Hi all, I come to you a humble man. I have a story followed by a question, or questions. In my early twenties I assembled a 71 C10 short wide. I had the motor and trans from a truck I wrecked as a teen. Motor is a 283 bored .060, fully forged and balanced aftermarket (other than the crank) rotating assembly, way too much cam, 461 heads freshly machined, 2.02/1.60 valves, roller rockers, dual valve springs, performer rpm manifold and 750 cfm edelbrock 1407. I ROUTINELY see 7000 rpm, and have for the last 30K miles. This truck was my daily driver for three years, 50 miles a day and I got an average of 23 mpg as described above. I ran a 11.73 quarter on 89 chevron gas. This is the little motor that could. I've recently started havin trouble at high rpm. Over 5200 or so it pops. Like its getting more fuel than it should. Still pulls hard, but not like it should be. I'd estimate a loss of 75 hp above 5000 rpm. Also, this was also accompanied by serious backfiring through the exhaust, closed throttle, above 2000 rpm. In both scenarios, I'm seeing bright flashes coming from under the truck. During the day. Knowing I needed to anyway because the old girl sat for the last year and a half, neglected, I rebuilt the carb. Full rebuild. The only change that made was it now pops during free rev and backfires on the way down. I'm thinkin tune up, it's been 20k miles. Also, this is a points/condenser setup. No electronic ignition. Dwell set at 38, base timing at 18 btdc. My question is- can someone throw me a frickin bone here? Am I just missing somethin obvious? That's what it feels like. I may throw a cap, rotor, plugs and wires at it. Like what $60? Father's Day is comin up. Anyway.... Any ideas welcome, thanks in advance, over the years I've found myself reading the pages of these forums and being led to an answer. After three weeks of good weather and no cruise I'm hurtin for help. I just want the beast back.
Thanks, I'll try that. Less than ten bucks for a fix and I'd get a good look at the points and the inside of the cap. I had no idea they could absorb moisture, thanks again
Have you checked your valve springs? If your springs were anywhere close to 'stock', after the use you describe I would expect them to need replacement,( hopefully before you 'swallow a valve' when one of those worn-out springs finally says : "I'm outa' here!") Your description of your engine's symptoms is a classic story of worn out valve springs!
They're double springs, comp cams race units- not to say they aren't worn out. That little motor has seen some serious high rpm use so that's a possibility I guess. Lets hope it's not a $300 set of springs.... But thanks for your input sir
How old is this setup? How many miles? Maybe it's just time to go through it? Wear, tear and maybe a little abuse can take it's toll.
Try the ignition fixes first but I go along with the valve springs getting soft. I have built and raced a lot of high winding SBCs and never trusted the springs for more than one season.
If it has points, file and reset the gap. This is one of the big advantages of a converted electronic system for me. The surface of the points can and do foul up when sitting for a long time. The extra resistance doesn't show up until the higher RPMs. It doesn't cost anything and it may cure your problem. If you don't have a point file, I would not be surprised. They are still available but probably not stocked by most places. One of those things that only old farts would know about...guilty
Thank you all for the ideas. The point filing and condenser will be the definite starting point. And frankly I'll throw plugs cap and wires at it before I go big and change the springs. I would think the onset of this problem would not have been as sudden as it was if it were springs too- gradually starting to backfire at high rpm and getting worse with more driving. It does lose oil, as with any no pcv system like mine. Just a breather. But the oil stays clean.... Very very clean. So not much blowby can be occurring. These old blocks have that road draft tube vent on the back, looks like that's where most of my oil goes, from the shiny firewall I have. Naysayers: you are entitled to your opinions, I am new here and I'm not tryin to make enemies. I have enough that already know me and my truck. Granted, my truck is an unlikely animal. It does exist nonetheless.
I thought the dwell was supposed to be 28-32 degrees. Or do you want them closed more for the high rpm? saltflats beat me to it.
I wouldn't Change a thing. Sounds like you're out running and getting better MPGs than my blown 327 and in a heavier truck to boot.
Yeah closed longer for more precise high rpm timing. Even with the higher dwell I have to ballast (add resistance) to my coil hot wire. Seems any more than 11v at the coil spells dead condenser within 1000 miles And that's a shame about the 327 sir. If you have the time, here's a (in my stupid opinion) viable cause for such voodoo: My 71 pickup equipped with 4" drop rear springs 2.5" front spindles and coilover rear shocks has a pretty low center of gravity. The motor in its current state (not running like crap as it is now but built as it is) makes a pretty marginal amount of torque and horsepower at less than 2500 rpm. That's approximate launch rpm, and when it launches, being only a 291 ci motor it spins a little but hooks well and as soon as it reaches 4000 rpm or so I dump all the fuel I can down that little mouse and I have personally seen the tach read 7700. When I jam it into second around 70 mph, it grabs hard and rarely spins. This is around 4-4500 rpm (bottom of the powerband) and it doesn't take much longer to run on up to 7000 rpm, 120 mph. In second gear. Or maybe I'm just a liar.
First off: I'm sorry about that little tirade there..... I'm just tired of people that recognize how unlikely my beat up truck story is and automatically assume it's a lie. I realize it a very uncommon set up and if you saw the truck and my hillbilly butt in it you'd definitely think it was a lie. I would too. I have just taken a heap of lip about it from people who know nothin, or very little about true power and now my yah-yah trigger is a little edgy. Anyways... I'm sorry, thanks for the input. The problems were where most fingers were pointing. Points and condenser. Dwell was a steady 38 deg up to 4500 or so then it was very erratic, as it should never be. And after much dismay and too many six day work weeks I replaced the points/condenser with a high rpm set made by accel. Runs very much as it should now. Just needs a couple burned plug wires replaced and it'll be back to makin me feel like a much richer man than I am. I did turn it about 6600 rpm last night and it sounded good aside from some erratic misses from the burned wires.... Some Jegs hi-po wires are on the way As a foot note- I think the points were "floating" at high rpm, maybe from routinely seeing 7000 rpm on a $8 set of autozone points.... And I think the condenser was causing the backfiring maybe? Who cares the BEAST IS BACK!!! Y'all have a good one
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