Sputtering/won't rev past 3500rpm...

[Jayru]

Like the title states, she won't rev past 3500rpm. Idles like a dream and makes great power up to 3500, but after that she breaks up real bad and won't accelerate anymore.

The car doesn't blow out any black smoke, indicating a rich cond.

Any idea's guys?

Also, There's rust peices in the new fuel filter. Should i just keep changing filters/re-filling the gas and see if they go away/clean themselves out? Or do i need to boil the tank?

Thanks for any help,

Jay

[240ZX]

Sounds like you have some work cut out for yourself! I would check, clean, and or replace all the fuel system filters and screens, as required. It sounds like you just have some sort of restriction or blockage in the fuel delivery. Anything below 3500 rpm does not require much fuel.....however, when putting the throttle down for more power, the engine starves for fuel. Also check the fuel pump output after doing the filters and screens. When was the last time you did a tune-up? Hope this assists you in some way.

P.S. Rust in old Z gas tanks is not uncommon. Sometimes when it is pretty bad, rush flakes can actually block off or plug up the tank outlet. Best to just clean out the tank at this point.

[Jayru]

Thanks.

The Fuel pump and filter have been replaced along with the 2 screen's removed. This was to correct a non starting issue.

Aside from the rusty tank, i don't know if fuel would still be the problem then?

Edit: I notice you say filters (plural) is there another one besides in the engine compartment?

Could it be ignition? I still have the single points dist. But the points/condensor are farely new. How could i check the ignition under load to see if that's the problem. Like i said, it idles and revs great up to 3500 then it hits a brick wall.

Thanks,

Jay

[ChrisA]

Edit: I notice you say filters (plural) is there another one besides in the engine compartment?

Hi Jay, some Z's with carbs had an electric fuel pump mounted back by the tank on the right side of the rear carrier. If your car has one of these, there is a filter on the bottom of the cylindrical pump. My 73 had one and the filter in the electric pump was so clogged I had some of the driveability issues you are having. I removed the complete electric pump and my problems went away. I also installed the good Z SU carbs also.

Good luck,

Chris

[Jayru]

Interesting. What determined which cars got the pump? I have a 72 240 with the original round top SU's.

I'll have to crall under there tomorrow and see if it's there. Although i don't hear anything kick on or run while the car is on.

The fuel does barely fill up the bottom of the filter though. If you spin it sideways, it just trickles in. I would think the suction from the pump would fill the filter with fuel almost completely. So maybe i do have a blockage somewhere?

[ChrisA]

Jay, I'm not sure when the electric pump was put into production.

The fuel filter on my car is usually around half full when running and you say your's barely fills the bottom. I suspect a blockage somewhere. If you feel like getting messy, you could pull the drain on the fuel tank and when its empty pour some fresh fuel in to try and flush out any large bits.

Another thing is to put a small one gallon can in the engine bay and have your new fuel pump draw directly out of the can and see if she'll run past 3500. I know that might seem dangerous but if you secure things it would work for just a test run.

Chris

[Jayru]

This is so strange, I already did what you suggest about the gas can when i was diagnosing the no start problem after i put the new pump on. I didn't drive/rev it but it ran and the filter was still only barely full.

I'll try it again after i check for the electric pump. Can't get under the car until tomorrow though, i'll keep you posted.

Thanks,

Jay

[Bambikiller240]

Golly Gee, It sounds like the old RUST and CRAP in the tank and fuel lines issue that is so common on these cars. Where did I hear that mentioned before???? Oh, yeah here it is....

http://www.classiczcars.com/forums/showthread.php?t=15674&page=1&pp=15

Maybe in Posts 2,4, & 8

[sblake01]

Also, this issue has been mentioned in several other threads. Crap in the tank will hamper the performance of a carbureated car and virtually stop a fuel injected car. Been there, done that. Seven years ago, I was lucky enough to find a known-to-be-good used tank and replaced my clogged-up-from-sitting-four-years tank with it.

[beandip]

Chrisa and Jaru the electric pump was used starting in '73 to help the fuel starvation problem caused by the heat boiling the fuel in the fuel rail and pump. The electric pump keeps cool fuel flowing through. There are filters in the inlets of the SUs check and see if there still in there . Most have been removed by now , but yours may still be there and clogged. My 2 cts.

[Greatwhite]

Are you on a tight budget? If not, why don't you do a complete overhaul of the fuel system. It would be a lot faster to buy all new lines, filters, fuel pump and a rebuild kit for your carbs and replace all thoses old parts. That way your almost garanted it will work and last longer. Sorry just thought I'd add my two cents

Good Luck, Justin

[Jayru]

the electric pump was used starting in '73 to help the fuel starvation problem caused by the heat boiling the fuel in the fuel rail and pump. The electric pump keeps cool fuel flowing through. There are filters in the inlets of the SUs check and see if there still in there . Most have been removed by now , but yours may still be there and clogged. My 2 cts.

Ok, so my car definatly doesn't have one then (72). Yea, i removed those filters when you mentioned that in my fuel pump thread. They weren't clogged, but i yanked them anyway.

Thanks