backfire problems 302

Anthony's Son · Post by **Anthony's Son** » August 28, 2011, 1:20 am

well dad wont let my uni come to the top of the hill until i get my mustang on
the road... soooo i got it running but can't get it right... i have checked
timing and vacumes... it idles pretty good.. but it keeps back firing back
through the carb wen i try to give it gas... i think i might go get a rebuild kit
tomorrow for it but wanted some opinions.. let me know any ideas

banjopicker66 · Post by **banjopicker66** » August 28, 2011, 6:46 am

Zak: I would hold off the rebuild kit for now - let's try to eliminate other possible causes first. A little bit more information will help, can you answer these questions?

1. Has the engine run right for you at all?
2. Have you made any changes to it since it ran well?
3. Anything special or non-standard about the engine, such as a performance cam or aftermarket ignition?
4. What size and type of carb does it have?
5. Did you use factory specs for timing? What are they?
6. Did you do a tune-up, and replace any parts? What parts did you replace (or not replace?)

Try the following steps, too, and see if they help.

1. Remove the vacuum advance tube, plug it and the nipple, and see if that helps.
2. Remove the hose for power brakes, plug it and try that.
3. Try retarding the ignition timing, in stages, a little at a time.
4. At night, in the dark, start it and check the plug wires for blue sizzle. It needs to be very dark with no lights on. If you see blue electric sizzle, it means the spark is not fully insulated, and you may be crossfiring.

Personally, I think it will be an ignition issue, but we will see.

Finally, Zak, we all here really like to help young folks like you, especially those who like Ford trucks!
But, you would do much better, and get more respect to use proper punctuation. I know that your generation uses a slang form of English and spelling quite a bit, but it can be difficult to read, and to understand the information being communicated.
So help us out, and we can help you out more accurately.

Post back what you find out when you test!

John

MadMaxetc · Post by **MadMaxetc** » August 28, 2011, 8:04 am

Fire comes from a spark. In order for it to get to the carb the intake valve would have to be open when the spark plug is going off.

My bet is the timming is off 180°.

cooter · Post by **cooter** » August 28, 2011, 8:29 am

your firing order may be wrong so check the plug wires or the cam may have chewed a lobe off, check rocker arms to see if one is loose to verify this

Anthony's Son · Post by **Anthony's Son** » August 28, 2011, 8:31 am

banjopicker66

"1. Has the engine run right for you at all?
2. Have you made any changes to it since it ran well?
3. Anything special or non-standard about the engine, such as a performance cam or aftermarket ignition?
4. What size and type of carb does it have?
5. Did you use factory specs for timing? What are they?
6. Did you do a tune-up, and replace any parts? What parts did you replace (or not replace?)"

1. I have not been able to get the motor right since I put it in.
2.
3. Motor is stock with headers and MSD ignition
4. Has an Edlebrock Performer intake and Carb, but not sure on the size, it was on another motor when I got it. The other motor ran great with it, until it spun a rod
5. Yes I looked them up on Google. I tried two different specs. "1-5-4-2-6-3-7-8 and 1-3-7-2-6-5-4-8"
6. Yes, I changed the oil, plugs, and anifreeze

unibody madness · Post by **unibody madness** » August 28, 2011, 8:32 am

Have you had the distributor off?
IF you have is it possible you got it off a tooth?

Anthony's Son · Post by **Anthony's Son** » August 28, 2011, 8:41 am

yes I have had the distributor out of the motor when I switched motors. I have set it with the first plug being top dead center both ways. I have tried both 180, but i think i might go out and try that again.

R Pope · Post by **R Pope** » August 28, 2011, 9:27 am

If it runs at all, the timing is not 180 out.
My guess is, there's an exhaust pushrod out of place, or an intake valve being held open. With an exhaust valve not opening, there is still a chamber full of fire when the intake opens. At idle, there is not enough fuel in the cylinder to cause a problem, but crack the throttle and BANG!
Your two firing orders are the right ones depending on what cam you have. Check the order carefully, that is the simplest cause for your symptoms.

Anthony's Son · Post by **Anthony's Son** » August 28, 2011, 11:25 am

Well I just went out and played with it, and it idles great now, but still when you give it gas it wants to back fire and it sounds like it has a slight miss whenever I rev it up.. took it down the road and back and it seems to have nearly no power between the backfire and miss.. I really want to take it for a drive today... but its looking like that isn't going to happen

Anthony's Son · Post by **Anthony's Son** » August 28, 2011, 11:42 am

It is spitting the gas back out the little overflow needles on each side on the top... idk if the helps anyone or not.

Post by **Greg D** » August 28, 2011, 12:01 pm

You aren't running the stock EFI fuel pump with a carb are you?
EFI fuel pump is designed for 50 lbs or so of fuel pressure - carb likely can't handle more than about 6. It will push open the needle & seat and flood the carb - this could explain gas coming out of it.
You can run the stock fuel pump with a carb but you need a fuel pressure regulator that has a return line. There are ones out there for EFI to carb conversions.

Anthony's Son · Post by **Anthony's Son** » August 28, 2011, 12:08 pm

No, I am running a mr. gasket electric fuel pump. I think 4-10 lbs or something close to that.. it ran great on the other car

Post by **Greg D** » August 28, 2011, 1:26 pm

Just checking.
If I remember right this is a 90s Fox Chassis Mustang?
You install an earlier carbed fuel tank then? or swap out the in tank pump/sender assembly for a carbed setup?

banjopicker66 · Post by **banjopicker66** » August 28, 2011, 1:48 pm

Anthony's Son wrote:banjopicker66

4. What size and type of carb does it have?

4. Has an Edlebrock Performer intake and Carb, but not sure on the size, it was on another motor when I got it. The other motor ran great with it, until it spun a rod

Sounds like the carb is generally fine, except for the spitting - it depends on how long it sat dry since it last ran on the other engine.

Spitting gas causes
1. Pressure too high - Note that the in-tank EFI pump can force fuel at high pressure right though the other one - what is the actual pressure at the carb?
2. Floats no longer floating properly - how long since it ran on the other engine? The synthetic floats may have gone bad if left dry.
3. Dry/bad/dirty needles and seats - again, depends on how long the carb sat dry since it last ran on the other engine.
4. Floats adjusted incorrectly - probably not the case, since it worked OK on the other engine.

Anthony · Post by **Anthony** » August 28, 2011, 2:15 pm

It sat approximately a month and a half.. the pressure at the carb should be alright, it was on the other motor.. I'm trying to upload a video.. maybe it will help explain also..

Forgot I was on dads computer.. haha

62galxe · Post by **62galxe** » August 28, 2011, 2:46 pm

Check the accelorator pump on the carb. With the motor off activate the accelerator at the carb. you should see it squirt 2 small streams of gas into the carb. If the pump doesnt work you get a lean condition which can cause a backfire through the carb

Anthony's Son · Post by **Anthony's Son** » August 28, 2011, 5:54 pm

video of what it's doing guys... sorry its so long...

http://www.youtube.com/watch?v=rQpg9HHOqH8

<iframe width="420" height="345" src="http://www.youtube.com/embed/rQpg9HHOqH8" frameborder="0" allowfullscreen></iframe>

62galxe · Post by **62galxe** » August 28, 2011, 9:06 pm

Make sure the 2 wires from the MSD box to distributor are not backwards.

thcrays · Post by **thcrays** » August 28, 2011, 9:34 pm

I have a quick suggestion from your video that might help. I see that you have the vacuum advance from the distributor connected to the full manifold vacuum port on the drivers side of the carb. Which is going to give you full manifold vacuum at idle. Which would bring the advance in as soon as you start it up. I would suggest that you switch the vacuum line to the timed vacuum port on the passenger side front of the carb. That might help your conditions. Then recheck base timing etc...

I hope that helps.

TC

Anthony's Son · Post by **Anthony's Son** » August 28, 2011, 9:43 pm

thanks guys.. i will try that tomorrow