Gunson Carbalancer and SU dashpot oil

K

Keith Coman

New Member
A couple of Barry Cades that may prove useful to someone:

1. Gunson Carbalancer - after putting the vacuum seal unit into the carb mouth, give the carb a small blip. This will lift the little pointer to get a reading. The idling suction is sometimes/usually not enough to lift the pointer on its own. [The carb must be blipped anyway before taking a reading - so just do it a second time with the Carbalancer in place.]

2. SU dashpot oil - yes there are many different ideas on what oil to use. One that I'm getting good results with is a product sold as "Air Tool Oil" for use on such things as compressed air impact wrenches etc. Sold in bottles at all places where home workshop air compressors and related gear are retailed.
 
Hi Keith

I'm afraid I'm old fashioned - I simply don't believe in the carbalancer and am much more comfortable listening to the hiss via a length of old heater air delivery tube!

Seems to be a consensus on here that ATF G is pretty good in carb dashpots. And since all BW35's leak (except those that have been Harvey'd of course!), we all have lots of it lying around!

Chris
 
Chris beat me to it but I agree, the guy that recently tuned my car said the best way to balance the carbs is by listening with a plastic tube as the gauges won't give you an accurate reading and as far as oil, I was using 3 in 1, he tipped that out and used ATF instead.
 
my carbs ate the ATF I put in. It pinks less under full throttle with 20-50 in it, seems to work quite well, better than the ATF. I also go with the pipe for balancing, I checked it once with a balancer and it was exactly the same.
 
1396midget said:
my carbs ate the ATF I put in. It pinks less under full throttle with 20-50 in it, seems to work quite well, better than the ATF. I also go with the pipe for balancing, I checked it once with a balancer and it was exactly the same.
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Funny you should say that about your carbs 'eating' the ATF, a week or so after having the car tuned it seem down on power so I checked the dashpots and had to top them up again :? Maybe I experienced something similar as I was surprised they needed topping up so soon. Pardon my ignorance but 20/50, are we talking normal engine oil here?
 
yup, engine oil. tis what's recommended in the original book, though dashpot oil is a wide ranging debating topic! My SU book is all on about adding watch oil to thin it and things.

same oil as goes in the car works best for me, so far.

Not sure if it ate it or if it just fired it all out of the top.
 
I have a carburettor balancer (suction meter) that belonged to my Dad which is in the photo below. Harvey has exactly the same one.

PC210195.jpg


I find it very useful and reassuring to be able to set each carburettor to draw exactly the same volume of air.

Ron.
 
Mikep said:
as the gauges won't give you an accurate reading
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There's no requirement for an "accurate" reading, you're not measuring the airflow itself, only checking that both are flowing the same, so how accurate the guage is is of no consequence because you're using the same guage on both carbs.
 
harveyp6 said:
Mikep said:
as the gauges won't give you an accurate reading
Click to expand...

There's no requirement for an "accurate" reading, you're not measuring the airflow itself, only checking that both are flowing the same, so how accurate the guage is is of no consequence because you're using the same guage on both carbs.
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Sorry my mistake, I didn't mean accurate as such, what I mean't to say, going by the chap who tuned my carbs, he told me more often than not when you balance the carbs by the gauges and get them both spot on then take the car for a drive you sometimes find when you get back and re-check them they are out of sync again. He told me that even though the gauge shows them in balance they aren't really the same and the only way to set them is by ear as you can then match the sound between the two.
The bottom line is I have to get someone to do it for me because as you see this really isn't my area of expertise :LOL:
 
Mikep said:
harveyp6 said:
Mikep said:
as the gauges won't give you an accurate reading
Click to expand...

There's no requirement for an "accurate" reading, you're not measuring the airflow itself, only checking that both are flowing the same, so how accurate the guage is is of no consequence because you're using the same guage on both carbs.
Click to expand...

Sorry my mistake, I didn't mean accurate as such, what I mean't to say, going by the chap who tuned my carbs, he told me more often than not when you balance the carbs by the gauges and get them both spot on then take the car for a drive you sometimes find when you get back and re-check them they are out of sync again. He told me that even though the gauge shows them in balance they aren't really the same and the only way to set them is by ear as you can then match the sound between the two.
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Regardless of whether you balance them with a guage or with a pipe, if they alter when you drive it that will happen whichever method you use. I think he's talking b******s myself, and the worst thing about that he's using your lack of knowledge to do it.
 
On account of deafness I find the Carbalancer the most practically useful way of doing this job and my original post was specifically aimed at those readers who like to use this neat device. It sure works and eliminates much of the guesswork.

My understanding is that SU specifies a light 20 weight oil for its dashpots. Multigrade 20-50 engine oil may thus be too heavy when the weather turns really cold. A bit of internet searching will show that there are a huge number of personal preferences out there for the job with a popular choice for example being motorcycle fork oil. As noted at the start, air tool oil is my preference.
 
That is entirely possible, Dave. The tolerences required to make them consistent are, I suspect, beyond the capabiliies of British mass production of the period!

Chris
 
not only that, but finding 2 rover V8's in exactly the same state of tune and age of components might also be an issue! Whatever works well!
 
I bought some Penrite SU dashpot damper oil from Beaulieu Autojumble one year, just to try, and it seems to work well, carbs seem quite responsive, with no flat spots. Its quite a thin oil, much like compressed airtool oil. Wasn't expensive, so I thought I'd give it a punt. Might switch to ATF when that truns out, but it doesn't seem to need topping up very often, only about once a year.
 
Well after the discussion here about what oil to use I decided today to empty out the ATF fluid that I had used, if I'm honest the car seemed like it had a flat spot, and re-filled with 3 in 1 oil, my word what a difference that has made :D the throttle response is better and the flat spot has gone, so it appears that my car is fussy. It's strange that each car is different it seems and some prefer different oils to others :?
 
It's interesting to note that a driver's manual for a period car stipulates that multigrade oil should not be used in the SU carb's dashpot. Back in those days I used to put in 3-in-1 oil - if I remembered to top the d-pot up at all.
 
Good carb balancing equipment goes in both intakes at once and uses one central gauge.

They are very sensitive and it would take 'some' set of ears to compete with it IMO

To differentiate what is pitch as opposed to volume passing through is beyond my ears, even though I can do them good enough to run fine until I have the correct tool to hand :)

As Harvey says, any gauge does the trick if you can move it quickly from side to side without altering the throttle position :wink:
 
GrimV8 said:
Good carb balancing equipment goes in both intakes at once and uses one central gauge.

They are very sensitive and it would take 'some' set of ears to compete with it IMO
Click to expand...

That was the Churchill kit that I used at the Main Stealer, and I've seen for sale occasionally on ebay, but they've never been the complete kit, to service both 2000's & V8's, there's normally only what's needed for the 2000's for some reason, and they won't do 2200's either, so not a lot of good if you want a tool to do all of them. If I saw one complete for sensible money I'd have it, but I'm not holding my breath....
 
You can make a perfectly usable and accurate carb balancer with a long piece of washer type tubing,a couple of squares of ply and some thin oil .
The squares of ply blank off the carbs,they have a hole drilled in them and the pipe pokes through another hole (one piece on each end of the pipe).The pipe hangs down and some oil is added which settles at its lowest point.The size of the other hole in the ply is varied so that with the engine ticking over the oil is drawn part way up the tube rather than being siucked straight into the carb. .If the air flow/suction on one carb is greater than the other the oil will be drawn up higher on that side.By altering the opening of the throttles so that the oil is level the carbs are balanced.
I'm sure there's a picture of this set up somewhere on the net.
 
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