440 IC backfiring

[derf]

Hi All;

Trying to get the 440 out the door, Rebuilt one final and some rollers on the same side. Problem is with the engine, after 50 years who knows the history, but it doesn't want to run without some choke and it backfires like hades....especiall at lower rpms. It did get up to 2000 rpms.....

The compression is equal at about 125 psi, the distributor looks like it has new points rotor and cap as well as I looked at the centrifugal weights. In all the distributor looks great. the carb got cleaned today and looks kinda ok but I do have a needle and seat problem causing some flooding. Flooding, but the backfiring sounds to me like running short of fuel........????

For the odd moment it settles down it sounds sweet. I am thinking of a vaccum leak so I sprayed some blaster around the carb mount and manifold but it didn't change a thing.

I will be back to it in a day or two, but all suggestions are welcome as I may very well be stumped...

I read the posts often and enjoy the forum a lot. The founders and participants are to be congratulated on such a well run and easy to use site.

Many thanks ,,,,,,,,,,,,,,,,derf.......

[Stan Disbrow]

Hi,

Change the spark plugs. I've had this happen, and it's usually a cracked insulator, which is danged hard to see. They look good, but spend half their time firing to the side rather than the end. Screws up everything.

After that, check the timing with a light (which is fun because you have to scare up a 12v battery to power the light).

Later!

Stan

[derf]

Thanks Stan;

I will take your advice and pick up a pair of new plugs.

I did use a 12 volt battery for the light and set the timing full throttle with the "spark line" even with the bottom edge of the peep hole as I understand the manual to describe the setting. I will be having another go at the carb as well.

I thought 125psi was darn good compression and she chugs like a trooper without missing a beat with at certain rpm and choke half on. I think the engine is sweet, just needs some fine tuning ??? ...

Any other ideas, always welcome.........derf......

[Tigerhaze]

Hi Derf-

If it is a M-S carb, they are really finicky about the adjustment screw positions to run correctly, especially when governed under throttle. I would suggest follwoing the adjustment of the three screws (I believe they are idle screw, air screw, and power screw) in the manner and order the manual describes. Otherwise it will run rough and cut out especially when given throttle (governed).

If the needle is sticking, that can definitely have an impact. I would also check the float to make sure it is not sticking in the down (fill) position which can also cause flooding.

Just some thoughts.

[H-D]

If it's backfiring (out the carb), then I'm with you, it's lean (or the intake valves are too tight & 125 psi compression puts the lie to that). The mixing chamber/emulsion tube lower holes being restricted (among other things) CAN cause such as this. There used to be glaring warnings against cleaning fuel metering orifices with lengths of wire; I feel that with ethanol 'enhanced' gas, this page should be torn out of the manuals. I saw just today a Honda lawn equipment carburetor service sheet which depicted handled wires for cleaning jets. If needle & seat leakage was the issue, your mixture would be excessively fat & prone to 'afterfire' (old term) out the muffler due to the slower burning characteristics of a 'fat' mixture. The prior posters' suggestions are quicker & easier so....

[Gil]

The term "backfire" is used today to cover a number of different occurrences more than just its original meaning. Generally any engine combustion causing a loud ignition bang is often referred to as a "backfire". As H-D mentioned, there are common causes for backfire and afterfire and they generally relate to some problem with timing of the spark, mixture of the fuel, or seating of the valves. You seem to be well knowledgeable and on the right track if these are the problems.

I might suggest one other possibility I have seen on these two cylinders. If the carburetor is working fine but the ignition is not firing reliably, the gas does not ignite in the cylinder and the next engine cycle compresses an inordinately heavy mixture of fuel which can cause your "backfire like hades". I would check your ignition wires (switch, coil wires, distributor input wire insulator, spark plug wires, etc) and as Stan said, the plugs (I recommend Autolite 216's).

The good news is that by the time you solve this you will have replaced, inspected, and repaired all of the carburetion and ignition components on your crawler and be good for at least a couple of years. Happy Veterans Day. Gil

[derf]

I did clean up an old carb I had from 420IC and put it on as a test. I havn't had a chance to adjust it yet but it seems as though the problem still exists. Not so much now as it is not hunting as it was because the governor is unhooked. (Carb wasn't meant for this tractor).

It will not idle slow without a lot of choke and even then will not idle down without quitting.. and or backfiring. The term backfire in this case means kicking back through the carb, (point well taken Gil) And yes I did switch in a couple of used plugs I had although the ones in there look near new.

Right Tigerhaze, I am thinking that the float may have been draging on the casting causing the flooding, I'll get that carb back on soon to see if flooding is gone.

Thanks to all for the tips, I'll get her done with a bit more time, my son has a big yard up the hill to plow this winter.

.........derf........

[Stan Disbrow]

Hi,

Yep, I had some fun with a slight intermittent in my ignition switch (the ILBD) that would cause backfire and afterfire to occur at the same time! The whole intake and exhaust would load up with unburned fuel mixture at working RPM and when the switch made again.....

This does not sound like your issue now, though. Just an FYI to stick in the back of your head for another day.

BTW, some 100 low lead aviation, or 100 no lead racing, fuel is an excellent carb cleaner.

Later!

Stan

[CELSESSER]

Stan,
Not to derail the thread but when you mentioned the 100 octain Avgas it reminded me of something that I have been trying to find information about.
For my big chainsaw it is recommended to use the highest available octain gas to make the fuel mix to help keep the operating temp down. With todays crappy ethinol concoctions and the likelyhood that the premium grade of gas has probably been sitting in the tank for quite a while, I have been concidering Avgas as an option. I think that it is formulated for long storage life and has little in it to cause varnish. Does Avgas 100 contain lead and would that or any of the additives or lack thereof contraindicate mixing it with a good 2 stroke oil for use in 2 strokes?
Dealers and small engine guys here just look at you like you just escaped from the assylum. Either they don't want to think out of the box(small boxes) or they want to keep rebuilding carbs or selling new equipt each year.

Just thinking,

Chuck

[57pilot]

In aviation circles the 100 octane gas you refer to is called 100LL (LL = "Low Lead") because it has less lead than the old formulation for 100 octane. But you should be aware that "Low Lead" is a relative term since it is my understanding that 100LL avgas has about 4 times as much lead in it as the old "regular" leaded car gas (mogas) had. To the best of my knowledge, avgas does not have additives of any kind other than lead.

I haven't used 100LL in my chainsaw but I have destroyed one chainsaw using ethanol containing fuel.

[CELSESSER]

57,
That is part of the problen. In my area of the country I believe ALL automotive gas has ethanol blended, just at lower levels than E-85.
Is Racing fuel 100 octain simmilarly free of additives and lead? I know it is more expensive than avgas.

Chuck

[Lavoy]

I think 100LL is one gram of lead, 100 leaded is 2 grams, and if I remember correctly, leaded car gas was also 1 grams. It may not have been grams as unit of measure, can't remember now.
Lavoy

[Paul Buhler]

Around here the boat marinas sell alcohol free gas which is better to use in two strokes. Am I understanding correctly that aviation fuel has tetra-ethyl lead in it?

[Lavoy]

Yes it does.
Lavoy

[KenP]

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