popping on acceleration

petehall · Mar 11, 2016

I have a tractor that idles good and when I accelerate ,it begins popping and backfiring
It then levels out
Does anyone know whats going on
Ive adjusted valves,rebuilt carb,and checked for vacuum leaks???
thanks for any help

Mike M · Mar 11, 2016

Sounds like it's running lean ? Richen up the load fuel mixture.

gene bender · Mar 11, 2016

I would put a timing lite on one wire at a time while increasing speed to check if spark remains constant thru the speed increase to tell you if dist is bad points ect.

David G · Mar 11, 2016

Either running lean or bad ignition / plug wires.

It takes more spark under load to overcome the increased cylinder pressures, so ignition system quality becomes an issue.

rustyfarmall · Mar 11, 2016

(quoted from post at 12:53:53 03/11/16) I have a tractor that idles good and when I accelerate ,it begins popping and backfiring
It then levels out
Does anyone know whats going on
Ive adjusted valves,rebuilt carb,and checked for vacuum leaks???
thanks for any help

Have you allowed sufficient time for the engine to warm up?

guido · Mar 11, 2016

Hello Petehall,

I second Mike M diagnosis, lean mix! Does the carb have a pump diaphram? Late timing could also be the cause, more likely the mechanical advance then late ignition timing,

Guido.

Bob · Mar 11, 2016

Unless it has a mag, he may as well check the operation of the centrifugal spark advance while the timing light is hooked up.

JOCCO · Mar 11, 2016

I agree with the others BUT is it popping through the air intake or exhaust??? It could be a valve to seat issue.

petehall · Mar 11, 2016

The tractor is MF 135
The carb has idle air mix screw and power adj screw on bottom of bowl,no diaphragm
It has a rebuilt dist. and problem was there before I changed dist.
Ive had the carb apart a couple of times and rebuilt once.
could it be the power jet wrong or damaged????
It pops when I pull the throttle back but will line out in seconds??/
Thank you Everybody for the info so far
Pete

petehall · Mar 11, 2016

Jocco
popping fire out carb intake as well as exhaust at different times????
Mainly the exhaust !!1
sure has me stumped !!!
Im leaning towards the valves as well but I need any ideas before I pull the head.
I just hate throwing parts at a problem that may be not be there.
We all know that feeling
LOL
pete

Jerry/MT · Mar 11, 2016

Fuel float level too low, mixture too lean, wrong initial timing, stuck centrifugal advance, bad spark plug wires, weak spark are a few things that come to mind..

John B. · Mar 11, 2016

I agree with Bob that your mechanical advance is not working in your distributor. The cars & pickup trucks from the 60's & 70's will back fire thru the carb when the centrifugal advance diaphram goes bad or the mechanical advance weights rust and lock up.

Steve@Advance · Mar 11, 2016

Popping out the intake and exhaust sounds like erratic spark. Spark plugs can do strange things, I've wasted lots of money and time because plugs "looked" good! Could be a loose connection in the ignition circuit, maybe vibration affecting a bad connection, corroded ignition switch, arcing points, bad condenser, bad cap or rotor, bad wires. Put an analog volt meter on the + terminal of the coil, see if there is any fluctuation of voltage. Would you consider electronic conversion?

Another possibility is vacuum leak or too lean. Easy test is play with the choke, see if partial choke improves the performance.

A steady popping out the intake, especially under load, is an indication of a flat exhaust cam lobe. Also look for broken valve springs, sticking valves, especially if there is rust or condensation in the valve cover.

Donald in MN · Mar 11, 2016

check the intake manifold gaskets could be making it run lean

LarrySTN · Mar 11, 2016

When it starts popping pull the choke part way out, if that makes the popping go away, you probably have plugged transition ports in the carb or the load mixture is too lean. Popping like you described usually indicates a lean mixture. Leaking manifold gaskets or valve problems show up at idle rpm before they show up at more rpm.

rustred · Mar 11, 2016

most times its a worn cam lobe on the camshaft that causes popping through the carb. it is not the carb or wires or plugs. but you are not telling if this popping is from the carb or exhuast. and when you adjusted the valves did you check the lobe lift on the valves?

cannonball · Mar 12, 2016

petehall · Mar 12, 2016

Larry
Yes,If I pull the choke out while popping on acceleration,it lines out quicker
most of the popping coming out exhaust

Determined · Mar 12, 2016

(quoted from post at 14:53:53 03/11/16) I have a tractor that idles good and when I accelerate ,it begins popping and backfiring
It then levels out
Does anyone know whats going on
Ive adjusted valves,rebuilt carb,and checked for vacuum leaks???
thanks for any help

Sometimes the basics get overlooked.

-Double and triple check firing order, paying attention to distributor rotation.
-Plug gap
-Points gap.
-Coil polarity and voltage, ballast resistor circuit.
-Compression.
-Fuel pump, fuel filter, float level, air filter.
-A tachometer with an inductive pick-up used on each plug wire will identify intermittent misses.
-Bad fuel.

From what you write, I would lean towards it being a carb/fuel issue.
If so equipped I would be looking at the accelerator pump in the carburetor and it's linkage first.

guido · Mar 12, 2016

Hello Petehall,

A partially blocked emulsion tube would be my next guess if the carb has one, but you said you went through the carb. How about a power tuning using a vacuum gauge? If want to try that i'll post the instructions for you,

GUIDO.

petehall · Mar 12, 2016

Guido,
Im not familiar with an emulsion tube,can you describe it?
thanks
pete

petehall · Mar 13, 2016

I MAY have found the problem
I replaced the dist because of shaft thrusting too much but did not check point gap on new one
I adjusted points(they were way too close) and bingo no popping !!!!!!!
My mistake,just assumed they would be adjusted coming from a rebuild shop
Thanks for ALL the GOOD info you sent to me
pete

popping on acceleration

Member

Well-known Member

Well-known Member

Well-known Member

Well-known Member

Well-known Member

Well-known Member

Well-known Member

Member

Member

Well-known Member

Well-known Member

Well-known Member

Member

Member

Well-known Member

Member

Member

Well-known Member

Well-known Member

Member

Member

Similar threads