Has anyone tried these new electronic balancing devices which let you compare one venturi's airflow with another? They seem to be sold for motorcycles but presumably could be used for our Solexes. Do you just stick a hose in the venturi or does there have to be some sort of seal between hose and venturi? It would be good to get all four venturis sucking exactly the same amount at idle, using those tiny air-bleed adjusters to get the flow just right and compensate for slight differences in the fit of the four butterflies.
This is the sort of thing I mean:
http://www.calamander.co.uk/twinmax/twinmaxmk2.htm
Any other ideas on how to get the balance perfect? I once tried a Gunson's carbalancer on a 2x40DCOE installation and it didn't really work, because as soon as I put a significant restriction in the venturi (which the Carbalancer was) there was too much draw on the jets and it all went to pieces.
John
Carburettor balancing
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Ed Levin
Re: Carburettor balancing
John,
That "Twinmax" is quite a device. I have absolutely no idea how it might work, nor used the Gunston device. But I find is quite easy to balance my 40DCOEs with a dead simple airflow meter, like this:
http://www.webercarbsdirect.com/STE_SK_p/sk.htm (it requires a DCOE adapter).
I'm sure there are more sophisticated devices (surely there are few devices less sophisticated), but it works quite well enough.
That "Twinmax" is quite a device. I have absolutely no idea how it might work, nor used the Gunston device. But I find is quite easy to balance my 40DCOEs with a dead simple airflow meter, like this:
http://www.webercarbsdirect.com/STE_SK_p/sk.htm (it requires a DCOE adapter).
I'm sure there are more sophisticated devices (surely there are few devices less sophisticated), but it works quite well enough.
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Peter Cripps
Re: Carburettor balancing
John,
I use the same type of meter as Ed ... it seems to work well, and I don't think it adds any significant restriction to the airflow.
Peter
I use the same type of meter as Ed ... it seems to work well, and I don't think it adds any significant restriction to the airflow.
Peter
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tim
Re: Carburettor balancing
I tried a gunson once and it was rubbish!
I use a 1/4inch bore hose which I hold/rest just on the bottom of each venturi in turn and stick the other end in my ear. It is fairly quick to get similar sounds from all and I am sure it is as accurate as anything. There will be slight differences anyway from even the pair of venuturies due to butterfly accuracy. Try it it is cheap and works. The balance screw should go to a minimum tickover when at balance point. Either side of the balance pointthe engine is out of balance which can be seen "lumpy running". I have found that the side that is "shut down" when out of balance (on a slow idle - yes I know you have had idle speed problems John which I still believe are due to air leak on the manifold) the idle mix screws generally have no effect.
Tim
I use a 1/4inch bore hose which I hold/rest just on the bottom of each venturi in turn and stick the other end in my ear. It is fairly quick to get similar sounds from all and I am sure it is as accurate as anything. There will be slight differences anyway from even the pair of venuturies due to butterfly accuracy. Try it it is cheap and works. The balance screw should go to a minimum tickover when at balance point. Either side of the balance pointthe engine is out of balance which can be seen "lumpy running". I have found that the side that is "shut down" when out of balance (on a slow idle - yes I know you have had idle speed problems John which I still believe are due to air leak on the manifold) the idle mix screws generally have no effect.
Tim
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Michael Beattie
Re: Carburettor balancing
John
Reading the blurb on the Twinmax, it talks about brass adaptors, I assume these screw into the manifold, behind each carb ( certainly my HF has two holes for such a device to be screwed into) you'd just have to make sure that you get the right treaded adaptor.
I have an even older air flow meter than the ones mentioned above ( it's been in the family for obver 40 years) and it does the job perfectly. The money for the Twinmax isn't bad and being screwed into the manifold it should, in theory, be even more accutare, as it is alway a "fully sealed" reading.
Mind you I know pleanty of folk who do just fine with Tim's ear method ( I suppose it just depends how much it costs to transport him, his tuned ear and his bit of pipe to your location !!! )
Michael
Reading the blurb on the Twinmax, it talks about brass adaptors, I assume these screw into the manifold, behind each carb ( certainly my HF has two holes for such a device to be screwed into) you'd just have to make sure that you get the right treaded adaptor.
I have an even older air flow meter than the ones mentioned above ( it's been in the family for obver 40 years) and it does the job perfectly. The money for the Twinmax isn't bad and being screwed into the manifold it should, in theory, be even more accutare, as it is alway a "fully sealed" reading.
Mind you I know pleanty of folk who do just fine with Tim's ear method ( I suppose it just depends how much it costs to transport him, his tuned ear and his bit of pipe to your location !!! )
Michael
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Huib Geurink
Re: Carburettor balancing
Good idea to use the hose. I will try it.
Note that setting the balance screw to minimum rpm at idle is only correct if the idle screw is fully retracted.
If one carb closes when turning the balance screw it cannot go more closed than closed so the other carb will open and vice versa. If the idle screw is set, the carb on which it sits won't be able to fully close.
Observing the spindles with idle screw fully retracted when turning the balance screw is a very good starting point. With a bit of practice it is dead accurate.
Balancing by setting the idle to minimum with the balance screw with fully retracted idle screw is usally possible with the Solexes. As a result of the high wear on barrels and valves the engine won't stall when the idle screw is retracted.
It is my preferred method for Solexes unless they are new or professionally rebuilt.
A second check is to see if the drop in rpm when closing the mixture screws is equal for all 4 barrels. If the mixture screws on one carb give less reaction than on the other, you can "give that carb a bit more" with the balance screw and play with that. Or pull plug leads one by one and observe drop in rpm (I never do this). Or bend a thin steelwire at 90 degrees and hang it in the idle jet one by one and observe drop in rpm (I have never done this)
On Dellorto's and good Solexes I use the 4 column Carbtune. The Dellorto's have a vacuum connection on each barrel. For the Solexes I add M5 holes on nr 1 and nr 4 on the inlet manifold.
If you really want to match all 4 barrels by using the bypass screws, you need the 4 column Carbtune and add the holes in the manifold.
Note that setting the balance screw to minimum rpm at idle is only correct if the idle screw is fully retracted.
If one carb closes when turning the balance screw it cannot go more closed than closed so the other carb will open and vice versa. If the idle screw is set, the carb on which it sits won't be able to fully close.
Observing the spindles with idle screw fully retracted when turning the balance screw is a very good starting point. With a bit of practice it is dead accurate.
Balancing by setting the idle to minimum with the balance screw with fully retracted idle screw is usally possible with the Solexes. As a result of the high wear on barrels and valves the engine won't stall when the idle screw is retracted.
It is my preferred method for Solexes unless they are new or professionally rebuilt.
A second check is to see if the drop in rpm when closing the mixture screws is equal for all 4 barrels. If the mixture screws on one carb give less reaction than on the other, you can "give that carb a bit more" with the balance screw and play with that. Or pull plug leads one by one and observe drop in rpm (I never do this). Or bend a thin steelwire at 90 degrees and hang it in the idle jet one by one and observe drop in rpm (I have never done this)
On Dellorto's and good Solexes I use the 4 column Carbtune. The Dellorto's have a vacuum connection on each barrel. For the Solexes I add M5 holes on nr 1 and nr 4 on the inlet manifold.
If you really want to match all 4 barrels by using the bypass screws, you need the 4 column Carbtune and add the holes in the manifold.
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Stephan
Re: Carburettor balancing
I use a mecury manometer (also called "carb stick") I bought this years ago when I raced a Fiat 128 with twin Webers. I dont think you can buy them any more, mercury is not enviormentally friendly.
Carbtune that Huib talks about seems to be a good alternative. www.carbtune.com
I think the important thing is to take the measurements on the engine side (intake manifold) as opposed to the airfilter side. This way regardless of whats happening in the carb barrel each cylinder will get the same charge.
Its all a matter of how accurate you want to be, I have known cars that run quite well tuned with the ear method, others tuned with the "uni-syn balancer" tool, but the best will be if readings are taken off the intake manifold.
Carbtune that Huib talks about seems to be a good alternative. www.carbtune.com
I think the important thing is to take the measurements on the engine side (intake manifold) as opposed to the airfilter side. This way regardless of whats happening in the carb barrel each cylinder will get the same charge.
Its all a matter of how accurate you want to be, I have known cars that run quite well tuned with the ear method, others tuned with the "uni-syn balancer" tool, but the best will be if readings are taken off the intake manifold.
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John Simister
Re: Carburettor balancing
Thank you all very much for your suggestions. Currently I have the carbs balanced by Huib's method of making sure they're both fully closed with the idle screw wound right out, and it seems about right with all four mixture screws having an approximately equal effect. But I was just after that last nth of accuracy using the air bypass adjusters as I think the idle could be a little smoother. At least it's now idling at a sensible speed and pulls keenly well past 6000rpm.
That tool of Ed's looks interesting although getting it to seal against the Solex trumpets with their flattened edges might be difficult. Anyway, lots of food for thought here. I'll have a go with the ear and tube method first.
Thanks again
John
That tool of Ed's looks interesting although getting it to seal against the Solex trumpets with their flattened edges might be difficult. Anyway, lots of food for thought here. I'll have a go with the ear and tube method first.
Thanks again
John
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Peter Cripps
Re: Carburettor balancing
This is a very interesting thread. By accident, I discovered the method of adjusting the balance screw for minimum idle, so it's good to hear that it's an 'approved' technique!
One other thing that I've noticed is that when idle is smoothest, and the 4 mixture screws have similar effect, the airflow at the input to the carb trumpets is not identical. I concluded that there's probably air getting in elsewhere, maybe around the butterfly spindles. So adjusting for equal airflow is never going to give exactly the right idle condition ... unless of course the measurement is made after the carbs, on the intake manifold.
In any case, all of this only applies at idle or small throttle openings. Once the butterflies are open any distance, balance is going to depend only on the butterfly angles being the same on all carbs. At least, that's how I see it.
Peter
One other thing that I've noticed is that when idle is smoothest, and the 4 mixture screws have similar effect, the airflow at the input to the carb trumpets is not identical. I concluded that there's probably air getting in elsewhere, maybe around the butterfly spindles. So adjusting for equal airflow is never going to give exactly the right idle condition ... unless of course the measurement is made after the carbs, on the intake manifold.
In any case, all of this only applies at idle or small throttle openings. Once the butterflies are open any distance, balance is going to depend only on the butterfly angles being the same on all carbs. At least, that's how I see it.
Peter
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Ed Levin
Re: Carburettor balancing
To make that airflow synchrometer work properly with DCOEs and similar carb throats, the manufacturer makes a tapered rubber collar that seals against the throat--perfectly effective.
I don't know the proper procedure for Solexes is exactly th esame, but here's the way to synchromize and set the idle on a pair of Weber DCOEs:
Screw all of the idle mixture adjustment screws fully home and then out 2.5 turns. If you are using DCO/SP carbs then start at one turn out. Start the engine and let it reach normal operating temperature. This may mean adjusting the idle speed as the engine warms up. Spitting back through the back of the carburettor normally indicates that the mixture is too weak, or the timing is hopelessly retarded. If this happens when the engine is warm and you know that the timing is OK, then the mixture will need trimming richer on that cylinder. Set the idle as near as you can to 900RPM.
Using an airflow meter or carb synchroniser adjust the balance mechanism between the carbs to balance the airflow between them, if the rearmost carb is drawing less air than the front, turn the balance screw in a clockwise direction to correct this. If it is drawing more air, then turn the balance screw anti-clockwise. If the Idle speed varies at this point, adjust it back to 900 RPM, to decrease idle speed screw in an anti-clockwise direction, to increase, screw in a clockwise direction.
When you are sure that the carbs are drawing the same volume of air, visit each idle mixture screw, turn the screw counter clockwise (richening) in small increments (quarter of a turn), allowing a good 5 - 10 seconds for the engine to settle after each adjustment. Note whether engine speed increases or decreases, if it increases continue turning in that direction and checking for engine speed, then the moment that engine speed starts to fall, back off a quarter of a turn. If the engine speed goes well over 1000RPM, then trim it down using the idle speed screw, and re-adjust the idle mixture screw. If engine speed decreases then turn the mixture screw clockwise (weakening) in small increments, again if engine speed continues to rise, continue in that direction, then the moment it starts to fall, back off a quarter a turn. The mixture is correct when a quarter of a turn in either direction causes the engine speed to fall. If that barrel is spitting back then the mixture is too weak, so start turning in an anti-clockwise direction to richen. During this procedure, the idle speed may become unacceptably high, so re-adjust it and repeat the procedure for each carb barrel.
After all the mixture screws have been set, the idle should be fairly even with no discernible 'rocking' of the engine, if the engine is pulsing, spitting or hunting then the mixture screws will need further adjustment. If the engine is rocking or shaking then the balance is out, so revisit with the airflow meter/ carb synchroniser.
I don't know the proper procedure for Solexes is exactly th esame, but here's the way to synchromize and set the idle on a pair of Weber DCOEs:
Screw all of the idle mixture adjustment screws fully home and then out 2.5 turns. If you are using DCO/SP carbs then start at one turn out. Start the engine and let it reach normal operating temperature. This may mean adjusting the idle speed as the engine warms up. Spitting back through the back of the carburettor normally indicates that the mixture is too weak, or the timing is hopelessly retarded. If this happens when the engine is warm and you know that the timing is OK, then the mixture will need trimming richer on that cylinder. Set the idle as near as you can to 900RPM.
Using an airflow meter or carb synchroniser adjust the balance mechanism between the carbs to balance the airflow between them, if the rearmost carb is drawing less air than the front, turn the balance screw in a clockwise direction to correct this. If it is drawing more air, then turn the balance screw anti-clockwise. If the Idle speed varies at this point, adjust it back to 900 RPM, to decrease idle speed screw in an anti-clockwise direction, to increase, screw in a clockwise direction.
When you are sure that the carbs are drawing the same volume of air, visit each idle mixture screw, turn the screw counter clockwise (richening) in small increments (quarter of a turn), allowing a good 5 - 10 seconds for the engine to settle after each adjustment. Note whether engine speed increases or decreases, if it increases continue turning in that direction and checking for engine speed, then the moment that engine speed starts to fall, back off a quarter of a turn. If the engine speed goes well over 1000RPM, then trim it down using the idle speed screw, and re-adjust the idle mixture screw. If engine speed decreases then turn the mixture screw clockwise (weakening) in small increments, again if engine speed continues to rise, continue in that direction, then the moment it starts to fall, back off a quarter a turn. The mixture is correct when a quarter of a turn in either direction causes the engine speed to fall. If that barrel is spitting back then the mixture is too weak, so start turning in an anti-clockwise direction to richen. During this procedure, the idle speed may become unacceptably high, so re-adjust it and repeat the procedure for each carb barrel.
After all the mixture screws have been set, the idle should be fairly even with no discernible 'rocking' of the engine, if the engine is pulsing, spitting or hunting then the mixture screws will need further adjustment. If the engine is rocking or shaking then the balance is out, so revisit with the airflow meter/ carb synchroniser.