What Does a Dirty Air Filter Look Like?

[1966Step]

Embarrassed to show this so lay it on me, but I have a question. This is my new vs. old air filter.. Is it clogged? lol! My new local shop rebuilt the carb (on their recommendation) and didn’t change out the air filter. .I assumed this would be done (isn’t that normal if you are going through the trouble of rebuilding a carb?) When I got it back it Idled fine..but was backfiring some (finally blew out the muffler when trying to start it the other day) and bucking when laying off the gas (accelerates OK). So checked the air filter and this is what I had...probably causing a few problems.

Gonna learn how to use/test with vacuum gauge today if it warms up enough and I’m interested to compare readings for both filters out of curiosity now and then take her for a short drive (no muffler).

[cwcarpenter98]

Yeah, I'd say that was a bit clogged up

[kwmech]

Don't even know how they could have adjusted the carb properly with a filter that plugged up

[1966Step]

True! Just checked again just to see the effect and the vacuum gauge is wavering a bit, but 14 on old filter, 16 on new which is fairly significant, but still low. Just tried taking her for a drive and not happy occasionally backfiring and not very smooth only going 30. However, seems to idle fine. I’m wondering if my blown muffler is altering back pressure and causing some issues. Any ideas?

[AussieinNC]

The pic shows a poor quality repair by the shop....

Your backfiring and stumbling, plus the vac level of 16, tells me your ignition timing os a little retarded from optimum....

If you dont have a timing light, advance the timing a little at a time until the engine pings under acceleration then back it bak just a little until the linging stops....

Check all rubber hoses going to the carb and manifold for cracks...any present will bleed off vacuum....

Good luck

[1966Step]

Thanks so much for the suggestions Aussie. I will try tomorrow.

The other issue I am having is the engine hot light will now come on after a short drive and idling for 5 min. and not so when driving down the road. The shop also replaced radiator, water pump, & thermostat (again upon their recommendation).

I just wanted to get this truck right to trust it on a recent road trip so I went with their recommendations and now feeling totally ripped off. Plan on taking it back, but wondering if I can even make the 5 mile trip at this point and also trying to learn what is going on. Hopefully, adjusting the timing will get me there. Thanks again!

[AussieinNC]

Overheating is also another sign of retarded timing....

What temp thermostat did the shop install?

New radiator?....new water pump?

Did they do a compression test to see if a head gasket was leaking?

Did they run a chemical test on the water in the radiator to see if there is combustion gasses present?

Did they flush out the block of the engine to clean out the old rust before installing the new radiator?

If it was me, I would be looking at another shop...

[1966Step]

Thanks Aussie, That's good to know about overheating being another symptom of retarded timing.

I don't know if they did a compression test, chemical test on the water, or if they flushed the block. They did replace the valve cover gasket. The are all good questions for me to ask.

Also, regarding the thermostat, The cold light does stay on noticeably longer when warming up. I’ve since learned there were 160, 180, and 195 options and saw somewhere that 180 is what I need. Unfortunately, I don’t know what came off.

I started going to this shop when they replaced my 373 rear to 307 last year which my regular “shade tree” mechanic wouldn’t touch and they did a great job. Now, I’m having second thoughts about them but just want to get her right and try to learn along the way esp. before I sink more $$ into this.

The truck did make it on a 400+ mile road trip after the work was done and didn't start backfiring (7 times) until the ride back. However cruising speed was not super smooth unless the gas was on.

Thanks again!

[Dead Parrot]

It is getting hard to find a "does it all" shop. If this shop did a good job on your differential, then don't be afraid to have them do more rear end work.

By the same standard, they don't appear to have much of a clue on how to repair or tune the fuel system on a non-computer motor. At the very least, they should have called and suggested a new clean air filter.

I would check your PCV system. A bad valve or clogged filter can cause issues as the carb is normally setup for the extra air from the PCV system. If they missed that dirty air filter, good chance they missed a dirty PCV valve and filter.

Maybe I missed it but what motor/carb etc?

Normal t-stat on a mostly stock SBC is a 195.

Might make sure the cooling system was properly purged of air, otherwise some can be trapped and mess up the cooling.

[kaycee]

Like the guys said above alot of so called SHOPS can rebuild them but they don't rebuild the throttle shaft =bushings . I had a problem with mine doing the same thing backfire every once in awhile and come to find out the primary throttle shafts were worn out. I assume you are running a quadrajet

[1966Step]

Thanks KC, That's interesting to know. I am just running a single Rochester B. Just pulled plug 1 below and it is black and looks pretty bad (and so was 2) One cause among many others can be a dirty air filter which I was very guilty of. Gonna run and grab some new plugs and take that variable out of the equation for now. Thanks again!

[vince1]

I'd start with a compression check.

[geezer#99]

Are you sure it’s dirty or is it just one of these.

https://www.ebay.com/itm/BLACK-14-x-...75.c100623.m-1

[1966Step]

Well it probably started as one of those Couldn't barely see a light through it. .I'm taking Vince1's advice and ordering a compression tester and a thermometer to check the temp. Took her for a brief ride tonight (max 30 mph) and hot light is coming on after about 15 min after the cold start, warmup and short ride (only 1 backfire) and then sitting for 5 min.

Pretty soon, I'll have all the equipment to figure out what's going on. Just need more daylight, time, and warmer/dryer weather on my side..

All this engine diagnostics stuff is new learning for me (after 20+ years of mostly putting around the block with no problems. I appreciate everyone chiming in with helpful advice.

Thanks!

[kaycee]

I got one of those thermo guns from Harbor freight for like $15 on sale ,are you still running the stock gauge/light ? Did you change thermostat?

[1966Step]

Got a thermo temp gun coming tomorrow. Still have stock dummy light. Thermostat was changed as well as water pump and radiator at shop. Not sure what temp they installed and I’ve seen 3 listed for the 292 engine(160, 180, 195), but I noticed it is now taking longer for the cold light to go out but way faster to come on after stopping now (since “work” was done). However, I haven't been idling more than 5 minutes much in the past to test that theory.

Advanced the timing about ¼ inch outer rotation and fired her up and seemed much better. The vacuum went to 18-19 Took a brief ride w/no backfires and was better but hot light still came on after 5 min of idling after my short ride. Still need proper timing but felt like I got it at least a bit closer.

Weather here is not ideal for outside work but I will dial in the timing when I get a chance. There’s a lot to learn there for me. Trying to do baby steps to monitor performance and better understand the effects of each thing I do. At least today, I’m feeling like I made some progress! Thanks!