Well I never made it to the track. I was on the way down there with my friend and wife in the truck and this 2000 camaro SS pulls up beside me and reved his engine. The road was open with no traffic so when the light turned green I nailed it. I hit about 4,500 and it started backfiring real bad so I grabbed second started again at about 4 grand. To my surprise I smoked the camaro though even though I had 2 extra people. THe guy was a good sport about it and just said wow and gave me the thumbs up and drove off. I now had to figure out what was wrong so I tried tightening down the carb and checking the pertronix gap and still no luck. I then ran my tank out of gas almost and filled it up to the full mark to eliminate bad gas. I went home and got my neighbors carb off his 390 and put it on my truck and still had backfire. Put my carb back on and put new carb gaskets in with still... no luck. I am stuck. All of the vaccum hoses and plugs are good. I do hear a hiss but can't decide whether its the carb just being a carb or if something else is leaking. I would hate to think its an intake gasket but its not a consistent backfire. It does it at all different rythms so I am almost for certain it isn't just one cylinder. It idles like normal. It is even worse now that I have driven it a little. What gives? I didn't make it to the track but I did win a race I was expecting too loose by a long shot. Those 3.70 gears made more of a difference than I thought they would. I'm going to try and run a new positive wire from the coil to the ignition. It has to be either spark or a vaccum leak.

 

Cool!

That reminds me of when four of us in my friends Shelby KR beat a guy in a hemi 'Cuda on Whittier Blvd. back in the good 'ol days.

As far as the hissing, could be just carb. talk but have you tried spraying every with Gumout to find a possible leak?

Barry

 

You didn't talk about the 'awsome look of surprise' on his face! Everybody thinks trucks are slow!

I'd look to a vac leak because you've already tried a different carb. If you hook up a vac guage does it pull a steady vac? I like the old carb cleaner sprayed around the intake trick, cheap and effective.

 

Check the header bolts, One may have worked loose after that 2 hr starter change out.
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In the cool still quiet of night, you can hear chevies rusting away.

 

Got a question about the gumout. How does that trick work. I always use starting fluid (cold engine only) and when you find the leak the engine speeds up. I'm definitely going to try that. I am leaning towards ignition a little too. The positive wire is going to get replaced. I wish it was just a header gasket or even a starter at this point John much less a loose bolt but the headers just don't leak. :+

 

Hi
just a thought here. When you get a misfire at high RPM and its NOT vacuum related, I would check for an internally shorted coil OR a heat/vibration fatigued duraspark module(if you have one on yr truck)
however in your case, I would check for a vacuum leak FIRST then consider ignition!

Good Luck

regards
Ben

 

Well I thought about the vaccum leak and if I did have one I would think <- (not always a good thing for me) that it would idle rough so spraying starting fluid around shouldn't have any effect unless it was stumbling at idle... Then I was also thinking that at one time I lost a vaccum cap from the vaccum tree and it lost a lot of power but didn't backfire. I have no power loss until it backfires now. I just swapped the coil and put a new connector on the postive terminal. No luck. I am out to check the plugs now. I have the pertronix II ignition which is about 1 month old but still a possibility. We'll see. Thanks for all the help.

 

The carb. cleaner works the same way as starting fluid but it's a lot safer, you can do it on a hot engine without it blowing up in your face. Use the straw on the nozzle for a pinpoint spray. Without the straw, the spray can "fog" and be sucked directly down the carb. giving you a false indication that you found the leak. I do little squirts at a time and wait for the engine to catch up. Have found that old hoses can be porous too.

I think you're right that it might be something else though. If the ignition is crapping out at high rpm, try this. Assuming you are running bigger plug gaps, close them all down to around .034" and see what that does. Also make sure that the 7,8 plug wires are not too close to each other. If they have to overlap, do it like an "X". Also try putting a timing light on it and watch the flashes as you rev it. If it's ignition breaking up you should be able to see the flashes go erratic.

Another possibility is either your valves are floating or one or more are sticking.

Barry

 

Well I think I figured it out. When I changed over to pertronix it was because it was backfiring kind of like it is now.. I checked the gap on the module again and it was exactly .030. I over gapped it and it would barely pull its own weight. I under gapped it probably about .020 and it pulls hard to 5500 and starts backfiring a little but not as bad. This could mean either I'm not getting enough power to the module or the module is going bad. The plugs look exactly like the "this is correct" picture.

 

Here is some more info: I took voltage readings off of my postive coil wire. It has 12.75 volts with the key on and not running. Idling it has 12 volts and at 2,500rpm it goes all the way down to 9. Is this normal.

 

I don't have any hands-on experience with the Pertronix unit but my Unilite system voltage stays rock hard up to the redline.

I'm wondering if the supply voltage to the unit is also dipping. Does it come off the "+" of the coil too? My guess is that's whats killing it. Maybe somebody could measure their Pertronix system for a sanity check.

Barry

 

Yeah it comes off the positive and negative sides. I replaced the wire from the firewall back to the coil to eliminate the 30 year old wire bundle but it didn't help. I can't find where that bugger goes once it goes inside the cab.

 

Sean, I have been reading your post's and can't help wondering if you are running Champion plugs. When I worked at the dealership I cured a many vehicle with plug "breadown" or bustin' out. Champion's would not run in a Ford,4,6,8 cyl. it didn't matter. I wouldn't run anything but good old Motorcraft,I had one customer that had put in a new set of Champ's, brought it to the shop for breaking down, put it on the tune up machine, told him what it was, he was doughtful till I put a used set of motorcraft's I had changed out doing a tune up on another customer's truck and cured it! From then on he would jokingly ask for used plugs. Btw, I just bought the reg. pertronix ignitor & coil, but haven't had time to put it in, I am going to run a new wire from the switch to the coil. Enough rambling, woody

 

>Yeah it comes off the positive and negative sides. I
>replaced the wire from the firewall back to the coil to
>eliminate the 30 year old wire bundle but it didn't help. I
>can't find where that bugger goes once it goes inside the
>cab.

Mine changed over to the pink resistor wire and went toward the switch. I just bought some new wire and tapped into one just before the pink resistor wire, then cut the resistor wire out and ran straight out to the coil.

If you've got the pertronix coil, you can bypass the resistor wire. I didn't do this at first then found it later and it made a difference.

I've also heard that the resistor wires can go bad over time.