240260280z

Eureka?.... you could have the weird lids with the long casting arms holding the hinge deeper in the bowl..... or you could have the corresponding extra long fuel needles causing the same problem. thanks to ztherapy as mentioned above

Send some more pics. The intake vacuum will draw the fuel ....not the gravity difference in stock level and 5mm below stock.... it is the top of the jet orifice hole (0.100") and the point in the needle that really matters for fuel metering. The problem with 5mm down is that you can run out of fuel on a long straight stretch. The only ways i can think of to reduce running out of fuel is to raise the fuel pump pressure (but keep it safe) or make the fuel bowls "effectively larger" If you have fuel bowls with the front drain you can connect a large hose or another bowl in parallel as a "dish/reservoir" the levels will be 5mm lower but more fuel will be pooled in that reservoir. Likewise for a quck and dirty you can make crazy long 2' hose to connect fuel bowl nipple to jet nipple to hold more fuel .... just secure it carefully and keep away from the manifold... or use a 1' hose with some sort of sealed can in the middle to be the reservoir. Here is how an SU turbo gets more fuel.... this is sort of the idea but you only need one inlet and float and the second bowl is just a reservoir. For your 5mm down problem it don't know... is the small orifice on the end of the hard return line of the fuel rail missing? Are the fuel bowl tops somehow sealed so that pressure builds up...this is a guess as it should cause fuel to flow out the jet normally? i hope this gets you in the race

TWM-Throttle Bodies-3004 Series DCNF

I saw the first seat in person. It looks fab and is very comfortable too.

Looks much better! I hear you on the heat.... good plan.

Maybe mount the SU Fuel Bowl cover/float assembly to a screw on lid for a plastic container like a small peanut butter or relish container. Mark a stripe 20mm down from the inner roof of the float bowl cover and test away. You could possibly start in the kitchen sink with a 4psi pressure regulator attached to the faucet then check with gas on the motor.

I wish him well but I'm a Greg Ira fan

there will be more z's in your life... i will bet on it be sure to drop by and say hi every now and then

I am with Mathieu. I ran 40 advance at idle on a triple weber 240z and could get momentum from stop with no ping if gently accellerating..too much pedal made it ping. It was a quick experiment when setting the timing. I ended up with 20 at idle and 38 at max.

I became a Z addict in 2003 and was very active in learning about the Z I just bought. I enjoyed writing tech tips as I learned so as to help others but some friends at work betrayed me in 2005 and I had many challenges from 2006 until last summer. I did manage to collect some data and tech tips that were in limbo and post to this site in articles as well as put some new ones up. I also had a fun project to restore a series one that was a nice break from the tough times. Here is a tech tip that was lost on the net:77 280z Clutch master and slave

77 280z Rear Drum Brake Job

The missing link: 240z 260z 280z 280zx Datsun Fan Clutch Rebuild

Found this online needle profile comparison tool when working on a tr4a yesterday Minty SU Needle Compare-o-rama

Found this online needle profile comparison tool when working on a tr4a yesterdayMinty SU Needle Compare-o-rama

Thanks all!

hmmm looking at the FSM again and it is more precise than at first glace....it gives different corner weights for the front so a bit more care is needed. Nissan seems to address this by having a 1/2" longer spring on the passenger side 15.2" vs 14.7"

It would be interesting to see how it works out if you complete the experiment. I am curious to see the ride height (compressed height of spring) vs number of cut coils and how it relates to the xls tool I made. I did some spring research yesterday and John Coffey mentioned in a post that shocks can have more of an effect on the perceived roughness than springs when driving. He knows suspension so it could be fun to see what happens.

Jeff, Revised with the following: Vehicle Weight: 2332 lbs (72z and two 150lb drivers per 72 FSM) Weight Ratio (F:R) 48.2:51.8 per 72 FSM This is for the front: [TABLE=class: grid, width: 500] <tbody>[TR] [TD=align: center][/TD] [TD=align: center]Uncompressed Height (Inches)[/TD] [TD=align: center]Compressed Height (inches)[/TD] [TD=align: center]Spring Constant (ft-lbs)[/TD] [/TR] [TR] [TD=align: center]Stock[/TD] [TD=align: center]14.25[/TD] [TD=align: center]11.40[/TD] [TD=align: center]197.00[/TD] [/TR] [TR] [TD=align: center]1.0 cut[/TD] [TD=align: center]12.63[/TD] [TD=align: center]10.10[/TD] [TD=align: center]222.26[/TD] [/TR] [TR] [TD=align: center]1.5 cut[/TD] [TD=align: center]11.82[/TD] [TD=align: center]9.45[/TD] [TD=align: center]237.48[/TD] [/TR] [TR] [TD=align: center]2.0 cut[/TD] [TD=align: center]11.01[/TD] [TD=align: center]8.81[/TD] [TD=align: center]254.94[/TD] [/TR] [TR] [TD=align: center]2.5 cut[/TD] [TD=align: center]10.20[/TD] [TD=align: center]8.16[/TD] [TD=align: center]275.17[/TD] [/TR] [TR] [TD=align: center]3.0 cut[/TD] [TD=align: center]9.39[/TD] [TD=align: center]7.51[/TD] [TD=align: center]298.90[/TD] [/TR] [TR] [TD=align: center]3.5 cut[/TD] [TD=align: center]8.58[/TD] [TD=align: center]6.86[/TD] [TD=align: center]327.09[/TD] [/TR] [TR] [TD=align: center]4.0 cut[/TD] [TD=align: center]7.77[/TD] [TD=align: center]6.22[/TD] [TD=align: center]361.17[/TD] [/TR] </tbody>[/TABLE] This is for the rear: [TABLE=class: grid, width: 500] <tbody>[TR] [TD=align: center][/TD] [TD=align: center]Uncompressed Height (Inches)[/TD] [TD=align: center]Compressed Height (inches)[/TD] [TD=align: center]Spring Constant (ft-lbs)[/TD] [/TR] [TR] [TD=align: center]Stock[/TD] [TD=align: center]14.25[/TD] [TD=align: center]11.18[/TD] [TD=align: center]197.00[/TD] [/TR] [TR] [TD=align: center]1.0 cut[/TD] [TD=align: center]12.63[/TD] [TD=align: center]9.91[/TD] [TD=align: center]222.26[/TD] [/TR] [TR] [TD=align: center]1.5 cut[/TD] [TD=align: center]11.82[/TD] [TD=align: center]9.28[/TD] [TD=align: center]237.48[/TD] [/TR] [TR] [TD=align: center]2.0 cut[/TD] [TD=align: center]11.01[/TD] [TD=align: center]8.64[/TD] [TD=align: center]254.94[/TD] [/TR] [TR] [TD=align: center]2.5 cut[/TD] [TD=align: center]10.20[/TD] [TD=align: center]8.01[/TD] [TD=align: center]275.17[/TD] [/TR] [TR] [TD=align: center]3.0 cut[/TD] [TD=align: center]9.39[/TD] [TD=align: center]7.37[/TD] [TD=align: center]298.90[/TD] [/TR] [TR] [TD=align: center]3.5 cut[/TD] [TD=align: center]8.58[/TD] [TD=align: center]6.74[/TD] [TD=align: center]327.09[/TD] [/TR] [TR] [TD=align: center]4.0 cut[/TD] [TD=align: center]7.77[/TD] [TD=align: center]6.10[/TD] [TD=align: center]361.17[/TD] [/TR] </tbody>[/TABLE] You may wish to cut 1/4 less coil off the rear to keep it higher than the front. 3 coils cut from the front and 2.75 cut from the rear would be ~ .6" below stock.

jim we have the same geek gene Love your lesson... spot on. btw Pics of that series one please Hopefully I'll have the metal roof on the shed this weekend and pics to counter

Trying to get this data. Thanks

1 month old 72 for reference here is a 71

Jeff, I just made an xls spreadsheet for estimating your front spring compression. Here are the numbers and spring constant changes: Stock Chevette Spring Front Compressed Spring Height 11.27" Spring Constant 197.00 lbs/inch 1.5 Coils Cut from Stock Compressed Spring Height 9.60" Spring Constant 237.48 lbs/inch 2.5 Coils Cut from Stock Compressed Spring Height 8.29" Spring Constant 275.17 lbs/inch 3.0 Coils Cut from Stock Compressed Spring Height 7.63" Spring Constant 298.90 lbs/inch 3.5 Coils Cut from Stock Compressed Spring Height 6.97" Spring Constant 327.09 lbs/inch 4.0 Coils Cut from Stock Compressed Spring Height 6.31" Spring Constant 361.17 lbs/inch I think you are at 2.5 coils cut from stock so the compressed height should be close to stock of ~8". I would only cut 0.5 coils at a time on the front until you get it where you want. The spring constants climb significantly. FYI: I used a car weight of 2,244lbs (estimated as car and one 150lb driver) and a 47/53 front/rear weight distribution. If anyone can give better weight and distribution I'll plug it in.

Excellent!