misfire... carb issue??

[old school truck dude]

You gotta have a light with a knob on it to see total timing. You turn the knob and keep light pointed at the crank with it showin zero and read on your light how many degrees youve set the knob to. You can get it where itll run pretty fair by ear, but it will need dialed in with a good light. May have to goof around with the dizzy a bit to get that set just right.. How many turns out are the mixture screws on the carb? If its more than 2 1/2 or so maybe go up a jet size or 2 in your primaries. Makes a big difference, it will hit a lick at idle if thats what its supposed to do lmao. It aint hard, dial it in. Backfire in the carb and bogging on acceleration means its lean or not enough advance. Backfire out the exhaust is trouble. Nothins 100% but just sayin usually. 

[Kyle]

well i got the advance turned up to 10 degrees and the primaries float level set. idle screws around 1 1/4 out if i remember right when i set it before at 4 degrees. although right now it dont wanna idle very smooth but its not rough either. it has good get up and go but when i mash the throttle it kinda bogs and u can feel it not run right but its not backfirin. and if i drive it normal and let overdrive engage and the torque converther lock up it really boggs and has like no power when i press(not stomping) on the gas to the point i can barely drive it in OD. im not sure if thats the carb loadin up or what.... do i maybe need to drop the fr down to 6 and/or reset the idle screws? or even give it 2 more degrees advance?

[Squirell]

Are you setting the timing with the vacuum advance unhooked and vacuum line plugged? Also I would concentrate on getting total timing(3000 rpm) to somewhere between 32-36 degrees. As far as lookup what is the power range of your cam, is it locking up below the power? If not carb may need to be tuned

[old school truck dude]

Thats a good question.. Also, maybe it would help to come out with the mixture screws a little bit at a time and step up the idle speed if need be to keep it runnin. you want it to be a tad rich.. That idle circuit in the carb has an affect on acceleration.. Now that you have more advance, are ya hearin any spark knock/detonation..? If not, could go counter-clockwise on the dizzy just a teeny hair more.. Go easy, dont do anything excessive.. Theres a sweet spot there somewhere, ya gotta kinda go back and forth till ya hit it.

  Base timing is set with no additional advance from any other source whether mechanical or vacuum or electronic and the vacuum line plugged. This will let the motor run but not be overly powerful. The advance curve is the way whatever system it is that youre using to increase the advance to the dizzy's timing of the spark. Total timing is the total amount of advance your system can apply to your dizzy. To get peak power, the advance curve, total timing, and base timing must all be correct. You got that box, is it adjustable?? Does it have knobs or screws you can adjust? Some of them you can do from the driver seat.. Them ones are some cool beans, yup..  

[Kyle]

Are you setting the timing with the vacuum advance unhooked and vacuum line plugged? Also I would concentrate on getting total timing(3000 rpm) to somewhere between 32-36 degrees. As far as lookup what is the power range of your cam, is it locking up below the power? If not carb may need to be tuned

yes. line unhooked and pluged. cam range is 1600 to 5600rpm. when the rpms drop is goes down to the bottom end of the cams power band but not under. and i havent tuned the carb idle since ive advanced the timing and reset the fuel bowl, and i prolly need to drop the fuel pressure down a psi to 6psi(carb is goot for 5-7)...

Thats a good question.. Also, maybe it would help to come out with the mixture screws a little bit at a time and step up the idle speed if need be to keep it runnin. you want it to be a tad rich.. That idle circuit in the carb has an affect on acceleration.. Now that you have more advance, are ya hearin any spark knock/detonation..? If not, could go counter-clockwise on the dizzy just a teeny hair more.. Go easy, dont do anything excessive.. Theres a sweet spot there somewhere, ya gotta kinda go back and forth till ya hit it.

   Base timing is set with no additional advance from any other source whether mechanical or vacuum or electronic and the vacuum line plugged. This will let the motor run but not be overly powerful. The advance curve is the way whatever system it is that youre using to increase the advance to the dizzy's timing of the spark. Total timing is the total amount of advance your system can apply to your dizzy. To get peak power, the advance curve, total timing, and base timing must all be correct. You got that box, is it adjustable?? Does it have knobs or screws you can adjust? Some of them you can do from the driver seat.. Them ones are some cool beans, yup.. 

idle screws do still need to be reset. and i set them by vac guage for what gives max vacuum at idle. and no im not hearing any knock or detonation that im aware of. and i was thinkin bout stepping up the advance another 2 degrees anyways to put it up to 12. then retune the carb set pressures and floats all at once and see where that puts me. no mine aint adjustable. its just a regular 6al box with rev chips. runnin a 6k chip atm. and its just there, i dont run my motors that high EVER

[old school truck dude]

The vacuum guage will get you very close, but ya still might be able to squeeze a bit more out of that motor if youll just do what works best as opposed to what is SUPPOSED to be best according to test equipment, since  youre not usin a dyno. Nothin beats trial and error youll never know how far you can turn the screws out till you go too far and it doesnt run as good as the last setting, and youll never know how much base timing you can run till ya make it ping and have to back off of it a little..

[Kyle]

in the future i will be puttin it on the dyno. but for now i want to tune it the best i can with actual numbers i can reference with.

got the fuel pressure guage hooked up today, and for some reason its reading like 3.5psi..... and this is off of the fpg port thats specifically for the pressure guage amd theres no leaks in the line and no kinks, its stainless braided line....

[Cannaert]

Is it still doing it at 3.5 psi.  I had to back mine all the way out for a few minutes of run time before it began to bring the PSI up to 5 PSI.

[Kyle]

Is it still doing it at 3.5 psi.  I had to back mine all the way out for a few minutes of run time before it began to bring the PSI up to 5 PSI.

Yep infortunately. Ive driven it a couple times now and hasnt changed. Dont know if its the guage and the line needs to be bled or what. I havent touched the regulator yet

[Eroq]

Check your pkugs, see how theyre burning   rich/lean

How old are the wires? Ive ran in to brand new parts being bad quite often, mainly plug wires!

[Squirell]

in the future i will be puttin it on the dyno. but for now i want to tune it the best i can with actual numbers i can reference with.

got the fuel pressure guage hooked up today, and for some reason its reading like 3.5psi..... and this is off of the fpg port thats specifically for the pressure guage amd theres no leaks in the line and no kinks, its stainless braided line....

if u only have 3.5 your probably running out of fuel

[gator82]

I once had a 64 truck with a 400 and it had a quadrajet that did the same thing except I had no power, I bought a 625cfm manual choke Carter off a buddy and it cured that problem, thing moved after that. If you can get your hands on a good Carter you could try that.

[Kyle]

Check your pkugs, see how theyre burning   rich/lean

How old are the wires? Ive ran in to brand new parts being bad quite often, mainly plug wires!

wires are about a year and a half old. ill be orderin some new ones next week just to know they are good. these worked great with the 350 but this has way more ignition. thinkin bout getting the superconductors again...

in the future i will be puttin it on the dyno. but for now i want to tune it the best i can with actual numbers i can reference with.

got the fuel pressure guage hooked up today, and for some reason its reading like 3.5psi..... and this is off of the fpg port thats specifically for the pressure guage amd theres no leaks in the line and no kinks, its stainless braided line....

if u only have 3.5 your probably running out of fuel

it makes sense but what i dont get is that the regulator is made for a 4.5-9psi range, how could it be below that pressure? and the carb is made for 5-7. can a carb even run with it that low?

I once had a 64 truck with a 400 and it had a quadrajet that did the same thing except I had no power, I bought a 625cfm manual choke Carter off a buddy and it cured that problem, thing moved after that. If you can get your hands on a good Carter you could try that.

unfortunately i am no longer made of money anymores lol went well over 4x the budget for this motor and spent a good chunk of change on this 670 holley street avenger

[4x4xdodgeman]

why not check the wires with ometer? why just buy new if old are good. if your motor stumbling off idle, you need bigger squrits in the carb. its not timing. but you need fuel pressure up some. if you where closer to me would help you out on the carb.

[Hammerlane]

checking plug wires is as easy as lifting the hood in the dark.. watch for sparks.

[Kyle]

i had visually checked the wires before, not bad but aint new. theyre due for new ones, theyve had plenty of miles put on em already....

i boucght another FP guage tyhat hooks directly in line with a barb fitting and did that in between the reg and carb. got that set to 6psi, and the guage in the cab was showin only 4 psi, maybe the 4 ft hose is the culprit, i dont know. but for now im just gonna use it as a reference to see if i have or lost pressure

but this afternoon, got the pressure set float levels set, reset the idle mixture(ended up going inwards more with the screws) and left the timing at 10 degrees. runs a helluva lot better. very responsive. although flooring the throttle from idle(in park) there is a slight, slight, almost misfire. has bout 16 inches vacuum at idle so it may be running small on jet sizes but it doesnt stumble with the power shot that i can tell

[Kyle]

i played with it some more today, bumped up the idle to 14 degrees, switched the vac advance line to the port on the side of the metering block that its supposed to be on and reset the idle mixtures. so now when its idleeing it has 14 degrees but immediately when throttle is applied i get advance. its VERY peppy in the bottom end in park. drives good, idles well(16 inches of vac). only issue now is when in park under a hard throttle it backfires through the carb once but doesnt spit and sputter. and when its in overdrive and torque converter locked, i can give easy throttle and it wont stumble, but half or more it will, but it isnt backfiring. i tried the lightest vac spring and it got worse, and it seemed to be better runnin the heavier spring, but it seems to be lacking a lil in midrange with it.... checked the timing at 2500 rpms and it seems to be pulling around 40 degrees advance

[Yetti]

your engine vacuum still sounds low to me. I wonder if you have a valve or two on the tight side? did you adjust them when it was on the stand or when it was in the truck running? if you adjust them running it might get you 3-5 more inches of vacuum at idle.

as for switching the dist advance to the ported vacuum, that should help a bunch. sounds like you may still have a "lean pop" as you hear it as a backfire. get the regulator up the 5-7 psi and it might do much better and get rid of the pop

[randycrane79]

if your having issues with the carb at iddle and running fine till you goos it or gradual gas it it is gonna be the pop off valve inside the front bowl on carbs hollley used this to stop over load and fuel fires and when it pops or backfires 1 time it blows it and czuses this problem trust me i have built alot of holley carbs and deal with them alot so holley came up with this deal you can block it off instead of changing valve and works good block kit is like 50 or ya can buy another valve for 25 and be ok just dont back fire it i bet 100% it will fix the problem

[Kyle]

your engine vacuum still sounds low to me. I wonder if you have a valve or two on the tight side? did you adjust them when it was on the stand or when it was in the truck running? if you adjust them running it might get you 3-5 more inches of vacuum at idle.

as for switching the dist advance to the ported vacuum, that should help a bunch. sounds like you may still have a "lean pop" as you hear it as a backfire. get the regulator up the 5-7 psi and it might do much better and get rid of the pop

valves if anything are on the loose side. i adjusted em in the thruck cuz i had to preplace the head gaskets cuz the heads leaked. did it by firing order and did it all properly. tried the carboad valvecover but all the oil pressure just shot it all over and through the holes and it just leaked out the back of the head cuz it didnt drain fast enough too.... as for manifold vac ur sayin, i have it off the upper port on the carb where holley says to use, has no vac at idle but once that throttle is moved it sucks a bunch of vac. i have the pressure set at 6(which holley reccomends i run it at 6-6.5) right now by an inline guage between the regulator and the carb

if your having issues with the carb at iddle and running fine till you goos it or gradual gas it it is gonna be the pop off valve inside the front bowl on carbs hollley used this to stop over load and fuel fires and when it pops or backfires 1 time it blows it and czuses this problem trust me i have built alot of holley carbs and deal with them alot so holley came up with this deal you can block it off instead of changing valve and works good block kit is like 50 or ya can buy another valve for 25 and be ok just dont back fire it i bet 100% it will fix the problem

it idles and runs just fine, its just when i stomp on it hard it has issues and when in overdrive it stumbles at half part throttle or more. and the valve ur talkin bout, i looked into it, i thought mine bein a brand new holley it has the blowout protection already in it?