Engine Problem

Mon Jun 23, 2014 3:42 pm

A portion of this post is a repeat also in my earlier post.

I am having a problem with a rough running engine. . I am using a pony tank. It starts easily and idles good with almost full choke or if the idle air adjustment is fully closed, no choke. As the throttle is increased it begins to run rough unless you begin to close the choke. This continues up to about ½ throttle where you have the choke almost fully closed. (I have driven it on level ground with this setting and it runs smoothly). At this point you cannot add more throttle without it running rough and finally stopping regardless of the amount of choke. When it starts running rough I tried spraying carb cleaner into the choke and it immediately stopped running. My first thought was that it was a carb problem. I have a good stream of fuel out the bottom of the carb when I remove the plug or the main jet. I sent the carb to one of our carb gurus and it came back with several new parts. When I installed it there was no change in the way the engine operated so for now I am assuming it isn’t the carb.
As a little background info -- It is a 6 V system with a magneto and the engine was recently completely rebuilt—bored to .040, new rings, pistons, valves etc. I have new plugs, plug wires, mag coil, points, condenser, distributor cap and rotor. Nothing but the starter and the mag kill switch are wired in at this time. I believe that the timing is good. I static timed it with No 1 at TDC and No. 1 fires just as the mark on the pulley aligns with the pointer. All plugs are firing at TDC when I hand crank it. Valves were adjusted to spec and so were the points. I checked the points today but not the valves. The rebuilt engine has a total run time of only about 45 minutes mostly in 5 minute increments.

Compression results taken today with the engine warm, all plugs removed and using the starter were:
No.1 –125
No.2—140
No.3—125
No.4—140

I also used a vacuum gauge connected to the port on the manifold just above the carb.
Results are below.
Engine warm, mag grounded out with kill switch, and cranked over with the starter. Choke and throttle were closed and the idle air adjustment was closed:
Vacuum gage fluttered between 5 and 14 inches

Engine running at low idle, no choke and with idle air adjustment closed:
Gage flutters between 13.5 and 15 inches

Engine at ½ throttle and ¾ choke:
Gage steady at 8.5 inches—More or less choke engine dies.

Any suggestions as to what I should do next would be appreciated.

Glenn

Re: Engine Problem

Mon Jun 23, 2014 4:11 pm

Glenn, with what you have described you still may have a carb problem. There are tiny holes in the veturi that may be clogged. also just because you are getting a good flow of gas out the metering jet doesnt mean it is getting to the intake. I have also had similar problems. It turned out to be a bad coil in the magneto. First if it were me I would look deeper into the carb. Check for worpage where the two halves of the carb mate and also where the carb mounts to the intake.

Re: Engine Problem

Mon Jun 23, 2014 4:25 pm

I agree with Clark, sounds like plugged galleries or orifice within the carburetor. Try a can of carburetor clean in the gas tank. Might work, might not.

Internet search for "vacuum gauge reading chart". The charts will provide a better indication on the problem. Check to see how fast the flutter occurs.

Re: Engine Problem

Mon Jun 23, 2014 4:28 pm

Glenn, you didn't get your carbs mixed up, did you? :lol: :lol: :lol: Sounds like the "Stump the Experts" one.

Re: Engine Problem

Mon Jun 23, 2014 4:46 pm

Bighoss,

This is the carb that the experts had working well at the Bash. You are correct in that the tractor is acting just like the one at the Bash did with the Haunted carb on it. I am beginning to think that it is me that is haunted.

Glenn

Re: Engine Problem

Mon Jun 23, 2014 6:21 pm

Clownfish wrote:Engine running at low idle, no choke and with idle air adjustment closed:
Gage flutters between 13.5 and 15 inches


Sounds about right for running a belly milker :)

Re: Engine Problem

Tue Jun 24, 2014 12:00 pm

Definitely not getting enough fuel to the cylinders.

You've got plenty of compression and plenty of vacuum.

Fuel to the bowl is only part of the equation, and that's what you confirmed by opening the carb drain. The carb has some internal passage blocked.

Re: Engine Problem

Tue Jun 24, 2014 4:25 pm

Clownfish wrote:This is the carb that the experts had working well at the Bash.

Was this carburetor working well on the tractor in question at the Bash, or on Bill's tractor?

Re: Engine Problem

Tue Jun 24, 2014 8:02 pm

Don,
This carb was working well on the "TEST" tractor at the Bash. When I got home my Cub wouldn't work with it. It acted very similar to the "Mystery" carb on the test tractor at the Bash. I opened it and filled the bowl with alcohol and noticed that it was leaking a small amount at the bottom of the feed tube (Discharge Nozzle). The threads that the feed tube screws into were damaged and it could not be tightened. The leak was so small that I didn't think it was the problem but I wanted to make sure. It now has had a Helicoil installed and no longer leaks. My tractor just won't run with it and that is why I think there may be some other problem. It worked on the tractor at the Bash and won't work on mine. I have ordered a new (rebuilt) carb from McDonald's and hope to have it tomorrow. If it doesn't work I"ll have try harder to find another source of the problem.

Glenn

Glenn.

Re: Engine Problem

Wed Jun 25, 2014 12:24 pm

I have the new(Rebuilt IH) carb from McDonalds and with it on the Cub it runs basically just as it did with the other carb. At idle runs well with no choke and idle air adjustment open only about 1/4 turn. Any change from this setting requires more choke. Increasing engine speed results in rough running engine unless more choke is added until you reach a point that increased choke doesn't help and increasing throttle results in very rough running until it dies. Same with both carbs. With the new McDonalds carb I may(?) be getting just a little bit higher RPM before it dies and one time it backfired before just before quitting. The plugs are slightly wet with black oily residue after running a short time. I assume that this is due to having the choke almost closed while running. I have tried to make sure that all passages in the carbs are open.
Could it be a timing problem? I have checked , checked, and then rechecked the timing numerous times. I static timed it and the mag fires just as the notch on the pulley aligns with the pointer when hand cranking. I also checked the spark plug and NO. 1 fires when the pointer and the notch align when hand cranking and I have confirmed that it is on the compression stroke. When I was installing the governor I had trouble making sure that the gears meshed so that the marks (dots) lined up since it was hard to see. It was possible that I was off by one tooth but when I static timed it and got it to fire just as the pointer and notch on the pulley were in alignment I assumed that everything is good. Is this correct? The only thing that I know to recheck that I haven't already rechecked at least once is the valve adjustment.

ANY suggestions will be appreciated.

Glenn

Re: Engine Problem

Wed Jun 25, 2014 1:07 pm

Magneto. Do you hear the magneto's impulse coupling click when cranking over the engine?

Timing light and external battery, you can check to see if the "advance" is working.

One or two notches in the pulley?

Two spark plug wires on wrong spark plug?

Timing light on each spark plug, looking for misfires.

Checked for air leak between intake manifold and block.

Vacuum gauge tests to help identify the problem.

Probably my best suggestion. Trailer the tractor to a Cub fest and have the guys check it over. Several hands on folks, much better than making a written guess.

Compression test results?

Re: Engine Problem

Wed Jun 25, 2014 2:00 pm

Eugene,

Answers to some of your questions. (How do you paste from a previous post to show that you are addressing an item from that post?)

Magneto. Do you hear the magneto's impulse coupling click when cranking over the engine?
I do hear the click from the impulse coupling and get a bright flash on a spark plug tester plugged into the coil each time it clicks


One or two notches in the pulley?-----One notch on pulley.

Two spark plug wires on wrong spark plug? Timing light and external battery, you can check to see if the "advance" is working.
I do not have a timing light but I am looking for one. Any suggestions on one that would be appropriate for a cub with magneto and not too expensive? I believe that all spark plug wires are on the correct plug. I have checked numerous times hoping this was the problem.

Timing light on each spark plug, looking for misfires. I have used one of the spark plug tester lights and it appears that each is firing.

Checked for air leak between intake manifold and block. Sprayed carb cleaner around manifold and used propane from a propane torch and got no indication of a leak. Also see vacuum test results.
Vacuum gauge tests to help identify the problem.

I used a vacuum gauge connected to the port on the manifold just above the carb.
Results are below.
Engine warm, mag grounded out with kill switch, and cranked over with the starter. Choke and throttle were closed and the idle air adjustment was closed:
Vacuum gage fluttered between 5 and 14 inches

Engine running at low idle, no choke and with idle air adjustment closed:
Gage flutters between 13.5 and 15 inches

Engine at ½ throttle and ¾ choke:
Gage steady at 8.5 inches—More or less choke engine dies.


Compression test results?

Compression results taken with the engine warm, all plugs removed and using the starter were:
No.1 –125
No.2—140
No.3—125
No.4—140

Probably my best suggestion. Trailer the tractor to a Cub fest and have the guys check it over. Several hands on folks, much better than making a written guess.
Agree 100% but since I am located in South Alabama I probably won't be able to bring it to a Cub fest anytime soon. If I don't have it fixed by the next DSCF I'll have it there since it is with in about 3 hours of me. Hope I don't have to wait that long .

Thanks for the suggestions.

Glenn

Re: Engine Problem

Wed Jun 25, 2014 4:46 pm

Clownfish wrote:Any suggestions on one that would be appropriate for a cub with magneto and not too expensive?


I have a cheapo Equus one that I got as part of a set of "diagnostic tools" from Pep Boys that works well enough for me. I think the whole set was about $30 on sale - also included a vacuum/fuel pressure gauge, compression tester (only a rubber plug, tho) and a remote starter switch.

It's designed for 12v, but bright enough even when connected to a 6v battery as long as there's some shade.

Re: Engine Problem

Wed Jun 25, 2014 7:24 pm

Glenn, sorry to hear about your problems. Have you considered changing the plugs again? It is rare but I've had plugs quit before, even bad ones out of the box. D21 is a bit hotter. Does the misfire or rough running happen only at higher RPM and does it start before or after the engine is warmed up? If it's after warm-up, could be something going on with the coil (I think you said you put in a new one). Last, look closely for any breakdown in the insulation of the wires in and around the coil and any connections that could be jumping to metal. Have you tried to run it at night in the dark without any lights around? Could be fire leaking to ground at the higher RPM. I had this to happen once on an auto distributor ignition. The insulation was bad on the wires and when the distributor moved to advance the spark I could see it arc to ground. I realize this is a rare situation but something else to check. Good Luck. Stan

Re: Engine Problem

Wed Jun 25, 2014 9:26 pm

Clownfish wrote:........ (How do you paste from a previous post to show that you are addressing an item from that post?)......

Click on quote in the corner of the post you are wanting to quote. The whole post will be copied into the "typing box".
You can delete parts of it as I have done here so the whole thing isn't repeated.
You can also break it up into parts with a little cut and paste work. Each quote starts with (yes, it's mispelled so it will show up and not actually be a quote :wink: ) [qwote="Clownfish"] and ends with [/qwote]

If you put some space in between sections and add the appropriate start and end quote (copy and paste) you can respond to each individual question.
You can also take out extra space and start your response right after the quote or on the next line.

You can also quote from different people in the same response. Just place your cursor where you want the next quote to go and scroll down to their post and hit quote. It will appear in the "typing box" where your cursor is.

Hit preview before submitting to make sure it all looks the way you want. I have several times on this :D

Edit for spelling. (I should have previewed it one more time :lol: )