using UNI-SYN tool

[TexasKnucklehead]

The HS6s I have mounted on my freshly rebuilt TR3 engine were rebuilt years ago, but never used until a few months ago. The engine runs fairly smoothly, but I'm sure adjustments are needed. After replacing the needle/seats, fuel no longer leaks from the over flows. The pistons snap back to the bottom when it's not running. The lift pin causes either piston to rise a small amount when the engine is not running. When the engine is running (about 2400 RPM), the front carb piston is above the point where the lift pin would raise it to, and the rear piston is not. The vacuum line is removed and plugged. My UNI-SYN tool (that I've never before used) does not seem to work. The float never rises. Even if I use my tiny 1.0 hp shop-vac to suck on the instrument, the float rests at the bottom. Am I not using the tool correctly?

I purchased it years ago (perhaps from TRF) as Edelbrock model 4025.

Carb adjustments are new to me. I'd like to learn, but not sure how to start and appreciate any advice.

 

[Andrew Mace]

Forgive my stating the possibly obvious, but there is an adjustment on the Uni-Syn that can be opened or closed; chances are it's closed too far so that no vacuum is acting upon the little "float" in the Uni-Syn?

 

[Geo Hahn]

I think Andy's got it. You adjust that thumbwheel until the ball floats in a convenient spot for reading. The instrument is compartive, not an actual measurement so the scale is just there so you can see when the reading is the same on each carb.

In case it isn't obvious (since you apparently don't have the instructions and indeed I do not know if mine even came with instructions) you loosening the linkage between the carbs to do the individual adjustment. Also, the upright tube swivels a bit so yu can get it to true vertical for your SUs.

 

[Geo Hahn]

Found this on the web, it's instructions for the motorcycle version but the principle is the same:

https://www.jegs.com/InstallationInstructions/300/350/350-4027.pdf

 

[TexasKnucklehead]

It came with directions. I read them again. I suppose the "thumbwheel" is the center section with a spring between it and the frame. Using the same shop-vac, I can lower it until the float slams against the top, but I have to remove the vacuum before the float will drop back down. (I am unable to get the float centered in the tube.) It's probably because there is way too much air flowing compared to when the engine is running, but I think I have more of a clue how to use it.

I still don't know why one carb piston is so much higher than the other.

 

[TR3driver]

I still don't know why one carb piston is so much higher than the other.

The running height of the pistons is (or should be) a very good indication of relative air flow. In fact, with the H6 carbs, I much prefer to use the SU tool kit for checking synchronization (which effectively compares the piston height). If it will work with the HS6 (I think it should, but haven't tried it), then I would suggest selling the Unisyn, buying a SU tool kit, and using the difference to buy dinner.

If you have verified that the pistons are not sticking in the domes (which can sometimes happen after storage as the domes are very easy to dent), and that there are similar springs installed inside each dome; then the problem is likely that your throttles are not synchronized. It's also worth checking that you don't have carbs with the later bypass valves (which sometimes open inappropriately).

I don't have a reference at the moment, but when I tried to use my Unisyn, I could not close the throat enough to raise the ball without upsetting the mixture so badly that the engine would not run right. Somewhere, I found instructions that said to run the tube with the ball at an angle, so the throat could be open farther and still move the ball. Having the tube only about 30 degrees above horizontal worked much better for me.

Another way to verify relative air flow is to use a length of tubing (like heater hose) to listen to the hiss at each carb throat. Although somewhat subjective, I find that this method is plenty close enough (even with my bad hearing) to get the engine running good. Some years ago, I helped a club member with a poorly running Spitfire by just setting the carbs by ear (not even a hose) in a restaurant parking lot. He told me later that it had never run so good!

 

[JohnnyMead]

I know its an automotive icon, but I never had much luck with the Unisyn. I figured I was not handy enough to adjust it. Years ago I bought the dial-type air meter (Moss sells them I think) and have had no problems with getting readings.
John

 

[martx-5]

I know its an automotive icon, but I never had much luck with the Unisyn. I figured I was not handy enough to adjust it. Years ago I bought the dial-type air meter (Moss sells them I think) and have had no problems with getting readings.
John

I thought I saw the one you're referring to at Moss awhile back, but can't seem to locate it on their site now. The one you are talking about is on the right in this link. Of course, the infamous Uni-Syn is on the left. I've used the STE Synchronizer before, and it is much better then the Uni-Syn.

 

[JohnnyMead]

This one looks like what I use:

https://www.duckyimports.com/servlet/Detail?no=5

 

[SkinnedKnuckles]

I'm not sure what the instructions on the Uni-Syn say, but the key is to only have it in place for 1 second or less - preferably less. Otherwise, as Randall & others have found it disturbs the flow too much.

I place the indicator tube as near vertical as possible to minimize friction. Quickly place it on the carb inlet to see where the "float" goes, and remove it. About 1/2 second is all it takes. Screw the center plate in or out to get the float about midway in the chamber and you're ready. Do it a couple of times to be sure the measurement is repeatable, then move to the next carb and see if the flow is higher or lower.

I found it also helps to darken the graduations on the tube with a sharpie or wax pencil. also - when I finally break mine I may go to another type, but it works fine for now.

 

[swift6]

My Uni-syn hasn't left the drawer for a few years now. Reverted back to a piece of tubing held up to my ear and listen to the whistle. Just make sure you place the tube in the same spot on each carb.

 

[TexasKnucklehead]

I took the UNISYN apart. It seems to not be very well made and probably leaked at several places where air should enter the graduated tube. Now the float will go up (occasionally) but goes all the way to the top when it does. -and it usually requires the unit to be against the carb long enough to hear the RPMs change before it moves upwards (more than a few seconds). I did 'synchronize" the carbs by listening to the hiss from each one, and now both pistons are about the same height and rise together when the accelerator linkage is snapped.

It's idling smoother, but I think the UNISYN is not very user friendly, or not working properly. Unless I bottom out the center plate, the float rests at the bottom of the tube. I know both carbs are sucking air because I can block the air inlet with the palm of my hand for a second and feel it, and when pulling away, the piston rises quickly then returns down (on either carb).

I have the tube as close to vertical as possible, but wonder if that plastic float is getting stuck or something. The float does move up and down inside the tube, if I rotate the tool up and down. I'm sure I'm getting a good seal between the air intake of the carb and the UNISYN. If the engine RPM is too high, will that effect the ability to adjust the tool so the float can be centered?

 

[poolboy]

Tell you what; when you have to spend more time adjusting the Unisyn than adjusting the carb, I'd say it's time to put the Unisyn back on the shelf.

 

[Andrew Mace]

I took the UNISYN apart. It seems to not be very well made and probably leaked at several places where air should enter the graduated tube....

Something tells me that, like so many other things in life, <span style="font-weight: bold"><span style="font-style: italic">they don't make 'em like they used to!</span></span> :frown:

My Uni-Syn is approaching 40 years old. It was well made, and it still functions as well as it did when I first bought it circa 1971. I still keep it carefully in the original box (do they even come in boxes any more, or are they all blister-packed?).

I get the feeling that using or not using one of these is akin to the Coke v. Pepsi, or Ford v. Chevy (Triumph v. MG?) or boxers v. briefs debates. Not sure there's a correct answer in any of those...except Coke v. Pepsi, where I firmly believe Royal Crown beats them both!

 

[SkinnedKnuckles]

Tell you what; when you have to spend more time adjusting the Unisyn than adjusting the carb, I'd say it's time to put the Unisyn back on the shelf.

That's the truth! The only other thing to offer is that if the float in the Uni-Syn is binding, take it apart and wash the tube & float with dish soap, then dry. I've done that twice with mine - it's 20 years old. If the "float" doesn't easily go from top to bottom when you tilt the thing upside down & such, it's not functioning as it should.

 

[Rick_in_Seattle]

There is an excellent video thats been around for a while, "Just SU" put out by ZTherapy (they're Z guys at heart, but really know SU carbs). Many Triumph clubs have a copy; you can buy one from the usual suspects. It's truely an excellent way to develop confidence in rebuilding, maintaining, and tuning our carbs. The Uni-Syn is covered in detail; do what they do and you'll find it an easy tool to use.

So, does this post damage my lurker status?

 

[DNK]

Rick,do you know Mark Zenor. Fellow Seattlite, Well really somewhere past Puyallup really. He's got a couple of TR's in his stable. Also has a Norton in his living room. Or had one. Might be finished by now.

And by the way .Once you post your Lurker cherry is busted!

 

[vivdownunder]

Also after about 40 years, I've still got the Uni-Syn in it's original black and yellow box with instructions. First time I'd realised it was a Los Angeles supplied product, not British. Instructions give best method for Porsche and Corvair, but zip about LBC's. Price back then was $10.95 for the Model A.

Sometimes I break it out, but find that listening through a short length of heater hose is just as accurate. The inlet manifold balance pipe copes with any minor suction variance

Viv.

 

[vivdownunder]

Oh, I should have mentioned that the problem with the Uni-Syn is it can cover up the suction holes on the aircleaner face of SU carbies. I use it with a small length of 2" OD radiator hose between the Uni-Syn and the carby, and it works much better.

Viv.

 

[SkinnedKnuckles]

Oh, I should have mentioned that the problem with the Uni-Syn is it can cover up the suction holes on the aircleaner face of SU carbies. I use it with a small length of 2" OD radiator hose between the Uni-Syn and the carby, and it works much better.

Yep - it covers ALL those holes. That's why it should be in place less than a second. Interesting thought on the hose, though...