RebekahsZ Posted November 26, 2011 Share Posted November 26, 2011 I just gave my L24 long block to my buddy and he put it in his 1970 240z. He installed the triple Webers and a 280zx electronic distributor from his old engine onto my long block. We cranked it and set the timing. Car ran really rough with an irregular exhaust burbble and some snapping and popping, so we moved to synching the webers. I set the idle mixture screws for leanest mixture without slowing the engine speed (essentially 1-1/2 turns off bottom) and balanced the carbs as best I could and the engine smoothed somewhat and ran much better under power. However, the unisys bead bounced erratically in the air column on cylinder #6 (closest to firewall). We sprayed starting fluid all over that carb trying to find a vacuum leak, but had no luck. I balanced my triple Dellortos regularly on this same long block, and I don't recall the unisys bead bouncing like this before and the car ran smoothly and produced good power and was competitive at autocross. He will check compression tomorrow looking for a bad valve and we will swap in my fixted plate distributor. Anybody have a suggestion for what type of an issue produces a bouncing unisys bead? Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted November 26, 2011 Share Posted November 26, 2011 Doesn't #6 feed the brake booster? Maybe that's a hint. Quote Link to comment Share on other sites More sharing options...
RebekahsZ Posted November 26, 2011 Author Share Posted November 26, 2011 Aha! I know that the brake booster is bad-I drove the car last night and it takes a lot of middle pedal. I'll try capping the fitting and see what happens. Thanks for helping. I'll post the results. Quote Link to comment Share on other sites More sharing options...
johnc Posted November 26, 2011 Share Posted November 26, 2011 Don't use a Unisyn. Buy a Synchrometer: http://www.duckyimports.com/servlet/Detail?no=5 Quote Link to comment Share on other sites More sharing options...
RebekahsZ Posted November 26, 2011 Author Share Posted November 26, 2011 (edited) johnc-thanks for the advice-you are the bomb! Thanks for weighing in. Anyway, I have a synch-ing tool similar to the one you linked me to, but I haven't been able to use it on my buddy's car due to very long intake manifold runners and long velocity stacks-the stacks are against the brake master cyl and the inner fender-it is a tight fit even with his unisys bubble-type meter. We don't know if we can just remove the velocity stacks since they slide into the carbs instead of just bolting on like my Dellorto velocity stacks (I dont know what else they influence internally). Let me know if we can just pull them and we will use my meter directly on the carb body. I tried to get him to take one of my SU carb sets, but like me, he likes the pretty triples. Is a bouncing flow indicative of anything other than a vacuum leak? Would miss-firing cause it? My buddy lives about 20 minutes from me. I've got him checking compression, switching to my newer plug wires (he installed his old ones) and re-checking the capping of his brake booster port (it is already capped-thanks cygnusx1!). The car blows a little black smoke (not bad) under hard throttle, but no blue smoke. I test drove it last night and it drove pretty well under load at higher rpm, but we all know that seat-o-pants dyno means nothing and that high rpm can just mask a problem. I understand that a bad cylinder/valve can affect flow, but it is the fast-frequency fluttering or bouncing that has me stumped. Hoping for more advice. The plus side of this story is that in exchange for my help and a bunch of my old parts, Jacob is in the process of trading some 240sx tuner parts for an '88 ZXT LSD for me! Cast your bread upon the waters... Edited November 26, 2011 by RebekahsZ Quote Link to comment Share on other sites More sharing options...
johnc Posted November 26, 2011 Share Posted November 26, 2011 I would pull the v-stacks or make a 90 degree elbow out of silicone hose that slips over the outer end of the v-stack. As long as you use that elbow on every venturi you're fine. I would ignore the Unisyn results, whatever they are, and re-test using the Synchrometer. Quote Link to comment Share on other sites More sharing options...
RebekahsZ Posted November 26, 2011 Author Share Posted November 26, 2011 (edited) Let me see if I understand correctly: The carbs will run fine without the velocity stacks? Sorry, I just don't know ANYTHING about weber side drafts... And I am SO thankful to be out of the side draft game myself. Edited November 26, 2011 by RebekahsZ Quote Link to comment Share on other sites More sharing options...
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