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Senior Charter Member
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Discussion Starter · #1 ·
I'm working out the bugs on my intake. I'm currently just trying to get it to idle decently.
Once the engine gets hot, the throttle sticks at around 2500rpm. I tried loosening the set screws on the crank between the throttle bodies which did help but now I'm sure that the openings of the butterflies are not the same throughout anymore. I can kind of gap them with a feeler gauge but that's not very accurate either.

How are people calibrating the flow on each throttle body on the intake? Is there a flow meter available? Where can I get one?
 

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Don't have all of the answers for this. I used to have a tool called a unisyn that would measure flow through each stack. It wasn't all that easy to use because it reduced flow to the stack it was on. Then I saw the system that the MC guys were using for 4 carbs. I got one and plumbed into each webber stack. Works well, but some cylenders don't flow as well as others. With 8 stacks two of these should work well. Go to a MC mechanic to find out where to buy them. They do require a vacuum port in the stack airstream. Most have this. This assumes you can't monitor this electronically in your system using o-2 sensors etc. Scottt
 

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FFCobra Fanatic
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2,596 Posts
Scotts right, you can use a Unisyn. I used mine on Al's car to find the problem. Once it was balanced, all he needed to do was fine tune the "numbers".

I used mine for years on side draft carbs. Works fine in conjunction with a vacuum gauge for those older models.
 

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FFCobra Craftsman
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2,854 Posts
The motor cycle one I had used Mercury as the indicator. Basically attach to each carb and sync them by having all vacuum levels equal out. The Instructions were very explicit about not bliping the throttle while you have it plugged in.. I had a brain fart once and I had a rough idling bike that was about to kill off so I grabbed a hand full of throttle to keep her alive.. the results took about a month off my life due to my ignorance about cleaning up spilt mercury in my youth!

Not sure if you can still purchase this model.. hope there is a safer unit out there now?
 

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FFCobra Captain
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3,440 Posts
If you've got a good ear you can balance multiple carbs/throttle bodies simply by putting a length of hose into the mouth of the carb (long enough that you don't have to stick your ear right next to a running engine) and comparing the whistle to the carb you're using as a reference.

If that method doesn't work for you, a roll your own differential manometer like this works much better than Carbalancer and similar products.

HTH
 

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FFCobra Fanatic
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1,038 Posts
Originally posted by UKCoupe:
If you've got a good ear you can balance multiple carbs/throttle bodies simply by putting a length of hose into the mouth of the carb (long enough that you don't have to stick your ear right next to a running engine) and comparing the whistle to the carb you're using as a reference.
I have used the hose method more years than I want to admit to. I started tuning MGs and Triumphs with a Unisyn. Worked very well, but when I saw a high-end mechanic using a hose to sync, I got curious. I tuned the next car with a hose and then checked with the Unisyn. The carbs were perfect! It is also much faster.
 

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Charter Member
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The UniSyn looks like this.

It is the easiest way to do it and works well if there is no crossover between the carbs or stacks. Every time you adjust a stack it will change the idle speed and affect the other settings. Just keep going from stack to stack until they are all the same. You will get a feel for it. That is the idle adjustment which you do with the idle stops if it has one on each stack. (I have only done carbs)

The next step is to set the throttle linkage so it is just off idle and adjust the linkage so the readings are all the same. This allows each stack to come off idle in Sync. If it has a wide open stop, you can eyeball it. The Sync is not critical wide open.

That is the easiest way. The best way is to build 8 J-Tube manometers with a little brass pressure sensor that slips down into each stack. I use alcohol and water with food dye instead of mercury and it works fine. It is a lot of work, but I will walk you through it if you are interested. It is really only necessary in systems that have a crossover between throats. The UniSyn does not work well it that case because it restricts the flow of the throat being set.

Jim
 

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Senior Charter Member
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512 Posts
Discussion Starter · #8 ·
Thanks for the feedback!
UK, I'll try out the $4.00 gizmo tonite... oh crap, it's my wife's birthday today. Guess I'll have to do it tomorrow.
 

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FFCobra Craftsman
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607 Posts
www.racetep.com has a Synchrometer Tool that is designed to synchronize Weber carbs. It fits Wayne's stacks perfectly, and does a good job. I think price is $50-$60 bucks.

David
 

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Senior Member
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5,559 Posts
David,

How is your stack setup running? Last I knew you weren't thrilled with the tuning issues related to them...

Brian
 
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