Go to a dyno. Have a professional tune the engine and carbs with scientific data.

[PeWe]

Dyno with air/fuel ratio meter is the way. You can waste a lot of time and still not get it right. Very important that the dyno guy run bike slowly, increase the throttle in small steps to verify the 2000-6000 rpm area to see correct needle settings. Pilot jets can have some influence in the lower area when taking off and a little bit more.

Main jets are usually rather easy to find out when twisting full on a road but good to have on the graph. Too lean float bowl setting can be seen here too. Especially if the carbs differ which the plugs indicated. (I have 4-4 so I could measure each)

I did 3 dyno runs last year. First showed way to rich needles, 11-12 area (2000-6000rpm). Second showed OK needles but lean at full on 2 carbs. Third time rather OK with adjusted floats. (I had messed with them a year before so I understood the difference on only 2 carbs.)

[q2418130103p]

A combination of laziness and cheapness has meant that I haven't taken your suggestions of going to a dyno like a should.  But, I have made a handful of changes and, for posterity I guess, here are those numbers.  Reminder this bike is a CB550, 595cc 10.5:1 pistons, ported head, webcam 58a

July 2018
Main Jet         120 -> 115
Air Jet            250
Throttle Valve 2.5
Needle           YY8
Clip position   4 -> 3
Slow jet         60
Valve seat      3.2
Starter jet      45
Air Screw        ~1 -> ~1.25

The bike ran well, idle was fine i guess, WOT was very good, 1/3 throttle was bad.




August 2019
Main Jet         115
Air Jet            250
Throttle Valve 2.5
Needle           YY8
Clip position   4 -> 2
Slow jet         60
Valve seat      3.2
Starter jet      45
Air Screw        ~1.25

This change was terrible!  Partial throttle barely worked at all.





August 2019 #2
Main Jet         115
Air Jet            250
Throttle Valve 2.5
Needle           YY8
Clip position   2 -> 4
Slow jet         60
Valve seat      3.2
Starter jet      45
Air Screw        ~1.25

The was MUCH better.




August 2019 #3
Main Jet         115
Air Jet            250
Throttle Valve 2.5
Needle           YY8
Clip position   4 -> 5
Slow jet         60
Valve seat      3.2
Starter jet      45
Air Screw        ~1.25

Not a huge change, probably not worth changing it again.  Plus, this probably means its just on the rich side of correct, which I think is a good way to go.




September 2019
Main Jet         115->120
Air Jet            250
Throttle Valve 2.5
Needle           YY8
Clip position   5
Slow jet         60
Valve seat      3.2
Starter jet      45
Air Screw        ~1.25

This means they are close to the factory settings, the only difference is the airscrew is a bit lean and the clip position is 1 step richer.  I did one pull, slowly rolling the throttle and it had nice acceleration the whole time.  I did a second pull immediately after and that one was extremely fast.  I'm sure this means something.