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#1 Luke1981

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Posted 10 January 2019 - 12:19 PM

Q: Trying to tune my tripe Su`s on a 202, i`ve got myself a little carb synchrometer tool to measure the vaccum which works well but do i have to set the SU`s to a certain reading or is just getting the three to be reading the same good enough? example, can i set them all to read 7 on the synchrometer or should they be at 10? (they are just random numbers to try explain what i mean)



#2 LC-GTR-1969

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Posted 10 January 2019 - 02:19 PM

The numbers are not really important, what is important is that you have all three synchronised at idle as well as at about 3000rpm... I would aim for idle about 1000rpm or 1200rpm if its got a pretty big cam. Make sure you have a pressure regulator and set it about 3psi. 



#3 Luke1981

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Posted 10 January 2019 - 04:39 PM

Ok cool, yeah I've got a regulator but it's only set on 1.5 psi, I'll try what you said and see how it how's. Thanks for the reply

#4 LC-GTR-1969

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Posted 11 January 2019 - 08:10 AM

try to set running pressure, ie set the regulator when the car is running... this mainly applies if you are running an electric pump. 



#5 hanra

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Posted 11 January 2019 - 08:12 AM

Not sure of your linkage set up, but on my Twin SU's I have to ensure the throttle linkages are all slack and then synchronize the carbs. 



#6 S pack

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Posted 11 January 2019 - 10:33 AM

Not sure of your linkage set up, but on my Twin SU's I have to ensure the throttle linkages are all slack and then synchronize the carbs. 

Ensuring the throttle shaft of each carb is independent of each other is essential when balancing a multiple carb setup.



#7 LC-GTR-1969

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Posted 11 January 2019 - 12:43 PM

yes, each carb needs the linkages disconnected in order to synchronise them. How you do this depends on the linkage system, some you can just loosen the linkages, but hex bar you will need to remove the linkages



#8 Luke1981

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Posted 11 January 2019 - 01:05 PM

Yeah i loosen each linkage and do it that way, the only problem i have is what reading they should be at and the timing

#9 S pack

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Posted 11 January 2019 - 01:22 PM

Yeah i loosen each linkage and do it that way, the only problem i have is what reading they should be at and the timing

As has already been stated, it doesn't matter what number on the syncrometer you set them too, as long as the balancer tool allows sufficient air flow to not affect the engine idle.

Coincidentally I set mine to the 7 on my scyncrometer, I use one of these https://vwparts.airc...SK-p/ste-sk.htm

 

I found at the 7 position the movement of the needle on the syncrometer seems to be a bit more stable, if that makes sense.



#10 Luke1981

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Posted 11 January 2019 - 04:18 PM

As has already been stated, it doesn't matter what number on the syncrometer you set them too, as long as the balancer tool allows sufficient air flow to not affect the engine idle.
Coincidentally I set mine to the 7 on my scyncrometer, I use one of these https://vwparts.airc...SK-p/ste-sk.htm

I found at the 7 position the movement of the needle on the syncrometer seems to be a bit more stable, if that makes sense.



#11 Luke1981

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Posted 11 January 2019 - 04:23 PM

As has already been stated, it doesn't matter what number on the syncrometer you set them too, as long as the balancer tool allows sufficient air flow to not affect the engine idle.
Coincidentally I set mine to the 7 on my scyncrometer, I use one of these https://vwparts.airc...SK-p/ste-sk.htm
 
I found at the 7 position the movement of the needle on the syncrometer seems to be a bit more stable, if that makes sense.


Thats the same tool I've got and i set them at 7 as well as that's where the rpm sets at about 1000

#12 Luke1981

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Posted 11 January 2019 - 04:25 PM

try to set running pressure, ie set the regulator when the car is running... this mainly applies if you are running an electric pump. 


Mines a mechanical pump and I don't have a gauge, just a little round regulator with markings on it and you just turn the knob on top to whatever psi. Not sure how accurate it is but does the job

#13 LC-GTR-1969

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Posted 14 January 2019 - 10:57 AM

Mines a mechanical pump and I don't have a gauge, just a little round regulator with markings on it and you just turn the knob on top to whatever psi. Not sure how accurate it is but does the job

 

I would invest in a guage, I think you can get them for about $70. The numbers on those regulators are not always co-aligned to pressures when running. 

 

 

Thats the same tool I've got and i set them at 7 as well as that's where the rpm sets at about 1000

 

The number is honestly irrelevant. Ive had webers idling with 4Hg/h and my 2 inch SUs are about 10Hg/h. Choke size, carb size, manifold type, idle speed requirements, all dictate where it will end up. 

 

Asking what number to look for on a synchrometer is like asking what size steak will satisfy a man, too many variables at play- give it what it wants (the car, not the man/steak).

 

You sync up the carbs to within .5hg/h at the idle speed you can live with. 1000rpm is pretty typical with SUs on holden 6s, you can run them a bit lower but then there is not mych leeway in traffic with overfueling etc.. 



#14 LC-GTR-1969

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Posted 14 January 2019 - 11:00 AM

Yeah i loosen each linkage and do it that way, the only problem i have is what reading they should be at and the timing

 

I presume you mean ignition timing- is your dizzy stock?

 

What cam shaft you running? What head (small chamber / open chamber)? What compression ratio?

 

In a mild setup with a small cam you will probably get away with a stock advance curve in a blue HEI dizzy- but if you have a bigish cam, you would probablty want less advance built into the dizzy- so you may want about 16 at idle, 32 total for a 16 degree advance curve in the dizzy, all in by about 3500rpm... If you are running loweish comp, and a biggish cam, you could up the initial timing to about 20 and run a 12 degree advance curve all in by 3000rpm. 



#15 Luke1981

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Posted 14 January 2019 - 08:51 PM

Ok cool. Thank you all for your help




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