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11-01-2003, 11:27 PM | #1 |
Don't say "Oops!", Doctor
Join Date: Nov 2003
Location: Houston, TX
Posts: 677
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Troubleshooting the new (to me) truck...
A few weeks ago I picked up a 1968 CST LWB with a 327, factory air, TH400, Posi, and other goodies. The body's a little rough, but nothing out of the ordinary. I'm having some ignition and/or fuel troubles, though that are driving me wild.
Here are the symptoms: - Runs best when cold (choke on), but a little miss can be heard. The miss gets worse when warm. - When warm, she "stumbles" a little off the line. In other words, the truck hesitates and cuts out for a second or two when throttle is applied from a dead stop. - On occasion, the truck is hard to start (almost like it's flooded) when allowed to warm-up then shut off for 5-10 minutes. When it does start, a cloud of grayish smoke comes out the exhaust. - Good oil pressure except at hot idle when it drops to nearly zero and a slight knock can be heard from the bottom-end. - Starting today, the truck is throwing an all-out hissy fit. Now it's backfiring pretty regularly through the carb when under a load and I'm hearing a "ticking" noise that varies with engine speed and sounds like it's coming from the distributor. If I put it in drive, take my foot off the gas, then tap the throttle it will backfire once through the carb then rev up relatively smooth. These problems have been getting progressively worse as I've been driving the truck. What started as a little miss has manifested itself into a truck that doesn't like to run. The engine was supposedly rebuilt a few years back by a competent mechanic, but I'm treating it like a completely "unknown condition" engine. Here's what I've done so far: - Replaced cap, points (yes, I know... HEI is on the way), condenser, plugs, and wires. BTW, the plugs looked okay, but were carbon fouled. - Confirmed the timing at 8-degrees. - Replaced the fuel filter, air filter, and PCV valve. - Visually inspected for obvious vaccum leaks. - Verified that the power valve (or whatever that damn thing is called on a Quad) wasn't stuck. - Verified that the secondaries were closed all the way. - Literally drowned the carb with B-12. Once while running and again while shut off (and left to sit overnight). - Confirmed that the distributor looks okay. The base plate can be moved, the rotor doesn't turn backwards, nothing is cracked/missing/loose, the springs are on. - Confirmed that the vaccum choke pulloff is working as it should. Note that the engine doesn't ping (detonation) or smoke (other than described above). My thinking is one or more of the following: So, does anybody have any ideas what I might be looking at? Stuck valve? Broken spring? Flat cam? Possessed carb?
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'Mutt 1968 CST LWB: R.I.P. 1967 Chevelle: TPI 454 beast 1967 C10 SWB: Claimed when Bumpster didn't put it on his list |
11-01-2003, 11:58 PM | #2 |
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hmmm
Sounds like the possessed carb.....
Just my 2 cents....
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David M Proud Owner of A 67 C10 Shortfleet 350/350/3.73 |
11-02-2003, 12:06 AM | #3 |
Don't say "Oops!", Doctor
Join Date: Nov 2003
Location: Houston, TX
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That's what I'm leaning towards, too. The truck did sit for at least a few months (reports vary from 1-3 years) before I got it. Plus, I have no idea what the yahoos did to get it running (bought the truck at auction - used to be a well-respected mechanic's daily driver until he passed away). Guess it's time to start carb shopping.
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'Mutt 1968 CST LWB: R.I.P. 1967 Chevelle: TPI 454 beast 1967 C10 SWB: Claimed when Bumpster didn't put it on his list |
11-02-2003, 12:48 AM | #4 | |
Where's my beer?
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Quote:
BTW, Welcome to the board from PA, got any pics of your truck? |
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11-02-2003, 12:50 AM | #5 |
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i'd change the oil and filter and add a quart of marvel-mystery-oil and runn it for awhile to clean out the engine
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11-02-2003, 01:03 AM | #6 |
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sounds to me like your backfiring isnt ignition related but actually a lean pop due to the carb either being fubarred or wayyyyy out of adjustment. im gonna lean towards carb needing a new home in the trash
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Owner of North Point Car Care in Dundalk Md. We specialize in custom exhaust on both modern and classic vehicles. We are a full service auto shop from classics to modern vehicles. Feel free to contact me with questions. I will give a 10% discount to any board member. |
11-02-2003, 05:49 AM | #7 |
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try some carb cleaner..........and maybe fuel system cleaner..........
if it sat with old fuel...........
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11-02-2003, 07:14 AM | #8 |
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'Mutt
<Guess it's time to start carb shopping> I wouldn't jump off of that cliff just yet. Q-jets are pretty easy to rebuild, at least if memory serves (and that's a BIG if these days). I've had a number of them over the years and used to rebuild them occasionally.......25+ years ago. Have you checked into availability of a rebuild kit? However, if your set on a replacement there are several on E-bay. Here are links to a couple of them http://cgi.ebay.com/ebaymotors/ws/eB...tem=2439556638 http://cgi.ebay.com/ebaymotors/ws/eB...tem=2439952116 Mike
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All men are self made, but only the successful ones will admit it. Last edited by EGLIDERIDER; 11-02-2003 at 07:17 AM. |
11-02-2003, 11:15 AM | #9 |
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Location: central Ill. USA
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Hesitation off idle sounds like not enuff accelerator pump shot. Also on old carbs, the bodies tend to warp and you can see it by running a straight edge across the throttle body. Even with a new gasket there can be a slight vacuum leak. A flat file will smooth it out easily.
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69 C10 longbed: 357c.i. /TH400/3.73s/AC/ beige primer/saving $ for paint ______________________________ |
11-02-2003, 11:36 AM | #10 |
Weapons Of Construction
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Location: Colorado, USA
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My truck backfired a while back. I didn't know it at the time, but a vacuum cap had blown off when it backfired.
It would idle okay, but there was a distinct miss on acceleration. The vac cap was on the #8 intake runner. I was checking plugs, wires, dizzy cap, rotor, carb and all kinds of stuff when I stumbled upon the missing cap which was not in an obvious place. Fixed her right up! Use a can of carb spray to look for vacuum leaks if everything looks to be in place. I also agree that it could be your accelerator pump.
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1971 GMC 2500, 402/TH400 4.10 Daily Driver Lafayette, CO |
11-02-2003, 07:24 PM | #11 |
Don't say "Oops!", Doctor
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Location: Houston, TX
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A quick update...
I did a visual inspection for vacuum leaks. The PCV valve was about 1/2 way in, but that was it. I also did a carb cleaner check for leaks and came up empty. I also snuck out last night to see if I had a "light show" under the hood. It was pitch black. Finally, I pulled the vacuum advance line while idling. The engine slowed down and stumbled. The line pulled good vacuum. Normally she runs better when cold, but not this time. The truck had been sitting for over 12 hours and the miss was immediately apparent first thing. Bummer. I'm probably gonna do a two-fer swap. I've got a line on a good carb and HEI unit. Meanwhile the truck will have to sit in the corner and think about what it's done. Bad truck! BAD TRUCK!
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'Mutt 1968 CST LWB: R.I.P. 1967 Chevelle: TPI 454 beast 1967 C10 SWB: Claimed when Bumpster didn't put it on his list |
11-03-2003, 02:22 AM | #12 |
Recovering Truck Driver
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yours sounds like my 72 C-10.....same symptoms. Mines definitely the accelerator pump (long story short, don't take shortcuts when rebuilding carbs.......lesson learned)
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67 K-20 350, SM465, Eaton rear, 4.56 no spin option 00 Dodge 2500 4x4, 24V cummins, 5 speed Chad South Central Nebraska |
11-03-2003, 02:25 AM | #13 |
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Did the truck sit for an extended period of time? How old is the gas in the tank? Just a thought..
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11-03-2003, 08:05 AM | #14 |
Don't say "Oops!", Doctor
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Location: Houston, TX
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I've driven several tanks of gas through it. What started as a little miss has progressively turned into this problem.
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'Mutt 1968 CST LWB: R.I.P. 1967 Chevelle: TPI 454 beast 1967 C10 SWB: Claimed when Bumpster didn't put it on his list |
11-18-2003, 06:34 AM | #15 |
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vacuum leak at the brake booster if you have power brakes can cause all sorts of problems.
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11-18-2003, 06:42 AM | #16 |
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oh yeah watch your heat riser 2could cause some problems also
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11-18-2003, 02:48 PM | #17 | |
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Re: Troubleshooting the new (to me) truck...
Quote:
The first time, about 10 years ago, it took a valve job to fix it. Do a compression test. At least test the side with the noise. If you have compression pull the valve cover with the noise under it. I started mine with the valve cover off. It was obvious what lobe on the cam was almost flat. That rocker arm hardly moved and ticked like crazy.
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'70 cab, '71 chassis, 383, TH350, NP205. '71 Malibu convertible '72 Malibu hard top Center City, MN |
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11-18-2003, 03:07 PM | #18 |
It's a catastrophic success.
Join Date: Jan 2003
Location: Oklahoma
Posts: 2,077
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Like mrein3 said"do a compression check" You may have a bad head gasket or worse a cracked head from setting(improper antifreeze)and white smoke is a sign of water.
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11-18-2003, 10:04 PM | #19 |
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smoke=black ritch fule blue oil white coolant
step1 verify problem step2 atempt to duplicate step3 check tsb or recal(known concerns) step4 locate diag.info step5isolate root cause step6 fix or repair per diagnosis step7 verify repair step8 back to step 2 step9 bye bye |
11-18-2003, 10:24 PM | #20 |
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If the the truck has a lot of miles on it you may want to check the play in the timing chain and gears. If they have not be replaced or the engine rebuilt there could be enough wear that it could be throwing your timing off. Just my 2 cents.
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1970 Chev C20, 2wd, LB, 350 4BBL, muncie 4spd, 4:10 limited slip. 2002 Chev 2500HD 8.1L Allison, 4X4. 1996 Chev S10 Blazer, 4X4. 2006 Jeep LJ Rubicon |
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