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Post Info TOPIC: 307 timing


- Ben #2 -

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307 timing
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Changed the timing on my behemoth 307 today to help cure a stutter/bog in the top end. 

So it's a 69 307 with a qjet and edelbrock performer intake and 2" exhaust through manifolds. I'm running the points distributor. I had about 4 degrees advance at idle and when I was 3/4 or more throttle above 60 mph, I'm getting a bog or stumble. I can let off just a little and it clears up but get back on the floor and it's right there. I advanced timing now to about 12 degrees and still no pinging but the bog is still there, though now it's above 75 ish Mph. It seems to be less power in the lower end though now. 

So, keep adding timing or do I have a jetting problem or something else? Going to try and drive it a bit tomorrow and check plugs. Pipe tips are sooty black but I did have 2 plug wires not sparking since about Rambo's BBQ.....  Hopefully December I can start going on my big block, so long as the sleds cooperate this year....



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68 Malibu 307/PG. For now.....



- Mike -
Puyallup, WA


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If it's a stock cam you shouldn't go much above 12-14 degrees. I think the carb probably needs cleaning/tuning. I'd check the condition of the points too.

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'67 Chevelle -- 383ci, Jerico DR4 4 speed -- 3.19 1st gearset, Gear Vendors Overdrive/Underdrive, Strange S60 w/3.54 gears

'70 Camaro -- In the works TT 6.0L, 4L80E, ??? rear end 



- Ben #2 -

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Stock cam. I just disassembled and cleaned the carb before I put it on. Not saying I did it all correctly, but it seemed fine. I filed the points when I installed the motor but I may look at a general tune up with wires, plugs, points, set dwell, etc. Just realized the cap is even pretty loose on the distributor. 



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68 Malibu 307/PG. For now.....



- wondah whooooaman-
Colorado Springs


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I think you have a points problem.  Get rid of them and get a Pertronix module or option B find a set of Accel high performance points.  If you don't have the dwell/timing set correctly or the points are worn that will cause problems like you describe.  I really doubt its the carb.



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Mark
69 Chevelle SS
"Carpe Jugulum"
"Only those who have never learned self-restraint fear reasonable discipline" T.R. Fehrenbach

http://www.chevelles.com/showroom/data/500/showpic1.jpg
http://www.chevelles.com/showroom/da...ium/motor2.JPG
http://www.chevelles.com/showroom/data/500/breakout.JPG


- Ben #2 -

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Just looked it over pretty good. I don't think the vacuum advance is working. I put my vac tester on it and it can't even build vacuum. 



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68 Malibu 307/PG. For now.....


- Ben #2 -

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Got the vac advance in and it's stumbling even worse. Got new cap, rotor, plugs and wires. Going to get new points and condenser too and try it. I was talking to a friend and he thought the dwell could be way off so I'll get the new stuff and just start fresh. 

Also got an air filter set up since I didn't have one on it, just the qjet breathing the open air. 



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68 Malibu 307/PG. For now.....
Ben


- RAMBO -Mill Creek, WASite Administrator

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How is your fuel filter? is it before the fuel pump or after it?

When i first got my 66 cutlass, it ran like shit. Thought it was the old carter carb on it, changed over to a holley, still ran like shit. Found black chunks in the fuel bowls when i took it back off and opened it up.

Previous owner told me he had gas tank boiled the year before- and it was clean, i dropped the tank and removed the sensor, and it looked like new inside...

Problem was his filters were after the fuel pump, and the pump itself was still full of whatever crap was causing his problem before the tank cleaning... I replaced the pump (and cleaned out the carb) everything was fixed from then on.

Not saying thats your issue, but something to consider. If tuning doesn't help- open up your carb top plate and see if there is any junk inside there. I like to run the clear plastic fuel filters on new project cars so i can see if the gas is clean or gross.





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Ben R.

1968 Chevelle 300 - 454 / 4spd



- Ben #2 -

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It has a clear plastic filter between pump and carb. I need to change it because it's old. I plan on dropping the tank soon to clean it and fix the fuel sender. Also wondered if my fuel pump was bad because that filter would be dry after sitting a couple hours. But the last couple weeks, it's been staying full. Hoping to do all the ignition tune up stuff this week and change that filter, then see how it runs. 

I've been reading where some people say to ditch the filter in the qjet inlet and just run the clear plastic filter. Anyone have input on that? The reasoning given was less restriction. But I honestly don't think my 307 is pushing the fuel system to its limits. 



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68 Malibu 307/PG. For now.....



- Erik -
Snohomish, WA


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My '69 originally had a 307 in it and I never had an inline fuel filter and never had an issue.

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Erik
'69 Chevelle Sport Coupe, EFI355, TH350
'68 Chevrolet C10 Stepside Project, 292, t-56, C4 IRS (project)
'77 Chevrolet K20 Silverado LWB, 400CI, TH400
'91 Chevrolet V3500, TBI Gen V 454, 4L80E, Lifted
Ben


- RAMBO -Mill Creek, WASite Administrator

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only reason i was suggesting that was because his car sat for years & years before he got it and dropped this motor in it.



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Ben R.

1968 Chevelle 300 - 454 / 4spd



- Ben #2 -

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Got in new cap, rotor, points, condenser, plugs, wires. Its running a lot better. Dwell right where it needs to be and timing about 8 degrees. Also got an air cleaner setup on it. 

Still has a bit of a bog that seems to happen when secondaries open. Also kind of surging now at higher rpm and 3/4 or more throttle. i checked the floats when I rebuilt the carb but I'm wondering if either they aren't right or if the fuel pump isn't keeping up. 

 



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68 Malibu 307/PG. For now.....



- Mike -
Olalla, Wa


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Vacuum leak maybe, or squirter size?

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- wondah whooooaman-
Colorado Springs


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If you’re still running the Qjet, tighten the rear butterfly’s a quarter turn.



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Mark
69 Chevelle SS
"Carpe Jugulum"
"Only those who have never learned self-restraint fear reasonable discipline" T.R. Fehrenbach

http://www.chevelles.com/showroom/data/500/showpic1.jpg
http://www.chevelles.com/showroom/da...ium/motor2.JPG
http://www.chevelles.com/showroom/data/500/breakout.JPG


- Ben #2 -

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I'll try tightening the butterflies. 

I was wondering about a vacuum leak also. I'm going to vac test the trans solenoid. It's shifting at like 10-15 mph so not sure if there's a leak in there maybe?

Not sure on squirted or jet size In the qjet. 



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68 Malibu 307/PG. For now.....


- Ben #2 -

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I looked at the procedure for the butterflies and mine was pretty good but I tightened them up a little bit. The vacuum canister in the trans wouldn't hold any vac so I replaced that with another one. Couldn't find any other vacuum leaks. One wire on my alternator was broken too so I fixed that. It's definitely better now. But the pass side exhaust donut is pretty much gone. Big backfires when I let off the throttle. Going to replace that before I do anymore tuning. It's doing fine all through rpms in low gear but in high it's still surging a bit a 3/4 or more throttle and just feels like it's dragging a weight at full throttle. Instantly better if I let off to about 2/3. 



-- Edited by Bskredsvig on Thursday 12th of October 2017 11:17:28 AM

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68 Malibu 307/PG. For now.....



- Jason -
Marysville, WA


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Hey Ben,

It sounds like it's running lean. I had a similar problem with the Q-jet on my 79 Malibu. Because I didn't have quick access to jets for it, I drilled my primary jets .003" and made sure to chamfer the holes by hand with a larger drill bit.
I also found the float level low. Both those changes made mine happy. If you pull it apart to do the work be sure to post up the jet sizes and measure the metering rods with a dial caliper.

This is a very good book to help you understand the inner workings and secrets of the Q-jet. I read mine cover to cover and found it very insightful.

https://www.amazon.com/Rebuild-Modify-Rochester-Quadrajet-Carburetors/dp/1932494189

Best of luck.

Jason

P.S. Put your base timing up to 12* and make sure the advance is no more than 35* when it stops advancing WITHOUT THE VACUUM ADVANCE HOOKED UP. My mild 350 likes that also.



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69 Chevelle SS 
454 10.4:1, Engle HFT cam 244/260 at .050", .570 lift, 850 Mighty Demon Carb, TH 350, 10" TCI 3500, 12 Bolt 373's, 28x10.5 slicks 

Best Time at Pacific 6/20/2014, 11.96 @ 110 mph.

79 Malibu: 350 with Vortec heads, Performer Intake, Q-jet, TH350, 3.31 gears

Tow rig: 82 Chev C20 Scottsdale 454



- Ben #2 -

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I will probably pull it apart after I get time to do the exhaust gasket. Very familiar with drilling jets so may try that. 

I'm at 8 degrees now with vacuum not hooked up. I'm hesitant to go further because at restart when warm it doesnt seem happy. 



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68 Malibu 307/PG. For now.....


- Ben #2 -

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Got my carb apart. It's a qjet 17080213. Also says 2343 CPX I've gathered this is a 1980, Chevy carb from a manual. 

Main Jets are 73. Primary rods say 48M (possibly 49M?). Secondary rods



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68 Malibu 307/PG. For now.....


- Durand -

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Pull a plug.
The color or lack of will tell you a lot.
If needed put one new one in and run it around a few miles and then check it.

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- Ben #2 -

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The older plugs that I pulled out looked pretty good.  They were a nice toasted marshmallow color, maybe a little light. Haven't checked the new plugs yet. Assuming I'd need to do a full throttle plug chop, but now I've got the carb apart. 



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