My 71 started bucking real bad on a weekend drive. I checked out all the ignition stuff, looked OK. Pulled the fuel filter and sure enough there was rust in the gas in the filter. Last fall i had leak in the top of gas tank repaired (welded). The guy who did the work said th rest of the tank looked clean and thought the tank had been taken care of by a P.O.

The filter had been in about year (8 thousand miles). I put a new filter and she seemed to run OK.

Note that I ran the car only occaisonally since the tank repair because I put her away for most of the winter (occaisonal drives when it was dry out).

I ran it maybe 300 miles total, but never ran all the gas out before a fill up.

I have a mechanic in town that I use sometimes who has owned three 240 Z's himself. He said the guy who fixed the tank likley filled it with water before he welded and it not be unusual to have some water left in there that may have caused some rust over the winter when it sat.

He recommended adding ISO gas drier.

I drove to town this week, put the additve in and topped her off. On the way back she started running like crap and eventualy I had to tow her back home.

MY mechanic said some rust probabaly got through the filter and into the carbs. I pulled the tops off the float chambers and looked around but im really not sure what i should be looking for.

Any suggestions?

Get yourself one of the clear aftermarket fuel filters. You'll immediately be able to see when there's any debris coming through and can replace the filter element on the side of the road if you have to.

Here is my guess: Either your filter got plugged again and or, on the float chamber there is a needle valve and a screen filter maybe these got plugged. Take an empty two liter bottle and put one of the hoses that comes from your fuel rail to the float bowl into the bottle. Crank the engine over and check for fuel flow. If you find a plug use compressed air and some carburator cleaner to clear it. You might also consider having the tank flushed.

Ed thanks for the advice on the screens inside the float chamber. I have an old set of SUs and looked at that screen on the tool bench. BUT any tips on how to pull it off the bowl that's on the car? I can pull the top of the chamber off and take it out that way, but I'm afraid I will bend the float itself trying to pry that bolt of that holds the screen. Also, does the bolt have to go back on with it's hole perfectly aligned to the fuel intake? it appears that's what those little brackets are for???

PS, I can now get the car to run, poorly, by starting it with the high idle screw turned in to run at about 2000 RPM. if you blip the throttle, it stumbles rather than accelrate smoothly. So anyway im getting gas, but not properly.

Another likely place for a clog is the pick-up tube in the gas tank. They have no screen and if rust flakes are in the tank they will be sucked right into the unscreened pickup tube. As Ed mentioned, have the tank completely flushed.

........ and if the tank is rusty inside, get the rust removed and have it sealed. Otherwise sooner or later you'll be dealing with this again.

deadflo, you don't have to take the bowl off to clean the filter, needle and seat. They are all in the top that you pulled off of the bowl. The float comes off of the top by pushing the rod that goes through both sides of the float bracket. That is the easy part. Make sure you don't bend the bracket Once you get the float off, use a 10mm or 12mm I can't remember what size exactly but you can remove the brass looking hexagon thing screwed into the bowl top. this is where your neede and seat is located. There is a tiny tiny tiny spring that keeps the needle from sticking in the seat. do not lose this spring. otherwise, use some carb cleanear and spray everything down. put it back together, make sure your carbs are tuned, (make sure they are both pulling the same amount of air and gas mixture). If you don't know how to do this, I strongly recoment that you go to www.ztherapy.com and buy their video. Now your car should run great.

The SU carbs are the heart of your Z. If they are not happy, you will not be happy. Don't worry, SU carbs are very easy to work on.

But.........

None of this is going to do you any good if you have rust in your gas tank.

mark, thanks for your assistance. I actually was able to remove the outside bolts on the float chambers to remove the little screens while still on the car. the screens actually looked completely clean, but i did spray some carb cleaner into the intake to clean out the needle assembly. But after I put the bolts back on and tried to start it i had gas leaking out of both float chambers. Not sure why at this point...

So I am getting gas to the carbs.Also I confirmed carbs were in balance two days ago before I tracked down the dirty gas filter.(before it really started bogging down)

But after I put the bolts back on and tried to start it i had gas leaking out of both float chambers. Not sure why at this point...

That's an indication that the check valves in the carb bowls are stuck in the open position. This can happen when debris gets in there.

Just in case it's not obvious, the idea is to maintain a constant level of fuel in the float bowls. When the level drops the float drops and the valve opens, allowing more fuel to come it. When the float rises it presses on the valve and cuts off the supply. If the valve sticks fuel will come out.

I think MikeW and I are talking about the same thing. He is calling it the check valve and I am calling it the needle and seat.

The needle I am refering to is not the needle you see when you lift up the damper. I may be calling it a needle and seat when in-fact it is the check valve. Either way, you should take the tops of your fuel bowl off and follow my instructions to remove the brass hexagon shaped thing in the fuel bowl top. Inside this is what Mike is saying can get stuck open. you will find that inside the hexagon thing there is a component with a rubber-like tip(needle). This tip comes to a sharp point. When your fuel float rises(when bowl is full) this tip pushes up into the (seat) to stop fuel flow.

It only takes a speck of dirt to clog this thing therefore leaving a gap for fuel to continue to pass into your bowl.

remember your fuel pump (if manual) is trying to pump fuel into the fuel bowls everytime the engine turns over.

This is a easy fix and your car will magically start running better.

You should also buy, or make a gasket to seal the top of your fuel bowl to your bowl. Gas spilling out right above red hot headers is not a good thing.

You should also buy, or make a gasket to seal the top of your fuel bowl to your bowl. Gas spilling out right above red hot headers is not a good thing.

According to Scott Bruning (the original ZTherapy guy) the factory solution of having the fuel go through the rubber hoses to the air cleaner isn't really any better. It ends up pooling at the back of the air cleaner and still drips onto the exhaust manifold.

I did use the term "check valve" just to differentiate from the needle inside the carb itself. I believe "needle valve" is actually correct. Another thing Scott recommended to fix this problem is called a "grosse jet" to replace the needle valve. I don't think they're available any more, however.

I do remeber the term "grosse jet" Mike. I think if you buy one of Scott's remanufactured carbs the use one instead of the needle valve.

By the way Mike, check your private message. I asked you a question regarding another topic.

Mark

Here is a picture I took a while back. It might help shed some light on the subject. Also you will notice a little cardboard "L" I use this to adjust my floats.