70chev Posted March 28, 2011 Share Posted March 28, 2011 All right so my Monte has developed a horrible miss, rough idle, and the gas mileage has dropped to about 7 miles to a gallon and it smokes like crazy , (stock 350). it has a quadrajet on it. I did a compression test there as follows: #1 cylinder 160 PSI #2 170 PSI #3 160 PSI #4 175 PSI #5 160 PSI #6 150 PSI #7 160 PSI #8 160 PSI So, is it my engine or carb? If it is my carb, should I go with a Holley or Edelbrock? All comments will be will be helpful! Thanks, Wayne Quote Link to comment Share on other sites More sharing options...
zmanabba Posted March 28, 2011 Share Posted March 28, 2011 The compression test looks good. Some stuff you should check before you throw a carb at it. What color is the smoke? Blue smoke would be oil. Probably not rings with the good compression. Could have bad valve seals/worn guides and are fouling plugs. White smoke would be coolant. Head gaskets probably ok again due to good compression. But could be bad intake gaskets sucking coolant. Black smoke would be unburned fuel. Which could be due to carb dumping too much in to engine. Likely culprits are stuck needle and seat or sinking float. If it is the carb I would rebuild it rather than replace. The q-jet is an excellent carb when working right. Hopefully it is the carb it is the easiest to fix. Good luck, David Quote Link to comment Share on other sites More sharing options...
70chev Posted March 28, 2011 Author Share Posted March 28, 2011 The smoke is blue and black......no white smoke Quote Link to comment Share on other sites More sharing options...
CrazyDavey Posted March 28, 2011 Share Posted March 28, 2011 blue=oil....black=fuel compression looks good, if it's blue on startup and then disapates that's valve seals. Rough idle plus black smoke points to carb.... Quote Link to comment Share on other sites More sharing options...
Mike 57 Posted March 28, 2011 Share Posted March 28, 2011 blue=oil....black=fuel I agree, and the blue could come from too much fuel washing the oil from the cylinder walls. I would check the choke pull off, the Qjet can be rebuilt unless you are looking to change carbs Quote Link to comment Share on other sites More sharing options...
stangeba Posted March 28, 2011 Share Posted March 28, 2011 What has changed, taking it from running great to missing? Bad tank of gasoline, over revving the engine, sitting all winter. Have you done the basics like looking for a carbon track inside the dist cap and testing or replacing the spark plugs and wires, checking the coil tower for cracks. What isn't stock GM parts? Try (at night when dark) looking under the hood for sparks from the wires to the head or exhaust manifolds. Spray a mist of water on the wires and look (get a second person to help) again for sparks while under load from light brake torquing of the engine (carefully). Over half of my spark plug wires went bad over the winter several years ago. Tested them with an ohm meter and couldn't believe it. Good luck. Bruce Quote Link to comment Share on other sites More sharing options...
DavidTX Posted March 28, 2011 Share Posted March 28, 2011 It probably would benefit from a treatment of Sea Foam. It is available at all repair part sales and at Walmart. Quote Link to comment Share on other sites More sharing options...
Mikstudie Posted March 28, 2011 Share Posted March 28, 2011 Give it a small vacuum leak,if its a rich fuel mixture that should make it run better.Small leak!!!!! If it leans out and runs better probably a carb problem. Q-Jet is a fine carb. Quote Link to comment Share on other sites More sharing options...
70chev Posted March 29, 2011 Author Share Posted March 29, 2011 I have put a can of seafoam and 2 bottles of heat and that did not help. Changed plugs and wires and that was also a no go. The car ran fine shut if off, a while later started it up, had a bad miss, when I put in in gear it idles very low ( around 300 RPM and the car just skakes. Whan I get it out on the highway it runs ok but smokes like crazy as soon as a slow down the miss comes back. Quote Link to comment Share on other sites More sharing options...
Mike 57 Posted March 29, 2011 Share Posted March 29, 2011 What type of distributor? Did you change the cap and rotor? Did you look at the choke pull off to insure it is working? Coil good? How is the spark? Qjets are a good carb it may need rebuilt. When you pulled the plugs what did they look like? were any worse than others? Look down the carb while it is idling is it dripping fuel off of the boosters? float may be bad some of the plastic/fiber swell. Just some ideas hope they help Quote Link to comment Share on other sites More sharing options...
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