fuel starvation

Post by **Garrie** » Sat Jan 20, 2007 10:06 pm

I am hoping someone can help me with this; 2 door minor running Marina 1275 with SU carb etc from the same. petrol pump is electric as per Minor (and new). Car drives beautifully up to 80 ish (needle dances around a lot at this speed) and will maintain this for hours on light inclines and flat. Any larger hills and I get a loud, fast knocking from the engine area (not like the fast ticking of the fuel pump) and a loss of power and I have to throttle back to 50ish when he will pick up again and the knocking will stop. This can be repeated many times on a journey and can occur if I have an enthusiastic and prolonged take off from lights etc. It must be fuel flow related but the fuel pump is new and has great output, I have replaced the tank to pump pipe and am at a loss what to try next. It is very annoying when I am trying to blow off modern tin and run out of steam. Any thoughts gratefully received.

Post by **8009STEVE** » Sun Jan 21, 2007 6:01 am

Is the fuel tank vented?

Post by **picky** » Sun Jan 21, 2007 11:33 am

if you recreate this issue by driving up a hill, and as soon as it starts happening turn off the ignition and stop. then check if there is any fuel in the fuel resevoir. if not then you can confirm that this is fuel flow related as you suspected. It might be that the carb needle/ other carb settings work for flat inclines but when the engine has to work harder eg. when going up a hill or accelerating quickly the carb is not letting enough fuel through. does the problem still occour when you have the choke fully on??

hope this helps you out...

Post by **ricombi** » Sun Jan 21, 2007 3:04 pm

I've dealt with a similar problem on a Series 2A Land Rover, right down to the loud knocking. The mechanical pump had been by-passed on the engine and it was being fed straight through an electric pump. Everytime you throttled hard or went up a steep hill there was a loud knocking and the engine would lose power till you backed off.

Everything was tried, and as picky says when stopped and checked the float bowl empty. The whole issue was actually rectified by fitting a higher pressure fuel pump, and now it runs with no issues at all.

I would look at the needles first, as picky says, because its cheaper, but if that doesn't work I'd consider some form of high pressure pump, such as a Facet road pump. You may need to fit a regulator to this too, between the pump and carb if you get this far.

Hope this can help you.

Post by **bmcecosse** » Sun Jan 21, 2007 3:59 pm

Could be air flow - limited by the air cleaner. Try it with air cleaner completely removed. Could also be ignition timing - or just weak mixture because the it's not the best needle for the job. Could also be exahsut system creating high back pressure - is it large bore and free-flowing ? And yes - it could be fuel flow - but if it's a new pump it should be ok. Test it by pumping into a gallon can and see how long it takes to fill the can. Then work that back to equivalent mpg figure. ie If it takes 5 minutes to fill the can - that's 12 gallons per hour. If you were going at steady 60 mph for that hour - - that would be 5 mpg!! If you had been doing 90 mph - it would be 7.5 mpg !!Obviously excessive - but you see the point i'm sure. Provided it can fill the can in under 10 minutes - it should supply all the fuel you can reasonably use.