kenward1000

carb balance with Twinmax

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new 71 240z owner.  just balanced pair of SU dome carbs with Unisyn, using instructions from ZTherapy.  car now runs OK, but thinking it could be better.  for my 70's Ducati twins, use my Twinmax electronic carb balancer.  two hoses go to two fittings, one on each intake manifold.  no moving a single air flow meter back and forth, can easily see relative vacuum suction, easy to tweak idle speed for pulling same vacuum at idle/5000rpm, tweaking so each carb starts increasing vacuum at same time, when throttle is opened.  wondering if anyone else has tried this or mercury sticks.

could do an experiment by drilling/tapping carb insulator blocks (could also use the intake manifold itself) for the 5mm x 0.8 threads.  the fittings are capped after adjustment is complete.  opinions are welcome.

 

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Funny - my buddy has a twinmax that I borrow for the annual tuning on my carbed Duc. Never thought to use it on the SU’s though. Would certainly be an improvement over the unisyn in accuracy (super sensitive) but I have had a unisyn in my toolbox for almost 30 years (bought it for my 64 Corvair convertible RIP) and always associated the unisyn with cars and the Twinmax with bikes...

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I guess the biggest thing is figuring exactly where to tap the carbs

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Cool. Never heard of such a device. I like it.

I think drilling and tapping vacuum holes to test vacuum would work great. My only concern is that I'm not sure the phenolic spacer is thick enough to do that without cracking it. You might have to go right into the carb body or intake manifold right behind the carbs.

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The drill size for tapping a 5mm hole is only 4.3mm (17/100") out of a thickness of 14.7mm so will have 5.2mm of material remaining on either side of the hole.  thinking just center the hole between any two stud holes, center the hole across the thickness.  An open Q is how well the material will put up with tapping, ending up with good threads.  Since the vacuum stub will remain in the insulator, could just install it with some loctite. 

Going to experiment with the insulators because they're easier to replace if screwed up, they're straightforward to fixture in the drill press vise, don't want to remove the intake manifold.

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I think the phenolic will take to drilling and tapping quite well. I'm with you though on how robust the threads are. I think the threads will be of good form and quality when initially formed, but there just won't be much meat there.

Don't over tighten the adapter fitting, and you would probably be OK. I agree that something to seal the threads would be a good idea. You need it to seal, but you don't want to crank it in too tight to achieve that seal. I think silicone sealant would be a good choice too. Doesn't have to be a thread locker. Just something to seal the threads.

Good luck with that project. I think it would be cool to try that balancer tool on the Z carbs!

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I love the simplicity of my Unisyn and it seems to me if you check and double check, it is pretty darned accurate. Just my opinion. 

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Permatex #2 would be a good choice to seal the fittings without having to overtighten them.

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Connected the vacuum spigots to the insulators today.  Measured and marked the center of a side, pilot drill 0.1090" then tap drill 0.1695"  Tapped with M5 x 0.8, threaded the brass spigots in with a thin layer of Permatex #2.  Keen to try this out. 

FWIW I can't diss the UniSyn; that's what Z Therapy recommends!  This is just an experiment based on my years of balancing twin carb motorcycle engines like BSA, Triumph, Norton, Ducati.

 

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I like the Uni-Syn for high RPM balancing check when the air flow is high.... but the STE Synchrometer is very accurate and repeatable.

 

It works nicely for SU's at ~ 7 to 11 kg/h (depending on calibration) for idle.

You can pull the rubber lip out a bit to expose the holes in the throat then dial up the rpms so that the front carb is at 35 kg/h then move to the back carb to adjust the balancing screw to get the same 35 kg/h

 

Note: The BK Black version is 1-35 kg/h but the SK Silver  version is 1-30 kg/h. The black one is better for SU tuning.

 

 

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1 hour ago, kenward1000 said:

FWIW I can't diss the UniSyn; that's what Z Therapy recommends! 

As much as I love ZTherapy's work, they also reccomend that you throw your flat top carbs in the garbage, and a few of the members here have proven that to be completely wrong.

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Looks good. Drilling and tapping that phenolic was a treat, wasn't it. I would describe it as "crisp" and easy to machine.

Looking forward to hearing how it works when you get the meter on it.

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