USA1LT1

Hi all,

My '67 327/300 engine starts hard, idles rough and smokes quite a bit. This afternoon, I replaced the fuel filter and took the float bowls off to see if there was any obvious dirt in the carb. I also set the idle mixture screws 1 1/2 turns out.

The car still runs rough and smokes and smells like unburned fuel. I also see exhaust smoke coming up from under the passenger side exhaust manifold. Could this be something like a stuck heat riser valve?

I still have yet to pull the plugs, check the timing or replace any distributor parts but thought I'd see if anyone has any suggestions for what to check next.

I appreciate your help!

:chevy

Plasticman

First all, before changing anything else, look at the plugs! And keep track of which cylinders the plugs came out of. The plugs will tell you an awful lot about how the engine is running and where some of the possible problems can be.

Is the smoke black from too rich a mixture? Or white/blue due to oil burning? Or white (no blue tint) due to too lean, or possible water entering into the cylinder(s) from a bad gasket/crack in block or head.

Examples of plug readings: A single plug looking a sooty dry black (center insulator color), isolates the problem to just the items associated with that cylinder (plug, wire, possibly the dist. cap., combustion seal for that cylinder). 2 or more plugs black, can mean ignition system problems (again wires, cap, points or condenser, rotor, dist. itself - bushing wear, advance circuits not working, etc.) but could also be a carb. problem. 4 plugs (2 on one side, and 2 on the other) can mean a problem with one side of the carb. (assuming you have a dual plane manifold - all stock C1 and up manifolds are of this type) If the plug is actually wet with fuel (smell it to check for gas smell), that cylinder is not firing (ignition or carb. related, but would bet on spark plug or wire). Oil fouling is black greasy wet, and is indicative of bad rings or a cracked piston, or very bad valve guides. Water entering into combustion chamber is normally seen as little white specks on the insulator (not a good sign).

A leakdown test would also be handy in telling you the condition of each cylinder's combustion seal. These testers are available from Summit or Jeg's, but you also must have an Air Compressor capable of supplying 100 PSI with enough flow for the tester to function properly (a min. of a 1 HP probably).

Other items, check the choke to see that it is opening. And look down the throat of the primaries while idling, and see if any raw fuel is "pouring" into the engine (at idle, the fuel should only be supplied via the idle passages under the throttle plates).

Also, setting the idle screws 1 and half turns out is just an initial setting. Best method I use is with a vacuum gauge connected to set the screws for maximum steady vacuum at specified (or desired) idle RPM, and then turn each in approx. 1/4 turn to lean the mix slightly. If 1/4 turn in makes the engine run rough, then go back to original max. steady vacuum reading, and leave them there.

The smoke you are seeing at the pass. side exhaust manifold probably indicates a bad "doughnut". This is a type of circular gasket that is used to seal the exhaust pipe to the heat riser housing. Some "bubba's" forget to reinstall the steel support ring back into the center of these gaskets, and that causes them to fail real quick. Could also be the flat gasket is defective that seals the heat riser to the bottom of the exhaust manifold. Check to see that the heat riser is "free" when the engine is cold by moving the exterior counter wgt. (should be spring loaded in the up position when cold, and you should be able to freely move it downward 90 degrees, and then when released, it should pop back up). Your running rough problem "could" be caused by a stuck riser in the up position (the bypassing exhaust flow back through the intake would overheat the intake manifold and carb., causing the fuel to boil and flow into the engine). Does the problem occur right away, or only when the engine has been running for a while (to reach normal temp)?

Good luck,


[Modified by Plasticman, 1:17 AM 2/9/2003]

Vetterodder

It could be as simple as a bad plug but until you look there is no way to know and there is certainly no way for anyone to diagnose your problem until you do. Something as simple as a dwell adjustment could be the cause of your problem. Unless you know that it's already been done recently, replace the points, cap, rotor, plugs, and wires. Your problem may still be elsewhere (carb?, valves? timing chain? cam? distributor? etc.) but you will have eliminated the cheap stuff. The smoke from the exhaust manifold is most likely oil leaking from a valve cover.

DansYellow66

I don't know if this is an original 67 engine or not, but if it has a PVC valve, make sure it's clean and not gummed up. Also check plug wires by setting the idle up a little and pulling and grounding each wire at a time while watching the tach. If you find one where the engine speed stays the same after the wire is grounded, you either have a bad wire or fouled plug. Best bet, if there is any doubt as to their condition, is to replace the wires, plugs, distributor cap and rotor. Same with points and condensor. Even if you have a weak engine, this may get it back to running in acceptable shape for a while longer. If none of this helps, a compression test and leak down test, as discussed above, need to be done. :confused:

SWCDuke

The heat riser valve is easy to check. It should be closed and move when cold and open when hot.

Your problem could be something as simple as a bad plug wire. Measure the resistance of all and look for a consistent ohms per foot reading. If any are out of bed, replace the whole set.

You should also do a compression and/or leak down check to get a baseline on the engine's internal condition.

All the other suggestions are good. Do a THOROUGH tuneup by checking the fuel system, ignition system, and PCV system for proper function against spec.

Duke

USA1LT1

Thanks everyone for the advice. I won't have a chance to mess around with the car until next weekend, but I'll check back in and let you know if I'm able to isolate the problem. :seeya

USA1LT1

Hi All,

Here is an update on my problem. I checked the heat riser counterweight and it is stuck solid. I can't tell if it is in the up or down position but the flat part of the counterweight is at a 45 degree angle to the ground so I think that may be the closed position. Also I'm getting gas leaking out onto the intake manifold near the throttle shafts.

Is it difficult to change the heat riser? I suppose it would be an easy fix at a muffler shop..

Thanks for all your advice - you guys are the best :seeya

Plasticman

USA,

Sounds like it is partially open (normally the counterweight is horizontal when closed, and rotates downward 90 degrees for full open).

As for changing it, sometimes easy, but most of the time hard. Problem is trying to remove the nuts on the 3 verticle exhaust manifold bolts that hold the heat riser on. If you feel lucky, you could try to undo these 3 nuts (but don't twist them so hard that you break the studs off!). For most people, better off taking it to a shop where they have the experience to deal with it.
A little "hot wrench" application does wonders to remove these nuts (heating the nuts up with an Ox-Acy torch). If one of the previous owners was an enlighten type, perhaps he installed brass nuts instead (much easier to remove). Some use Anti-Seize on the stud threads, but I find that over time, it washes away (or just plain disappears), and then the nuts still rust on solid.

You will need the doughnut gasket, the flat gasket, and a new riser. Also might need the steel insert tube that goes inside the doughnut gasket (depends upon what you find).

The gas dripping from the throttle shafts is not good. Can certainly be due to overheating caused by the stuck riser, or it may something else like a bad needle & seat in the carb. At any rate, get it fixed and change your oil (it will have gotten a lot of that raw fuel into it).

Good luck, and keep us informed about how the fix goes,
Plasticman