escapedan

My 1973 240z (2.6L engine; no smog equip) initially starts and runs normally. It runs fine for 5-10 minutes then, for lack of a better description, the engine starts cutting out at about 65 mph (any gear). I can hear the carbs "sucking air", but it seems to be starving for fuel and/or spark. With the clutch depressed, it will rev to ~4,000 rpm and again cuts out. It gets progressively worse until pull off the freeway.

Once I get off the freeway and drive on the side streets, it seems to work fine again so long as I dont get above ~45mph. Also, it then rev's all the way to redline as if nothing was wrong. I'd sure appreciate any suggestions before I go buying fuel pumps, ignitions, etc....

Here are some basics:
- 240z chassis, 2.6L engine (emissions equip removed), SU carbs, standard 240z distributor with points (ok, stop laughing), upgraded coil, 5-speed trans, headers, etc.

NismoPick

Have you checked all the basics?
Timing?
Carbs in sync?
Spark plugs?
Any fuel / vacuum leaks?

duowing

I looked at a 73 one time and it was doing similar things. For a bit it would run as if nothing was wrong. Then it would start acting sputtering, or even stall at speed. You'd then mess with it for a while and it would run ok. Then stall etc. It'd take a long time to restart then eventually it'd run again. Very similar to your issue. Turned out to be a bad fuel pump. The pump itself had been a replacement pump at some point and the owner found out there was a recall on the pump. All I remember was him saying it was a pump from Mr. Gasket I think.

escapedan

Thanks for the replies. So far I have changed the fuel filter and fuel lines. It does not seem to be "stalling" at speed now, but something still doesn't feel right. It feels like the car is "missing" while driving on the freeway, especially at steady speeds. I've checked the compression to ensure I didnt have a bad engine, but all seems good. I picked up a pertronix tonight and will install it tomorrow. I think I'm going to swap out the fuel pump as duowing suggested above.

Nathan DePriest

I own a 74 260Z and i am having the exact same problem with mine. The fuel pump is not the original and was replaced when i took it into a bunch of num nuts who messed it up even worse than before. the original fuel pump was broken but the one on it now is extremely loud and may be deffective. the car purrs like a kitten but at exactly 65MPH it starts to lose power exactly like explained above. i really have no idea what to do to it any more. please help out.


you can also reach me at Nate4801@yahoo.com. thanks

NismoPick

Welcome to ZDriver! Have you done these steps I mentioned above?

Nathan DePriest

Thank you. um yea i do have a problem with the whole vacuum issue. because when i got the car it was old and eroded. we took alot of it apart and ended of forgeting where some things go... thats what happens when you have a 15 year old working on a car. i have a book that shows me where to put the hoses because right now i have alot of unhooked things from the air filter to the engine. should i probably hook all of those up then see how it runs then?

Photoguy360

I have a 240z (72 Man)I bought not long ago. When I looked into my problem these are some options. (Yes I've also bought brand new Fuel pump and ensured filter was clean.)
#1 The 240z has a second pump in the acual gas tank.
#2 I have not cleaned out the gas tank so rust or old sedament may be the problem.
#3 Before I bought it, it was sitting for 10 months or more so the fuel may contain some water or turned to lacquer.

FYI there is more info online, getting rid of rust in gas tanks such as do it by buying a stripper and coater, or have a shop dip clean then coat it.

my fuel tank has a drain hole but have not messed with it yet as I'm still fixing other things to make it street legal and able to pass state insepection.
No title yet.

Hope this helped

hoov100

no 240z (or any s30/s130) has an in tank pump, also the s30 didnt get secondary fuel pumps until 74, which where mounted next to the tank.

escapedan

UPDATE - My 73 is still having the "Stalling at Speed" issue, but I believe I've found the cause. For some reason it is pulling massive vacuum between the brake master cylinder and check valve - so much so that it causes the vacuum hose between the brake master cylinder and check valve to literally collapse. Important note - this began shortly after installing rear disc brakes, but not immediately after. Once it gets to the point where there is no free flowing vacuum, the car dies while driving. It will rev (sometimes) with the clutch in, but will not accelerate at all with the clutch out. I performed a "tracheotomy" on the road by puncturing a hole in the vacuum line and inserting a relief valve, which got me home, but is clearly not a permanent fix.

So, question is has any experienced similar vacuum issues? If so, was it a faulty brake master cylinder? Booster? Any help would be appreciated!

theramz

Check the lines from the tank to make sure the main feed line isn't switched to a higher position on the tank making it "run out of gas" at speed. When it runs out of gas it takes a while to purge the air in the lines. Explains the slow but certain recovery.
The vac hose to the booster is a form hose and should not colapse. If the smog and all other sources of vacuum are blocked off it could colapse an incorrect gage hose. The anti backfire valve on the manifold cross tube should open the carbs on deceleration to prevent excessive vacuum. Get a vacuum gauge and check it at idle and higher.

duowing

Your brakes will be harder to use, but you could just try plugging off the line to the brake booster to see if that's your issue.

myxtaz

One thing that has not been addressed is float levels . If the float level in carbs are not set correctly the engine could just be running out of gas. Also if you have crud in the tank the chunks could block off the flow in the end of the pickup tube. When the need is diminished when the RPM drop off the chunk drops away and the flow is restored. This is what we found on my friends 240. COATING !?! It is a two edged sword. The vary best is to have the tank ZINK COATED . If you try and coat the inside your self, be aware if ANY of the coating comes loose your in trouble just look for another tank. The gas will get under the coating and it will start failing all over. With the baffel in the tank you cannot see past it .
At least where I live , good 240 tanks are hard to find.