Long story short: recently my 1972 blazer has been running like sh*t, to say the least. It has left me stranded twice now, and I’m ready to resolve this issue. So here goes. A few weeks ago, I took the blazer out for a Sunday drive around town, got some gas and went to Lowes. However, when I came out of Lowes and tried to start it, a loud pop sound came from the carburetor. I opened the hood and saw some lite smoke coming from the air filter. I’m guessing that it came from the carb. I waited a few minutes and gave it some gas, the engine turned over; then again there were a few more pops from the carb area, followed by more lite smoke. I waited about a half hour and tried starting it again It started, however when I gave it gas or put it into gear, the engine fluttered, then died. So I had it towed home. I waited a few days, and tried starting it up. This time, the engine ran fine. Drive it around for a few hours and everything ran great. Yesterday, I took the blazer out for a drive and had the same problems. This time, after waiting for four or five hours, I tried starting it and everything ran fine. Drove it home and parked it. Could this be a fuel problem, dirty fuel filter, dirty gas? Any help would be greatly appreciated.
CK5
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engine pops
- Thread starter scasey28
- Start date
Sounds to me like the carb is flooding over once you shut the engine off. The next time you shut it off, open the hood and remove the air cleaner and look for any fuel dripping from the venturi's.
Crap in the fuel system somewhere that clogs up passages in the carb, too high of a float level, or extreme heat causing fuel expansion.
While checking the float levels, it turns out that the front float is running to high. As soon at I started unscrewing the sight plug, fuel started pouring out. So turned off the motor and did a couple ¼ clockwise turns. However when I started it back up, now no matter how many times I turn the adjusting nut, the fuel level doesn’t rise up to the sight plug. I’ve turned the adjusting nut like 10 rotations and still no fuel in sight. Do I need to keep adjusting it? From what the factory manual says, it looks like just a couple of ¼ turns and the fuel level should rise or fall. Also I checked for any possible fuel dripping from the venturi's and it looks clear. Thanks.
Sounds like you have a Holley? If so the float may have came disconnected from the needle and seat assembly. You will have to pull the fuel bowl to check for that. Also now that i'm thinking it's a Holley carb and you said there was a loud "pop" that could have been a backfire which is known to blow power valves in Holley carbs and will make it run rich.
Yeah you’re right, it is a holly 650. The popping sound comes from the engine compartment area. I started pulling apart the front fuel bowl. I have two fuel lines leading into the carb. One going to the front bowl, and one to the rear bowl. Given that I really have no idea what I am doing, I am taking baby steps in order to understand what I am doing and what is going on. I well Pull apart the front bowl and see if I can see if any parts are disconnected. I really appreciate all your advice, and will get back to you in a day or two. Also, do I need to disconnect the battery before I disconnect the fuel lines from the carb? Thanks again.
There are a couple books out there on Holley carbs that are pretty good and have LOTS of helpful info in them. You should see about picking them up and reading through them and you will really have a good understanding of the Holley carb and how to tweak and tune them properly. I used to be the go to guy when it came to Holley carbs but i haven't played with them for close to 20 years now.
3 on the tree
1/2 ton status
Unless Holley has changed, that "adjusting Nut" is actually a jam nut. You back the hut off, and use a screwdriver on the slot in the middle of the nut. The screw and nut are 2 different pieces.
If it is an older Holley, then the backfires you heard, have probably blown the power valve.
If it is an older Holley, then the backfires you heard, have probably blown the power valve.
Yeah the adjusting nut is two separate pieces. I’m in the process of disassembling the card right now. I went out and bought a Haynes Holley carb manual. So far, everything seems pretty straight forward. I think that there are two power valves on my carb. How can I tell if their blown? I’m guessing that I have to dismantle the whole carb in order to get to them? I‘ll keep ya posted on what I find. Thanks again.
I bought a rebuild kit for carb, and started rebuilding piece by piece. As far as I can tell, all the gaskets looked good. I cleaned all the lose parts, and now the carb is in one piece. I'm going to install it in a few minutes, alone with a new fuel filter. Any recommendations?
Sorry for the lag in responding. It’s been raining buckets here for the past week or so. I got the carb installed and tried starting the motor. However the engine just turned over. It’s like there is no fuel getting to the carb. It’s supposed to stop raining for a few days starting tonight. After work tomorrow I’ll play around with the carb and test to see if fuel is getting into the carb. I’ll you know how it goes tomorrow.
Ok so today I got the engine to start, however almost instantly gas started pouring out of the front fuel bowl vent. I unscrewed the needle and seat to check for anything that could be causing the seat from preventing the gas from over flowing. Everything looked clean and clear, so I reinstalled the needle and started the engine again. Once again gas spouted out the front vent. So I took off the carb and maybe tomorrow I’ll take it apart and see what could be causing this. You guys have any ideas? Thanks
bigbadchev84
1/2 ton status
what kind of carb? I would check for a stuck float
The carb is a Holley 750. If it was a stuck float, wouldn't the engine just run really rich, and not shoot gas out of the front fuel bowl vent? I was under the impression that the needle and seat control the on and off flow into the fuel bowl?
70gmcjimmy
Registered Member
The needle is operated by the float so if the float is stuck in the open position or adjusted too high it is holding the needle off of the seat and then direct pressure from the fuel pump will fill the bowl until it comes out of the vent.
The "jam nut" is actually the screwdriver slot and the float adjusts by turning the nut under it. I don't have a double pumper here for a pic but if you have the bowl off, break the slotted screw loose, hold it from rotating with the screwdriver and turn the nut under it to see which direction lowers the float level.
I hope this helps---Later---DAC
The "jam nut" is actually the screwdriver slot and the float adjusts by turning the nut under it. I don't have a double pumper here for a pic but if you have the bowl off, break the slotted screw loose, hold it from rotating with the screwdriver and turn the nut under it to see which direction lowers the float level.
I hope this helps---Later---DAC
Last edited:
DAC,
Today I took apart the front fuel bowl and checked the float and needle. Everything checked out, as I turned the needle, the float lowered and rose. However when I put everything back to together and started the engine again, gas poured out of the front vent. As of now I have the carb off and might think about rebuilding the whole front end of the carb tomorrow. Thanks for the tips and if you think of anything else let me know. Thanks.
-Scott
Today I took apart the front fuel bowl and checked the float and needle. Everything checked out, as I turned the needle, the float lowered and rose. However when I put everything back to together and started the engine again, gas poured out of the front vent. As of now I have the carb off and might think about rebuilding the whole front end of the carb tomorrow. Thanks for the tips and if you think of anything else let me know. Thanks.
-Scott
Ok so I have some good news. Yesterday I spent most of the day working on the blazer. Here is how things went. After rebuilding the carb, I installed it and still engine wont start, however this time no fuel came pouring out of front vent. Finally I figured the problem was somewhere in the ignition system. I removed the cap and rotor and found lots of moister in the cap and the rotor covered in lime deposit. I replaced both, and tried starting the truck. Everything worked right away. Although the carb still needs to be adjusted I was able to drive the truck around the block. It looks like that maybe some rain water drips down behind the hood and cowl, and onto the cap. Now I need to find a rubber cap that will cover the cap to help prevent moister from getting into the cap/rotor. Does anybody have any ides on how to cover the cap?? Today I think I will install some weather stripping between the hood and cowl. Thanks
-scott
-scott
70gmcjimmy
Registered Member
Hey Scott,
Congrats on getting to run around the block in your Blazer! Can't wait till I'm able to do that that in my K5.
That moisture and crud in the cap may have been from years of condensation, but as you said rain dripping on it ain't good. When there is a bad cap on the truck, just humidity can cause major issues much less direct contact with water.
Is your hood seal OK? There is supposed to be a rubber seal that sandwiches between the top of the firewall and the cowl that has a lip that extends up to the hood. There should be no need to build a distributor cover if that seal is in place.
Later---DAC
Congrats on getting to run around the block in your Blazer! Can't wait till I'm able to do that that in my K5.
That moisture and crud in the cap may have been from years of condensation, but as you said rain dripping on it ain't good. When there is a bad cap on the truck, just humidity can cause major issues much less direct contact with water.
Is your hood seal OK? There is supposed to be a rubber seal that sandwiches between the top of the firewall and the cowl that has a lip that extends up to the hood. There should be no need to build a distributor cover if that seal is in place.
Later---DAC
