paulm84944

i bought a '70 911T non-running. it had been sitting for years but i was told that it ran but backfired when put away. after points and clean gas i got it to start but when cold it backfired terribly (out the carbs). i sent the carbs to carbs etc. to be rebuilt (weber 40). after installing them i still have the same lightshow when i start the car. i'd like to check my timing but can't keep the car running enough to use a light. after it warms up it runs smoother but definately not right. if i floor it in every gear i can drive it around but that doesn't work in the city. it really seems to smooth out at full throttle. any ideas what i should do next would be greatly appreciated.

Porschephanatic

When you stated "clean gas", did you drain the tank and flush the lines? I hate the thought of old varnish in those new carbs! Usually backfiring up through the carbs is caused by a lean condition, or is the exhaust black and smokey,indicitive of a rich condition? Did you gap and replace spark plugs? I resurected an old MGB for my uncle, and condensation had corroded the spark plugs far beyond usable condition. Hope this helps. Please keep us posted. I love to see old machinery brought back to life!

paulm84944

i drained the tank by syphoning and after new premium added i disconnected fuel lines at carbs and let electric fuel pump run for 1 quart. that's what makes me think it might be a sluggish fuel pump. it took a while to run a quart of fuel. what is the normal flow rate for an electric fuel pump for '70? would a slow fuel pump produce this result? also, i did install new plugs, rotor, cap and wires. thanks!!! --Paul

Porschephanatic

Your car probably came equipped w/ a Hardi type electric fuel pump. There is a plug in the valve housing of the pump that allows you to access the filter. This may need to be cleaned as well. I'm sorry, but I don't know off-hand the flow rate or @ what pressure to test, but after you clean your pump filter you should see a dramatic improvement. Hope this helps.

paulm84944

i saw a picture of this hardi fuel pump in the haynes manual but i don't think that's the pump on my vehicle. i'm sure that's the pump it once had but now there's a different looking one that's zip tied to the back side of the front axle bar. i just came in from laying on the garage floor under the car and didn't like what i saw. i do believe that it's starving for fuel because if i pump the accelerator it stays running but if i let it run at any even rpm it backfires and stalls. i'm assuming that the accelerator pumps on the carbs are supplying the carbs with enough pumped fuel to keep running but there's not enough there when not pumping the gas pedal. when the weather here gets a little nicer i'll get it up on blocks high enough to install a different pump and see what that brings. i think it's displaying all of the symptoms of a low fuel condition. do any of you guys have any other thought on this? thanks--paul

Porschephanatic

Paul, you probably already know this, but I didn't. I read another post recently warning of too much fuel pressure from aftermarket pumps not designed for your car,"or your carbs will look like fountains!" I wish I knew who to give credit to. Good luck. <img border="0" alt="[typing]" title="" src="graemlins/yltype.gif" />

Groovilator

Paul ;
Whenever a car sits for a long period of time it would be prudent to not only flush the gas tank,but steam it out and seal it.Hope this helps.

Groovilator

Paul ;
Whenever a car sits for a long period of time it would be prudent to not only flush the gas tank,but steam it out and seal it.Hope this helps.

lateapex911

I see two major clues here: 1-the problem existed previous to your ownership, and 2, it seems to run on full throttle and higher RPMs.

So, as more RPMs equate to more fuel, I tend to doubt that the fuel pump is the villian. But clean and replace all filters anyway.

I would concentrate my efforts on the carb. Check the idle and low circuits. (I really don't know my Webers like I should)... but I would start by doing some jetting work. Read your plugs as you go, and you should see some improvement. JMHO&gt;&gt;&gt;

Good luck! Let us know how it works out!