Carburettors continued light at the end of the tunnel?

Greetings to my faithful reader! I hope you haven't lost interest during my latest lull in activity. I am still awaiting my new floats. Motorsporttools-uk (trading through Ebay) may be cheaper, but they are no-where near as prompt in dispatch as Eurocarb. They took 4 days to mail the floats and another 2 to arrive! Great if you don't mind waiting- but its hard to wait if you are stuck like this....

Its been bloomin' cold here, and although I have forced myself out to the car, it wasn't pleasant. To be frank, the weather may even have been the source of some of my problems! Well anyway, if you recall I was getting a series of non-sensical observations suggesting that my fuel was both too high and too low at the same time! I'm now pretty sure that a good part of this was down to my battery: this was clearly on the way out and making it supply juice in below zero temperatures was obviously not a good idea. I had taken the slowing of the pump ticks to mean that the fuel had reached pressure... whereas in reality it probably owed more to battery failure and fuel bowls may not have been filling properly. Recharging improved matters no end and both carbs immediately pee'd copious fuel out of the trumpets as soon as I energised the ignition- clearly what had previously appeared as too low a fuel level setting was actually very high! However, resetting the floats on the front carb to 15mm then gave me far too low a level again. It seemed I could get levels of 25mm (overflow) or 32mm but nothing really in between. Now the battery has been eliminated as a cause of this variation I had to look elsewhere.

The web guides suggest that in order to check fuel levels (floats out) you should connect the fuel line, energise the system and wait 30 sec for the float bowls to fill. I can say categorically that this doesn't work- certainly not if you are disconnecting the fuel hoses as I have now started to do, because each re-connection introduces air locks into the hoses and these do affect the carb fuel levels even though they probably should not. Its necessary to loosen the fuel pipe-to-carb unions to bleed the air out and bring fuel to the carbs before they will fill properly. Luckily for me the outer casing of my fuel hoses has already fallen off (!) eventually I will recover with "Roundit". However at the moment I can at least monitor fuel flow and airlocks easily. Its probably also a good idea to crank (or preferably run) the motor for a little while if you can before resting it (motor stopped, fuel pump on) for 10-20 seconds to let the levels settle. This will ensure that you get consistent values at each test. However the fact remained that I was still getting fuel levels about 30 mm at a 15mm float setting instead of the expected 27mm.

It was at this point that I happened to notice the droop down distance of the floats seemed to have become rather large. I had become rather obsessed with achieving an exact 15 mm  float setting and hadn't appreciated that as I changed this by a variety of tab and arm bending steps I was also altering the float droop. This is controlled by the stop tab at the rear of the float arm yoke. Droop had crept up to around 35mm and in a man of my age excessive droop is never something to be welcomed! To be fair I hadn't really thought that this setting could have any bearing on fuel level and so had paid it little attention. Its tricky to adjust this tab but I managed to bend it inwards and set the droop height back to 25mm as per Mr Hammill's advice. Check floats again, reassemble, retest...  Hey presto fuel level now  27.3 mm with floats set at 14.9mm!!! Joy and rapture!! I have no idea how or why the droop distance affects fuel level but my experience here was that it does. So, front carb now behaving!! ****
***Sadly this didnt stand the test of time and in subsequent measurements it reverted to 30.9mm again. I have no idea why, I have even changed the floats and still get the same fuel level. Currently I'm thinking that this must result from performing the determination on a slope. What ever the true fuel level, I am now confident that all floats are set correctly and this level of fuel is sufficient for running.
 I have added a summary of how I would do this floats out test in future to my original post on float level adjustment. Its chronologically out of place but might assist anyone who is just looking for a method and doesn't want to go through all of my struggles.

Float yoke set. Droop adjustment tab at rear, with forked float adjustment tab in front.

... Joy sadly short lived as I now set about resetting the rear carb. It too had an excessive droop distance and so I set the floats back to as close to 15mm as I could make them and the droop to 25mm. I re-pressurised the fuel, but the fuel level was still low at 30mm despite my best efforts.  However on the credit side, with both carbs set up as specified, the motor did start and actually ran rather well after it had settled down. I was able to run it up to temp for the first time and observed a charging voltage, good oil pressure and eventually a water temp reading on the gauge. The thermostat opened and I got water circulation through the heater- thankfully without leakage from my newly repaired hoses although I was unable to confirm whether the otter switch works or not. Furthermore of course, I have no idea how the motor would behave under load but it wasn't all bad news. I'm pleased it was running so well.

My next step was to set the timing with the strobe. Set statically I had achieved 8 deg btdc when tested by strobe. Using the strobe I reset this to 10 deg btdc at idle speed. I had hoped that this would improve running and possibly the fuel drippage problem but sadly this was not the case. If anything the motor runs rougher now than when set at 8 deg btdc. So matters are improved, but I would be deceiving you if I said that the fuel-in-the-trumpet problem was now solved, its not! Although the front carb (apparently with the correct fuel level) looks pretty much cured, there is still fuel visible in both barrels of the rear carburettor suggesting that this carb at least is running very rich.  I think the timing change has shown up these defects in carburation so I need to re-address this problem. Given my progress to date, I may be going around this loop for a while!

Tim Engel does mention that although the enrichment devices fail so rarely that there is no description of them in any book or on any site I can find, they can fail occasionally and when they do they can allow excess fuel through. This failure he states is usually down to the "washer"... sadly there is no washer listed on the Dellorto parts diagram in this area, but I believe this is because its usually supplied as part of the choke piston (fitted into the bottom a little like the washer in the piston of a plumbing ballcock valve) so it might be necessary to renew the whole piston.

In order to test the cause of this difference between carbs I swapped carburettor lids/float assemblies. The front carb still ran well but the rear still flooded. I therefore conclude that the flooding problem is not related to float setting or enrichment device, but must be determined by the lower part of the carb.

Currently I am wondering if the anti reversion spacers are fitted correctly (cone towards engine). These spacers reduce backflow of gases from the manifold and such a backflow might push fuel through the overflows and acceleration pump. My blog shows that I had fitted them correctly but can I be sure?

The second thought that occurs to me is to suspect the acceleration pumps themselves. Mr Hammill advised leaving them well alone- so I have (!) but this does assume that they have been set up correctly in the past and I have no guarantee of this. Since the motor has had a very chequered history the pumps may well  been "tweaked" to offset some other problem in the past. Since the motor has now been rebuilt and the carbs cleaned and rebuilt, then any such tweaks would now be out of date.

In order to check these points I had to remove the carbs again. Immediately this showed that there was no problem with the spacers, these were indeed correctly installed with the cones pointing in towards the motor.

Anti-reversion spacers- fitted the right way round!

 When I took the spacers off it was clear that cylinders 3 and 4 (rear) had been running rich with a deposit of soot around the manifold edges. This is to be exected given the excess fuel in these two barrels but it again indicated that I needed to sort out the carburettors, and given that fuel levels are definitely not too high (if anything maybe a little low), the two items that could be responsible for over richness: To my mind the front running candidates are the enrichment device and acceleration pump.

Inlet manifold cylinders 3 and 2 - note excess sootiness around inlet for cylinder 3 (lhs) compared with that for cylinder 2 (rhs).

I had difficulty in getting my head around the operation of both of these and  I have therefore written my own "take" on their operation, servicing and adjustment which I will move to a second post. This at last enabled me to sort out the excess fuel in the trumpets.