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New 351W Missing Problem at Higher RPM
Just recieved a rolling chassis build from Lonestar. Engine is the 351W with 750 Holley Avenger, MSD and Mallory ignition, with Roller rockers, and Mid range cam, with World Performance Iron Heads.
It was tuned in Texas and said to run fine. In michigan it misses on some cylinders at around 3600RPM under load from the secondaries. Tried leaning the carb out and seems to help some, but affected lower end tuning. Plan on getting a mechanic to "tune up" this brand new car with 150 miles, but wondered if any other readers have experienced this problem! I was told it may be due to temp and or humidity differences from Texas. |
What do the sparkplugs look like. It could be the carb or the ignition, you need to eliminate the possibilities.
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I could be something as simple as a cracked plug or a bad plug wire/connector. Start with the simple - cheap things before you start throwing money at it.
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Heck, it could even be free, like if the distributor's rotor is loose.
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I've had a simular problem where my engine was missing at higher rpm. In fact, I really didn't notice until I got it up on a dyno and saw it on the graph. I had previously had the car dynoed 2 weeks prior and was surpised when I took it back to the dyno and it was down 25hp.
It turned out that the metal piece in the cap that contacts the rotor had fallen out and the rotor was arching the gap. Replaced the cap and the motor gained 25 hp...:D Samurai |
thanks guys, I check some of the plugs and the wires and the cap and all seemed OK. I plan on taking it to a good mechanic and have him check it out.
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The last car I bought was a 93 pontiac bonneville. It had a stutter under accelleration and couldn't decide what gear it wanted to be in. The owner popped the hood, I just looked at it for a moment, touched nothing, but saw a sparkplug wire not connected. Said nothing about that, bought the car cheap right then, and fixed it in ten seconds at the gas station on my drive home. Disconnected sparkplug wire that was it.
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I pulled all the plugs last night and 5 out 8 were very black with carbon. Most were not gapped correctly. If anyone can confirm what autolite 25 plugs should be gapped at this would be appreciated. I was told .55 for MSD ignition so i set them there.
Most plugs were .33 to .40, with one being .18. Have not tried it yet, but will this weekend . |
mark check the initial timing then total advance you may have to retard it a bit Ron
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I had this problem once...
Had a van once that did the same thing.
The coil had a crack in the top of it, that allowed some of the oil to get out. The mounting bracket had a sharp edge to it, and so every time we would replace the coil (along with everything else trying to "nuke" the problem), it would crack the top of the coil again. Finally an old guy at a no where gas station in Nebraska showed me what was wrong, and why. Eric |
I also had a high end miss that took months to sort out. It turned out to be the "star" shaped thingy (retractor?) in my Durasapark slightly rising up at higher rpms. The fix was a new pressure fitting to snug it down. I agree with the opinions to change wires, cap, rotor, plugs , do careful visual check of all distributor wires, connects and test again. If it is consistent at the same rpm I would guess ignition.
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poor runner
lots of good help here. you should try and run it on a dyno with Air fuel meter and then you can ajust out the rich lean problem. should not really cause a miss just run poorly . i dont agree on the .55 gap should be .38 or .40 range thats kind of wide, can cause miss if to short or to tall. i am not sure how they ran MSD with Mallory setup. usually only MSD runs its parts. but on the dyno you can see the miss and if power problems. also check you timing, if its off you will be chasing your tell. be careful . i have seen personally poorly marked harmonic balancers so check for original marks. i picked up 20 hp and 30 torque when i learned the timing marks were off an reset the timing back to 30. on my 289. gotta like that it was free. keep us posted on what you have done and find. shouldnt be to difficult, easy to do plugs wires. then dist. or box.
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Thanks guys I may re-gap the plugs back to around .40 which is where most were when I got the car. I think it may be in timing and will check it out tonight.
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Final result after having a mechanic buddy check it over was:
The floats needed adjusting, both front and back were low. The engine was starving for fuel when the secondary kicked in. It runs like the "beast" it should now. Boy what a ride. Now I know why you guys love these cars and buy wider tires.:cool: |
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