I cant figure it out! 2 carbs and still same carb backfire. I did my timming both ways. im at 15 adv and still pops. I can do high rpm and it will be fine but its from idle to gas it pops. Its a new crate engine so i would thing no valve is stuck and im not 180 off... I redid my manifold so redo the seal and nothing is working. SOMEONE HELP!!!

 

Have you sprayed carb cleaner around the intake to check for leaks? If you used silicone sealer around the ports you probably still have a leak. It could also be under the intake where its leaking. If it isnt a vac leak, then it is timing or a collapsed lifter/flat cam lobe. Also some engines pop when cold when no choke is applied, chryslers are notorious for cold backfires and blown power valves.

Are you sure you have the timing set right? Did you disconnect the vacum advance when you set it? What is the total timing you are getting and have you recurved the distributor yet? 15 btdc might not be enough for your combo, the 289 in my Cougar liked alot more than that for initial. Keep advancing it and see if the poping continues, if it goes away then it was probably a bit retarded.

Too bad you arent in northern michigan.. We could set it up for you.

 

Set your timing to 6 or 8 btdc and try again. It is either the firing order or the timing.

 

Is the vacuum advance hooked up?

 

Yeah, 15 is way too high for the timing. 6-8 is what they generally perform best at. Go back and double check your firing order one more time.

 

RPM will also matter when you're setting your timing due to the mechanical advance. I generally set mine at 1000 rpm to have a solid reference.

One other problem could be the damper itselft. I've seen dampers that have slipped, making the timing marks inaccurate. If you can, tune the timing by watching a vacuum gauge. Set the timing such that your engine produces the max vacuum at idle. Be sure to adjust your idle each time you change the timing to get accurate results. After you do this, check with a timing light to see where your damper reads. If it isn't in the 8-12 ballpark, you may need to replace the damper.

 

Hello,
I had the same problem. I did everything, including adjusting the vavles 3 times, swapping carbs, regapping the plugs, replacing the plugs. After working on it for about 2 weeks, i decided to make sure the firing order was right for the 10th time. I checked the book and it matched up, but i decided to check a different source. Sure enough the two sources had different firing orders for the same engine. I set it up like the 2nd source said and sure enough it ran like a charm.
Hope this helps!
Matt

 

hey guys, yeah i took off my vac advance and i went back to 6 btdc, still pops. I think it is the rpm manifold, i swapped it with my old 289 edelbrock performer because it has a lower idle. yeah michigan to cali is a little far man ha thanks guys and ill let you know how it goes. ohh yeah and i will check another source for firing order, i dont really trust the book i have.

 

Dont need a book, its in the faq...

Firing order.
289-302- 15426378
351 and 5.0 - 13726548

One or the other.. number one is passenger side front, number 5 is drivers side front.

front of car.
5 1
6 2
7 3
8 4

 

mine is a crate 302/5.0 from ford, i have it for 289/302 mabey ishould run the 5.0 order?