So I've got this 305, its a gm rebuilt engine with about 85,000 miles. The previous owner said it was completely stock and it was in a delivery van before powering my illustrious machine. Strangely it has a very lopey idle. Other than ripping the engine apart (which I can't do now), is there any way to tell if this thing has a bigger cam than it should? Also could the lopey idle be a symptom of some problem with the engine?

 

Did you check for vacuum leaks? That might be the source of the lumpy idle.

 

Most of us like a lopey cam sound

A choke not coming off as it should could make for poor idle too....

 

Yep, I'm digging the sound, but I just want to make sure this engine is 100%.

 

Could always measure the valve lift - wouldn't say much, but it might give an idea if its a stock cam or aftermarket.

 

If you are worried about the engine condition, check your sparkplugs. They are a good source of info about whats going on inside the engine.

Also if there is a sudden drop in fuel milege, sudden drop in engine power, it starts running hot, has low oil pressure, making new noises like clacking or clicking, or smoke is blowing out the tailpipe, THEN its time to worry.

A little lope at idle isn't anything to worry about. If it runs well with a little lumpy idle its just a bonus.

 

I'd guess a plug is arcing out.

 

If your timing is way off, it could give ya cam'd out idle. This condition could be compounded by other parts being worn as well. But chances are if your timing was off that much, you would notice a drop in performance.

Max

 

#1 cause is a vacuum leak/idle circuit too lean.
#2 cause is a stock cam mistimed one tooth advanced. I've run into this before with rebuilt engines that "didn't have a home".
It's easier to eliminate #2 and then troubleshoot #1.

 

If it was a stock rebuild for a early-mid 80s fullsize Van, the Cams are the same as the L69. The L69 has a bit more lump to it than the LG4 stick does.

 

Yes, but through a typical F-body single exhaust it still shouldn't sound very lumpy. My '97 LT1's cam it roughly the same size and has basically no lump (though to be fair, an LT1 is a much more refined running engine than a carb'd L69 - I used to have an L69 in my '83).

If it sounds cammy, then theres probably something wrong, unless it actually does have a bigger cam in it (why I suggested measureing lift - will not tell you the cam specs, but if it measured something like .500 lift, then you know something has changed over the years). Check the ignition system first, check for loose/worn/damaged plugs, check the plug wires, make sure they fit tight at both ends and are not broken or cracked. Take off the distributor cap and check inside for cracks or for moisture. Check the ignition timing with the ECM disconnected (if you have one). Should be between 6* and 10* usually. Does the choke work when the engine is cold (if you have a carb)? If it doesn't close enough, it can sound pretty rough untill it warms up if it runs at all. My first Holley had no functioning choke untill I got an electric choke kit for it - it sounded really rough and cammy when you started it cold like that.

 

I just changed the wires, plugs, cap and rotor this week...and it's about 30 degrees warmer than normal in January so the engine does sound a little smoother. Its not race car lopey, but I think I notice more because I'm used to a stock Lb9, which was very smooth. Either way I'm having a mechanic tune the q-jet this Monday because I've been a fuel injection guy until 2 weeks ago.

Thanks for your responses everyone.

 

my old lg4 had one hell of a "lopey/rough" idle, mainly due to a crapped out carb and fouling plugs