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ollie

SU Carb Sync Kit

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Hi everyone,

I ran across this carb sync kit that is made by a Rolls guy and will work for our SU's.  I should have it by the weekend but if you're like me and are looking for an option other than the uni-sync you might want to check it out:  https://www.britishtoolworks.com/product-page/su-h6-carburetor-synchronizing-kit  I think this will be more accurate (for myself anyway) since you can measure both carbs at the same time, sort of similar to the original SU carb tuning with the metal rods.  

Cheers

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It will be interesting to see the results comparing piston lift to air flow.  Both are different parameters that are related.

Piston lift due to suction due to air flow can be different in each carb for the same airflow due to piston binding or lack of sealing or needle setting.

If you can get your hands on a wide band O2 sensor, then run the car just on the front carb, then on the back carb and compare a/f for each. It should be ~29 for each.

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So tell me more about how one would use a wide band O2 sensor with a car like ours don't those need to be threaded into the exhaust like a typical modern O2 sensor?   I clearly need to do more reading...anyway my bar is set pretty low as my carbs have not been well tuned.  I've read yours, and many others, summaries for tuning SU's and finally spent the time to understand these better so the car is running so much better.  When I saw this kit that allows for readings of both carbs it seemed to make sense to me.

 

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There are O2 sensor fitted pipes that are inserted into the exhaust to sample the gas. 

 

To balance the fuel and air, there is a trick: lift the back piston all the way up to add 100% more air and no fuel to the air/fuel mix gulped by the front carb. The car should be able to chug along on just the first 3 cylinders.  A normal a/f at idle is ~14.7 but by adding more air, it will jump to ~29 while chugging.  Repeat by  lifting the front piston and running on the back 3 cylinders.  Adjust the jet heights to get the a/f ~ 29 on each carb and exactly the same. Double check and re-balance the air flow then repeat the a/f adjustments. It is iterative.  You can either do this at 700rpm (idle) or at ~2200rpm (off idle).  I prefer the off-idle optimization as this is where balance is critical and driving is more fun than idling 🙂

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hahaha definitely.  If you have a particular brand of wideband O2 sensor that would be great to know, all the ones I have found so far are the threaded type but I sure could look harder.  Cheers

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1 minute ago, 240260280 said:

Gravel rules 🙂

 

ollie, I'm keen to see if matched height equals balanced air flow. Please keep us posted!

For sure, thanks for posting that wand...it looks very similar to the rolling dyno smog test they used to do here in town.  I'm going to try that in pipe band one and will order an O2 wideband kit tonight.  There's a set of triple mikuni 44's i can't get out of my head so as soon as I get the SU's dialed in I will go make the car run like crap all summer while I sort those out 🙂

1 minute ago, 240260280 said:

 

 

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The kit from British Tool Works arrived today so I used that as motivation to leave the office early.  The tools arrived very well packaged and are of a high quality as far as I can tell  anyway.  I warmed up the car and while I the salt on the roads will keep me from a road test I can say that I am super impressed with the results.  Here are 2 pics, one before I fired the car up and one after balancing.  The cool part is you can easily see what the carbs are doing not only at idle but under throttle too.  Needless to say that when I first fired the car the readings were way out.  One thing I figured out is my linkage was a bit wonky so one carb was always running faster so once that was sorted all went well.  

Anyway I am super pleased with this tool and if you need all the help you can get like I do with carbs, I whole recommend this kit.  Kelly is the fellow who makes it at British Tool Works.  Let me know if you have any questions.

Please ignore my origami of a heat shield, it is temporary until I can fab one up as that Spirit Garage header is way more prominent than the Stahl one was which is now a tripping hazard in my garage which I really should do something about.

Cheers everyone.

20190208_151655.jpg

20190208_160430.jpg

Edited by ollie

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This is super cool. Can you still close the hood? I would like to drive it like this and mount a camera inside. Then I could see which needle stations are being used under certain load conditions! 

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I would not be able to close the hood and the shaft needs to be straight in order to function correctly. You could perhaps cushion the hood for a quick and safe run on empty road to read the gauge from the car.  I could clearly see the readings from the drivers seat but I wouldn't recommend it.  

I do have a unisync and could definitely try reading flow on that at 3000 rpms later today.  I will report back. 

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Cool tool. It's not a direct measurement of airflow (like the flowmeters are), but it's better than nothing.

I assume set them to zero (or at least the same between the two) to match them before starting the engine? There's no guarantee that the distance from the top of the carb dome to the piston inside is the same between carbs.

I would also be a little tentative about driving around with those on the car. You won't have any suction piston damping and will lean burst when you press the gas pedal. One backfire (front fire?) and your dial indicators will likely be slammed to the limit and probably damaged.

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Ollie, where are your choke cables coming out of your firewall?  You have the cables coming over the top of the engine, just wondering if they are going out of the normal driver side firewall opening, or you moved them over to the passenger side.

 

Also, like the cable clamps on the valve cover!

Edited by duffman

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Set to zero with the car off then adjust with the collar if necessary...the brass fitting screws into the same threads as the damper so it is sealed.  I should load up a video but this shows the tool in action, albeit on a rolls:  

 

 

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27 minutes ago, duffman said:

Ollie, where are your choke cables coming out of your firewall?  You have the cables coming over the top of the engine, just wondering if they are going out of the normal driver side firewall opening, or you moved them over to the passenger side.

 

Also, like the cable clamps on the valve cover!

Hmmm...mine is a 73 so perhaps my chokes route differently?  They do route through the firewall via the factory provision as far as I know anyway.  I will take a pic later on if that would help. 

If anyone has a good heat shield solution to clear that header I'm all ears!  

 

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