221 cui stumble and backfire

[TDS]

Hi

I finally got my 1935 back on the street but only to run into at new issue :-)
The engine has had a complete rebuild at a machine shop and I therefore took time to rebuild both the carb and the dist. to make sure everything is in perfect condition.

I’m running a Holley 94 carb with 0.050 jets and a 7.5 power valve.
Idle screws are 1, 5 turn out from bottom.
Float is set 1 11/32 and float drop 1 7/16.
Link is set at standard (middle hole)

The dist. got new points, set to 0.014 and the vacuum brake has one turn in.
Timing is set by TDC on piston 1 and advanced with 2 lines on the dist. from TDC clockwise.

It starts immediately and runs perfect at idle.
But when I drive the car it will not take rpm above 40 kmt in second gear and 60 kmt in third without stumble and some backfire trough the exhaust.
Hard to say how many rpm as I don’t have an rpm gauge.

When I depress the pedal, at standstill, it’s the same rpm issue, just a bit more backfire.

I need advice - thanks

[39topless]

Even though the engine was rebuilt, your symptoms indicate sticky valves could be an issue. Have you tried dribbling some Marvel Mystery Oil down the carb at about 1000 RPM until it begins to smoke and stall? Might do the trick. You may also want to pour about 1/4 pint of the MMO into the tank with each fill up (petrol).

[petehoovie]

Make sure the spark plug wires are hooked-up correctly from the distributor to the plugs. What's the story on that 94 carb?....Rebuilt?

[uncle max]

The first backfire likely blew your powervalve.

[FlatheadTed]

Run the revs up with one wire 1/4 -3/8 from the head ,if it turns from blue to a weak yellow spark then its a ignition problem .If it runs better with your foot flat to the floor or the choke out a little its a fuel problem ,possible dirt in jets ,Pump ,or blocked line ,vacume leak .Pull the carb top to see were the level is .Ted

[petehoovie]

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Originally Posted by uncle max

the first backfire likely blew your powervalve.

Bingo!

[bullrunmotor]

I had similar problem a year ago with flathead missing under load in second and third. Turned out to be condenser. Bought a car years ago that owner had given up on fixing because of a bas miss-and it ended up being a crossed up plug wire.

[1935coupe]

Originally Posted by bullrunmotor

I had similar problem a year ago with flathead missing under load in second and third. Turned out to be condenser. Bought a car years ago that owner had given up on fixing because of a bas miss-and it ended up being a crossed up plug wire.

same here ran great at idle and just above then try to pull out into traffic and would start to misfire bad on all cylinders condenser was the problem

[39topless]

Originally Posted by uncle max

The first backfire likely blew your powervalve.

It is back firing through the exhaust.

[Mike in AZ]

did you run-in the cam and lifters??....Mike

[TDS]

Im sure the sparkplug wires are connected correct but I will check again :-)
The shop told me it was ready to go. They adjusted the lifters.
Sticky valves could be the problem - will try som MMO.
The condenser is new but I will try exchange it with my spare.
Will post update..

[colin1928]

Check for a vacuum leak

[BUBBAS IGNITION]

The 35 helmet doesnt like rpm with the large strap points and large point cam. ( later ones used individual points with small distributor cam.
I run a ton of these on a tester and they commonly just dont want to rev up much above 3000 or so without point bounce. New points with some added (bending) tension usually will fix the problem.....

[rotorwrench]

One more item that can have similar symptom is a weak fuel pump.

[scicala]

Originally Posted by uncle max

The first backfire likely blew your powervalve.

I agree, except the original post said it was an exhaust backfire. Sounds like a weak ignition problem. Possibly unburned fuel in the exhaust popping when the ignition does fire. A carburetor related issue (bad accel pump or lean condition) would pop out of the carburetor.

Sal

[sortkaffekop]

Fuelpump!

[scicala]

Originally Posted by sortkaffekop

Fuelpump!

Not for an exhaust backfire.

Sal

[sortkaffekop]

Been through same symptoms: Small bacfires and hesitation/misfiring at speed.
TDS: All parts are new or rebuildt. But what about the fuel pump?

[FlatheadTed]

A Holly 94 will not work with a 35 manifold ,due to the heat riser hole feeding exhausted into the base of the carb ,Ted

[rotorwrench]

Terminology has always been a bit off when it comes to the term "backfire". It doesn't explain whether it was a carburetor fire or an exhaust fire. The dictionary refers to both for the term but the technical definition is a fire back through the induction system. A fire in the exhaust is an "after fire". It is sometimes difficult to tell which is which unless the exhaust sound like a cannon going off.