1931 Buick 60 series fuel handling problem...

[Str8-8-Dave]

So I finally got my 31 Buick down off the jack stands after 4.5 years and drove it.  Biggest problem?  Backfiring, apparently lean condition backfiring, can be mostly prevented by running with partial choke.   I replaced the float in the car with a Balsa replica of the original float, then added some thickness to the float to get it to displace a little more fuel in the bowl when the bowl is fully filled by the fuel pump.  I did this to correct fuel level in the bowl which was just above the low-speed nozzles causing a rich idle. I'm running an original float arm and float valve.   I turned the air control adjustment on the Marvel 10-795 carburetor in quite a way, it is adjusted below flush with the end of the ratchet spring, (flush with the ratchet spring is the recommended starting adjustment), to make sure the carburetor air valves were not opening too quickly and causing backfire, that didn't have much if any effect. 

I'm considering a few other causes for the backfiring:

 

1.  Fuel pump just doesn't have capacity to keep the float bowl full

2. Adding thickness to the float may have limited float valve travel, I.E. when the float is all the way down, is the float valve open enough to NOT RESTRICT fuel flow, or is the float valve causing back pressure preventing the fuel bowl from staying full?    

3. I don't know what condition my venturi blocks are in, could they be the culprit?

 

Ok carburetor experts- I know I'm trying to defy the laws of gravity by trying to make my Buick run correctly on a carburetor that says "Marvel" on the side of it.  The Marvel carburetor has to stay.  Any other ideas you can contribute highly appreciated...

 

Dave 

 

The first 2 pictures are of the balsa float replica I made from the original cork float.

 

The float was sealed with SIG hot fuel proof Butyrate dope before and after assembling to the float arm.

 

 

 

 

This is the original float valve.  It is still in the car today.

 

I had a rich idle condition I couldn't solve by adjusting the air control valve.  I removed the bowl and nozzle plate and checked to make sure there were no leaky

gaskets between the nozzles and the nozzle plate that would allow fuel to bypass a nozzle causing the rich condition.  The gaskets were good.

 

The maximum fuel level in the bowl must be slightly below the height of the low-speed nozzles to prevent fuel from dribbling out of the nozzles instead of being

drawn out of the nozzles by vacuum.  In this picture I measured the height of the low-speed nozzles to be 9/16" below the top of the bowl casting.

 

I scribed a line on the inside of the bowl 5/8" below the top of the casting to indicate maximum fuel level to prevent low speed nozzle dribbling.

 

After putting the carburetor together and reassembling to the car I found the fuel level was above my scribed line.  In this picture I have added thickness to the float

to achieve the desired fuel level in the bow.  The next picture shows my float modification. 

 

I added a 1/8" thick piece of sheet balsa to my balsa float to displace some fuel in the bowl so the fuel level would stay below the maximum fuel level line above.

 

Note in the picture below the air control is already adjusted below flush with the ratchet spring.  Adjusting the air control even further below flush with the ratchet 

spring (richer) and the car, after thorough warmup, backfires unless the choke is partially closed. 

Edited August 29, 2022 by Str8-8-Dave (see edit history)

[DonMicheletti]

I had a similar problem with my '31 right after restoration. It drove me nuts trying ti track dowm.

 

The problem...I forgot to install the condenser.

[Lahti35]

I just rebuilt the marvel on my '25 Nash. I'm still running the original needle and seat myself though also as I couldn't get the old set out. 

 

My needle valve does shut off the fuel coming into the carb at the level I set which is 1/16 below the low speed nozzle. I did have an issue with my float catching on the front inside of the fuel bowl, the casting inside was rough and the nitro float was a tad too big. It caused a flooding issue on mine. I had to trim it a few times to get full free movement. I verified this by leaving the cover off and priming the vacuum tank so I could watch it all work with the car off in real time. Took me a few tries to get it to work to the fuel level mark I scribed inside the fuel bowl.

 

I did replace the venturi on mine (it was somewhat cracked and the hole was oblong) and made sure to carefully adjust the jet to be centered in the hole. Mine was able to be installed upside down which is not correct, I had to pull it and flip it over, LOL. 

 

I set my low speed jet needle to the factory setting but then opened it a bit due to so so starting. The knob on mine had a nip that lined up with a post in the carb as the factory setting. My air valve knob is set to the factory spec. 

 

I went through my carb twice, and was very careful with it. Once I verified everything was functional (blocked off the hot air system also and made sure the tube inside the heat riser had no pinholes also) it would start. After fattening up the low speed jet some on attempt #2 it would start and idle perfectly. I know I'm a tiny little bit rich at the moment but I can't fine tune until the clutch is back in. 

 

I did take the car around a bit before I got into the clutch repair but it was running fine, plenty of power and no hiccups or backfiring. 

 

I also went through and set my ignition timing to factory settings, it was out a bit due to previous adjustments by owners past. This may have helped some but the marvel on my Nash was the main culprit. Broken choke, original soggy cork float, way low fuel level, crud in the passages, petrified gaskets, and air leaks galore... oh my!

 

 

 

 

 

Edited August 29, 2022 by Lahti35 (see edit history)

[critterpainter]

Any chance the tubes in the heat riser assembly leaking exhaust into the intake?

[Mark Shaw]

8 hours ago, critterpainter said:

Any chance the tubes in the heat riser assembly leaking exhaust into the intake?

This is the very first thing to check.  If your heat riser liner is perferated, the fight with your Marvel carb will be futile.

[Str8-8-Dave]

15 hours ago, critterpainter said:

Any chance the tubes in the heat riser assembly leaking exhaust into the intake?

Absolutely not.  Running just fine now, no more backfire, no choke required except briefly while starting cold.  It was the Marvel carburetor indeed.  I took it apart and blew out the gook in the filter screen in the bottom of the fuel bowl, removed and cleaned all the metering nozzles, replaced the venturi blocks with repros machined and sold by Mario Coviello (32Buick67) and installed most of a Carburetor Shop kit arranged for and custom made thru John Hardgrove (CarbKing).  The major piece I replaced from the kit was a correct air valve spring which the spring I removed was not.   I also made one more slight modification to my balsa float.  I filed a small slot across the bottom of the float that gives clearance to a diecast rib in the bottom of the float bowl.  Since I thickened my float at the bottom to lower maximum fuel level in the bowl to be 1/16" below the top of the low speed nozzles and since the cast rib in the bowl is what the float contacts when it is all the way down in the bowl, filing a coincidental slot allows the float to settle lower in the bowl which opens the float valve a bit more.

 

I did swap out the heat riser, not because there was anything wrong with the tubes, they were sound as a dollar.  But that riser is a hybrid 1932 riser that came with the car with throttle shaft I modified to accept 31 heat control and throttle linkage.  it has larger throttle bores and butterflies than the original 1931 riser.  Later I acquired another healthy, correct throttle size riser from Pete Phillips and built it up.  My heat riser system remains fully functional from the dash control to the riser and diverter valve.  The engine that used to backfire when the throttle was opened now happily takes throttle.  I've had the car to 60mph without carburetor issue of any kind. 

 

The last drivability item I'm working on is engine vibration.  I first thought the vibration might be wheel balance but where I noticed originally the vibration started at around 35mph in third gear I have now found the same vibration starts at about the same engine rpm in second gear or first.   That isolates the vibration to engine.  The first thing I will check is points synchronization.  Up to now I have relied on static timing, engine off, volt ohm meter check of point opening at 11-degree BTDC cylinder 1 timing mark and again 90 degrees later, cylinder 6 at the Syn6 flywheel mark.  My next move will be to verify or correct the initial timing and synchronization with a stroboscopic timing light while the engine is idling. 

 

If I can't correct the engine vibration with careful synchronization of the points, I will be suspicious the rotating assembly in this engine may be out of balance a bit.  One question I don't have and probably can't get an answer to, is, when the engine was overhauled were the original iron pistons used or does the engine have aluminum pistons, or worse yet a mixture of aluminum and iron pistons?   That stuff was all done by someone else.  Switching to a few or all aluminum pistons would change the engine balance.  Stay tuned. 

 

 

This first picture shows the engine with wrong heat riser absent of heat control linkage and jury-rigged throttle linkage.

 

The riser that came with the car had nice thick healthy throttle tubes, but it had larger than 1931 60 series (1-5/8" vs 31' 1-5/16") throttle tubes and butterflies and

lacked the coordinated cam roller linkage parts like the unit on the left.    

 

Also missing were the warmup throttle levers, again, correct for '31 shown on the left, riser that came with the car actually had throttle link jury rigged to work where

the 31' warmup parts would reside.

 

Another view of the hybrid riser before I modified it.

 

While it bolted up to the intake manifold and Marvel 10-795 carburetor the casting was physically wider and used a longer throttle shaft than 31' 60 series risers. 

Therefore, I could not use an original 31' throttle shaft.   The riser on the left is a broken correct 31' riser from which I was able to cannibalize the linkage parts. 

I modified the ends of the longer shaft to accept the 31' heat control, throttle and warmup throttle linkage parts, converting the round shaft ends to correctly oriented

flatted ends. 

 

 

This is the hybrid riser after throttle linkage conversion.

 

 

A view from the top shows thick, probably replaced, throttle bore tubes.  They were exhaust leak free, and

the engine had great manifold vacuum with this riser.

 

This is the riser I got from Pete Phillips.  It was a bare riser, no linkage parts, didn't even have

the exhaust shutoff butterfly at the exhaust inlet port.  I made the butterfly and installed it on

a shaft cannibalized from another junk riser.  I bought the rest of the linkage parts from Mario

Coviello.

  

 

Here is a bench-build picture of the riser setup using the riser Pete Phillips sold me and the diverter valve that came with the car.  Pete sold me a diverter valve

too, but it didn't allow the exhaust crossover tubes to line up properly on the car.  

 

Here is the new riser setup on the car before i added the overhauled carburetor.

 

This is the carburetor kit I purchased from Jn Hardgrove at The Carburetor Shop.  It included a correct calibrated air valve spring, all gaskets, all new fasteners and a

NOS Marvel float valve.  I opted to keep my balsa float instead of using the supplied Nitrophyl item.

 

The spring that was in the carburetor is on the left and was too long and had a very soft continuous spring rate.  The correct spring on the right came from the overhaul 

kit, is 1.5" long, has a fairly soft starting spring rate but the rate steps up quickly when the first coils start to compress.

 

These are the original venturi blocks, diecast pot metal affairs, very fragile.  The one on the left has some chips missing out of it.

 

Another view of the original venturi blocks which for fragile 90yr old pieces are in remarkably good shape, but still not good.

 

Pictured here are the solid machined replacement venturi blocks Mario Coviello had machined up.  This view is from the bottom before the fuel bowl and nozzle plate

was reinstalled.

 

A view from the top of the carburetor of the new venturi blocks with bowl and nozzle plate installed.  Those are the business ends of the low-speed nozzles just

visible in the center of the holes on the venturi blocks.

 

The little screen in the bottom of the float bowl is designed to keep crud out of the metering nozzles.  Unfortunately, if it becomes plugged, the nozzles starve for fuel.

I carefully cleaned it.  That rib in the center of the picture is what the float comes to rest on when the float bowl empties. 

 

Some time ago I added 1/8" of balsa sheet to a float that started with the same profile as the original cork float.  I did this to limit the maximum fuel level in the bowl

to keep it just below the tops of the low-speed nozzles to prevent gravity-flooding and subsequent too-rich mixture at idle.  Since the car required choke to run at road-

speed I thought the additional thickness of my float might be preventing the float valve from opening far enough to keep up with the fuel consumption.  I didn't want to

give up all the added balsa which displaced enough fuel to keep the maximum level below the low seed nozzles so rather than just shave off what I added I put a relief

channel in the balsa which allows the float to open the float valve a little more without removing a lot of balsa which might have made the car run slobbering rich at idle

again.  

 

Pictures of the finished carburetor ready to go back on the car.

 

 

This cute little bracket was missing from my car, another item I spotted on Dave Dunton's original car.  I was going to buy an old rusty one on E-bay but finally decided

to make one.  It attaches the center screw stud on the air cleaner assembly on one end and to a diverter valve mounting stud on the other to support the cantilevered

weight of the air cleaner so inertia loading on rough roads didn't cause the pot metal air inlet to snap off and deposit the air cleaner on the top of the road splash pan.

 

This is what all that stuff looks like on the car and working correctly.

Edited September 18, 2022 by Str8-8-Dave
Arrange pictures, captions (see edit history)

[Mark Shaw]

Dave,

    Excellent photos and descriptions...  Great Job!  Do you happen to have spare pot metal levers that operate via the hand throttle linkage rod?  Mine were broken and I would like to cast some aluminum replacements. 

 

[Str8-8-Dave]

On 9/19/2022 at 11:57 AM, Mark Shaw said:

Do you happen to have spare pot metal levers that operate via the hand throttle linkage rod?

Mark- sorry to say I do not have a spare set.  I had to transfer parts from the black hybrid riser to the correctly sized riser.  You might check with Rand Broadstreet at Vintage Carb.  He sold me the trashed riser I cannibalized to get the linkage parts I have.  Last I knew his e-mail was BROADSTREETLTD@msn.com  

 

Dave

Edited September 21, 2022 by Str8-8-Dave (see edit history)

[Str8-8-Dave]

On 9/18/2022 at 4:45 PM, Str8-8-Dave said:

The last drivability item I'm working on is engine vibration.  I first thought the vibration might be wheel balance but where I noticed originally the vibration started at around 35mph in third gear I have now found the same vibration starts at about the same engine rpm in second gear or first.   That isolates the vibration to engine.  The first thing I will check is points synchronization.  Up to now I have relied on static timing, engine off, volt ohm meter check of point opening at 11-degree BTDC cylinder 1 timing mark and again 90 degrees later, cylinder 6 at the Syn6 flywheel mark.  My next move will be to verify or correct the initial timing and synchronization with a stroboscopic timing light while the engine is idling. 

So I worked on the points synchronization theory last night and today.  I dug out my old Mac Tools inductive timing light which I haven't had out of the box in a few years.  I had actually been looking for a new timing light for use on 6-volt systems and found none I thought were worth spending money on.  Lo and behold my Mac Tools light is switchable between 6 and 12-volts.  I hooked up the light, opened the flywheel timing cover and warmed the car.  After it was warm enough to come to a good slow idle I tried to check the #1 cylinder timing to the 11 degree flywheel mark and quickly discovered I couldn't see it.  I tried again on #6 cylinder where you would expect to see the Syn6 mark appear and I just couldn't make out the mark.  I shut the engine off, removed the distributor cap and used the electric starter to rotate the engine watching the rotor approach #1 position, then used a screwdriver to pry on the ring gear teeth to finish aligning the 11 degree mark.  I found an old bottle of white Testor's plastic model enamel and a very fine artist brush and added a white line right over the timing mark, then repeated the exercise for the Syn6 mark.  That paint was so old I decided to call it a night and let the stuff dry.  This afternoon I warmed the engine up, got it idling slow and tried to see the timing marks again.  On the #1 cylinder I got a nice white line in the timing window about half the distance from the center of the window to the bottom edge of the window opening.  That indicates #1 cylinder is probably advanced 2-3 degrees more than 11 degrees which is probably just fine.  I moved my timing light to the #6 cylinder wire and saw as close to an identical image as I could judge, white Syn6 line about halfway between center of the timing window and the bottom edge.  I decided to leave the timing set just the way it is, everybody seems to think I should advance the timing beyond the factory starting timing anyway and so it is a couple degrees advanced.  Assuming the original springs and advance limit holes produce the specified full advance timing I would have had 34 degrees total at factory initial timing.  If I have 36-37 degrees total with the slightly advanced timing I doubt that is too much for the low compression lump running Sunoco ethanol free 89 octane off-road fuel.  

 

On the one hand I feel good that the strobe timing light confirmed my static points timing and synchronization to the letter.  That timing was done with engine off, condenser and coil disconnected from the points circuit, first at the 11 degree mark, then at the Syn6 mark with a Fluke volt/ohm meter across each point set.  I'm also very happy with my carburetor job, there is no throttle hesitation and the car will idle right down reliably.  The car runs really well.

 

On the other hand I'm still trying to find a source of vibration that appears to be engine related.  I'm not going to pull the head to make this next check, but I want to know if this engine is running stock iron pistons or if they were replaced with aluminum slugs.  I will probably remove a couple of spark plugs and either stick a magnet thru the plug hole to see if pistons are magnetic or maybe use a bore scope for a look-see.  If they are aluminum they are probably lighter than the iron pistons and if no attempt was made to balance the rotating mass to accommodate the lighter aluminum pistons that may explain why it vibrates a little.  If anyone else has an idea feel free to chime in.

Edited September 21, 2022 by Str8-8-Dave (see edit history)

[Mark Shaw]

15 hours ago, Str8-8-Dave said:

You might check with Rand Broadstreet at Vintage Carb. 

Dave,  I called Rand and no luck.  He only makes the float bowl covers for Marvel carbs.  Any chance you could send photos and dimensions so I can cast my own in aluminum?

Thanks,

Mark

[Str8-8-Dave]

4 hours ago, Mark Shaw said:

Any chance you could send photos and dimensions so I can cast my own in aluminum?

Thanks,

Hi Mark- You just want info on diecast parts correct?  I will take pictures and mark them up.

[Mark Shaw]

18 hours ago, Str8-8-Dave said:

You just want info on diecast parts correct?

Yes, thanks...

Mark

[Str8-8-Dave]

On 9/21/2022 at 11:58 AM, Mark Shaw said:

Dave,  I called Rand and no luck.  He only makes the float bowl covers for Marvel carbs.  Any chance you could send photos and dimensions so I can cast my own in aluminum?

Thanks,

Mark

Ok Mark- this is how I spent my summer vacation- pictures and drawings of the riser warmup throttle linkage parts.  If these are hard to read after you download them PM me your e-mail address and I will send the scans to you.

 

Cheers-

 

Dave

 

The "0deg" line is a reference line drawn at right angles to the flat at the bottom of the throttle shaft hole.  The cast rib and

centerline of the hi speed needle lever on the right side of the picture is 94 degrees from the reference line.  The warmup 

throttle lift pin is 192 degrees clockwise from the reference line and the setscrew boss is 328 degrees clockwise from the 

reference line. 

 

Besides being turned sideways by the AACA web gremlins the center to center distance from the throttle shaft hole to the

warmup throttle pin is hard to read.  It is .625"

 

The high speed needle stud on the left side of picture is a separate steel stud with a rivet shaft that was installed in a hole in the lever and set on the back side.

The set screw hole is 1/4-28 thread.  The warmup throttle lift pin on the right side is cast integrally.

 

 

Edited September 24, 2022 by Str8-8-Dave (see edit history)

[pmhowe]

Hi Dave,

Just a thought: You might want to recheck your engine mounts. A bad or a loosely mounted engine mount can exacerbate any mild vibration. I’m guessing you replaced yours, so check to make sure they are firmly secured.

Phil

[Str8-8-Dave]

Hi Phil,   I hadn't thought of engine mounts since someone else installed the engine.   I'll look into that.   Thanks for the tip. 

[Bloo]

3 hours ago, Str8-8-Dave said:

Ok Mark- this is how I spent my summer vacation-

This is indeed a top quality post, and what makes this site great. No, I don't need these parts, but If I could paste more than one thumbs up on this I would.

[32buick67]

Mark,

Not sure exactly what items you need, but here might be some additional helpful clues to the hand throttle system.

 

https://1933buickregistry.com/products/1932-1935-buick-throttle-control-lever-204

 

https://www.ebay.com/itm/225010977399?hash=item3463b30a77:g:S9IAAOSw4DBilhwp&amdata=enc%3AAQAHAAAA4D6JSaQyJovZ78wg%2FxpRhvKsV1mel4aCLVFCPKIVRKB%2BFNpO9f5zMaBzfub6Qfg1c%2FmhXuPhEreSaKMolJnzAHtZcBweFQlczz51NMbmq0uKWFbM%2Fn7BOW487BG6NOVKVxAiMzAxTrstoKD3FHkLQIBN1R55U8%2B4GG%2B3pWOG0ZTGvX3SjUlWm1Cr3HLpYQuiGp0bOR6s5z1XwGzrAUbf%2FXRTrcXQUTy6cApftg%2BD0c2e2I3337cLw9wlIZTJOlGmeGbqphlooQ8EdTe2hyIXTckb8wd26xrDXfr%2BKCk9cBpX|tkp%3ABFBMlNPHne5g

 

I might have a spare Marvel #12-200 lever, but I have to check, let me know if this is something you need to get your hand throttle functioning.

 

Mario