bullzed Posted June 18, 2011 Posted June 18, 2011 Hey everyone, well we've been struggling with the engine in my 280 for a while now and it's currently at the stage where it has completely new electrics (plugs, leads, points, cap etc) and the fuel and return lines have been checked, filters all replaced and timing set perfectly, however it still continues to give us problems. At the moment, the car starts okay, idles okay (as far as we can tell with the cam), however when in the rev range of about 1200 - 3000 it will cough and miss and jerk and generally runs like a hairy goat. However when the cam takes hold at about 3.5k (it's a fairly lumpy cam) it no longer coughs or misses and it's acceleration is flawless. We've noticed that it can be driven around in the higher rev range without being too much of a problem however just in the lower range it coughs and splutters. Is this possibly a problem with the idler jets? It has twin SU flat-top clones on it at the moment, and to sum it up, the closer your foot is to the floor, the less it misses and coughs. Anyone had problems like this before? And I apologise but I don't know the cam specs, the motor was assembled prior to me getting it. Any information is appreciated Quote
MaygZ Posted June 18, 2011 Posted June 18, 2011 I'll say it before everyone else does - Get rid of the flat tops and replace them with round tops (or triple webers ). How long has the cam been in? Has it ever run well with this cam? Points or elect distributor? How's the dwell - if points? If you disconnect the vacuum advance and drive it does it cough and fart for further up the rev range? Unless the cam is an absolute monster, it shouldn't 'hunt' at idle. That is to say the idle rpm should remain constant. The old Torana boguns think that a motor 'hunting' sounds good, but they are wrong. I suspect it would benefit from having the timing advanced a fair bit. MaygZ Quote
NZeder Posted June 18, 2011 Posted June 18, 2011 I'll say it before everyone else does - Get rid of the flat tops and replace them with round tops (or triple webers ).Nothing wrong with the flat tops if setup and working correctly. Just most don't know how to get the to work correctly and tell you they are junk. Quote
chris240 Posted June 18, 2011 Posted June 18, 2011 it could be that your jets-needles need downsizing.....ie too much juice being fed at low to mid range.. also could slightly help if you ran a hotter plug , ie one step increment only... this may help burn off a 'little" more fuel. are you using 5 or 6 series ngks ? just thoughts anyway. good luck anyway Quote
bullzed Posted June 18, 2011 Author Posted June 18, 2011 I'll say it before everyone else does - Get rid of the flat tops and replace them with round tops (or triple webers ). How long has the cam been in? Has it ever run well with this cam? Points or elect distributor? How's the dwell - if points? If you disconnect the vacuum advance and drive it does it cough and fart for further up the rev range? Unless the cam is an absolute monster, it shouldn't 'hunt' at idle. That is to say the idle rpm should remain constant. The old Torana boguns think that a motor 'hunting' sounds good, but they are wrong. I suspect it would benefit from having the timing advanced a fair bit. MaygZ I'm legitimately thinking of changing to a set of triple mikuni's or dellorto's, depending on what shows up next on the FS thread The cam has been in the motor since I've had it, which is now 21 months. It used to run well with this cam. Then the whole fiasco with a damn hose clamp getting into the 5th and 6th cylinder shagged everything up, Matt came round here and noticed that my lash pads were literally ginormous. They were aftermarket, looked like they'd been made in someone's garage, they were horrible, made the rockers sit on a wild angle. Ever since I've changed the lash pads we've been having problems with fuel and ignition. I currently has points, I really want to upgrade to electronic dizzy, (I have another '82 280zx with EFI and a different dizzy to mine, don't know if this is an electronic dizzy), so it may be possible for me to switch that over, yes? I've heard it makes a real difference to the driveability of the car. As for the vacuum advance, we used to run the car without it (obviously not intentionally), and it ran better than it does now. We only noticed it wasn't connected properly when the car started coughing and carrying on. I very much doubt it is a monster cam, it doesn't 'hunt' but rather, during it's rev rhythm, sometimes it stops short as if it's missing (really hard to notice with my exhaust). it could be that your jets-needles need downsizing.....ie too much juice being fed at low to mid range.. also could slightly help if you ran a hotter plug , ie one step increment only... this may help burn off a 'little" more fuel. are you using 5 or 5 series ngks ? just thoughts anyway. good luck anyway As for the jets, I doubt they're too big, I've had this twin SU setup for about 17 months running fine, then all of a sudden, it all hits the fan. I'm running a BP6ES at the moment, I heard BP5ES is one step hotter and they're more suited to road use? It could be a problem of the plugs becoming wet, running too rich at idle, so the BP5's may be a good idea. It's just curious that all of a sudden it all seems to be playing up. I have been thinking and a lot of other guys I've talked to have said it too, if it were electrical, it wouldn't be spasmodic, it would be continuous, yet it only occurs in a specific rev range, which brings it down to fuel delivery, right? Any more information/thoughts/experiences would be really helpful, thanks guys! Quote
bullzed Posted June 18, 2011 Author Posted June 18, 2011 Also one other thing to note. Where the distributor currently sits shows that it's a tad retarded. The problem is, if I advance it, It appears to be igniting before the piston gets to the top of the cylinder because the car has trouble turning over and starting. Is this normal? Or should it start freely? Quote
Moderators Zedman240® Posted June 19, 2011 Moderators Posted June 19, 2011 Is the cam an aftermarket or reground? If you have access to a standard cam, I'd install one and see what happens. Quote
peter mc Posted June 19, 2011 Posted June 19, 2011 please post some picks of the cam at tdc it sounds like it may be out ,or call me and i will talk you Thru it will pm you my number Quote
bullzed Posted June 19, 2011 Author Posted June 19, 2011 Is the cam an aftermarket or reground? If you have access to a standard cam, I'd install one and see what happens. I'm not too sure whether it's a regrind or an aftermarket cam. It was put in the engine before I bought it so I'm really not sure. I can get some pictures of it probably by Tuesday afternoon. I'll upload them to the thread. Cheers guys. Quote
1600dave Posted June 19, 2011 Posted June 19, 2011 Then the whole fiasco with a damn hose clamp getting into the 5th and 6th cylinder shagged everything up, Care to elaborate ? Quote
Cozza Posted June 19, 2011 Posted June 19, 2011 Gday Ive recently been having a similar sounding problem of running rough at low throttle but great once your foot is into it. Car was really fumey and I found that the front 3 plugs were fouling during city driving but no probs on the highway. Turned out to be float level was way too high in the front carb. Just a thought. Good luck Mick Quote
salty Posted June 19, 2011 Posted June 19, 2011 get it dyno turned by a competent tuner, then take note of all the settings for later Quote
bullzed Posted June 20, 2011 Author Posted June 20, 2011 Care to elaborate ? http://www.viczcar.com/forum/index.php/topic,8234.0.html Turned out to be float level was way too high in the front carb. I'll make sure to check that this afternoon when I get home. Also is there any way to detect a vacuum leak around the inlet manifold or a fracture? As for the dyno, that's some cash that I probably don't have at the present moment in time hahaha. And I'll probably wait until after I get the triples on as they're much fiddlier. Whilst I'm not too happy with yet another problem, I like when they lead to upgrades Quote
neRok Posted June 20, 2011 Posted June 20, 2011 is there any way to detect a vacuum leak around the inlet manifold or a fracture?get a squirty bottle with some water in it and spray around areas. when engine note changed, it because the water has been sucked in somewhere. you might see it bubbling too. some people use crc or other things, all the same idea. Quote
bullzed Posted June 20, 2011 Author Posted June 20, 2011 some people use crc or other things, all the same idea. I heard that if people do this with CRC, it can cause engine damage when it gets sucked in and combusted. Dad decided to pull off the whole intake manifold to check for fractures so now I'll have to check it manually. Thanks guys. Quote
bullzed Posted June 22, 2011 Author Posted June 22, 2011 Just to bring this thread to a close. While I had the intake setup pulled off, I decided to pull apart and rekit the carbies. Turns out that one of the pistons had been stuck down with some sort of build up (I hadn't suspected this because I'd pulled them apart only about 3 months ago). Put that back on yesterday arvo. Threw in a set of BPR5ES-11's and now everything seems to be perfect. The car pulls up to about 7k and no longer coughs in the low rev range. Cheers for all your help guys, much appreciated. Quote
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