Hey guys,

Im the proud new owner of a 1971 olds cutlass. It has a very rough idle, like its missing on 1 or 2 cylinders. The car has a newer hei distributor that was recently installed by the PO, new wires, and new plugs. In adddition to the rough idle, the engine is REALLY down on power. It runs alright but doesnt really get out of its own way.

I believe the engine is all stock except the PO said its bored .040 over. I have not had the heads off to find out if that is true. The engine is topped with a Rochester Q jet 17057204 which I read is off of a 77 vette. Ok, so i swapped the Q jet off for a Holley 4779 750dp I had laying around just for fun. It ran even worse. (the holley has 73 jets up front and 80 in the rears) After adjusting the floats I started on the idle air adjustments. The engine idled like crap pulling 10-13in of vacuum if I richened the mix at all. The engine idled amazingly when I leaned the mix out but then I would get a backfire through th carb with any throttle and it would die. I know only what I have read online about tuning carbs but maybe some of you guys have an idea.

Now when the Q jet is on it drives alright and will hold idle, but not well. The timing is set pretty far advanced. I have the vacumm advanced hooked up to manifold vacuum. It will only run if I advance the crap out of the timing. So, what am I missing here guys? Also is q jet a crap carb for this? It is a 77 smog carb. I would like to get the holley going but as you have read, its not working out. Thanks for reading and sorry for being long winded

 

I am having trouble getting the cammed rebuilt 403 to idle down properly. Needs very advanced timing, retarded and the vacuum and power drop WAY off. What is your timing at? Maybe try w/o vacuum advance first.

Ck your plug wires' firing order carefully, sounds like 2 are swapped.

If not that easy, then do a full compression check to rule out serious issues.

I can get you a real 71 Olds carb if you like. Sometimes they show up for cheap on epay.

 

Like above I believe there are 2 wires swapped or a ginormous vacuum leak!

 

The firing order is correct as long as its 1-8-4-3-6-5-7-2. I have looked for vacuum leaks. I found 2 but wouldnt be surprised if there were more. Why would it Idle perfectly when I leaned out the carb? The timing is way advanced. Too advanced for my timing tab. It has to be 1in advanced of the tab itself

 

You might check to see if your distributor is a tooth off.

 

I agree. Also IF there is an aftermarket cam in there, that changes everything. Use a dial back timing light. You can dial it back to "0" and it will tell you where your at with your advance.

 

That doesn't matter, you'll just have to spin the distributor around more. Timing is timing.

Do like Octania said, check everything else first. Then rebuild the Holley. Those jet sizes are a pretty good start for a 455. Then make sure you don't have any other vacuum leaks.

Keep us posted.

 

Have a different person ck the firing order... For confirmation.
beware of wires that run out of sight.

Still missing? Pull wires 1 at a time. Any 1 that makes no difference is a source of your trouble. Found 2 [and only 2]? swap those wires, see if it gets better.

Any cylinders that make no difference is where to start looking for incorrect plug gap, bad plugs, bad wires, corroded dist'r cap, intake leak, poor valve action due to excess slack in the valvetain, etc.

 

OK a lil update. I have checked my firing order mutiple time. I am 100% certain it is correct. I set the timing to 12 degrees with the vacuum advance disconnected and blocked off. It barely ran. I hooked up the vacuum advance and it ran better but still poorly. I pulled every plug as mentioned above but no one cylinder felt different than the rest. Here is where Im really baffled. I swapped 4&7 on the off chance that a 4/7 swap cam had made its way in there. It started up and is running exactly the same. How is this possible? I have not been able to check compression. My gauge is old and I found a crack in the hose.

 

What effect does partially closing the choke or partially covering the the primary side of the carb with your hand have on idle quality when the engine is idling? Does it cause the vacuum readings to increase and the engine to smooth out?

 

What about a cylinder balance test? I.E. pull one spark plug wire at a time while it's running. Connect a tachometer. If you disconnect a wire on a good cylinder, you will see a slight drop in idle speed. Even if the plugs are new, it doesn't mean they are all good. Also, check your cap and rotor to make sure nothing is arcing.

I would check youtube for a demonstration on how to do the balance test. There is a way to do it from the distributor cap using little pieces of vacuum line and a test light.
The test will tell you a lot about what's going on.

Definitely do a compression check like Octania suggests, too.

 

OK Guys, I did a compression test this morning. Now I did the test with the engine cold so these readings are not as good as they could be.
Cylinder:
1-118
2-115
3-130
4-125
5-115
6-125
7-125
8-125

Im not terribly happy this the 15+/- difference but at least I have compression in all cylinders. So looking at this, I would assume that my running issue is either a timing (or distributor), fuel or vacuum issue. Hope this helps

Thanks Fred

 

Those compression numbers are pretty low. Put a couple squirts of oil in each cylinder, see if there is a big improvement in compression. Does the engine have a aftermarket camshaft? If it has a lot of overlap that could account for the lousy compression. You might also check the timing chain, if it has excessive slop or is assembled one tooth off that could cause your issues.

 

X2 on the chain - was my first thought.
If it had adjustable lifters, I'd also be looking for a couple too tight!

 

Well the cam timing will have to wait to winter. Im pulling the engine and resealing it. Also installing a new higher performance cam. While Im here, how can I tell what compression pistons I have when I have it apart? The PO stated that he got a shortblock .040 over. Im going to go through the engine but Im not too familiar with oldsmobiles. I will probably throw a cloyes timing chain kit on as well. Any suggestions while I have it apart?