Tecumseh help

[Steve Kraus]

Lawn Boy mower with Tecumseh 4-stroke-cycle vertical shaft engine. Primer bulb, non-adjustable carb.

I've been repairing / tinkering on mowers and other power equipment engines since I was 10; not an expert by any means but some level of experience. This has me stumped.

The engine seemed to have carb issues. It would take many pushes off the primer bulb to get it to start. Sometimes I would take off the air cleaner and shoot some gas from a spray bottle right into the barrel and then it would start easily at least for a few seconds and in some cases continue to run successfully and sometimes not. I once cut part of the lawn with a paper towel wadded into the carb to partly choke it to get the mix okay.

So I dismantled the carb for cleaning and afterwards it was a better but still not totally right. I was looking online for a carb rebuild kit when I saw I could buy the entire carb--or a knockoff--for like twelve bucks. I installed it and the engine ran well. They've dumbed the design down to where there is no more actual speed control...you bend a tab that controls governor speed tension. I did that; even used a strobe to check speed.

Used it a number of times and it was fine.

Now I cannot even get it to try to start.

My old trick of shooting in some gas did get a few partial starts but now nothing.

So...no spark or no gas, right? Shooting in some gas manually would eliminate that possibility.

So no spark?

I took it into a dark area and with the plug off but wire still hooked up and the plug grounded with a clip lead I could see a spark when I cranked the engine. I replaced the plug -- new last year -- anyway. No change.

Shooting in some gas as described does put out tiny puffs of smoke when I crank, puffs that are not there with the plug disconnected. But nothing like a true partial start. No sound other than what I make by pulling it.

I started to think there is something really unusual going on. Like a valve stuck open or something. Nope...I pulled the head and they appear to be working fine.

The only thing I can think of is that the spark is too weak. Or that the new carb is so bad that the mix is so rich that there is no way to light it off.

Before, grasping at straws and buying a new, potentially unnecessary, magneto, I think maybe I will try to give the old carb a good cleaning and put it back on.

[trader_4]

If the theory is that it's getting way too much gas, how about draining the gas or disconnecting the hose and then trying to start it with some spray ether? I had a similar experience here with my mower, spark, wouldn't fire at all with starting fluid sprayed in, etc. Finally it started and ran fin e after, I guess it was flooded. You'd think if it was flooded, the spark p lug would be wet, but mine wasn't. Cut off the gas, take plug out, crank m any times to clear it.

[Iggy]

99% percent of the time it's just a clogged Fuel Jet from debris in the gas tank, which is very easy to fix. Be more careful in fueling or add an in-line fuel filter ( Definitely, clean that before you do anything else, as I've never had to replace nor even clean any mower's carburetor and never had the magneto go bad. This is the best video that shows the simple procedure "EASY FIX! HONDA PRESSURE WASHER that will not start after storage (plugged carburetor main jet)"

[Steve Kraus]

If it's a clogged jet then shooting some gas directly in should get it to at least sputter. In the past it always got a 5 second vrooom out of it. Let's say, though, that this technique is making it too rich this time for some reason. But then crank crank crank crank crank would eventually reach the point where it is just right just for one crank and it would either vrooom or at least sputter.

But lets say the cheap knockoff carb suddenly decided to go way too rich. Then it won't do anything and shooting additional gas in will only make things worse.

On that theory this morning I opened the old carb made sure the holes at the bottom of the brass plug were clean and reinstalled it. Again...nothing. Not even the slightest hint of anything. Tried shooting gas in again and still nothing.

This makes me lean (no pun) towards ignition issues even though I could see it sparking in my test. But maybe it's really weak. That sparking was in open air. It could be much more feable in a high pressure situation. I wish there was a way to test for that.

I can try removing the carb and trying to get it to do something by spurting in a little gas or maybe put the intake tube on, stuffed with something wet with gas. Enough screwing around with it and at some point the mixture will cross into the acceptable range at least for one crank. But I'm thinking I will still get nothing.

[Iggy]

replying to Steve Kraus, Iggy wrote: Yep, you might be in the 1% and it's a bit much to type (don't worry, no tools are over $10), so here's a very good video for all of those ignition check and fix procedures "Lawn Mower Won't Start: Spark Plug and Ignition Problems"

If none of that works, then since you've been running it rich for a while or off and on, you may be dealing with the wrong end and need to torch or scrape the carbon off the muffler. Very uncommon for 4-cycles to build-up enough to choke-out the engine, but definitely worth removal from the checklist.

[makolber]

the timing could also be off..

did you hit something with the blade?

do you know about the "shear key"

mark

[trader_4]

Not to hijack his thread, but I had another thread here about my Sears leaf blower, how the carb would not pump gas. So, I too bought one of those Chinese carbs. I reported the other day how great it worked, it started on the first pull. I used it for about an hour that day it worked great. Today I went to use it again, this time it was hard to start. I finally got it to fire though, and then it ran fine again, I used it for about 20 mins. Half an hour later, it won't start!

Like Steve's this one acts like it isn't getting gas. The plug was dry, I checked it has spark. So, like Steve, I sprayed some starting fluid right into it, figuring it would at least fire on that. No joy. Tried several times, with the choke on full, half, off etc. I tried holding the throttle wide open and pulling it many times, as you'd do if it was flooded. The only thing I did to it was that when it was last running, I adjusted the idle speed screw so it idled a little faster. I even tried unscrewing that a turn, back to about where it was. The way it's supposed to start is a few pumps of the bulb, pull it with choke on full until it fires, then half choke and pull till it starts.

Finally gave up for the day. I'll let it set until tomorrow and try again. Maybe it's time for a new blower. But it's funny that it's similar problem to Steve's, even though this is a 2 cycle, different carb, etc.

[Iggy]

replying to makolber, Iggy wrote: Yep, that's at 3:38 in the video.

[Iggy]

replying to trader_4, Iggy wrote: I do question the new carb and hopefully your experience directs him to reinstalling the old original carb. I can't imagine the metal stuff being a problem, it's got to be inferior gaskets and diaphragm in your case.

[trader_4]

h-help-1151432-.htm

The mystery remains, if it's a problem with the new carb failing in just tw o days, why won't it fire on ether? Like Steve said, you'd think you'd get it to do something with that sprayed in. I'm thinking maybe it got floode d out,though at least at first the plug was bone dry. I'm letting it sit overnight, plug out, try again tomorrow.

[Steve Kraus]

I put the old carb back this morning. Still nothing. I opened it and checked it out before I did. Even if it was gunked up and not giving gas my shooting some gas in (I tried it the normal way first) should have given me at least a sputter if not a 5 second vroom.

I do not recall hitting anything that could have broken the shear key. And the current difficulties started with it not starting but still giving the

5 sec vroom after gas was shot in. It did that a couple of times and then nothing. Unless the shear key partly broke, was temporarily back in alignment and then went out of alignment again.

I th> reply> I do question the new carb and hopefully your experience directs him

[Iggy]

replying to Steve Kraus, Iggy wrote: Sounds good. Follow the 2nd video and don't take anything for granted. Just because you replaced the spark plug doesn't mean it can't be cracked or incorrectly gapped. Blow-out or Ream-out the fuel line and replace it if it has any holes or splits. Make sure the Kill Switch Cable is secure and operating as it should. It's not always easy, but it's always permanently repairable. Let us know when you find what the problem was, it's always great to hear about success and especially bizarre situations.

[Steve Kraus]

I thought I knew the answer to this but I better check: Does the terminal on the magneto get grounded to activate ignition or grounded to kill it?

I believe this is a fully solid state unit; no points. What resistance readings should I see from that terminal to ground, from the plug wire to ground, and from the plug wire to that terminal?

[Iggy]

replying to Steve Kraus, Iggy wrote: It grounds to kill the mower. Again, I've never had to deal with any of it, but according to Continuity Testing and the 2nd video (@ 2:10)...if the wire's good you won't get zeros (it doesn't matter what the numeral(s) is), if the wire's bad and needs replacement you'll get just 000's.

[trader_4]

Did you check for compression? I just did that on my leaf blower that's giving me trouble. I held my finger over the spark plug hole and pulled it a few times. I can feel a little suction, no pressure. Sounds like a stuck piston ring or worse. Should have a gauge to do it right, but mine is so bad it's obvious. At least that's the theory of the moment.

[Steve Kraus]

I wasn't really concerned about the wires themselves.

[Iggy]

replying to Steve Kraus, Iggy wrote: You may want to reconsider that.

[Steve Kraus]

I got it to sputter like it was firing on a few turns but no vrooom. I did go back to the new carb but that seems unrelated as I got it sputtering on the old as well. This is with many pushes of the primer or shooting some gas in with a syringe.

I think I will eventually need to drill and tap the intake tube opening on the block as it seems on the verge of stripping. I know air getting drawn in will screw things up but for now I am convinced that is not the issue as I do have it fairly tight and I had already put on a new gasket but now I've got sealant as well. Also, shooting several CC's of gas would richen it massively.

So someone said to check the flywheel key:

This is what I see. Is that off? And if it is is it enough to prevent operation?

I can get a new magento assembly for about $12-13. Is weak spark sufficiently likely to make that worth a try? My other mower also has a Tecumseh engine. If they are the same or similar it might be a simple swap to see if that's the issue.

[mike]

I've never seen one like that. All mine have the same width slot in the shaft and the flywheel. Yours seems off, but it looks like it was designed that way with an offset key.

FWIW, all my Tecumseh starting problems have been carburetor related. I've soaked them in carb cleaner in an ultrasonic cleaner, then put in a new kit with no improvement. Done the same a second time with no improvement.

Put Seafoam in the gas. Waited a week. Starts a lot easier. Still won't start with the electric starter, but does if I pull the rope really hard.

I have a 40 year old Briggs lawnmower engine that still starts like new. I won't buy another engine with a tecumseh carb.

[trader_4]

Looks OK to me. Did you check compression?