AC Owners Club Forum
AC Owners Club Forum => Ace, Aceca & Greyhound Forum => Topic started by: TTM on December 06, 2016, 08:56:07
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Hello,
What does everyone use to tune their Solex carbs on the Bristol engine?
I heard good things about the vintage Motometer unit(s) but I would rather buy something new, and most of the modern "snail"-shaped synchronizers look like they won't be a trivial fit with the Solex inlet flange.
Thanks in advance for your thoughts.
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I used a Uni-syn for years.
They are still available online for 30 bucks. I think I paid 6 or 7 in 1960.
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I use two methods. The first is with the Crypton Synco Check air flow meter which has a rubber cone for round bell mouth carbs and if you remove the cone there is a flat rubber pad which sits over the intake on the Solexs, they work in any orientation. You get them on 'rip off bay' occasionally which is where I got mine from. The other is to use manometer tubes and not the Bristol way with mercury that you can accidentally have sucked into the engine or with manometer fluid. In motor cycle circles you can get a four (or two) column manometer that uses steel rods. If you drill the spacer below the carbs and fit small brass tubes, then the individual manometer pipes can be connected to each carb, the height the rods rise will tell you which carbs are open more than the other ones. The higher columns will show a greater vacuum hence butterflies need to be opened. Because the rods are all together then you can check that they are also opening together as the throttles are progressively opened. The firm is called Carbtune and are or were based in Belfast, so do a search for them or get the motorcycle comics that come out on Wednesdays. I am just about to balance the carbs on one of my motorcycles after rebuild and they are a godsend. Of course if you have the Weber carbs then the vacuum take offs are already fitted. Both methods are a two minute check now for out of balance butterflies.
Hope this helps.
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Just checked eBay and there is a Crypton Syncro Check for sale at £75 and loads of the Carbtunes from around £40.
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I use a simple piece of hose to listen to the volume of air being ingested by each carb to ensure the butterfly valves are set equally.
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Hmm, I haven't got three ears.
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I to use the hose method and just listen, you just have to ensure you put the hose in the carb mouth the same distance. you soon learn to hear the difference. I use this on all sorts of carb set ups, su, Solex, Webbers etc.
My dad taught me, long before all these meters.
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Thanks for the helpful replies so far.
quote:
Originally posted by MuffinIf you drill the spacer below the carbs and fit small brass tubes
Upon reading different period documents from Solex it would appear that 32 PBIC carbs feature a vacuum nipple hidden behind a screw plug on the throttle body housing, and that this vacuum nipple should be connected to some vacuum pipe on engines where ignition timing is vacuum-driven.
Could that plug screw be the one just below right of the plug for the main jet hex plug on the picture below? It seems way too small for hiding a nipple of some sort...
(http://www.356carburetorrescue.com/images/DSC02519-1.jpg)
I do not have access to the car right now to check for myself.
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I got confused and for some reason assumed that the Solex carbs on the Ace Bristol engine were 32 PBIC when they are in fact 32 PBI-6, which is actually just what's already mentioned in the AC owner manual (I know, RTFM and all that...).
The only difference I could spot between the two is the separate throttle body housing on the PBI-6 mating to the actual body of the carb with a 4 bolt pattern.
There does not seem to be picture on the Internet of PBI-6 carbs, but this illustration of the 32 BI shows a similar construction, and suggests that the vacuum port should be plugged with a screw plug labeled number 16.
(http://www.ruddies-berlin.de/grafik/32pbi1.gif)
Looking at the PBI-5 as used on some Jaguars, the vacuum port seems to be left open :
(http://www.limora.com/media/catalog/product/cache/1/image/9df78eab33525d08d6e5fb8d27136e95/6/1/61397.jpg)
So what is on your engines, gentlemen?
Are your holes plugged or not? (pun unintended)
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Very interesting. popped out and had a look, and found that -
Front carb - no plug, but it appears that the hole is blocked further in. Also it appears that there is no thread in the hole for a screw-in plug.
Middle carb - plugged
Rear carb - as front
I notice that in the photo above, the hole on the carb on the right is threaded and the one on the left isn't. Though maybe it's badly lit?
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Good feedback, thanks.
Solex most likely used a single mould of the throttle body housing and the hole may or may not have been drilled through the port as the housing made its way down the production/supply/logistic line, depending on engine application.
As decades of use saw carbs wearing out and ultimately needing overhauls that in some cases may have required replacing the throttle body housing for any reason, it could be that drilled housings were mixed up with non-drilled ones depending on what carb rebuilders had on the shelf at that moment.
Would be interesting to hear from other owners, to see if we have a trend.
Now to get back on topic, an open side port would be useful to measure vacuum when synchronizing the carbs.
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Here is a picture of my center carb. I blew inside the port with a small pipe but as the picture suggests it is definitely plugged. All three carbs are the same. Just thought I would share.
(http://mapage.noos.fr/tjmm/ACOC/Solex.JPG)
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I have already mentioned that as the carbs did not have vacuum take offs I fitted brass tubes to the spacer blocks/throttle linkage adaptors. If you use the carb tune manometer set up then you can monitor the vacuums from each carb with out having listen to the hiss individually from each carb. If you have the Bristol work shop manual it shows this set up but with 'U' tubes and mercury columns and caps on each carb - I made some caps and tubes and it was a pain. Problem with using mercury is that if it is inadvertently ingested into the engine it has an affinity to the lead in the main and big end bearings. The other advantage with these manometers is that having balanced the butterfly opening at tick over, then you can observe any difference when setting the idle mixture plus you can check that each butterfly is opening equally as you open the single throttle linkage which is not possible with the ear and tube set up. I dread to think how far out the carbs were on the Cooper S's I had in the sixties having tried that method and checked with the carb tune set up that I now have.
There is another Crypton Syncro Check on eBay at less than £20 at the moment.
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Hello Muffin,
Yes, I duly took note that the spacer blocks could be drilled to receive proper vacuum ports fittings. However I feel a bit precious with the car and would feel better without drilling anything, unless it is absolutely needed.
What carbs did you have on your Mini?
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I eventually ended up with 11/2" SU's and a 731 cam plus all the other mods. I was in the Merchant Navy then so could not have it too tuned because my girl friend(wife) at the time used it when away, though I subsequently found out that she would often use all the performance through the gears when frustrated by twonks in Jaguars and MGB's.
Regarding the vacuum take offs on the spacers, I will take a photo of mine as they are really unobtrusive, if you really are reluctant then I would really go for the Synchro-Check flow meter as it much more accurate than the 'pipe in the ear'. If you want to try out all three systems then you are quite welcome to see them working, I live in South Shropshire.
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Muffin, thank you very much for your help. I am not in the UK unfortunately otherwise I would have taken you up on your kind offer.
I just ordered a new Edelbrock Uni-Syn synchronizer. It seems to be a copy of the original MotoMeter Synchro-Test a friend uses and originally recommended to me. I did not feel comfortable ordering a used Crypton Synchro Check as the ones that occasionnaly pop up on ebay seem to have had a life, understandably. Looking forward to using it on the Solex and on the SU carbs of my other vintage British car.
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Pleased to say the Uni-Syn did its due. The airflow at tickover is so low that the adjuster on the synchronizer needs to be almost completely close otherwise the floater in the gauge won't take off.
Thanks again everyone for your helpful input.
By the way, which engine speed at tickover is everyone looking at with their Bristol engine?
Reason for asking is that mine reads "high" on the rev counter (about 1200 rpm), but the engine does not sound like it is running that high. I have not been able to read on a recommended idle speed in the owner's manual. I also wonder if the calibration of my rev counter could be slightly off.
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It turned out the high idle speed was caused by excessive play in two throttle spindles. The corresponding volume screws were out way more than on the tight spindle to get the same plug colour, confirming how more much air was being aspirated through the loose spindles.
Now with rebushed throttle housings and 3 nicely tight spindles I have been able to reduce idle speed from 1300 rpm to 1000 rpm when hot, and 700 rpm with the timing knob fully out (full retard). By then the engine stumbles a little bit but runs more or less fine. The Bristol manual mentions an idle speed when hot of 800 rpm, which is quite a bit lower than 1000 rpm?
Do other folks on here with a 100D2 engine run theirs at the same idle speed or lower?
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Well, after the Uni-Syn synchronizer I purchased another useful tool in the shape of a digital timing light. I could not understand why the engine would begin to stumble when I tried to lower idle speed to below 1000 rpm, but that was just because 1000 rpm on the rev counter was actually 500 rpm as registered by the timing light... another question answered.
The timing light also allowed me to spot a little bit of point bounce while gradually increasing engine speed, up to only 2000 rpm. Is point bounce a common occurrence with the standard Lucas distributor? My car has not run much since the distributor was rebuilt and the engine runs pretty well I would say.
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TTM,
This does not feel quite right as if the tachometer vs timing light tacho has a linear offset it would mean you would hit the redline at half the actual red line-- I would have thought you would notice it only having half the available rev range to use. I know some distributors turn at half the engine revs due to gearing but as I dont know how your timing light rev counter works hard to say. One other possibility is you could be running on 4 cylinders rather than 6 at low rpm.
I would be tempted to hook up a separate rev counter to the coil to check whats what, or try the timing light tachometer on on another car whos dash is known to be correct.
Graham
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This is a good point you make here Graham. I ignore how the rev counter works exactly, but I can say that I did push the engine to a shade below an indicated 6000 rpm at a few occasions and thankfully it responded much better than what I would expect from a healthy normally-aspirated 2L petrol engine running at just 3000 rpm. I have made sure that there was no turbo or compressor in the engine bay.
Under full load, the howl of the engine suddenly changes to an aggressive bark at 5000 rpm with a definitive bump in acceleration, and if I look at the specs of the D2 engine running the Sports camshaft, 5000 rpm corresponds to peak torque rpm, so I would imagine that the rev counter works more precisely where it matters most? What I can observe though would for sure be a bit strange if it's supposed to work in a linear manner.
I tested the timing light on a spare car that runs fuel injection, and the rev counter, the engine speed indicated through the ECU software and the timing light registered all three the same engine speed, so at this point I am not sure the timing light could be any faulty.
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As you say it would appear to behave in a non linear fashion.
However you have brought up a very good point for many who set their cars up a idle using Tachometers getting on for 60yrs old -is the dash RPM the real RPM.
It made me go and refresh my mind as to how tachometers work and it would appear that pre1960's its current sensing and later on voltage sensing over a fixed time. I cant imagine its mechanical (though my Bristol 400 has that and is 1949).
I use a digital timing light a lot but mine does not have RPM--I use a Gunsons hand held meter for RPM and cross check vs dash tacho as I tend to be suspicious of single readings having been led a merry dance on a few occasions with my CRS temperature gauge among other things (invested in a fluke IR gun for that one).
Graham
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Graham,
Thank you for this information. I had no idea how the original Smith tachometer worked.
By the way, if my tach works correctly when driving around, and that will necessarily be at engine speeds above 2000 rpm, do you think that erroneous readings at lower engine speeds could point to a faulty "voltage regulator" (assuming there is even one) or anything else in the electrical system starting off from the dynamo?
As far as I can tell, all other gauges including the AMP meter work correctly, or at least do not seem to return overly suspicious readings.
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The Greyhound has a mechanical rev counter and works exactly like the speedometer, a rotating magnet inside a steel 'drum', the faster the magnets rotate - driven by the cable from the distributer - the further the magnets pull the 'drum' - connected to the needle - round and hence indicates speed. Chronometric speedometers and tachometers use an escapement mechanism similar to a clock. useful when you blow the engine up as the last rpm reading is retained.
I would suggest that you have the timing light set up wrong or not connected to the coil the right way round, depends whether you are negative earth or as originally on the Greyhound positive earth. I daresay the instructions presume that you are connecting up to a modern car which uses -ve earth.
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Hello Muffin,
I searched for information regarding the car being positive earth, and I found that the dwell plug should be connected to the SW coil post. I did not check dwell angle which my timing light can also do, but I guess the actual dwell would be 60° minus the dwell value observed by the timing light.
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You can tell whether you are -ve or +ve earth by looking at your battery connections. If as originally built the +ve terminal will go down to earth. I assume your term for dwell plug is the coil lead to the distributer? The sensor wire for your timing light on most instruments connects to this wire, and as I converted my heap to the modern polarity -ve earth then the coil-points lead is connected to the either -ve or sw terminal of the coil.
There are no electronics in your rev counter other than the light bulb if it is as built. Discrepancy between your light and rev counter must be something wrong with the way you are setting the controls on your strobe light. I would prefer to believe the cars rev counter. My ticker is usually about 800rpm any lower then the revs drop off 50ish when dipping the clutch. The dwell angle, not percentage for a 6 cylinder engine generally should be about 35deg + or - a couple of degrees I think mine is 36deg with 0.016" points clearance, but it is some time since I last checked.
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Having written the above, sat down for a cuppa (tea), and cogitated, the coil is marked CB and SW. When I check with my all singing and dancing diagnostic kit I connect my instrument to the CB terminal if I want to check the revs or dwell, try that with your strobe light.
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So you connect your dwell pick up to the CB coil post on a car that was converted from positive to negative ground?
I am not sure I understand what dictates, physically and electrically talking, why the dwell pick up (or green plug) should be plugged to either of the coil posts. The manual of my digital timing light states that it should be used for negative ground cars only, and that the dwell pick up should be connected to the negative coil post.
If I compare how an ignition coil is plugged on either a positive or negative ground car, I think I (mis?)understand that the requirement is more to connect the dwell pick up to the ground coil post regardless of positive or negative earth, no?
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Muffin,
You were right - the dwell plug of the timing light must be connected to the CB coil post otherwise no dwell signal is measured.
By then the dwell reads 22 but since the car is wired in positive earth, and the engine being a 6 cyl, actual dwell is therefore 60-22 = 38°. I replaced the points recently and adjusted them according to the manual, for what it's worth.
However, the 500 rpm error between actual engine speed and the rev counter seems more or less constant through the rev range. More than happy to live with it though, now that I know I do not really need the rev counter to monitor actual engine speed.
Also, for engine speed the timing light does not care whether its dwell plug is connected or not. It seems to be just calculated from the signal of the inductive clamp, as the number of cylinders is configurable when switching on the timing light (if the engine is 2 or 4 strokes can also be configured, for what it's worth).
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Good morning Gents,
In my relatively successful quest to tune the engine I have reached the point where I need to adjust the float level in the carbs to solve a problem with what seems to be some slight fuel overflow issue that appears at random.
Upon researching through the Internet I found that Porsche made a special tool to adjust the float level on the Solex 32 carbs used on some early 356s and even if the B32-PBI6 on the Bristol may slightly differ from the ones used on these 356s, it looks like that tool could also work well on the Bristol engine.
What does everyone on here us to adjust the float on their Solex carbs?
Since we now have the possibility to attach files (thanks to the admins for the forum upgrade, by the way), here is what the Porsche tool looks like.
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Hi,
P78 is the float setting tool for Solex carburetors, but not for 32PBIC, rather for 40 PIIs. I do have P78 and I'll check this afternoon if it works on my spare set of 32PBI-6. For sure the level will be different but could be marked beforehand. P78 is available at several Porsche spare sources.
Ignacio
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Hello,
Nevermind the level engraved on the P78 level tube, it shouldn't be too difficult to use it with a Solex 32. Does yours come with room to fit the main jet?
Looking forward to hearing if yours fit your B32-PBI6 carbs. Thanks for checking.
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So, I spent some time checking out this topic:
I took the Bristol 32 BI carb, a Porsche 356 32 PBIC and a Porsche 356 40 PII-4 from my stock,
As well as tool P-78. This is what I found:
threads: interestingly enough both German 32 PBIC and British have metric 8x1.00 starters so the attachment for checking the bowls would be the same. 40s have a different M11x1.00 that matches P-78 tool.
So in theory you could machine an extension M8 to M11 to use the tool. There is an M7x1.00 extension available, that is for the zeniths also used on porsches 356. At this point I also had a look at the factory preA and A model workshop manuals as those are the models that used the 32 solexes.
The method for adjusting the fuel high in the bowl is the traditional which involves taking out the top cover.
I also checked the potential attachement to P-78 to the 32's....the lowest level indicated by the tool will still be too high compared to the maximum that the 32 will need. So the tool is not usable.
32s have way smaller bowls compared to the big, deep bowls of the 40's needed for the S-90/SC/912 series and P-78 was design for those clearly. Also there is a good reason for this tool as 40s do have an outside bolt to regulate the float high without taking apart the top cover.
So, long story short, P78 won't work and in fact won't make much difference as you need to remove
the cover anyway.
Ignacio
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In the recent past I have used a set of 3 main jet holder covers modified (drilled and brass tube soldered in ) for clear plastic hose to be attached that you clip vertically on the carb body --they were lent to me by a fellow Bristol enthusiast and he had made small clips to hold them all upright. It worked quite well though crude and bear in mind the engine (in a Bristol 400) is on an incline anyhow.
How do you know that its not the needle valve thats faulty, or perished washer? I just looked at a old needle valve I have spare & disassembled and its also possible for debris to trap there if your inline filters are not working.
I have also had the actual float get pin-holed in the past and it just sinks and the car ( a lotus elan on webbers 40) just runs super rough all the time.
It sounds like you have a more subtle issue though more detail might help. A lot of the fuel rails /washers are prone to leakage if not assembled correctly.
Speaking to a knowledgeable friend tonight he also mentioned that the height should be adjusted by different washer thickness rather than bending the tab.
Graham
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Good morning,
Excellent information and feedback, thank you very much Ignacio and Graham.
I will remove all 3 carb covers and proceed with an in-depth inspection.
I may ask a mate with a lathe to turn proper fittings that would sit in place of the main jet holders, with provisions for connecting plastic tubes.
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Good evening,
It turned out that the flooding issue was simply caused by a leaky needle valve in the second carburettor.
I replaced all three with new ones and adjusted them to the same height in their respective covers as the previous two fuel-tight ones and the problem disappeared right away.