madkaw

It hasn't been a very good week and the Z doesn't want to run right. I have actually been able to find time to work on it, which usually is a problem. But after hours of troubleshooting and working on the car I seem no closer to an answer.It's one of those troubleshooting nightmares that has caused me to walk away before I do something stupid----like give up Z-ing. Symptoms are erratic and only sometimes can I duplicate. I am scratching my head and loosing heart and motivation. I love my Z, but it hasn't been fun lately just working on it while we have had the best weather all year. I will try and describe my issues-though it will sound vague; I have been around the world and back so my descriptions might seem lucid. The engine sounds like it has a miss and won't idle as smoothly as it used to. It feels down on power. Laboring might be a good description of the idle. At first-- cylinders 4-6 seemed to be the culprit. Plugs looked dark and #4 was the worse. But how does half a mikuni run rich? I also had number look dark, but for the most part, everytime I checked 1-3 looked lean or no color. Now most of this has been idle time in the garage, but those general plug reading were after a drive also. I have seen the plugs 4-6 look both clean and dark during all this troubleshooting, but #4 has been the most consistantly fouled. My AFR's bounce around quite a bit at first . I have dual exhausts so I only have the O2 sensor in one side or another. At first the sensor was in cylinders 1-3 and the reading were not bad, but erratic, not stable at idle. it would run at 14 and start a bouncing routine and then look lean. I switched the o2 sensor to the rear bank and it was pig rich-like 10.5-11 at idle-hence the dark plugs. I had to turn the pilot screws on 4,5,6, in a 1/2 turn just to get the AFR's to 13.5. Keep in mind that my jetting is at a known good setting that has worked great before. I've ran these pilots jets and screw settings with no issues before. I have checked floats and they are spot on. I have pulled the covers after running and they are all at the same level. All my pilot screws were replaced and all the tips are in excellent shape. I suspected ignition or my Megasquirt because of the randomness of the issue. But I replaced all components with a 280zx dizzy and wires and no change. Replaced the plugs too. Ignition timing checked with the dizzy and the megasquirt. I checked all valves and adjusted as necessary-nothing to crazy. Vacuum guage only show.ed 12HG at idle taken from a port on my vacuum log. I thought that a bit low. Sprayed everything down with started fluid and could find nothing. I removed the complete vacuum log assembly and capped off all port openings. So there is nothing hooked to the intake. Checked torque on intake bolts and noticed one exhaust flange nut very loose at the very end of the header. I hooked up a coolant pressure tester to see if pressure was building anywhere --- as in a bad HG. I set the tester at 13psi, the same as the cap and pressure rose slightly to 15psi and stayed. No bubbles in radiator and level seems to be the same. Nothing in the oil. Compression test done 1-205 2-205 3-205 4-215 5-205 6-210 Not sure what to make of those readings, but cylinder 4 jumps out at me a little. I'm pretty sure these are within percentage limits of each other. So I proceed to switching out carbs. I swap the 3&4 for 1&2. I run the car and bingo, #2 is now fouled-I found it. #2 would have been #4 cylinder so it must be one side of my carb. So I switch out pilots, and e-tube(which should have much to do with idle). Now #2 isn't fouling, but the engine still idle like sh!t. I should say that I checked all the O-rings when I had ALL the carbs off. This is what i meant about nothing being conclusive or concrete. I have run and cleaned plugs several times and nothing seems very consistant. I had to walk away after about 10-12 hours in the last two days. Not sure if a bad intake gasket would cause such issues, or a avccum leak in general. At first my gut said HG, and I'm not totally convinced it's not, but no definite eveidence to warrant pulling the head off. Valve timing? Well it's not so easy for me to determine this. I have an adjustable sprocket and I degreed this cam in many moons ago. I will have to really ponder on how I will check my valve timing. I have looked down in the hole to see if my chain adjuster popped out or something, but didn't see anything alarming. Could the chain jump a tooth? Unlikely if not impossible, but there is no quick way for me to determine this. My gut says HG or Valve timing(ignition is safely eliminated), but don't want to go on a gut feeling. Give me some ideas guys

Thanks-keep any ideas coming. Chokes-maybe-but I would think it would foul both sides are carb, and I did check them Jets have all been used before with no issues. I could swap around e-tubes I guess. Not sure what could go wrong with them.

I need some insight here guys. Having an issue with running rich on certain cylinders. Primarily #4 runs rich, but 3 is fine. How does that happen that one half of a carb runs rich. Floats have been checked as well as fuel pressure. Ignition has also been eliminated from the equation. I also did a coolant pressure test for a blown HG. Cylinders read 180-190 on cylinders 4-6 Getting ready to pull carbs off completely to look everywhere. These carbs have been very consistant as far as pilot adjustments, but now I have to turn #4 way in to keep it from fouling out. I will be blowing out passages to I guess. I have been having the biggest issue with cylinders 4-6.

I would comment that my direct linkage works flawlessly. I couldn't imagine cable being any improvement. It can be done!

I believe that depends on what e-88 head we are talking about. An early e88 with bigger valves will down around 41.5. The earlier head will not be a fully OPEN chamber like the 42 or 47 head.

My observation has been the opposite. Engine purrs and sounds so much smoother with a rich mix. Exhaust sound is fuller if that makes sense. I really don't think these carbs were designed for lean driving. Probably has much to do with the Tau layer. Love my Mikunis but ready to tune without my hands smelling like gas

From all I have read-don't go with a thicker gasket to lower compression. Keep the squish tight to fend off detonation. So far good luck with my Nismo 1.25mm

Valve guide seals can't be stock with that size cam so check that. Unshrouded combustion chamber will lower CR a bit. So the competition cam will clear pistons okay?

Not sure what pic you are refering to Walter, but the one above shows how I clearanced the bores. My block is .040 over , but I did it for breathing reasons. I'm pretty sure the engine calculator shows 10.25:1 with stock chamber size on a L28 flat-top.

Look familiar:) Except mine is a E-88. Sure the exhaust wasn't upgraded also. I'd see if those aren't 35mm. Clearance would need to be checked for sure, or just unshroud everything including the cylinder bores. I would mic the cam to see where it comes in at. Maybe you do have something there too! L28 block would put you at about 10.25 I think. That's my next step. I already have the flat top block sitting on a stand

You haven't given enough info for a proper answer. What engine? Be specific about performance upgrades. Ignition? What's your jet settings? Did this problem just happen recently?

Yes sir- a bit rich ! Feel free to share you Mikuni experiences- that's how we learn

Duals with SU's. With good speakers or headsets I think you'll enjoy. Triples with same exhaust

Whatever exhaust you run you have to run a resonator(s) to keep the drone at bay. I'm running 2" duals and turbo straight thru magnaflows. It gives a deep tone, but I run mufflers at the rear and 2 resonators also. I'm getting ready to replace my glasspack(resonators) with straight thru 3" magnaflows. The cheap glasspacks wore out fast and the exhaust got annoying after a while. Run the biggest muffler you can fit and a chambered will probably be quieter then my turbo straight thru. I would think a 'performance' chambered would give a good sound. I went thru great lengths to make my dual exhaust, but have no regrets. i have owned many hot rods and this exhaust sounds better then all of them. The little L6 can sound deep and rich with the right set-up. I also run headers too.

I'd grab it if it's any good and cheap. You can always resell it to someone else. It would be an excellent choice if you decide to use it.

Tune - tune - tune Dyno before , then after like Carl said. I got 155rwhp from my L24 with SU's and all of Carls suggestions.

My L24 ran 155 with SU's, but a lot of mods. Didn't have the torque of the L28 , but close. I've driven a stock well maintained L28(77) and I was impressed

Yep, that's a healthy engine. Maybe just leave it alone-ha! I guess there is always the arguement that one dyno reads higher then another. I wish more guys would dyno there engines so they have a number for reference anyway. So now for future projects if you use the same dyno you can see (real) improvements. Now take it to your local dragstrip and see if can get 15's

I can't make out the graph and blow it up to see-argh

Damn, Looks like that dash is crack free. Ditto on the nice find. You are way ahead of the game with a solid chassis. Don't fret, we have a lot of Z assemblers on staff here to assist.

We'll consider it as helping you with the first stage of restoring . The PO did all the tearing down for you- A good body saves ton of time an money so you are ahead of the game. Get some pics up!! Welcome

My buddy has a lift and if I ever have time enough I am going to get over there. I need to experiment in duplicating this noise without actually moving. With my Wildwoods I can balance all my braking up front and try loading the driveline . A buddy also recommended rocking the car in gear which would be easy enough on a lift. I will have camcorder in hand to record this moment if I get it work!!! I have to pop on two new mufflers/resonators anyway and maybe swap out trans, so why not just do it all.

So LSD also .

Jim, Thanks for the report. This is a r180? My clunking still persists and it has been definetly worse since going all rubber. I like your idea and wish I had some old urethane bushings to tear up like that. Keep us updated, might be my next project!