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itb balancing method question

General engine tech -- Drag Racing to Circle Track

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Belgian1979
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itb balancing method question

Post by Belgian1979 » Fri Feb 28, 2020 3:50 pm

I finally constructed a simple fluid manometer that I connect to each bore to balance my itb's. Prior I used this:
https://www.ebay.co.uk/itm/Carburetor-S ... 2282858327
I could never get the thing to run close to even AFR's while using that synchrometer and suspected that it was not accurate enough.

As TB's are paired units (DCOE type), I cannot individually set them when they are paired. So what I did was set the best flowing bore on each pair equal to the best flowing bore on the master. I then added bypass air to the others to get them all close (close as in within an inch or so). This worked quite well.
However, when running the engine at higher rpm's the differences increases with a difference of about 7-8 inches between the best and worst flowing one. When returning back to idle they seem to want to run out of sync again. Still alot better than when only using the sync meter though.

So what is the trick here? Set them at higher rpm and let them be what they are at idle? Keep it as is?

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Re: itb balancing method question

Post by MadBill » Sat Feb 29, 2020 12:36 am

I've used a number of synchronizing devices over the years, but always come back to the Uni-Syn.(Google Uni-Syn.) Its adjustable venturi allows very accurate comparisons from bore to bore at a wide range of air flows and the 'pea' is sensitive to pressure pulses without obscuring the average readings.

o Do you disconnect the linkage to snyc the TBs at idle?
o What happens if you then open one by hand and then ease it closed vs. letting it snap shut; does it return to the same flow each time? If so, it's probably the linkage that's hanging up when the idle flow doesn't return to the same base number.
o How about if you repeatedly open and close the throttles; are the idle flows different every time or do they each settle to a single value?
o Do you adjust the linkage separately, i.e. hold the RPM slightly off idle with the linkage and adjust to achieve synchronicity?
o If you do, does it stay in snych as you further raise the speed? If not, the linearity of the linkage varies among its elements.
o It always amazes me how sensitive an engine is to IR synching. The most minute bore-to-bore flow variation is audible and sensible upon tip-in. I'm not sure how it compares to your device, but for really good tip in sound and feel, the Uni-Syn pea needs to be +/- 2-3 mm of the same height among all the bores.
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Re: itb balancing method question

Post by Belgian1979 » Sat Feb 29, 2020 3:38 am

Hi Bill,
Thanks for the reply.

When typing in uni-sync I seem to get 2 devices: one is a set of vacuum gages and the other is a type of device that you put on your stack with a glass pipe. I assume you mean the last one. I don't have that.
Guess that it works somewhat similar to the fluid manometer.

As for your below questions:
1. Yes, since this is a crossram, it has the following a center pivot with 2 metal bars and connections to a lever that is connected to the main bodies on either bank. It's this lever that has (i) a bolt that you can loosen to adjust the shafts of the main bodies and (ii) an idle speed set screw and (iii) and end stop that is adjustable. See the picture below. The connection between the body pairs is formed by a slotted aluminium piece that has 2 set screw in each of them (alu-black-alu piece in the pictures)
Image
Image

2. this is difficult to perform, if I shut one pair, let's say a non-master, the engine will seriously drop in rpm. So it affects all others as well. On the carb sync tool that I have it goes back to the same. When trying to turn the shafts to equilize them to the master, and thightening the nuts on the centerlinkage between the bodies they seem to want to go back to the original setting though. I really need to pull it down a lot which is a bit of a juggling act.
3. Didn't try that, but will do that asap.
4. I adjust by noting the reading on the master (where the tps is connected to) and the one with the highest flow). I go to the master to the other side and disconnect the lever from the shaft there and turn the shaft to obtain the same reading on the master's best flowing bore. I then disconnect the center connections by loosening the 2 set screws on the master side and turning the shaft of the slave on each bank to set the flow in the highest flowing bore to the same value as that of the main master.
5. I never really checked for having the same reading at higher rpm, assuming that once synchronized at idle they would remain the same. The bodies should be at the same height and are operated from the same central point (the start in the picture). I would assume they are are identical both in length and in angle.
6. I agree it's incredibly sensitive to everything.

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Re: itb balancing method question

Post by digger » Sat Feb 29, 2020 4:39 am

how are the DCOE pairs coupled?

the first thing to do is make sure the shafts on adjacent pairs are coaxial with an alignment fixture this minimises the change in relative position with throttle angle

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Re: itb balancing method question

Post by Caprimaniac » Sat Feb 29, 2020 4:48 am

Bill is putting up some important questions here.

I want to bring up something that came up in my thread on IR carbs this winter. It is more important with synced carbs at middle and higher throttle than at idle. So sync at 3000 rather than 900.

I would quit looking at runner afr, in all but high load/ higher rpm situations, and then maybe only in the collectors...

Do you have some kind of an idle speed control on your engine? It came to my knowledge the other day ( in another forum) that Jenvey has a electronic device that can control your idle. I suggest you have a look at this device and it’s capabilities. I will post a link later, if i’n avle to remind myself to do so....
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Re: itb balancing method question

Post by modok » Sat Feb 29, 2020 5:32 am

synch the linkage.

Sometimes doing that with the engine off is ok if the design is super solid,
More often it needs to be running.

Hold the throttles open with the linkage, Off the stops at 2-3k rpm, and adjust till it's even.
On a 4 or 6 you can just hear it, no meters needed, tho maybe not a V8 because they run wonky naturally. :P

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Re: itb balancing method question

Post by modok » Sat Feb 29, 2020 5:43 am

And I'm not necessarily insulting your linkage....
The vibration of the engine, and the airflow pulses acting upon the throttle blades WILL make it work different. Sometimes better.
i had a motorcycle where the throttle would not return with the engine off, but soon as you start it.....worked perfect.

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Re: itb balancing method question

Post by allencr267 » Sat Feb 29, 2020 6:39 am

How far off are the pairs that oughta be equal, a bit or a bunch? Twist'em or reset blades &twist if really off.

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Re: itb balancing method question

Post by Belgian1979 » Sat Feb 29, 2020 7:43 am

digger wrote:
Sat Feb 29, 2020 4:39 am
how are the DCOE pairs coupled?

the first thing to do is make sure the shafts on adjacent pairs are coaxial with an alignment fixture this minimises the change in relative position with throttle angle
There is one brass axle going through it from one end to the other with ball bearings on each end of them. The blades are attached to that axle.
Not sure what you are saing about being coaxial. The bodies sit on the manifold runner faces. These were machined, so I assume they were setup from the factory.

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Re: itb balancing method question

Post by Belgian1979 » Sat Feb 29, 2020 7:45 am

modok wrote:
Sat Feb 29, 2020 5:32 am
synch the linkage.

Sometimes doing that with the engine off is ok if the design is super solid,
More often it needs to be running.

Hold the throttles open with the linkage, Off the stops at 2-3k rpm, and adjust till it's even.
On a 4 or 6 you can just hear it, no meters needed, tho maybe not a V8 because they run wonky naturally. :P
yes, it can only be balanced with the engine running. At initial setup I loosen all linkages and idle set screws on push the blades in their bores shut as far as they can go. Then reconnect them, then set the 0 and 100% TPS calibration after which I start up the engine. At that point they are out of balance and require rebalancing them.

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Re: itb balancing method question

Post by Belgian1979 » Sat Feb 29, 2020 7:47 am

Caprimaniac wrote:
Sat Feb 29, 2020 4:48 am
Bill is putting up some important questions here.

I want to bring up something that came up in my thread on IR carbs this winter. It is more important with synced carbs at middle and higher throttle than at idle. So sync at 3000 rather than 900.

I would quit looking at runner afr, in all but high load/ higher rpm situations, and then maybe only in the collectors...

Do you have some kind of an idle speed control on your engine? It came to my knowledge the other day ( in another forum) that Jenvey has a electronic device that can control your idle. I suggest you have a look at this device and it’s capabilities. I will post a link later, if i’n avle to remind myself to do so....
Yes, that was suggested as well. To balance them at higher rpm. Kinda difficult as I need a way of keeping it at that.
Anyway, it has IAC but I always balance with the valve completely closed. The current session was done with the IAC completely removed and all lines plugged (only the map tube is still connected)

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Re: itb balancing method question

Post by Belgian1979 » Sat Feb 29, 2020 7:49 am

allencr267 wrote:
Sat Feb 29, 2020 6:39 am
How far off are the pairs that oughta be equal, a bit or a bunch? Twist'em or reset blades &twist if really off.
When using the sync tool, they are out as much as 30% in AFR. After using the fluid manometer they were a lot closer.

I just found that the set screws for the linkage connection have a point at the end. I think that may explain the changing of airflow when tightening them as pushing a point onto a round shaft is bound to create some change. I'm going to grind them flat.

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Re: itb balancing method question

Post by modok » Sat Feb 29, 2020 5:16 pm

I don't recommend backing off the idle stops to see how far the throttles can close.
Think about it, it doesn't matter how far they can close. Why would it matter? Getting the throttles perfectly centered is a huge frustration, and once you get that perfect it's only temporary, because if the throttles actually DO touch the bore when running, it'll wear out the bore until it doesn't touch anymore :roll:

Just hold the throttle cable stationary at 2-3k rpms with....vise grips, or copper wire, ect, and synch the LINKAGE, you can do it.

Then adjust the idle.

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Re: itb balancing method question

Post by modok » Sat Feb 29, 2020 5:27 pm

For initial setup cut a .006"? (more or less as needed) feeler gauge in half, and put one half on either side of the throttle blade and close it against that, then adjust the idle stop screw until it's just right. This way your throttle bodies start out bench set with equal gap. The reason for two feelers is to eliminate the variance throttle shaft clearance. Once set I would make equal adjustments to all. Variance in idle airflow can be fixed with your air bypass adjustment.

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Re: itb balancing method question

Post by digger » Sat Feb 29, 2020 5:45 pm

Belgian1979 wrote:
Sat Feb 29, 2020 7:43 am
digger wrote:
Sat Feb 29, 2020 4:39 am
how are the DCOE pairs coupled?

the first thing to do is make sure the shafts on adjacent pairs are coaxial with an alignment fixture this minimises the change in relative position with throttle angle
There is one brass axle going through it from one end to the other with ball bearings on each end of them. The blades are attached to that axle.
Not sure what you are saing about being coaxial. The bodies sit on the manifold runner faces. These were machined, so I assume they were setup from the factory.
So its not a DCOE which is usually two seperate shafts and two seperate bodies connected by a coupler that allows rotation phasing? its one thing for the face to be flat but the two shafts that get coupled need to be coaxial which requires the bodies to be correctly positioned when bolted down as there is usually clearnace between the bolt and bolt holes so the bodies can be angled relative to each other which affcets the coupler phasing

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