Cliff's Quadrajet Parts and Rebuild Kits
Quadrajet Problem Solving => Diagnose a Quadrajet carburetor problem => Topic started by: fussfeld on July 04, 2021, 05:06:52 PM
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Background:
HEI ignition
Stock-ish cam---like 184/195 @ .50"---- so decent vacuum etc.
Only thing that was done, immediately prior to this problem was to adjust the secondary throttle plates(not air flaps, the plates) to open more.
Prior to all this, the engine would start within 1 crankshaft revolution if not less cold. Hot, it would start with a little cranking and maybe sometimes pushing the pedal down about 1/2 way---still very acceptable to me.
So, where we stand now is the engine may not start cold---50/50 chance. And even if it does start, it doesn't start normally----more of a putter to start with lots of cranking. The engine WILL NOT start hot unless you wait at least an hour.
Here is a video to better illustrate: We see here at about 9 seconds we hear the electric fuel pump come on. Then at about 15 seconds, i give it a shot of gas. Then about 7 seconds of cranking and only when i press the pedal down---(look closely at the top left corner to see the accelerator pump pushrod move) does it start.
https://www.youtube.com/watch?v=QCqjXfUrdco
What would this tend to indicate? Also, i know the choke flap probably shouldn't be flopping around during cranking. i have since fixed that, but it didn't make a difference.
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Have you tried a couple of pumps on the gas pedal?
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Not yet.
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You'll notice it only started when i gave it another shot of gas. Since the choke was closed (yes i know flopping around, but still generally closed), thus when i gave it more gas the throttle opened too, but did not let it more air (choke unloader isn't adjusted right). Does this indicate i am lean and thus need more fuel as you suggested?
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Tried 3 pumps before starting. No real difference----it only started when i stepped on the pedal.
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Do you have proper voltage/current to the HEI at all times?
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Do you have proper voltage/current to the HEI at all times?
i would assume so. i can get it started---just with a lot of cranking and some pedal.
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i think i need to add here (after unable to sleep at 3pm for a while and had time to think),that the engine just does not want to run below 800 rpm. So, i feel this is likely tied in with the hot start problem-----If that's the lowest i can get it run and it shuts off at 800, then IF things were normal, if i were to restart it, it would idle at 800. But it DOESN'T WANT to run at 800----so why would it start?
So, that's the hot start issue.
Cold start? i don't know yet.
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There is no room for assumtions.
A weak ignition system is a good recipe for hard starts and a poorly running engine.
You need to check and verify the ignition system ahead of adjusting the carb.
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i agree that ignition should be checked before carb. But wouldn't the video tend to indicate that ignition likely is NOT the problem?
Anyways, then, what's the best way to check the ignition?
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confirm battery voltage @ 12v plug at distributor
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There is no room for assumtions.
A weak ignition system is a good recipe for hard starts and a poorly running engine.
You need to check and verify the ignition system ahead of adjusting the carb.
Pls see below:
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confirm battery voltage @ 12v plug at distributor
Note: i don't know the EXACT numbers (because i didn't write them down---lesson learned) but they are close.
Battery sitting = 12.56
Battery while cranking = 11.50 ish
Voltage at red/ ignition wire with key "on" = 12.56
Voltage at red/ ignition wire while cranking = 10.8 ish. Is this good enough for HEI to start engine?
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Sounds about normal. factory HEI setup or originally points?
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2 Volts is a lot IMO. Could be a voltage drop in the ignition switch. If you are careful you can take apart and clean the contacts. I use contact cleaner only, do not sand the contacts. I've even got lucky just spraying contact cleaner in the switch and working it.
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Anyways, then, what's the best way to check the ignition?
With engine running, check the voltage at BAT post on HEI.
Should be the same as over + and - on battery.
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Sounds about normal. factory HEI setup or originally points?
HEI
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UPDATE:
i basically got it (somehow) back to normal: It starts within 1-2 crankshaft revolutions.
All i did different was to take the idle tubes out, blow them out with compressed air and ran a wire thru them. Also, blew the area below the idle tubes (idle wells?) out.
i'm not 100% convinced this solved the problem because i did not see dirt or debris come out.
Nevertheless, the cold no start/hard start seems to be solved?
i was previously afraid to take the tubes out because i had never done it before. But i followed the directions in the book and they came out rather easy.