Topic: 76 CB550 Cafe build

[GV1390]

Some clean work going on in here, homie! It certainly is a great feeling hearing the bike start up after all the hard work put into it.

[tshrey]

The bike is damn near done, have a couple trivial little things to fab before it could be on the road.  I need help tuning it though.  I've never done anything with carbs and it is shows.  I have the air screws at 3/4 turn out, more in or out only lowers the idle, so that seems like the right setting.  I have the throttle stop set to generate an idle of 1500 rpm.  This seems high, but if I lower it at all the bike just dies.  It simply smells rich, although this could be how old things without FI and cats smell.

I can ride it down the road and it responds well to throttle, haven't had the throttle open more than about 1/8th of the way because the road I'm using is basically just a really long driveway.  So basically at this point the other jets aren't really doing anything, but maybe they need to be changed?

As a review, this bike has CR26 carbs, an MRieck stage 2 port job on the head and 596 pistons in it.  I have the following jets installed:

Pilot Jet 55
Air Jet 220
Starter jet 35
Main jet 95
Clip position 4 from the the bottom

All these settings were from others who had the same setup.

Any suggestions?  It would be awesome if I could do something besides look at this thing after 4 years  

If anyone is remotely close to Long Island, NY who can tune carbs I will put it on a trailer and come to you.

[Godffery]

Here is what we had for those carbs on a bike with Stock Bore, Mild street Cam & 4 into 2 Baffled Pipes.

 Main:     105
 Needle:  YY8 clip 2 
 Pilot:      65   
 Idle Screw:  1 1/2 turn 
 Air Jet:   220

[tshrey]

Did it idle ok? At what rpm if you recall? Doing a search on here I found FunJimmy saying he had to keep it at 1500 rpm with these carbs but then he found an intake leak and a 'cam issue'.

I forgot I do also have 650 cams on this.

[Godffery]

Did it idle ok? At what rpm if you recall? Doing a search on here I found FunJimmy saying he had to keep it at 1500 rpm with these carbs but then he found an intake leak and a 'cam issue'.

I forgot I do also have 650 cams on this. Are

Yes, 1500 is pretty normal for that application.  The tricky spot will likely be threw the 1/4 to 1/3 throttle position, that is where the fuel pickup transitions from the Pilot jets to the mains. The throttle bodies are so big on these Carbs, compared to the vacuum supplied by the 550 motor, that they will loos a bit of the Venturi effect until the rpm is up in the 3k range.  Especially if you try to wack the throttle open too quickly.  But after the motor catches up to the Carbs, it should pull like a freight train.
 I lightened Crank may help remedy this characteristic, but when going that deep in the motor, then you might as well stuff in a Big Bore Kit as well. 

[tshrey]

Ok, if 1500 is where it has to idle I guess I'll stop futzing around with it.

What do you call a big bore kit? I went up to the 596 dynoman kit.

[Godffery]

Ok, if 1500 is where it has to idle I guess I'll stop futzing around with it.

What do you call a big bore kit? I went up to the 596 dynoman kit.

There is or at least was a 605 kit available.  Not sure if they are still being produced, I haven't looked for one in a while.

[tshrey]

I'm just rechecking everything that is easy to access while I have the carbs off.  I've moved up to a 60 pilot jet to see if that helps anything.

While I'm in there I pulled the valve cover to check out everything.  The service manual shows the notch in the cam shaft that you align with the top of the head as pointing forward when 1&4 are at top dead center.  Mine is pointing backward?  Would the engine even run if I had all the valves off by 180 degrees?

[tshrey]

Google search made me feel better.  Didn't think about crankshaft turning half the speed of the cam shaft, so either way is fine.  Pretty annoying that the service manual shows a drawing that is physically impossible - you can't have the notch at 3 o'clock and have the first lobe of the cam point up.

going back out to button everything back up now

[Godffery]

 Good Catch!
Before I could reply to your previous post, your next post just said what I had discovered myself some years ago, about that misleading drawing error.
Hard to believe such a mistake can be in print for Sooooo long, without ever being corrected.?!

[tshrey]

Rear brake fabrication is done.  Took a lot longer than I expected.  Used stainless rod that I was worrying about getting the threading right on when I realized I could just weld on socket head bolts and cut the length to what I needed.  Everything is lined up for where I want the brake lever, but if I have to adjust it I can add a small bolt to the lever that actuates the brake switch to give me adjustment there. Actuator at the lever is a little clunky, I might trim it down a bit but it works well and is very solid.





Need to make a license plate mount with light to let me slap a plate on this and run it down the street without attracting attention.  Getting really close.

Also, does anyone know a source for rear shocks that have a variety of spring rates?  I'm running the generic japanese shocks from Cognito, but they are built for stock weight bikes.  This thing is over 100 pounds lighter and the shocks barely move with me on the bike.  Cognito said they don't have other spring rates for them.  Not looking to spend Fox-type money on this.

[Blackfin5]

On the jetting, I just went through this with my CR26s on my 550.  My engine is a bit more stout with 592 pistons, a Stage III head, lightened crank, 4 into 1 exhaust and pods.  I settled with 110 mains, 65 pilots, Y8 needles on 4th clip, and with air screws 1-1/2 turns out.  Caveat - I'm not at sea level, at 3000+ elevation. Follow Godffrey's suggestion with 105 mains and 65 pilots.

[tshrey]

De Vinci muffler that was on the bike was just too loud.  Found a generic canister with a dB killer on Amazon.  Had to fill in some areas on the connecting pipe with weld and need to clean that up, but this sounds a lot nicer and is much quieter.  Came with a sticker, apparently I snagged an Akropovic muffler for $59    I'm surprised they spelled Akropovic right...

[tshrey]

Threw my Vermont plate on the bike and went for the first ride on the street.  Couple things I noticed:

1) Having a turn signal button on the throttle hand is almost impossible to use, the cable housing for the Domino is very wide.  May have to change to a 3 button switch on the left hand for both turn signals and horn.
2) The 95 mains definitely feel too small, engine runs right out of nuts when I get on the gas.
3) I've never had a 5 speed bike before - what rpms do you guys see at 65 mph?  It seems pretty freaking high at 50 mph.  I may change sprockets to get the gearing taller.
4) The CR carbs return spring is ridiculous for riding, not the kind of thing you notice when running it in the garage.  I will have wrist fatigue after a 15 minute ride if I leave it alone.  What have others done for that?  Just develop Popeye arms?

What is the redline on this engine?

[tshrey]

Pulled the carbs today and went up to 105 mains.  While they were off I removed the secondary throttle return spring and lubed the cables - I realized I never did the lube after remaking new cables.  That made a huge difference, but when I started the bike the revs took a lot longer to drop without that secondary spring on.  Didn't think that would happen with a push-pull throttle, but whatever.  Put the spring back on, throttle is still a lot better with the cables lubed.

Also removed the tubing for the choke system and just put vacuum caps on those nipples.  All I need for a cold start on this setup is the extra blast of fuel from the choke, even with 35 starter jets it is just ridiculously rich so it never starts.  So pull the choke on, turn it over and hear it fire a couple cycles then choke off and give it a bit of throttle to fire up.

Ordered an 18 tooth sprocket for the front to bring the revs down.

[tshrey]

Realized I never did anything other than static timing so i got the timing light out earlier.  Few degrees advanced when I did that, but then revved up the engine and never saw it advance.  I really haven't been impressed with the power of this setup when I get on the gas, I was thinking I'm just spoiled by my other bikes but now I guess the ignition isn't advancing so that isn't going to help on the power front.

Still can't get this thing to idle much below 2k.  It runs at 2k, I turn the idle screw back a bit and it drops to 1500 but then it will just slowly get lower and lower until it stalls.  I know the vacuum of a 550 is a little low for the CR carbs, maybe because the engine isn't broken in at all I have even less vacuum and that is the issue?

[tshrey]

More looks at the timing. The reason I never saw it advance is that even at 2k rpm it is fully advanced already. Is that really the rpm that is supposed to happen at?  I can't get the bike to stay running at an rpm low enough to look at the non-advanced mode. Maybe my springs are worn out?

[Godffery]

 2 k dose seem rather low for the advance to already be maxed out.
 I have come across a number of bikes that the timing advance springs are stretched beyond there service range. I've herd some on this list, say that they clipped off the loop on one side of the spring, then bent one coil out to act as the new loop, and it worked.  I personally have not tried that (I've just replaced them) because it seemed the new spring rate would be rather difficult to calculate.  So unless we get conformation from someone who has done it, I would consider it rumor at this point. 
 As far as setting the timing; I have found that any of these bikes that has non-stock Intake, Carburation, Exhaust, Etc. dose Not like to run on the stock timing setting. So threw trial & error, I've worked out that setting the timing plate about 3 degrees advanced puts it more in 'The Sweet Spot' for idle & acceleration off idle.

[tshrey]

Thanks for the response.  I thought working on carbs would be enough of a problem, now I have to play with 40 year old mechanical advancers.

I am ready to do just that with the springs.  One thought - since I'm running a CB650 cam should I look for a CB650 advancer?

I see everyone on this list talking about degrees, how do you figure that out with only the stock marks?  ie, what is the degree difference between the T and F marks on the advancer,  I can use that distance as a yardstick for adjustments.


One actual update to the bike, I now have pretty much everything set on the chassis.  I switched out the cheap 'Japanese standard shocks' from Cognito to a set of TEC shocks with lighweight springs (still cheap, just adjustable).  The previous set was made for a stock bike, I'm now over 100 pounds lighter and I had about 2mm of static sag   With the new setup I'm at 25% and I can actually feel the suspension working underneath me.  I'm fabbing up a license plate bracket now and will be transferring my VT plate to NY to get this thing legally on the rode.

[tshrey]

SUCCESS!!!!  Apparently the bike doesn't like to idle with 30 degrees of timing advance....  I pulled both springs off the advancer, clipped off the loop and extended the last coil into a new loop.  Now goes to full advance a little above 3k.  More importantly, I can get the bike to idle now at 1400 rpm.

[SOHC4 Cafe Racer Fan]

That can appears (could be a trick of the camera) to be a bit low and could scrape when you lean the bike over.

[tshrey]

I think it's ok, it's tucked in pretty far.  I'll try leaning the bike way over by hand and see what hits first.

Went for a longer ride, a couple miles.  I see what everyone means about ringing these things necks, it really likes running above 6k.  Mid throttle transition is still a little funky, I'll play with the needle clip over the next few days.

Also, wrong about the idle.  It will idle at 1500 rpm if I hold the throttle steady, but no matter where I put the idle screw it is never consistently happy.  Get it set up once with a 1500 rpm idle, next time I'm on the bike it either won't idle or stays at 2500 rpm.  I'm about ready to say screw it and put stock carbs back on this thing.

[Shtonecb500]

I love all my stock carbs lol.

[tshrey]

Pulling the CR26 kit off.  It will be going up on the for sale board if anyone is interested.

[Flexia]

Rear brake fabrication is done.  Took a lot longer than I expected.  Used stainless rod that I was worrying about getting the threading right on when I realized I could just weld on socket head bolts and cut the length to what I needed.  Everything is lined up for where I want the brake lever, but if I have to adjust it I can add a small bolt to the lever that actuates the brake switch to give me adjustment there. Actuator at the lever is a little clunky, I might trim it down a bit but it works well and is very solid.



Need to make a license plate mount with light to let me slap a plate on this and run it down the street without attracting attention.  Getting really close.

Also, does anyone know a source for rear shocks that have a variety of spring rates?  I'm running the generic japanese shocks from Cognito, but they are built for stock weight bikes.  This thing is over 100 pounds lighter and the shocks barely move with me on the bike.  Cognito said they don't have other spring rates for them.  Not looking to spend Fox-type money on this.

I have been looking for a small break switch like this for a while now.  Where did you find it at?