VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1912-1928 1928 motor spits and backfire through carb

Hi chaps,
i have been chasing this problem for a long time.
the car is running a Carter RAKX-O carburetor it runs
great round town or under verying load, but under a
constant up hill load I can field the power drop off
and she starts to spit and backfire through carb.
I am running Autolite 3077 plug and have read some
reports about retarding the spark and have tried that.
I have replaced the fully recondition vacuum tank
with a low pressure in line electric pump (hate to say
it from a Ford shop)still no change. The carb is fully
reconditioned new venture, standpipe and idle tube sealed
in place, plus been all rebushed. new needle valve with float
set at 31/64". Found when I had a new heat box made when
I was restoring the car they had left the baffle out between
air inlet and flexie tube to carburetor, i installed new one
car run really smoothly, but still problem there under constant load (can some one help i'm at whits end)
CHEERS
John Dix

This is exactly what happens when you go up a hill with 3077's. I was told that they are brilliant, but not for me. I replaced with 3076 and have not had a problem since. That is the first thing I would do. Purchased through E-Bay from Melbourne.Beyond that spitting and backfiring through the carburettor also means loss of fuel supply but you have a fuel pump in-line so that shouldn't be an issue.

Dixies;
It sounds like you have a very slight vacuum leak in your fuel system. Good luck trying to find it. You might want to disassemble your vacuum tank and check for debris at the bottom of the tank. I had the same problem and found rust collected at the flapper valve in the bottom of the tank.

Throw away the 3077. They are to hot and selvignite when you drive uphils and heavy load. My be the gas in US have other specification than gas in other contry. Try Champion W 16 Y or Autolite 3076

May the mixtion of gas and ethanol could be "the sinner"? The ethanol creates a higher working engine temperature. Try to fill gas without ethanol (E 0).

I have run 3077s in a couple of '28s with nary a problem. Run what ever gas comes out of the pump. Spitting, backfiring, etc. is most often too lean a mixture. With a vacuum tank you have to be aware that pushing down on the pedal past where the engine tries to pull harder only results in lower vacuum and then loss of fuel. Have helped several that had electric fuel pumps installed. Almost all have had problems with erratic engine performance. The fuel pressure is too high for the old carburetors (needle/seat designed for a couple feet of gravity flow. Pressure regulators have proven to be in reliable at the low outlet pressures required. Have one fella that has a special valve replacing the needle/seat and he has not had any problems with electric pump trying to overfuel the carburetor.

There is a BIG difference in the heat range between 3077 and 3076 plugs. If it works then by all means do it. I run my '28 engines with additional advance (enough so you can't turn them over cold without retarding the spark).

Gidday Fellas,

Is running 3077's with original vac tank set up, old glass bowl fuel filter attached to the firewall and no modern electric pump crap and I add one litre of diesel per tank of fuel to keep things lubed up a little.

The old chevy has now travelled 2500 miles (3800kms) since we dragged it out of the shed and began the restoration and it will run along the freeway and country roads at 47mph (72kph) all day.

Total miles showing on the speedo is 12,900 miles

These cars are simple machines so keep them that way, but each to their own at the end of the day!

Have a Merry Christmas

First off I've run 3077'for over 5000 miles, never missed a beat.
I've driven up the longest a steepest hills with no loss of vacuum.
It sounds to me like a small vacuum leak. there ar a number of
things you need to look at:
1 the brass thingo in the inlet manifold has no leaks, use some plumbers tape on the thread tomake sure.
2 the size of the copper line between the manifold and vac tank might be too big.
3 check that the very small pipe in the top of the vac tank isn't bloked
in the middle of the top of the tank
4 there's also a hole in the side of the top in the middle fitting where the inlet pipe goes, make sure its not blocked
5 the inner tank of the main tank has a bakelite flapper valve and if it is not seating right will cause trouble
6 make sure the top of the vac tank, with the top off is nice and flat, often they're not as the screws pull the thread up
7 the gasket in the top cover, it must be fully sealed or it will suck air, I use 2 mil neoprene and cover both sides with aviation gasket seal, the red stuff, as it stays wet.
8 at the inlet of the tank, remove the fuel line and relace with a small section of plastic tube, run that in a can on your running board and run the car for a while, you'll be able the see when the vacuum sucks up the fuel.
Get rid of the electric fuel pump as the pressure is too high, one of my mates engine bay caught fire and did many thousands of dollars to repair it becuase of the electric fuel pump.
BTW I've done 50,000 miles+ on a vac tank, and a mate has done oever 80'000 miles.
I hope one of these things help
BTW 3077's arent available any more, Austolite discontinued them.
Chris

As Maxwell Smart would say,

The old 3077 versus 3076 debate.

My 28 ran like a snail for over 30 years on W14's and 3076, changed to 3077 never looked back. But one word

Timing, Timing, Timing. Oh did I say timing?????

The Red Chev Burped, Spat and Missed in one spot on one uphill during testing. Thinking it was electrical I changed everything at least once, no success. Went back to 3076, did not miss, but power was down.

Finally in desperation, ever so slightly retarded the distributor, solved the problem, and this became the new fully advanced position.

Grant And I did a similar thing for Monty, same result.

Every engine though the same can behave different, fuels are different in other parts of the world etc.

So if 3077's or W89's are not for you, don't whine and moan, suck it in, try another combination till you get it right.

Don't throw away the 3077's if they don't work for you, send them over here to OZ, we will have them, as they are now out of production.

Have a very Chevy Christmas and a happy New Year.

Cheers

Ray

Hi Chaps
many thanks for your reply's. I have a set of 3076 plugs on order, sounds like where the problem is. And yes Ray I,m still going to play around with the timing as those 3077 certainly give more power.But if i can,t get it right in goes the 3076 and it looks like the 3077 have found a new home across the big ditch in Aussie. Will keep you all posted
Cheers
John Dix

Good Luck John Dix,

For what it's worth I think we only backed off the fully advanced timing on Monty by about 1/8 inch maximum (pencil line). As good as 77's are they demand 100% spot on timing. Maybe they are the Prima Dona of spark plugs. I run my ignition points at 25 thou and the plugs at 30 thou. Some State Side Chev 4 owners run plugs at 35 thou, but I have never ventured there yet.

Cheers

Ray

Thanks Ray
that's my mission this weekend. I shall follow those specs. and keep you informed
Cheers
John Dix

Hi Ray
Thanks you were wright on the money, I copied your setting and have just got back from a good hill climb and the old girl didn't miss a beat
cheers
john dix

That's Great news John,

On what plugs, 3077's?

I will be very interested to hear your reply before I post why I think some Chev 4 owners don't like the 3077's

Cheers

Ray

Hi Ray, still on the 3077 plugs and back on the vacuum tank. Hill climb was from sea level to about 1000 feet over a distance of 4 kilometer or for the USA viewers about 2 and 1/4 miles and very bendy road,she pulled bloody well in top till having to drop her down a gear.cheers john dix

Thanks John,

You have confirmed once again what I suspect is the reason why some don't "like" 3077's.

THE REASON IS ITS TOO EASY TO THROW OUT THE PLUGS AND GO BACK TO A COLDER VERSION, SUCH AS 3076 or W14, RATHER THAN TO TAKE THE TIME TO GET THE ENGINE TIMING CORRECT.

John, your Chev is now the 3rd 4 cyl motor that has had so called 3077 problems corrected in the same manner.

In the case of a "souped up" Chev 4 engine or petrol in places where Bluezone lives I have no experience.

For the record I don't need to defend 3077's as they are now out of production anyway, apart from their equivalents. My Chev 4 runs fine on them, I have 6 sets which will see me out, so I don't really give a rat's as to whether people use them or not, except to stand up and say YOU MAY BE WRONG, CHECK YOUR FACTS.

Open your minds fellas, as maybe, just maybe, there may be a better way.

Regards

Ray

Ray,
There are plenty more instances of 3077 plugs performing well than otherwise. I would not be surprised if the 3077 plugs were made again. A few years ago Autolite apparently make another run. They had been out of stock for a couple of years when they became available again. I have a few sets squirreled away also. Also have one engine running Champion W89-D plugs. Seems to run well.

Thanks Chipper,

Never got around to trying W89D, as the 3077 was always less expensive.

I hope your prediction is correct about Autolite, as they are also a popular plug for the "hit and miss" engine fraternity.

Thanks for the reply.

Merry Christmas and a very Chevy New Year.

Ray

I have been using 3077 plugs for the last 2 years in my 27 (with a 28 motor) and prior to that used Champion W16Y, I only changed to 3077 out of curiosity as to whether I got a noticeable difference in performance. Both work well and pull up a decent hill nearby in third comfortably.

On a run including plenty of hills 20 mpg. I am happy with either.

Bob

I have the A/C 'B' plugs in mine. What a differance from using 3076 or 78S plugs. They are hard to find but if you get a chance to buy them don't pass it up. They are the original plugs.

The 78S is an excellent plug of choice, PROVIDED, you are using the old plugs with the 3/4 reach. The current 78S is only a 1/2 inch reach and is not recommended.

For a 'driver', the 3077 would be the plug of choice.

The A/C "B" would be a plug you would keep in safekeeping for use in the Best of the Best judging.

Hi To you all,
Many thanks for your reply's and a Mary Xmas and new year. I shall not be changing from the 3077 until I have too, as the old girl is running so well ( Hope to do so good touring in the next couple months)
Cheers to you and many thanks for your feed back
John Dix