Tired 307 bogs badly under acceleration...

JimmyDuncan

JimmyDuncan

Well-Known Member
Until the wonderful day when I can install the new engine and trans into Frank the Tank (66 Impala), I'm stuck with a fairly tired 307 with unknown heritage and a 2 spd powerglide... The 307 is in need of some remedial care... I need it to last for the rest of the year and I hope to do a few runs with the local Chevrolet Club... There is a fairly long club run at the end of this month...

307.jpg

Currently it struggles to start when it's been sitting for a while... But, I think I've narrowed that down to the fuel draining out of, or drying up in the carb, because it starts quickly after turning over for a while and if switched off, starts easily immediately after (even when still cold)... I'll try turning it over a few times to get the fuel primed, before pumping the gas and attempting to start, next time I get a moment.. See if that helps.

The main issue that makes Frank less fun to drive, is that if I give it anything other than light throttle from a standing start it bogs badly and almost dies... Once moving it seems fine and at idle it is ok (but not great...).

When I first got Frank, December last year, I changed all the spark plugs, because they were all pretty badly fouled.. I pulled the #1 plug this evening and it is back in a similar condition...

no1 spark plug.jpg

My limited knowledge and online searching tells me this is an indication of running too rich...?

no1 spark plug 2.jpg

Now, the Rochester 2gv carb has no choke (it's supposed to have a divorced choke, but its not fitted), which I doubt is the cause...It doesn't get very cold here.. and Frank doesn't get many drives at highway speed, usually just cruising around... but, I doubt that's the cause either...?

I noticed tonight that the choke vacuum diaphragm hose is split, so I will replace that.. Could that be a cause?

Based on reading what I've found in Grumpy's links on trouble shooting, I have ordered and am waiting on a fuel pressure gauge to plumb into the fuel line near the carb, a spark plug tester, a piston stop to verify TDC is correct on the timing marks...

I have a compression test kit, which I've never used, but, based on the articles and videos online, seems to be pretty simple to use...

Current timing checked with timing light shows 8 (before TDC?) which seems about right?

I need to pop open the distributor (a delco model which can be adjusted externally) and check all looks ok in there and I have a multimeter which shows dwell, so I will look into that too...

Anyway...... Long story short... ha! Based on your vastly more experienced opinions, in what order should I be doing all these tests...? Which are more likely to identify the cause of the engine driving shit....? Where do I start?

I'm happy to do all of them, as it will be good learning for me, but, where should I start and what should I be looking for as far as signals of the cause of the issue?

If you need other information or pictures of things let me know.

Thanks guys!
 
the first thing Id try is moving the ignition timing to about 12 vs 8 BTDC, and see if you notice a difference,
then ID MAP the ignition advance.(SEE LINK BELOW)
your plugs show the cylinder heat is too low, it may be the result of an overly rich mix, too much fuel pressure, or the floats in the carburetor adjusted too high, or a really dirty air filter,but it looks like the ignition timings a bit retarded, and never reaches full ignition advance, you might also want to try the next hotter heat range spark plugs

http://garage.grumpysperformance.com/index.php?threads/verifying-your-real-advance-curve.4683/

by the way, thanks for posting clear pictures it always helps a great deal
 
grumpyvette said:
the first thing Id try is moving the ignition timing to about 12 vs 8 BTDC, and see if you notice a difference,
then ID MAP the ignition advance.(SEE LINK BELOW)
your plugs show the cylinder heat is too low, it may be the result of an overly rich mix, but it looks like the ignition timings a bit retarded, and never reaches full ignition advance, you might also want to try the next hotter heat range spark plugs

http://garage.grumpysperformance.com/index.php?threads/verifying-your-real-advance-curve.4683/

by the way, thanks for posting clear pictures it always helps a great deal
Click to expand...

Awesome, somewhere to start!

Also, I'm still running a points distributor (HEI will be on on the list of things to order...), am I right that dwell will impact timing? If so, what do I need to set dwell to before adjusting timing?

I had noted how much I appreciated the clear pictures that Rick posted and figured I'd try to do similar :)

Thanks!
 
An update for you Grumpy :)

I had a short window of time this afternoon to try your suggestions.

I pulled all the plugs and gave them a quick clean (I'll look into hotter plugs soon) and then fiddled with the dwell, adjusting it down slightly to about 31-31.5 (it was hard to do on my own, I need to get a set of alligator clip leads for the multimeter..), then I adjusted the timing (with the vacuum hose disconnected) to about 10-12... I wasn't sure from what angle I was supposed to view the timing from..? Directly above? Side on?

Anyway, The change in how smooth the car ran with those adjustments was noticeable! It seemed to idle a little faster, but mainly I could give it gas without the near dying! I took it out for a quick run and it was much improved to drive, but, there is still a smaller, but still noticeable bog when I accelerate.

I'm still waiting on a fuel pressure gauge to check for too high fuel pressure (is that likely with what I assume is a stock pump?), I'm not sure about floats in the carb... (guess that's a whole new area of research..) and the air filter looks fine. Its a K&N filter in a stock air cleaner housing (would taking it for a quick spin without the air cleaner to rule that out be a safe idea?)

I was too short on time to do any more fine tuning.... My plan for later in the week is to adjust the dwell again to about 30? Then adjust the timing to 12 as you recommended. I will then map the ignition advance. I think there is some adjustments needed on the carb idle also..

Thanks a lot, it seems we are on the right track at least :)
 
points1.jpg

dwellmeter.jpg


http://www.amazon.com/Actron-CP7605...d=1431533398&sr=1-1&keywords=tach+dwell+meter
having a dwell meter makes accurately setting point dwell far easier
but you can rather easily upgrade the older chevy ignition
http://www.pertronix.com/prod/ig/ignitor3/default.aspx
http://www.summitracing.com/parts/pnx-71181/overview/

http://www.superchevy.com/how-to/67498-hei-coils-modules/
the dwell setting is 28 to 32 degrees.

http://www.summitracing.com/parts/pnx-44011

http://www.howacarworks.com/ignition-system/checking-the-dwell-angle



 
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grumpyvette said:
but you can rather easily upgrade the older chevy ignition
http://www.pertronix.com/prod/ig/ignitor3/default.aspx
http://www.summitracing.com/parts/pnx-71181/overview/
Click to expand...

Do any of you guys have experience with the Pertronix upgrade? How does it compare to a new HEI? It looks like a MSD Streetfire is going to be a similar price..? Or is there value in upgrading to one of the more expensive MSD billet HEIs? If I upgrade (be that to pertronix or HEI), I will use it with the 383 when that goes in.
 
I've set the dwell to 30 and the timing to 12 BTDC and the tired 307 is running a lot better than previously. With the new idler arm and sway bar bushes I installed, it steers and drives the best it has since I got it :)

But, there is still a noticeable bog for a split second when I plant it..:( Do I try more advance?

I'm not sure of my total timing... Am I correct that I set the timing light to 36 (I've read a few times that 36 was about right) then run the rpm up till I see the timing mark hit zero..? Then if it isn't on zero at max, then adjust the timing to make it so?

I still need to check the advance curve, but when I was running it up through the rpm with the timing light on it, it looked a bit like it might be climbing steadily then pausing for a bit, then increasing again... Could that cause an issue immediately after planting my foot?

I plumbed in a fuel pressure gauge and get a consistent 6psi.. I recall reading 4-5psi was the goal... Is 6 too high? Could it be a problem..?

I haven't replaced the plugs yet, as I didn't want to foul up a new set, should I do that now? and try the hottest heat range up? Would the plugs being as they are now, impact the off idle acceleration?

I noticed that while working on the dwell and timing that the fumes were really really strong.... I haven't left it running for that long in the garage (doors open, rear out the door) before, but it was really bad.... Could it be the idle settings..?

I could imagine that the old 2bbl Rochester is in need of some love....? But, spending money on it seems like throwing money away...

Also, there's a intermittent clunk from underneath the car, which I have read can be cracked flex-plate or loose bolts on the torque convertor..? Can I check/tighten those from underneath? Or do I need to remove parts to get to them to check?

That's all my questions for now..... :rolleyes:
 
the symptoms seem to indicate the carbs accelerator pump adjustments are not correctly set up and/or the float levels and idle adjustments not set up correctly.
once the carbs correctly adjusted the plugs should clean up some what, but if they are particularly fouled (and thats not always obvious by sight) they won,t run nearly as well as new plugs, ,now DON,T go buying plugs more than one heat range hotter as it could cause more issues than youll want to deal with like burnt rings and detonation damage.
your correct that putting a good deal of cash into the old carbs rather wasted, and youll want a decent intake and carb anyway

http://www.summitracing.com/parts/wnd-8501/overview/

http://www.summitracing.com/parts/dem-1901/overview/

http://www.summitracing.com/parts/dem-1904/overview/

https://www.enginekits.com/350-to-383-stroker-kit.html

http://www.summitracing.com/search/part-type/engine-rotating-kits
you should be able to put the car up on 4 sturdy jack stands and have a buddy turn the rear wheel back and fourth while you look under the car for bad u-joints or loose flexplate or converter bolts, loose wheel bearings etc.
 
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Grumpy said:
youll want a decent intake and carb anyway

http://www.summitracing.com/parts/wnd-8501/overview/

http://www.summitracing.com/parts/dem-1901/overview/

http://www.summitracing.com/parts/dem-1904/overview/

https://www.enginekits.com/350-to-383-stroker-kit.html

http://www.summitracing.com/search/part-type/engine-rotating-kits
Click to expand...

So, these are the parts you'd recommend for the 383 build Grumpy?

I'd have imagined a higher CFM carb, but, for sure will take your recommendation over my uninformed ideas :) I guess I'm used to seeing lots of build articles with "750 double pumper!" in the list.. ha! But, I'm starting to figure out that there are some common practices that may not be best practices... :rolleyes:

What do you like about the Demon 1901?

The Weiand Speed Warrior, is there a reason this is your choice over the Edelbrock Airgap? I see that the Speed Warrior has a slightly higher rpm range and is cheaper? Is it true that the Summit intakes are re-badged Weiands?

Weiand
wnd-8501_oh.jpg


Summit
SUM-226010.jpg


The cynic in me says they purposefully use a blurry picture for the Weiand... Ha!


Thanks again Grumpy, you're a legend!
 
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http://www.summitracing.com/parts/dem-1904/overview/
a 750 cfm demon like this will produce more peak power,than a 625cfm carb on that same intake manifold and the 625cfm will be a bit more responsive and will generally provide plenty of flow for a larger car, with a 383 like that with an auto trans that will spend 90% or more of its time cruising and not racing.
your choice, either size cfm rated carb will work well, if you really want to push for max peak power, go with the 750cfm, if your going to spend most of your time with the car used as daily transportation the 625 cfm has some minor advantages for low and mid rpm band drive-ability, either will be a huge improvement over the current carb and intake. and you won,t believe the difference in power a properly built 383 has over the current 307 with that carburetor , if you concentrate on the 383 build rather than the 307 you'll most likely find a good combo.
Ive seen several tests where the wieand and edelbrock intakes tested on the same engines , and results were very similar especially if the divider in the plenum was cut to 1/2 its height, but in real world testing I find a 1" open spacer under the carb generally works even better than cutting the plenum divider, but at the cost of some low rpm responsiveness on SOME engine combos so testing on individual cars and the ability to tune and diagnose what your seeing is critical

http://garage.grumpysperformance.com/index.php?threads/carb-tuning-info-and-links.109/

http://garage.grumpysperformance.co...spacers-and-related-intake-modification.1038/

http://garage.grumpysperformance.com/index.php?threads/carb-intake-test.58/
 
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On every "carbed" car that I have, I always toss out the mechanical and swap in an electrical + pressure regulator. Although I drive my cars regularly, they don't see daily use and the bowls dry out quickly. The electric pumps (I turn on for a few seconds before starting) prime the carbs. It starts up much faster this way.
 
DorianL said:
On every "carbed" car that I have, I always toss out the mechanical and swap in an electrical + pressure regulator. Although I drive my cars regularly, they don't see daily use and the bowls dry out quickly. The electric pumps (I turn on for a few seconds before starting) prime the carbs. It starts up much faster this way.
Click to expand...

That sounds like a good idea for the rebuild for sure. Is that something I can do sooner and run with this tired engine and just keep the same set up for the new engine?

What are the parts I should be looking for...? Models/brands? I haven't even considered fuel pumps and regulators.... Any good links?
 
Definitely; I even mount them on stock engines. You'd have to calculate the GPH output needed for your target application so you can grow into it. Also make sure that you can swap fittings if your fuel line diameter needs to grow to accommodate the upgraded needs.

Another concern is noise. The typical electric fuel pump can be noisy - particularly if you do not insulate it from the sheet metal you mounted it on. With the engine running it is less audible... and if you don't care, well then it's not even an issue :D
 
After a wheel alignment and balance Frank is MUCH nicer to cruise around in! Along with the tuning changes suggested by Grumpy, I'm loving driving him about.. Slowly... :rolleyes:

There is still a minor shudder at about 50mph, but I'm pretty sure the answer from the tire store will be to replace the other two tires... which will have to wait....

I went to start figuring out the advance curve and saw that the weights were covered in surface rust and weren't moving very freely, and the springs were pretty feeble... I gave them a bit of a clean up, on the car with small wire brush (which felt like it helped a lot), but I think replacement is going to be the solution.. I'll look into a mid range HEI dizzy soon. I read on Chevytalk that I'll need to replace the under dash ignition wire with a larger gauge, as the stock wire on a 66 is not able to cope with the requirements of a HEI.. I'll have to research that more.

I've seen mixed reviews for the MSD Streetfire dizzys..? They seem a good price, but are they good value?

Thanks Grumpy for the support with the basic tune-up! I just need to get the rear lap seat-belts adjusted (shortened) a bit to make car-seat installs easier and me and the kids will be going everywhere in Frank on weekends!:D
 
I'm glad to help where I can

http://garage.grumpysperformance.co...ing-tools-abrasives-sources.10683/#post-46209

http://garage.grumpysperformance.com/index.php?threads/porting-can-help.462/page-3#post-27245

http://garage.grumpysperformance.com/index.php?threads/air-die-grinders.1831/#post-4763

http://garage.grumpysperformance.com/index.php?threads/carb-intake-test.58/#post-49542

http://garage.grumpysperformance.co...olishing-combustion-chambers.2630/#post-48319

http://garage.grumpysperformance.co...obvious-but-obviously-is-not.8485/#post-39276

http://garage.grumpysperformance.co...k-for-in-a-good-engine-combo.9930/#post-38054

http://garage.grumpysperformance.co...-by-step-guide-with-pictures.5378/#post-32456

https://www.enginekits.com/350-to-383-stroker-kit.html

http://www.summitracing.com/search/part-type/engine-rotating-kits
 
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So, I have a Performer RPM intake in hand and I'm thinking I'll could spend a few $$ and get the new carb (probably the demon 625cfm) and a new dizzy (or a pertronix ignitor II kit) as soon as, so I can replace the stock intake, 2bbl rochester carb and delco points dizzy on the tired 307.

My question/concern is that the intake and carb combo may be too much for the tired 307 and I'll actually get very little improvement (maybe even none) with the effort of the swap.. Yes, I will need the parts for the 383 down the track, but, the $$ could go towards parts for that now and I could leave the carb for later...

Is the Performer RPM intake and a 625cfm vac secondary carb going to wake up the tired 307? Or just be same same..?

I could also probably just spend $50AUD on a rebuild kit for the 2bbl carb now and that may show some improvement...?

the dizzy upgrade seems like a must, as the old one has rust on the advance mech and the springs are not what they used to be... So, I'll do that soon either way..
 
obviously I,m not there to check everything but Id bet the swap to a new 625 cfm or 750cfm carb and intake makes a noticeable improvement even on the older engine
 
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Ever thought about cleaning up the dizzy springs are cheap and elbow grease is free. Yes the carb you want for the 383 and the one for the 307 arenot gonna be the same. Used edelbrocks are usually cheap not sure about in your neck of the woods. But concentrate on the 383 if that is your goal. A little sacrifice now will pay off later. Focus lay out a budget and a plan and stick to it!!!! Other wise you are settling on that 307 car parts add up quick money is tight it's proper planning that makes projects happen. I would try not to purchase anything that cannot be used for your other engine build. Fuel system stuff ok the carb is a tough one but me I would buy the carb for the 383.
 
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