VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1929-1932 1931 Chevrolet Plugs, Timing, MPG

been helping a friend with his 1931 2 Door Sedan. he called me this weekend said he left his neighborhood and the car died. after going through a few things, i asked him to physically check the fuel tank with a stick or something that would reach the bottom of the tank, and guess what NO fuel.

he said he averages about a 100 miles on a tank. it is a stock 1931 and has Autolite 386 plugs, last time i was there i did check them. they were a little black and all were gapped right around .25" car fires right up every time, runs fine, not a hitch. points look great, distributor cap is like new. i did not adjust or tweak anything bc of it running and starting without a hitch. one of his old timer friends did the last tune up years ago.

based on his estimated traveling, which is usually around town 25-40mph stop and go, he is getting around 10mpg. is that acceptable or should it be better ??

should i do a complete check and regap the plugs, points, tweak timing ?? or let her ride...

Hello BearsFan315,
Bill Barkers www.1931chevrolet.com should help you with preferred settings. Home page-recent updates-Feb 2011 sort by category(HERE). Read the discussion of original versus preferred tune-up settings.

10 mpg is low. Most get 15-18 mpg at 30-40 mph. Some a little better. We gap the spark plugs 0.040" with modern coil and advance the timing 2-4 deg. That compensates for the higher octane rating and ethanol in the mix. I also run some Autolite 386 plugs in some of my early sixes.

on my next trip out i may take my timing gear

see where it is running

also check the point gap

may also take my rpm took to see where it it running at idle

he does not want to tweak it as it runs fine, but if we can make it run better then may be worth it :)

well around Thanksgiving i called my friend to see if he had been driving his Chevrolet, as we had completed his punch list of items including got horn working, new exhaust, fixed hinges, handles, and other things.

he said he had not driven or run it since i was there that day. each day i was there, no matter what we did, he wanted to start the car and make sure it would run before i left. yes even when we installed the new horn and wires. just his insurance that everything is ok. he said he would try to get it out in the next week or two. considering that he was driving it almost every other weekend, weather dependent.

well he called me and stated that he went out and fired it up, and was letting it warm up, usually about 5-10 minutes before he takes it out. he said it just died while idling. he said he tried several times to get it to fire up but no go, even tried using starting fluid, thing.

so sunday i drove out with a few items in had to take a look. knew we need fuel, fire, air to run. checked and we had fuel, pump was pumping, carb bowl was full, jets squirting, etc... so on to fire, pulled cap and had spark at the points. cleaned them up and ended up knocking a wire loose. and found out that wire 4 was fried at the distributor end. the brass end was corroded and over have gone, covered in black, then looking in the distributor end where it was connected, it was black, all of the brass insert was gone !! also on wire 5 on the distributor end was lose. so we hunted and found a local parts store that has a coil wire we could use for a new end and replaced it, put on a new cap, reset the points gap to .018" checked all wire ends spark and cap, put a little dielectric grease on the dist wire ends (at owners request) and closed it all back up. car tried to fire, but ran really weak, was like half power, but was not missing. just very faint and blah. could not pinpoint the issue, so called it a night and drove home.

it has Autolite 386 plugs, the wires are the carbon core type 90degree galv on plug end, straight brass on the dist end. it has run fine for years, fires up and just runs and drives no issues on that end till this.

my thought is to start at square 1, do a complete tune-up. reset timing, put in new plugs, wires, cap, rotor, coil, points, points insulator. either Autolite 386 which the owner likes, or AC C-87. gap either to .040" timing to 18Deg, Points to .018" and see what happens. then tweak it as needed from there. same thing i recently did on my 1930.

First parts to replace are the spark plug wires. Carbon core wires have no place being on a 1931 Chevrolet. You need metal wire core wires!!! The resistance of the carbon cores is likely your problem. As the wires flex they create small gaps in the carbon that increases the resistance. The '31 coils don't put out the 30-60k volts like modern ignition systems so any loss weakens the spark. Coupled with 0.040" gap results in even weaker spark.

thanks chipper, that was first on the list along with a condenser. the coil did NOT look old, but not sure on its age and use. the car stays in garage, but shows it age.

Whatever you decide to change I suggest you do one item at a time so you can pinpoint the problem.

Steve... yeah i was debating if i wanted to chase the problem or just replace it and go from square 1. consider i have to order parts and it is a 2hour drive one way. would have to make sure i have all the parts in hand to do a complete job anyways. want to reduce the number of trips and the duration spent out there hunting.

he had a friend that used t maintain/service the car but passed away several years ago. also he has zero mechanical aptitude. the car is driven regularly. some changes/updates have been made over the years by others. it is running a 6v alternator vs a generator, and works great.

i would start with new wires, then go from there, but to know exactly what it was i would have to swap back the old and only have 1 new part at a time to know that was the problem. second would probably be the condenser, then coil, then plugs.

Carbon wires are a big problem as Chipper mentioned. Don’t they blame everything on carbon these days!????

ok so spent Saturday out chasing the tuning problem... ordered all the tune up parts from TFS and had them shipped to me after my last visit. i figured use what i need and he would reimburse me for the parts, and parts not needed i would pay for and keep in stock for my 1929 or 1930. packed up my pars, and a few tools and away i went.
upon arrival first task was to swap out wires, took my time and did it one by one, and then tried to fire it up, sounded like it was trying and wanted to but no luck. so did a coil swap, same ordeal no luck. decided to phone a friend and talked with Chipper about what it was doing, what i had done, etc... he talked me through the testing the ignition system via jumping the spark off the coil wire. i could barely get it to jump 1/4" and a weak spark at that. so based on Chippers insight swapped out the condenser., well so i thought. dug through my box twice and could not find one, and was thinking that i KNOW i packed everything from TFS in the box. then it clicked... TFS was out of stock said 4-6 weeks, so i was going to order one locally and pick it up like i did the coil (coil was in stock) but never did. so now we are dead in the water. luckily the number DR-70 popped in my head so i called the local autoparts store down the street from us and they said they had one in stock. so away we went. got it and got back, installed it, and you know that is an undertaking, as you got to dissemble the puzzle and put it back together in a small tight little space.in the proper order of course. luckily it was replaced some time ago and had a hex nut vs the cursed rectangle nut in there. and a small stubby wrench made life easier. also adjusted points while in there since we were messing with that area, i did bring my 29 starting crank tool so made that a lot easier to set points via turning the distributor to where i needed it to set the points. point them at .018" put distributor back together, and checked all wires, firing order, and tried to fire it up. it fired up and started after a few cycles. it was a little rough running, and was missing. was an occasional puff out the exhaust in the smooth ticking run. so killed it , trying to figure out why pulled all wires validated each one that he ends were on correctly and in the copper, and tried again, but same ordeal. intermittent miss. could not figure out what, why, so back to Chipper
after a few minutes of talking he attributed it to the .020" spark plug gap. so i pulled all the plugs, cleaned them up with some fresh gasoline and a wire brush. then regapped each one to .040" and tried to fire up, no go, so loosened up the distributor and turned it a hair counterclockwise to advance timing a tad, (remembered this from chippers discussion as well as gapping to .040" and advancing timing to 18) tried to fire and bammm fired up. it was running a little rough, so i loosened up the distributor and timed/tuned it by hand. retard till it sputters, then advance til it runs the fastest rpm, them ack off a tad. and tightened it down. let it idle and warm up, then stepped on accelerator to make sure it would not stumble sputter or die. and sounded really happy.

so out for a test drive, made him drive since he drives it all the time, usually once or twice a month. he was very very happy with it, ran smooth, and he said is was the best it ever accelerated or ran. i did call shipper back to send out gratitude and appreciation for his time and input from both myself and the owner.

so hopefully he can drive it and enjoy it now with simple maintenance. other than on the way back the horn just started blaring and would not stop, a had to get out and pull the wire to disconnect it. think it is the new horn s-wire touching the new bushing, so may need to file down the s wire ends a tad to eliminate that issue.

thanks to Chipper for all his time effort and vast knowledge as well as everyone on here, The owner is happy once again as he can drive and enjoy his freshly tuned 1931 2 door.

I was more than glad to be able to help from 1500 miles away. Keeping as many old Chevrolets out on the road is one of my goals. When you have been driving these old beauties for over 50 years you remember a few things about keeping them going.

!! Thank You !! As always Chipper, plus great to chat with you and catch up

Owner called me on my way home. I was initially concerned, but he said after i left he took his wife out for a half hour drive and not a glitch. cars runs better then it ever has, since he started driving. he can not get over the acceleration and pick up that it has now.

I am going to get him to track his mileage to see if his MPG increase, considering he was only getting 10MPG.

also seems that his gas gauge/sending unit is NOT working, the gauge always reads empty.
so maybe check out the electrical on that, starting with the ground on the sending unit as well as continuity in the wiring from the tank to the gauge.

anyway to test the gauge to see if it works, without removing tank or sending unit.

worse case, will have to get a new one and swap it out. always fun dropping a tank in these older cars.
read on a 1931 there were 2 versions on the sending unit, single & dual float, along with opening being larger on one of them requiring a custom flange to adapt.

BearsFan315, what is this starting crank tool you speak of?

the crank used to start the car by hand...

goes through the hole hidden by the fancy chromed cap bottom of radiator, into the front engine crank pulley

lol, oh ok. I thought it was some kind of hand activated starter button or something.

Ok, after reading this discussion, I did not see what the MPG should be.

My 31 Coach (garaged it's entire life and nothing EVER swapped out - 88 years and not a speck of rust) runs like a dream. But I have also only gotten 10 mpg and 100 miles on the trip odometer all the time. I have had it for 6 years and never questioned it since it runs so smoothly.

What should I be getting? (Or should I stick to "if it ain't broke, don't fix it"?)

per my understanding and the numerous discussions on here a 1929-32 properly tuned should average between 15-18 MPG

I don't know about the 29-31with the updraft carbs but on my 32 with the original carbs I could only get 10-12 MPG. Swapped it out for a later replacement and it jumped to the 15-18 that you mention. I can only guess that the updraft carbs may have been simiilar with better MPG depending on the model of the carb.

15-18 mpg with proper timing, spark plug gap and carburetor in good condition. That is starting in 1927 and continuing for many years.

What about if you forget and leave the choke about halfway out for the first 40 miles??

.....Not that I have done that more than once.

Several things happen to include, greatly reduced gas milage, fouled plugs, and build up of carbon in the cylinders. I would at least remove and clean the plugs and then go for a drive to clean up the rest of the problems.