carburator problems...

dr0pt0pf0rd

New Member

Apr 10, 2005

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Nov 4, 2005

#1

• Nov 4, 2005

• #1

ok heres the deal...

had a 3.8L... blew it up... pulled it out... and put in a carbed 5.0. now... i can start the engine fine. it idles perfectly. if i slowly give it throttle its fine. it will gain rpms... so on and so forth. but if i juice the throttle to half or more, it backfires. large flame comes out the driver side of the carb. next problem... once the car heats up (approx. 4 minutes idle time) it starts backfiring every few seconds and eventually stalls out. i can literally see a flame comming out of the driver side of the carb when it backfires. i checked the timing. i readjusted the carb mixture screws. nothing has helped. any ideas?

holley 600
edelbrock performer intake
82 mustang 5.0 block
comp cam roller tip rockers

im beginning to think it could be a bad valve seat. once the heads heat up... maybe they are expanding and one of my intake valves isnt sealing properly. tell me what you think.

 

thumper460

Founding Member

Jul 24, 2000

3,022

2

56

Orange Park , Fl

Nov 4, 2005

#2

• Nov 4, 2005

• #2

Used engine?? pull the valve covers and check out the valve train!! Look for broken or stuck valve springs. with a bad spring.. it will work at the low rpm, but when you bring up the revs the spring fails and the valve doesnt perform and thus the back fireing thru the carb..

Just me.........................

Thumper

 

dr0pt0pf0rd

New Member

Apr 10, 2005

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Nov 4, 2005

#3

• Nov 4, 2005

• #3

yeah its used. but freshly rebuilt. im gonna try flipping the carb around to make sure its a valve. if the backfiring stays on the driver side, then its a valve. but if it flips to the passanger side, its the carb. i will also check the valvetrain tonight.

 

M

mr.b

Founding Member

Aug 30, 2002

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Nov 4, 2005

#4

• Nov 4, 2005

• #4

do a leakdown test. are you checking the timing with the vacuum line off the advance canister?

 

PuterAmI

Member

Mar 29, 2003

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Madison, Alabama

Nov 4, 2005

#5

• Nov 4, 2005

• #5

Does that Holley have PV blow-out protection? The older ones did not and you didn't say if this is a new one or not. A backfire will waste the PV and it will dump fuel into the intake.

Yet, backfires up through the carburetor are always linked to timing in some way. Is this an HO motor or not? The two have different firing orders according to the cam.

 

dr0pt0pf0rd

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Apr 10, 2005

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Nov 4, 2005

#6

• Nov 4, 2005

• #6

its a brand new holley carb. it cant be my firing order cause it runs fine at idle when its cold. im gonna try a compression test once it heats up.

edit : unless the firing order is different by only 2 cylinders

 

dr0pt0pf0rd

New Member

Apr 10, 2005

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Nov 20, 2005

#7

• Nov 20, 2005

• #7

*bump*

i still havent fixed this problem. any one else have any ideas? winter is coming and its gonna be cold to ride my yamaha around in the snow.

im ready to rip the heads off and rebuild them... im sick of not driving.

 

Dark Knight

Founding Member

Feb 1, 2000

2,578

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Chandler, Az.

Nov 20, 2005

#8

• Nov 20, 2005

• #8

double check your firing order, it will run with the early firing order.. it is the stock cam, right?

what kind of heads are on it? pedestal mount rockers? double check the rocker arms to make sure they arent to tight and holding a valve open..didnt need any shims?

check the ditributor cap and rotor too, as RPM's increase you might be getting some arcing.

 

dr0pt0pf0rd

New Member

Apr 10, 2005

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Nov 20, 2005

#9

• Nov 20, 2005

• #9

oh now he tells me... "check your firing order..." after i figure out today that i was using the HO order and not the standard order... problem solved. car runs great now. thanks.

 

Dark Knight

Founding Member

Feb 1, 2000

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Chandler, Az.

Nov 21, 2005

#10

• Nov 21, 2005

• #10

PuterAmI said:

. Is this an HO motor or not? The two have different firing orders according to the cam.

Click to expand...

if you used the 1 5 4 2 6 3 7 8 order, it probably doesnt have the stock cam
they changed to 1-3-7-2-6-5-4-8 in 82

 

dr0pt0pf0rd

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Apr 10, 2005

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Nov 22, 2005

#11

• Nov 22, 2005

• #11

well a new problem has become apparent... since the car never really warmed up... because it would just stall out, the water pressure never built up either. but now that it runs good, ive found that my cooling system has some serious issues... blown heater core, wrong radiator (constantly burning off coolant in the form of steam... why...? i dont know) ...its just a mess...

but i did get a pretty sick video of my 2 only donuts that i did with the new motor. i just parked it for the winter. now its time to rip it out and rebuild it again. with some 351 heads... mm mm good.

 

C.Harris

Da Boss

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Dec 20, 1998

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Nov 22, 2005

#12

• Nov 22, 2005

• #12

If the engine has been freshly built and recently dropped in the engine bay, it may have a trapped air pocket in the cooling system. The 302s are notorious for trapping air when the system has been completely drained and refilled again. You will need to scavenge any air pockets out of the system, hopefully the problem will be resolved. Believe it or not, I have also heard of thermostats being put in incorrectly. Also, some of the older t-stat designs stayed in the closed position when they malfunctioned...the newer designs are built to actually open in a case of failure, thus allowing the coolant to still circulate. Also check for perculation...bubbles in the coolant could be signs of a blown head gasket.

 

dr0pt0pf0rd

New Member

Apr 10, 2005

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Dec 4, 2005

#13

• Dec 4, 2005

• #13

ive been told my numerous people that 302's are known for air pockets. so thats where im going to start. i know its not a head gasket cause i just did those 2 weeks ago. (had coolant in my oil... but actually wasnt the head gaskets. it was a leak on my intake manifold.) anyways... im assuming if i remove my head core hose that leads to the core... and let the car run... it will "burp" out any remaining air pockets. anyone try this?