Engine stumbling - Grassroots Tractorsports

I'm in the middle of a long, drawn out deathmatch with an older John Deere tractor.  Trying to find info on various tractor forums is challenging, so I'm going to ask more general theory questions to people who know some stuff.  Here we go...

1970ish John Deere 1020

3 cyl gas engine

It will idle just fine, but if you put it under load it stumbles really bad.

Ignition points and condenser have been replaced to fix a no spark condition.  Successful, ran fine after that, but soon started stumbling.  Fuel filter was clogged.  Replaced.  Fixed.  Clogged again.  Replaced.  Not fixed.  Still stumbling like a motherberkeleyer.  Carb cleaned and rebuilt.  No joy.  Same problem.  I need to avoid throwing parts at this and hoping it works.  This tractor needs to work and I don't have tons of money or time to get it to that point.  Exhaust is pretty black under acceleration, so I'm either getting way too rich of a mixture or ignition is screwy.

My thoughts:

It sure seems like this has to be fuel related because that's where I started having problems, but I've been through it with no resolution.  I'm going to swing by the JD dealership to get a new adjustable power jet - I don't think the needle is seating at all, so my adjustments are all out of whack, but I think it should be lean in this case.

I checked spark from the coil again, and it seems weak.  Can a weak spark masquerade as a rich fuel mixture?  I have a spare coil that I'll put on tonight, but this is driving me nuts so I had to ask.

Timing.  After replacing the ignition components, I adjusted timing by ear.  Low compression, low performance engine, so this has worked for me before but I have to question it since I'm having problems.

Valves.  I haven't touched them.  They should be inspected, but I don't really want to add variables to the situation.

I think I'm still having fuel issues, but I really want to hear if weak spark or ignition timing can cause the same problem set.  Is there anything else, probably really simple and/or stupid, that I am overlooking?  This is a ridiculously simple engine.  It should be so easy.

https://www.yesterdaystractors.com/cgi-bin/viewit.cgi?bd=jd&th=576429

do you have your timing marks set correct?  are your points set correctly?  Seems timing related..

https://www.yesterdaystractors.com/cgi-bin/viewit.cgi?bd=jd&th=78499

Fueled by Caffeine said:

https://www.yesterdaystractors.com/cgi-bin/viewit.cgi?bd=jd&th=576429

 

do you have your timing marks set correct?  

 

https://www.yesterdaystractors.com/cgi-bin/viewit.cgi?bd=jd&th=78499

These, and yes weak spark can mask as running rich. 

Lots of bad new condensers sold today. Look at your points. If they are burned already file them and try another condenser.

Thanks for the quick responses.

I don't know if the timing marks are correct.  I haven't touched anything up front or inside the engine, and it ran fine before it lost spark.  I didn't really want to yank the radiator to check timing, but it sounds like that is going to happen.

I'll check the condition of the points tonight.  I have the old condenser still as a spare.

Gap is a good baseline for points, and but dwell is really the critical parameter. 

Did you set the points based on gap or dwell?

Too little dwell  (too large of a gap) can cause weak spark, a specially as rpm increases. To much dwell (too little gap) can cause coils and points to get hot at low rpms and cause ignition problems.

Any adjustment of points will also change the timing, so reset timing after adjusting points. 

I set points by gap.  I did note that the spring with the new points was way stiffer than the old one, but it sounds like that would help this situation if anything.  Sounds like I ought to check condition of the points and then timing before doing anything else.

A weak spring will cause high rpm problems, a stiff one should be fine.

Put the old condenser back and see what happens.

New ones are turning out to be absolute garbage. MSD condensers can be added to the outside of the distributor if they don't fit inside and seem to be reliable.

Piggy-backing another one into the system will quickly show you if the current one is bad, the running will smooth right out.

I keep a known good condenser with alligator clips on it in my tool box for this reason. I even bring it on tours with me because I've had condensers go bad in the middle of a trip.

Failing that, if the system is 12v, you can use the points to trigger a Ford TFI module which fires the coil. This takes the high current away from the points and merely uses them as a switch, they last almost forever after this because they work until the rubbing block wears out. I've done this conversion a few times now.

If the condenser doesn't solve the problem, I would try adjusting the points to the low end of the spec for gap and give it a try.
 

I would also make sure the contacts on the points are meeting flat, if they contact crooked (at an edge) it can cause issues as arcing can erode the small contact  area,change your gap and/or increase resistance.  

The distributor has to come out to swap the condenser, so I'll adjust the points gap to be a bit tighter while I have it out.  The points don't meet perfectly square, but they aren't too far off.

Don't replace it then. Just connect the lead from the condenser to the negative terminal on the coil and ground the body of the condenser to something on the engine. You just need to get it into the system to test it.

This is not a suggestion that it's not the ignition stuff being discussed, but the steps you described:

1. runs good
2. filter clogs runs bad
3. replace filter and it runs good again
4. filter clogs and it runs bad
5. replace filter doesn't fix it

...make me wonder just how much crud is in the tank, and whether there's another obstruction; do these things have petcocks like a motorcycle? A junction at the tank that could catch sludge?

More simply, if you pull the fuel line off the carb and let it flow into a catch can (at about car height so you're not helping it with additional drop) does it flow strongly and not taper off? (I'm assuming this is a gravity-feed arrangement; there are presumably tests for cranking fuel delivery if it's got a pump)

In other words, you cleaned the filter and the stuff downstream, but I'm wondering about upstream. Is there a sock or other prefilter in the tank?

I have been thinking along those same lines and not making progress, which is why I started asking other questions.  It does not have a petcock.  I haven't determined if the tank has an internal filter, but I drained the tank and blew compressed air up into the tank through the fuel line.  It didn't seem to have much resistance to that.

Fuel flow from the tank is a bit slower than I expected, but it's way faster than the tractor could actually use.  It uses an electric fuel pump.  I have not checked flow after the pump because the exhaust has been pretty black.  I figure it's getting more gas to the carb than it can handle.

In other news, my wife just called me and said the riding lawn mower caught fire, so that's cool.  From the picture she sent me, it appears the only damage is the air filter housing, so not a huge deal, but the hits keep coming.

Running lean usually pops forward into the intake, or sounds like a nasal "whaaaaa" under load.  Since a tractor is lower RPM, sometimes it's hard to detect or it sounds like a gurgling or a really fast drdrdrdrdr like a tongue trill

Running rich makes misfires and pops out the exhaust

But, if you have a fixed needle/jet and it ran fine before, I don't think its the jet.  I think it's the fuel, or debris in the fuel.  Here's what I do.  Take the filter out.  Stick a hose on the shut off and open it to drain it into a gas can.  Close it. Put the gas back into the tank through a fine mesh screen funnel.  Repeat several times and you'll likely notice an increasing amount of gunk in the funnel

The other option I've done on my Puttin Johnnies is to drain the tank and let it dry out a day or so.  Then get in there with a shop vac and suck out stuff.

It's also possible that you don't have the float at quite the proper level.  I was just doing a carb for a Ford 601 Workmaster.  If you set it too low, it starves for fuel under load.  Set it slightly too high and it dumps fuel out the air horn.

Given your symptoms; runs, clogs, clean, runs, clogs, clean, I think it is  fuel issue.  Eliminate that factor and then move on if it doesn't fix it.

I owe a few people a beer.  I put the old condenser on as ShawnG suggested - attached at the negative post of the coil with the body grounded via jumper cable to the battery.  Once it was warmed up, removing the jumper from the battery terminal made it sputter and run like crap.  Reconnect and it ran pretty well.  So I pulled the distributor adjusted the points a little tighter, put in the old condenser, reinstalled the distributor... no spark.  It was dark so I called it a night.  It's really easy to accidentally ground the condenser and points connection to the body of the distributor.  I'm sure that's what happened.  I checked it with a meter before reinstalling, but my guess is pressing the distributor cap on moved some stuff around.  I'll get that fixed tonight.

It has an "adjustable power jet/needle".  Marvel Schebler carb by the way.  I think some of the internal threads are berked, not allowing it to thread all the way to its seat.  As such, I am having a hard time finding a healthy starting point for the finer tuning.  The dealership is two miles from my house.  I should just drive there and buy a replacement.  I'm not thrilled about paying John Deere dealer prices, but they'll have it on hand.

I think the float height is too high.  I just adjusted it up to match the spec (0.25" measured over the gasket) when I cleaned the carb, but it's tough to start because it wants to flood.  You have to let it run with no choke for a minute or so before giving it any gas.  This would be fine, but it's getting colder outside, and it doesn't want to do that, so you have to manipulate the hydraulics the whole time to remove that load from the system.  After it's warm it seems to run decent, but I think it's still rich.

I appreciate the help from all you guys.  We have friends getting married on our property in a couple weeks and we obviously want the place to look perfect.  No tractor means ugly property.  Our friends appreciate your help too.

bigeyedfish said:

In other news, my wife just called me and said the riding lawn mower caught fire, so that's cool.  From the picture she sent me, it appears the only damage is the air filter housing, so not a huge deal, but the hits keep coming.

Your wife mowing is a plus

With the amount of grass we have and my work schedule, if she didn't mow, our yard would be a rainforest.  Plus, I think she likes a break from the kids asking her questions all the time.  But yeah, it's definitely a plus.

In reply to Placemotorsports :

My wife appreciates the zen of making straight lines almost as much as I do.   LOL.  Put the FM headphones on, shut off brain, make yard pretty.

Glad you're making progress.

Well, I put eight or ten hours on it this weekend, and I think it's running better than it ever has in the year or so that we've owned it.  Still running a bit rich throughout the entire rev range I think, but I'm inclined to call it good enough.  Occasional misfire at high RPM with no load, but it's running really well under load.

Also, the mower is good to go.  Looks like a mouse nest caught fire and melted the air box a little, but it ran fine this weekend.

One more week of working our asses off, then we'll get to relax a little bit.  This year has really been doling out lessons in staying calm when it seems like you're screwed.

This tractor just got its first workout of the year, and it had me thinking back about this ordeal.  You guys were a life saver, and I still appreciate it.  Back when I originally posted this, we were prepping our property for a friend's wedding and running out of time.  It was a sweet relief when it started running properly.