Dang, I picked up a engine miss :(

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toolmanmike

toolmanmike

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Just before I left for a car show in Dubuque, I picked up a miss at idle. The car ran good over and back but had a shake at idle. When I got home I messed with the carb but no change. I hooked up my cylinder balance analyzer to cancel cylinders and #4 is weak. I switched plugs and wires but no change. Tomorrow I hope I have time to pull the valve cover and see if there's a broken spring or a adjuster that backed off. A bent pushrod would be nice although I haven't pushed it past 4,000 rpm. I hope it's something simple. Wish me luck.
Toolmanmike
 
Is this motor new?
 
Push rods just don't bend for no reason, I would hope that isn't it.

There is too much it could be. If the motor smooths out with more throttle opening I would look more at the carb idle circuits getting plugged. Is it a Holley/Demon carb, those metering block gaskets can be a pain in the butt to seal right.

Any chance you have a known good carb you could swap on?
 
dodge freak said:
Push rods just don't bend for no reason, I would hope that isn't it.

There is too much it could be. If the motor smooths out with more throttle opening I would look more at the carb idle circuits getting plugged. Is it a Holley/Demon carb, those metering block gaskets can be a pain in the butt to seal right.

Any chance you have a known good carb you could swap on?
Click to expand...
We think along the same lines. I'm thinking about all possibilities and hoping for simple causes. My original carb is too worn so I replaced it with a Edelbrock I had. If it a carb problem, it worked good until this morning. I hope to check it out tomorrow.
 
I think I'll start by pulling the valve cover for a look. Then a compression test.
There's a strange noise too that seems to be related to the miss. Not very loud like a rod knock but kind of muffled. Strange.
 
wow, on the freshly built 273? I do hope it's simple, you've gotta lotta love in that engine, Hope ya get it straightened out in due time, buddy...

-James
 
toolmanmike said:
I think I'll start by pulling the valve cover for a look. Then a compression test.
There's a strange noise too that seems to be related to the miss. Not very loud like a rod knock but kind of muffled. Strange.
Click to expand...

Edelbrock carb should be ok, those are good carbs, a bit off on hp but smooth running, hassle free.

The noise issue reminds me of the time one of my rocker shaft bolts snap off. It was an end bolt and the rocker shaft bend up and the last valve would not open much at all. Funny thing is it ran ok at high rpm's. At idle it was bad, really bad but smooth out at higher rpm's.

Yep pull the valve cover. I missed it at first and a compression check pin pointed the cylinder and I shined the light and there it was. I got the broken bolt out with an easy out but wasn't easy, lol. Was just about given up and I said screw it, if the head is coming off so a machine shop can get it out, they might as well get the broken easy out with it and I heated it up and crank the easy out hard, and then harder-I was going to break it but then the bolt turned!

Good luck again, 8)
 
I pulled the valve cover off and everything looked good. I did a compression test and the readings were all over the place. #4 cylinder was the weak one and it had 135# and 150# with a few squirts of oil. #6 was a low too but all the rest were in the 140#-155# range. The engine only has a few hundred miles on it and I would guess that the rings aren't seated yet which could make for uneven compression. I wouldn't think the 130# compression would be low enough to cause a complete dead cylinder. I think I need to put it back together, adjust the valves and take the carb top off for a look inside and may-be blow out the idle screw passages and make sure the acc. pump squirters are even.
 
betcha its the edelbrock carb i had the same problem stumble at idle and a knock i looked everywhere for the knock almost sounds like the flex bolts have come loose on a torque convertor or a broken valve spring same weird knock took the carb off cleaned it shoved it back on and wa laaaaaaaaaa what the knock sound was still baffles me. Check your oil for gas in it and make sure yer running a fuel pressure regulator with that edelbrock.thats the first time ive ever had that weird problem but then again first time i ever had a edelbrock instead of a holley
 
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