Z dies during high speed acceleration

[ChrisA]

Hey Chris, I noticed you said you rebuilt SU's. Maybe the carbs are starving in fourth when you stomp it. But wouldnt it starve in any gear? Maybe the bowls are staying full till she's really drawing fuel. Might check the floats.

ChrisA

[cj71z]

That was my first thought yesterday. I'm going to try to get them dialed in, clean the banjo screens and get a new fuel filter. This will help with the fuel flow better to the motor. When this happens I pull over and my rpms drop down to like 200 then gradually increase back to 800 where it idles. If my timing was off wouldn't the car go back to idle when this happens if I put in the clutch?

Thanks

Chris

[e_racer1999]

i was having a similar problem.... i replaced the dizzy and found that the problem went away when i advanced my timing all the way, then backed off if it pinged...

as far as the revs dropping, THAT sounds like fuel starvation. it's common in Zs, mostly when braking, however there are many other possible causes..

[MarkOS]

Another thought based on an experience I had...

If any fuel lines are bent too far so that they've crimped themselves they could be letting through just enough fuel to run on, until it's really sucking it down, then it'll die until you back off and wait for the floats to refill..

Happened to me and for about a week I couldn't figure out why any acceleration above 70km/h made the car die... damn previous owner.

[dogma420]

electric fuel pumps were installed on a lot of 240z's outside of the US...you have the wires there for it...the 260z carbureted came with the electric pump (I had a 74 at one point)...all 280z due to fuel injection have the high capacity fuel pump back there.

Just a FYI.

I have the hesistation a little bit, always for me it's caused by the spark plugs fouling because of a head gasket leak....

[cj71z]

O.k I got to work on the Z today. I changed the fuel filter cause it was kinda dirty. I cleaned out the banjo filters and readjusted the float levels to around 14.5mm from the top on the metal on the float to the recessed area inside the float cover. I also advanced my timing to 15 degrees. I ran the car at 3000 rpm with the vacuum advance on and adjusted to distributor to get around 30-35 degrees advance. I also bought some staight 20w from the auto parts store and changed out the carb oil. I started her up, readjusted the mixture, this time a little rich and went for a drive. She ran fine on the street until I held her in third gear at around 3k rpm for a while then it happened again. She just died on me, when I pressed the gas it sucked air, but no acceleration. Now I'm thinking definately a fuel issue. The mixture on the front carb seems to change lean on me if I jab the throttle then check it shortly after. According to what I've read when you lift the piston 1/16" the idle should rise then fall to normal if the carbs adjusted correctly. If it rises and stays high then it's rich and if it stumbles then it's lean. I'm thinking about running a inline FP guage to check the pressure going to the carbs. I think it's supposed to be between 3-5 psi, is that correct? I'll check the lines to make sure there are no kinks, but is there anyother way to diagnose other than making my own air/fuel mixture guage with an 02 sensor to find out what's going on? Thanks for all the help everyone, I'd buy you all a beer if you were here

Chris

[Zedrally]

Might be time to blow out the fuel line with HP air.

The 260 exhibited problems similar and was cured by blowing back the line. Out came a piece of string... Don't ask....

[e_racer1999]

^^good idea... or paybe a new (or rebuild) fuel pump...

[cj71z]

Today I got to work on her again. I bought a inline FP guage and came back home. I started checking things and found that my + wire from the distributor to the module had nearly broken in half :tapemouth So I go and rewire with new connectors and everything now is nice and clean and tight fitting. Before I started it I plumbed in the FP guage and blew back through the lines going to the carbs, then the return line and they seemed fine. I took on the fuel filter and blew back to the tank, plenty of bubbles. The the return line back to the tank. Seemed there were no problems so I put it back together and fired her up. She started fine, but soon began to bog and then died, not to be started the rest of the day :disappoin I searched and searched and found that my fuel pump must have gone bad when I blew air back into it???? The pump seems to suck, then on the out stroke push the fuel back out the pump to the filter???? I finally found one at the end of the day, but wasn't able to get it installed yet. Maybe my pump was on it's way out? Anyway I'll try again on Friday.

I'm gonna flush my cooling system and bypass the hot water to the intakes, she seemed to run on the hot side (3/4 on the guage) and I'm wondering if the hot intakes, coupled with my ceramic coated header vaporized the fuel before she could use it. That may be why my mixture settings seem to go lean when the car gets hot.

If my car still runs hot what do you guys think of this replacement radiatorJagsthatrunradiator seems like a good deal since a to recore mine to a 3 core will cost about 270$ or so

Thanks for your help, I will figure this out, she will not beat me

Chris

[dogma420]

Try running it when the car is cold...if it does it when it is cold, then it isn't vaporizing fuel. Pressure of the Fuel pump itself I don't think has anything to do with it. When it dies, you might try pulling off the tops of the float chambers and looking at how much fuel is in there....or physically look in the SUs with the air filter housing off and see if its getting fuel when the piston is high up....

When blowing air through fuel lines, you don't want to blow through the fuel pump...

[cj71z]

When the car is in normal operating temp(about the middle of the temp guage) I tune the mixtures correct. I take it out for a drive and she gets a little hotter when I drive around for a while(about 3/4 or a little more on the guage). I come home and check the mixtures and it seems like now there running lean. It was pretty stupid of me not to disconnect the fuel pump, at least with a new one I'll know it's working properly(50$ mistake :stupid: ) I never pulled the carbs apart when it dies cause usually it happens while I'm on the highway. I'll find a road with less traffic and if it happens again I'll check the carbs to see how much fuel is there.

Chris

[Zedrally]

I'm convinced this is fuel supply problem. Re-check the fuel lines for blockage, use HP air to back blow the line, reason is that while you may be able to blow [mouth] the line this may not actually dislodge whatever is causing the blockage. As I said in my first post I had exactly the same problem, simply blowing back using your mouth does not give you any indication of a partial blockage, use HP air....going off to eat my words now.....