Jump to content

Bogs off the line, backfires out teh carb, and not enough power


Recommended Posts

we just put a 650 cfm thunder series edelbrock carb on my friends 72 ford galaxie 500, with a 400M V8, as well as a performer series aluminum intake manifold, on a stock motor with custom exhaust. everything finally went together after much swearing and re-reading of directions. the problem is we can't get it tuned right for the life of us.

 

we're pretty sure the timing is off but it starts up great as long as its warm enough. the car really bogs or stalls off the line.

 

you can't really give it more than 1/4 gas otherwise it'll start sputtering and die. also when the car is just sitting there and we mess with the throttle and rev the engine a little the carb will sometimes backfire (scared the piss out of me when i was adjusting something on the carb and it shot flames in my face). once you hit about 20mph you can punch it.

 

the car isn't accelerating as hard as it should, even in the high end. it kinda feels like its struggling and somethign is holding it back. sometimes it will just suddenly haul ass or be really slow. we think the backfireing is from a combo of lean mixture and bad timing. we're gonna try to fix the timing this weekend.

 

just to make sure you get the right timing by removing plug from cylinder one, turn the motor over, feel for when it starts to push air out of the spark plug hole, then make sure the rotor is pointed at cylinder 1. now do we have to make sure that the cylinder is at its highest point or is it good once we start to feel it push air? once we get that running, how are you supposed to make that that is the ideal timing for that setup? we havea timing light, my friend knows how to use it but i don't so if anyone wants to explain that would be cool

 

thanx

Edited by Pballer2005
Link to comment
Share on other sites

A backfire is unburnt fuel igniting in the exhaust gas. Unburnt fuel can be attributed to either insufficient air or RICH stoichiometery; NOT lean.

 

The timing light should be powered by your battery and clamped onto one of the spark plug cables, it uses induced current to flash everytime the vehicle's capacitor (ingnition coil) discharges.

 

With the flashbacks, I would say your flooding the carb and need to cut the fuel back some. Your engine sounds like it's drowning in gasoline.

Link to comment
Share on other sites

A backfire is unburnt fuel igniting in the exhaust gas. Unburnt fuel can be attributed to either insufficient air or RICH stoichiometery; NOT lean.

 

The timing light should be powered by your battery and clamped onto one of the spark plug cables, it uses induced current to flash everytime the vehicle's capacitor (ingnition coil) discharges.

 

With the flashbacks, I would say your flooding the carb and need to cut the fuel back some. Your engine sounds like it's drowning in gasoline.

 

sorry i didn't make it clear, it's backfiring out of the carberator, not the exhaust. at first i thought the same thing, though, but when i looked into trouble shooting and everything in the book sais that its too lean. that's why i'm confused. the owners manual sais that backfiring through the carb, surging, and bogging off the line are from a lean mixture or a vacuum leak, but we already made sure that their where no vacuum leaks. for all we know our timing may so fubar that its igniting fuel before the valves even close.

 

"Lean conidition: Poor off idle throttle response, idle that flutters a little after a throttle blip then slowly returns to the idle that you've set, popping back through the carbs when the throttle is blipped. "

 

"Engine backfires. Possible causes: Carburetor set too lean"

 

"From what you described I would say fuel. Check the rubber hoses at tank and

at fuel pump, backfiring threw car indicates a lean condition or out of time

engine"

Edited by Pballer2005
Link to comment
Share on other sites

Use the timing light to eliminate the possible fubar condition.

 

I am going to assume the carburetor has been properly calibrated. As such, you may have poor mixing that is resulting in a wet intake and fuel condensing within the throttle body (which could flash, hesitate, and otherwise create lean stoich' symptoms).

 

The mixing problem is born from maintenance or design issues, you may have a dirty carburetor or something that is restricting the flow. I have very little experience in this area since I was only beginning to learn about carburetors when I switched from Holleys to CVCC. In CVCC these problems are RARE.

 

If the stoichiometry is lean, I would suggest adjusting the mix screw to correct the stoichiometry. Since I don't think this is the case, despite what the book says (yeah, I think you and I are smarter than a stack of paper), I would not suggest adjusting the fuel mixture until you eliminate other possibilities, lest you singe the hair from your brow.

Edited by James Matteu
Link to comment
Share on other sites

Use the timing light to eliminate the possible fubar condition.

 

I am going to assume the carburetor has been properly calibrated. As such, you may have poor mixing that is resulting in a wet intake and fuel condensing within the throttle body (which could flash, hesitate, and otherwise create lean stoich' symptoms).

 

The mixing problem is born from maintenance or design issues, you may have a dirty carburetor or something that is restricting the flow. I have very little experience in this area since I was only beginning to learn about carburetors when I switched from Holleys to CVCC. In CVCC these problems are RARE.

 

If the stoichiometry is lean, I would suggest adjusting the mix screw to correct the stoichiometry. Since I don't think this is the case, despite what the book says (yeah, I think you and I are smarter than a stack of paper), I would not suggest adjusting the fuel mixture until you eliminate other possibilities, lest you singe the hair from your brow.

 

please verify that the firing order is correct and the the spark timing is set. If all checks out okay adjust mixture screw on the carb 1.5 turns out from bottomed out. gives yu a good starting point. it should run better. adjust accordingly. If it still does it you might have a lot of play on your timing chain causing the valves to open sooner or later than it should. causing the intake backfire. also verify mixture by reading the spark plugs to see if you are running rich or lean. Happy revving

Link to comment
Share on other sites

please verify that the firing order is correct and the the spark timing is set. If all checks out okay adjust mixture screw on the carb 1.5 turns out from bottomed out. gives yu a good starting point. it should run better. adjust accordingly. If it still does it you might have a lot of play on your timing chain causing the valves to open sooner or later than it should. causing the intake backfire. also verify mixture by reading the spark plugs to see if you are running rich or lean. Happy revving

 

given that everything worked fine before the new carb and intake was installed so the valvetrain should be okay so i'm pretty sure its a timing/mixture issue. i hate messing with timing cus his oil pump his also driven by the distributor shaft and its a bitch to deal with. we're going to see what we can do with the mixture tonight and then we'll fix the timing this weekend. after that i'll let you guys know how its running and if its anything spectacular i'll see if i can post a video.

 

another question, when it got that random power surge, why was it doing that, and once we get everything adjusted right will that be the kind of power we should be getting cuz it pulled hard as hell.

Link to comment
Share on other sites

given that everything worked fine before the new carb and intake was installed so the valvetrain should be okay so i'm pretty sure its a timing/mixture issue. i hate messing with timing cus his oil pump his also driven by the distributor shaft and its a bitch to deal with. we're going to see what we can do with the mixture tonight and then we'll fix the timing this weekend. after that i'll let you guys know how its running and if its anything spectacular i'll see if i can post a video.

 

another question, when it got that random power surge, why was it doing that, and once we get everything adjusted right will that be the kind of power we should be getting cuz it pulled hard as hell.

 

thanks for clearing up that it was running fine before carb and intake install. set the carb as i said before so that should get it running decent enough to rule out fuel as the problem unless it popped the power valve. (holley right? old one or new one with upgraded power valve) sounds like the timing is really off. If the mixture was too rich or too lean it would cause the surge as it ran better when it got the proper fuel. Let me know how it goes. any fire balls send pics. I had that happen before my ears were ringing.

Link to comment
Share on other sites

thanks for clearing up that it was running fine before carb and intake install. set the carb as i said before so that should get it running decent enough to rule out fuel as the problem unless it popped the power valve. (holley right? old one or new one with upgraded power valve) sounds like the timing is really off. If the mixture was too rich or too lean it would cause the surge as it ran better when it got the proper fuel. Let me know how it goes. any fire balls send pics. I had that happen before my ears were ringing.

its the edelbrock thunder series carb. and yeah when it back fired i fell off the front of teh car and was seeing stars for a minute. i laughed after i realized what happened but man that scared me. that old crapy fabric that lines the hood catches sooo easily too, gotta watch out for stuff. prolly not good to breathe the dust from it either... thanks for the help and i'll let you know how it goes

Link to comment
Share on other sites

its the edelbrock thunder series carb. and yeah when it back fired i fell off the front of teh car and was seeing stars for a minute. i laughed after i realized what happened but man that scared me. that old crapy fabric that lines the hood catches sooo easily too, gotta watch out for stuff. prolly not good to breathe the dust from it either... thanks for the help and i'll let you know how it goes

 

the hood latch hook hurts too. edelbrock carbs the same as a carter just shiny.

Link to comment
Share on other sites

its the edelbrock thunder series carb. and yeah when it back fired i fell off the front of teh car and was seeing stars for a minute. i laughed after i realized what happened but man that scared me. that old crapy fabric that lines the hood catches sooo easily too, gotta watch out for stuff. prolly not good to breathe the dust from it either... thanks for the help and i'll let you know how it goes

 

I had an 86 monte with a mildly built 350 in it that would backfire out the carb had if I got on it from a dead stop. Eventully I cought the air filter and the under hood liner on fire. The carb was an old edelbrock 4barrel 750 with a wiend stealth intake. Couple timing issues we ran into building it (we were dumb kids at the time) installed accel supercoil kit backwards 180 degrees. Timing was entirely reversed and the car still ran! intalled the timing tab to the wrong bolt holes on the block. timed it initially off the tab in the wrong spot and that obviously didn't work. We also had the distributor off by one tooth too. It ran then, just ran like crap until we fixed it.

 

ultimately we had to use a vacum timing setup. from what I hear using a vacum setup is actually the most reliable. Using a timing light is hard to do unless its dark enough and there is possibilities for error when eyeballing it. with the vacum gauge you can just look at the gauge and when it hits the right vacum at the right time you have it dialed in right.

Link to comment
Share on other sites

  • 3 months later...

reviving an old thread but over time alot of the problems have magically dissapeared. the engine idles fine, it will bog off the line if you give it full gas, but once the revs build it pulls much harder than before. no more backfires, hard starts, etc. and we haven't changed a thing other than just putting miles on the car. is there a break in period on a carb and intake? we both agree that the car is over carbed and that it needs a blower.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...

Important Information

Terms of Use | Privacy Policy | Guidelines
We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.