Apologies Dear reader - I have reworked this entry to try and remove the repetition and improve clarity.
Well having sorted the pedal box and now refitted the dash I was able to try starting the motor again to see the effect of the float level alterations;
The news wasn't good! The car refused to start, at first I suspected ignition failure but this was quickly excluded and I found that the car started perfectly if the carb intakes were treated to a squirt of Bradex Easy Start! This pretty much excluded timing or ignition faults and pointed the finger squarely at fuel supply. Fuel was visible moving along the carb feed tubes, I did add more to the tank as levels were low and the gauge was registering below. I had suspected that the pump might be struggling, but adding more fuel changed nothing. There was nothing for it; I had to revisit the fuel levels in the carbs. I think it will help if I refer to the adjustments that can be made as "clearances"
Float clearance- measured between carburettor top (with gasket) and float top is the gap above the float when the needle valve has shut- smaller this clearance the higher the float (and thus the fuel level the bowl) before the valve shuts.
Fuel clearance- the distance above the fuel to a fixed point in the carb, namely the top of the internal pedestal. The Lower this clearance measurement, the higher is the fuel in the bowl.
To check adjustment I monitored the fuel clearance values using the floats-out method. I removed the choke connections for simplicity and I found that if the fuel inlet pipes are disconnected at the carb after the bowls have been pressurised, pressure is cancelled; excess fuel can be collected in a small container for re-use and and there is very little extra fuel to leak into the bowl from the needle valve as the carb tops are removed. Cumbersome and awkward but it was do-able. Doing the test this way I was much more confident in the results and discovered that the fuel clearances were higher than expected; 30.2 mm in the front carb was as I thought, but that in the rear carb was even higher at 32.8mm, meaning that fuel levels in the bowl were much too low.
Floats were still set at the 15mm clearance value where I had set them when last adjusted. This setting gives much lower fuel than expected and I suspect means that the floats have themselves been bent so that float level no longer correlates even approximately with fuel depth. These low fuel levels appear to be too low to allow the motor to start so I had no choice but to re-visit the adjustment.
The float clearance is set by bending the tab- bending it away from the arm and towards the needle will hold the arm off the valve, depressing the float. This means the valve will close when the float is in a lower position and so increases the measured float clearance. This also means that fuel in the bowl can now close the valve at a lower level so less fuel will be in the bowl; in other words fuel clearance will be increased. Bending the tab towards the needle increases float clearance and increases fuel clearance; it lowers fuel levels and weakens the mixture. Conversely bending the tab away from the needle allows the float to ride higher before the valve is shut- this will mean higher fuel levels are needed before the valve is shut off. Bending the tab away from the needle will decrease float clearance and decrease fuel clearance fuel levels will rise and richen the mixture. BUT the tab can only function in this direction if the tab is the first thing to contact the valve. You cannot raise the float (ie decrease float setting) for ever using the tab. When the tab is bent so far towards the float arm that the arm itself contacts the needle before the tab then further tab adjustment will have no effect. It seems that this will give a minimum float clearance obtainable of around 12mm and in fact applied to both of my carbs. The picture below illustrates the problem as the valve is now closed by the float arm and the tab is no longer making contact.
I adjusted the tabs with a small pair of snipe-nosed pliers to decrease float clearance (raise float) by a few mm to around 12mm with the tabs just in contact with the valve body, and repeated the tests. Very fiddly because the fuel hoses have to be disconnected and reconnected in each check. I was able to obtain higher fuel levels (floats out) of 27.2 mm in the front carb and 26.3 mm in the rear. Float settings that gave this were around 12 mm, again supporting the idea that the float arms may have been bent. This was close enough to the desired fuel level to prompt me to run a starting test and now the motor fired up easily. It tended to race because the new throttle cable wasn't properly adjusted (it needed to be screwed in to the bulkhead to place the adjustment range within the adjustment possibilities of the cam-cover screw adjuster but this was easily done). The motor then ran reasonably well (bearing in mind that it has not been adjusted for dynamic timing).
However, I still have the problem of fuel puddling in the carb throats which I had hoped was solved! I did get a short video of this happening- I should say that I know the motor sounds rough in this video- but its not been set up yet for dynamic timing.-Adjusting the timing may in itself help improve the situation.
This was worse than before! Obviously very disappointing! In the rear carb at least it seems that fuel is now streaming from the acceleration jet as well! This looks like a stuck float in this carb but I need to investigate a bit more.
Update:
Well I have to confess I am totally baffled by these carbs! I remeasured the fuel clearances and found that both were now higher than I had expected from my determinations above. I repeated the tests to get some consistency and both were coming out at 30mm rather than the 26-27mm I had obtained before. I think the difference is due to improved technique (disconnecting the fuel hose before raising the carb lid). This is still too low but its about the maximum adjustment possible on the float arm and I can't decrease float clearance to raise fuel levels (decrease fuel clearance) any further. I checked with Eurocarb that their recommended replacement 170 needle does not require an alteration in float setting. The trouble is my findings have now led me to two mutually incompatible conclusions!
My first problem is that setting the float at 15mm gives me a fuel clearance of 32mm and not the expected 27mm; at this level fuel depth in the bowl is too low for the motor even to run! Resetting them to 12mm clearance (the minimum I can obtain) decreases the fuel clearance to around 30.5 mm. This is still way off the 27mm desired, but it does mean that the fuel depth is raised by 1-2 mm, and at this point the motor will start. I.e. this finding implies that my fuel levels are too low and I have insufficient adjustment in the float to reach the desired fuel clearance value of 27mm.
Secondly, if fuel levels are too low then fuel overflow should not be a problem. In my case turning on the fuel pump and filling the carb bowls is fine- no overflow is evident. However, this brings me to my second problem in that if the motor is actually started and run for a short while, then fuel overflow soon becomes obvious! This implies that fuel levels are now too high!
It doesn't seem likely to me that I could have a fuel levels in both carbs which are both too low and too high at the same time! I've thought about it a lot and maybe the following features might be involved:
1. Perhaps the floats are very bent- disconnecting the expected correlation between float and fuel clearances- although they don't look that way.
2. Perhaps the floats are tending to stick or jam when the engine is running (and therefore vibrating) leading to leakage and overflow when running.
3. Perhaps float buoyancy has been altered such that they don't rise as fast and so do not shut off the needle valve as quickly as they should when the motor is running and rapid valve operation is required. However, if the floats are too heavy then they should float lower in the fuel and fuel levels should be higher at any given float setting not lower.
4. One possibility I have had at the back of my mind (and have been trying to ignore) is that the inlet valves might be leaking allowing gas pressure to pressurise the carb and force fuel from the float chamber through the acceleration pump- although I suspect this wouldn't explain overflow through the venturi.*
5. Ignition timing wrong (and it is!) Trouble is I don't want to set it up with the strobe since I don't want to run it with fuel leaking out!
6. Poor battery failing to run fuel pump to correct pressure unless motor running and alternator supplementing power. This could lead to low fuel levels in my test but higher when running... Seems like a long shot but I will charge it up in case.
I'm not altogether sure if 4 or 5 could be an explanation, and as I'm not anxious to strip the head off again (with its associated gasket costs), I think that at this stage, and given the possibility of bent float arms, I have to try a float swap. The 8.5 g floats aren't available any more from Eurocarb who only stock 7g. Further they are expensive at £42 for each float assembly (plus postage). I was able to find 8.5g floats and save about £20 on the pair by shopping around. I will fit these and re-test all clearance values. Its probably also a good idea to do a compression test and look for leaking valves... possibly even maybe screw up my courage and set the timing...?
* I should add that I did eventually check compression values. Gratifyingly they were all very similar at 175, 175, 172 and 170psi. This similarity means I can probably discard this outside possibility... thank goodness!!
Well having sorted the pedal box and now refitted the dash I was able to try starting the motor again to see the effect of the float level alterations;
The news wasn't good! The car refused to start, at first I suspected ignition failure but this was quickly excluded and I found that the car started perfectly if the carb intakes were treated to a squirt of Bradex Easy Start! This pretty much excluded timing or ignition faults and pointed the finger squarely at fuel supply. Fuel was visible moving along the carb feed tubes, I did add more to the tank as levels were low and the gauge was registering below. I had suspected that the pump might be struggling, but adding more fuel changed nothing. There was nothing for it; I had to revisit the fuel levels in the carbs. I think it will help if I refer to the adjustments that can be made as "clearances"
Float clearance- measured between carburettor top (with gasket) and float top is the gap above the float when the needle valve has shut- smaller this clearance the higher the float (and thus the fuel level the bowl) before the valve shuts.
Fuel clearance- the distance above the fuel to a fixed point in the carb, namely the top of the internal pedestal. The Lower this clearance measurement, the higher is the fuel in the bowl.
To check adjustment I monitored the fuel clearance values using the floats-out method. I removed the choke connections for simplicity and I found that if the fuel inlet pipes are disconnected at the carb after the bowls have been pressurised, pressure is cancelled; excess fuel can be collected in a small container for re-use and and there is very little extra fuel to leak into the bowl from the needle valve as the carb tops are removed. Cumbersome and awkward but it was do-able. Doing the test this way I was much more confident in the results and discovered that the fuel clearances were higher than expected; 30.2 mm in the front carb was as I thought, but that in the rear carb was even higher at 32.8mm, meaning that fuel levels in the bowl were much too low.
 |
| Testing rear carb fuel level via floats-out method. |
Floats were still set at the 15mm clearance value where I had set them when last adjusted. This setting gives much lower fuel than expected and I suspect means that the floats have themselves been bent so that float level no longer correlates even approximately with fuel depth. These low fuel levels appear to be too low to allow the motor to start so I had no choice but to re-visit the adjustment.
The float clearance is set by bending the tab- bending it away from the arm and towards the needle will hold the arm off the valve, depressing the float. This means the valve will close when the float is in a lower position and so increases the measured float clearance. This also means that fuel in the bowl can now close the valve at a lower level so less fuel will be in the bowl; in other words fuel clearance will be increased. Bending the tab towards the needle increases float clearance and increases fuel clearance; it lowers fuel levels and weakens the mixture. Conversely bending the tab away from the needle allows the float to ride higher before the valve is shut- this will mean higher fuel levels are needed before the valve is shut off. Bending the tab away from the needle will decrease float clearance and decrease fuel clearance fuel levels will rise and richen the mixture. BUT the tab can only function in this direction if the tab is the first thing to contact the valve. You cannot raise the float (ie decrease float setting) for ever using the tab. When the tab is bent so far towards the float arm that the arm itself contacts the needle before the tab then further tab adjustment will have no effect. It seems that this will give a minimum float clearance obtainable of around 12mm and in fact applied to both of my carbs. The picture below illustrates the problem as the valve is now closed by the float arm and the tab is no longer making contact.
 |
| Non adjustable float shown with the carb top in the near vertical position in which float height is adjusted. Float arm hinge uppermost, float arm to right. Forked adjustment tab below arm engaged with the narrow spring loaded section of the needle protruding from the needle shoulder. The needle is seated by the float arm itself and the tab is not controlling float setting. This means that 12mm is the minimum float setting obtainable. |
However, I still have the problem of fuel puddling in the carb throats which I had hoped was solved! I did get a short video of this happening- I should say that I know the motor sounds rough in this video- but its not been set up yet for dynamic timing.-Adjusting the timing may in itself help improve the situation.
This was worse than before! Obviously very disappointing! In the rear carb at least it seems that fuel is now streaming from the acceleration jet as well! This looks like a stuck float in this carb but I need to investigate a bit more.
Update:
Well I have to confess I am totally baffled by these carbs! I remeasured the fuel clearances and found that both were now higher than I had expected from my determinations above. I repeated the tests to get some consistency and both were coming out at 30mm rather than the 26-27mm I had obtained before. I think the difference is due to improved technique (disconnecting the fuel hose before raising the carb lid). This is still too low but its about the maximum adjustment possible on the float arm and I can't decrease float clearance to raise fuel levels (decrease fuel clearance) any further. I checked with Eurocarb that their recommended replacement 170 needle does not require an alteration in float setting. The trouble is my findings have now led me to two mutually incompatible conclusions!
My first problem is that setting the float at 15mm gives me a fuel clearance of 32mm and not the expected 27mm; at this level fuel depth in the bowl is too low for the motor even to run! Resetting them to 12mm clearance (the minimum I can obtain) decreases the fuel clearance to around 30.5 mm. This is still way off the 27mm desired, but it does mean that the fuel depth is raised by 1-2 mm, and at this point the motor will start. I.e. this finding implies that my fuel levels are too low and I have insufficient adjustment in the float to reach the desired fuel clearance value of 27mm.
Secondly, if fuel levels are too low then fuel overflow should not be a problem. In my case turning on the fuel pump and filling the carb bowls is fine- no overflow is evident. However, this brings me to my second problem in that if the motor is actually started and run for a short while, then fuel overflow soon becomes obvious! This implies that fuel levels are now too high!
It doesn't seem likely to me that I could have a fuel levels in both carbs which are both too low and too high at the same time! I've thought about it a lot and maybe the following features might be involved:
1. Perhaps the floats are very bent- disconnecting the expected correlation between float and fuel clearances- although they don't look that way.
2. Perhaps the floats are tending to stick or jam when the engine is running (and therefore vibrating) leading to leakage and overflow when running.
3. Perhaps float buoyancy has been altered such that they don't rise as fast and so do not shut off the needle valve as quickly as they should when the motor is running and rapid valve operation is required. However, if the floats are too heavy then they should float lower in the fuel and fuel levels should be higher at any given float setting not lower.
4. One possibility I have had at the back of my mind (and have been trying to ignore) is that the inlet valves might be leaking allowing gas pressure to pressurise the carb and force fuel from the float chamber through the acceleration pump- although I suspect this wouldn't explain overflow through the venturi.*
5. Ignition timing wrong (and it is!) Trouble is I don't want to set it up with the strobe since I don't want to run it with fuel leaking out!
6. Poor battery failing to run fuel pump to correct pressure unless motor running and alternator supplementing power. This could lead to low fuel levels in my test but higher when running... Seems like a long shot but I will charge it up in case.
I'm not altogether sure if 4 or 5 could be an explanation, and as I'm not anxious to strip the head off again (with its associated gasket costs), I think that at this stage, and given the possibility of bent float arms, I have to try a float swap. The 8.5 g floats aren't available any more from Eurocarb who only stock 7g. Further they are expensive at £42 for each float assembly (plus postage). I was able to find 8.5g floats and save about £20 on the pair by shopping around. I will fit these and re-test all clearance values. Its probably also a good idea to do a compression test and look for leaking valves... possibly even maybe screw up my courage and set the timing...?
* I should add that I did eventually check compression values. Gratifyingly they were all very similar at 175, 175, 172 and 170psi. This similarity means I can probably discard this outside possibility... thank goodness!!
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