Back in the game! Backfiring.

renaissance man · #1 (**permalink**) 10-24-2022, 11:38 AM

Well, it's been 20 years! I have my original car back from the 1990's!
I am getting her back on the road but, she is backfiring under load. I am in need of some ideas to look at?

Engine: '65 289 HiPo. .10 over, ISKY Cam. Holley 650, MSD 6A ignition, mechanical fuel pump.

- replaced the plugs. They were .035 gap. New plugs; .044 gap. The .044 gap I understand, is better with a higher performance ignition.

- 3 issues: Car needs 4-5 turnovers to get her to fire unless I spray starter into the carb.
- under load, she backfires quite a bit with some hesitancy as well. You can hear it. It did this with the old gapping plugs as well.
-Lastly, when I turn off the ignition, she will "Run on" for about 3 seconds before shutting down.

I haven't yet checked the timing

Any thoughts are greatly appreciated!

Appreciate you guys! Can't wait to meet up again!

bobcowan · #2 (**permalink**) 10-24-2022, 12:25 PM

If it's been sitting a while, consider stuck floats in the carb. Also consider that the lifters are gummed up and stuck, holding a valve open.

sunman · #3 (**permalink**) 10-24-2022, 01:51 PM

After 15-20 years the bowl gasket accelerator pump holes on the bottom swell up and block off accel pump gas.
I buy a new DP Holley for every motor and this is the only problem I’ve had.
It’s something to check for sure.
Sounds like timing problem tho.

eschaider · #4 (**permalink**) 10-25-2022, 01:34 AM

When the engine is back firing under load and dieseling when you shut it down it is lean with possibly to much timing, but definitely lean.

LG57 · #5 (**permalink**) 10-25-2022, 06:02 AM

Also, check inside the distributor cap. Corrosion in there can cause backfiring and hard starting.

twobjshelbys · #6 (**permalink**) 10-25-2022, 08:59 AM

Backfiring for me was always rich...

renaissance man · #7 (**permalink**) 10-26-2022, 08:11 AM

On a side note, while I'm investigating the carb, I'm thinking of just going "All In" and investing in an Inglese Webber intake.

jhv48 · #8 (**permalink**) 10-26-2022, 09:20 AM

Your plugs will tell you whether you’re running rich or lean. If all 8 look normal,
the next bet is an ignition breakdown. Corrosion in the distributor cap is an excellent starting place.

renaissance man · #9 (**permalink**) 10-26-2022, 01:41 PM

Here are the old plugs that I removed.

twobjshelbys · #10 (**permalink**) 10-26-2022, 02:03 PM

Those plugs look awful. They're fowled pretty bad. I wouldn't declare rich or lean until I replaced them and started over. I can see why it might want some extra kick from starter fluid. Put in some new ones and see what happens.

Second, what is all the rust on the exposed part of the plugs? Was it stored in a very humid area?

eschaider · #11 (**permalink**) 10-26-2022, 06:32 PM

Something worth while keeping in the back of your head is that, if it ran well before you put it up and it does not now, then something broke, deteriorated or at least changed while the car was being stored. You should try to find that "something" before you begin changing out a lot of other potentially still good pieces. When you do and when you replace it the engine will behave like it did before you put the car away.

Chicagowil · #12 (**permalink**) 10-27-2022, 06:49 AM

I am having similar issues with my 67 Mustang. When I first went to get it running, it was discovered that age and E85 fuel had caused the rubber fuel line from the tank to the hard line had eroded and collapsed. It was replaced and suddenly, I had fuel flow. Now I wonder if some of that rubber had made its way into the carb. Also, the carb had set "used" on my shelf for some time.

After looking at several sites, I think my carb is both "dirty" in the bowls and suspect the power valve has failed. I hope to remove it and tear it open this weekend.

renaissance man · #13 (**permalink**) 10-27-2022, 08:16 AM

@Chicagowil

I found that "Speedy Stop" Gas stations have a 90 "No Ethenol" fuel. It has a Blue Handle. $3.99/gallon.

renaissance man · #14 (**permalink**) 10-27-2022, 08:23 AM

@twobjshelbys

Tony, When I sold the car, 20 years ago it was in Iola, TX. about 3.5 hours east of where I am. Definately more humid. All of the chrome has bubbled on the bumpers and mirrors, a rat was building a nest in the DS pipe. When I started it, nesting material and corn flew out. Only 333.3 miles were put on her in 20 years!

renaissance man · #15 (**permalink**) 10-27-2022, 08:27 AM

Quote:

Originally Posted by twobjshelbys

Those plugs look awful. They're fowled pretty bad. I wouldn't declare rich or lean until I replaced them and started over. I can see why it might want some extra kick from starter fluid. Put in some new ones and see what happens.

Second, what is all the rust on the exposed part of the plugs? Was it stored in a very humid area?

Stored in E. Texas. Def. a lot of humidity! Since getting it back to the Austin area, oil is changed, coolant changed. Plugs that came out were gapped at .035. New plugs gapped at .044.

She still hesitates at highway speeds. I'm thinking maybe the timing is off?

Tommy · #16 (**permalink**) 10-27-2022, 10:07 AM

Quote:

Originally Posted by renaissance man

I'm thinking maybe the timing is off?

Keep in mind that timing is more than just the distributor placement. Given the years of inactivity, you may want to check the centrifugal and vacuum advance mechanisms too.

twobjshelbys · #17 (**permalink**) 10-27-2022, 10:22 AM

I'm going to assert the gunk on those plugs took a long time to build up. It's not new since you took it out of storage. So I'm not surprised it still runs bad. Start the debug tree.

renaissance man · #18 (**permalink**) 10-27-2022, 12:03 PM

New plugs in at .044. going to check mechanical and centrifugal advance this weekend!

Gaz64 · #19 (**permalink**) 10-27-2022, 02:57 PM

Since it starts normally with starter fluid, you have proved engine mechanical and ignition system is fine.
Your carburetor or fuel quality is the cause.
What is the list number of your 650 Holley?
How long since the carb has had a rebuild?
How old is the fuel?
Gary

renaissance man · #20 (**permalink**) 10-27-2022, 06:57 PM

Quote:

Originally Posted by Gaz64

Since it starts normally with starter fluid, you have proved engine mechanical and ignition system is fine.
Your carburetor or fuel quality is the cause.
What is the list number of your 650 Holley?
How long since the carb has had a rebuild?
How old is the fuel?
Gary

I believe you are correct about the mechanical and ignition system being good. Still might need a tune, but you’re right it’s probably good. The carburetor has never been rebuilt so that could definitely be an issue. I’m literally thinking of not going through with it and just replacing it with a weber induction system. The fuel could also be a problem. It had some fuel in it but I do not seem to have a drain for the gas tank? The gas could be as much as two years old maybe three. So I put some fuel stabilizer into it. And then topped it off with fresh fuel hoping to dilute anything else in there. My concern though was if I did drain the tank, what do you do with 10 or 15 gallons of gasoline?