Topic: CB550 - CR29s is this the best it gets? Will CR26s be better street carbs?

[Tintop]

Don't have any experience with CR needles, but do have lots with SU's.  So maybe this will help.  A 'richer' needle has a thinner taper, which allows for more fuel.  With the SU's the needles have different tapers that vary in the amount, and position on the needle (needle height is always the same).  As an example - if you wanted to richen the mid range, but keep idle & top end the same you would look for a needle profile (there are charts) that is the same dimensions (dia) top & bottom, but with a thinner transition in the mid area (than current needle).

Changing the clip position will effect the how & when the gap between the needle & seat changes (fuel flow from main).  Lowering (higher clip position) generally leans it, and raising it (lower clip position) richens.  If the YY8 & 105 was good then try measuring the dia every 1/8" (or less) to develop a needle profile, then do the same with the YY7.  Comparing the profiles will give you an idea of what's happening as the needle rises.

[turboguzzi]

try to follow the standard procedure of getting your main jet sorted for best max hp first, otherwise you'll be chasing your tail around.
hard to that on the street.
 just one dyno session where you can WOT immediately will tell you what you need as a main, and then you can play with needles as much as you want on the street for better partial throttle response. 

[turboguzzi]

here you go

http://www.factorypro.com/tech/tech_tuning_procedures/tuning_FCR_Burns,Pat.html

"Main fuel jet:

The proper main fuel jet will give best full throttle performance, but also affects mixture as far down as 1/8 throttle. I know you don't believe this second part, because I didn't believe it until I saw it happen while tuning an extensively instrumented test engine. Suspend your beliefs about the main fuel jet only affecting mixture when the slide is all the way up & the needle is all the way out of the needle jet and think for a minute. The main fuel and air jets feed the emulsion tube which feeds the needle jet and jet needle. When a more fuel rich emulsion is bled past the same restriction (needle jet area minus jet needle area), the engine gets more fuel. You must select the full throttle jetting first. If you go and find a needle that works with the wrong main jets, it won't work with the right ones, and you'll have to go through the needle selection process all over again when the main jets are correct. Trust me. "

[akabek]

I would definitely have to agree with the statement above.  When using YY8 needles I find the 105 mains to be the best combination with my engine, exhaust, ignition and carb setup.  I swapped the needles for YY7s and I found the 105s were too rich at >75% throttle.  This makes it a little difficult to lock in your mains depending on the needles you are using.

Right now I have the following jetting: 
Mains 105
Pilot 65
Needle YY8 - 6th position (second last from the bottom)

With this setup I am still lean on the low end.  The bike will accelerate smooth with a gradual twist of the throttle but I want to be able to snap the throttle an any time.  Above 6500RMP the bike responds to a WOT.  I ordered some 70 pilots so hopefully they show up on Friday.

I know a dyno would be ideal but is there an indicator on when to go with a richer needle?  My setup allows for a lot of air flow so my setup calls for more gas into the mix.  If I change the pilots to 70s and the mid section is lean I assume this may mean I should look at richer (YY7) needles?

[turboguzzi]

sorry,  save me from backtracking the data. what was the stock setup you received your carbs with?

IMHO, pilots have nothing to do with your problems.

indicator for richer needle? assuming that you got your main jets right, start lifting the stock needle groove by groove, and do WOT from say 5000. if you dont see an improvement, then go to richer.

and what ignition are you running, still the dyna? i simply dont thrust them, seen too many running problems with them that seem like carb issues. just to make sure you are not chasing an igniton problem, you could refit the points for a while and see if something improves.

[akabek]

I purchased the CR26 CB550 kit from Power Barn.  It came with the CR26 carbs, 77-78 intakes with vacuum ports, and new rubber boots.  I did not buy the pods as I am running the factory stacks with ITG socks.  This was the initial setup:

mj = 105
pj = 55
jn = YY8
MAJ = 220
SJ = 35
TV = 2.0

I am using the Pamco Ultimate ignition.  It comes with the ignition unit, 2.5 Ohm coils, NGK plugs and wires.  The bike starts with no effort at all and the top end acceleration is impressive. 

I can try the 7th position to see how it performs.  I did try the YY7 needles in the 4th position with the 105 mains  and the bike hesitated > 75% throttle like it was too rich  If I go with YY7 needles would I need to go to 102 or 100 mains?

[turboguzzi]

ok, last try...

you are doing it upside down, first find the right main jet, needles need to follow. preferably on a dyno where you can hit WOT right from the start.

I rest my case

[akabek]

ok, last try...

you are doing it upside down, first find the right main jet, needles need to follow. preferably on a dyno where you can hit WOT right from the start.

I rest my case

I am not sure what you mean??  I started with the mains and 105s work the best.  The reason why the pilot has changed and I tried the YY7s earlier was because I miss diagnosed the carbs which turned out to be a dirty petcock resulting in fuel starvation.  Now I am dialing in the needle and last will be the pilot....

[turboguzzi]

hope i am not upsetting you with me trying to help....

if you write: "If I go with YY7 needles would I need to go to 102 or 100 mains?" it sounds like you are going back to adjusting the main jets to the the needles and not the other way round, like it should be, that's all.

So then, if 105 runs best (with WOT at 8000-9000) then stick with it and touch only the needles. 

Big question is, how do you know 105 is best? Not an easy thing to check on the street. you should be testing in third- fourth - fifth gear on a straight and open road, stopping to put bigger jets or smaller. Run again, compare and even then it will be just seat of the pants + plug chops. that's where dynos help. maybe try to use an acceleration recording app on a GPS smart phone...

and just in the name of science, try reducing a bit the spark plug gap. PAMCO - SHMAMCO, who knows, your ignition might be a bit weak at the mid revs range. Ignitions with exposed components on a PCB don't exactly shout quality or inspire my confidence, but that's me

off to pack the car for a race in the weekend, so you have a break from me

[akabek]

turboguzzi I appreciate the feedback and no you are not upsetting me.  A couple of weeks back I put the YY7 needles in and when the throttle position was >75% there was hesitation like it was running rich.  In hindsight that could have been related to another issue.

In anycase the reason why 105 feels right is because of the way the bike responded when I compared it to 100 and 110s.  The 105 acceleration was clean with no hesitation.  Moving forward I am leaving the 105s in and adjusting the YY8  needle height.  If the YY8s are too lean I will move on to the YY7 and go through the various clip levels.  I understand the Dyno is the way to go but I want to do the best I can before I make the trip to a shop.  I live North of the city so I can jump on country roads within a few minutes to wind out the bike.  I only do a few runs in a day just in case word gets out....

[FunJimmy]

A couple of weeks back I put the YY7 needles in and when the throttle position was >75% there was hesitation like it was running rich.  In hindsight that could have been related to another issue.

This is the issue I'm having with YY8 needles, but I would have guessed lean in my situation.
Will try YY7 for comparable.

[akabek]

This is the issue I'm having with YY8 needles, but I would have guessed lean in my situation.
Will try YY7 for comparable.

This is what I am having trouble with.  To jet a carb you start with the mains.  Using YY8 needles I found 105s accelerated well on the high end.  When I changed to rich YY7 needles I experienced hesitation on the top end.  You may be right Jimmy that > 75% throttle is now lean.  If this is the case it makes it a little more difficult to find the correct main jets.

[FunJimmy]

This is what I am having trouble with.  To jet a carb you start with the mains.  Using YY8 needles I found 105s accelerated well on the high end.  When I changed to rich YY7 needles I experienced hesitation on the top end.  You may be right Jimmy that > 75% throttle is now lean.  If this is the case it makes it a little more difficult to find the correct main jets.

While disruptive, my hesitation (6000-7000) runs through and I finish with a solid rush to redline.
I need to resolve this flat spot if I'm going to spank the 750's in the hood. 

[FunJimmy]

Took the easy way out and dropped the bike off at a local speed shop.
They have a brake dyno, so tuning specific RPM ranges is pretty simple.
We've got similar engines and exhausts so I'll post what jet/needles etc I end up with.

[akabek]

Took the easy way out and dropped the bike off at a local speed shop.
They have a brake dyno, so tuning specific RPM ranges is pretty simple.
We've got similar engines and exhausts so I'll post what jet/needles etc I end up with.

I don't blame you.  At some point I will dyno my bike.  Your setup has a hotter cam than mine but I am running stacks with filter sock so I think my jetting will be more rich.  It will be interesting to see what they come back with.

[akabek]

Took the easy way out and dropped the bike off at a local speed shop.
They have a brake dyno, so tuning specific RPM ranges is pretty simple.
We've got similar engines and exhausts so I'll post what jet/needles etc I end up with.

Hey Jimmy, when do you expect to get the bike back?  I ordered more pilot jets so I am on hold for the moment. 

[FunJimmy]

Hey Jimmy, when do you expect to get the bike back?  I ordered more pilot jets so I am on hold for the moment.

I'm away on buisness for a few days and hope to have it back Thursday or Friday.

[akabek]

Hey Jimmy, any updates?

I had some success over the weekend.  I think part of my problem is I need to go on longer rides to access jet changes.  I pull the tank off again and cleaned up the petcock one more time but it was nothing really to clean out.  My jetting is currently sitting at:
Mains - 115, pilot - 60 and YYK 6th position.  My plugs must be fouled because I took the bike out and it did not want to accelerate but I kept riding.  The more I road the better it got.  Yesterday I went out again and the bike was hesitating for the first few minutes.  After filling up at the gas station with premuim I went with my wife for a 70KM ride.  On the low end she accelerates well with a gradual twist.  The mid section I have go WOT and it accelerates crisp but >75% throttle she seems to be lean.  Before I touch the mains I am going to put some fresh plugs in just in case they are fouled.  If I get top end hesitation I will go to 120s but the bike was running well.

[akabek]

Due to popular demand today I dropped my bike off at the shop for a Dyno session.  Unfortunately they were unable to complete my jetting due to some issues they found.  This may be why my plug chops where so out of whack recently.

The tuner noticed the bike would idle fine sometimes and other times it would cut out.  He checked the voltage at the coils and found at times there was a voltage drop which he said effects my idle.  He suggested I run a new line from the ignition with a relay to the coils so I get proper voltage.  The wiring harness is almost 40 years old so I don't doubt it may be losing voltage.  When I installed the coils I noticed the wires seemed like a small gauge so there is room for improvement.  I wonder if anyone makes a new wiring harness for the CB550.

The other issue he brought up that I was concerned with is my timing advance.  When accelerating to 3500RPM the engine falls short of the advance marks.  My mechanical advance expands to the stops so there is no pin blocking it.  I am wondering if my Pamco unit is faulty. 

He said my ITG filters were too restrictive so when he ran the bike he removed them.  He said I should contact Sudco to see if they can suggest filters to put on the stacks.  I asked him about pods and he said to stick to the stacks.  These issues give me an explanation on why my plug chops were all over the place.  I thought I was losing my mind.

This is where my jetting is now
105 mains, 50 pilots and YY5 needles (clip level unknown).  His assumption is when my electrical issues are sorted out my jetting will change to 102 mains, 45 or 40 pilots and YY5 needles.

Any feedback is greatly appreciated.

[Tintop]

The ITG filters can pass more air than your engine can use, ie they can support likely 2 to 3 times the HP you are making.  The one on my 550 is rated at up to 300hp.  If there is a 'restriction' there it is because the inner face of the filter is too close to the bell mouth, and is disrupting the air flow.  This is an issue with the 550 if the stacks are longer than the originals, as the frame rail restricts the allowable space to get sufficient interior clearance in the filter.  That said, this would only have an effect at sustained WOT, not at idle.

As for the Pamco and advance issue it is likely the springs are weak in the mechanical advance.  The Pamco only replaces the points, it still uses the original mechanical system for advance.  This is not like a Boyer (or similar) which replaces both the points and mechanical system with a magnetic pick-up, and electronic advance.  If the springs are weak a mechanical system will reach its full advance early.

[akabek]

The ITG filters can pass more air than your engine can use, ie they can support likely 2 to 3 times the HP you are making.  The one on my 550 is rated at up to 300hp.  If there is a 'restriction' there it is because the inner face of the filter is too close to the bell mouth, and is disrupting the air flow.  This is an issue with the 550 if the stacks are longer than the originals, as the frame rail restricts the allowable space to get sufficient interior clearance in the filter.  That said, this would only have an effect at sustained WOT, not at idle.

As for the Pamco and advance issue it is likely the springs are weak in the mechanical advance.  The Pamco only replaces the points, it still uses the original mechanical system for advance.  This is not like a Boyer (or similar) which replaces both the points and mechanical system with a magnetic pick-up, and electronic advance.  If the springs are weak a mechanical system will reach its full advance early.

I will reinstall the filters and make sure I extend them a far as possible from the bell mouth of the stack.  The filters may have moved and blocked the air intake jets while they were running the bike.  Next time I will only apply filter oil to the exterior of the filter.  I will clip off half a coil from the springs and reshape it.  Apparently the spring mod only helps at idle from what I read but it is worth a try.  I found a new wiring harness available from parts n more.  Before I look at replacing the wiring hardness I will check the coil hot wires with a meter to see if I can track down the voltage drop location.

[turboguzzi]

well, you cant say i didn't warn you very early on....

http://forums.sohc4.net/index.php?topic=123033.msg1396653#msg1396653

the fact that you were having strange response to your jetting changes was a clear show that something was amiss with ignition.

[akabek]

well, you cant say i didn't warn you very early on....

http://forums.sohc4.net/index.php?topic=123033.msg1396653#msg1396653

the fact that you were having strange response to your jetting changes was a clear show that something was amiss with ignition.

I am not an ignition expert but back then I was using the Dyna S ignition with 5 ohm coils which to my understanding works differently than the Pamco setup I use now.  I do not recall having issues with top end hesitation.  By the end of last summer I had the bike running reasonable well with CR29s but it was still rich and it did not like to idle below 2K RPM.

This past spring I installed the Pamco ultimate kit.  Shortly after I ran into jetting issues where the bike would not accelerate beyond 70KPH.  This was due to fuel starvation which was corrected by cleaning the fuel petcock filter.  Than I was experiencing on and off top end hesitation.  After syncing the carbs and checking the timing I realized the advance was not working.  I pulled it apart to see if their was a pin (common on CB550s) blocking the advance mechanism and there was not.  I can move the mechanism right to the end stops.  Tonight I am going to do the advance mechanism spring mod to tighten up the action.  If that does not work I will buy a used advance mechanism to try.  Last night I went ahead and ordered a new wiring harness which will hopefully correct my low voltage at the coils.  After 40 years that harness is do for a refresh. 

[Tintop]

Make sure the filter oil your using is for the foam type.  Do not use K & N oil (for paper filters) it will break down the adhesives used to bond the filter together.  Best way to oil a foam filter is spray the outside and gently work it into the foam with your fingers.  Wear disposable gloves, and then lightly wipe any excess off with a paper towel.   Also wear gloves when installing freshly oil filters.

The springs control the rate at which the 'bob' weights move out.  The weight of the 'bobs' determines when the advance starts versus a given spring rate.  The combination determines the advance curve.

+1 on carbs being blamed when it is an ignition issue.

[bwaller]

I replied to this but it vanished.  OR more like it I replied some other damn place!

I use Ramair dual sock foam filters but regardless I use a plastic clamp to hold them against the back of the bellmouth flange. This keeps them in place and gives 45mm from the BM opening to back of the filter. It's not ideal but I prefer to use a filter. They in turn contact the frame downtubes so yeah space is limited. I just mist the outside of the filters with oil & let them sit to soak a little and finally squeeze them in a paper towel to remove excess. Don't overdo it, certainly nothing inside.

If you're stuck trim the advance springs. It's tough though ending up with both springs exactly the same tension. (and they should be) Perhaps watch Ebay for a new one.

Do install a relay for the coils. This way you can run a heavier 12V wire to power the relay and the kill switch then only triggers the relay so full power available. Even with a new harness your switches won't be. There is a schematic on this site somewhere.

You need to cover all the bases.