Engine not running good

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toolmanmike

toolmanmike

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My 273 just isn't running right. I need to check it all out and find out why. It idles rough (sounds like it has a pretty big cam in it) and smells rich at the tail pipe. It accelerates good but runs out of poop at 4000 rpm. I romped on it hard
a while back and hit some rough areas on the street. The engine stalled and gas was running out of the carb. I tapped the carb with a screwdriver and got it started but it has been idling rough since. I took the carb apart yesterday for cleaning and inspection and everything looked good. It's not running lean. I did the ''old hand over the carb and watch for increased rpm trick" and killed the motor so it's not a vacuum leak although it sounds like it. The initial timing is set at 15. I think I'll pull the plugs for a look and pull the valve covers for a valve adjustment and look for a bent pushrod or something. I should pull the distributor and double check the gear position too. It may be a tooth off. In the past few weeks of occasional driving it seems to be getting worse. It doesn't sound or feel like a dead miss but more like a carb bleeding over and dribbling fuel out the boosters. (I checked that too, doesn't seem to be doing that either). I'm stumped. Any suggestions? I know, these things are hard to diagnose over the internet. toolmanmike
 
Hey Mike,sorry to hear your still having issues.It sounds like a day of diagnosing is in order.What carb are you running?plugs/wires/cap?With this being a new engine,you might have a defaulty part.It,s happened to me before.Good luck.
 
Mike, don't pull the dist. Check your timing against what you "know" you had set last. A big change in timing would tell you if the cam drive slipped a tooth. the dist. itself CAN NOT get "a tooth off."

Do both idle screws have an affect? Did you blow out the passages in the carb with some pressurized carb cleaner?

Take your dist. cap off, and wrench the engine ccw/ cw until the rotor just moves. This will give you an idea of the slack in the chain. Anything more than 10* movement of the timing mark is too much.
 
The timing hasn't moved since I set it last. I wondered if I set the gear in wrong from the start. (when I rebuilt the engine last year)
I cleaned and blew out all the passages in the carb and the mixture screw adjustments do effect idle quality. I can darn near kill the motor by turning either screw in to it's seat and it will run rough when I back it out to the rich side.
I haven't checked for timing chain slop but I installed a new Cloyes double roller when I rebuilt it a year and 2000 miles ago.

Mike
 
The gear position does not matter. If you can get the timing set, that's all you need.

The only reason (on most engines) that a specific distributor/ gear position is specified is so:


the assembly line folks can "wrench, repeat."

the wires "lay" nice"

the tuneup guys "see" what they expect.

You can actually just shove the gear in any -old- way

drop the distributor in any old way.

Bring up no1 ready to fire, and.....wherever the rotor is pointing, plug the no1 wire into that hole, and it will run JUST fine.

As I said only thing that "can" be wrong is the cam drive, or maybe balancer outer rim slipped an timing marks are wrong, but of course if it slipped IN YOUR CASE this would not have changed the timing.
 
Mike,
Start off with the basic diagnosing.
Pull the spark plugs and read them...While out you could do a compression test.
Check your timing and if it good you could leave that timing light hook up and everything routed out of way fan,header etc...
See if you can position your timing light so it is under your wiper blade so it is point at you and a zip tie holding the trigger on....Test drive it up to your 4000 rpm point and when the problem occurs does the spark become erratic....
Put a vacuum gauge on it,how much does it pull at idle ,does the needle fluctuate...
What kind of carb are you running?

You could balance test the motor by pulling plug wires one at a time while running to see how much rpm drop each cylinder does when you pull spark from it.

If one or more cylinder have little to no drop in rpms,that is where you will go to further diagnose.
For example,your primaries are feeding different cylinders,if one side of the primaries is not operating properly certain cylinders would be affected.
A vacuum leak at a particular port in the intake would affect that cylinder.
If it is running rich,I do not suspect it to be a vacuum leak...
I suspect a carb issue unless you are not getting a strong spark...
What ignition system you running?

If you bent a pushrod,I feel that you would notice that dead miss...
Valve adjustment would not hurt though...
Hope some of this helps,
TXDart
 
Oh if it is a older Holley you are running,I would suspect a blown power valve...
But they usually will blow black smoke out the exhaust....
TXDart
 
67Dart273 said:
The gear position does not matter. If you can get the timing set, that's all you need.

The only reason (on most engines) that a specific distributor/ gear position is specified is so:


the assembly line folks can "wrench, repeat."

the wires "lay" nice"

the tuneup guys "see" what they expect.

You can actually just shove the gear in any -old- way

drop the distributor in any old way.

Bring up no1 ready to fire, and.....wherever the rotor is pointing, plug the no1 wire into that hole, and it will run JUST fine.



As I said only thing that "can" be wrong is the cam drive, or maybe balancer outer rim slipped an timing marks are wrong, but of course if it slipped IN YOUR CASE this would not have changed the timing.
Click to expand...
I always was able to static time any engine regardless of where the distributor was installed. I agree with you there.


I timed it by ear and it still didn't improve. I am running the original balancer and the mark does jump around a bit. Something it did before I rebuilt it.
 
TXDart said:
Oh if it is a older Holley you are running,I would suspect a blown power valve...
But they usually will blow black smoke out the exhaust....
TXDart
Click to expand...

I am running the original AFB. I have been through the cleaning and adjustments twice. The throttle shafts are tight and it responds to adjustments. I have a Edelbrock AFB I can try to see if anything changes.
 
TXDart said:
Mike,
Start off with the basic diagnosing.
Pull the spark plugs and read them...While out you could do a compression test.
Check your timing and if it good you could leave that timing light hook up and everything routed out of way fan,header etc...
See if you can position your timing light so it is under your wiper blade so it is point at you and a zip tie holding the trigger on....Test drive it up to your 4000 rpm point and when the problem occurs does the spark become erratic....
Put a vacuum gauge on it,how much does it pull at idle ,does the needle fluctuate...
What kind of carb are you running?

You could balance test the motor by pulling plug wires one at a time while running to see how much rpm drop each cylinder does when you pull spark from it.
If one or more cylinder have little to no drop in rpms,that is where you will go to further diagnose.
For example,your primaries are feeding different cylinders,if one side of the primaries is not operating properly certain cylinders would be affected.
A vacuum leak at a particular port in the intake would affect that cylinder.
If it is running rich,I do not suspect it to be a vacuum leak...
I suspect a carb issue unless you are not getting a strong spark...
What ignition system you running?

If you bent a pushrod,I feel that you would notice that dead miss...
Valve adjustment would not hurt though...
Hope some of this helps,
TXDart
Click to expand...
I have a small tune up machine that cancels cylinders. I will do a cylinder balance test and also a vacuum test. I had the same problem with the original dual point and installed a Pertronix kit in a different dist. with no change. I also installed a new coil along with the kit. I am using the original AFB and have been through it twice to double check passages and adjustments. I have a Edelbrock I can try if needed. I changed valve lash specs from stock (.013/.021 )to what Isky reccomends (.015 intake and exhaust.) I wonder if a valve or two is too tight.

I'm going to the Nationals next week. After I get home I hope to have some time to check it out.
 
Thanks for the help and suggestions guys. I will check it out when I get back from the Nats. in a week or so. I hope it's something stupid I overlooked.
 
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