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'72 hard to start

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maty111

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I have a '72 blazer. edelbrock carb, newer fuel pump from napa. if it sits for a long time, say a week. It is hard to start. I can crank the motor till the battery dies, and nothing happens. if i spray some starter fluid down the carb, it fires right up, and the truck runs fine. I dont get it

matt
 
Edelbrock carbs seem to lose fuel faster than say, a q-jet. I have an Edelbrock on my 76 blazer and it can sit overnight and take 10-15 seconds to fire up in the morning. On the other hand my 79 blazer with a factory q-jet can sit 3-4 days and fire up as soon as you turn the key. I don't have an exact answer as to why it won't start without starting fluid after sitting a week other than my neighbors cj5 does the exact same thing. It's obvious that the fuel drains out of the carb and that fuel is not coming back to the carb until the motor starts running off the starting fluid, the question is why. I can offer you some suggestions though, you could install a one way check valve type thing in your fuel line somewhere between the fuel pump and carb, so that fuel can't drain out of the carb. Or you could install an electric fuel pump with a switch in the cab and run the fuel pump for a few seconds before you start the truck, it should fire right up then. Hope I have been of some help, though I'm not as smart as most of the fellers on here. Im sure someone else will chime in and cover anything I missed or failed to say.
Good luck!
 
76k5 pretty much nailed it. I had the same problem, annoying as hell but just the way it was.
As to why you have to use the starter fluid, my guess is that the mechanical fuel pump doesn't pump fast enough to pull the fuel from the tank through an empty line at the speed that the starter spins the engine.
 
An electric pump will cure this problem...

I had more than one Carter AFB and Edelbrock carb (practically clones ) that would not fire up after I let the truck sit more than a few days..

I blamed the ethanol gas,it evaporates rather quickly compared to the good old leaded gas old engines were designed for..the bowl dries up in a day or two,and by the time the fuel pump gets fuel from the tank to the carb,the battery is about dead..even with a hand choke,fully choked!..

I added an electric pump and the engine would fire up on the third turn after letting the pump run a few seconds before cranking..

I'm not so sure that was a good thing though,because it now started so fast,I could hear a bearing rattle until oil pressure built up !..:doah:
 
so i pressurized the fuel system with a shop vac. i found a small drip near the fuel pump. fixed
I also install a check valve right there.
I hope that solves , or at least helps...

different problem, or so i think

when its running, say a traffic light, and it is in drive and my foot is on the brake, it feels like its running of 4 cylinders. every once and a while it will die.
any ideas?

matt
 
If the drip was from the hole in the fuel pump its time for a new one. I remember mine was having the same problem when it was carbed and when I investigated I found fuel leaking from the hole and was told that was an indication of a hole in the diaphram (hmm that may be the first time I tried to spell that) in the pump. Mine started much better once I replaced the pump.
 
About the feeling of the 4 cylinders thing, there are several things that could be causing that... The 2 main things that come to mind are either a misfire or your idle is set too low. If the truck sounds good and feels good when accelerating off of a stop and does not stumble or shake or anything and feels like it has the power that it should than its probably not a misfire. Try adjusting the idle screw on your carb and see if that fixes the problem, not sure what carb you are running but regardless the idle screw should be fairly easy to find, right near or on the throttle on the carb. I have had both problems with my 76 blazer. If you turn up the idle and that doesn't fix your problem than report back and give us an update. If you think it's a misfire than with the engine idling pop the hood and start pulling plug wires off the motor, 1 at a time, just pull a wire and listen to the motor to see if you hear a change in the idle and if so, put the wire back on the plug, this indicates that the cylinder is live, if you do not hear a change then you've found a dead cylinder, and that's your misfire. Hope this helps.
 
If the diaphram in the pump leaks out of the weep hole in the pump casting,gas can also be pumped into the crankcase--so if the pump is bad,you have to change the oil and filter too,or risk engine damage from oil dilution..

The 4 bbl carb has two idle mixture screws and one idle speed screw..
I use a vacuum gauge to adjust each screw until I reach the highest and steadiest reading,then open the screw an additional 1/4 turn (otherwise it'll be too lean during a cold start and warm up)...

Each screw affects 4 of the cylinders,so it they are not adjusted equally or if only one of the two main jets gets clogged by dirt it will feel like it isn't firing on all cylinders..a vacuum leak will do that also,and can affect acceleration and idle too,as already noted..
 
No change. Fires on all 8. Feels like it misses. I just ordered a hei conversion from pertronix. Hope it helps..
 
Does it seem to miss more when you first apply the brakes?..
Might be the brake booster failing,letting it leak vacuum when the brakes are applied..
Could be a base gasket on the carb to intake is not sealing right or the gasket is failed--Edelbrocks are "square bore" and often when they are put on a GM intake with an adapter,the gasket fails to seal all the way around and cause issues like this..a vacuum gauge will help diagnose this..you can spray carb cleaner around the base of the carb using the "straw" and listen for any change in how it idles ,that will show up any vacuum leaks..

Another possibility is maybe a lifter is "pumped up" and not allowing a valve to close fully...a compression test would help pin that possibility down..
I have seen engines with a few cylinders low on compression run decent above idle,but idle roughly and stall out at idle speeds--once you rev it up above idle it'll tend to smooth out..but if a lifter pumps up it'll usually make it backfire through the carb or exhaust at higher rpms also..
 
I just finished my hei/pertronix conversion. I also replaced the gaskets under the carb and replace a couple vacuum lines. The truck idles a lot better. It was probably a small vacuum leak...

I still don't know what to do about the hard starts after it sits a week. maybe a aftermarket performance mech fuel pump?
 
It is probably the gas evaporating from the carb bowl after sitting,todays ethanol gas evaporates fast--an electric fuel pump will fill the bowl faster than a mechanical one will,but you will have to let it run a few seconds to prime the carb if its empty,before cranking it over....a mechanical pump needs the engine cranked over to "pump", so it wont matter which one you use,it'll still need to be cranked over awhile till the carb gets fuel..
 
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