carbon fouling and losing power under load

Joe-from-MO · Oct 9, 2014

I wasn't getting anymore hits on my last post so i thought id try a new one. My ih 674 (gas engine) loses power under load. I dis-assembled the carb and cleaned it very meticulously, replaced seals and re-installed. No change. I tried pulling the choke out a little when it was acting up but this only made it worse. I cleaned out all the fuel line, all the fuel screens, and even pulled the ports off the bottom side of the fuel tank and cleaned anything out that may have been inside of the tank. Still no change. The tractor idles pretty good and starts up easily. I've noticed a little more black smoke coming out the exhaust than normal and the plugs were all black and sooty. I replaced the plugs but this didn't help. Any more ideas would be greatly appreciated. Thanks all.

Bud Tierney · Oct 10, 2014

Not familiar with your 674, so don't know if it has any model idiosyncrasies, so will say, in general:
Black smoke (gasoline engine) means too rich---this matches both that choking makes it worse and the plugs being black and sooty (your new plugs should be the same now or soon)...
But Steve has a point: if you have ignition problem where spark intensity falls off at higher RPMs, could be case of weakened spark not buaning all fuel completely and exhaust looking too rich...
Suggest you post this on IH forum here and/or IH tractor website (redpower??) where more people familiar with your engine might see it...Good luck.

RBoots · Oct 10, 2014

Had a problem similar to that with mine, would
idle good, but not rev up. Maybe yours doesn't
have it, but on mine it was the electronic fuel
shut off was failing and sticking half open and
choking off the fuel supply. Depending on which
carb you have, both of the 674's on our farm
have Marvel-Shebler carbs on them, but the
other one, before we got it, had managed to get
a a piece of wire through the hole in the fuel
shutoff near the needle, preventing it from
closing. On the other one, I needed to use the
tractor, and I had another Marvel carb with the
adjustable main jet needle on the bottom of it
and screwed that in where the fuel shutoff
solenoid goes. Works fine, I think the main
reason for the fuel shutoff solenoid was to
prevent dieseling when the tractor was shut
down. As a matter of fact, I still havent changed
the Marvel jet out on our one tractor, works
great, just havent thought about it, and I have
more important things to fix, so it will probably
stay that way for a while longer lol. Ross

David G · Oct 10, 2014

timing could be slow.

Steve@Advance · Oct 10, 2014

Sounds like running too rich on the main circuit.

Have you tried disconnecting the air filter from the carb? Could be a restriction in incoming air.

Is the main jet adjustable? If not, sounds like somehow there is excess fuel getting by the carb. High float level, clogged air bleed, cracked housing, missing drill port plug, etc.

Does this have points? If so check the distributor shaft bushings for wear. Also check the centrifugal weights, be sure they are free and working.

D beatty · Oct 10, 2014

Have you checked to see if you have weak spark ?

old · Oct 10, 2014

Black smoke says it is running way to rich. When was the last time you serviced the air cleaner it could be clogged up. Or the main jet is set to rich if adjustable

Joe-from-MO · Oct 10, 2014

I checked the spark and it seems good. I guess. It jumps a good 1/4 inch or so. My carb is the zenith carb and as far as i know there is no adjusting the main jet. The shut off solenoid has been removed at some point before I owned it and they put a hex head bolt in place of it, but from what i can tell the function is off or on so the bolt should suffice. I haven't really run it long with the air cleaner off so I'll give this a try. Could the timing be off? I heard that on front mounts this is almost never the case but what should I look for? Is it a matter of pulling off the head and measuring tolerances or can I check with a light? Thanks alot for all the input. I really appreciate the help!

Joe-from-MO · Oct 10, 2014

Ok here is an update. I thought i looked the plug wires over well but obviously i didn't because as i pulled #4 for the second time i noticed as i pulled the boot back a little that it was corroded pretty badly. So know i'm off to get some replacement wires and hopefully this will solve the problem.

RandyB(MI) · Oct 10, 2014

I would have to agree with the guys pointing to weak spark. You have the right amount of fuel , it just isn't burning it. Just because a plug / wire will fire outside the engine or even at idle doesn't mean it will when rpm/fuel/compression pressure increase. I had a PT Cruiser that started / ran and drove perfectly unless you pushed it to the floor to accelerate fast and it would fall on it's face. Checked a million things. Finally replaced plug wires and cured it completely. Accelerated like new. Points/CONDENSER/cap/rotor/wires and maybe even coil. You can't burn all the fuel without spark. Stuck open float/needle valve is about the only way you can "overfuel" a gas motor. (that would show up more at idle)

carbon fouling and losing power under load

Joe-from-MO

Member

Bud Tierney

Member

RBoots

Well-known Member

David G

Well-known Member

Steve@Advance

Well-known Member

D beatty

Well-known Member

old

Well-known Member

Joe-from-MO

Member

Joe-from-MO

Member

RandyB(MI)

Well-known Member

Similar threads