1955 Century, no power, runs rough

[Pete Phillips]

I'm not having a good day. I am working on a gorgeously restored 1955 Century convertible (when I get frustrated with the '39 Special that won't start--see related post). This '55 Century has a bad miss in the engine, and accelerates like it has three cylinders. The car has been sitting in a garage for about 6 months with little use. You can eat your lunch off of this engine, it is that clean and nice--always well cared for, from what I can tell. I replaced the points and condensor, thinking that might be the reason for the miss. No change. Points are correctly gapped (.015). I removed all spark plugs and cleaned them. They were a little bit carboned up, but otherwise in good shape. I cleaned and gapped them (.030). No change. I checked the plug wires (good shape) and they are in the correct firing order on the cap and on the engine. Distributor cap is clean and nearly new, no cracks. Rotor is clean and nearly new, no corrosion. Carter carburetor looks clean and squirts out gas from both jets evenly into the primaries. The engine starts fairly quickly but idles a bit rough. I don't think the timing is off because it cranks evenly, not slow then fast like bad timing. All of the plug wires are seated properly on the plugs and on the distributor cap. All of the wires inside the distributor have insulation, no shorts nor breaks nor loose connections there. WHAT am I missing? This car runs like a piece of crap! It can barely get out of its own way! The exhaust heat riser valve is not blocked. There is no undue valve train noise, and I do not think any valves are stuck in the cylinder heads. I took the car out on the road, thinking that giving it some exercise might help whatever the problem is, but no change.

ANY suggestions are more than welcome!

Pete Phillips, BCA #7338

[Buicks Rule]

Pete,

The vacuum advance and or the mechanical advance might be stuck-not working.

Could have bad plug wire since carbon cores don't show damage when broken internally.

Could be stale gas/bad gas that just won't burn.

Vaccuum leak? at brake booster or under carb.

MTBE fuel goes stale quick and can soften accel pumps so that the work sort of but move enough fuel to cover the opening throttle plates.

Is switch pitch working correctly on tranny?

Any chance it's got double wall exhaust system. These were used a lot because they are very quiet, but the inner wall can collapse without the outer wall showing the damage.

Bill

[The Old Guy]

Pete, you might also look at the carb. You may have a power valve stuck, or a plugged hig speed jet.

[old-tank]

Pete

Try a known good coil, try wire core vs carbon string core plug wires, use non resistor plugs of the proper heat range, then rebuild the carb.

Willie

[Guest brh]

Since all plugs are firing evenly, I don't think it could be an individual wire, or the ignition system. My suspect is the fuel.

[special55]

Pete,

Are you sure there isn't something mechanical going on? You can do a quick compression check at each cylinder to ensure everything is OK there. If you want to do a quick check through a vacuum gauge on it. There should be about 15in. of vacuum at idle. If not I would suspect something internal.

Is the choke opening up once warm? If not it could be getting sucked closed and flooding the engine a bit. If that's the case you would probably be seeing some black smoke out of the exhaust.

Good luck.

[brad54]

Basic, but make sure the distributor wasn't installed 180-degrees out of time.

It'll run way out of time, but very poorly.

-Brad

[55PackardGuy]

Vacuum leak(s)?

[Guest Skyking]

Check the coil. Also check the resistor. My 55 Special had it mounted on the firewall.

[pphil]

i think it may be the carb.

when the float stuck on mine it

would run rough but wouldn't pull out of its

own tracks.

just my two cents worth

scott

1964 wildcat 425 2-4bbls 4-speed

[Guest imported_NikeAjax]

I would sugest pulling all sources of vacuum, including the choke stove, but make sure the car is warm so that the choke is open. See what a vacuum guage is reading with ALL, not most, but ALL vacuum sources removed. Relace one by one the vacuum lines, shutting the motor off each time you replace one and starting up again and read the guage. If it's not a vacuum leak, pull the cover off of your carburetor, be very careful not to bump the floats when you do this. Look for water, or where water has been: it will look like chalk, you know what the teacher writes with? Be sure to look at you needle and seat area VERY carefully; take the floats out and make sure there's no crap in there, again, chalky build-up!

With the motor cold, pull the radiator car and then start it up, look for bubbles: bad head gasket!

Hope this is a help,

Jaybird

[55PackardGuy]

Jaybird,

That's a neat trick for checking vacuum line connections--the gauge should read higher each time you replace a line, correct? If vacuum is still low with everything connected, then it could still be an intake manifold gasket or crack, couldn't it?

[Guest imported_NikeAjax]

Roger that! You can try sraying a bit of water or WD-40 around the bases of carb and manifold; if the motor speeds up, you have found the area in question.

Hope this helps too!

Jaybird

[Pete Phillips]

I appreciate all of the suggestions. I have now done a compression test of all cylinders, and have between 138 and 150 pounds of compression on them, so I don't think that is the problem. There is no vacuum leak that I can find--tested for that with starting fluid sprayed on all carb., intake, and power brake vacuum joints with car idling, and no change. I followed the car yesterday, as it was being driven, and there is virtually no exhaust smoke, so it does not seem to be running rich or leaving unburned gas in any of the cylinders. The car still idles roughly and does not accelerate worth a #!!**. I took the top off of the carburetor today, and there is a little bit of sediment in the bowl, but not much. All jets appear to be clean and clear. I guess I will rebuild the carb. while I have it disconnected. This miss has really got me puzzled and frustrated. I guess replacing the plug wires and checking the distributor advance is next.

Pete Phillips

[Patrick W. Brooks]

Good Morning Pete: Give the gasoline in the tank some thought. This has been a problem for me in the past. In fact, this weekend when coming back from the Heartland Regional in Collinsville, Il. we filled up the 1940 the morning we left. It was a nonbrand station and when getting on the highway it started to run as though it was missing on the hills and when trying to accelerate. Since I had gone through the entire system I thought it might be the carb because I had readjusted the idle screws before leaving to go to Collinsville. However, the car had run perfectly on the 350 mile drive down. I just kept driving for 100 miles and pulled off to fill it up. After this it lessened and after the second fill it was gone completely. There is no doubt it was bad gas and draining this tank and putting in some high octane might help. I had no aceleration and a miss or jerk on hills. Post your final solution and good luck. Patrick W. Brooks

[special55]

Pete,

Does the engine lack power both in gear and out?

What I mean is can you rev the engine up when it is just sitting there in park/neutral? If the problem is only in gear then you may want to start thinking about things like hung up brakes, trans problem, etc.

If it happens out of gear as well you may want to put a fuel pressure gauge between the fuel pump and the carb. The pump may not be supplying enough pressure.

Just a couple more things to think about.

Good luck.

[brad54]

The post on the gas got me to thinking a little more:

Could be that the fuel sending unit is plugged, and starving the car when it needs more gas. Again, happened on mine. It'd start and idle, but wouldn't drive. Really frustrating, because I had a clear fuel filter up by the carb, and it would always be full when I was tinkering with it. Brought the rpm up one day while I was working, and watched the fuel filter drain empty. Then it filled back up. The pick-up tube was so full of varnish that I couldn't blow through it. There was a tiny little pin-hole in the varnish allowing gas to flow into the fuel line--the tube was easily 98-percent closed off.

Could also be the fuel pump is dying. Again, happened on my '54 (I learned a lot on that car...)

It'd run and idle, but I had to "jump start it" by giving it a little shot of gas down the carb (kept a plastic soda bottle in the trunk for this). Once it got running, the suction of the engine would siphon gas up the fuel line, through the worn out fuel pump, down into the carb. If I'd romp on it a little or accelerate fast, or sometimes idle at a light, the siphon wasn't enough to keep up with the engine's demands and it'd sputter. If I accelerated very slowly, it would let me get up to a decent speed (had a manual trans in it).

If it isn't electrical, check the gas tank and fuel sending unit. Also wouldn't hurt to disconnect the fuel line at that point and blow some compressed air through the line to see what comes out. The fuel pick-up tube in the tank doesn't have a screen over it, so you can pick up trash, which will plug the line. If the air from your airgun doesn't free-flow through it (blows back past the gun) there could be an obstruction.

Guess where I learned about the plugged pick-up line and the need for a screen...

-Brad

[Marc Futterman]

Hi Pete,

So sorry your having such bad problems, and sorry I don't have any suggestions, your better at this than me.

Marc

[Pete Phillips]

UPDATE: I've done more work on this '55, including a complete carburetor rebuild. There was some crud in the bowl, but not real bad. It still runs rough and lacks power, both in gear and in neutral. I put new gas in the tank, so do not think stale fuel is the problem. I checked for vacuum leaks with WD-40 spraying as suggested above, and there are no vacuum leaks. The exhaust system all looks to be fairly new, so I don't think there is a collapsed double walled exhaust pipe or other restriction. The exhaust butterfly valve works fine. I am beginning to think the problem is just the compression in the cylinders. The shop manual called for 160 lbs, if I remember correctly, for a Century with Dynaflow, and most of the readings I got from the compression test were 138 to 145, with a couple of cylinders reading 150 lbs. The car starts up right away, and has good spark at the coil attachments. Spark plugs are the correct AC size and heat range called for in the shop manual (44-S, if I remember correctly).

Pete Phillips

[old-tank]

Hi Pete

I don't think it is the compression...my blue and white 55 compression is 110-125 and runs smooth and has decent power (not like my others that have 150-170). When I first got my CVT it looked and ran bad. Someone had been tinkering with it for a few years and it had new plugs. On a hunch I installed a used set from one of my other cars and it was off to smoking the tires and doing 'Dukes of Hazzard" manuvers off road on my place.

My point: put in a known good set and let us know...,

Willie

[JohnD1956]

This may be totally off the wall, but does this engine have a bad harmonic balancer. I could swear ( as a matter of fact I did) that I heard 56 was the first year for harmonic balancers, but I have no idea is that is true. Anyway, the balancer on my 56 spun on the crankshaft over a period of time. The key just cut the inside of the balancer's shaft and it spun about one full inch at the keyway. As a result, the timing marks were way off. I finally found out about the balancer last year and put on a replacement. The car still ran terrible till I redid the timing which instead of being 5 degrees BEFORE TDC was close to 7 degrees AFTER TDC.

Also, I had a bad hesitation on starts which seemed to disappear when I put some marvel mystery oil on the points breaker plate and then dropped somemore on the centrifugal advance weights. There is a small hole in the breaker plate which was marked as an "oil" hole. I've had the car since 1975 and didn't know about that.

If it's not one of the many ideas posted already, I'd suspect a jumped timing chain. I know the 56 used metal gears on both ends but I put on a new set and chain when I did the balancer and now the old girl runs like a charm. The old ones may still be good, I don't know. I just figured after 50 years, we got our money's worth out of em.

[Patrick W. Brooks]

Good Morning Pete: I know how frustrating these things can be. From what you have done so far it sounds like an electrical problem. That is easy to say from a distance, I know. Is the distributor cap cracked or is there a short inside the distributor because of frayed wires or a bare wire contact? Have you run the engine in the dark to see if you can see any electrical shorts from plug wires etc? When the plug wires were made was the wire bent back under the contacts to insure a good contact? Does the engine have a good ground wire? I believe the ground on that car ran from the back of the engine to the fire wall and sometimes they are not reinstalled after restoration work. On all my cars I have installed a ground wire from the rear push rod cover bolt to a good ground (straight eight engines). Have you tried a known good condensor and coil? Is the ignition switch good and are the leads tight in and out of it? Keep us posted. Patrick W. Brooks

[Ron Green]

Install a new cap and rotor. I just spend 3 weeks recently with a vehicle that would idle rough after about 45 minutes of running. The cap had a hairline crack that could not be seen by the eye and this cap only had 300 miles on it. It would be ok until it got warm and then the crack would separate ever so slightly and short things out.

Years ago I had a new cap out of the box that was bad, it happens. For the couple of bucks replace the rotor as they sometimes short out to the shaft via a hairline crack on the underside. Had this happen recently also. Replace the plug wires if they are over 3 years old. Its always nice to have some of these electrical items around just for troubleshooting these kind of things. Good luck!