My 72 240z does not have high end power

[cswistock]

I have a 72 240z. When I bought it two years ago it had a rebuilt engine, performance cam, header, stock carbs. The problems I have are it tends to run hot, gets poor gas mileage and the power seems to stall at higher RPM and sounds like a jet at higher RPM (from the motor not the exhaust). It never misses or stumbles, it just stops accelerating. I have replaced the cam with a new stock cam. That quieted down and helped it run a bit cooler, but it still has the problems. The dwell is correct and the timing is correct. Both the vacuum advance and centrifugal advance are working. The rear carb is running a bit rich (black plugs on the back three) but the carb is adjusted as lean as I can make it. Below 4k RPM is has good power and the motor is quiet even at full throttle. Any ideas?

[beermanpete]

Two things come to mind:

1) The timing mark is wrong and therefor the timing is wrong. Check the accuracy of the timing mark.

2) The exhaust is very restrictive for some reason. Bent or bashed pipe, internally collapsed muller, etc.

[cswistock]

I replaced the exhaust front to back with a new header, 2" exhaust and new muffler. The old header leaked and all I smelled in the car was exhaust. So I don't think it is that. Also I set #1 to TDC on firing position and verified the timing mark (I thought the same thing). The timing seemed a bit advanced to me, but I don't get any knocks. Could being too advanced cause this?

[Zforce]

Check your float level, gross mixture is set by the float level,you should be able to see fuel just below the nozzle buy squeezing the fuel pipe. Also make sure the fuel nozzle is flush with the jet bridge with the choke off, then with the mixture nut turned all the way up index the jet needle by losening the set screw just enough to allow movement of the needle and pull it out so you can carefully set the piston back down and gently press the piston down into the nozzle. Now remove the piston and tighten the set screw, it's ok if the jet needle is not flush with the piston, now set the mixture nuts. Why are you running such a tiny exhaust pipe ? 2 1/4 minimum.

Edited July 10, 2011 by Zforce

[Zs-ondabrain]

I say go to a 2.5" exhaust. Seems to be perfect for the Inline 6 and definately allows it to breathe at higher RPMS.

OK, so your dwell and points are all set.... I discovered a simple solution to alot of distributor issues..... Pull the Distributor and the sleeve it goes into that bolts to the front cover of the motor. Use brake cleaner to remove ALL the surface grease and oil on all 3 peices (front cover, sleeve and distributor) Then surface them a little using the red Scotch-Brite pads to make the best Metal to metal Contact. Check the steel plate on the bottom of the distributor as well. Then Put is all back together and bolt it down tight without breaking the bolts.

The Problem is the grease, dirt and oil minimize the Ground needed for the points to transfer the signal as well as needed. Once you get a good or better ground, the power to the points will work better and hopefully give you a higher RPM range.

I just did this to tomg61's 240Z because he couldn't Rev over 3000 RPM. Cleaned his Distributor and ground surfaces, cleaned his power wires and battery cables and she hits 7000 RPM without ANY problem. The 240Z's have bad Grounding problems. Fix these and you'll be surprised at the results. Especially in the ignition department.

Dave

[Zforce]

Yeah I actually ran a seperate ground wire from the dizzy to the block and from the alternator to the chassis just to be sure.

[tlorber]

1) an electronic distributor really helped my car wind out. 2) You may not be metering enough fuel at high rpms. I've found that, with SU's if they are running perfect at idle, they will be a bit lean at the higher end, so I set mine slightly fat of where they want to be at idle to compensate. Some of this can be mitigated by needle selection but I haven't had the time to get into it.