Author Topic: Carburettor synchronizer?  (Read 16942 times)

TTM

  • Full Member
  • ***
  • Posts: 184
    • View Profile
Carburettor synchronizer?
« Reply #15 on: December 14, 2016, 18:28:00 »
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.

TTM

  • Full Member
  • ***
  • Posts: 184
    • View Profile
Carburettor synchronizer?
« Reply #16 on: January 15, 2017, 14:28:36 »
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.

TTM

  • Full Member
  • ***
  • Posts: 184
    • View Profile
Carburettor synchronizer?
« Reply #17 on: May 14, 2017, 14:59:05 »
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?

TTM

  • Full Member
  • ***
  • Posts: 184
    • View Profile
Carburettor synchronizer?
« Reply #18 on: June 18, 2017, 16:24:20 »
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.

Flyinghorse

  • Sr. Member
  • ****
  • Posts: 349
    • View Profile
Carburettor synchronizer?
« Reply #19 on: June 19, 2017, 16:58:07 »
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

TTM

  • Full Member
  • ***
  • Posts: 184
    • View Profile
Carburettor synchronizer?
« Reply #20 on: June 19, 2017, 19:44:31 »
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.

Flyinghorse

  • Sr. Member
  • ****
  • Posts: 349
    • View Profile
Carburettor synchronizer?
« Reply #21 on: June 19, 2017, 23:23:24 »
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

TTM

  • Full Member
  • ***
  • Posts: 184
    • View Profile
Carburettor synchronizer?
« Reply #22 on: June 22, 2017, 09:44:31 »
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.

Muffin

  • Newbie
  • *
  • Posts: 15
    • View Profile
Carburettor synchronizer?
« Reply #23 on: June 22, 2017, 10:05:01 »
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.

TTM

  • Full Member
  • ***
  • Posts: 184
    • View Profile
Carburettor synchronizer?
« Reply #24 on: June 22, 2017, 22:50:22 »
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.

Muffin

  • Newbie
  • *
  • Posts: 15
    • View Profile
Carburettor synchronizer?
« Reply #25 on: June 23, 2017, 13:16:21 »
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.

Muffin

  • Newbie
  • *
  • Posts: 15
    • View Profile
Carburettor synchronizer?
« Reply #26 on: June 23, 2017, 13:33:12 »
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.

TTM

  • Full Member
  • ***
  • Posts: 184
    • View Profile
Carburettor synchronizer?
« Reply #27 on: June 23, 2017, 14:28:59 »
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?

TTM

  • Full Member
  • ***
  • Posts: 184
    • View Profile
Carburettor synchronizer?
« Reply #28 on: June 25, 2017, 15:06:26 »
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).

TTM

  • Full Member
  • ***
  • Posts: 184
    • View Profile
Re: Carburettor synchronizer?
« Reply #29 on: December 28, 2017, 10:08:45 »
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.