james lambert 3,059 Posted June 26, 2014 Report Share Posted June 26, 2014 I have this miss...it comes and goes at about 6000rpm to7000rpm Its bugging the crap out of me, i just cant stand it! I have been through every thing that makes any sense, swapped carbs eliminated the 6a box, the coil the wires compression test, check valve adj. I just built this engine and it only has about 3k miles on it this miss just showed up one day, to piss me off I guess I cant decide if its ign or ind????? or WTF Got any great ideas?? 327cid .030 bore Keith Black flat tops 2.02 early fuelies manley h beam rods large journal steel crank CL77s main studs ect Crower cam.. very close to hottest GM hyd perf cam Crower springs retainers locks performer rpm intake 750 race demon carb hooker hedders hamburger pan and windage Msd pro billet dist Msd 8.5 mm wires Msd 6al ign box Quote Link to post Share on other sites
storm6490 2,768 Posted June 26, 2014 Report Share Posted June 26, 2014 (edited) ethanol gas! j/k ground strap check carb filter check pcv check fuel pump check plug wires and plugs check. correct jets. check manifold vacuum level. Wish I was there. Sounds like a good mystery. Good luck! Edited June 26, 2014 by Stryker0946 1 Quote Link to post Share on other sites
james lambert 3,059 Posted June 26, 2014 Author Report Share Posted June 26, 2014 It comes then goes away, not fuel, I swaped carbs no vacuum leaks, done wires and ign box plugs. I havnt changed the fuel pump, but the filter is clean Quote Link to post Share on other sites
wasrNwarpaint 184 Posted June 26, 2014 Report Share Posted June 26, 2014 test with a vacuum gage look for any fluctuations in the reading that sync with the miss, if nothing unusual get it on a scope looking for electrical issues 1 Quote Link to post Share on other sites
james lambert 3,059 Posted June 26, 2014 Author Report Share Posted June 26, 2014 It only shows up above 6000rpm, i dont like to rev it that far with no load. I pretty much have to drive it to reproduce the problem I took a 4 pin gm hei module and wired it to the msd distributors mag pick up and to a seperate coil. then took power and ground direct from battery. that eliminated the electrical system before the distributor as well as the coil and 6al box. wires and plugs have been swapped as well. the mag pick up in the dist has not been changed, but cap and rotor were swapped . like I said this is a mystery miss Quote Link to post Share on other sites
grutiantor 0 Posted June 26, 2014 Report Share Posted June 26, 2014 whats your plug gap set at? miss randomly on all cylinders or just one or two specifically? Quote Link to post Share on other sites
james lambert 3,059 Posted June 26, 2014 Author Report Share Posted June 26, 2014 whats your plug gap set at? miss randomly on all cylinders or just one or two specifically? Its hard to say, it acts like all cyls, just a hesitation and stutter. Gaps are r45 @ .035 about 14btdc.....7000ft above sea level Quote Link to post Share on other sites
Sim_Player 1,939 Posted June 26, 2014 Report Share Posted June 26, 2014 A few ideas.. http://wiki.answers.com/Q/What_causes_an_engine_to_sputter_at_high_RPM Are any plug wires close together? Quote Link to post Share on other sites
james lambert 3,059 Posted June 26, 2014 Author Report Share Posted June 26, 2014 This engine was built to go to 9k It has the valve springs to make that with out floating a valve. A cam that will go there. an ignition that will do it. rods that can live at 8k or more all day long A good balance with flywheel and pressure plate (not the disc) it was running perfect for 3000 miles, and I pushed it up to about 7800 rpm many times, with no problem at all. The wires are the best MSD makes and are new, also they are loomed properly. I know I could run plug gaps up to .060 but the question is what changed. I came from perfect performance to this high rpm miss The plugs look perfect brown electrode, porcelain is pure white Its not a lean miss, but i may rich it up a little built lots of high end engines....this is strange Quote Link to post Share on other sites
wasrNwarpaint 184 Posted June 26, 2014 Report Share Posted June 26, 2014 just because the wires are new doesn't mean its not the problem..(with electrical you cant assume its works because its new)..eliminate the wires as a possibility by using an ohm meter to check the resistance of each wire from the cap to the plug wire end....resistance readings should all be relatively the same if you should find an anomaly in one reading replace that wire and recheck your readings Quote Link to post Share on other sites
HB of CJ 1,263 Posted June 26, 2014 Report Share Posted June 26, 2014 (edited) Ahhh.... a blast from the past. This one may be easy for this Old Coot. Water in the gas. Bad low octane gas...the 2.02 heads need good stuff. Point bounce. Change out the valve springs. Lean high rpm fuel mixture multiplied by the aforementioned things. Enjoy. Back in 1967, I traded a whole expensive shit load of guns for a 1957 Chevy 2 door. Hope this helps. HB of CJ (old coot) "You got "three on the tree"?...you're shitting me!!" Now we are going way back! What do your plugs look like? If you are set up for 9000 rpm, then you may have a mis match of components. No need to rev that high. Also consider lifter pump. Edited June 26, 2014 by HB of CJ Quote Link to post Share on other sites
james lambert 3,059 Posted June 26, 2014 Author Report Share Posted June 26, 2014 Here is the car, It HAS to run just right. 1968 SS RS 3 Quote Link to post Share on other sites
Spartacus 1,619 Posted June 26, 2014 Report Share Posted June 26, 2014 Was going to mention plug gap too.... what about timing? You could try backing off or even advancing timing to see if it changes. Does it change with engine or outdoor temperature? Nice ride! Quote Link to post Share on other sites
james lambert 3,059 Posted June 26, 2014 Author Report Share Posted June 26, 2014 just a few days after building this engine , I drove it to AZ on the rt66 run from seligman to topac, It was 106 deg on one of the days, engine ran at 165 right on the thermostat. 1600 mile round trip, not a miss. Timing is exactly were I put it, wires ohm out fine. About the only things unknown aat this point is the mag pick up in the distributor and the fuel pump Quote Link to post Share on other sites
termite 463 Posted June 26, 2014 Report Share Posted June 26, 2014 Jim, I was going to mention floating a valve/valves, but you said the springs would handle it. Might be worth it to check them and make sure. Quote Link to post Share on other sites
Maxwelhse 1,285 Posted June 26, 2014 Report Share Posted June 26, 2014 (edited) Crower cam.. very close to hottest GM hyd perf cam Jim, I was going to mention floating a valve/valves, but you said the springs would handle it. Might be worth it to check them and make sure. Doesn't mean a lifter isn't failing (or defective) or a push rod/rocker arm isn't ever so slightly bent and causing odd geometry. My money is on valve train since it's only at high RPM. 7k is asking a lot out of a hydraulic cam no matter the quality. I don't want to start a pissing match but 9k on a hydraulic cam is just begging for trouble. Crower SOLID cams are legendary... I don't actually know anyone running one of their hydraulic cams (to the extent that I didn't even know they made them). If I missed something and it IS a solid cam, and everything else checks out, I'd probably pull the valve springs and check their rates on the bench. Edited June 26, 2014 by Maxwelhse Quote Link to post Share on other sites
Matchgrade 27 Posted June 26, 2014 Report Share Posted June 26, 2014 You can be leaning out because the fuel supply can't keep up with the carb demand on the high end. I wonder what your fuel pressure is over 6 grand. It should be at least 7 pounds. Quote Link to post Share on other sites
Maxwelhse 1,285 Posted June 26, 2014 Report Share Posted June 26, 2014 You can be leaning out because the fuel supply can't keep up with the carb demand on the high end. I wonder what your fuel pressure is over 6 grand. It should be at least 7 pounds. He say's he's confident that it's not a lean miss, but $50 on the dyno would prove it. Good thought. Quote Link to post Share on other sites
gunman1 1,753 Posted June 27, 2014 Report Share Posted June 27, 2014 A lot of guys in my Corvette circle have scrapped the MSD ignition because of shit just like what you've described. One of the guy's offered to give his whole setup for free, I turned it down. Funny thing....I'm running damn near the same build that you described in my Vette, just with the original 350, I'm also running the original ignition system too, just all rebuilt. Try putting the stock ignition back in if you still have it, just for shits and giggles. Good luck with it, and let us know what you find out about it. Quote Link to post Share on other sites
james lambert 3,059 Posted June 27, 2014 Author Report Share Posted June 27, 2014 The assembely is solid to 9 in terms of( it wont fly apart) ie top shelf rods pistons crank main studs fluidamper balance ect well....not the very best pistons i could have got...Kieth Black? The crower cam is 288/296 497/504 its in Straight up Crower claims 6200 peak, but desk top dyno shows it good for quite a bit more. Its been real close to 8k a bunch of times and is still pulling good, I set hyd lifters to zero lash, then about .030 down, they wont (pump up) quite as early keeps the valve on the seat at a little higher rpm. and they will start clattering real quick at the first sign of wear or something wrong in the valve train. Max is right, I am pushing the limits of a hyd cam. I prefer solids (roller) for real race stuff, but this is just my street car. And I drive it on long trips, has to run on pump gas But every now and then.....a street car has to put up or shut up. This car needs to rpm pretty high as it has a 4.11 gear, a disc brake posi from a 70 camaro...about 2'' wider than it should be. I put a tremec 5 speed in it.....1.68 to 1 over So I have my cake and eat it too, the low gear to launch off the line...the over for the freeway running Quote Link to post Share on other sites
james lambert 3,059 Posted June 27, 2014 Author Report Share Posted June 27, 2014 A lot of guys in my Corvette circle have scrapped the MSD ignition because of shit just like what you've described. One of the guy's offered to give his whole setup for free, I turned it down. Funny thing....I'm running damn near the same build that you described in my Vette, just with the original 350, I'm also running the original ignition system too, just all rebuilt. Try putting the stock ignition back in if you still have it, just for shits and giggles. Good luck with it, and let us know what you find out about it. I eliminated the MSD 6al and coil early on, Last thing I did today was to pull the distributor and replace the pick up. That didnt fix it . Its going to have to be something in fuel delivery maybe the sock in the gas tank I am pretty sure...it will turn out to be the LAST thing I check 1 Quote Link to post Share on other sites
Voltia 375 Posted June 27, 2014 Report Share Posted June 27, 2014 (edited) We need more info. Does this happen every time at that engine speed and gear? Does it happen once and stay gone? Does it pulse, like every few seconds? How did you "eliminate" the ign box and coil? Is it missing, or falling on its face? A miss is ROOOOOOOOOOOOAR-PAP-ROOOOOOOOOOOOOOOAAAR and falling on its face is ROOOOOOOOOOOOOOAR-bluuuuuuuuuuuuuuuuuuuuuh-rrrrRRRRROOOOOOOAR Misses are usually electrical, falling on your face is fuel or air. Also, does this happen near a shift point? Torquey engines twist and move wires, some wires have bad connections. Edited June 27, 2014 by Voltia Quote Link to post Share on other sites
james lambert 3,059 Posted June 27, 2014 Author Report Share Posted June 27, 2014 We need more info. Does this happen every time at that engine speed and gear? Does it happen once and stay gone? Does it pulse, like every few seconds? How did you "eliminate" the ign box and coil? Is it missing, or falling on its face? A miss is ROOOOOOOOOOOOAR-PAP-ROOOOOOOOOOOOOOOAAAR and falling on its face is ROOOOOOOOOOOOOOAR-bluuuuuuuuuuuuuuuuuuuuuh-rrrrRRRRROOOOOOOAR Misses are usually electrical, falling on your face is fuel or air. Also, does this happen near a shift point? Torquey engines twist and move wires, some wires have bad connections. Its a miss you can feel it kinda break up a little then pick up run a bit repeat Its at high rpm over a normal shift point. I used poly motor mounts, they dont twist much, and I have seen engines torque over and stretch wires to failure, then flop back and run normal. I went to a parts store this morning bought a GM 4 pin hei module, the kind in a mid 70s GM hei distributor. That module will trigger from any mag pick up, and most crank triggers pin w to the MSD pick up + pin g to MSD pick up - pin b to coil+ and to +12v pin c to coil - I wired direct to battery this eliminated the cars electrical system and the MSD 6al box, I also used a different coil The only part in the ignition not eliminated was the pick up in the distributor, I replaced that later with a new MSD part No joy, max w thinks valve train...possible for sure! The carb was about the first thing I swapped out, both carbs have sight glass.. bowl levels were good. But it may be right on the edge of starving at max rpm, then when you slow down the bowls catch up. It doesnt fall off like it ran out of fuel.... With the electrical out of the way...not much else it could be but fuel delevery Quote Link to post Share on other sites
JESS1344 508 Posted June 27, 2014 Report Share Posted June 27, 2014 JIM, IT'LL BE SOMETHING SIMPLE......... DO YOU HAVE SIDE-HUNG OR CENTER-PIVOT FUEL BOWLS, WITH THE SIGHT PLUG IN THE SIDE, TO CHECK FUEL LEVELS (PRESUMING A HOLLEY CARB HERE)? MAKE SURE FLOATS ARE AT PROPER LEVELS, AND THERE ISN'T ANY TRASH IN THE FUEL LINES, THAT AT HIGH RPM (AND FUEL PRESSURE) WOULD BE FORCED DOWN INTO THE NEEDLE SEAT, BLOCKING IT. MESSED WITH THE NEOPRENE FUEL LINES LATELY? ALL IT WOULD TAKE IS A SMALL PIECE OF THAT NEOPRENE........ DISCONNECT THE FUEL LINE(S) AT THE CARB, PULL THE COIL WIRE, AND HAVE THE FUEL LINE(S) EMPTYING INTO A CLEAN CONTAINER. ROLL THE ENGINE OVER, SO THAT THE FUEL PUMP GIVES ABOUT FOUR SQUIRTS, AND SEE IF IT PUKES ANY TRASH. IF THAT'S CLEAR, CHECK THE NEEDLES AND SEATS FOR TRASH. WHAT TYPE OF FUEL FILTERS DO YOU HAVE IN THE CARB? IF IT'S THE ONE THAT LOOKS LIKE COMPRESSED GRANULATED BRONZE, HOW DID YOU CHECK IT? IT CAN LOOK PERFECTLY CLEAN, BUT BE PLUGGED SOLID. LET THE GAS EVAPORATE OFF OF IT, AND THEN TRY TO BLOW YOUR BREATH THROUGH IT, HARD (THINK LOUIE ARMSTRONG). IF IT WON'T FREELY PASS YOUR BREATH, IT'S PLUGGED. ANOTHER OLD TRICK, PULL OFF ONE PLUG WIRE AT A TIME, AND SEE WHICH CYLINDER DOESN'T MAKE THE ENGINE MISS WORSE. YOU'VE NARROWED IT DOWN TO THAT ONE CYLINDER AND ITS COMPONENTS, IE, PLUG WIRE, PLUG, LIFTER, VALVE SPRINGS, VALVES, VALVE SEALS, PISTON, ROD, ETC. ANYONE HAVE A FIBER OPTIC VIEWER TO RUN INTO THE CYLINDERS? IF SO, SEE IF YOU CAN SEE AN EYEBROW SHAPED IMPACT MARK ON A PISTON TOP, FROM A VALVE STRIKE. THAT VALVE WILL BE BENT, IF ONLY SLIGHTLY. A CROSSCHECK ON THIS, IS TO RUN A COMPRESSION CHECK. JUS' MY $.02. 1969 PLYMOUTH ROADRUNNER CHRYSLER TRU-BLUE 383 CID 750CFM HOLLEY DUAL LINE - DOUBLE PUMP 50CC ACCELLERATOR PUMPS, FORE AND AFT 80 JETS IN THE PRIMARIES, 85'S IN THE SECONDARIES EDELBROCK TARANTULA INTAKE ACCELL DUAL POINT DISTRIBUTOR ACCELL WIRES CRANE FIREBALL 510 HYDRAULIC CAM CRANE ANTI PUMP-UPS STOCK 10:1 COMPRESSION PISTONS OIL PRESSURE JACKED TO 80PSI WITH A 1/4 NUT UNDER THE RELIEF SPRING I-2 SHIFT GOVERNOR PLUG IN THE VALVE BODY, FROM A 1970 TORQUEFLIGHT, FOR A CRISP I-2 SHIFT 4:88 POSI-TRAC REAR GEARS, WITH 25" TALL TIRES (MAKING THE 4:88'S PROBABLY 5:00+) RED-LINE 7500+ RPM JESS1344 Quote Link to post Share on other sites
james lambert 3,059 Posted June 27, 2014 Author Report Share Posted June 27, 2014 4.88s The Tarantula DATES you , must be an old fart like me. Apx .500 lift double valve cuts in pistons....no valve interference. Only misses 6k and up, hedders are about same temp on all 8 with an ir thermometer. same miss with two carbs. Two inline 3/8 fuel filters ....clear no resistance Demon and quick fuel carbs , both dual feed dual pump center hung mechanical Quote Link to post Share on other sites
termite 463 Posted June 27, 2014 Report Share Posted June 27, 2014 I went to take a shower and think about it, and I think I've figured it out. When you nail it really hard, the front end wants to raise up, and the gas is running back into the tank, same principle as jacking up the rear end when we wuz kids to get more gas to the carb, Yeh, that's it. But all kiddin aside, I still think it's in the valve train. Quote Link to post Share on other sites
nukeme70 7 Posted June 27, 2014 Report Share Posted June 27, 2014 (edited) I'm almost embarrassed to post here, as I am a casual mechanic, and don't even know if this is applicable, but it might be... I had mushy brakes a while back, changed out all the obvious things, was dreading changing out the master cylinder, then found the problem was the vacuum hose had gotten mushy from heat, and everytime I mashed the brakes, the hose would collapse. $0.90 later, 10 minutes to change the hose, and my brakes were great. Please be gentle on any mocking...I don't even know if the vacuum system comes into play in your situation, but if so, might be something to look at. Edited June 27, 2014 by nukeme70 Quote Link to post Share on other sites
james lambert 3,059 Posted June 27, 2014 Author Report Share Posted June 27, 2014 I'm almost embarrassed to post here, as I am a casual mechanic, and don't even know if this is applicable, but it might be... I had mushy brakes a while back, changed out all the obvious things, was dreading changing out the master cylinder, then found the problem was the vacuum hose had gotten mushy from heat, and everytime I mashed the brakes, the hose would collapse. $0.90 later, 10 minutes to change the hose, and my brakes were great. Please be gentle on any mocking...I don't even know if the vacuum system comes into play in your situation, but if so, might be something to look at. Mocking a person trying to help, will never happen. Vacuum leaks make lean mixtures, lean pop in exaust, hard to start, fast eratic idle, and over heating. So YES you are correct! vacuum hoses and leaks can cause all kinds of trouble. I only have two, one to the brake booster and one to pcv, both are ok. But Thanks for the idea! In the morning I am going to pull the fuel pump and drop the fuel tank. Its about the only thing left to do or I could just go bang my head on the wall Quote Link to post Share on other sites
JESS1344 508 Posted June 27, 2014 Report Share Posted June 27, 2014 (edited) JIM, YEAH, 63,,,,,,,,,,,,, DON'T KNOW WHAT A DEMON CARB IS, BUT I THINK I COULD STILL FIND MY WAY AROUND A HOLLEY............... IS THERE A FUEL FILTER IN THE CARB, WHERE THE FUEL LINE GOES INTO THE CARB, AS ON A HOLLEY? THAT'S THE ONE YOU BLOW THROUGH. DOES THE DEMON HAVE A POWER VALVE IN THE JET PLATE (DOES IT HAVE A JET PLATE?), AND COULD THE DIAPHRAGM BE BLOWN? DO THE ONE PLUG WIRE OFF AT A TIME TRICK, AND SEE IF YOU CAN ISOLATE IT TO ONE CYL. CHECK NEEDLE AND SEAT FOR TRASH. JESS1344 Edited June 27, 2014 by JESS1344 Quote Link to post Share on other sites
Voltia 375 Posted June 27, 2014 Report Share Posted June 27, 2014 Ok, based on your response, I don't think it's fuel. I bet you've got a cracked connection someplace. Check your coil ground. I think the engine torquing through the shift is causing you to momentarily lose ignition. It's probably something stock and dumb on the 12V or ground side of the ignition system. Just go tug on all the wires, even the dumb ones. Quote Link to post Share on other sites
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