philipj

38 Century Driveability Hiccups...

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Finally took the car out today after working on it for a couple of months! It idles very smoothly, except while under load I get a little Hiccup... Anything over 30 MPH and I get a blip, blip, blip...@$!%! I had it up to 45 MPH. Wonder if I have the mixture a little too lean. It is set up about 1-1/8 turns. Points are new and set up @ 0.15, the plugs are the R45 set up @ 0.25 with a new condenser as well. Temperature is 175°-180° and oil pressure at idle 25-30 psi. I did not replace the plug wires or checked the timing. The vehicle starts right up, so I figured it can be that far off.

 

What should I check next? Would carbon build-up cause this problem?  When I first started the car some of it came out through the tailpipe. Big enough to see on the ground...

I imagine years of an improperly adjusted carburetor, a malfunctioning manifold bypass valve, and little service would contribute to this problem...

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In my opinion the first thing to do is run a compression test. If the cylinders are within 10% of each other it can be made to run smooth, if not it will never be as you want it. 

 

Edited by LAS VEGAS DAVE (see edit history)
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I don't think you can adjust the cruise mixture, only the idle.

 

Check the timing.

 

Too much timing will cause the engine to kick back on itself. It could easily start well with the timing advanced (or not). There are too many variables to guess.

 

Does it have the factory cover over the plug wires? If so, you could try removing it.

 

The top of the rotor has to make contact properly with the center of the distributor. IIRC on the Buick, it is spring loaded carbon brush in the center of the bottom side of the distributor cap. Make sure it is there and sticking down to contact the rotor.

 

Look at the ends of your ignition wires for big balls of blue corrosion, especially under the boots at the distributor cap end and coil.  Some darkening of the brass wont hurt. When you see the blue mess you will know.

 

Are the plug ends of the wires booted or bare? There could be trouble here too. Inspect.

 

You can check wires with a multimeter if you have one. Resistance will be a few ohms if they are copper, around 2k ohms if they are resistance wire, with the long ones higher than the short ones, maybe as much as 3k ohms. This wont tell you anything about the insulation, and they could pass this and still be bad, but USUALLY a wire that blows out its insulation also fails the resistance test, so it is a useful thing to check.

 

 

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When I first got my 1937 Century, it was running very rich due to a carburetor problem. That black soot was quite an issue with it running too rich. After I got the carburetor straightened out, it was still acting like it was running rich, black smoke under acceleration, etc. Lots of people thought the car ran really well. I was convinced that it was running like it should but I later figured out that it was just barely firing. The plug wires and distributor cap contacts were showing lots of sign of corrosion. After I replaced the points, plug wires, and distributor cap and rotor, the car no longer has any black smoke or soot coming out of the tailpipe under acceleration and it runs much better than it did before. Check all of the wiring and contacts in the ignition system. Clean or replace them as needed. Check and adjust the timing as necessary and make sure your vacuum advance is working correctly in the distributor. If you take care of all of those, I suspect your car will run much better.  

 

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If you haven`t done it and no telling if it`s ever been done, the rocker arms may need to be adjusted.

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I can certainly check the plug wires for resistance, they have rubber boots also, but they're old about 15 years. It seems that to most of you guys this is an electrical problem as opposed to a carburetor problem... I was surprised to hear the valve adjustment as a cause of a misfire... There is no soot, smoke or anything coming out of the tailpipe now, only after the first startup...

 

What are the timing specs . for this? Remember it is a 1947 engine...

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http://www.carnut.com/specs/gen/buick40.html

 

Apparently its the "ADV" mark. I am not finding a specification in degrees.

 

A "hiccup" sounds like either over advanced timing, or a cylinder that goes away under load due to excessive resistance in the ignition. Yes, it could be a lean misfire due to a carb problem, but that is tougher and more expensive. Start with the easy stuff.

 

Octane selectors are usually set in the middle to start. Still hiccups? Try retarding it a bit. If that doesn't help, it probably isn't timing. Once the trouble is sorted, you can probably run a little more advance than stock... I think. I will defer to the straight eight Buick drivers on that.

 

Don't forget to check your vacuum advance.

Edited by Bloo (see edit history)

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I believe there are two, one in the intake manifold and another in the distributor... I will have to see how this is set up right now. Running 89 Octane.

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Well, I just looked at the car and it seems to me that what they call octane selector in the distributor are simple the two bolts used to advance or retard... No other means of adjusting. Just 40's lingo! As for the vacuum advance, what is the best way to assure it is working properly? 

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44 minutes ago, philipj said:

As for the vacuum advance, what is the best way to assure it is working properly? 

 

You disconnect it's line, and suck on it with a vacuum pump, or maybe you just suck on it. It is kind of tough on these old ones because there is no hose, and the little pipe runs all the way to the carb, it is tough to get a seal for a test.

 

With the distributor cap off you can watch for movement. These cannot leak air at all. You should be able to move the breaker plate in the distributor, and it should not snap back until you release the vacuum.

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The Octane Selector is basically a pointer and a scale on the bottom of the distributor. Your later engine may not have the Octane Selector on the distributor. You adjust the timing for your normal octane and set the pointer at zero. If you were then to be driving in an area of the country that had a lower or higher octane fuel available, you could then adjust the timing using the pointer and scale, and then when you were back home with your "usual" octane fuel, you could simply readjust the distributor using the pointer and scale without needing to use any tools other than the wrench to loosen and tighten the distributor bolts. In the 1930's that was necessary. Today, it will still enable you to make slight adjustments and then return it to the original adjustment, but probably not anything you will use with modern fuels and driving conditions. 

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Very interesting concept and practical for the day regarding the octane selector... It is actually a good idea to have marks to go to. Regarding the vacuum advance, I am able to move the plate and it snaps back. Other than that, replacing the line and lubricating the distributor is all I have done... Wish I had other tools to do this test right but I will give it a try...

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Here is a photo of the octane selector.

The scale is bolted to the block and the pointer is attached to the distributor body.

If nothing else, it makes it easier to get the engine back in time if you remove the distributor for some reason - like new points.

DSC_5309.JPG

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And I thought I knew EVERYTHING!  I have never seen one, that I remember.  We had '39s and I had a '40. I do not remember them having that. 

 

  Now I know.

 

  Thanks

  Ben

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That is a pretty neat feature... All and all and despite the car not being 100% my wife and I went for a night ride and enjoyed the car immensely... Next week I hope to cure the driveability issue and go to the next thing. Plug wires are at least 15 years old with insulators, but I will replace them... Any recommendations for vendors?

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9 hours ago, MCHinson said:

The Octane Selector is basically a pointer and a scale on the bottom of the distributor. Your later engine may not have the Octane Selector on the distributor. You adjust the timing for your normal octane and set the pointer at zero. If you were then to be driving in an area of the country that had a lower or higher octane fuel available, you could then adjust the timing using the pointer and scale, and then when you were back home with your "usual" octane fuel, you could simply readjust the distributor using the pointer and scale without needing to use any tools other than the wrench to loosen and tighten the distributor bolts. In the 1930's that was necessary. Today, it will still enable you to make slight adjustments and then return it to the original adjustment, but probably not anything you will use with modern fuels and driving conditions. 

Yes, but remember that when Buick was equipping their cars with Octane Selectors, premium fuel AKA Ethyl was 78 octane.

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Trying to drive the car as much as I can... I actually hit the 60mph mark and felt pretty good. Seems smooth and steady at that speed, more so than 35 mph... If we have good weather tomorrow evening, I am going back out again...:)

 

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Octane selector eliminated starting with 1939. Explanation according to the 39 Shop Manual was it was infrequently used. My 39s distributor has a vestige of the pointer cast into the base between the mounting bolts. Same is true with the distributor in the 47 engine I have installed in my 37. As Grimy noted premium fuel for these cars was 78 Octane,so we should be able to slightly advance the timing on our prewar cars to take advantage of our 87 and 89 fuels today.

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So you think that advancing the timing will smooth the car out completely? I always thought that you could risk damaging an engine if the timing is too far advanced...  The question is if I stick to 89 Octane fuel,  how far from the 6 BTDC should I go? Advance it a little does not yield a specific number that I can work with, unfortunately; whereas if you say, set your timing light at 2 ATDC I can actually compare the results and make changes...

Edited by philipj (see edit history)

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Watch out for a frozen heat riser between the intake and exhaust manifolds.  Its operated by an spiral thermal spring on one side of the manifold and a counter balance weight on the other side. Make sure that this mechanism operates freely. Mine was frozen in my '37 and caused the carburetor to get too hot, making the engine feel week and feeble above 40 mph after ten minutes of driving. 

 

Even though I managed to get it free (copper hammer repeatedly on both ends of the hinge pin), there is enough residual rust in the hinge pins to prevent proper operation. To remedy it I set the mechanism to a non-heat position (full frontal CW) and putting the thermal spring on backwards to keep it permanently in the non-heating position. The car runs fine now at all speeds. Since I don't drive the car in winter weather I really don't need to have this device operating.

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And if you do get carburetor icing, just idle for 5 or 10 minutes, shut it off, go and fetch your sun glasses, jacket, bottle of water, better clothes etc, then start up and drive away with no icing. The warm manifold will fix the problem.

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All humor aside, since I am not finding anyone with a similar experience, I am going to recheck my point gap and timing with a different light... I also have a new problem where the car does not start at the first crank when hot... It starts at the first crank when cold only. Wonder if I have to revisit the carburetor again...@#$!! Could the float height be too low? I wonder... Other than that, with a properly functioning heat riser valve and new rebuilt fuel pump, I don't know where to go...

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