Metzman510 Posted March 1, 2020 Report Share Posted March 1, 2020 My 69 510 is running a stroked and bored L16 with a ported and polished SSS head, a mild street cam, and a set of side draft Mikuni 40's on a short Mikuni manifold. Displacement is now about 1800cc. The car has a header, and a nice exhaust with a bung for an O2 sensor. I have installed a "Dizzy-Matchbox" electronic ignition with the matching high energy coil, and the timing is set at 10 deg BTDC. I have been working through this car for the last month getting it back on the road, it had sat for almost a decade in a garage when a friend located it. Just before it was parked some less than wise person tried monkeying with the jetting to get the car running on E85 type fuel and that is where it stayed until I towed it home. Here are my cars cam specs: Cam (have specs, manufacturer unknown) similar to a SSS cam or a Comp Cams 280S-10, .450” lift, 274 duration, IO-31 BTDC, IC-63 ATDC, EO-67 BTDC, EC-27 ATDC (222 duration, IO-5 BTDC, IC-36 ATDC, EO-30 BTDC, EC-1 ATDC, @ 0.050” lift) Valve lash is 0.008”, Exhaust 0.010” cold. Good to 7000 RPM My "problem" is that I can't get the car to idle lower than 1,100 RPM. It's not that it doesn't idle, it idles fantastic, always returns to 1,100 RPM +100 RPM never lower. Today I went back through and made sure all of the mechanical adjustments for the carbs were sound. synced the carbs, ran the idle speed adjustment screws all the way off the throttle plates, then brought them back to just touching, then re-synced the carbs. I reset all of the idle mixture screws, made sure the linkage arms are the same length, made sure the throttle linkage is pulling the linkage arms against the throttle shaft arm holding it against the idle speed screws, etc etc. No luck, car still idles solidly at 1,100 rpm. My Innovate LM-2 digital wideband O2 exhaust reader says the car is running lean at idle. it registers a 15.7 to 16.0 instead of the desired 14.0 to 14.6. I'm beginning to think I might need to go up a pilot jet size (currently 62.5's and mixtures at 2.5 turns out) in order to get the idle richer and drop the idle speed. I sprayed the intake down with carb spray today and there is no obvious air leak. Questions: 1) Has anyone else out there in Ratsun land worked through a similar situation? Did you successfully resolve it and now have a car or truck that idles solidly in the 8-900 RPM range? 2) I have read on other Z-car oriented forums that the Mikuni PHH carbs should be jetted so that the pilot circuit (idle to low midrange) functions properly when the mixture screws are set at 1.5 turns out. It seems that the general opinion is that you jet for that screw setting, not use the screws to adjust the mixtures to work with what you have. I believe my pilot jets are on the small side, so am considering going up a size to correct the air fuel ratio and am curious if it will drop the idle some also? 3) I know some cams require a higher idle, but I would think that a mild street cam would idle down nicely? 4) The car doesn't ping or knock, so the timing set at 10 BTDC should be close to on the money, the vacuum advance and the mechanical advance are both fully functional. Anyone know what max advance should be so I can try setting the car's timing at higher RPM and letting the idle timing settle from there? Quote Link to comment
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