popping through carb
#1
04-10-2006, 02:25 PM
popping through carb
A little background. 83 F150 4wd 302 carb'd. Original motor threw a rod, but was running fine before. Found an 86 302 out of a Mustang. Swapped motors, used our intake and dizzy because it didn't have one.
Put #1 at TDC on Compression stroke (piston up, timing mark on 0) Correct? Started motor, found some minor vac leaks, and son broke ears off carb where you mount it, changed carb from my other truck that we just drove. Set timing at 9 degrees for now, idles like a new kitten. Firing order is 1-5-4-2-6-3-7-8 checked 3 times. Wires came off other engine and were good.
Now to the problem. Idles good, but when you give it a good kick of the throttle it pops through the carb, also when you let out the clutch and start to go it pops. Not a pop-pop-pop-pop, but a single pop everytime you give it gas. You can slowly give it gas by hand out of gear and it revs fine. Do I still have a vac leak or do you think the cap or wires messed up from the time it took to swap them between motors ( a week )or do I have the dizzy in wrong? I was assured the motor was good, they are reliable and I do believe them.
Sorry for the long post but I wanted to give all the info I could.
Put #1 at TDC on Compression stroke (piston up, timing mark on 0) Correct? Started motor, found some minor vac leaks, and son broke ears off carb where you mount it, changed carb from my other truck that we just drove. Set timing at 9 degrees for now, idles like a new kitten. Firing order is 1-5-4-2-6-3-7-8 checked 3 times. Wires came off other engine and were good.
Now to the problem. Idles good, but when you give it a good kick of the throttle it pops through the carb, also when you let out the clutch and start to go it pops. Not a pop-pop-pop-pop, but a single pop everytime you give it gas. You can slowly give it gas by hand out of gear and it revs fine. Do I still have a vac leak or do you think the cap or wires messed up from the time it took to swap them between motors ( a week )or do I have the dizzy in wrong? I was assured the motor was good, they are reliable and I do believe them.
Sorry for the long post but I wanted to give all the info I could.
#3
04-10-2006, 04:37 PM
Senior Member
you might post this in the pre-97 forum, you'll have a better chance of hitting someone witth carbeurator knowledge there
If it's only when accelerating it's not a wiring/firing order issue, else it would happen that way all the time...
Popping flames through the carb would be a timing issue I think. SO, here's a couple of suggestions:
1-- doublecheeck the connections. I forget if the distributor has a mechanical advance or electronic--- but if it has mechanical, make sure the vaccuum advance is hooked up properly. If it is electical, make sure the wires are in good shape.
2. Time it again. I know you say you timed it initially, but a lot of times I have knocked mine out of alignment as I am tightening that bolt. It's easy to do.
3. Doublecheck your timing in a different way. Sometimes the harmonic balancer spins a little bit so that the timing mark on the pulley is off. (I don't know if the 302 is prone to this problem but it happened on my 250 and my 300). When it happened to me, I timed it, it ran like crap. I doublechecked everything, it still ran like crap. It had me mystified until an 'oldtimer' suggested this method- get a vaaccuum gauge and hook that up, see what it reads. Adjust the timing till you get the highest possible vaccuum, then retard it 1 degree. This is correct timing-- and believe it or not, it is spot on every time and can be more reliable than using a light.
Once you do this, check the timing again with your light (or just take it for a test drive) and see what happens.
4. Wait for someone else to come along who knows more about carbs.
If it's only when accelerating it's not a wiring/firing order issue, else it would happen that way all the time...
Popping flames through the carb would be a timing issue I think. SO, here's a couple of suggestions:
1-- doublecheeck the connections. I forget if the distributor has a mechanical advance or electronic--- but if it has mechanical, make sure the vaccuum advance is hooked up properly. If it is electical, make sure the wires are in good shape.
2. Time it again. I know you say you timed it initially, but a lot of times I have knocked mine out of alignment as I am tightening that bolt. It's easy to do.
3. Doublecheck your timing in a different way. Sometimes the harmonic balancer spins a little bit so that the timing mark on the pulley is off. (I don't know if the 302 is prone to this problem but it happened on my 250 and my 300). When it happened to me, I timed it, it ran like crap. I doublechecked everything, it still ran like crap. It had me mystified until an 'oldtimer' suggested this method- get a vaaccuum gauge and hook that up, see what it reads. Adjust the timing till you get the highest possible vaccuum, then retard it 1 degree. This is correct timing-- and believe it or not, it is spot on every time and can be more reliable than using a light.
Once you do this, check the timing again with your light (or just take it for a test drive) and see what happens.
4. Wait for someone else to come along who knows more about carbs.