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  #121  
Old 08-20-2019, 07:09 AM
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Bob- I would love for that to be the root of the issue. I'll double check tonight. When I originally installed my old distributor, it was 180 out and the engine would backfire, sputter, barely run at all. Currently, it starts right up and idles decent, but a little rough. Then when revved above 1k rpms, vibrates and sounds like ass.

I need to post a video and maybe someone can pick up on something I've not mentioned.

Daniel
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  #122  
Old 08-20-2019, 07:45 PM
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This afternoon I removed the distributor and plug wires, reset the engine to TDC, reinstalled the dist and wires...no improvement. Put my timing gun lead on all plug wires and verified they were all firing.

I then adjusted/closed the carb idle screws on all four corners and it seemed to reduce the vibration...maybe 30%. I noticed #1 plug was fouled again when I was setting TDC, so I'll replace them all and continue to tune the carb. Also, I shot the header tubes with the infrared gun after adjusting the carb and the temps were much closer to each other.

Lastly, I removed the counterweight on the flywheel and weighed it. Mine weighs 161 grams and the PRW tech I spoke to yesterday said it should weigh 156.1 grams. He said more than a couple grams could effect the balance. I know 5 grams isn't much (weight of a quarter), but I'm hoping with it being so far from the crank centerline, it's causing the vibration. Fingers crossed. I'm going to have him send me another...with the correct weight.

Daniel
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  #123  
Old 08-21-2019, 08:23 PM
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PRW is sending me a 156.1 gram counterweight that'll be here Friday.

On another note, I did a compression test today-
1- 215
3- 215
5- 210
7- 215
2- 215
4- 215
6- 205
8- 210

I'm ready to get the vibration solved and drive.

Daniel
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  #124  
Old 08-25-2019, 05:56 PM
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Good news, the engine vibration seems to be gone/acceptable. I installed the replacement flywheel counterweight and that reduced the vibration about 20%. Then I tuned the carb with a vacuum gauge and that reduced it another 70%. I initially had the corner idle screws out 1.5 turns per Holley. With that, I only had 4hg of vacuum. I adjusted the screws until I had 11hg of vacuum at idle and 20hg at about 2500 rpms. The corner idle screws are at about 1/2 to 2/3 of a turn out from fully seated.

I believe the remaining 10% is just me not being used to a big cammed stroker motor. I visited my painter on Saturday and he has a 68 Camaro with a 383 stroker and has as much vibration in the steering wheel at idle as I do now.

My engine temps are much better as a result. It sits about 190-195* at idle.

I have 3 current issues I’m working on:
-after about minute of idle, the exhaust starts to “pop” every few seconds. I guess the pop would be considered a backfire
-when I let the clutch out and I’m coasting, the car surges/bucks
-when I shut the car off, I have engine run on for a few seconds. I can get around this by cutting it off in gear. But I’d rather fix it properly.

I feel that these issues are tied to the carb and I need to continue to tune it. But, I don’t really know what to do next. I did retorque the header bolts and sprayed carb cleaner around the carb hunting for a vacuum leak, but didn’t get an rpm change.

Daniel

Last edited by DWC; 08-25-2019 at 08:52 PM.
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  #125  
Old 08-26-2019, 08:49 AM
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That is great news! The rest of your issues sound timing related to me. What are you using for a distributor and ignition?
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  #126  
Old 08-26-2019, 11:01 AM
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Lance- I have about 35* total timing (15 initial, 21 mechanical advance). I have an MSD billet distributor, MSD Street Fire ignition box, MSD Blaster SS coil, Taylor 8mm plug wires, and Autolite 3922 plugs. All of those are new.

Daniel
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  #127  
Old 08-26-2019, 08:55 PM
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You should consider getting the car tuned at this point. Might not be easy finding someone that knows how to tune a carb unfortunately. I agree with Lance. Your current issues are carb/timing issues.

Glad you go the vibration figured out.
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  #128  
Old 08-26-2019, 10:04 PM
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run on is usually timing, maybe carb if the engine isn't worn out. I'd verify TDC (ie make sure your timing mark is accurate) then throw a light on it. Most SBC like around 18 initial and 18 mechanical. But I'd be surprised if 15 initial caused run on. Is the carb new? If not, did you put a rebuild kit in in recently? Also, not sure if i saw what you said you had the idle set at...
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  #129  
Old 08-27-2019, 07:18 AM
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Trey- Funny you say that. Yesterday, a friend gave me the number of a local guy that tunes carbs. I have a few more things to try on the carb, and if those don't pan out, I'll probably take it to him.

I hope I can figure it out on my own, because I'll need that knowledge/skill in the future with this car.

Steve- The carb is new. The idle is about 900rpms. I'm going to pull the carb and check the transfer slot adjustment. My idle mix screws are only about 1/2 a turn out. I think the car maybe idling partly on transfer slot fuel. At least that's my understanding from reading the past few days.

Daniel
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  #130  
Old 08-27-2019, 10:54 AM
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So, in this day and age, there are better ways to control timing than mechanical advance. I have a couple spare MSD 6AL-2 boxes that when used with a locked out distributor you can use to make the timing whatever you want it to be whenever you want it to be. I ran one for about 5 years on my 383 before swapping to EFI couple months ago and it worked great. You can even tie in a MAP sensor to really tie the timing to load as well as RPM.

When I watch the display now of what my Holley EFI ECU is doing to my timing to control my idle and cruise...it blows my mind. I'm not suggesting that you switch to EFI now (but you would love it if you did) but watch this display to see how my ECU makes my stroker idle like a 2016 Camaro.

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