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#1 |
Registered User
Join Date: Jan 2018
Location: TN
Posts: 263
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Bog/rough running at 70mph
I've been chasing a weird issue on my daily. 350/HEI quadrajet c1500. The truck will drive great but around 65/70 mph on hills especially it bogs down. The vacuum gauge will drop to around 5 from the normal 15-20 and the truck will start to shake/vibrate. Seems like it's coming from the drivetrain. There is a deep droning noise you can hear. It will hold 70 but it doesn't sound like it likes it. If I let off the gas it feels like the motor "catches up" and the vacuum gauge goes back up and the truck stops vibrating and drives better. If I'm going down a hill it will go 70 no problem. Any ideas? I'm thinking the distributor isn't advancing right. Timing is set at 12 btdc. How would I check this? Thanks guys.
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#2 |
Senior Member
![]() Join Date: Dec 2013
Location: Gods country East,Tn
Posts: 8,545
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Re: Bog/rough running at 70mph
Sounds like fuel starvation , start with a new fuel filter before tearing into the ignition
__________________
![]() 1967 Factory short bed - Old school '71 - 350 / 4bolt / 487 heads / Edelbrock C3BX Muncie M-22 4 speed / Hurst Comp plus Factory 12 bolt posi 3.73 / 255-70-15 Smoothed firewall / Factory cowl induction Power disc brakes / power steering / 3.5-5" drop |
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#3 |
Registered User
Join Date: Aug 2009
Location: Bowser
Posts: 13,594
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Re: Bog/rough running at 70mph
When you replace the fuel filter, check the volume the fuel pump puts out.
Should fill a quart jar in 30seconds or less. |
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#4 |
Registered User
Join Date: Mar 2016
Location: hickory, ky
Posts: 1,278
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Re: Bog/rough running at 70mph
Rebuild your q jet. Just went through the same crap. It was an Edlebrock though. This cheap junk they call gas eats them up.
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:My build thread http://67-72chevytrucks.com/vboard/s...d.php?t=807535 1972 K10 swb/1968 Camaro 350/4spd 1955 210 2 dr sedan/1998 RCSB Z71 |
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#5 |
Registered User
Join Date: Jan 2018
Location: TN
Posts: 263
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I'll give that a shot. It's a rebuilt qjet from National Carbs in Florida probably about two years old. I'll pick up a new filter for it from napa tomorrow and see if it helps. Thanks guys.
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#6 |
Senior Member
![]() Join Date: Apr 2016
Location: Cypress, TX
Posts: 3,683
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Re: Bog/rough running at 70mph
I bought my Quadrajet from National Carburetor when they were offering lifetime warranty. Did yours have that warranty? I noticed recently they don't mention it on their website any more. When I bought mine there was a choice of whether to buy it with the lifetime warranty for some additional money. If yours has the warranty you can contact them and send it back and they will work on it and send it to you. I sent mine back one time so far.
But fuel filter first thing to try and less trouble to do. Last edited by dmjlambert; 01-18-2023 at 12:06 AM. |
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#7 |
Registered User
Join Date: Jun 2010
Location: Upland Ca
Posts: 4,143
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Re: Bog/rough running at 70mph
Also check the "sock" filter on the inlet tube in the gas tank. Another thing you could check is the total advance, should be about 34 to 36 degrees total timing at 2,800-3,000 rpm. Good luck, Lee
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1972 C10 SWB, Air, PS, PB, 350/350THM. Second owner. 1965 Corvette roadster, 44K miles, 327/365 SHP, 4 speed, side exhaust, knockoffs, teak, second owner (bought in 1970), Have ALL numbers matching components. My frame off restoration thread: http://67-72chevytrucks.com/vboard/s...d.php?t=556703 |
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#8 | |
The Older Generation
![]() ![]() ![]() Join Date: Aug 2006
Location: Montezuma, Iowa
Posts: 25,477
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Re: Bog/rough running at 70mph
Quote:
LockDoc
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Leon Locksmith, Specializing In Antique Trucks, Automobiles, & Motorcycles (My Dually Pickup Project Thread) http://67-72chevytrucks.com/vboard/s...d.php?t=829820 - |
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#9 |
State of Confusion!
![]() ![]() Join Date: Jul 2002
Location: Gulfport, MS USA
Posts: 46,844
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Re: Bog/rough running at 70mph
I agree with the fuel sock issue. Only other thing I have run across is fuel line size. is it 3/8" or 5/16" line. I had a original 6 truck with v* swap that ran fine until the engine really want fuel at high speeds.
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Bill 1970 Chevy Custom/10 LWB Fleetside 2010 Toyota Tacoma PreRunner SR5 Double Cab - DD Member of Louisiana Classic Truck Club (LCTC) Bill's Gallery Life isn't tied with a bow, but it's still a gift. Live simply. Love generously. Care deeply. Speak kindly. Leave the rest to God! |
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#10 |
Post Whore
![]() Join Date: Feb 2016
Location: Portland Oregon
Posts: 11,084
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Re: Bog/rough running at 70mph
Asto the OP's question. To check the timing advance hook up a timing light and while looking at the timing mark on the balancer rev the engine up. The mark should move about an inch. This the very basic test to see if the mechanical advance is working. For more detailed information there are dozens of videos and other articles on the interweb that detail how to set the timing properly.
On the fuel side a quick and easy check would be to remove the gas cap and do a test run. That would tell you if your tank isn't vented properly. You didnt mention what year or how modified your truck is. That information may help us troubleshoot. Also any rubber hose between the fuel pump and the tank should be checked to see if it has collapsed. If it looks flat it may be collapsing and restricting flow to the fuel pump. Good luck and keep us posted on what you discover.
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Thanks to Bob and Jeanie and everyone else at Superior Performance for all their great help. ![]() RIP Bob Parks. 1967 Burban (the WMB),1988 S10 Blazer (the Stink10 II),1969 GTO (the Goat), 1970 Javelin, 1952 F2 Ford OHC six 4X4, 29 Model A, 72 Firebird (the DBP Bird). 85 Alfa Romeo If it breaks I didn't want it in the first place The WMB repair thread http://67-72chevytrucks.com/vboard/s...d.php?t=698377 |
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#11 | |
Registered User
Join Date: Jan 2018
Location: TN
Posts: 263
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Quote:
The truck is a 69 1500 lwd 2wd. Goodwrench 215 hp V8 sitting in the i6 position. I'm running an ancient edelbrock sp2p intake. The truck is as stock as I can keep it. I'm running a 1969 original air cleaner housing as well. The fuel lines have not been swapped over to the v8 size. Thank you for the advice on the timing. It's good to hear this is probably just an issue with fuel starvation and not timing. I will keep y'all updated when the parts arrive. Posted via Mobile Device |
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#12 |
Senior Member
![]() Join Date: Apr 2016
Location: Cypress, TX
Posts: 3,683
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Re: Bog/rough running at 70mph
Under the cab there is probably a short piece of fuel hose that goes between the hard line from the gas tank to the hard line on the frame. And at the engine there is another short piece of fuel hose that goes from the hard line on the frame to the fuel pump. You probably replaced the one going from frame to the fuel pump when you put in the engine. I suggest inspect the one under the cab and if it has not been replaced before you may need to replace it. If it is very old or maybe original be careful because it can crumble in your hand when you give it a squeeze and the gas will siphon out of the tank all over the floor or ground. Since you are going to be removing the sender to put a new sock on it, it means you will be disturbing the hard line that goes from the tank to under the cab and will cause movement at the fuel hose under the cab. The truck original fuel hose was not rated for gas with ethanol, but make sure your new one is. Since ordering a sock you may also need the fuel sender rubber grommet for when you put the sender back in the tank.
I'm not 100% sure on the fuel hose arrangement for 6 cylinder because I have an original V8, so my info may not be completely accurate. |
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#13 | |
Registered User
Join Date: Jan 2018
Location: TN
Posts: 263
|
Quote:
My sending unit was replaced about 4 years ago. I ran rubber fuel line from the sending unit to the metal line under the cab due to the original line breaking. Now that y'all have brought up the collapsing issue I'm going to replace that with a metal line and set it up like it would have been from the factory. I haven't taken it for a spin yet but progress is progress. Posted via Mobile Device |
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#14 |
Registered User
Join Date: Jan 2018
Location: TN
Posts: 263
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Re: Bog/rough running at 70mph
I meant to update this a while ago but better late then never. The fuel filter helped the truck. But it is still having that stumble at 60-70. I advanced the timing to around 14-16 before tdc and it ran better at high speeds. I'm thinking maybe the vacuum advance may be not working now. Still a strange situation. New fuel lines are on order as well.
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#15 |
Senior Member
![]() Join Date: Dec 2013
Location: Gods country East,Tn
Posts: 8,545
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Re: Bog/rough running at 70mph
The Small block Chevy engine that built America using 50+ year old technology in stock form is one of the most basic engines to survive 50+ years and still be a favorite engine in many muscle cars and trucks , They will run with gas that smells like turpentine , 5lbs of oil pressure , No air filter , Vacuum leaks , points ignition , and keep going ! Add an HEI and good maintenance and you've got a runner , Always start with the basics fuel/ compression and spark .
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__________________
![]() 1967 Factory short bed - Old school '71 - 350 / 4bolt / 487 heads / Edelbrock C3BX Muncie M-22 4 speed / Hurst Comp plus Factory 12 bolt posi 3.73 / 255-70-15 Smoothed firewall / Factory cowl induction Power disc brakes / power steering / 3.5-5" drop |
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#16 |
Registered User
Join Date: Jan 2019
Location: St Peters, MO
Posts: 439
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Re: Bog/rough running at 70mph
Since you mention timing and vacuum advance, I recall having a similar issue when getting my truck on the road where it seemed to bog/lunge when cruising on the highway at a specific speed.
When building my truck, I installed a new GM HEI P/N 93440806, which came with an aggressive vacuum advance (added 20 degrees at 7.5" per a spec I found on-line). Mechanical advance for that HEI at 2400 RPM is rated at 16 degrees. After messing around and trying out different combinations, I figured I was getting too much total timing at high vacuum/cruising, so I changed the vacuum can to a Standard Motor VC204: 14 total degrees advance, 10-12 max advance, starts at 7-9". That really seemed to do the trick. I'm running my vac can off of the manifold port, and have 12 degrees of static timing (IIRC). I've tried it both ways and my engine prefers the canister on manifold vacuum. Since then I've had to replace the GM coil and module and went with Davis Unified Ignition (DUI) parts, which really woke up the engine, maybe not related but it runs way better than it ever did on the stock GM HEI. I know my specific details likely don't apply to your situation, but thought it might give you a few ideas. Maybe block off your vacuum advance and see if there's any difference, give it the ol' suck test or replace it with another? Here's a good explanation & reference for some common GM vacuum canisters, their specs and typical applications: http://outintheshop.com/faq/Vac%20Adv%20Spec.pdf
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1967 C20, 350 SBC w/Comp roller cam, 700R4 w/3.42 posi, PS, 4-wheel PDB, Old Air AC & GM Tilt column. |
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#17 |
Registered User
Join Date: Apr 2022
Location: Moorpark, CA
Posts: 755
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Re: Bog/rough running at 70mph
OP
confirm your vacuum advance is working correctly. Ideally use a mighty vac and increase vacuum to what the truck makes and confirm the VA travel is not sticking. |
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