good troublershooters needed

[chevysteve2]

ready to pull my hair out.

I have a crate zz 502. everything is new on this motor. I changed the stock (224/236 @ .50)cam to a 236/242 @.50, put in roller rockers. The problem I have is when it hits 5000rpm it misfires. I have a mighty demon 825 cfm. I have a 6al box. I have changed the carb with a 850 DP and it still misfires. I sent the msd box back to the factory and they tested it and said it is good. MSD said that the box will work the same at all rpm, along with the magnetic pick up in the HEI distruberter. I changed out the coil with a another blaster 2. A friend said he thought I had weak valve springs. the stock springs have 135 at the seat. the comp cam springs that the camshaft calls for, have less seat pressure. the new cam has .20 less lift. I spent 700 bucks on a chassis dyno and tuner today and parts. My tuner could not figure it out. A visual check was peformed on the springs. The car runs excellent, good idle, but when it hits 5000 it falls on its face. Hp peaks at 3500 and slowly tapers off until 5000 it steeply falls off. The jettting was almost dead on, he fattened up the primaries to get it perfect. The A/F ratio stayed at 12 the whole time. He put in new plugs and wires and a new msd billet distruter. timing was at 34 total. nothing changed. The next thing I will do is put new springs in. Is ths a waste of money? Does any one have a suggestion?


thanx,
steve :arrow: :evil: :evil: :evil: :evil: :evil:

[lanham]

You should check what switches you have to your ignition.I had a similar problem with a high end miss and it ended up being the toggle switch to my ignition box.May not be your problem but a $5.00 toggle switch can be a nightmare too.

[topsportsman1]

Whats the spark plugs gapped at?

[gs97s10chevy]

what are you running for a stall?

[cepx111]

First a question.
Did the motor misfire above 5000 before this cam change?

If it DID the problem is not in the cam change or springs pressure etc more than likely something else I.E. electrical bug somewhere in ignition.

If it did NOT misfire before then its definetly pointing to something in the cam change.
I. E. incorrect cam to crank alignment or inadequet spring pressure, improper valve installed height etc.
Sounds like not enough spring pressure for the cam to me, and just because the springs are new as you say in the motor doesn't mean they have the right spring pressure required for the cam you installed.
Its always a good idea to install new springs ANYTIME you install a new cam, saves headaches and give peace of mind when you do run into roadblocks such as this by simply eliminating major things like springs right off the bat.
However it could be something as simple as a cam being out of degree, I'd double check that then springs next.
Goodluck, Charles

[gimmemud]

Almost deffinatley spring pressure.

[SST4530]

If you have an eltronic tach,(most do) it could be shorting out at around the 5000 rpm range. I had this happen with a Mallory tach once. Almost never figured it out. :)

[chevysteve2]

I checked all the easy stuff first, the ignition switch, the converter flashes out before 5000, I experminted with different plug gaps, and I disconnected the tach. Today I Ordered a set of springs and I will let you guys know what happens when they are installed. Thank you all for taking the time out to help.

steve :P :P :P

[SST4530]

Hope the springs do it for ya! :)

[john858]

could be your high side chip .

[chevysteve2]

I installed the springs and the car did the same thing. I called MSD tech and was told it could be electro magnetic interferance. I disconnected the alternator wire and belt did the car did the same thing. I put foil on the magnetic pick up wire, didn't work either. I am going to try to rev it up to about 4000 and cut the fuel pump when the weather permits, to see if that is causing interferance. I have a spare BBC with a bad crank if all else fails I will build my spare motor and drop it in the car, at least I will know if it is a mechanical problem. because I have had 3 carbs on the motor already. If anybody Knows of a race shop with a excellent reputation in southern calif. send me a PM. By the way the car did this before I changed the cam.

thanks for all your help
steve

[binderman]

Could it possibly be fuel reversion?

[johnracer]

Does it have a full exhaust system on it? Could be restricted cat or mufflers....

[gimmemud]

Have you changed out the rev limit chip in the msd box, I have seen a few of those go bad.

[gs97s10chevy]

If your stall is to tight it will cause this problem.

[27keith]

As posted before, Whatever you are using for an "ON switch" change it. Painless rocker switch, toggle switch, anything its a 5 or 10 dollar fix!!!! I chased a bad Painless switch for 4 weeks. Racecar idled fine and you could roll into throttle till a certain rpm before it started missing. If you matted the thing it was breaking up terribly from the get go. Would not have believed it till I had it happen to myself.

[jayss10]

check your balencer to make sure it hasent spun ,i had a new 1 do it on first run,it was 22 deg. off it took me a 1/2 season to find the problem ,it was a new, bhj :?

[kw89425]

what is your valve lash setting?

[chevysteve2]

The car has been sitting through the winter. But I tried messing with it a little. The converter is a nitrous holeshot that flashes out about 2900 rpm with this motor. The cam is a hydralic roller I have set the preload from 1/2 to 1 turn. My next plan is to borrow a friends distrubeter and wire up a second battery that is just dedicated to running it. That should take all electrical gremlins out of the equation. I have changed the electrical switch. The exaust is 3 inch flowmaster that dumps right before the rear axle. The blancer has not slipped on the elasometer. I have changed the areomotive return fuel system, to a dead head system. I do apprecate all the input from everone, and can't wait to flog my car above 5000rpm. :twisted: :shock: :lol: :twisted:

[adragrcr]

I'd check engine ground and wire guage on voltage supply and terminals connecting the wiring.

[olds48]

My 496 used to break up REAL bad right at about 5500-6000.Electrical checked out okay,fuel pressure was not dropping and plugs looked fine(didn't appear to be lean)Talked to an old-timer down the street,first thing he asked was what size power valve was in my Dominator.I told him plugs,front and rear.He said put one in the front.Idle vaccum measured about 5.5-6" and I stuck a 4 in it.No problems since.I don't fully understand it ,but food for thought anyways.I have found in the past that ignition problems and fuel delivery problems act almost identical.Look at everything and don't get tunnel vision on the electrical system.JMO :D

[bbcheat]

I had that happen on a 358 one time. I switched distributors, wires, Msd,valve springs. Come to find out the spark plugs were too hot, range wise. Sometimes it is the simplest things. Good luck!!