Topic: Help tuning CycleX dual carbs

[fdbrat]

So I got this set up for $300 ebay. No extra jets at all.

It fires up easily, at idles nice. I can snap the throttle. Idle returns nicely.

When I ride it, it runs ruff. Choking and such.

76 Cb750F
Dyna S Ignition
Straight pipes

Cycle X dual carbs vm34's

Main jet #240
Slow jet #35
Needle tube jet 159#0-2
Needle #6dh8
Stacks

Needle set at leanest mark
AFR screw set at 1/2 turn out

Slides adjusted at WOT
Idle bench synced running at 1,000 rpm

Who has had luck tuning these carbs?

I've gone through them cleaned them very well. Not sure what to do next. Any help would be great.

[calj737]

I believe that the kit is from Murray of Murray's Carbs. Pop him an email murray@murryscarbs.com

"Murray's Carb's Complete pre jetted and tested Mikuni kits including custom intake Manifolds for CX500 GL500 CX650 GL650 and 650 engines installed in the 500 frame CB750 DOHC no frame mod dual 34mm Mikuni kits GL1000 GL1100 GL1200 Dual 38mm Mikuni kits Or our new Quad 34mm Mikuni High Performance Kit bolt them on and go! The New site is almost ready in the mean time if you need something e-mail Murray@murrayscarbs.com"

[Cqyqte]

What do the four plugs look like after a ride?  My bet is the center two cylinders are off on mixture.  The carbs are touchy to get balanced between inner and outer cylinders.  I made myself an adaptor which provided me a centered line (a wire held in the exact center of the tube), placing the adaptor on the carb horn allowed me to point the carbs directly at the center of the "Y" of the intake manifold by lining up the line on the adaptor with the needle in the carb and the crease of the "Y" in the intake.

Once I achieved the angle of the carb all four cylinders reflected similar mixture levels, it was just a matter of determining the jetting.  I ran with 240 mains, 3rd clip needle, 159 0-2 needle jet, 22.5 pilot jet, 3 turns out PMS and the advance 1st curve above stock on a PowerArc ignition.  But I ran with K&N tapered filters.

[Cqyqte]

Forgot to mention my motor was built with Streetfighter 849cc pistons with a custom 4-1 Mac pipe fitted with my design of a Supertrap baffle.

[fdbrat]

I wish I had the Murray Manifolds Calj737.
I am cheating the carbs turned out. As I haven't modified the frame yet.
I did pull the plugs today. I figured they must be all fouled up after trying many combinations to get it right.

I cleaned the plugs, poped them back in. Re set the float. And it is now ride able. But still coughing a bit when I gun it.

I do think I'm still to rich on the needle.

Hey Cqyqte... Do you think I should try a leaner needle or go a step down on the mains?

Thinking I'll order a tad richer slow jet.

Thoughts???


And Cqyqte. Your bike looks amazing. Well done man.

[fdbrat]

http://youtu.be/52uQpZYFsPg

[Cqyqte]

Before changing anything I would take her for a ride and do some plug chops at several throttle positions.  Mainly WOT as it will tell you if your 240's are correct or not, I'm thinking they are good.  I suspect the pilots are big and causing the plug fouling, but don't swap them out until you do some chops.  How easy does it start when cold, do you need to choke it or does it start first try?  If it doesn't need choke then you can bet the pilots are way too big.

Carb tuning is a process of patience, and find that creating a chart of the parameters helps immensely.  As you change a setting and recording how the bike runs with that setting will eventually start to paint a very clear picture of what's need to make the settings perfect.  I create an EXCEL spreadsheet and I have a column for each adjustable setting or part. 

[gerhed]

On my Cycle-X carbs it was "choking" every time I really got on the throttle.
Talked to Cycle-X and they sent me new needles with a different taper.
The situation improved.

[fdbrat]

I'm tying not to bother Ken at cycleX. Their website specifically says don't come to us with a problem with a product, if you didn't buy it from us.

They are cycleX carbs and manifolds. But I got them from a guy who gave up.

Cqyqte I've ran at WOT. Low end and mid to high is better if I snap it fast. But nice and gradual it still bogs out. Catches and then bogs.

I think I'll order jets one step leaner and richer for the piolts and mains. I'll try a combination to see what improves.

I'll write down the results.

Well I'll report back some time after the first, when I get paid.

[Cqyqte]

Without seeing the colour of the plug that is created at the throttle position you are working blind.  Clean your plugs, install them and go run the bike at that throttle position which causes the bike to fall flat for at least 2 minutes (long flat straight road) is the only way you will get an indication of what's wrong.  If you don't do it this way you might as well stand in front of a mirror and yank your hair out handful at a time. 

One other thing you mentioned that you bench sync'd the carbs, have you sync'd them since using a set of gauges or manometer?  If not, then that could be some of your problem as well.  Read any carb tuning paper or article and you will be told there is no way to shortcut the process.  I have been in the business for more than 35 years and carbs are still the toughest part.  How's the compression level on the four cylinders are the numbers per cylinder real close or are they all over the map, because that will throw a wrench into carbs that have been set up by a bench sync only.

[fdbrat]

I did clean the plugs. And I can't ride well at full throttle. It dosent like it.

I'll get new plugs on the first and do a chop.

[Cqyqte]

You need to identify the symptoms of what it is doing at WOT, either a rich set of symptoms or lean.  Can you describe what it does, does it backfire, does it bog down, does it improve if you choke it???

[Retro Rocket]

does it improve if you choke it???

I know a few people i would like to try that out on...

[fdbrat]

My bad.

It dosent require the choke to start.
Fires up pretty easy.
If accelerating very fast and let off the throttle it will pop pop a bit.

Not to bad tho. Pop pop could be due to lean, unburnt fuel, and or the straight pipes.

I can't really hit WOT with out it choking out. If I snap it it likes it more. But if I apply throttle slowly it chokes.

It dosent really have a choke, it has a starting curcuit. It adds more fuel and air.
When I activate it, the engine speeds up to about
I'm unsure as to what this means as to the fact it has the strange starter curcuit.

[Cqyqte]

Based on the fact that it starts with choke I would say your mixture screw is set too rich or pilot jet is too big.  The fact that you can snap the throttle and it will take it also sounds a s if you are too rich.

[fdbrat]

I just checked my bank account... I was really hoping I was rich. Now I'll just have to wait till the first. Hahaha.

[Cqyqte]

Yes, this is an expensive sport/hobby and you must never expect that you will get what you spent when you sell them.