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#1 | |
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Join Date: Feb 2017
Location: Cypress, Texas
Posts: 42
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Re: '69 C10 327 SBC Off Idle Stumble / Misfire Help - I feel like I've tried EVERYTHI
Quote:
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1969 C10 Stepside (PERCY - tribute to CDE) 1996 Chevrolet Tahoe 2-door / 2WD LS5.3/4A (ROBYN) 1998 GMC SLE Regular Cab Short Bed Fleetside 4.3/4A (LUCY) (driver) 2000 JEEP Cherokee Sport XJ 4x4 4.0/4A (RUBY, son #2) 2013 VW GTI Driver's Edition 1.8T/6A (GRAU GEIST, son #1) 2016 BMW X5 xDrive50i MSport 4.4L N63/8A (SCHNEEWITTCHEN) |
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#2 |
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Location: massachusetts
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Re: '69 C10 327 SBC Off Idle Stumble / Misfire Help - I feel like I've tried EVERYTHI
Hi Keith, Do a compression check and see if that tells you some thing! I had a broken valve spring on one cylinder and chased the ignition and fuel systems and did not find the problem until a compression test and a visual on the valve springs. At least you will know if you have a tight engine!
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#3 | |
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Join Date: Feb 2017
Location: Cypress, Texas
Posts: 42
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Re: '69 C10 327 SBC Off Idle Stumble / Misfire Help - I feel like I've tried EVERYTHI
Quote:
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1969 C10 Stepside (PERCY - tribute to CDE) 1996 Chevrolet Tahoe 2-door / 2WD LS5.3/4A (ROBYN) 1998 GMC SLE Regular Cab Short Bed Fleetside 4.3/4A (LUCY) (driver) 2000 JEEP Cherokee Sport XJ 4x4 4.0/4A (RUBY, son #2) 2013 VW GTI Driver's Edition 1.8T/6A (GRAU GEIST, son #1) 2016 BMW X5 xDrive50i MSport 4.4L N63/8A (SCHNEEWITTCHEN) |
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#4 |
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Join Date: Aug 2009
Location: Bowser
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Re: '69 C10 327 SBC Off Idle Stumble / Misfire Help - I feel like I've tried EVERYTHI
Check for uniform rocker movement.
I’ve used tall pieces of cardboard as oil deflectors when running the valves. When you set them just start with #1 and back off each nut until they click and then tighten just enough to be quiet. Do all that way. Then shut the motor off and adjust all to 1/2 turn. Sometimes if you’re adjusting the preload too quick you can cause the motor to stumble and die. Half a turn gets you close depending on whose lifters are in it. Factory setting is likely 1 turn but not all lifters are created the same. Some design differences from cam company to cam company. Then do a compression check. |
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#5 |
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Join Date: Jan 2007
Location: Puyallup, WA
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Re: '69 C10 327 SBC Off Idle Stumble / Misfire Help - I feel like I've tried EVERYTHI
Your HEI specs sound fine, just have to verify it’s working properly. After your rewiring job, it should be getting the full 12 volts, so just verify that to be sure. Is the vacuum advance adjustable? Normal HEI spark plug gap is .045, but if DUI suggests .050 for their unit, keep it there.
Since you’re a little confused on timing, here’s the skinny. Initial timing is just the engine by itself without any mechanical or vacuum advance added in. Rotating the distributor adjusts it and gets the engine in the ballpark to ensure its working well. Basically a coarse adjustment. Total timing is the engine’s initial timing, plus however many degrees of mechanical advance the distributor has. This fine tunes the initial and mechanical advances together. To adjust it, the engine is rev’d to high rpm (3-4K + rpm, depending on the spring strength) until it stops advancing, which is when full mechanical advance is reached. Personally I just take the springs out (don’t lose them!) and rev it between 1500-2000 rpm to set it because, #1, I’m not too fond of the engine screaming at 4K rpm while my head is under the hood, and #2, full mechanical advance is achieved at a much lower rpm without the springs holding it back. Using your engine and 36 degrees total timing an example….24 degrees mechanical advance, plus 12 degrees initial timing, equals 36 degrees total timing. 24+12=36. That’s your total timing. Then there’s the vacuum advance. The vac advance is used to add an extra amount of timing to increase the engine’s efficiency during low load situations; idle and cruise. Rich mixtures burn quickly, lean mixtures do not. Idle and cruise are lean operating conditions and need the extra timing from the vac advance to burn the lean mixture efficiently. So to achieve this, your vac advance must be plugged in to manifold vacuum. Timed, or ported vacuum, is used for emissions equipment your engine may be required to run, such as EGR valves, smog stuff, etc. Our trucks aren’t encumbered with that, so we can use the vac advance to its full advantage. Adding too much timing will cause detonation, so 10-15 degrees vac advance is plenty. Once hooked up to manifold vac, the extra timing will increase the idle, so you can lower it back down to 750 rpm and you should be able to adjust your idle mixture screws as outlined in the manual. Here’s a timing article written by a GM engineer…more than you want to know I bet, ha, but invaluable info: http://www.camaros.org/pdf/timing101.pdf Valve adjustment is a great idea as well. Use Comp Cams’ EOIC method for adjusting them dead on.
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72 C10 lwb fleetside -stock 350/350 combo |
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#6 |
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Join Date: Apr 2008
Location: Md
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Re: '69 C10 327 SBC Off Idle Stumble / Misfire Help - I feel like I've tried EVERYTHI
Just changed the gap in my spark plugs, old ac plugs I was told .045-.050.....went back to .035...runs alot better...Just my 2 cents I know nothing about high voltage coil...etc.
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#7 |
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Re: '69 C10 327 SBC Off Idle Stumble / Misfire Help - I feel like I've tried EVERYTHI
As I mentioned I suspected the distributor and or module is not working correctly...
Your mentioning dropping the plug gap down to .035 and it runs better, confirms a lack of high voltage for the spark system... To check the system, drop in a standard HEI distributor setup and retry your test drive...dont be surprised if it fixes the off idle stumble and misfire... ![]() ![]() ![]() ![]() ![]()
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Family and country before all others... 2006 Chevy Silverado (Daily Driver) 2012 Chevy Equinox ![]() ![]() ![]() |
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#8 | |
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Join Date: Feb 2017
Location: Cypress, Texas
Posts: 42
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Re: '69 C10 327 SBC Off Idle Stumble / Misfire Help - I feel like I've tried EVERYTHI
Quote:
Same story with the plugs, originally gapped at 0.035 and A86's then went to AP86's gapped at 0.050. Same result. I tried Performance Distributors on the phone all day today and got a busy signal so I sent a message. They do offer to have customers send in the units for testing and repair and if they don't find anything, they charge a $25 service fee so that's a viable option if I can't rule ignition out.
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1969 C10 Stepside (PERCY - tribute to CDE) 1996 Chevrolet Tahoe 2-door / 2WD LS5.3/4A (ROBYN) 1998 GMC SLE Regular Cab Short Bed Fleetside 4.3/4A (LUCY) (driver) 2000 JEEP Cherokee Sport XJ 4x4 4.0/4A (RUBY, son #2) 2013 VW GTI Driver's Edition 1.8T/6A (GRAU GEIST, son #1) 2016 BMW X5 xDrive50i MSport 4.4L N63/8A (SCHNEEWITTCHEN) |
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#9 |
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Re: '69 C10 327 SBC Off Idle Stumble / Misfire Help - I feel like I've tried EVERYTHI
Thx for the update...
This may sound silly,,, but there is a good ground strap in place between the engine block and the cab of the truck? I have witnessed a simple missing ground strap drive guys insane for weeks.... ![]() ![]() ![]()
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Family and country before all others... 2006 Chevy Silverado (Daily Driver) 2012 Chevy Equinox ![]() ![]() ![]() |
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#10 | |
Registered User
Join Date: Feb 2017
Location: Cypress, Texas
Posts: 42
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Re: '69 C10 327 SBC Off Idle Stumble / Misfire Help - I feel like I've tried EVERYTHI
Quote:
__________________
1969 C10 Stepside (PERCY - tribute to CDE) 1996 Chevrolet Tahoe 2-door / 2WD LS5.3/4A (ROBYN) 1998 GMC SLE Regular Cab Short Bed Fleetside 4.3/4A (LUCY) (driver) 2000 JEEP Cherokee Sport XJ 4x4 4.0/4A (RUBY, son #2) 2013 VW GTI Driver's Edition 1.8T/6A (GRAU GEIST, son #1) 2016 BMW X5 xDrive50i MSport 4.4L N63/8A (SCHNEEWITTCHEN) |
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#11 |
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Join Date: Aug 2009
Location: Bowser
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Re: '69 C10 327 SBC Off Idle Stumble / Misfire Help - I feel like I've tried EVERYTHI
Sounds like a float problem.
When you check the float level also check the float drop. It has to be set right too. |
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#12 |
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Location: Fairbanks, AK
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Re: '69 C10 327 SBC Off Idle Stumble / Misfire Help - I feel like I've tried EVERYTHI
Quote: “I lowered the idle to 650 RPM or so, set initial to 12° (it was confirmed only the 4° off from my initial 16° setting so timing was accurate anyway) and 36° at 3000-3200 RPM.
I ran the engine at various RPM in the garage while working on this and getting to operating temps. This was likely 25-30 minutes as I was doing a few other things, looking at vacuum (dropped about 8-10" due to idle speed)” Quote Your initial post said you had about 20” of vacuum at idle. Does this mean you now only have 10” vacuum at idle? That is way low. Barring a vacuum leak somewhere, such low vacuum indicates possible valve issues as discussed in other posts
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#13 |
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Re: '69 C10 327 SBC Off Idle Stumble / Misfire Help - I feel like I've tried EVERYTHI
A couple of items that may help. It sounds like backing the timing off helped. Have you verified that your timing marks for TDC are correct?
Misfires while turning does suggest a float level problem. When you check the float level make sure that the floats are not fuel soaked or if brass that they have no fuel inside of them. Also check that they move freely when holding the air horn level and at angles to mimic the forces felt when turning. Your plug wires could have high internal resistance that may be changing as you move the wires. Here is what I use to test plug wires and spark power. https://www.amazon.com/Lisle-20700-C.../dp/B00IXMA1RY Have you tried wiring the choke open to take it out of the equation? It is quite possible that you have more than one problem contributing to your symptoms. Here's a link to a valve adjustment procedure. https://www.crankshaftcoalition.com/...raulic_lifters
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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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#14 | |
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Join Date: Feb 2017
Location: Cypress, Texas
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Re: '69 C10 327 SBC Off Idle Stumble / Misfire Help - I feel like I've tried EVERYTHI
Quote:
HO455, thanks for the updated response. Yes, I've verified TDC and the marks several times. My new mark is about 4° behind that of the original mark on the balancer. Noted on the floats, I appreciate this information, I will check this as well. Regarding the choke, I have not wired it open but have run several settings. I may give this a try as well but the choke seems to function properly and visibly open when it's supposed to be. Another note, the same situation was apparent with the old Carter AFB as well, it had the same or similar problems with the old carb and intake set-up. Thanks for the link on valve adjustment, I'll plan to tackle this on the upcoming weekend and visually inspect the springs as well.
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1969 C10 Stepside (PERCY - tribute to CDE) 1996 Chevrolet Tahoe 2-door / 2WD LS5.3/4A (ROBYN) 1998 GMC SLE Regular Cab Short Bed Fleetside 4.3/4A (LUCY) (driver) 2000 JEEP Cherokee Sport XJ 4x4 4.0/4A (RUBY, son #2) 2013 VW GTI Driver's Edition 1.8T/6A (GRAU GEIST, son #1) 2016 BMW X5 xDrive50i MSport 4.4L N63/8A (SCHNEEWITTCHEN) |
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#15 | |
Registered User
Join Date: Feb 2017
Location: Cypress, Texas
Posts: 42
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Re: '69 C10 327 SBC Off Idle Stumble / Misfire Help - I feel like I've tried EVERYTHI
Quote:
__________________
1969 C10 Stepside (PERCY - tribute to CDE) 1996 Chevrolet Tahoe 2-door / 2WD LS5.3/4A (ROBYN) 1998 GMC SLE Regular Cab Short Bed Fleetside 4.3/4A (LUCY) (driver) 2000 JEEP Cherokee Sport XJ 4x4 4.0/4A (RUBY, son #2) 2013 VW GTI Driver's Edition 1.8T/6A (GRAU GEIST, son #1) 2016 BMW X5 xDrive50i MSport 4.4L N63/8A (SCHNEEWITTCHEN) |
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#16 |
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Join Date: Feb 2017
Location: Cypress, Texas
Posts: 42
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Re: '69 C10 327 SBC Off Idle Stumble / Misfire Help - I feel like I've tried EVERYTHI
Thanks again geezer, I will be checking the float and float drop this week.
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1969 C10 Stepside (PERCY - tribute to CDE) 1996 Chevrolet Tahoe 2-door / 2WD LS5.3/4A (ROBYN) 1998 GMC SLE Regular Cab Short Bed Fleetside 4.3/4A (LUCY) (driver) 2000 JEEP Cherokee Sport XJ 4x4 4.0/4A (RUBY, son #2) 2013 VW GTI Driver's Edition 1.8T/6A (GRAU GEIST, son #1) 2016 BMW X5 xDrive50i MSport 4.4L N63/8A (SCHNEEWITTCHEN) |
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#17 |
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Location: Falls City, Nebraska "100 Miles From Nowhere"
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Re: '69 C10 327 SBC Off Idle Stumble / Misfire Help - I feel like I've tried EVERYTHI
Run your valves again to verify you dont have one or more hanging open. Use the EOIC method, never mind cutting a valve cover. Secondly, maybe I missed it but what cam & lifters are you running? Thirdly, find a proven functional carb off another small block with comparable cam and heads just to verify a carb problem. Surely a friend or board member, perhaps a local speed shop or drag racer has a carb laying around to loan for a couple of test hits?...Lastly, read up on mods to the accelerator pumps on those AFB carbs. With those heads and a comparable semi race cam a stock 600 cfm AFB squirter aint going to cut it. I'm thinking either more volume of the squirt, and/or a longer duration of the squirt will make your 327 snap to attention...I'd loan you a proven Cliff Ruggles Quadrajet if you were closer and running a spread bore intake...Good luck, your well on your way to becoming an expert AFB guy!
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Michael of the clan Hill, "Two Seventy Two's" 71 1-ton Dually 350 4-Speed 71 C/50 Grain Truck, 350 Split-Axle 4-Speed 02 3/4 ton Express 14 Indian Chief Vintage 1952 Ford 8N, "Only Ford Allowed On The Property" ![]() "Be American, Buy American" ![]() |
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#18 | |
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Join Date: Feb 2017
Location: Cypress, Texas
Posts: 42
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Re: '69 C10 327 SBC Off Idle Stumble / Misfire Help - I feel like I've tried EVERYTHI
Quote:
Regarding the cam, it's mild at best, no lope or choppy idle but I cannot be certain what the specs are on the cam and lifters. I'd say its similar to what may have been in this 327 stock and I doubt it was one of the HP 'Vette units. My knowledge is that it was from a '65 Nova but even this could have been 275HP+. Noting again that I had the previous Carter AFB 600 CFM with similar issues, this makes me believe it's not the carb since my dad was a carb guru and rebuilt AFB, Holley and Q-Jet's for a hobby. I'll definitely take a look at a borrowed carb if the float adjustment doesn't do the trick as well as accelerator pump alternates. Thanks again for the comments and encouragement!
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1969 C10 Stepside (PERCY - tribute to CDE) 1996 Chevrolet Tahoe 2-door / 2WD LS5.3/4A (ROBYN) 1998 GMC SLE Regular Cab Short Bed Fleetside 4.3/4A (LUCY) (driver) 2000 JEEP Cherokee Sport XJ 4x4 4.0/4A (RUBY, son #2) 2013 VW GTI Driver's Edition 1.8T/6A (GRAU GEIST, son #1) 2016 BMW X5 xDrive50i MSport 4.4L N63/8A (SCHNEEWITTCHEN) |
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#19 |
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Join Date: Feb 2017
Location: Cypress, Texas
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Re: '69 C10 327 SBC Off Idle Stumble / Misfire Help - I feel like I've tried EVERYTHI
I'm posting the following picture of the lifter valley just to determine if anyone sees any lifters which look out of position or sequence. I know I need to verify / adjust the valves but figured one of you may be able to visually see something wrong here. I don't know what position the engine is at this point, it was when I was installing the new intake and carb. Just figured it may help identify an issue with the valves if present.
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1969 C10 Stepside (PERCY - tribute to CDE) 1996 Chevrolet Tahoe 2-door / 2WD LS5.3/4A (ROBYN) 1998 GMC SLE Regular Cab Short Bed Fleetside 4.3/4A (LUCY) (driver) 2000 JEEP Cherokee Sport XJ 4x4 4.0/4A (RUBY, son #2) 2013 VW GTI Driver's Edition 1.8T/6A (GRAU GEIST, son #1) 2016 BMW X5 xDrive50i MSport 4.4L N63/8A (SCHNEEWITTCHEN) Last edited by SRT8-X; 10-30-2018 at 12:57 PM. |
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#20 |
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Re: '69 C10 327 SBC Off Idle Stumble / Misfire Help - I feel like I've tried EVERYTHI
Remember that when you do the valves again, if you do it cold and use the eoic method, wiggle the slack out of the rocker. Twisting the rod is harder to get zero lash right on.
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#21 |
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Join Date: Jan 2007
Location: Puyallup, WA
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Re: '69 C10 327 SBC Off Idle Stumble / Misfire Help - I feel like I've tried EVERYTHI
Another thing to look at is the accelerator pump assembly. I once had the rubber plunger un-seat itself from the pump rod and was floating around freely. It sort of worked still, but it obviously wasn't doing it's job right. I pulled it out and re-seated it, but it did it again a couple days later. So I bought the following accelerator pump assembly and that did the trick: https://www.edelbrock.com/carburetor...mbly-1470.html. The blue plunger at the end of the assembly in the pic is what I'm talking about.
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72 C10 lwb fleetside -stock 350/350 combo |
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#22 |
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Join Date: Jul 2015
Location: Central Coast, CA
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Re: '69 C10 327 SBC Off Idle Stumble / Misfire Help - I feel like I've tried EVERYTHI
Noticed the crankcase breather hose is plugged in the photo - maybe that is just because you have it apart so just a reminder to have some means of venting the crankcase.. no venting could definitely cause tuning issues.
My 1970 350/350 truck has the stumble issue but not often enough to be a problem - I believe on mine it is the stock torque converter not very well matched to the torque curve of the cam. So the posters who have asked about your cam I would second their questions - your cam specs are important to have documented in solving your issue. I can affect the stumble by adjusting my vacuum secondary rate but that adjustment seems to change with the weather.. |
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#23 | |
Registered User
Join Date: Feb 2017
Location: Cypress, Texas
Posts: 42
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Re: '69 C10 327 SBC Off Idle Stumble / Misfire Help - I feel like I've tried EVERYTHI
Quote:
As noted, the cam is likely a stock or extremely mild grind, it has a smooth idle and no aggressiveness so I'd suspect a low end power range. I will probably be replacing the cam and valvetrain, possible aluminum free flowing heads too, after everything is ruled out. Thanks for your comment.
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1969 C10 Stepside (PERCY - tribute to CDE) 1996 Chevrolet Tahoe 2-door / 2WD LS5.3/4A (ROBYN) 1998 GMC SLE Regular Cab Short Bed Fleetside 4.3/4A (LUCY) (driver) 2000 JEEP Cherokee Sport XJ 4x4 4.0/4A (RUBY, son #2) 2013 VW GTI Driver's Edition 1.8T/6A (GRAU GEIST, son #1) 2016 BMW X5 xDrive50i MSport 4.4L N63/8A (SCHNEEWITTCHEN) |
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#24 |
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Join Date: Aug 2009
Location: Bowser
Posts: 13,629
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Re: '69 C10 327 SBC Off Idle Stumble / Misfire Help - I feel like I've tried EVERYTHI
Have you checked the valve lash yet?
That’s the first thing you should do. |
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#25 |
Registered User
Join Date: Feb 2017
Location: Cypress, Texas
Posts: 42
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Re: '69 C10 327 SBC Off Idle Stumble / Misfire Help - I feel like I've tried EVERYTHI
Geezer, I have not had a chance to work on the '69 since Monday. Will be resuming this evening and Saturday. I'm taking all suggestions into account and will verify everything but I wanted to look at the carb to verify since this is recommended on new units anyways. I'll be pulling the covers to check the valve lash regardless. Thanks.
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1969 C10 Stepside (PERCY - tribute to CDE) 1996 Chevrolet Tahoe 2-door / 2WD LS5.3/4A (ROBYN) 1998 GMC SLE Regular Cab Short Bed Fleetside 4.3/4A (LUCY) (driver) 2000 JEEP Cherokee Sport XJ 4x4 4.0/4A (RUBY, son #2) 2013 VW GTI Driver's Edition 1.8T/6A (GRAU GEIST, son #1) 2016 BMW X5 xDrive50i MSport 4.4L N63/8A (SCHNEEWITTCHEN) |
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