Author Topic: CB550 - CR29s is this the best it gets? Will CR26s be better street carbs? (Read 38037 times)

akabek · « **on:** June 16, 2013, 05:50:33 PM »

So I have my carbs running great right through each gear but the problem is at idle. It does not want to idle below 2K and it is running rich. Some info on the bike:

1975CB550F
592 big bore
electronic ignition, coils, wires
ported head, valve job
CB650 cam
MAC 4-1 header with cone engineering muffler
Steel Dragon stacks with BBR filters

The CR29s are jetted with the following:
main 120
slow 65
needles YYK8 (7th position)
air jets 240
mixture screw 1 3/4

I did a carb sync but no improvement. Should I go down to 60 pilots or do CR29 carbs just run rich at idle??

MRieck · « **Reply #1 on:** June 17, 2013, 04:38:07 AM »

Drop to a 60.

turboguzzi · « **Reply #2 on:** June 17, 2013, 05:00:01 AM »

open mixtures screws to 2.5 out or even more....

akabek · « **Reply #3 on:** June 17, 2013, 06:06:37 AM »

Both responses make sense. At what point do the mixture screws no longer work telling me I should drop down to a 60 pilot?

Doctor_D · « **Reply #4 on:** June 17, 2013, 11:12:35 AM »

If you're in the 7th position on the needle - you're using the wrong needle. Seven is the bottom, ie: richest, needle position. If that's where you have it and you're getting an acceptable 1/4 to 1/2 throttle cruise mixture, then go to a richer needle. If it's in the top clip, you obviously want to go leaner.

akabek · « **Reply #5 on:** June 17, 2013, 11:48:52 AM »

I am going to have to open a Keihin CR store soon with all jets and needles I am accumulating. I am using YY8 needles but I also have YY7 and YY5 needles.

This takes me back to my original question. If I turn my mixture screw out 2 turns or more should I be considering a leaner (60) jet? If I drop down to a richer needle (YY7) should I go with a leaner (60) pilot jet?

turboguzzi · « **Reply #6 on:** June 17, 2013, 12:03:17 PM »

i managed to make the bike idle good enough (for a race bike) just unscrewing by one more turn.

i managed to make 29CRs with "stock" needles work with both a 500c.c. and an 810c.c. motors, just changing cheap dellorto main jets. 500 liked 120-125, the 810 115 and the needle dropped one slot from mid position (leaner).

akabek · « **Reply #7 on:** June 17, 2013, 06:55:18 PM »

Tonight I turned back the mixture screw 2 1/2 turns and replaced the YY8 (7th position) needle with a YY7 (richer) in at the 5th position. My first trip around the block the bike hesitated at the low end. Than I took it out on a major road and the engine pulled right through the gear much better than before. I check my plugs at idle and they are still rich so I need to lean the mixture screw another 1/4 to 1/2 a turn. Tomorrow I need to take the bike on the highway and run it out a bit so I can see how it pulls through the gears but I think it pulled more than before. I am wondering if my plugs are fowled from running rich preventing the bike from idling? Can the plugs get cleaned up with highway riding? When I dial back the mixture screws tomorrow I may try a new set of plugs to see if the bike will idle.

Tintop · « **Reply #8 on:** June 17, 2013, 07:06:07 PM »

If the plugs are already blackened you need to install fresh plugs to get an accurate reading.

FunJimmy · « **Reply #9 on:** June 17, 2013, 08:12:02 PM »

Interested to see what you end up with.

turboguzzi · « **Reply #10 on:** June 18, 2013, 12:35:25 AM »

Quote from: akabek on June 17, 2013, 06:55:18 PM

Can the plugs get cleaned up with highway riding?

That is often called "italian tuning"

Hit the Milano - Bologna autostrada (or any other cop-free straight stretch) and keep it WOT for 1-2 minutes a few times. cleans plugs really nicely as well as dislodges any carbon deposits from valves and piston tops. do it at night and you will most likely see glowing pieces of carbon flying out the exhaust pipe in your rear view mirrors

very satisfying

if cops still stop you tell them you were just cleaning your plugs.

johno · « **Reply #11 on:** June 18, 2013, 02:05:36 AM »

Thats a fast bit of road TG,
last time I caught a taxi from airport into Milan their were 4 of us passengers crammed in the cab with luggage, no room for seat belts and the driver didnt go under 160 KPH........I was #$%*ting myself man as he chatted away saying he knows where the polizia are. Mate if the cops were driving fiats no problem hey

turboguzzi · « **Reply #12 on:** June 18, 2013, 05:07:31 AM »

well, since they introduced multiple cameras that calculate your average over a 10-15 km stretch, doing milano- bologna in an hour at 200kph/120mph average is a thing of the past, or at least during the day.... at night time cameras seems to be off or not work so well recognizing the number plate. dont ask me how i know

01Thomas · « **Reply #13 on:** June 18, 2013, 01:12:03 PM »

The average-speed cameras down here snap you from the front, and motorbikes down here don't have numberplates in front... The moral of the story? Perform your italian tuning on two wheels rather than four!

Quote from: turboguzzi on June 18, 2013, 05:07:31 AM

well, since they introduced multiple cameras that calculate your average over a 10-15 km stretch, doing milano- bologna in an hour at 200kph/120mph average is a thing of the past, or at least during the day.... at night time cameras seems to be off or not work so well recognizing the number plate. dont ask me how i know

akabek · « **Reply #14 on:** June 18, 2013, 06:08:24 PM »

First off putting the new plugs in allowed me to idle the bike closer to 1000-1500 RPM which was good. With new plugs I ran the bike at idle, pulled the plugs and they were bright white. I turned the mixture screws in 1/2 a turn at a time, pulled the plugs waiting for a tan color to appear. Something did not seem right as I turned them in a few turns and all of a sudden the plugs went from white to black. My guess now is that I may have fouled the plugs again as they are black so I may need a new set. Was my process wrong? Should I ride the bike around the corner and then idle it before pulling the plugs to check the color?

I left the mixture screws, set the idle around 1500 and decided to go on the highway. With the current jetting the first 1/8-1/4 throttle it hesitated slightly but than takes off. Maybe my mixture screws are too lean causing the low end hesitation. Once I am at a high RPM I noticed the clutch slipping so it is time to soak my new Barnett rings for clutch upgrade.

Tintop · « **Reply #15 on:** June 18, 2013, 06:50:50 PM »

Sounds like a lean flat spot to me.

akabek · « **Reply #16 on:** June 18, 2013, 07:42:23 PM »

Quote from: Tintop on June 18, 2013, 06:50:50 PM

Sounds like a lean flat spot to me.

That is definitely the case but what is the best way to check the plugs at idle? My plugs went from white to black and nothing in between. I thought I would see signs of the plug getting some color as I made the mixture screw more rich.

turboguzzi · « **Reply #17 on:** June 18, 2013, 08:04:07 PM »

just to make sure as often ignition problems mask themselves as carburation issues..... are you running 5 K ohm resistor caps and resistor plugs (R type)? if not, please do, could be the reason for at least part of your problems

Tintop · « **Reply #18 on:** June 18, 2013, 08:05:29 PM »

Good call TG.

akabek · « **Reply #19 on:** June 19, 2013, 03:49:40 AM »

The bike has the Dyna S ignition, Dyna 5 Ohm coils and DW200 wire set. The caps show NGK XD05FP 5K ohm and the plugs are NGK DR7ES

turboguzzi · « **Reply #20 on:** June 19, 2013, 04:45:37 AM »

ok, good but have to say that i am not a big fan of dyna-S.... seen too many failures.
got to be added that 29s on a 600 for street use are very much on the large side. people usually put 29 on breathed on 750-836, etc, or race only 500's like me. As you sure know, CR have rather primitive idle circuit so expecting to idle really nice on such a small motor (for 29's...) is maybe optimistic.
what did you use for carb to head rubbers?

Tintop · « **Reply #21 on:** June 19, 2013, 05:26:24 AM »

Have agree TG re 29's being oversized for a 600 street motor. Over size carbs will give good top end, but the bottom end will suck. Doesn't matter on a race motor, but good idle to mid range is what you want in a street motor, where the torque is made.

Looking at the parts diagram I don't see an accelerator pump, so it will be difficult to fix a lean flat spot on the transition. Maybe different slide cutouts? Possibly Doctor D has some suggestions.

akabek · « **Reply #22 on:** June 19, 2013, 05:54:56 AM »

I am using brand new factory rubber boots. After they stretched out a bit I was able to get them on easily and seat well on the carbs and intake.

When I was using the YY8 needles 7th position (richest) I did not have any lean spots. I changed my needles to the richer YY7 needles 5th position and there is a slight hesitation on take off. I was PMing someone on another forum and they have a similar build CB550 (with CR29s and same jetting but YY8 5th position) and they said they were able to get it to idle at 1100-1500. I am trying to get confirmation but I think he is running pods where I have stacks on mine so his jetting should be different. He suggested checking my carb sync which I will do again when I get it to idle below 2K. Something I noticed is after my quick highway ride it did not want to idle below 2K.

When I put the new plugs in it did allow me to get a lower RPM idle. Since I barely used the plugs can I clean them with brake cleaner? I did not pull the plugs after the highway ride to check color.

I definitely need to do the clutch with the slipping I was experiencing so I will order a new oil seal, and soak my plates.

bwaller · « **Reply #23 on:** June 19, 2013, 07:27:33 AM »

I can't offer more suggestions that you haven't already received, plus I don't know those carbs. I also can't say enough good about dyno tuning, especially when the operator has experience. You may chase your tail around a long while trying to dial this in. It is very frustrating work when you don't do this every day. Try your best, if you don't get it to where you're happy start searching for a dyno shop without the fancy sign out front. Perhaps an hour or two out of TO.

I don't mean to piss you off or all the guys that claim that 29's are the ticket for this street bike, but my experience has always been the opposite. I call it Bigcarbitis. You should get it reasonably good with your 29's but there will be issues you'll have to live with. I have one with stock 22mm PD carbs that is quicker than my stock 750. It's not cool with those carbs but it pulls cleanly to an honest 115mph.

Good luck akabek, stick with it, but also don't rule out dyno help if you get to that point. Just think when finished, you'll be able to re-coup some dough from all those extra jets you've aquired. Believe me I know!

Doctor_D · « **Reply #24 on:** June 19, 2013, 07:48:38 AM »

Quote from: Tintop on June 19, 2013, 05:26:24 AM

Have agree TG re 29's being oversized for a 600 street motor. Over size carbs will give good top end, but the bottom end will suck. Doesn't matter on a race motor, but good idle to mid range is what you want in a street motor, where the torque is made.

Looking at the parts diagram I don't see an accelerator pump, so it will be difficult to fix a lean flat spot on the transition. Maybe different slide cutouts? Possibly Doctor D has some suggestions.

With a smaller engine, larger carb combination - the richer slide will give a stronger signal at the needle jet orifice on tip-in and could be the answer to his bogging issues. If he has to go too rich at idle to get good throttle response, then a richer slide cutaway is likely in order.

But, the real answers should be found on a dyno. The tip-in AF is very obvious during testing.

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Author Topic: CB550 - CR29s is this the best it gets? Will CR26s be better street carbs? (Read 38037 times)