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excessive fuel in carb

 
dka2205
I love my Chevy Chevette!
Posts: 4
Joined: 10/12
Posted: 10/19/12 07:52 PM

hey everbody im new so bare with me. 73 k1500 with a 350 has a rochester quadrajet, edelbrock performer high rise intake and cam kit with hydraulic lifters cheap summit headers dual 2 3/4 exhaust with thrush turbo mufflers and a points to HEI conversion kit. ive been having an extreme amount of fuel sittin in the middle of the carb when i fire it up, it idles fine but when i hold the throddle cruisin it will not hold there until its caught up with all of the fuel sittin in it it smells like its runnin rich rebuilt the carb same problem. i switch carbs it runs like a pile of dog *** but doesnt have the excessive fuel.. the air/fuel mixture screws dont work either way i cant get it to bog down like its suppose to does this mean i have an intake manifold gasket leak or are my carbs f####ed? i recently found out the stock timin chain comes stock retarted 13 degrees i had to buy a double roller from eddie. that didnt change anything with the carb problem though. emissions test at idle was 1200 at 950rpm and 5533 somewhere between 25 to 3000 rpm vaccumm starts at 5 warms up to 7 and cruisin off throttle @ 2000rpm will finally hit 10.. one giant cluster *** after another any help please?  

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68scott385
I mow my lawn and find Chevys
Posts: 1994
Joined: 10/09
Posted: 10/19/12 08:35 PM

make sure your float level is set correctly

while you have the carb apart doing that check the float to make sure it doesn't have a hole in it and filling up with fuel causing the fuel to spill out of the fuel bowl and cause all sorts of problems

what type/brand fuel pump are you running? stock? aftermarket? ... what fuel pressure are you running ... Qjet doesn't need anymore than 5-6psi, much more and the pressure will cause fuel to push past the needle & seat  
68scott385 68scott385 68scott385

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pepsi1
I mow my lawn and find Chevys
Posts: 1718
Joined: 09/11
Posted: 10/19/12 09:02 PM

First welcome to CHP dka2205:

  A stock or near stock cam should bring you to 14" to 16" of Vacuum. Now was the Vacuum that low before you changed the timing chain. I haven't heard of a timing chain being retarded 13* that's a lot. So where is the ignition timing during all of this?
 Because I think thats where most of your problem comes from!Is the engine backfiring or popping through the carb. Doing anything strange. Something doesn't JIVE...LOL...

1A.Adjust the float level down in the carb if you can?
1.Maybe you have the valves adjusted to tight. It's causing the intake valves to close late and give you a low Vacuum.
2.That could be the reason you can't adjust the carb.
3.The timing chain is the reason to degree the cam
4.I use for the street a cloyes roller timing chain #9-3100.
5.Base timing 12* if a vacuum advance remove the vacuum hose and plug it. set your base timing 12* hook the vacuum hose and bring you engine speed up to 2000 RPM and set you total timing at 30*
6.I really want to know where TDC is. Changing the timing chain, it doesn't make sense....
7.To answer your question about an intake leak, I doubt it. If you had an intake leak the engine speed would be high how knows where it could go. 2000,3000RPM?
  Do this drop the float level in the carb. Or if someone has a 650 spread bore Holley with a vacuum secondary. Change it over.
Send us the exact specs for the cam. Lift and duration...
Set your timing. Do all those things first. Good Luck

Bob  

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waynep71222
I have an SS396 tatoo
Posts: 448
Joined: 03/12
Posted: 10/20/12 08:04 AM

a few things....

swapping the spread bore holley is a decent idea...

if you want to stick with a quadrajet...

can you post the number stamped sideways on the drivers side of the float bowl behind the throttle linkage...  there are several variations  in quadrajet models..

there are about a dozen quadrajet articles spread out in the many magazines on this site.

but it could also be several other internal carb problems..

there are several circuits inside the carb...

at idle.. the fuel mixture is limited and controlled by the idle mixture screws..

above idle..  you have the idle transition circuit..
this feeds from the slots near the idle mixture screw tips.. so the engine does not lean out as you open the throttle and the airflow across the boosters is not fast enough to pull fuel up and over..

quadrajets have an spring loaded primary rod holder...   when running the manifold vacuum pulls the rod holder down against its stop.. this is where the  primary mains start delivering fuel.. this rod holder has adjustable stops...  depending on which carb you have..   if the stop is too far down.. as the main circuits come on.. the air fuel goes lean... and you have to tip your throttle in farther...  if the adjustment is too high.. it will be rich and again stumble...

since quadrajets have a tiny primary.. you end up with this adjustment being critical for drivability..   this adjustment is called the APT...  adjustable part throttle..

you could also have leaking plugs in the bottom of the float bowl.. epoxy can fix this problem..

identify which carb number you have..


Quadrajet Primary Circuits  

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dka2205
I love my Chevy Chevette!
Posts: 4
Joined: 10/12
Posted: 10/20/12 10:13 AM

okay the carb number is 17059520 under it is 2798 not sure if you need those ones i believe its a 79. the rebuild kit said something about it being for a 454? my dad went to the 350 above for the same year and set the float for that model and it is a brand new float i looked it over before and after theres no holes. stock fuel pump havent checked the fuel pressure yet ill do that today. cam duration is 234 int and 244 exh lift is 4.88 int 5.10 exh timing is set at 10. went for 8 it backfired same with 12. 10 was the best it ran without any backfiring either through carb or exhaust. also after rebuilding the carb i read on a forum theres a screw or something of the sort that adjusts the piston for the needles thats only on this carb that that i have this would be the APT correct? if so how do i adjust it when rebuilding it wouldnt move either way or come out and the kit said nothing about it, so i went on assuming it was stationary and non adjustable? thanks again for your help  

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68scott385
I mow my lawn and find Chevys
Posts: 1994
Joined: 10/09
Posted: 10/20/12 10:33 AM

With that cam and without at least a 3.73 gear and 2500 stall convertor, that motor will run like a dog until it gets to 2500+ rpm. I have one, it sounds good at idle but doesn't deliver as well as other cams do. It's a UNIT approach. Heads, cam, intake, carb, torque convertor, rear gear ratio all have to work together.

Are you sure that the valves are adjusted correctly?  
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redneckjoe69
I mow my lawn and find Chevys
Posts: 2337
Joined: 03/10
Posted: 10/20/12 11:39 AM

Icon Quotedka2205:
okay the carb number is 17059520 under it is 2798 not sure if you need those ones i believe its a 79. the rebuild kit said something about it being for a 454? my dad went to the 350 above for the same year and set the float for that model and it is a brand new float i looked it over before and after theres no holes. stock fuel pump havent checked the fuel pressure yet ill do that today. cam duration is 234 int and 244 exh lift is 4.88 int 5.10 exh timing is set at 10. went for 8 it backfired same with 12. 10 was the best it ran without any backfiring either through carb or exhaust. also after rebuilding the carb i read on a forum theres a screw or something of the sort that adjusts the piston for the needles thats only on this carb that that i have this would be the APT correct? if so how do i adjust it when rebuilding it wouldnt move either way or come out and the kit said nothing about it, so i went on assuming it was stationary and non adjustable? thanks again for your help

sounds like your talking about the vacuum secondaries?    been a long time since ive had a rochester.    IIRC, there is a set screw on the back, drivers side.   unloosen it.   then there is a screw underneith it.   unloosen it.   when i say screw, they may actually take an allen key?   with no spring pressure, give it about 1/4 turn, then lock down the set-screw.   go for a test ride, and adjust as needed.    maybe somebody has a diagram or pics?

  i would figure out the flooding issue first.

  spray some starting fluid around the intake/carb to check for vacuum leaks.

  and your definetly gonna need an aftermarket stall with that cam if using an auto tranny.

   welcome to CHP! Cool  

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waynep71222
I have an SS396 tatoo
Posts: 448
Joined: 03/12
Posted: 10/20/12 11:46 PM

the 17059520 is for a 79 454 automatic in a chevy or GMC pickup.. 1/2 to 3/4 ton.

this carb does have an APT adjustment..  don't use a cut off bolt to adjust it.. this is just to show you where it is...

Apttool


i am curious about the BACKFIRE... is this on opening the throttle??  showing the accelerator pump circuit is not functioning properly... or showing that the main circuit is  too lean.. or too rich as it begins...

can you use a mirror..  with the air cleaner top off...    the choke open... engine idling.....

is there any fuel dripping from the booster venturis..   you may want to aim a timing light down the bore... so you can freeze frame the fuel drops if any. at idle.. there should BE NONE...

how about the accelerator pump discharge..??? do you get a nice squirt into both primary bores???

did you know that there were rochester dip stick tools... that could be inserted into the round vent hole to measure either the float height.. or to measure the height of the metering rod holder..  they are almost impossible to find any more..

let me dig into my pile of carb cores... take a few photos in the next few days... i should have something by tuesday..  

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dka2205
I love my Chevy Chevette!
Posts: 4
Joined: 10/12
Posted: 12/05/12 05:48 PM

Sorry its been a while i lost my internet. But yes i knew where the apt was i was unsure if that was what i was staring at. However i think someone might have messed with mine before i owned it my apt screw it pretty fat almost circular this normal? I have a manual 4 speed. But i was digging around a while ago and seen on a show that with the performer rpm q jet  

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dka2205
I love my Chevy Chevette!
Posts: 4
Joined: 10/12
Posted: 12/05/12 05:52 PM

Sorry phones stupid. Anyways with the rpm q jet they had problems with the carb the fuel wasnt atomizing so they had to mill down the divided plenum wall just like the air gap was or put a carb spacer on do you think this could be my problem or have nothin to do with it?  Thanks for your help very much appreciated.  

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waynep71222
I have an SS396 tatoo
Posts: 448
Joined: 03/12
Posted: 12/05/12 10:48 PM

well...  i would dig into the APT adjustment first..

the 454 carb is going to be jetted rich for a 350...  

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waynep71222
I have an SS396 tatoo
Posts: 448
Joined: 03/12
Posted: 12/05/12 10:59 PM

well...  i would dig into the APT adjustment first..

the 454 carb is going to be jetted rich for a 350...

do you have any other quadrajets you can post a carb number from.. see if you could rob the primary metering rods and jets out of .. the secondary rods and rod hanger are easy to swap in seconds...

there is a great q jet article over at high performance pontiac magazine on this site.. it has a chart with some of the metering rods by ID number arranged by size..

i guess i might have to spend the next month putting together a list of all the quadrajet carb numbers...  but also include the various jets and metering rod part numbers but also stamping numbers.. and after having them listed by carb number.. rearrange them by factory engine displacement..   perhaps even sort by brand and displacement..

this way a chart could be created showing metering rods on a graph...  but the graph is the displacement of the engine.. now that would be handy.. .  

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