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A Trouble Shared is a Trouble Halved


Bill Davies

An old maxim but how true.

I have as some of you are more aware than others fitted this past winter a Moto Guzzi 1064cc engine to replace a worn 2CV unit. Well the engineering was a doddle .... ha ha yes after some wrong roads the mission was complete .... OR was it.

On advice from some of our fellow Forumisti I purchased the ignition from Silent is going to be a panacea or along these lines. Now I have a friend in Edinburgh who spends his time instead of having a coffee, in a ritual strip and rebuild of his Dellortos while we set them up and he arrives in time to drink them, his training in the Army has him stripping the aforesaid in the dark. He has been fixing his carbs for some three years.

Now in such hallowed company how could I fail !!!

Well spectacularly if truth be told, the bugger would not start then fuel started to pour out of the carbs, a total nightmare. So I assumes that the best route is to "phone a friend" I calls up the well known supplier of Dellorto spares and they advise me that a smaller float set up is the answer, £90 lighter we press Start again and guess what fuel all over the floor.

Back to the start with the original float valves and behold the carbs are not leaking, so I have a set of small float valves spare now.

I am still not happy with the Silent Hektik set up so enter a discussion with their UK workshop and reset the parameters. Things are looking up, the engine is running a lot better and does not give me any real concern. So I go ahead and books me and trike onto the ferries for the Outer Hebrides Trip. All goes well and some 150 miles into the trip the engine has a wobbly and spits out the dummy. This is an engine crankcase problem and more of that later. Now it is a policy of our group when on a run that when one fills up we all do. I seem to be taking on a lot more than my fellow travellers!!! To this end I start to record my fuel consumption and when home I divi it up and find my consumption is 34mpg NOT GOOD.

Now I have a phone call to my Edinburgh pal to share my troubles with, it is a pity that over the phone one cannot share a G&T, or maybe a good thing I could get to like calling him. I have definitely got "over fuelling" and the said stuff is pouring out the bell mouths.

Wind back a bit .... . In order to create a fire OR explosion there are three requirements, fuel, air(oxygen) and a source of ignition. If any of the three are missing then it will not happen, trust me, I have been there. Too little fuel no bang, too much fuel no bang. No oxygen no bang. No ignition no bang. Now there are three main fuels used in engines, paraffin, petrol and Diesel, and they follow the same general rules of combustion. Paraffin is used in a refined case to power our jet liners, but take a cup of paraffin and throw a lit match into it and you DO NOT get combustion. The only way to start a fire is to adopt a wick to allow a flame to be formed. You can try this at home. Diesel follows the same lines as paraffin and again you can try this at home.

Petrol however is totally different DO NOT TRY THIS AT HOME. Petrol as a liquid is fairly stable it is the vapour that is extremely unstable and that is what we adopt in a manner that we hope is under control to power our cars. Please note that every year people are burned or worse when trying to light the family B&B using Petrol as a booster. The liquid does not burn but the vapour is lethal.

As has been said on the Forum the engine does not need to know how the fuel mix is supplied or how the sparks are generated, but if they are in the correct mix and at the appropriate time then we have Ignition.

We are now up to date with my problem so I phones my pal in Edinburgh and says I "I have got over fuelling" and in between our exchange we devise a Plan. Dump the excess fuel. But how?

Now like many of you I have a filter, lift pump and regulator to bring the fuel to the engine, the pump is working fine, I can hear it ticking away, so I allows it a few seconds and turn the key, well it starts but the right cylinder is not firing, too much fuel and it’s also dripping out the venturi. Some thing is causing the carbs to flood. My start procedure is totally wrong.

Now like many of you fine chaps I have fitted a Facet pump and regulator to control the fuel supply. Fine. But these pumps are Positive Displacement pumps that feed a set amount forward each pulse, as the fuel passes the regulator it controls the forward pressure .... OR does it. While the pressure is being controlled, the pump is merrily pushing more fuel forward whither it is required or not or whither the pressure is being exceeded, and this causes the fuel to push past the float valve. Yes the pressure is starting to rise as each pulse is squeezed into the pipe, and the net result is that the engine starts to OVERFUEL, combustion is not efficient, or may not be happening. In my case the exhaust pipe could be firmly gripped on the right hand cylinder, but not on the left hand one.

A search on Ebay reveal that the standard Low pressure system does not have a relief set up. However if you research the lift pumps used in Injected engines then their regulators have a dump port, in, out and return. This was the conclusion of our discussions, so I volunteered to be the trialist. My set up is a filter, pump, regulator all at the rear of the car with a 6mm fuel line to the carbs, the supply is split using a Tee at the front with some 300mm of pipe supplying each carb.

The plan was to interrupt the supply pipe with a Tee, and connect the 90 degree leg to the tank. This was mocked up with a fuel can and the result was a completely different engine, it started, accelerated and did what was expected.

Next morning the plot was done in a professional manner, properly connected at the engine end, and at the tank end a copper bend was silver soldered into the filler pipe. The pipes etc were securely fitted to the car and made ready for the off.

Now when in the past I switched ON and waited for the system to pressurise, I now turned the choke on, then turned the ignition and the engine started. I was able to move off with part choke, in the past I had to warm the engine. The engine stated to pull as expected and was very responsive. A quick blast around Ayr and down by Mr Trump’s new golf course, proved that with the "Dump" fitted there was NO reduction in engine performance, and that power was there when asked for, it now has plenty of grunt when asked for at all speeds. Back home and the engine cooled down I removed the plugs and found them to be clean and all old soot removed. The engine now ticks over at 1000rpm against the previous 2000rpm, a real challenge when selecting first in a non sincro box. Oh bye the bye do not grip my exhausts now or you’ll be in the Burns Unit with sore paws.

The moral of this story is "Ask a Friend" he may not have the answer but may inadvertently open a door during discussion or give you a push in the right direction. Thanks Tom.

Now I would encourage all folk who are experiencing fuelling problems to look in all the doorways as the "Poor Carb" is not always to blame. I hope that through this dissertation I have been able to convey how I resolved the problem. Having reported the results to Tom he has now ordered the parts to modify his car’s set up. As his pump/regulator/filter are at the front he is going to do a "local loop" in the bonnet to check the result, thus saving a line to the tank and the connection. We await his results.

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