HS-40 wont stay running

[Furious D]

I usually try to figure out these problems myself, but after 2 days of working on this problem I am stumped.


I have a early 70's HS-40 that was rebuilt around 7 years ago but never started. I changed the oil, checked for spark and put some fresh gas in it and nothing. Found the timing was a bit off so while I had it apart I checked the points and now it fires but only runs for about 10 seconds and dies.

It always fires right back up on the first pull, idles nice then dies again. If you try to give it any throttle it dies right away. I even pulled the carb off my old snowblower that runs great and it does the same.

I have also replaced the fuel line , Checked the float level on both carbs .

Any ideas what to check next? I might pull the whole ignition off the running motor and try that but for some reason I keep thinking its fuel related.

 

[roccosbike]

What year Tecumseh is it? If it has a cast iron flywheel with a plastic fan glued to it then check the magnets inside the flywheel to see if they came loose.They should have a space about a half inch between them if not theirs the problem.

 

[old-timer]

You might also make sure your gas tank is venting properly. Try running it with the gas cap off to see if it makes any difference.

 

[Bigjoedo]

Furious D,

I am not a Tecumseh expert, but I work on a lot of air cooled engines. I agree it sounds like a fuel issue or the engine would not start. Since the carb from the snow blower (that runs) it is not likely a carb issue. Did you try the HS 40 carb on the snowblower engine ? Is there good fuel flow through the new fuel line? Is something stuck in the fuel tank outlet? Did you try a new spark plug? Clean the points? Sometime, I have found plugs will fire great until they are screwed in and are working against compression. Had a weak coil on a Briggs that acted the same way, new coil and the engine runs great. Hope this helps.

Bigjoedo

 

[Furious D]

I had thought about the gas tank vent. I can see light thru the cap.

Plug is new,points are good and I have good blue spark. I seem to have good fuel flow. Pulled the bowl off and it was full of fuel.

I might swap the coil , Then points and condenser this week and see what happens.

Thanks to all, D

 

[metal man]

kinda sounds like a hs50 i had in the shop one time for repair . had a funky problem i never could get worked out . it would run strong and fine after i did the carb work and fuel line . but it would just die at random . just slow down and stop , if you were ready you could grab the rope and the second it stopped pull it and off it would go and run fine for a few then stop again .
worked on it for a week trying to find out why nothing seemed off it just died . asked the owner about it and told him i have no idea why its doing this :shrug: nothing i did to fix it should have caused this :shrug: he sits back and gets this grin on his face and :laugh::laugh::laugh::laugh: says kid its done that for the whole time i have had it . 5 years now its a done it guy i got it from same deal .
maybe check the valves :shrug: to see if they maybe hanging up on something if its not the coil .

 

[ogygopsis]

Furious, Whether he realizes it or not metalman may be on the right track. I'm not a Tecumseh man and never spent any time working on them but the Briggs motors have an exhaust valve seat insert. This insert will sometimes work loose and cause the motor to act EXACTLY like your Tecumseh. If this insert is what is causing the problem it will need to be replaced or sometimes it can be tightened by peening the edges. This is best left to an expert who knows what he is doing. Before you spend a lot more time with carbs, spark, etc. do yourself a favor and check to see if your Tech has an insert and what kind of shape it's in. Let us know what you find and good luck. Ogy

 

[metal man]

ogygopsis the tec insert is different then the briggs one from what i have seen scraping the blocks . its a figure 8 with both seats where briggs uses two round ones . if the insert is loose on a tec its scrap given its cast in the block .
i was thinking it could be more of a bit of crap in the port or maybe a guide hangin up .
what ever it is i hope we can find out and it gets fixed up and running so if i ever see one again i know what maybe wrong on it :thumbsup:

:facepalm:
just had something hit you say it was rebuilt 7 years ago and never started ? so its never been seen to work wright at all from then .
so maybe it not a new problem but a built in one
if the valves were put in and not set wright that will cause you some problems big time . as when you start it it could be pulling enough fuel to make up for the bad seal on a valve . but given a little heat the seal is gone and poof way way low compression .
dead motor and given its so little heat it would only take seconds to drop into the block and give a bit of a seal to again pop a few more times .

was thinking on what ogy said and about some of the old blocks i broke down and the old neighbor came to mind as he sent a few my way to get rid of and the one job i did for him poped in to mind . a old old briggs water pump jammed linkage had it sitting for years . he sent it in for repair and tune . well i got it going then boom stops working wright . ok fuel pumps gone south fine but even priming it it just kept getting harder to start . let sit all night in the cold and it would run for a bit (with prime ) then fall and not start . run like crap and just no idea as to its problem . well it was a neat one the valves were set in the block wore in from years of use wright . well the little i got it to start was enough to swell them from sealing . let it cool and it would run till they started to get warm then back to cutting out . check the valve lash could be a tight valve . would be the last thing you would think to check but it can cause running problems like this .
sorry for the long winded post ...... im bored and its raining :angry:

 

[ogygopsis]

Metalman, Figure eight valve seats; huh? I learned something today. I've never had much time for Tecumseh motors....too many carb. problems. And now I learned that you have to scrap the block when the valve seats go bad. Unbelievable. The suggestions in your previous post are right on. Hopefully, this will point him in the right direction and will help him solve his problem. Let us know what you find FD. Ogy

 

[Furious D]

Well the saga continues.

Pulled the coil/points and condensor off of a running engine and the same. It starts and dies, starts right up, dies again. Even dies when I spray a little starting fluid in the carb so I guess the next step is to pull the head.

Update: Pulled the head and found that the valves were fine but the timing was the culpret. It was firing before the valves were fully closed. The timing was right on the mark so I just static timed it and its running pretty good. I think I need to retard the timing a bit but other than that its ready to go.

Thanks to all for your help

 

[The Restore Kid]

I have one that JUST recently STARTED doing that.. An H35 I put together that was %60 missing... I've about thrown it in the river and gave up.. I know it's not my carb settings because that was great.. The tank is venting...

SO I went as far as change out the Condenser.. Because a bad condenser will give you carb problems.. The carb is actually working BUT THE SPARK is so weak and intermittent that it won't BURN the fuel you give it..

BUT, it wasn't the condenser either.... SO next step will be change the whole coil pack out, as coils will burn out and cause problems like that as well.. Run for a second, overheat and short out.. :mellow:

SO I am guessing mine is the coil......

YOURS most likely is a lack of fuel.. Especially if the carb has sat for 7 years.. The idle circuit might be plugged up... But if it WILL idle.. you probably just have the metering screws too lean....

Open them both up, like a turn or so, hold the throttle 1/2 open and see what happens...

 

[Furious D]

I have one that JUST recently STARTED doing that.. An H35 I put together that was %60 missing... I've about thrown it in the river and gave up.. I know it's not my carb settings because that was great.. The tank is venting...

SO I went as far as change out the Condenser.. Because a bad condenser will give you carb problems.. The carb is actually working BUT THE SPARK is so weak and intermittent that it won't BURN the fuel you give it..

BUT, it wasn't the condenser either.... SO next step will be change the whole coil pack out, as coils will burn out and cause problems like that as well.. Run for a second, overheat and short out.. :mellow:

SO I am guessing mine is the coil......

YOURS most likely is a lack of fuel.. Especially if the carb has sat for 7 years.. The idle circuit might be plugged up... But if it WILL idle.. you probably just have the metering screws too lean....

Open them both up, like a turn or so, hold the throttle 1/2 open and see what happens...

You missed my last post. It was timing. The plug was firing before the valves were fully closed.

I still dont know how it ran before but its running good now. I guess they got the cam/crank timing off a tooth when it was assembled.

 

[Phil1958]

i think what you were seeing is the extraneous spark that occurs at the end of the exhaust cycle. the ignition fires every 360 degrees of crankshaft rotation. if the valves are open during the compression stroke you would have a motor that pretty much wont run.