Seeking some guidance here...

[FGMonteLuvr]

I am still having issues with 'popping' noises from under the hood in the area of my carb (which I replaced with a professionally rebuilt unit) and trying to figure out a possible cause and fix. Car idles fine, but push the gas pedal and it starts acting up. When I really get on it, say revving it to about 3,000 RPMs and up, it sounds like that California firework show mishap last year. I know that the carb is pushing too much fuel thru too quickly for some reason and my timing is in need adjusting as this has yet to be done since I got her running. Keep in mind that she sat in a yard for nearly 2 decades. I've replaced all plugs, wires, starter, points, cap and rotary button in addition to the carb just to get her running. Haven't gone any further than that yet just to a lack of time and funds, and admittingly, know how. Guess that is going to be the next on my list. In the two years that I've had her, only 2-3 gallons of fuel ran thru, but has been the regular unleaded low octane instead of the 91 or higher that is stated in the owners manual. Does anyone else do this or am I the actual culprit of my baby sounding like she could explode at any given moment? My first '72 Monte I had when I was a teenager, I used the regular unleaded all the time and never had a problem. Guys (and Gals), I appreciate any and all advice I can get here as I really want to be able to enjoy my 'Mistress' this year!

[cny first gen 71]

Popping back up through carb under load may be something in valve train, rocker arm, push rod or possable lobe on cam bad. Something to look at. Pull the valve covers off and take a peek.

[footballubet]

After sitting that long you may have a stuck lifter. Pull the valve covers and check for a loose rocker arm. You may need to rotate the engine by hand and keep checking until that lifter is at it's low point to find it.

 

Good luck and keep us posted.

[overdrive]

I doubt it would idle fine if it has this problem, but I'll toss this out there anyway:

 

If your timing chain and gear set are originals, another possibility is that the timing chain and the cam gear are worn to the point the chain has jumped a tooth or more on the gear. The original cam gear teeth were made of some type of plastic and the teeth eventually start falling into the oil pan. I've changed several that did this. Don't replace with the same type of gear. You can check for this timing problem without removing anything but the distributor cap.

 

We can give details if needed.

 

Dan

[bigtankjones]

Popping through the carb my guess would be valve train. Bad Cam lobe or lobes. Like Steve said.

[Mo's70MCs]

You say it idles fine, but push the gas pedal and it starts acting up? I'd say you need to narrow down the problem, you say you replaced the carb, did it have the same problem prior to the carb change? If so, first you don't mention if you replaced the points "condenser" one that would give you some awful running if it were faulty, much like what you describe. A carbon tracked & cracked cap, would also make it run like crap, and at times intermittently. Though you say you've changed that.

 

All the info given above is very valid, specially if it has sat for a long period of time. The octane value of fuel would not have the adverse running conditions you're are experiencing. You have, I believe with the vague info you describe, something related to ignition timing, a firing order issue (crossed ignition wiring) or a valve train issue. I would do a compression test on it & set the timing statically, to see if it has a timing chain issue. Have you done anything in the way of a valve lash adjustment? That done wrong, would have you pulling your hair. Don't overlook the points condenser. Narrow your problem down, by doing a double check on every component, and make sure you adjust and understand one before checking the next. Is it popping and coughing out of the carb, and does it do it out the tailpipe?

[FGMonteLuvr]

Thanks Everybody! Looks like I'll be pretty busy next weekend looking into all sorts of different possibilities. Hopefully, it'll be just as nice of a weekend weather-wise as this one was.

[Grease]

With the engine ,running have someone acclerate while you feel the exhuast gas out the tail pipe. Does the flow increase greatly ? If this car has been sitting 20 years the exhuast could be plugged /rusted severly and not flowing exhaust out . I have seen exhuast pipes which were double walled pipe and the inner pipe can rust thru and collapse internally . This was on other GM products of late 60s early 70s vintage . I dont know if you have a stock (original )system in place or if the Monte even had this double wall pipe back in the day . Like I said I have seen it in other GM lines in that era.Just something else to consider .

[wallaby]

Does the car have fresh gas in it? My motorcycles run like crap after sitting thru the winter, fresh gas fixes that.

 

To be honest, when I read your symptoms I thought valve spring. A broken spring can have enough strength to run at low speed, but be way too weak to run at faster speeds. I had one break and it gave me fits trying to figure out what happened...the break was hard to see. Anyway, it's something else to look for.