|
|
Member
Posts: 35
Location: Yakima, WA | Hey all I'm having one heck of a time, looking for advice.
Car: 1955 plaza flathead 6, 3 on the tree.
Here is my issue:
Car idles great, but when I rev it up like when shifting from 2nd to 3rd at 20-25mph it stumbles.
I thought originally it was the timing so I have it set at 2* retarded and using my timing light I can see that it advances as it revs up.
Here's the weird part, I unplugged the vacuum line going to the vacuum advance and it still advances as it revs..
I also tried rebuilding the carb, the distributor, adjusting the accelerator pump linkage, and changing the idle mixture.
I can't seem to shake it, she doesn't wanna rev up very high to allow me to shift 2nd to 3rd I really have to lug it and then I can only go about 40mph top speed before the engine starts shaking.
What am I missing? Where do I look next? |
|
| |
|
Expert
Posts: 3780
   
Location: NorCal |
Timing will advance even without the vacuum because of the centrifugal advance feature in the distributor.
Your problem could be a plugged exhaust system, hook up a vacuum gauge and look for vacuum that decreases at higher engine RPM's with no load. |
|
| |
|
Expert
Posts: 1740
Location: Alaska | Is this the original engine, how many miles on it? If it sat for a while you could have very weak or one broken valve spring. You might just have sticking valves. I have seen both of these problems cause what you are describing. |
|
| |
|
Temporarily suspended to cool off
Posts: 316
| Just to add to things that could be wrong, fuel supply issues. Sometimes you get a blockage that allows enough fuel for the car to idle properly, but as soon as you put a load on the car it falls on it's face.
honestly your timing could cause it as well. 2 degree retard, are you meaning 2 degees after tdc? that could cause a car that doesn't run very well. set it at atleast 5btdc, if not 10btdc. If the car isn't spark knocking then you haven't over advanced the timing. I realize this isn't the stock setting for the timing but those settings were determined for fuels of the day. Low octane fuels that burnt quicker than the ethalated and otherwise higher octane fuels we have today that take longer to burn. Longer burn time means more spark advance is needed. |
|
| |
|
Member
Posts: 35
Location: Yakima, WA | I believe it is the original engine. If it were a sticking valve would I be able to hear it stick at an idle?
It idles very smooth just doesn't wanna rev up.
It may be fuel related its got lots of old gas (hasn't been driven much in 10 years). I'll substitute the fuel supply and try it again. Also my fuel filter looks like it dries up when engine is running but it always stays running. Just put on a new used fuel pump wonder if it is not pumping enough...
I'll try some things this week and let you guys know.
Thanks for the advice I will check everything mentioned.
Edited by HerbertsNatural 2015-09-07 4:24 PM
|
|
| |
|
Temporarily suspended to cool off
Posts: 316
| HerbertsNatural - 2015-09-07 1:22 PM
I believe it is the original engine. If it were a sticking valve would I be able to hear it stick at an idle?
It idles very smooth just doesn't wanna rev up.
Well if the valve is sticky it could be closing slowly. Which means you get the same symptoms that valve float gives you. So at idle, she's able to keep up and get the valve closed on time, but as the revs increase now the valve starts to float.
Now this could be caused by a guide, bent valve, or a worn the F out valve spring. You can try using some seafoam down the carb while reving the engine up. that does a decent job of freeing up stuck valves. No need to dump the entire bottle down the engine, you just feed in a little bit while the engine is running and reved up to around 2000-2500rpm. I actualyl do this to my engine as yearly maintenence. Keep the valves and guides nice and clean.
I guess the other thing it could be is point bounce caused by a worn out spring on the points. Now that I'm thinking ignition hell it could be bad plug wires resulting in a cross firing situation. I've seen that happen. I have my method for checking for this... few care to use it :P I just grab ahold of the plug wire with one hand, ground myself on the elbow of the same hand or with my thumb (you don't want to use the oposite hand, causing the current to cross the path of your heart is generally a bad idea) and see if I get nailed! If you feel spark comming through a wire, it's done. Working on my buddies Ultra Van a few weeks back in the dark I could actually see small sparks leaving the spark plug wire and sparking onto the metal retainer and carburators! No beuno! Maybe a distributor that's off a single tooth on the drive gear? that can cause rotor misalignment and when you rev the engine up, again, cross firing.
Start with the cheap, easy to do stuff and work your way through is the only option. Sticking your head in the engine compartment of an engine spinning at 3000rpm, not a lot of fun. Been there, done that, got the tinitus to prove it. I feel for ya dude.
Edited by Polybun 2015-09-07 4:54 PM
|
|
| |
|
Extreme Veteran
Posts: 580
| HerbertsNatural - 2015-09-07 4:22 PM
I believe it is the original engine. If it were a sticking valve would I be able to hear it stick at an idle?
It idles very smooth just doesn't wanna rev up.
It may be fuel related its got lots of old gas (hasn't been driven much in 10 years). I'll substitute the fuel supply and try it again. Also my fuel filter looks like it dries up when engine is running but it always stays running. Just put on a new used fuel pump wonder if it is not pumping enough...
I'll try some things this week and let you guys know.
Thanks for the advice I will check everything mentioned.
When I had a sticking valve on a flathead 6 in a 1949 Dodge pick-up the tappets were quiet at idle but when I revved it up you would hear very clearly the loud ticking tappet because of the increase of the gap between the tappet and valve stem. |
|
| |
|
Expert
Posts: 1740
Location: Alaska | Others are correct, check the simple stuff first. It could just be old gas in a dirty carb. It could be a coil breaking down. |
|
| |
|
Member
Posts: 35
Location: Yakima, WA | Bought a new coil, added a ballast resistor before the + of the coil, didn't change anything.
Set timing to 5* btdc and 10* btdc, no noticeable changes.
I substituted good fresh gss from a can, no difference.
Put some seafoam in my gastank to no avail.
Pulling vacuum off my intake manifold shows 5-10 lbs of vaccum, not a steady 5-10 lbs but dancing everywhere between. Spikes to 12 on occasion. When I rev (or attempt to, the issue has gotten worse after the seafoam) the vacuum dissapears and it will not rev up.
Also my timing seems to be retarding itself to maybe 12-14*btdc and I've got the distributor all the way adjusted to one side and am not getting more advance out if it since I plugged in the vacuum gauge to my intake manifold.
I did notice the heat riser flap thing in my exhaust manifold is broken and flops over when I have it running. It's very loose and a small amount of exhaust leaks out of there. Not sure if its clogged but considering pulling it off to check it out.
What does the vacuum tell us if its at 5-10lbs bouncing around the whole time at an idle and goes away when I try to rev the engine?
My gut also tells me that my carb floats are out of adjustment cause it seems to flood lately after I turn it off.
Edited by HerbertsNatural 2015-09-15 11:26 PM
|
|
| |
|
Temporarily suspended to cool off
Posts: 316
| the low vacuum could be a few things.
One, the ignition timing is way way off. You say it keeps moving, and going retarded as the engine revs? that's backwards, it should advance with a rise in rpm. If that's really the case then the rubbing block is probably coming off the points, which would actually explain the back firing, one of the origonal things I proposed, point bounce. In any case, ignition timing certainly affects manifold vacuum.
If that isn't it, then there really is a stuck valve, and that's why the vacuum is low. There would also be a noticable dip in manifold vacuum at idle when it hit the bad cylinder.
Lastly, low vacuum could just simply mean the engine is just worn flat the f**k out. It would have to be pretty darn bad to be THAT low on manifold vacuum but, it can happen. I've seen more than one engine out here in Oregon that the compression was so low that there was no way it would even start let alone run. The state of washington gifted us that little event back in 1980 and it killed a lot of engines around here. Volcanic Ash does not do pretty things to cylinder walls or piston rings... or valves... or main bearings (it gets in there too)... or really ... yeah it just pretty much screws up everything.
Anyway, I would start with points, that's something easy to check. If it won't hold time, has to be the points... well that or the distributor shaft is totally worn out. So yeah, just yank the entire distributor, give it a good once over. |
|
| |
|
Expert
Posts: 3577
Location: Blythewood, SC | You have burned the points. You must have a resistor in line between the coil and the points. I know it isn't there originally, but you must have a resistor in line between the coil and the points. |
|
| |
|
Expert
Posts: 1493
Location: Jamaica Plain, MA | Hey there! With respect: this is a classic. Doing a major tune up: "I also tried rebuilding the carb, the distributor, adjusting the accelerator pump linkage, and changing the idle mixture."
One thing at a time. It's really important to attempt one fix at a time and check the results after each step. Not that you didn't, but just saying.
Idle mixture doesn't have anything to do with going 25 mph and up-shifting. Under torque, it stumbles. It's a one of three things-- ignition, fuel and the mechanical functioning of the motor. Sticky valves usually cause a perpetual miss because they bend the push rods. I'd check things, like the points, or a fuel-carb problem (cruddy needle valve) or a worn out fuel pump. Unless it has really bad rings. I suggest: clean/rebuild carb again, check fuel for contamination (filter, replace all the fuel), set points, check plugs, and stop screwing with the timing (set it to factory spec), engine timing isn't controlled by ghosts or spirits, don't fuss over it, for now), change the condenser if you haven't, check the cap for wear, cracks and carbon scoring; and check or replace the fuel pump. I might suggest letting it warm up, choke it down and see if a leaky intake manifold is causing an over-lean issue. You should do a compression check, although the bearings in those L heads usually fail before the rings. It sounds like a worn motor and/or with a dirty needle valve, or old gas and/or a bad fuel pump. The good news: that motor is nice and simple. |
|
| |
|
Expert
Posts: 1819
Location: Vancouver, BC |
The car is a 1955 Plymouth Plaza, 6 cylinder, which means the car was built with a 6-volt, positive ground, system. That is - no ballast resistor. So, if this car has the original 6 volt, positive ground electrical system no ballast resistor is required.
On a negative ground system, the ballast resistor is added to the positive side to the coil. And on a positive ground system the ballast resistor should be added to the negative side.
|
|
| |
Flathead 6 won't rev up very much > stumbles runs rough
