Jump to content

39 Century, thoughts on hesitation, popping through carb.


Ken Wells
 Share

Recommended Posts

Greetings!

     Working on a series 61 Century for a friend that was previously owned by a fellow (now deceased) in Florida that was having overheating problems with the car, front end was disassembled, head pulled and reworked and new aluminum radiator purchased probably 15-20 years ago. 

     I got the car with the head installed, finished bolting the front sheet metal on including new water pump. The car started right up and idles beautifully, however if you rev the motor it stumbles, pops and will flame through the carburetor. I can close the choke about 2/3 closed and it will "take the gas OK".

     Things I have done/checked:

1. Gapped the points

2 Adjusted the timing (with a light, 6* BTDC)

3. Adjusted valve lash (.015" I&E)

4. Disassembled, inspected and cleaned the carburetor (accelerator pump OK)

5. Fresh gasoline

6. Good spark

7. Tried another known good condensor

 

Thoughts? Suggestions?

 

                            Thanks!

     

Link to comment
Share on other sites

1 hour ago, avgwarhawk said:

Check the firing order. 

Great suggestion and honestly had not checked until after I read your comment. Firing order OK.

 

Now thinking the valves are too tight. Book says .015" hot, I set them cold. Intake valves potentially not closing. 

Link to comment
Share on other sites

Poping &backfiring often associated with lean mixture condition, further supported by comment about choke. Just a SWAG, (scientific wild-ass guess)! Old school diagnostic tool-vacuum gage. Started learning with the 1940-1953 Motors manual. If you find one, there's a whole page with photos of vacuum gage faces with the needle acting differently in each photo and listing possible issues that can be indicated. Not a guarantee, but an aid to possibly point you in a logical direction. Set timing with it to. Kinda lost 'dark' art!

Edited by 2carb40 (see edit history)
  • Thanks 1
Link to comment
Share on other sites

3 hours ago, Ken Wells said:

I can close the choke about 2/3 closed and it will "take the gas OK"

That sounds like a vacuum leak, to me. Spray some starting fluid around the base of the carburetor and around the intake manifold where it contacts the cylinder head while the engine is idling. If it speeds up from the spraying, you have found your vacuum leak.

Pete Phillips, BCA #7338

Leonard, TX

  • Like 2
  • Thanks 1
Link to comment
Share on other sites

If it has sat for a while there could be a sticky valve in addition to slightly tight valves.   If you have a vacuum gauge, this would be the time to use it.     I am thinking of three possible issues. 1. sticky tight valve. 2. leak at intake to head 3.  Dist advance issues.   The vacuum advance plate in the dist has a habit of wearing notches into the body of the dist that won't allow the vacuum advance mechanism to advance the timing.    If this is the issue, Bobs Automobilia can help you  805-434-2963

  • Like 2
Link to comment
Share on other sites

On 12/31/2021 at 10:14 PM, critterpainter said:

Once you resolve the issue, the best way to adjust the valves for smoothness and power is to do it with a fully warmed up engine AT IDLE.  I know its a pain but you will see a difference.   also set the gap to a snug .016, not .015.

I did this exactly as described. Warmed the motor then used a .016"-.018" stepped feeler gauge. Set the idle way down and was able to set the valves where I am confident they are correct. 

 

I have determined the off-idle stumbling is a product of old methanol gasoline. Much better now!

 

Another classic back on the road

Buickdrive.JPG

Edited by Ken Wells (see edit history)
  • Like 3
Link to comment
Share on other sites

At this point the car should be driven to accumulate miles.  Hopefully the work done will have corrected any issues and the car should begin to run better and better as miles increase.  After about 200 miles recheck everything visually, verify dwell and timing and check idle vacuum.  If everything looks good, keep driving!  ;)

 

Oh, did you verify the vacuum advance is working correctly?  My '38 was backfiring intermittently when letting-off the throttle from 45~50 mph.  I found my vacuum advance diaphragm was leaking and I pulled the distributor, removed the breaker plate and cleaned-up everything, including the centrifugal weights.  So far, no more backfires...

Edited by EmTee (see edit history)
  • Like 1
Link to comment
Share on other sites

4 hours ago, EmTee said:

At this point the car should be driven to accumulate miles.  Hopefully the work done will have corrected any issues and the car should begin to run better and better as miles increase.  After about 200 miles recheck everything visually, verify dwell and timing and check idle vacuum.  If everything looks good, keep driving!  ;)

 

Oh, did you verify the vacuum advance is working correctly?  My '38 was backfiring intermittently when letting-off the throttle from 45~50 mph.  I found my vacuum advance diaphragm was leaking and I pulled the distributor, removed the breaker plate and cleaned-up everything, including the centrifugal weights.  So far, no more backfires...

Yes, vacuum advance is functioning. At first I noticed the vacuum diaphragm had popped away from the distributor, fixed that then tested with my Mity-Vac.

  • Like 1
Link to comment
Share on other sites

I think this problem has self-corrected. After 20 years inactivity, driving the car a few miles the hesitation seems to be resolving itself, fresh (100%) gasoline is probably the cure. 
 

Now on to electrical problems.

Kudos to Bob’s Automobilia for quality parts and fast delivery.

  • Like 1
Link to comment
Share on other sites

3 hours ago, Ken Wells said:

fresh (100%) gasoline is probably the cure. 

That, and maybe the valves were sticky due to old gas and/or oil deposits on the stem and are now working properly.

 

x2 on Bob's; that's where I sourced my rebuilt vacuum advance.  It's nice to have sources like Bob's and CARS out there to keep these cars on the road.

  • Like 1
Link to comment
Share on other sites

I would pull the distributor .....clean,  inspect, and lube the advance mechanism.    With that done you have eliminated one item. 

Lots of stories, myths, and fears for 1939 Buicks overheating.    As the former owner of one I had many trips that I watched the temp gage register much higher than I would like. 

I replaced a perfectly good water pump with no improvement.    I tried "water wetter" with no improvement.   With great difficulty, I replaced the OEM fan blade with an aftermarket flex fan with more blades. 

The best advice I received was not to overfill the radiator,  '39 was the last year of a non-pressurized cooling system and if you overfill the radiator,  it will expand and spit coolant on the ground. 

I purchased a couple a digital temp gages with the intent of getting a better reading on the actual temp at both the in and out of the radiator....never got that accomplished.... the factory temp gage has no numbers, 

just H and C    I also considered converting to a pressurized system.... found a remote Chevy coolant tank that had a pressure cap... was planning on adapting that to the factory radiator, but finding a location for the tank

was a problem unless it was mounted to the firewall... that messed with the looks under the hood. 

Good luck with the '39 

  • Like 2
Link to comment
Share on other sites

9 hours ago, Barney Eaton said:

I would pull the distributor .....clean,  inspect, and lube the advance mechanism.    With that done you have eliminated one item. 

Lots of stories, myths, and fears for 1939 Buicks overheating.    As the former owner of one I had many trips that I watched the temp gage register much higher than I would like. 

I replaced a perfectly good water pump with no improvement.    I tried "water wetter" with no improvement.   With great difficulty, I replaced the OEM fan blade with an aftermarket flex fan with more blades. 

The best advice I received was not to overfill the radiator,  '39 was the last year of a non-pressurized cooling system and if you overfill the radiator,  it will expand and spit coolant on the ground. 

 

Actually 1939 Buicks did have a pressurized cooling system but the cap was a sealing cap, not a pressure cap.  The pressure release device was the round thing on the top of the radiator that the overflow line connects to.    The most common cause of excessive overheating is a failed or failing bypass valve located in the lower half of the thermostat housing.   There have been many articles written about this issue and the repairs.

Link to comment
Share on other sites

On 1/16/2022 at 8:53 AM, RiKi5156B said:

bad accelerator pump. they will shrink and cause stumbling if it sits too long and dries out. fresh gas can bring them back 

My first thought was a bad accelerator pump but was not the case. I did discover slop in the pump linkage that caused a delay in the pump shot. The cure was fresh oil and gasoline, then put the thing on the road. The more I drove it the better it ran!

the car came to me with the front end disassembled and hadn’t run in many years. A couple months of tinkering and with the help of this forum there is another running 39 Century back on the road. 
she’s back home now with an appreciative owner. 

 

(BTW, in the background is my 97 Buick Ultra, daily driver W/308K miles)

CC7B37C7-1B9A-43BE-8C22-0964842288D4.jpeg

Edited by Ken Wells (see edit history)
  • Like 4
  • Thanks 1
Link to comment
Share on other sites

  • 2 months later...
On 1/16/2022 at 3:12 PM, Ken Wells said:

My first thought was a bad accelerator pump but was not the case. I did discover slop in the pump linkage that caused a delay in the pump shot. The cure was fresh oil and gasoline, then put the thing on the road. The more I drove it the better it ran!

the car came to me with the front end disassembled and hadn’t run in many years. A couple months of tinkering and with the help of this forum there is another running 39 Century back on the road. 
she’s back home now with an appreciative owner. 

 

(BTW, in the background is my 97 Buick Ultra, daily driver W/308K miles)

CC7B37C7-1B9A-43BE-8C22-0964842288D4.jpeg

The owner has decided to sell this car, message me if interested. (Moderators, please delete if not appropriate)

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share

×
×
  • Create New...