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After reading through the post and listening to the video it seems like there is not enough total advance. It starts real easy, almost too easy like the initial timing is set a little too far retarded, and it also seems to struggle a bit to get the rpm's up even with no load indicating there is no (or very little) additional mechanical advance.
Timing light at zero degree advance. Check ignition timing on cylinders #1 and #4. Both cylinders should fire at the TDC mark at idle and at or close to the advance mark at full rpms.
Timing light set on 180 degree advance. Check ignition timing on cylinders #2 and #3. Should have same results, TDC mark at idle and at or close to the advance mark at full rpms.
I have an excuse. CRS.
I forgot to say, if it's not getting enough total advance it will not have good power especially at higher engine speeds, but it will idle nicely and sound pretty good with no load.
if your timing was 180 it would not run at all, by the sound of it the timing is retarded / firing right at TDC,, advanve the timing till it doesnt bark so much. under a load i time cubs by ear. I advance the timing to the point where the valves ping. then back off. the further you can advance the timing on any engine the more torque developed. I have had cubs with the timing retarded so much that aluminim pistons would melt down blowing hot aluminum out the exhaust. Of course if you have cast iron pistons they would just get red hot.
Collector of Farmall cubs and cub cadets.Injoy helping people keep their cubs running. Years of experipnce.
Timing by ear. I've been told by many old timers that that's how you do it with these old 4-cylinder Farmalls.
My experience with trying to use timing lights seems to support it. The light is just all over the place...
The way you do it is advance until the tractor starts to stumble at idle, then back off until it's smooth. Ram the throttle to full and if it stumbles, back off a little more and try again until it doesn't.
Or try hand cranking it. If it breaks your arm, back it off a little more and try again until it doesn't.
I just timed mine with a light....At the TDC mark I had a slight miss right thru the 16 degree mark....I set TDC 1/4 to 1/2 way towards the 16 degree mark...The engine sweetened out and runs perfect....But the 16 degree mark stayed the same with the throttle forward....Go figure...Looking forward to hearing how you make out....Sure sounds like Eugene said, but if you've checked, you've checked....I take it you're using the distributer cap and not the plug for number one...I used the timing light between the plug and the wire on number one via the spring type connector.(I had the hood and tank off)....Good luck..Dave
In Memory of 58,286
I see in the video that it is a trimmed dash Cub? Is the serial number between 38500 and 40000?
Barn, serial # is 40230. R casting.
An update for everyone. I toyed with it a little more this afternoon. Determined to roll that distributor over and get the timing closer. And I do think I did get the timing closer. I think part of my issue was that my idle speed was adjusted too high. My digital timing light said my idle speed was around 700. I didn't think that was a big deal to have it a little high. Most folks bump their throttle up a little bit as soon as they crank it, right?
So anyway, I repeated a procedure of roll the distributor (rolling clockwise looking from seat or cap, top of distributor away from tractor) and turning the idle screw in a little. I think I quit when I was a little less than 30 degrees still to go to get to zero at idle. Which is about twice as good as it was. Still not change in power though. Tried to cut the PTO on last thing and it refused to get the blades spinning in 1st gear.
I believe the carb rebuild guidelines I read to set the idle screw at 1 1/4 turns back from all the way in as a start. I think I'm less than one full turn from being seated. It's still idling around 600 right now, quite a ways from the 475 RPM stated in the service manual. Should I worry about getting the idle down to around 500 first, and then work on the timing? Do I need to do them together? It occurred to me today that one of the reasons my timing numbers were off is that I was trying to compare an idle reading of zero degrees when my engine was turning 700 RPM.
It seems that it's going to be difficult to get it down to idle at 500 RPM. I need to go in and make sure the valves are adjusted correctly so I can be confident in this "turn until pinging occurs" timing technique. Not looking forward to either doing that with the carb still on or taking the carb off to do it. And then I've got a little oil issue I'll discuss in another thread.
Thanks for the help everyone that replied to this thread! And thanks to everybody for answering the PM's. I'm really at a tipping point of being determined to get the engine set correctly and anxious about pushing it to catastrophic failure.
'48 Cub 12V Conversion, Zenith Carb, Electronic Ignition
Compression numbers seem a little low to me. If tested wet and that's what you came up with. You need a pretty good engine to run a mower well with a cub.
Did you run SeaFoam through the crankcase and the gas? 1/2 bottle in each. Don't worry about the smoking after you put the SeaFoam in, the carbon is just cleaning up. Did you adjust the valves yet? The valve lash is important. This should also help with the compression numbers as well as power.
Idle speed can be anywhere from 400 to 700 .. some on the low side and some on the higher side. 700 rpm is not all that high so I certainly would not obsess too much on the idle speed.
That is for the idle air control - it adjusts air-fuel mixture only, and only at idle. To set idle speed, there is a screw on the throttle plate bracket.
Eddie - a 1959 International Lo-Boy named after my father in law, who who bought her new.
I did loosen the tube between the intake and the carb and slip in my Sea Foam straw. I opened up the RPMs to 1400-1500 or so and began spraying. Ofcourse gray smoke rolled out. I would spray for about 7 seconds and then it would sputter and I would have to stop for a few seconds to let it catch back up. I guess it was flooding? I mean I was shooting fuel enriched air directly into the carb. I repeated that several times until the tractor ran out of gas. Unscrewed the gas cap and sure enough, tank is empty. Didn't want to pour gas into the hot Cub, so I left it.
I think I had quit adjusting the timing when it was still about 30, and I know I have to get the timing down to zero at idle. I'll start adjusting the correct screw on the carb. I really should have thought about that. Not looking forward to adjusting the valves. Am I better off removing the carb? Or should I just work around it?
I bought a can of fuel system cleaner and oil additive while I was in the auto store today. I was looking for something that might help burn off some of the carbon that might be in the combustion chamber and maybe help with the blow by issue I may be having around the rings. Sort of a rebuild in a bottle to at least let me see what I've got. The fuel additive said to pour entire bottle in an empty tank and then fill to top. I'm thinking maybe 1/3 of the bottle with 7 gallons in the Cub tank would be right. And I guess I'll pour in the entire bottle of oil additive. It's sized for a 4 cyl engine, but I don't know if they size the bottle on displacement or oil capacity.
'48 Cub 12V Conversion, Zenith Carb, Electronic Ignition
Removing the carb will make the job a little easier. Valves are pretty simple to adjust. Won't take long at all. You'll see once you get going
Not knocking your fuel system additive, it may be just fine. But they also make Seafoam in a pour can, and I have been converted to using nothing but it. While not a miracle, I have seen it remove carbon from a Cub engine and make it run much smoother.
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