I've got a 90's Craftsman mower with the Tecumseh Vector VLV60-502015B engine on it. It starts up with no problems, and if left by itself, will run contentedly until it runs out of fuel. If I attempt to mow with it, however, even in light to moderate lawn grass heights (3-5"), the engine quits as if you'd flipped a switch.

I first suspected the coil, so I connected a spark strobe between the HT lead and the plug. I started the engine, and the strobe indicated a strong spark. I started mowing with it, and while the engine quit, the strobe continued flickering very strong, indicating a good spark until it stopped. I thought perhaps it was losing compression as it warmed, so I ran it for a minute, then pulled the plug and tested compression. It made 90psi at 5 pulls and 120psi at 10 pulls.

I then suspected the fuel, so I removed the fuel tank and drained it through the feed tube. The fuel ran very swiftly, and the tank did not have excessive debris in it (a film of slime in the bottom indicating dust that may have been drawn in during operation). I rinsed the tank and line, then removed the float bowl from the carb.

The float bowl was full, the float (plastic) was not low and floated properly. The float needle sealed properly, and the seat and needle tip were clean. There was a very thin film of slime in the bottom of the bowl, again indicating the dust in the tank. I cleaned the bowl, then turned my sights to the carb body.

The carb body was reasonably clean, but apart from the throttle shaft and butterfly, lacks any of the adjustments of the old-fashioned cast carbs. I removed it from the engine, ran a copper wire through each of the venturi holes in the throttle bore, and blew them out with air. I then reassembled the whole carb and reinstalled it.

The engine, as before, started fine with 5 primer bulb pumps. I began mowing, and it quit. I had to prime it again to restart it (which I'd been doing before, which made me think of checking the carb), and it ran smoothly. I left the engine running in place for five full minutes, and it never had so much as a hiccup. Another attempt at mowing made it quit again. I began to suspect the governor.

I removed the engine shroud, fuel tank, and carburetor, to expose the governor linkage. Referencing the manual for the V60 (not the same engine I know, but better than nothing, as I do not yet have the manual for the VLV60), it instructed how to adjust the governor linkage. I attempted to adjust it in either direction, but either way would either force the throttle closed or force the governor up. I reset it where it was, ensured full movement, and reassembled the engine, minus the air cleaner and primer assembly (so I could watch the throttle linkage).

It restarted as fine as ever, and when I started mowing, when the engine encountered resistance, the governor moved the throttle to the wide open position, and the engine quit. I restarted the engine, then put my finger between the throttle linkage and the carb body to keep it from forcing the carb WOT again. It ran while I mowed, but then bogged under the load and died.

The blade is balanced and sharp, the deck is at an appropriate height (2"), the gas is clean and fresh, the oil is too. The plug is recent and properly gapped, and the air cleaner has been blown clean (although it manifests this problem with no air cleaner whatsoever as well). There's no apparent vibration that might indicate a partly-sheared flywheel key or a bent crank. I have not yet removed the engine head to inspect the valves, but as the rest of the system is quite clean, I suspect they will be as well. They have never been adjusted while I've owned the mower, and I'm the second owner. The mower worked fine for some time, and after this problem cropped up, the owner threw it away and I resurrected it, but cannot get past this issue.

My thoughts are these:
1) The ignition is working properly. The coil is gapped correctly, and I have a strong spark from running to stopped. It runs fine so long as it is not placed under load, does not backfire or cough out the carb, so the timing is correct. It is not the ignition.

2) The compression is good, and it holds compression for some time (although I do not have a bleed-down tester to make sure how good the valves and rings are). The airways are unblocked. It is not the air intake.

3) The fuel tank is clean and flows well. The float bowl is clean, fills properly, and shuts off properly so the engine is not flooded. The engine runs fine with governor speed control (partially open throttle plate), and when I move the throttle linkage by hand to control the engine speed, the governor self-adjusts to speed or slow the engine. However, when the governor moves the throttle to respond to load, the engine dies and the throttle is forced wide open as the governor plate falls.

My theories:
1) The carburetor still has a blocked venturi, which precludes the full flow of fuel. I've cleared the venturi as best I can, and just today put the carb body into a bucket of Berryman's B12 Chemtool carb cleaner to soak, in case there's an intermittent problem or a blockage I can't reach through one of those tiny holes.

2) The governor gets stuck while the engine slows, and forces the throttle wide open, which leans out the engine too fast and causes it to die. The governor is internal, which will necessitate the disassembly of the engine.

I would appreciate any suggestions or input that might help!

Regards,
Nick

Your problem most likely lies in the carburetor float bowl. There is a plastic nozzle that has a small O-ring around the base, this must be in good condition and seal against the sides of the opening where it sits. There is another one inside between the metering jet and the bowl body. It is located behind the drain screw on the side of the bowl. This one has a tendency to swell up and restrict the flow of fuel from the metering jet. I would recommend replacing both of the O-Rings.

Best Of Luck...

30YearTech,

I noted the o-ring at the base of the red plastic nozzle, and it does indeed seal well to its bore when it is depressed to the mounted position. I did not note any other o-rings; there is an o-ring around the drain screw on the carb, but that certainly would not hamper operation, it's plainly only there to keep the fuel in. The drain screw does press against a spring, which in turn presses against a red plastic stopper. I do not know if there is an o-ring in the bore behind that stopper, I will look tonight.

Somehow I fail to see how this would affect the engine's response under load- I can let the engine run for quite some time, plenty long enough to drain the float bowl if it were not feeding properly, and it runs just fine. It's only when it encounters a load and the governor adjusts the throttle to increase engine speed in response to the load; the throttle is thrown wide open, and the engine dies. How does this bear on the float bowl? Is there something I'm missing?

Thanks,
Nick

30YearTech,

I noted the o-ring at the base of the red plastic nozzle, and it does indeed seal well to its bore when it is depressed to the mounted position. I did not note any other o-rings; there is an o-ring around the drain screw on the carb, but that certainly would not hamper operation, it's plainly only there to keep the fuel in. The drain screw does press against a spring, which in turn presses against a red plastic stopper. I do not know if there is an o-ring in the bore behind that stopper, I will look tonight.
I am not referring to the seal on the drain screw, in fact I never even alluded to it.

The "stopper" you are referring to is in fact the metering jet(ref # 40). There is or at least should be an O-ring between this jet and float bowl body(ref # 37A). This is how fuel makes it from the float bowl to the nozzle and into the carburetor body. The O-ring between the jet and body can swell up and restrict the flow of fuel metered to the carburetor.

Somehow I fail to see how this would affect the engine's response under load- I can let the engine run for quite some time, plenty long enough to drain the float bowl if it were not feeding properly, and it runs just fine. It's only when it encounters a load and the governor adjusts the throttle to increase engine speed in response to the load; the throttle is thrown wide open, and the engine dies. How does this bear on the float bowl? Is there something I'm missing?

Thanks,
Nick

Yes, there is plenty you are missing!

The problem lies with the delivery of fuel through the carburetor, NOT to the carburetor.

The engine requires very little fuel to run with no load, and at no load most of the fuel is delivered through the low speed circuit of the carburetor. When a load is applied and the throttle opens up, the fuel demand increases and fuel will normally begin feeding up through the nozzle. If the flow is restricted beyond the demand of the engine, then the engine will simply lean out and die. Remove the drain screw, spring and main jet (ref #40), remove O-ring (ref #37A) and replace. It may look like a small flat washer with a tiny hole in the middle, but it is in fact an O-ring, just the same as the one on the bottom of the nozzle. (They are the same part number 632547)

I am not referring to the seal on the drain screw, in fact I never even alluded to it.

Whoa, whoa. No need to get stuffy here. Have a look:

There is another one inside between the metering jet and the bowl body. It is located behind the drain screw on the side of the bowl.

Without too much mental agility, I think you can see how a person who is completely unfamiliar with the carb (such as I am) might think you WERE referring to the o-ring that IS behind the drain screw on the side of the bowl, just as you said!

The "stopper" you are referring to is in fact the metering jet(ref # 40). There is or at least should be an O-ring between this jet and float bowl body(ref # 37A). This is how fuel makes it from the float bowl to the nozzle and into the carburetor body. The O-ring between the jet and body can swell up and restrict the flow of fuel metered to the carburetor.

See, THAT helps. I was completely unaware that the tiny red plastic nubbin at the end of that spring WAS a jet; I removed the thing, glanced at it, didn't even think to look in its bore, and put it back together. I had no idea how the fuel got from the bowl to the main jet bore, and was curious about that very thing. Now I know.

I've worked on dozens of carburetors in my life, and nearly all the jets I've come across have been BRASS, with the rare exceptions being aluminum. I'd never think of having a PLASTIC jet, because in my mind and past experience, plastics + gasoline = mush. Obviously I am not a plastics engineer. I know that, not including the retro steel jerry cans, all 5-gallon fuel canisters are plastic, as are many automotive fuel tanks. I just never thought of making a JET with the stuff! :lol:

I will inspect the jet tomorrow, and will fish out and inspect its o-ring. If it is indeed deformed to the point of blocking the bore, have you any suggestions on how to prevent it from happening in the future? There may not be; for all I know it's a factory-mandated failsafe to ensure owners clean the carb at least ONCE in a blue moon! :tongue: I'm looking forward to that being the culprit.

Thanks again,
Nick

I apologize for being stuffy. Your response seemed somewhat argumentative and appeared to me that you were more intent on questioning my suggestions, rather than following up on them. Based on your initial post, I made the assumption that you were more familiar with this engine and carburetor then the average, and responded as such.

This carburetor is probably one of the easiest ones to work on that Tecumseh ever used. For some reason it has one of the worst reputations. As for keeping the O-Rings from deteriorating, I don't think you can. Alcohol and alcohol derivatives are very aggressive on rubber components, it's hard to find fuel without some concentration of alcohol.

Well, I don't think that was it. I inspected the jet, and while there were a couple 'boogers' of dirt in there, none of them were large enough to have blocked the jet either individually or together. I cleaned them out, and rather than being hard, they smeared. I removed and inspected the o-ring, and it was not deformed or too soft, so I reinstalled it and reassembled the jet, spring, and drain screw.

I haven't had a chance to put the unit back together, so I will try to do so tomorrow and will post back with a follow-up.

Thanks,
Nick