Backfiring through Carburetor

[Phil Simmons]

Hello to all....

MH T0-35 (4-cyl gas) was running when it was parked. It hadn't been used much this summer..no rain. Anyway, it wouldn't re-start later the same day it had been used. It hadn't been tuned in a long while, so here is what has been replaced / checked:

New Points set at .015 gap
New condensor (double checked wire connection, not grounded)
New rotor
New dist cap
New plugs
New coil

I am getting a nice fat blue spark from each of the 4 plugs, and no visible arcing of the plug wires.

On the other side of the block, I took the carb off, removed gaskets and let it soak in carb cleaner for a few hours. Blew carb cleaner thru the ports, blew brake cleaner thru the ports, and ran small copper wire thru each the ports / jets, etc. Checked float level, and it was already at 1/4". Carb was re-assembled with power jet screw seated then backed out by 1.5 turns...same with idle jet screw. I drained the gas tank, and put 2 or 3 gallons of fresh fuel. I am getting plenty of fuel from the carb bowl drain, and all seems to be in good order.

BUT SHE STILL WON'T START !!!! ARRRGH !!!

While cranking it, it is "popping" / backfiring through the carburetor pipe, not consistently, but fairly regular. (I have top part of air tube disconnected from air cleaner).

Only thing I haven't "messed with" is the timing, which I figure shouldn't be that far off, since it was running fine when it was parked. (?)

Anyway, I know I am missing / overlooking something, otherwise it would be running by now

Thanks in advance for any assistance you can provide.

Phil

 

[old]

Intake valve maybe be stuck and or the carb is set way to lean or you missed something in the carb making it lean also.
Hobby farm

 

[Don_G]

Phil,

This sure sounds like a timing problem. Have you checked that the plug wires are in their proper places on the distributor cap as per the firing order? You can check that the rotor is on #1 cyclinder with the #1 piston at just before TDC on the compression stroke.

Don

 

[Anonymous-0]

Clean the plugs, turn off the gas and see if it will start by squirting starting fluid into the carb.If it runs ,you have a carb problem.If it backfires through the carb, check the compression on each cylinder for a stuck valve.

 

[Anonymous-0]

Your point gap is too small. That changes timing. Should be .022" according to my MF-135 manual.

Timing should be 6 degrees before top dead center at slow speeds. Should move to 30 degrees before top dead center at 2000 rpm.

Plugs should be gapped at .025"

Check the centrifugal advance to see its not stuck advanced. That also upsets the timing.

My manual says idle screw open one turn, then adjust until it idles smoothly when warmed up.

Main jet starts 1-1/2 to 2 turns open. Set by "quickly moving the trhottle from ideel speed to full-open position. Open the jet until it accelerates smoothly. I open it a little more when plowing for maximum ground speed. I get a little black smoke but more power running on the rich side.

Gerald J.

 

[Jerry/MT]

You"ve changed a bunch of stuff and trying to sort out the problem is going to be time consuming.

You could have a timing problem, firing order problem, and/or a mixture problems. You say you have the requisite FAT, BLUISH-WHITE SPARK, so maybe we can assume the primary ignition circuit is up to snuff. (Are you sure the point gap is 0.015" ? I would have thought it was around 0.022" like the other Continentals.)

Check your firing order (1-3-4-2) and check your timing statically. Rotate the engine til you can feel pressure on your thumb from the #1 spark plug hole. This assures you are on the compression stroke. Now hand rotate the engine to the correct timing. Remove your distributor cap and make sure the rotor is pointing near the #1 spark plug terminal. If it is, put the cap back on and loosen the hold down bracket for the distributor. Turn on the key, put a paper clip or a bent piece of wire in the #1 plug boot, hold it near a good ground, and rotate the distributor slowly back and forth til you hear the spark snap. At that point you are statically timed. Do it a few more times to make sure that you have it right, then tighten down the distributor hold down clamp. Again verify that you have a FAT, BLUISH-WHITE SPARK. Then try a start. if it starts let it warm up and then check the timing again with a timing light and check the advance mechanism for function by advancing the throttle and noting the spark advance as the engine speeds up.

Reseat the power jet screw lightly and then turn it out 1-1/8 turns. reseat the idle jet and reset it to 3/4 turn. Accelerate the engine from idle to part power. This should occur smoothly with out hesitation or coughing. If it doesn"t open the power jet another 1/8th turn and repeat the accel. Continue until the engine accelerates smoothly.

 

[Kevin 600]

Phil:

Had the same problem with my 56 Ford 600, new points, rotor, cap and wires. My firing order for this tractor was 1,2,4,3 I had read on a forum that you ran the wires counter clockwise on the distributer cap. Had the same symptons, back firing through the carb etc. I'm a little embarassed to admit they should have been wired clockwise on the dist. Runs fine now.
Hope this helps.

 

[Anonymous-0]

The Z134 used in the TO35 the distributor turns conterclockwise if the wires are in the cap clockwise the numbet 2 and 3 wires will be crossed. If you are sure you have the number 1 plug wire in the right hole in the cap for number 1 If these things are not causing your problem then it is time to take a look at the valves. hope this helps some. If I can be of further email me
Big Deans Massey Ferguson web site

 

[Phil Simmons]

Thank you all for your ideas and suggestions.

Jerry/MT, you are right, a lot has been changed out, but it was somewhat methodical. I would change out a component, check for it to start, then proceed to the next item, like dist cap, plugs, etc. I always work on plug wires one at a time, so as to not mess up the firing order, but I am going to follow your advice and check it tonight. I set the point gap at .015" based on my parts supplier advice. I"ll go to .022" and see what happens. If that doesn"t do the trick, I guess I"ll try different mixture settings.

Again, many thanks to all for your help and advice. I"ll let you all know what it was when or if I ever figure it out !

Phil

 

[Phil Simmons]

Well, it would sure seem as though I"ve tried everything, with not much change in its behavior...still popping back through the carburetor while cranking....and not starting.

I changed the point gap to .022" and attempted a start, still acting the same way. I checked the firing order (counter-clockwise) and number 1 is firing on the compression stroke. Still have a good strong spark from each of the plugs, but when I pulled them out to check each of them, they each were somewhat "wet" with a black, almost oily residue on them, but they were still sparking strong. Wiped them clean and replaced, but still no start. I seated the jet screws and backed them each off by one turn only and attempted to start. At this carb setting, there was no popping while cranking. Incrementally opening the power jet by 1/8 turns, it started popping again at about 1 3/4 turns open.

It sure seems as though this would have been a simple fix, seeing how it had been running fine when it was turned off last time. It"s hard to think it is in the valves or jumped timing given that it ran fine before.

Anyway, thanks for all your suggestions and advice.

Phil Simmons

 

[Don_G]

Hi Phil,

Somewhat frustrating eh!
Back when I owned a repair shop my mechanics used to say if a gas engine has compression, fuel and the proper spark it will run. Have you checked the compression?

Don

 

[Jerry/MT]

Have you actually checked the timing? You said #1 is firing on the compression stroke but it actually must be firing at 6o BTDC or something to that effect. You really need to verify that your timing is correct as I suggested in my earlier post.
If your plugs have a black oily residue that"s usually due to a lack of oil control by the rings. Since you haven"t been able to start it I think it maybe gas and carbon from the cylinder head.
If your timing is correct and it won"t start, then a compression check is the next thing to do.

 

[El Toro]

The point gap is .022" the timing is 5 degrees BTDC. If your rotor turns CW your plug wires should be in this order: Hal
2-1
4-3 It the rotor turns CCW your plug wires need to be in this order:
1-2
3-4

 

[El Toro]

You can check to see if the engine has jumped time
by bring No1 piston to TDC on the compression stroke. Pull No1 plug near the radiator and hold your thumb over the plug hole while some hand cranks the engine. Once you feel compression drop a large handle screwdriver in the plug hole
and watch the screwdriver rise as someone slowly
cranks the engine. When it quits rising check your timing marks and then pull the distributor cap and see where your rotor is pointing. It should be at the No1 plug tower.

Have you checked your valves to make sure they're not sticking. Check the valve lash too and set them at.017" cold. Hal