I Have a 68 400 4 sp Convertable, edlebrock Carb, performer intake, fresh restore just got it out after 3 years and does not run good at all, although it did before the restore, the only thing I had really done to the motor was pull the Dist,carb,trany,not much else. Car seems to have crazy vibrations towards the end of every gear (3300-4000 rpm) Where do i start? Ignition? Carb? Vacume? Clutching?
well, we know its not bad gas. you just did the tank, yes?
thats a tough one. check everything. does it ONLY do it when your moving? and only in that rpm range? if so, i have put driveshafts in without centering the rear ujoint, and had similar vibrations. since you recently had your tranny out, that would be something to check. normally clutch problems will chatter while releasing the pedal, or just slip. see if you can get it to do this while standing still, under load. this will help you determine if its engine only, or drivetrain connected. i have even gone so far as to put a car on jackstands and simulate driving to chase down vibrations. sometimes even keeping the p. brake on for short periods to simulate load. be careful, and i hope this helps.
Start with the basics - make sure the timing is correct. If the carb has been off the car sitting on a shelf, check for vacuum leaks, float setting, stuck needle and seat. The Edelbrock carbs are easy to rebuild and the kits are readily available at any national speed type shop.
I tend to agree with Quenton - check timing first. If the engine was in the car when the body work was done with the carb on it, then it may be worth the time to pull the carb apart and clean it up.
Gas Tank Deffinetly not! Carb,nah.. has been off the car and wrapped in plastic and is brand new although the secondary does not seam to open while car is moving, sounds crazy mean in neutral. Timing maybe! To what degree should i set to? Hey what about some kind of Points or Coil problem? Maybe its time for HEI. driveshaft im not sure about , wouldnt it only vibrate at high speeds? this seems to run rough in every gear towards the latter part of duration, although, I do have a high speed vibration in the shifter at around 60mph i really dont think its related but ive been known to be wrong, this does seam to be driveshaft, would drive shaft also cause poor performance thru lower gears? I wouldnt think so, What do I know though I sell carpet for a living,lol. Who said Vacume leak? Im thinking Vacume also. Where do i start with that one?
It might also be "point bounce." I recall having this exact problem years and years ago when I was so much smarter and knew everything. I just can't remember how I fixed it, although I know I was pulling wayyyyyy too much advance ... like 50 degrees. I also replaced the points and set them with a dwell meter.
i would put all the origional stuff back on.i see no need for all that racing stuff unless you plan on taking it to the race track.if that is the case,you will need to also put a roll bar in that rag top
yeah, driveshaft problems dont normally show up till you're on the highway. i'm just throwing out ideas.
quenton's suggestion about point jump sounds plausible. i'd never heard of that before.i dont know what causes it. check that the advance plate isn't loose, and everything else in the dist. is in good shape. points and condenser are cheap. put some in and set them with a meter if you have one, otherwise just set'm w/ the feeler guage 'till you can get a meter.
vacuum leaks are easy to find. spray a little carb cleaner around any suspected areas-all hoses, all over and around the intake, and at the base of carb. if there are vacuum leaks, the idle will stumble.
ign. timing for a 68 400 engine is 9*btdc at idle speed with dist advance plugged. point gap is 0.016 with a dwell of 30*. idle speed i have two figures. with and without idle stop solenoid plugged in. i guess thats like a dashpot. i dont know if you have one, but the idle speed is 850 with sol. plugged in, and 650 without. all figures are with engine at operating temp and manual trans in nuetral.
I'm not sure if it's caused by points being gapped too wide or too close, but basically the spring that closes the points becomes weak over time, and as the distribtor turns the points open too far, then slam shut, which causes them to bounce open again (like a rebound). Sends too many sparks through the distributor and makes the car run like cr*p at high RPM.
New points, gapped right, and the correct initial timing should be the ticket.
If not, let me know ... I need to learn something today!
If not, let me know ... I need to learn something today! Q
i just did. point bounce. i do my points every 10,000.
how about this "a dead owl can't fly backward in the rain"
i dont know what it means, but one of the guys i used to work with said it all the time. esp when someone was using an improper tool or generally f**king up, so there must be something to it.
This late at night, it might make more sense to start this as another topic...
but, how about: "That guy could ruin a perfectly good anvil." I used to hear that all the time where I used to work. (Among many other unprintable things!)
Axles and related Driveshaft out of balance or bad u joint Bad trans bearings clutch/pressure plate throwout bearing engine mounts pinion lock nut backing out (bad rear)
Also, bad vibration/poor performance could be valvetrain related...bad springs?
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1967 Starlight black PMD Engineering 400 Auto 1968 Alpine Blue 400 4 speed 1968 Verdoro Green 400 HO 4 speed 2013 1LE 2SS/RS Inferno Orange Camaro.
