datsunlover Posted September 17, 2007 Share Posted September 17, 2007 Ok.. I'm not sure if this is a carb or ignition issue, hence the post here... here's the rundown; 350 chev, bored .040, cam is 'likely' (engine builder doesn't remember, it was a year ago) around a 480 lift 280*, 197 valve heads, everything is new in the motor.. maybe 100 miles on it now. Custom (read- homemade in my garage) Y pipe and single 2.5" exhast into a j/y muffler. Q-jet carb and stock HEI chev dist. Stock 350th/convertor. I know this isn't the best 'performance' setup, but I'm just trying to get it to run half decent here, and its in an 85 mazda rx7 so it SHOULD go like a bugger, even if it's not as powerfull as it COULD be... Anyway, I've had her out for a few runs now, and I'm pulling my hair out. It'll go like a bastard at wot, but won't idle well and almost sputters and dies sitting in gear. I can keep it running at a stop by two-footing it, but that gets tiresome. I 'think' the carb is set fairly close, as the exhast doesn't stink of fuel, and the plugs look good... but I admit I know little of q-jets, and I'm sure I'm not the first guy to mess with this particular one. I've cleaned it up and set the two screws about 1.5 turns out, evrything moves freely, and it seams to be in working condition... That said, I'm still leanign towards the ignition.. This is an old distrubiutor with new cap/rotor/plugs/wires/coil. When I start the car, it seams like there's a LOT of advance waww...WEr...waww...WEW you know? hard to put into words... anyway, once it does fire, it runs as if there isn't ENOUGH initial advance! Idles around 800-1000rpm, but drops to around 400 when in gear, Also, the aftermarket tach I have keeps going out.. IE; it reads just fine, and suddenly the needle drops to around 1000rpm and just sits there... ?!?!?! So I changed out the ign module, and coil and guess what? NO change. Car still bucks slightly at cruise, needs 'help' to stay runing while in gear, and refuses to idle at all. At this point, I think I'm just going to bite the bullet and spend another $179 on a BRAND NEW distributor (although I've spent over $100 on this one already... ) and go from there... unless this whole issue could be a carb problem? I dono.. anyone got an idea? Quote Link to comment Share on other sites More sharing options...
280zwitha383 Posted September 17, 2007 Share Posted September 17, 2007 Do you have a vacuum gauge or a timing light and have you used either of them? Quote Link to comment Share on other sites More sharing options...
datsunlover Posted September 17, 2007 Author Share Posted September 17, 2007 Do you have a vacuum gauge or a timing light and have you used either of them? Yes, and yes. This is also parts of the mystery... With motor idling, and the light on it, the timing mark on the damper is a LONG ways away from the last mark on the tab, which is marked 16* 'before' (which I take as meaning BTDC) IE; it's almost on the other side of the water pump, putting it roughly 28* advanced by my guess.. which makes sence to me, as far as the hard starting/cranking issue. Now, with the vacuum guage on it, (pluged into the intake port that ussualy feeds the tranny vacuum line.. it this ok?!?) it tells me the opposite thing; the guage I have is marked in Inch Hg starting at zero, going in increments of 2. 0-10 has markings saying 'late valve timing or leak at intake manifold' 10-14 says nothing 14-18 says 'late ign. timing' 18-22 says 'normal' At idle, its showing between 16 and 19, which would mean my timing is late?!? But that can't be because if I try to advance it anymore, it just wont start! Am I missing something here? I must be... Quote Link to comment Share on other sites More sharing options...
datsunlover Posted September 18, 2007 Author Share Posted September 18, 2007 Well, strange and wacky, but this afternoon as I'm messing with the car, the guy who built the motor shows up at my house out of the blue! So we go through evrything again, and evrything seams to check out... Hes saying because of the big cam/overlap, 18" of vacuum is not bad, and it does run/rev pretty well. Above 2k rpm it screams and makes very nice sounds. Idle? blahh.... SO we're talking, and it turns out one piece of the puzzle is now solved; The 8" damper he used on this motor is intended to be timed with the line facing UP, like through the 'window' area between a stock water pump and timing cover. (apparently, there are several diffrent styles) However, due to engin bay constraints, I have a 'short' style water pump which sits flush on the timing cover. Now, I didn't even think of this at the time (ha ha.. no pun intended) but I got a generic timing tab and bolted it on the SIDE of the timing cover, assuming it would work. So basicaly, the timing light is usless (for now) so we turned the dist. to put as much advance as it would take, and still crank/startup. Then we moved on to the carb, and it seams there are some gremlins lurking in there... sitting at idle, if you gently touch the accelerator pump lever, it cleans up and runs very nice.. for a few seconds. Not even a throttle blip, just a slight preasure on it. My engine builder says he's seen it a lot with older q-jets; idle circuit doesn't work properly anymore, (dirty, worn out, ect) causing bad idle/stalling, and also a bad transition from idle to power. It's not fouling the plugs, and after it's past the first few degrees of throttle, it's fine. But the poor idle condition, combined with the stock convertor dragging the motor down in gear, AND the big cam, all adds up... So I'm still wary of the ignition, but I think I'll be looking for a better carb first. (condition I mean, not just saying q-jets are crap cause mine's out of tune) Really, I'm ok with a rough idle, but the stock 350th tranny doesn't like it.. (still have to two-foot it a bit) and I don't like the 3 gear either, it's just what I had lying around. Really, this wouldn't be much of an issue if I had a stick, cause I'd be reving it up to take off, and the bog/miss wouldn't affect it much. I just had it out tonite, and it is quite a monster! Bogs from a standing start if I jump right on it, but a smooth steady push to the floor seams to work nicely! And even still, a light throttle take off is actualy quite a quick affair in this little car.. I'm gona have to watch it. Quote Link to comment Share on other sites More sharing options...
280zwitha383 Posted September 18, 2007 Share Posted September 18, 2007 They're a hoot alright! Happy tuning... Quote Link to comment Share on other sites More sharing options...
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