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#1 |
Registered User
Join Date: Sep 2008
Location: Trabuco Canyon, CA
Posts: 173
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Need your opinons!
Alright I have an odd 'problem' with my 350 and I think I know what it is but I'd like to know your opinions without tellin you my thoughts to see if we think alike before I go through the effort of fixin it to find out I was wrong.
Symptoms: 1. Poor fuel economy- 10 MPG or less when I should be gettin 12 to 15 (Q-jet 750cfm) 2. Badly fouled spark plugs(Only 2 months old and are BLACK) 3. Slightly low vacuum(fluctuates between 12-15 at idle) 4. Poor low-end power with great top-end power 5. Cannot run with proper timing settings(6-12 adv base and it dies on take-off in first of if you hit the throttle harder than feathering it) 6. Timing by 'feel' and it runs great but the mark is way off the scale(20-30 adv range base) Alright tell me what you think!
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1964 Chevy C10 a.k.a. Julie Ann H.E.I. cause its better to be pointless |
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#2 |
Registered User
Join Date: Nov 2009
Location: cremona alberta canada
Posts: 63
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Re: Need your opinons!
It sounds like you slipped a timing chain.
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65 gmc 930 292 4speed 700-18 duals 39k all original 65 chevy 10 long fleet parts truck 63 gmc 950 camperized bus 350 4spd 2spd axle 64 gmc 950 spare bus 53 gmc 1ton dual bus 79 gmc c20 short course offroad race truck 355 th400(www.wheel2wheel.ca) ![]() ![]() ![]() |
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#3 |
Intentionally Left Blank
Join Date: Dec 2008
Location: Broussard, LA
Posts: 355
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Re: Need your opinons!
The ring on the balancer could have moved.
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1965 C-10 Short Fleet 468/TKO 5-Speed 2004 2500HD Crew 496/Ally Blacked Out (SOLD!!) 1997 Formula WS6 2004 Jeep Wrangler (Sold) 2013 Jeep Wrangler (Sold) 2017 Jeep Wrangler (Blacked Out on 35's) 2011 GMC D-Max Dually Denali 3500HD (Sold) 2015 GMC D-Max Dually Denali 3500HD (Sold) 2018 GMC D-Max Dually Denali 3500HD (Sold) 2020 D-Max Dually Denali on 33x12.50's 1979 GMC Short Bed Step-Side 4x4 350/350 Low Miles |
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#4 |
Senior Enthusiast
Join Date: Feb 2007
Location: Spokane Valley, WA
Posts: 8,356
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Re: Need your opinons!
My guesses –
Because it’s a Q-Jet my first guess would be to check the plug in the bottom of the fuel bowl for leaks. This will certainly contribute to fouled plugs. Most people epoxy them in place during a rebuilt, and one outfit has a screw-in solution (I haven’t read it yet but I’ve read it’s on this website): http://www.cliffshighperformance.com/. Any of the following can contribute to fouled plugs and low manifold vacuum - Intake manifold end seals that are not sealing properly, intake side gaskets, carb to manifold gaskets, leaking vacuum hoses, or even a leaking vacuum advance canister. As noted above, the timing chain could be shot or jumped a tooth - or – if the timing cover/timing tag is not original, it could be in the wrong location. Some aftermarket covers with the bolt on timing tab do not correctly orient the mark. You can somewhat check the condition of the chain by watching the timing mark with a timing light while you raise and lower the rpm. It should move somewhat smoothly up and down. If it jumps all over it could be the slop in the chain is waving throwing the timing off. The vacuum advance could be dead. Easy to check with a vacuum pump or timing light. The accelerator pump in the carb could be dead or connected on the incorrect link setting. Easy to check by looking down the carb throats and operating the throttle linkage. And then there’s the option of checking vacuum gauge diagnostics, which may reveal bad valves, springs, etc. Good luck and let us know what you find. |
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#5 |
Registered User
Join Date: Nov 2009
Location: Cremona AB Canada
Posts: 370
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Re: Need your opinons!
I would go with the slipped timing chain ,it retards the cam thus lowering swept compression (bad mileage, fouled plugs, poor bottom end power,probably poor starting)also indicated by the need for so much initial timing, and the big indicator poor bottom end but good top end power
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62 GMC 910 short fleetside 454 super t10 14 bolt w/gov lock 70s c20 front discs (built in the 80s) 65 GMC 930 dualwheel 292 4spd all origonal 39k mi(my sons truck) 63 GMC 950 camperized school bus, (Gus the bus) 350 4speed 2 speed rear 64 GMC 950 "spare" bus 283? 4speed detroit locker 53 GMC 1ton dual wheel bus 78 GMC c25 short course off road race truck(son's truck) 355 th400 14 bolt (www.wheel2wheel.ca) 88 Peterbilt 379 longhood (hauls race truck) ![]() ![]() ![]() ![]() |
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#6 |
Registered User
Join Date: Sep 2008
Location: Trabuco Canyon, CA
Posts: 173
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Re: Need your opinons!
Yep, my thoughts were a retarded cam. Though I think the previous owner did it on purpose. But if I'm in there I might as well change the timing chain. But do I get a single or double row set? Or will either work?
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1964 Chevy C10 a.k.a. Julie Ann H.E.I. cause its better to be pointless |
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#7 |
Just here to tinker
![]() Join Date: Jun 2008
Location: Holland, MI
Posts: 3,692
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Re: Need your opinons!
A double is definitely a safe bet. There is nothing wrong with a single roller but a double roller gives that little bit of piece of mind and it can handle more power. Now, before you start pulling anything apart, be sure that the PO didn't put an early style harmonic balancer with a later style timing cover, ie: a balancer that is made to be time'd in the center of the cover vise an off-set (later model) timing mark. It's not common but I've had it happen to me.
Also, be sure that you replace one part at a time. If you start replacing a bunch of different things at once, your never gonna know what exactly the problem was and that, to me, is more frustrating than the problem itself. And be sure to get the basics down first: compression test, firing order, fuel filter yadda, yadda.....
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#8 |
Registered User
Join Date: Sep 2008
Location: Trabuco Canyon, CA
Posts: 173
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Re: Need your opinons!
Alright so I looked into the mixed balancer/cover idea and found that a balancer with a 30 deg offset would put the timing mark at the top of the balancer so I just hooked up my timing light, advanced the dial to 30 degrees and the mark was right on 12 so I adjusted it to 8 test drove it and it runs great! Looks like your probably right Corts60. I will still get a new timing chain and it looks like it might be time for a new balancer as well and when I put them in I'll check to make sure timing marks align and everything. Thanks for all the help guys!
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1964 Chevy C10 a.k.a. Julie Ann H.E.I. cause its better to be pointless |
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#9 |
Member of the longbed union.
Join Date: Feb 2009
Location: Killeen, Tx
Posts: 2,158
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Re: Need your opinons!
Maybe you should teach your retarted cam some school work to brighten it up. Sorry I just had to.
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Paul 88 GMC Crew Cab dually, 454/T400 64 LWB 400 HP 350/350T Bagged, under construction! Sold most of it! 92 S10 Iron Duke 5 speed, 5/7 drop for now. soon to be bagged. Sold http://67-72chevytrucks.com/vboard/s...59#post4637759 |
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