Fuel problem... exhaust gets LOUD

[Parkinglotslider521]

ok so here lately I have noticed something weird. its kind of a day to day change. one day it goes like hell, but its quiet enough to talk while accelerating.. The next day it is loud as hell but has no power. It happens in any weather, hot or cold, humid or dry. 

 

My setup is as follows: 

Weber 32/36

Unconfirmed aftermarket cam

tube header

210 head

base timing set at 15* advanced on a new dist. with new points.

 

Last time i pulled a compression check it was around 160 each cylinder.

 

[TENDRIL]

do these changes happen after driving a while ?

 

short trips?

 

and your certain that its loud out of the tip of the exhaust ?

 

on a different motor (mazda) , i had something similar but was predictable and it was a crack in the exhaust  mani.  wouls swell and shrink with driving long ways or short trips 

[datzenmike]

L16 is 12 degrees BTDC. Try that first.

 

Not much to go on, I would check valve lash and inspect the plugs and wires.

 

Check that the header is tight because the intake and the header flanges are usually different thicknesses. Nissan used single studs across the bottom with a cone washer and nut to bridge across them. The header flange is likely thinner and not clamping it, or maybe the intake is loose.

[Parkinglotslider521]

It literally changes when it wants to. If it's an exhaust crack, I would think it would be huge to change the power and exhaust note that much. It does have a small exhaust leak at the header flange. One drive, it's quiet, and chirps second no problem. Next drive, it's loud as hell, and it feels like i have 1000 lbs of shit in the back. I only run 93 octane, Plugs are 2 months old.

[ggzilla]

Try new plugs

[ggzilla]

On second thought ... I'd inspect the muffler first. Maybe is separated?

[Parkinglotslider521]

thrush welded muffler on 2 1/4 exhaust. fucktards at the exhaust shop welded the exhaust straight to the header, so no leaks there lol. i was just under her (giggidy) last night and didnt see any exhaust leaks at all. just checked my timing and its at about 13-14 degrees @ 700rpm. its not detonating. but i can back it off that extra 2* if really necessary

[smoke]

Hit the muffler a few times with your hand, see if you hear anything rattling around in there. Could be a baffle coming loose and blocking exhaust kinda.

[Parkinglotslider521]

Good idea smoke. I'll try that later. I did check timing when I got to work. Seemed to run goodthe whole way there, but it was about 18* advanced. When I checked it last night it was at operating temp, and its idling at 750rpm. So what could make my timing move.

[smoke]

Sticking weights, which could in a way describe your symptoms. Really retarded timing is going to change your exhaust note and give you no power. In other words, not advancing when it should.

[Parkinglotslider521]

I was just thinking the same thing. Any way to check for sure? Vac. Advance is operating normally.

[smoke]

Yeah, unhook the vac advance,put a timing light on it and rev it up a little. You should see the mark advance.

[Parkinglotslider521]

I should have worded my question better. If I disassembled the distributor what would I look for? I'll check running operation, but I would like a visual test on the guts to find out what's up.

[smoke]

Oh, rust many times, but it could just be a slight hang up on something, you will feel it when you move it with your hand if it's there.

[Parkinglotslider521]

Thanks smoke, I'll pull it apart when I get off work. I'll update soon

[Parkinglotslider521]

OK. Soon was longer than I thought. But I have confirmed that the advance plate is not sticking. Must be an exhaust issue, unless the carb is playing games. I will say that it has been running very well the pats few days. If and when I find an answer I will post it up.