Popping/Backfiring

Just the other day the truck started popping/backfiring. It does it occasionally at idle and constantly above 2000 rpm. it used to only do this when i was going down a hill in gear, like keeping it in 3rd to stay at a good speed and not need to use the brakes. I thought for sure it was a vac leak and found that the larger vac line from the intake to the brake booster was dry rotted in a few spots so I cleaned it and wrapped in electrical tape to seal. Inside the hose smelt like gas. The air filter also smells like gas. Ive re tuned the carb because i thought it was dumping too much fuel but it still pops/backfires. Any idea on what it is? All advice is always appreciated.

How's the ignition timing?

No clue. How do I check it? With a timing light?

Yes, time it with timing light. On my '88 B2200, I time to 6 BTDC with the vacuum advance to the distributor plugged, at about 900 rpm idle. Then connect the vacuum line, rev up the engine, and make sure that the timing mark advances when you rev up the engine.

A vacuum leak will wreak havoc on your timing, can make the advance kick in and out when you don't want it to.

Because I have AC, I loosen the AC belt, take it off the AC pulley and let it hang free, so I can see the timing marks on the lower timing cover.

There is no way I would tape a vac line and think that would work. I solve underground wire probs for a living, every time I see e-tape I just laugh. It isn't waterproof and it isn't air tight.

And vac hose is the cheapest material on your truck. Replace vac lines first, then start looking around. I'm speaking from recent experience on my sons truck. Hope that helps.

I will replace any vac lines that are dry rotted and try to check the ignition timing this week if i can borrow someones timing light. I appreciate the advice. I noticed today while looking around that the timing belt is loose(i think). Should it be able to touch the lower timing cover if i stretch it? Or should i see it stretch while it runs?

Wow, I wish I knew, I'd let you know for sure. I have only had my b2000 for a couple of weeks. Just noticed you have an '86 like me.

I'm going to grab a flashlight, run outside and see what I see, stand by.

Ooops, you said timing belt. I can't see that at all, lol.

Hopefully, a real motor head will advise you.

Timing belt shouldn't be too loose, it has a manual adjuster that is semi auto (on a 2200 at least), the tension pulley has a slotted hole and a spring, set the engine at TDC on cylinder 1, loosen the adjuster bolt, and the spring pulls the pulley over and gives the belt the right amount of tension, then you tighten the bolt again. The adjuster is acessable with only the upper timing cover off. I think the 2000 motor is the same.

If that belt is loose or has jumped a tooth it will run and drive (if it does) pretty poorly. If your exhaust doesnt have enough back pressure it could pop/ backfire (afterfire). But it should never do it at idle. If the ignition timing is off it could back fire wherever that distributor tells it to fire. Check the Top dead center and timing belt and borrow a timing light and set it like Cusser recommended.

I ordered a timing belt. Will be here tomorrow. I am going to check ignition timing later this week. I have noticed the air filter is extremely dirty ans smells like gas. There is a little bit of gas on plates for filter. I also noticed the vac line for the pcv valve smells like gas. Would this also be a cause of the belt jumping a tooth or ignition timing off? I am leaning towards timing belt slipped because I heard squeal from a belt and thought it was the alt belt but the timing belt looks like it rubbed something and seems a bit loose. Thoughts? Should I be looking at anything else while I'm doing timing?