Hesitiation at 3,800.....

[Weasel73240Z]

OK, now that I have the tranny taken care of, its time to work out this minor hesitation that I'm getting at around 3,500 or 3,800 rpms. I'm almost scared to get it running too well, the 4.11/4-speed combo is a real screamer, I almost lost the car sideways shifting from 1st to 2nd at 4,200 rpm's, pulling onto Route 44 today.

Background....stock L24, new ZTherapy carbs at about 3.5 turns out, (rebuilt) 280ZX dizzy with new vaccuum advance unit and new breaker plate (E12-80 unit is old - is this possibly a problem?), new MSD Blaster 2 coil. Dizzy has 8.5 degrees of mechanical advance (17 total) and vacuum advance works. I get about 25 degrees of total advance. Have initial timing set at about 12 or 13 BTDC. New NGK plugs (.025 gap), plug wires (8 mm NGK), rotor, cap. When I removed the plugs to inspect, I noticed the #4 plug was wet and fouled, the others were a nice white/brown color and dry...possible valve adjustment needed?

I'm still getting a slight hesitation when I accelerate hard at around 3,500 - 3,800 but it goes away when I get past 4,000 or so. Also, it seems like the hesitation is most notable in 1st gear, and less severe if I'm in higher gears. I tried pulling the choke levers up to richen the A/F mixture, no change. The problems happens at all temperature ranges. I don't remember getting this hesitation with the old points set-up.

I'm beginning to suspect that the alternator (original 40 AMP) isn't getting me adequate juice to fire the MSD coil at 3,500 - 4,000 rpm's, and I'm thinking about the 60 AMP upgrade that they sell at MSA.

Any ideas before I drop the $120 on the alternator upgrade. Am I totally off the mark thinking the alternator could be the problem? Also, if anyone has a good E12-80 module for sale, I'd love to carry a backup. They are tough to find in the boneyards up here in New England. Thanks.

[Zs-ondabrain]

The MSD only draws 1 amp for every 1000 RPM's so I doubt the 6 amps at full throttle has much to do with it.

Just for shits and giggles. adjust the dizzy down a little. Try it at 5 degrees and see what that does. Also, the blaster coil has a .700 ohm resistance and the stock unit is around 1.5 ohms (I think) Not likely an issue but there ya go.

[Weasel73240Z]

Also, the blaster coil has a .700 ohm resistance and the stock unit is around 1.5 ohms (I think) Not likely an issue but there ya go.

Thanks, I'll try dropping the timing back, but I remember it doing the same thing when it was at factory spec (7 degrees).

Also, pardon my ignorance, but what is the significance of the lower ohm rating for the Blaster coil? I have just enough electrical smarts to be dangerous.... :laugh: Just curious if the difference in ohm rating means that I may be best off going to the stock 280ZX coil, instead of the MSD.

[Zs-ondabrain]

I just dealt with a similar issue with coils, so I thought I'd throw that in to confuse you. Did it work?

Ignore it. If you play with the choke and see no difference, that tells me electrical, which leaves the dist. and coil. Check all your connections while you're at it.

Dave.

[Weasel73240Z]

I just dealt with a similar issue with coils, so I thought I'd throw that in to confuse you. Did it work?

Ignore it. If you play with the choke and see no difference, that tells me electrical, which leaves the dist. and coil. Check all your connections while you're at it.

Dave.

Yup...it did.

I guess I'll try a bit more with the fuel/timing before I go replacing anything. And yes, all connections were cleaned, or in most cases replaced with new gold-plated terminals. And I believe they're all tight, but it couldn't hurt to check again.:paranoid:

[Weasel73240Z]

Well I finally got a chance to work on the car for a few hours yesterday. After many timing tweaks/road tests, I think I found the best set-up for my Z.

I'm at 15 BTDC, and I disabled the vacuum advance. I'm still getting about 25 degrees total advance, even without any vacuum. Full advance seems to be about 40 BTDC at around 2,500 RPM's. In fact, when I attached the vacuum line, there is no change at all, still goes to 40 BTDC, no more. I not really sure why I'm getting 25 degrees of advance out of a dizzy that's stamped 8.5 (should be 17 degrees of mechanical advance), but its running great now.

Might still be running a little bit lean, as there is the slightest hesitation under HARD acceleration, but its higher up the powerband (around 4,400), and much less noticeable than before. Either way, I think the timing is where it needs to be, and some minor carb tweaks should have me all set.

[Curtis240Z]

Did you mean your spark plug gap is .035? Also try and richen the carbs a little.

[Weasel73240Z]

Did you mean your spark plug gap is .035? Also try and richen the carbs a little.

Plug gap is at .025. I had it at .035, but reduced it to .025 when I was working out these bugs. At one point I was thinking I wasn't getting good spark from the coil so I reduced the gap and never opened it back up. The plug gap was .025 originally (w/points) so I went back to that, but with the ZX dizzy I should try it wider. I'll try bumping it back up to .035 now that I seem to have the timing worked out.

I am also going to try to richen the carbs and see what happens. I just ran out of time yesterday before the Red Sox game started.

[beandip]

I am running .044" plug gap. The vacuum advance is done at lower rpm this is why you see no difference at the higher rpm. the vacuum advance is meant to give you better performance by adding advance when at low rpm and you open the throttle. When the engine reaches 700 rpm or so the mechanical advance is taking over and should be at full advance around 2500. The module is not causing the hesitation you are describing. Modules either work or don't. At least 99.9% of the time. Timing will depend on what the configuration is on your engine, the head and compression and shape of the combustion chamber, as well as the grade of gas you are using. Advancing the timing can defiantly cause predetonation that can be vary damaging. Just be aware. Just one more item what spark plug head combination are you using and has the head been modified? Arne was having trouble with his stock L-24 with this same ignition set at 9*advance! My L-24 from which was a '73 engine ran great at 12*. Now I am running a 280 with P-79 and 9.5 comp. set at 16*, on mid range gas. I can run regular but I don't. What about your float levels and what fuel presher are you getting while at while driving under load? This could cause the engine to flatten out at the upper end if it is leaning out do to lack of fuel.

Edited May 4, 2009 by beandip

[Weasel73240Z]

I finally got the Z just about dialed right in now. I'm running at 12* initial timing, which gets me to about 38* or 40* total advance (mechanical and vacuum).

The carb floats were set way too high. They are new (last year) from ZTherapy, and I'm not sure if I checked the float levels before I installed them. :stupid: Anyway, both floats were less than 1/8" from the top when I inverted them, but according to my FSM they should be around 1/2". I adjusted the float levels to 1/2" and that helped alot. The floats were so high that at 2-1/2" turns out, I must have been running really rich.

Next, I bought a Gunson Colortune....what a cool tool. I found out that my front carb was still running really rich, and had to dial it way back. I was trying to get the A/F mixture right using the lift pins on the bottom of the SU's, and listening to the exhaust note, but I wasn't getting it right. With the colortune, I got them dialed right in. I'm at about 3 turns on the back carb, and about 1-1/2 turns on the front.

The last thing that was causing me a problem is that the damper oil on the front carb was low. :stupid: I topped the damper oil off, and the Z runs like a bat out of hell now, with no more hesitation.

Now I just have to get the 5-speed rebuilt, because the 4.11/4-speed combo is no good for driving over 50 mph....but it sure if fun getting up to 50!

[beandip]

I have a color tune also, but it seems to me that it shows a rich mixture when the carbs are in good tune. I will put it this way. Set with the Color Tune the engine drives as if it is detuned. If I richen the mixture just a little , like a 1/8 of a turn or so, the engine runs smoother and even exhaust sounds, seem stronger. Also feels stronger, seat of the pants dyno. But the color of the flame is not all blue like they recommend in the instructions. It is certainly a good aid to getting them dialed in though.

Maybe I am being Paranoid about running lean and burning a valve. ??

Gary

[Weasel73240Z]

I still have a little bit of tweaking to do, and maybe I'll experiment with setting them a bit rich. Like I said, it feels alot better already, but I'll try adjusting them a bit richer and see if it feels stronger through the powerband.

Gary, when you say you tune them rich with the colortune, do you richen them until the flame begins to turn orange at idle? I did notice that when I revved the motor in neutral, the combustion flame did turn whitish, indicating a leaning condition. Should I tune them richer at idle, with the intent of hitting the bluish flame when the rpm's get up to 3 or 4K? I'm still getting used to working with the SU's, and although its getting there, I have a feeling I'm not getting the best performance I can out of them just yet.

Off topic, I finally get to see how my Z stacks up against other New England Z's in a few weeks. Theres a Z show in North Attleboro, MA at the place the that mine was originally purchased from, on June 27th.