truck backfires when driving
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truck backfires when driving
I just switched out my old carburetor with an edelbrock 750 cfm. I've got an 81 ford f150 with a 302 in it. I've been struggling to get it running without stalling out.. I've finally got it running, but when I try to give it some gas it backfires like crazy....What could be the problem? There is one bolt that i couldn't get on the carb.. It's like the threads in the hole are too stripped..could that be the problem?
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I personally wouldn't have put a 750 on a 302, 650 double pumpers have always taken care of me in the past.
Have you gotten the carb tuned, etc? Also, where is the location of the bolt that you couldn't get into the carb.
Have you gotten the carb tuned, etc? Also, where is the location of the bolt that you couldn't get into the carb.
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and as for tuning the carb.. I was going to buy a vacuum gauge later and tune it like that.
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yes. the bolt that physically holds it in place.. there are 4 that bolt it to the intake.. but one of them wouldn't catch any thread.. it's stipped on the inside or something... and yeah i bought it second hand.. I can't tell you if it was rebuilt or not.. I tried putting my old carb back on, and it was backfiring as well.
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Is that what you think ill have to do to get it to stop backfiring? i mean, the carb looks like its in good shape.
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From: Southern California
IMHO...
#1- vacume leak caused by missing nut/bolt on the carb base plate
#1b/fyi- attaching a carb that way also has a potential of warping the carb base plate (permanently) inducing vacume leaks (because of the failure to tighten the base down equally), may require a minor adhesive or doubling of the gasket to adapt to the warped base plate....though you want to verify this condition does exists 1st.
#2- Tuning....assuming the "back-fire" is out the pipes, and there are no vacume leaks, its an overly rich mixture.....390-600 cfm is the typical range of carbs for a stock/mild 302. The 750 can be made to work properly with proper tuning.
#3...if it is coughing up through the carb...cam/crank timing is out of phase, meaning it slipped time.
#1- vacume leak caused by missing nut/bolt on the carb base plate
#1b/fyi- attaching a carb that way also has a potential of warping the carb base plate (permanently) inducing vacume leaks (because of the failure to tighten the base down equally), may require a minor adhesive or doubling of the gasket to adapt to the warped base plate....though you want to verify this condition does exists 1st.
#2- Tuning....assuming the "back-fire" is out the pipes, and there are no vacume leaks, its an overly rich mixture.....390-600 cfm is the typical range of carbs for a stock/mild 302. The 750 can be made to work properly with proper tuning.
#3...if it is coughing up through the carb...cam/crank timing is out of phase, meaning it slipped time.
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Thread Starter
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Freshman User
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IMHO...
#1- vacume leak caused by missing nut/bolt on the carb base plate
#1b/fyi- attaching a carb that way also has a potential of warping the carb base plate (permanently) inducing vacume leaks (because of the failure to tighten the base down equally), may require a minor adhesive or doubling of the gasket to adapt to the warped base plate....though you want to verify this condition does exists 1st.
#2- Tuning....assuming the "back-fire" is out the pipes, and there are no vacume leaks, its an overly rich mixture.....390-600 cfm is the typical range of carbs for a stock/mild 302. The 750 can be made to work properly with proper tuning.
#3...if it is coughing up through the carb...cam/crank timing is out of phase, meaning it slipped time.
#1- vacume leak caused by missing nut/bolt on the carb base plate
#1b/fyi- attaching a carb that way also has a potential of warping the carb base plate (permanently) inducing vacume leaks (because of the failure to tighten the base down equally), may require a minor adhesive or doubling of the gasket to adapt to the warped base plate....though you want to verify this condition does exists 1st.
#2- Tuning....assuming the "back-fire" is out the pipes, and there are no vacume leaks, its an overly rich mixture.....390-600 cfm is the typical range of carbs for a stock/mild 302. The 750 can be made to work properly with proper tuning.
#3...if it is coughing up through the carb...cam/crank timing is out of phase, meaning it slipped time.
What am I supposed to do about that missing bolt... the bitch just wont go in it.
The backfire is out of the pipes.
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From: Virginia
As was mentioned, you need to use 4 bolts to hold the carb on. If you inspect the hole, there may be some good threads further down the hole, and a longer bolt may work.
If it's backfiring in the exhaust, then indeed it's a rich mixture, there is raw fuel getting into the exhaust and it's lighting off in the hot exhaust system. If you can, use a ladder or something if you need to, and take a flashlight and lean over and look down in the carb while the truck is running(be careful of the fan). If you see fuel dripping down into the engine, then that's a problem.
If this is the old style holley, you can adjust the fuel level without taking the carb apart. Turn the engine off, and on the passenger side of the carb there should be a large flathead screw on the side of the bowl front and rear. This is a site plug, and the fuel is supposed to be at the bottom of the hole. With the engine off, take a rag and put under the screw, and take the screw out. If fuel spills out onto the rag, the float level is too high. Do this for the rear site plug also.
If the fuel level is too high, look on top of the bowl. There should be another large flathead screw and then a large nut underneath. This is how you adjust the fuel level. You can also take this whole assembly out and check for dirt. There is one of these on the rear bowl also.
To lower the level, loosen the flathead screw with a screwdriver, and while holding the screw with the screwdriver, turn the large nut underneath with a wrench. Turn it clockwise to lower the fuel level. While holding the nut, tighten the screw back up and then start it, and keep doing this till the fuel is just at the bottom of the site plug hole on the side.
If you can't keep the fuel from pouring out of the site hole, then turn the truck off, take the flathead screw completely out, and then turn the nut with your fingers counterclockwise, backing the needle assembly completely out of the carb, and then pull it out. Inspect it, there may be a little piece of dirt caught in the needle so it's not closing off.
If it's backfiring in the exhaust, then indeed it's a rich mixture, there is raw fuel getting into the exhaust and it's lighting off in the hot exhaust system. If you can, use a ladder or something if you need to, and take a flashlight and lean over and look down in the carb while the truck is running(be careful of the fan). If you see fuel dripping down into the engine, then that's a problem.
If this is the old style holley, you can adjust the fuel level without taking the carb apart. Turn the engine off, and on the passenger side of the carb there should be a large flathead screw on the side of the bowl front and rear. This is a site plug, and the fuel is supposed to be at the bottom of the hole. With the engine off, take a rag and put under the screw, and take the screw out. If fuel spills out onto the rag, the float level is too high. Do this for the rear site plug also.
If the fuel level is too high, look on top of the bowl. There should be another large flathead screw and then a large nut underneath. This is how you adjust the fuel level. You can also take this whole assembly out and check for dirt. There is one of these on the rear bowl also.
To lower the level, loosen the flathead screw with a screwdriver, and while holding the screw with the screwdriver, turn the large nut underneath with a wrench. Turn it clockwise to lower the fuel level. While holding the nut, tighten the screw back up and then start it, and keep doing this till the fuel is just at the bottom of the site plug hole on the side.
If you can't keep the fuel from pouring out of the site hole, then turn the truck off, take the flathead screw completely out, and then turn the nut with your fingers counterclockwise, backing the needle assembly completely out of the carb, and then pull it out. Inspect it, there may be a little piece of dirt caught in the needle so it's not closing off.
Thread Starter
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Freshman User
Joined: Aug 2013
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As was mentioned, you need to use 4 bolts to hold the carb on. If you inspect the hole, there may be some good threads further down the hole, and a longer bolt may work.
If it's backfiring in the exhaust, then indeed it's a rich mixture, there is raw fuel getting into the exhaust and it's lighting off in the hot exhaust system. If you can, use a ladder or something if you need to, and take a flashlight and lean over and look down in the carb while the truck is running(be careful of the fan). If you see fuel dripping down into the engine, then that's a problem.
If this is the old style holley, you can adjust the fuel level without taking the carb apart. Turn the engine off, and on the passenger side of the carb there should be a large flathead screw on the side of the bowl front and rear. This is a site plug, and the fuel is supposed to be at the bottom of the hole. With the engine off, take a rag and put under the screw, and take the screw out. If fuel spills out onto the rag, the float level is too high. Do this for the rear site plug also.
If the fuel level is too high, look on top of the bowl. There should be another large flathead screw and then a large nut underneath. This is how you adjust the fuel level. You can also take this whole assembly out and check for dirt. There is one of these on the rear bowl also.
To lower the level, loosen the flathead screw with a screwdriver, and while holding the screw with the screwdriver, turn the large nut underneath with a wrench. Turn it clockwise to lower the fuel level. While holding the nut, tighten the screw back up and then start it, and keep doing this till the fuel is just at the bottom of the site plug hole on the side.
If you can't keep the fuel from pouring out of the site hole, then turn the truck off, take the flathead screw completely out, and then turn the nut with your fingers counterclockwise, backing the needle assembly completely out of the carb, and then pull it out. Inspect it, there may be a little piece of dirt caught in the needle so it's not closing off.
If it's backfiring in the exhaust, then indeed it's a rich mixture, there is raw fuel getting into the exhaust and it's lighting off in the hot exhaust system. If you can, use a ladder or something if you need to, and take a flashlight and lean over and look down in the carb while the truck is running(be careful of the fan). If you see fuel dripping down into the engine, then that's a problem.
If this is the old style holley, you can adjust the fuel level without taking the carb apart. Turn the engine off, and on the passenger side of the carb there should be a large flathead screw on the side of the bowl front and rear. This is a site plug, and the fuel is supposed to be at the bottom of the hole. With the engine off, take a rag and put under the screw, and take the screw out. If fuel spills out onto the rag, the float level is too high. Do this for the rear site plug also.
If the fuel level is too high, look on top of the bowl. There should be another large flathead screw and then a large nut underneath. This is how you adjust the fuel level. You can also take this whole assembly out and check for dirt. There is one of these on the rear bowl also.
To lower the level, loosen the flathead screw with a screwdriver, and while holding the screw with the screwdriver, turn the large nut underneath with a wrench. Turn it clockwise to lower the fuel level. While holding the nut, tighten the screw back up and then start it, and keep doing this till the fuel is just at the bottom of the site plug hole on the side.
If you can't keep the fuel from pouring out of the site hole, then turn the truck off, take the flathead screw completely out, and then turn the nut with your fingers counterclockwise, backing the needle assembly completely out of the carb, and then pull it out. Inspect it, there may be a little piece of dirt caught in the needle so it's not closing off.
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From: Virginia
Woops, that was dumb. For some reason I thought you had a holley carb. The edelbrock is not externally adjustable. You have to take it apart to adjust the float level.