The Gunson Colortune tool

Spot on regarding your feedback no doubt!

I believe for the most part usage of the term "Carb Sync" as depicted in the service manuals as Carb Synchronization of the Vacuum levels that most use. Obviously, the Colortune is not in the OEM manuals... :laugh: that refers to Air/Fuel mixtures.

The Morgan unit pretty much states the same regardless if they call it Carbtune.

Now the other little tool that has made all the pieces fall into play is the AF/R gauge.... Now were talking....

Wow, you have to have a '76 smogged? That's harsh.

That Colortune tool is definitely worth a shot, it would seem. Anything that demystifies what happens in the combustion chamber is a Good Thing.

A question on the O2 sensor: if you're only getting a composite number of all 4 cylinders, is it really that useful as a diagnostic tool? I could see the rationale on a turbo rig though, where leaning out can be... dramatic,

Yes indeed for one faulty carb and you'll see the measured change indeed...

Case in point, recently, after the 1075 build run @ a 65-75 mph run normally see ~ 13.8 - 14.3 AF/R measurement. She burped/hiccuped and I immediately let off the throttle fearing the worst (extreme LEAN condition) especially after blowing the previous engine up (piston #4 disintegrated) ... :blush:

She was running rough and noticed the was measuring ~ 20 AF/R (LEAN), Pulled the ckoke a tad to add more fuel to get home..... Found 2 choke plunger caps had busted thus increased air into the carb bodies...

Freakin polymer threaded plunger caps on these carbs, really? :blink:

Order off to SUDCO.... Replaced caps and carb re-build kits for all O-rings, float valves and float seats etc... and all better.... Purr's like a kitten and my measurements while running inform me she's just where she needs to be regarding my jetting....

These will fluctuate slightly due to time of year (AZ heat or Winter), elevations, humidity, gas (ethanol) etc...

Idle: ~ 10.5 - 11.3
Low - Mid Range ~ 13.5 - 14.3
WOT ~ 14.3 - 14.7

BTW, AZ no longer requires Motorcycle emissions....

Life is good!

It is great to have that information in real time, no doubt.

What are your thoughts on the Sudco carb rebuild kits versus the K&L ones that Z1 stocks? I'm re-doing all 4 BS34s on my J2.

When I got the stuff to rebuilt my VM29's (no kit's for them)
from Z1 the peice came with a Sudco sticker so I'd think Z1
source's them from Sudco.

zukdave wrote: If the mech. sync is not done BEFORE any tuning you will not get the screw's any were near even
just as OMR said his ain't close to even turn's out.
OK flame on.

Can someone answer this question please? The local bike repair shop owner stated that I needed to resolve the carb issues regarding not getting a cylinder firing and the air fuel mix. Only then would it be worth it to vac sync the carbs. Do I Need to vac sync or perfect the air/fuel first?? Or, do I run air/fuel, then vac sync, then confirm A/F???

Previously my 3rd cylinder was not firing, so I replaced the A/F needles on Keihin CV34 carbs. The 3rd cylinder required around 3-4 turns out to get the exhaust warm.

I just got the Gunson Colortune in the mail, and I am excited to use it.

BTW, here is the most recent manual: gunson.co.uk/items/pdf/Products/G4074-English.pdf
Questions: (pages will not
1) page 12 - Do I have the Variable Choke Carb or Slide Type Carb? Both sound applicable.

2) page 15 - Multible throttle body injection - help...

FaultedGeologist wrote:

zukdave wrote: If the mech. sync is not done BEFORE any tuning you will not get the screw's any were near even
just as OMR said his ain't close to even turn's out.
OK flame on.

Can someone answer this question please? The local bike repair shop owner stated that I needed to resolve the carb issues regarding not getting a cylinder firing and the air fuel mix. Only then would it be worth it to vac sync the carbs. Do I Need to vac sync or perfect the air/fuel first?? Or, do I run air/fuel, then vac sync, then confirm A/F???

Previously my 3rd cylinder was not firing, so I replaced the A/F needles on Keihin CV34 carbs. The 3rd cylinder required around 3-4 turns out to get the exhaust warm.

I just got the Gunson Colortune in the mail, and I am excited to use it.

BTW, here is the most recent manual: gunson.co.uk/items/pdf/Products/G4074-English.pdf
Questions: (pages will not
1) page 12 - Do I have the Variable Choke Carb or Slide Type Carb? Both sound applicable.

2) page 15 - Multible throttle body injection - help...

I think you have to use an iterative approach. Hook up you carb sync manometer, balance the carbs and then tune each cylinder with the Gunson, then check the balance and adjust if necessary and then recheck with the Gunson.. Each adjustment (fuel vs balance) will affect the other.

To help with carb Sync I found a paper clip the size I needed to set the slide gap. I know some folks use wire and that works as well just figured I would pass along another item.

Old Rider wrote: To help with carb Sync I found a paper clip the size I needed to set the slide gap. I know some folks use wire and that works as well just figured I would pass along another item.

What is the slide gap?

FaultedGeologist wrote:

zukdave wrote: If the mech. sync is not done BEFORE any tuning you will not get the screw's any were near even
just as OMR said his ain't close to even turn's out.
OK flame on.

Can someone answer this question please? The local bike repair shop owner stated that I needed to resolve the carb issues regarding not getting a cylinder firing and the air fuel mix. Only then would it be worth it to vac sync the carbs. Do I Need to vac sync or perfect the air/fuel first?? Or, do I run air/fuel, then vac sync, then confirm A/F???

Previously my 3rd cylinder was not firing, so I replaced the A/F needles on Keihin CV34 carbs. The 3rd cylinder required around 3-4 turns out to get the exhaust warm.

I just got the Gunson Colortune in the mail, and I am excited to use it.

BTW, here is the most recent manual: gunson.co.uk/items/pdf/Products/G4074-English.pdf
Questions: (pages will not
1) page 12 - Do I have the Variable Choke Carb or Slide Type Carb? Both sound applicable.

2) page 15 - Multible throttle body injection - help...

I think you have Keihin CV 34 carbs in which case:
1 you don't have slide type carbs so can disregard the slide gap. Your choke lever operates a choke flap also called a butterfly which blocks air from the air box
2 you don't have fuel injection so no throttle bodies

JR wrote: I think you have Keihin CV 34 carbs (YES) in which case:
1 you don't have slide type carbs so can disregard the slide gap. Your choke lever operates a choke flap also called a butterfly which blocks air from the air box

This makes sense now... slide=up and down, flap=rotation on center line.

So am I able to do one tune, then the other; or back and forth in search of unity? Any further confirmation of order or strategy would be great. Digging back in to the carbs and red wine...

Like Stazi said in his post #646334 above. Good advice