zev

Hey friends, I’m pulling my hair out chasing a tuning issue and I’m hoping someone can please help me. Here’s the setup: 1972 240z with a rebello 3L with triple Weber 45’s, 280zx matchbox distributor with mechanical advance and vacuum disabled, MSD 6AL2 ignition and blaster 2 coil. 65F9 idle jets which is what Dave sent the motor with years ago and tuned on his Dyno, so I believe the idle jet selection to be correct for this motor. It’s been running rough at idle and lean popping through the carb throats which is typically a symptom of a lean idle, so I richened up the mixture screws, but that did not fix the popping through the carburetors. I’m also getting an extremely rich air fuel reading between 10 and 11 at idle. After using an infrared thermometer on my headers only cylinder number 4 is getting up the temperature, about 475° and the other cylinders are running between 100 and 350° at idle. When I pull the spark plug wires off of the spark plugs with the engine idling I get no change in idle quality when cylinders 3, 5 and 6, are disconnected, meaning they are either fully dead or only firing intermittently. I believe the rich AFR is at idle is due to these cylinders either not firing or firing intermittently dumping raw fuel into the exhaust. I have the base timing set at 18°, but if I advance the base timing, the RPMs will keep climbing and it will run better and better all the way up to about 40° base, however, this has no effect on the dead cylinders and doesn’t cause them to come back online. Heres what I’ve done so far to diagnose / rule out. Confirmed balancer mark is at zero when cylinder one is at tdc. Confirmed valve clearances on all 12 valves Ran both compression and leakdown tests. Compression is 210 across all six cylinders and there is no leakdown on any of the cylinders. Verified firing order / spark plug wires running to correct cylinders. Put a timing light on each of the six spark plug wires and confirmed none of them are skipping. Removed all idle jets and carriers, blew them out with air and visually confirmed they are free of any obstructions. checked for vacuum leaks at carb and manifold. Swapped carbs around and symptoms didnt follow the carb. Replaced Coil, Spark plugs, plug wires, Distributor cap and rotor. Added a ground strap to engine block. Confirmed good power and ground to MSD box. None of this has had any change and at this point, I’m totally scratching my head. Does anyone have any ideas?

Great advice. Thanks Cary.

Wow, mostly pro-injection!! Anyone else who wants to contribute I’m all ears. also one other question… if my Webers are 45 with 38mm venturis should the ITB’s be sized at 45 also?

Hey All! I have a 72Z with a 3L Rebello stroker and triple Weber 45’s. The thing absolutely rips, but at low speed I have some drivability issues that I haven’t been able to tune out and I think that’s just the tradeoff of running DCOE’s. I’m considering working with chris at Godzilla raceWorks to have him install their Bosch ITB fuel injection setup but I’m curious how this will affect the overall power and throttle response. I don’t have a ton of experience with fuel injection but my assumption is that the car will have much improved drivability with the tradeoff of the gut-punch immediacy of the Webers? Can anyone advise me as to what the downsides are to making the switch? Thanks.

Hey Friends, I’m hoping people can offer some insights on a tuning issue I’m having with my 45 DCOE’s The car is a 72 240 with a rebello 3L stroker. Dave strongly suggested using the Chinese knockoff FAJS carbs, saying the machine work on these was much better than what he had seen coming directly from Weber, so that’s what we went with. He tuned the motor on his dyno and it runs beautifully all through the rev range with one big exception. Right at “tip-in” when I’m transitioning from fully closed throttle to say 1/8 or even 1/16 throttle there is ZERO progression, meaning that the throttle is either on or off, and this happens regardless of speed and RPM. Off the line I have to feather the clutch to keep the transition smooth which is fine, but if I’m heading into a corner and transitioning from the brakes to the throttle, there’s no way to get back on throttle without a big jerk, which in turn greatly upsets the suspension of the car. It feels like I have to overcome so much vacuum at the petal that there’s just no in-between from on or off throttle. So far I’ve tried bigger pump jets and tried blocking the economizers at the bottom of the float bowl and that made zero difference. I don’t think the issue is in the pilot jets since it doesn’t even feel like I’m getting into the pilot jet yet…it’s literally just the transition from fully closed throttle to ANY amount of throttle no matter how small. These carbs have 5 progression holes and Dave recommended drilling one of them out slightly, but before I go that route I wanted to see what other people think. I’m all for switching to genuine Webers if that would help, but both Dave Rebello and Dave at Pierce manifolds said the FAJS carbs are every bit as good. This stumble greatly affects the drive ability of the car so I’ll try anything to get it solved. many thanks.

Thanks all! I think based on the feedback here I will just stick with my 15x8 wheels and 225/50/15 tires instead of trying to punch out to a bigger size. Seems like the general consensus is that the offset won’t works, so I’ll stick to what’s tried and true

Thanks, that’s a great call.

Exactly, I am hoping to achieve a slightly more deep dish look at the wheels which is why I am looking at a slight negative offset.

Thanks for the reply. I feel like I’ve been reading so many forum posts on this topic that I am about to go blind. If I look at wheels with positive offset that won’t give me the deep dish look though, since it would move the spokes even further towards the outside of the wheel, right? I guess the answer is that I just need to roll the fenders more to accommodate the negative offset. Does adding offset negatively impact handling for a street car?

Hey All, I currently run 15x8 Rota RKR's (0 offset) on my 72 Z. There was a small amount of rubbing front and back but I rolled the front and rear fenders VERY slightly and now they don't rub, but only just don't rub so it's pretty close. The problem is I just can't stand the look of the zero offset wheel so I'd like to swap these out, but I also hate the super stretched look. I don't mind a little stretch, but nothing crazy. Can anyone chime in about their experiences with a 15x9 -13 offset and tell me what tires you used and what the rubbing situation is like? Or any general advice here of what I might want to look at in terms of a wheel / tire package for a 15 inch rim? Here's a pic of my current setup with the 15x8's Thanks!

300-400 is plenty for an S30. Thing must be nasty.

Killer. Is that on al L28?

Ha, that's too funny man. That thing is so clean! Love it. So you did the 8.8 in yours? Did you do the T3 setup?

280tq and 320hp on his bench dyno.The thing freaking rips and sounds evil. I put an exhaust cutout in it too for hooligan mode, which is pretty much all the time. Yeah, I also think the 8.8 might be overkill since the R180 has served me well so far AND STI's run them with similar power and torque figures and seem to hold together ok. For the tranny...I've been through the gauntlet: Stock 4 speed...blew it up. later 5 speed...blew it up Turbo T5 NWC...blew it up S13... currently making noise and one burnout away from...blowing up. The next step is the Godzilla Raceworks CD00 swap which will also be the first new, not rebuilt tranny this thing will have seen, so I'm hoping that get it done. I'm sure it has nothing to do with my driving style 😈

CLSD from a 2005 STI.