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78 stalls unless revved and then seems to need to overcome high compression (or something) to restart

egates

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Aug 14, 2009
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5
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Valley Stream, NY
My 78 started having a rough idle that got progressively worse. First, just rough idle one day that had me worried. So I checked it out a day or 2 later before I was supposed to drive it in a parade. It had a bit of a stumble to the idle but it was cold and was OK running fast choked. Then after about a couple miles, stalled at a stop sign but I think that's also because it warmed up and idle dropped. Then I had to get it about a mile back home. It got progressively worse stalling if I even slowed down for a stop sign until eventually I just gave up stopping but then it would even let me slow for a turn. It just died down the street and I pushed it spot on the street to park. The odd part is that when I would restart, it had a very hard time restarting it usually cranks freely and easily but now seems to really tax the battery to the limit that the battery light comes on as if it has to overcome pressure or resistance of some sort so that it really was difficult for it to turn over. I let it sit for a few days and checked it out again today and it was a fairly easy start, spinning easily but not staying running unless I rev it. After stalling, it would still do the thing where it would act as if there was something causing resistance or pressure and making the start very difficult. It would run if I rev it to about 1500-2500 but if I let it drop to about 1000 it would just die. I'm expecting something like a fuel pump problem. I was looking around and its very hard to see around that area - I don't have great facilities to work on this. I noticed that the hoses there are wet and it seems that one clamp is off one of the hoses but they are so crammed together that I can't even see how to get it back into place much less get in there with a screwdrive to tighten it. I'll just take it to my mechanic (flatbedding it, I guess) but what has me puzzled is this difficult starting that seems like the engine is locked up somehow.
 

Tom Bryant

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1959 black 270hp (9/2/69) 1981 Beige L81(10/20/80)
Is it blowing black smoke when this happens? Could be that the choke is sticking closed.

Tom
 

Tom Bryant

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1959 black 270hp (9/2/69) 1981 Beige L81(10/20/80)
Sounds like plenty of fuel so I wouldn't suspect the pump. You could take the fuel line off at the carb and have someone crank the engine wile you hold a cup to catch the gas and see how strong the flow is. Quadrajets used to use a fiber float. They would become saturated over time and sink or at least not be as
buoyant and not hold the needle valve closed when the fuel level was up. You may have raw gas flooding the engine. Check your oil for gas smell or over full reading on the dip stick.
 

Vettehead Mikey

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Not that far from Ottawa
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1973 Coupe
S. Quadrajets used to use a fiber float. They would become saturated over time and sink or at least not be as
buoyant and not hold the needle valve closed when the fuel level was up. You may have raw gas flooding the engine. Check your oil for gas smell or over full reading on the dip stick.

+1 this is my bet also.
 

stevolwevol

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May 28, 2015
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Michigan
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1977 light blue
This could be due to ethanol. I had my float changed to one that was compatible, but I still primarily run strait gas though.
 

egates

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Joined
Aug 14, 2009
Messages
5
Location
Valley Stream, NY
Now that you mention it, I noticed the oil level was a little over full on the dipstick.

I drained some oil out so it reads normal now. Still no luck. It runs fine if I'm revving it to 1500 or higher but if drops to below that it stalls.

Do I really want to get into replacing the float on the carb? My success with carb rebuilds is less than great at this point; I rebuilt the carbs on by GPZ550 and need to figure out why 1 of the 4 didn't work out so well.
 

LLC5

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Sep 28, 2004
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Wa.
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98 black 6spd convert.
No, as I was trying to start it, I saw gas splash out of the top of the carb but no smoke or fire.



That denotes possible improper firing time from either the cam or ignition. First things first, load test your battery with a carbon pile tester, you need to know it' good. If it is good, check carefully your cap and rotor and ignition coil for carbon tracks, any seen replace. Make sure the coil has a ground strap to it. Look under the rotor for carbon burn through to the dist. shaft.
 

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