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#1 |
Registered User
Join Date: May 2000
Location: Richmond, KY
Posts: 13
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My 67 C-10 250 three on the tree is not running as smooth as it used to.
The symptoms are: 1). It seems like it is running on 5.5 or five cylinders. You can really tell when you are trying to pull a hill. 2). When I shut it down after it operates under normal operating temperature, it has a loud backfire. We have recently converted the distributor to a HEI pointless ignition and replaced the carb a few months before that. The carb has never worked as well as the old one. I have tried to troubleshoot and have done the following. 1). reset the timing several times. 2). verified the wiring, distributor and coil. 3). I checked the compression to see if I had a valve problem. The book I have says the compression is 130 psi. From front to back, starting with the first cylinder, I range from 125-150. Cylinders 2-6 are within 5-10 pounds. The first cylinder is about 20 off from the others. Don't know if that is contributing to the problem or not, but wanted to check it anyway. I have not changed the plug wires, they are new, but I know that doesn't necessarily mean they are good. I checked the gap on the plugs when I checked the compression, they were all close, if not right on. I am frustrated and wondered if anyone has some tips before I hand it over to a garage. I checked some of the archieves and didn't see anything that addressed my issue. I am wondering if we have the distributor off a tooth? Or if the new carb is the culprit. Thanks in advance. ![]()
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1967 C-10 Custom, 250, 3 on the tree. |
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#2 |
Registered User
Join Date: Dec 2002
Location: Canada
Posts: 695
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Did the troubles exist before you converted to HEI?
Did the troubles exist before you changed carbs?
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1968 Chevy - 292 with a powerglide |
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#3 |
Registered User
Join Date: May 2000
Location: Richmond, KY
Posts: 13
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It never has run as good with the replacement carb.
I am a little leary of replacing it since it would run me around $100. That is a pretty expensive guess. There is supposed to be a good carb guy in town I was thinking taking it to. We have tweaked on it to our ability. The old distributor was wore out. It would backfire some when going down a hill. The cam was wore almost in a perfect circle. I was hoping it was something simple. This was my Grandpa's old truck. He bought it new, and I got it after he died. He would never give it to me while he was living. It only has 105K miles on it.
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1967 C-10 Custom, 250, 3 on the tree. |
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#4 |
Registered User
Join Date: Apr 2003
Location: Central PA....In the Berg of Nisbet
Posts: 790
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Maybe you got a bad plug? I have gotten Champions(Well, my buddy bought them.........I always use AC's) for our Farmalls that were bad, and they were brand spanken new!
My brother's 69 C-10 did the same exact thing.........But the shmuck who sold us the truck had put the plug wires on wrong...............It is a 250 and it likes to back fire, but I have the timing more advanced than it should be...............But man, pulling 300 bu gravity wagons up mountains with a 250 and 3spd, with 3.73 gears it runs like man out the straight exhaust stack we have on it!!!!!!!!!!!!11
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'72 K-20 EFI'ed 250 Inline/4spd stake body, Farm Truck '71 C-20 Cummins Diesel Powered, In storage thanks to $5.00 diesel! '69 3500 GMC 305V-6/4spd, Still under reconstruction.......... Inlines Rule! 6 soldiers standing is better than 8 laying down!!!!!!!! |
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#5 |
Registered User
Join Date: Jul 2002
Location: Cedar Hill, MO
Posts: 426
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It sounds like a timing problem to me. Might want to check if the distributor was put in at TDC for sure. Good luck.
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1969 Chevy C10. Dakota Digital Gauges, 383 Votex Engine, MSD 8361 Distributor, MSD 6A Unit, Demon Carb, Phoenix Transmission 4L80E trans, 3:73 Posi Rear End Early Classics 6 Lug Disc Brakes and Spindles All Stainless Lines |
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#6 |
Registered User
Join Date: Nov 2002
Location: Florida
Posts: 42
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sounds like a timing problem to me also
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1968 SWB CST |
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#7 |
Registered User
Join Date: Jan 2003
Location: Washington State
Posts: 8,834
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Hope the plug wires are for the HEI.
And assuming that you eliminated the yellow wire from the old distributor to the starter when you converted.
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1970 Chev CST 2003 Harley Fatboy 1975 Chevrolet Step Van 1956 Chev Bel Air 1977 Blazer 2WD For Sale $3000.00 1978 Blazer 2WD For Sale $7000.00 1978 Silverado 2005 Monte Carlo |
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#8 |
Registered User
Join Date: May 2000
Location: Richmond, KY
Posts: 13
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I am pretty sure the wires are the right type.
As far as the yellow wire to the starter, it is still there. What does that do?
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1967 C-10 Custom, 250, 3 on the tree. |
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#9 |
Registered User
Join Date: Jan 2003
Location: Washington State
Posts: 8,834
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Disconnect the yellow wire from the starter...........its not needed.
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1970 Chev CST 2003 Harley Fatboy 1975 Chevrolet Step Van 1956 Chev Bel Air 1977 Blazer 2WD For Sale $3000.00 1978 Blazer 2WD For Sale $7000.00 1978 Silverado 2005 Monte Carlo |
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#10 |
Registered User
Join Date: May 2000
Location: Richmond, KY
Posts: 13
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Thanks Bluebeard. That helped it some. It is running better after I removed that wire than it has in a long time. I don't know why, but it is.
I may get her back to normal after some more timing and carb tweaks. She may be back to purring like a kitten soon ![]()
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1967 C-10 Custom, 250, 3 on the tree. |
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#11 |
Registered User
Join Date: Sep 2003
Location: Franconia,N.H.
Posts: 1,029
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I know my 67 backfired because the carb was junk. as for the rest I have no clue
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(Only) Member of the CPNE Fan Club ![]() ![]() 67 C-10 350 with 3-speed tranny and 308 gears swb step ![]() 82 Z28 Camaro 355 small block over 350 hp and a borg warner super t-10 (blown engine) 72 Chevy K20 Suburban (future project) 70 Chevy K20 now 68 GMC K2500 2003 Chevy 2500hd ccsb 4X4 (daily driver) |
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#12 |
Registered User
Join Date: May 2000
Location: Richmond, KY
Posts: 13
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It is a prime suspect.
The truck has only had 3 carbs in its lifetime. The original was not as good as the second. The second was the best carb I ever had. I had to replace it with the one I have on it now. It is a rebuilt model, like the second, but has never performed well, in my opinion. I hate to guess, pull it off, and replace it with another near $100 dollard rebuild. Unfortunately it is not like the old days when I had these things laying around everywhere and changed them out once a week (or weekend ![]() ![]()
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1967 C-10 Custom, 250, 3 on the tree. |
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#13 |
Trying to stick with it
Join Date: Jul 2002
Location: Atlanta,GA
Posts: 115
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How long ago did you change the HEI. If i'm not mistaken the position of #1 on a HEI is different than a point type distributor. At least it is on a V8.
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69 Chevy C10 LWB somewhere in the pile of parts in my garage. 01 Cadillac STS as daily driver |
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#14 |
Registered User
Join Date: May 2000
Location: Richmond, KY
Posts: 13
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2-3 months ago, maybe longer. I don't drive it too much, maybe once or twice a week, especially since it is not running as good as it has been, and drinking extra gas.
Where can I find the firing order, if it is different than the stock distributor? Maybe I misidentified the distributor. The one I used was out of a 70 Nova 6 cylinder. It has an external coil, but no points. I was told that is what it was, but maybe that is not what it is.
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1967 C-10 Custom, 250, 3 on the tree. |
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#15 |
Trying to stick with it
Join Date: Jul 2002
Location: Atlanta,GA
Posts: 115
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I'm not sure of the firing order for a 6cyl with an hei, but on a V8 the firing order is the same but the position for the #1 spark plug wire on the distributor moves over one plug clockwise. I found that out the hard way, just rebuilt Holley four barrel and rebuilt HEI, fired up truck it ran rough then backfired through carb blowing out my power valve. Once I found out the Hei is a little different I was so mad. Never did fix the Holley, just replaced it.
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69 Chevy C10 LWB somewhere in the pile of parts in my garage. 01 Cadillac STS as daily driver |
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#16 |
Registered User
Join Date: May 2000
Location: Richmond, KY
Posts: 13
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That would explain why it seems like it is running on 5 or 5.5 cylinders. I think we have it timed right. We used a light and used the settings indicated in my manual.
It does run better after I removed the yellow wire from the coil, but still is missing something. I would figure it would run pretty nasty if the wires are one out or order. Has anyone else had experience with this? Firing order that is. ![]()
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1967 C-10 Custom, 250, 3 on the tree. |
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