Backfire Through Carb

[hillchevelle69]

This truck is an 85 bronco II 2.8L. It was sitting for a couple of years and i bought it about a month ago, i'm getting around to working on it first of all it was backfiring through the carb if you just hit the accelerater quickly and let off, it lets off a loud pop and you can see gas shoot out the carb. I got another carb off of another bronco, it does the same thing, the only thing that is on the new carb that was on the old one was this piece on the back that has 3 bolts and is shaped like a triangle, it has a plug in on it, i don't know what it is, but the carb i put on there didn't have the same type of plug so i took it off the old carb. other than the backfire it seems to run okay, it runs a little rich the timing is right, and it idles just fine. i did a compression test and these were the results: cylinder 1,2,4 were at 170 lbs. and cylinders 3,5,6 were at 130 lbs. i did not do the compression test with WOT. Any help would be much appreciated!

 

[PetesPonies]

well spark is happening when the intake valve is open. Either from the timing being off or the intake valve hanging open or being burned/chipped. Since you have decent compression, that should not be the problem.

 

[BeaterMan]

When you are timing it are you disconnecting the spout connector? Ionly ask because i forgot to replug it back once and my truck did the same thing as yours when it was unconnected. That or with a timing light you could see if your timing is advancing when ya increase the engine speed.

 

[adsm08]

I thought the 2.8 had a vacuum advance

 

[hillchevelle69]

I am going to try to set the timing again, thank you all for your answers, if the timing is correct, what should i do next? i have another 85 bronco i have been using for parts, should i take the heads off of that one? as far as i know there is nothing wrong with the top end of the motor, but it has also been sitting for a while. Thank you all for your responses

 

[hillchevelle69]

The timing is perfect.

 

[Shran]

I thought the 2.8 had a vacuum advance

The Duraspark distributor has vacuum advance and the stock TFI distributor does not.

My guess is that it's exactly what PetesPonies said.

 

[hillchevelle69]

im taking the heads off in the morning to get them redone, hopefully that solves my problems. thank you all for your help.

 

[kimcrwbr1]

did you check the timing after you plugged the spout connector in

 

[hillchevelle69]

I had the spout connector plugged in while i was timing it, should i time it with it unplugged?

 

[Bronco_Chuck]

yes the correct way to time it is to unplug the spout then time it to 10* BTDC then reconnect the spout.

 

[hillchevelle69]

SO which of the marks on the wheel is TDC. I can't read any marks or anything. the only thing i see are the deep cuts.

 

[hillchevelle69]

there is a mark on the balancer where someone has obviously marked where the correct timing goes, the timing does not change if the SPOUT is plugged in or not plugged in.

 

[kimcrwbr1]

It should advance to about 35 degrees at 2500 to 3000 with the spout plugged in unplugged 10 deg at an idle the big crack on mine is not even close to 10 take some steel wool or a scotch brite and scrub the damper the marks and numbers should be visible and are you using the pointer about two inches above the round hole to time to. if it dont change you have a distributor or wiring problem dont pull the heads just yet I will look up the spout test procedures. let me check the tech library

 

[kimcrwbr1]

In the tech library under TFI troubleshooting it will explain how to test the ignition step 8 is for the spout when you have it running and the spout is disconnected you should have battery voltage to the spout connector if not it is the harness or the computer at least that is how i read it