burned valve?

Ok having issues with motor has a bit of hesitation off idle runs really rough when I press the throttle in the driveway at about 1000rpms then it smoother out and then it misfires.i heard that if you have suction on Tue tailpipe it could be a burned valve so I took a piece of paper and put it against the tailpipe and it tried to suck it in on the 2,4,6,8 side of the motor. What are common symptoms of a burned valve

If you have recently done anything to the dist or wires/plugs...check & make sure the plug wires are on the correct cap connections according to the firing order. That happened to me recently when I changed put the plugs & had similar symptoms.

make sure none of the spark plus wires are burnt, also, check out your cap and rotor, because i fried by cap and rotor and it was doing the same things you were talking about for about a month before it failed finally, probably about time for a tune up anyways.



replace everything you see in the pic, (cap, rotor, control module) and see if that doesnt take care of the problem.

Already did its still there:/

and you checked all your spark plus wires? theres no burns or anything on wires were the insulation is gone and its exposed and could possibly arc? also, did you check to make sure ALL of the boots are on as tight as possible? if youve done all these, you may want to borrow a vacuum gauge, or buy a cheap one, and run a compression test on each cylinder, as long as there within 10 PSI of each other, you know compression is good. after that, i cant really think of anything else to look at, but, from personal exp. it seems like its almost always something to do with the ignition system that causes an idle problem in a certain part of the rpm band. usually if it happens at low idle its because you have a wire arcing and the engine runs poorly until the rpm climbs high enough that the distributor is making so much spark the arcing problem is no longer affecting the motor as bad.

and did you follow 77 malis advice and make sure firing order is correct? also, another thing i though of is your idle air control may possibly be sticking, to test that, you will also need a vacuum gauge.

You can put air into the suspect cylinder with an air hose say from a compression tester ,with the cylinder at TDC it should not escape. If you see it come from the carb -intake problem. From the tailpipe exhaust valve. Really sucks. I had a problem over the summer like that,still not exactly sure what it was but I replaced the heads and its good now. I think I had a receded valve seat .they were late 60's heads and the guy was supoosed to replace the seats with hardened ones when i had them done, but I dont think he did.

If you want to you can also check the valves by removing the exhaust manifold and turning the engine over by hand to check both the intake & exhaust valves on their respective strokes. If your prob is on the even side only as you suspect start there. W/ the engine @ TDC you can just follow the firing order as you turn and take a peak inside w/ a flashlight to see if the valves move up & down as they are supposed to. If you are turning the engine and you notice that one or more don't open or close all the way then you know you have a problem. You can also check for any signs of severe wear & tear too.

Thanks I appreciate all the advise ill let you know what I find

compression check, if the burned valve is enough to show a misfire while runnning do a compression check, if a cylinder is considerably lower than the rest id start with those valves.

It will be easier to check with the manifold off if you remove the wheel wheel & tire unless you enjoy gymnastics, LOL. I thought about this also though, it may be worth it to look under the valve cover first and check to see if you have a loose rocker or bent push rod. If you have over 80,000 miles on the engine the valve lash may be looser than it should be if a push rod is set too loose it will cause the valve spring to not compress the push rod down all the way on that stroke. See if you can easily move or turn the rockers by hand, if so the lash is loose.

No I adjusted the valves less than 2000 miles ago because of The miss its hydraulic cam and since I did the 4 speed conversion the miss is way more noticeable

Could it be a bad cam lobe? Try running for a little while with the valve cover off see if they all move.

billy-ray wrote:No I adjusted the valves less than 2000 miles ago because of The miss its hydraulic cam and since I did the 4 speed conversion the miss is way more noticeable

That's good then, rule that out. I would second Black Chevelle SS & do that compression check. You can rent the kits if you don't have one. It may be the path of least resistance for you at this point if you have an air compressor. What will suck is having to repair/replace the darn thing. Hopefully it's just one of them. Double check those plug wires are on there right, it's an easy mistake to make. When i goofed it the engine backfired so loud I thought I'd soil my shorts!

Another way to check is to do a vacuum gauge test.

first rule out ignition misfire and vacuum leaks and carb adjustment. You might have a plugged idle feed circuit in the carb. I had that happen when you lose half a carb (2bbl) you really notice it.

Then plug the gauge into manifold vacuum port on the intake. If it's got a regular drop then its very likely a bad valve.

I can't tell you what the readings should be if your engine is no longer stock, but the needle should be steady and not rapidly flickering.