High rpm miss!

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Kevin D.

Kevin D.

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My 70 340 seems to have a high rpm miss took it out to prepare for track tonite It pullls runs super up to about 5400 rpm then starts to miss but continues to 5800 red line.It is a 70 fresh 340 9.5 comp. j heads hughes cam and valve train. complete msd ign. edelbrock rpm performer 725 road demon deep pan 3200 stall headers 3.91 gears. What do you think valve float, bad springs? any thoughts would be helpful.Thanks Kevin.
 
What chip do you have in your MSD? It will start dropping cylinders as you approach the limiter, so if you have a 5800 or 6000 chip in it, then thats probably your problem. Put a 6500 chip in it and that should help.
 
The plug gaps could be to wide open OR you could be running lean. The running lean could be the floats or your just pulling in more air than gas at the higher revs.
 
I am running a 6200 chip with shift light set for 5800. Its kinda disapointing because it runs so strong up to that point.Have a carter strip mech. pump and 3/8 fuel line from tank.Thanks very much for your input.Kevin.
 
I will pull and check plugs had just put in new iridium plugs and gapped at 50 as I had read where you could go 60 with the new hi energy ign .systems. Kevin.
 
Kevin D. said:
My 70 340 seems to have a high rpm miss took it out to prepare for track tonite It pullls runs super up to about 5400 rpm then starts to miss but continues to 5800 red line.It is a 70 fresh 340 9.5 comp. j heads hughes cam and valve train. complete msd ign. edelbrock rpm performer 725 road demon deep pan 3200 stall headers 3.91 gears. What do you think valve float, bad springs? any thoughts would be helpful.Thanks Kevin.
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Hey Kevin, you say it's a fresh 340 did you recently do any new wiring under the dash? I had a mis a couple of times at higher rpms years ago and I believe it was a bad ground or loose wire. I redid the wiring the following year and never had it happen again. Jysnflem
 
I will be checking a few of these things. I hope its not the valve springs cause I have zero experience with them.Kevin.
 
my car had the same miss at the track.about the time i shifted into drive and pulled through from 5500-6500 rpm. come to find out the magnetic pickup wires in my dist.were grounding against the dist.housing and giving me a high rpm miss. it would miss in the burnout box and every once in a while had a miss driving through the staging lanes. did lots of funny things. would act like shutting off the key and back on really fast or just have a ignition pop miss in high rpm. put a new one in and works great.
 
Kevin D. said:
I will be checking a few of these things. I hope its not the valve springs cause I have zero experience with them.Kevin.
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Something else I was thinking of if you have MSD. Did you run all of your MSD wires thru the same grommet. The two distributor wires are suppose to be separate from any other wires. They can pickup feedback from other wires and cause problems. Jysnflem

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