plastic-idol
Well-known member
how can I test for vacuum leaks. I'm having a problem with what sounds like misfire, but I can't figure it out.
possible vacumm leak
- Thread starter plastic-idol
- Start date
is the misfire at idle?? do you have the pertronix 11?? i advised you about the pertronix 11 several weeks ago. if you think the problem is fuel related,spray brake cleaner around the carb-***if doing so have a fire extinguisher handy in case of a fire.plastic-idol":323ztthe said:
is the idle mixture too rich or lean. place a rag over the carb intake, if the idle speeds up you have a lean condition. check this out & advise. william
The problem can also result form a burnt valve. A vacuum gauge can help you troubleshoot that problem.
plastic-idol
Well-known member
thanks for the replies,
I have the petronix, but it 's not installed yet. the misses all happen at low rpms, either at idle or maintaining speed. the "mechanic" that worked on the car last claimed it was just the choke warming up, but I think he's just a moron. also, could it be a bad plug wire? if so, what's the best way to check the wires?
I have the petronix, but it 's not installed yet. the misses all happen at low rpms, either at idle or maintaining speed. the "mechanic" that worked on the car last claimed it was just the choke warming up, but I think he's just a moron. also, could it be a bad plug wire? if so, what's the best way to check the wires?
it could me a large number of things. if you suspect vacuum leak, get carb cleaner (never heard of using brake cleaner, but it's probably the same stuff) and spray around the base and carb gaskets to see. If the RPMS rise when you spray a particular area, then you know you have a leak. I've never had a vacuum leak cause a backfire or a misfire.
In your situation (yeah, you mech is an idiot, as are most these days with older cars) this is what I'd do:
1) Put the pertronix in. Maybe it's points that are too worn out. I found pertronix smoothed out my car when I first got it. Be sure to check your timing.
2) If that doesn't work, check plugs and wires. First, since wires are pretty cheap, just replace them, especially if you don't know how old they are. Then do a plug and wire check. TO do this: First pull one wire while the car is running. See if the engine starts running worse, or doesn't change. If the engine doesn't change, then you know that cylinder, plug, or wire is the problem. Also, each time you pull a wire, slowly put the wire back on the plug and see if you are getting a spark arcing from the wire to the plug before you put it on. If not, or you see a noticably weak spark, then something is wrong with either that wire or that part of the dizzy. THis is more obvious with a higher output coil, but even stock, you should be able to see the spark. Also, if you see a spark anywhere else on the wire, then you probably have a bad wire too. If you get shocked, even while holding the wire a few inches above the boot, then you have a bad wire. Don't worry, it'll surprise you more then anything, but it doesn't really hurt or anything (twitch...twitch...). YOu may also want to consider putting in new plugs, since once again, new plugs will cost you $6 (especially if once again, you don't know how old they are).
Check that stuff out and see where it puts you.
Slade
In your situation (yeah, you mech is an idiot, as are most these days with older cars) this is what I'd do:
1) Put the pertronix in. Maybe it's points that are too worn out. I found pertronix smoothed out my car when I first got it. Be sure to check your timing.
2) If that doesn't work, check plugs and wires. First, since wires are pretty cheap, just replace them, especially if you don't know how old they are. Then do a plug and wire check. TO do this: First pull one wire while the car is running. See if the engine starts running worse, or doesn't change. If the engine doesn't change, then you know that cylinder, plug, or wire is the problem. Also, each time you pull a wire, slowly put the wire back on the plug and see if you are getting a spark arcing from the wire to the plug before you put it on. If not, or you see a noticably weak spark, then something is wrong with either that wire or that part of the dizzy. THis is more obvious with a higher output coil, but even stock, you should be able to see the spark. Also, if you see a spark anywhere else on the wire, then you probably have a bad wire too. If you get shocked, even while holding the wire a few inches above the boot, then you have a bad wire. Don't worry, it'll surprise you more then anything, but it doesn't really hurt or anything (twitch...twitch...). YOu may also want to consider putting in new plugs, since once again, new plugs will cost you $6 (especially if once again, you don't know how old they are).
Check that stuff out and see where it puts you.
Slade
plastic-idol
Well-known member
Sweet, thanks
I'll try that out. I tried the carb cleaner and didnt' notice any difference by ear. I'll have to hook up a tach and try again. the plugs are new, as are the points, and neither look worn. I'll try the wire test and check back.
I'll try that out. I tried the carb cleaner and didnt' notice any difference by ear. I'll have to hook up a tach and try again. the plugs are new, as are the points, and neither look worn. I'll try the wire test and check back.
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