Stephen said:
Hello there I have some follow up questions regarding fuel consumption on my 1975 3500 auto, how much is held in reserve litres wise. My car smells very rich when running so I am going to get carbs set up, can they be set a little on the lean side or will this create other running problems . Is electronnic ignition a good move and is it simple to fit. Any tips on how to save on fuel will be helpful as I went onto reserve after 170 miles. I knew these cars used a lot of fuel but mine seams very greedy. Thank you Stephen.
Hello Stephen..
Just thought I would throw in my two cents worth - seeing as I've been using a 1974 3500 Auto as a daily driver for over a year now (my one and only car
)
When I first bought my car it had been sitting for many years in a garage up in Birmingham - so if your car has been sitting for a while, its likely the carbs will need a rebuild rather than just a tune.
My car used to run rich enough that motorcyclists who were behind me would pull up and complain that the fumes were making them cry (lol).. Fuel consumption was not something you could measure - and after putting in a gunson colourtune plug, it was clear that it was running very VERY rich (like black smoke that would hang in the air for an hour if you rev it rich.)
The No.1 carb (drivers side) was easily taught the value of petrol using a screw driver, but the other carb refused to listen.. Try as I might (even unwinding the screw fully) it was still rich..
It was only until I pulled them both off and began rebuilding them that I found out why. HIF6 carbs have an interesting choke mechanism, a cam with holes drilled in it that meters the fuel, at the far end is a rubber seal (which had perished) - this mean that this carb was essentially running at full choke all of the time.
I rebuild the carbs, put them back on, and then I could cruise around for ages without watching the fuel gauge following closely behind the tachometer..
Further improvements were made after I had new points fitted, I even bought a vintage snap-on dwell meter to make sure everything was perfect, then had a garage time it and balance the carbs..
I fitted an electronic ignition conversion kit from MGBD, fitted new springs and V8 BBV needles in place of the worn out BBG ones that were in there (jets were replaced when I rebuilt both carbs.) And somewhere along the line a cherrybomb ended up bolted to the back of it for MOT purposes :roll:
My engine is not original to my car (its a later goldseal engine) - you can tell this because its gold colour :wink: - and I use NGK BP5HS plugs opened up to 0.9mm (check your heads if they take short or long reach plugs) a scribe with a 90 degree tip will easily let you check this..
My current fuel economy (in London morning rush hour traffic) is 12.41MPG if you are careful, and 9.87MPG if you like to cane it along the A406 in 1st gear doing 60Mph :shock: (so not much in it really.)
I should mention that these figures were taken after my mechanic hooked the car up to a gas analyser and concluded that it was running lean - he then proceeded to ask me to richen the carbs by half a turn several times, until the HC's were at about 200 and CO was 4.87 or so.. It gave it more Oomph, and it still doesn't smell like petrol.. BUT I'm sure it was more economical before - even though an economical V8 is an oxymoron..
I will report back when I have done some more motorway cruising..
However, I drove all the way to York from London and used no more than half a tank or so a few months back.. Didn't calculate the MPG, though it was quite late in the evening, and I never dropped below 60~70Mph..
Hope this helps..
Note: The reserve tap seal might be leaking by now (this gave my car a slight petrol smell) - my reserve tap is in the engine bay at the firewall, and I saw it dripping fuel every now and then - so I changed it.. Changing it is no easy feat - best to make sure the tank is almost empty before attempting it! Otherwise it will gush out like a fountain.. Fortunately for me I have small hands
- so I got it apart easily and fitted the new viton seal from MGBD..