Engine random back fire when warming up and surging
June 13th, 2014, 07:27 AM
#1
Registered User
Thread Starter
Join Date: May 2013
Posts: 70
Engine random back fire when warming up and surging
A little back ground information.
Car is a 1970 delta 88 350 block. I have swapped the 2 brl carb for a edelbrock rpm intake and a 1407 carb. This was done when i was 13 so 19 years ago. I ran this car in 2000 my senior year of highschool and then it went into my parents garage when I went to college.
From 2000 to last year this car was only started at most 1-2 times a year. Finally I brought it down to SC last year and of course it was running really rich. I changed the plugs, wires, distributor cap, oil, filter. Didnt mess with the carb because I had to move to Georgia. Once i got to georgia I set the points and adjusted the carb and it was still running rich.
Fast forward to this week I finally rebuilt the carb. Once rebuilt I adjusted it with the vacumme gage and the idle adjustment screws are approx 1.75 out. This gives me about 20-21 on vacumme but the gage is fluttering. I set my idle around 575. also set the eletric chock to middle line.
After this i noticed that there was a lag between idle and pulling the throttle back but only in the beginning. From this i changed the fuel pump system on the carb to the top whole instead of the middle. This helped but know i get random misses only when the car is cold and it will be 1-3 over a 10-15 minute period once it warms up it is over. Next issue is that it surges at low power if i am just over idle just cruising down the road.
Where should i start:
Currently i was thinking of the following:
pull the plugs and check
check all plug wire connections and ohm reading
replace the airfilter as it has been on the car for 14 years
check the points again
Ideally i would like to get a aem uego for tunning but at this point the wife would kill me.
Help please.
Car is a 1970 delta 88 350 block. I have swapped the 2 brl carb for a edelbrock rpm intake and a 1407 carb. This was done when i was 13 so 19 years ago. I ran this car in 2000 my senior year of highschool and then it went into my parents garage when I went to college.
From 2000 to last year this car was only started at most 1-2 times a year. Finally I brought it down to SC last year and of course it was running really rich. I changed the plugs, wires, distributor cap, oil, filter. Didnt mess with the carb because I had to move to Georgia. Once i got to georgia I set the points and adjusted the carb and it was still running rich.
Fast forward to this week I finally rebuilt the carb. Once rebuilt I adjusted it with the vacumme gage and the idle adjustment screws are approx 1.75 out. This gives me about 20-21 on vacumme but the gage is fluttering. I set my idle around 575. also set the eletric chock to middle line.
After this i noticed that there was a lag between idle and pulling the throttle back but only in the beginning. From this i changed the fuel pump system on the carb to the top whole instead of the middle. This helped but know i get random misses only when the car is cold and it will be 1-3 over a 10-15 minute period once it warms up it is over. Next issue is that it surges at low power if i am just over idle just cruising down the road.
Where should i start:
Currently i was thinking of the following:
pull the plugs and check
check all plug wire connections and ohm reading
replace the airfilter as it has been on the car for 14 years
check the points again
Ideally i would like to get a aem uego for tunning but at this point the wife would kill me.
Help please.
June 13th, 2014, 07:30 AM
#2
major noob
Join Date: Sep 2013
Location: claremont, nc
Posts: 1,926
Sounds to me its getting to much air or your idle is too low just happened to me and my dad yesterday all we had to do was advance timing and she's around the town right now after a few months of no car
June 16th, 2014, 04:51 PM
#5
Registered User
Thread Starter
Join Date: May 2013
Posts: 70
So i did some work and here is the results tonight.
Checked fuel pump pressure by hooking a tee into the line to the carburator and it was fluctuating between 1 and 4 at idle once off idle it stayed at 2.
Now for the question did i check the fuel right or did something else need to be done like plug a return line etc.
Also reset the timing at 8 degrees at 1100 rpm.
messed with the mixture screws and got 17 in at 600 rpm.
I have a wide band coming and adjustment set for the 1407 carb.
now for the question is it the fuel pump as this should be reading a constant 5-6 from what the manual says.
whats everyones thoughts?
Checked fuel pump pressure by hooking a tee into the line to the carburator and it was fluctuating between 1 and 4 at idle once off idle it stayed at 2.
Now for the question did i check the fuel right or did something else need to be done like plug a return line etc.
Also reset the timing at 8 degrees at 1100 rpm.
messed with the mixture screws and got 17 in at 600 rpm.
I have a wide band coming and adjustment set for the 1407 carb.
now for the question is it the fuel pump as this should be reading a constant 5-6 from what the manual says.
whats everyones thoughts?
June 16th, 2014, 07:49 PM
#6
Administrator
Join Date: Oct 2009
Location: Poteau, Ok
Posts: 40,553
Whats your dwell, should be 30? Put your choke back to where it was. Is your timing steady? Is your timing advancing with rpm? Is the vacuum advance operating correctly? The 575 rpm idle speed is set in drive.
June 17th, 2014, 05:39 AM
#7
Registered User
Thread Starter
Join Date: May 2013
Posts: 70
Dwell is 30 on the money at 1100 rpm.
Cutlass,
Put your choke back to where it was. will do tonight
Is your timing steady? whats the best way to check this?
Is your timing advancing with rpm? I would guess yes as it is different at idle than at 1100 rpm
Is the vacuum advance operating correctly? When i unplug it from the carb the idle goes down. When it is installed on the carb the idle goes up. Is there another way to check this
The 575 rpm idle speed is set in drive. Actually set it in park. I will redo this tonight
Cutlass,
Put your choke back to where it was. will do tonight
Is your timing steady? whats the best way to check this?
Is your timing advancing with rpm? I would guess yes as it is different at idle than at 1100 rpm
Is the vacuum advance operating correctly? When i unplug it from the carb the idle goes down. When it is installed on the carb the idle goes up. Is there another way to check this
The 575 rpm idle speed is set in drive. Actually set it in park. I will redo this tonight
June 18th, 2014, 06:03 AM
#12
Registered User
Thread Starter
Join Date: May 2013
Posts: 70
Just an update:
Wasnt able to work on the car last night other than pull the fuel pump.
The wideband arrived but I have to get a outlet for my welder as we only moved into the house a couple of months ago.
Picked up a new fuel pump and hose for the fuel lines to the pump as well as from the pump to the carb.
I will try and atleast get the bung welded in and the fuel pump changed. Then we will see how it runs.
Now with the fuel pump do i need to block off the return line from the pump when check fuel pressure or leave it the way it is?
Wasnt able to work on the car last night other than pull the fuel pump.
The wideband arrived but I have to get a outlet for my welder as we only moved into the house a couple of months ago.
Picked up a new fuel pump and hose for the fuel lines to the pump as well as from the pump to the carb.
I will try and atleast get the bung welded in and the fuel pump changed. Then we will see how it runs.
Now with the fuel pump do i need to block off the return line from the pump when check fuel pressure or leave it the way it is?
June 18th, 2014, 08:35 PM
#13
Registered User
Thread Starter
Join Date: May 2013
Posts: 70
it was the fuel pump. changed it out tonight hooked up the gage and no more 2 psi. now 5-7 flutter at idle and above 5 with the rpm up.
tomorrow night hopefully i will weld in the bungs and hook up the wideband to dial the carb in.
tomorrow night hopefully i will weld in the bungs and hook up the wideband to dial the carb in.
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