Engine Silver Series LB wont stay running.

tlwright21

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I have a LB model 10304 series 6914509 that I bought new in 1996. It replaced a LB that was purchased in 1973- so you can say I bleed LB green.
Last summer it started giving me trouble starting up. would press primer 2-3x, engine would fire then die. If I continued to press primer over and over again it would eventually come up to speed and run. would take a long time though but once it was warm it would mow with full power. full disclosure-last summer I ended up hitting a bolt on the bottom of a fire hydrant that bent the blade and stopped the engine. Bought a new blade and resumed using but this was when the problem with engine running began. there was no unusual vibration afterwards like a bent shaft, but it took forever for it to get up to speed and starting running on its on without constant priming.

Last week I put in a new plug and cleaned air filter and it started right up and I mowed -no problem. thought I cured it.

This week back to same old problem. Now I think I may have low engine vacuum and it isn't pulling fuel through the reed valve. wonder if I may have damaged shaft seal but not sure and don't know how to ck. Engine will not staying running now unless you prime as fast as you can and then maybe it will run.

So this is what i have done in the last 24 hours. problem did not go away. still wont' run

1. cleaned air filter,
2 cleaned muffler
3 disassembled carburetor, cleaned jet, holder , needle, seat, float with carb cleaner. blew through all openings all clear
4. drained gas tank, checked fuel line,all clear no restrictions
5 took apart primer bulb, checked line, no leaks.
6. checked intake gaskets and float bowl gasket and they are intact
7. carb is getting fuel into bowl. Spilled out when i took apart
8 took off fuel cap and tried to start, made no difference

other than a possible problem with vacuum I'm wondering about the air vane settings or its spring tension. can someone tell me where the position of the air vane is when at full throttle? Im talking about is it in the center of the slot or to the right or left when looking at it from the rear of the mower? when it was running, right before it died, I got down and observed the air vane was all the way to the left. So i think that means the throttle plate is completely closed (full choke???). Is that correct, if not then what do i need to do? Not sure how the air -vane modulates the throttle, does it change position when the engine gets warmer or mowing in heavy grass, like a governor.

HELP Don't want to give up on the mower but its getting close
 
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jp1961

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Hmmm. Stopping the engine dead after striking an immovable object is not good. Is it possible you cracked the crankcase?

Regards

Jeff
 

tlwright21

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Hmmm. Stopping the engine dead after striking an immovable object is not good. Is it possible you cracked the crankcase?

Regards

Jeff

I guess anything is possible but the engine runs and i was mowing with it after I bent the blade. it started and ran last week with no problem after i changed plug.

the problem that i see now is the air vane is in the complete closed position when the engine fired up yesterday. why I dont' know. nothing was adjusted or changed to cause this. With this being the case the throttle plate is completely closed and that is why there is no fuel getting into the engine. I need for someone that knows LB to tell me where the air vane should be in the slot when it is running.

also quite a while ago the throttle lever on the handle quit doing anything. it was attached to the lever on the carb but when moved didn't do anything to the engine speed, which is all connected to the air vane.
 

unclelee

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You should be able to see moisture around the crank seal if it is the cause of your problems. It is very possible when you hit the fire hydrant bolt that it damaged the seal.
 

tlwright21

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You should be able to see moisture around the crank seal if it is the cause of your problems. It is very possible when you hit the fire hydrant bolt that it damaged the seal.

When I took the muffler off the other day I was inspecting the crank shaft seal area and there wasn't anything unusual there. No gas/oil moisture or anything that might look like blow by . I really believe that i have a issue with the air-vane not operating correctly.

I'm going to put back together and hopefully get it to run long enough to maybe manually hold open the air vane from the closed position. maybe install a new spring or fiddle around with the governor collar. I have never touched either in the 21 years I have owned it so I don't know why it would be off now. If that isn't it then i'm done. I'll have a LB for sale for parts.
 

lewb

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Crank out of phase? you will still get good compression but if the piston is not getting the spark at correct time will experience loss of power. There are not a lot of short blocks for this model but that may be your fix if this is your issue.
 

tlwright21

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Crank out of phase? you will still get good compression but if the piston is not getting the spark at correct time will experience loss of power. There are not a lot of short blocks for this model but that may be your fix if this is your issue.

How does a 2 stroke get out of phase? And how do you put it back in phase?
 

bogdaN

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I guess anything is possible but the engine runs and i was mowing with it after I bent the blade. it started and ran last week with no problem after i changed plug.

the problem that i see now is the air vane is in the complete closed position when the engine fired up yesterday. why I dont' know. nothing was adjusted or changed to cause this. With this being the case the throttle plate is completely closed and that is why there is no fuel getting into the engine. I need for someone that knows LB to tell me where the air vane should be in the slot when it is running.

also quite a while ago the throttle lever on the handle quit doing anything. it was attached to the lever on the carb but when moved didn't do anything to the engine speed, which is all connected to the air vane.

Here some pic,s of carburetor that show u that governor vane should be open.DanLawnboy 002.JPG
 

lewb

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How does a 2 stroke get out of phase? And how do you put it back in phase?

A violent stopping of mower/With a new crank, if you can find one. I would say if you cannot cure issue with carb adjustments your only process of elimination is the crank imho. You can spray carb cleaner or ether/starting fluid under mower while it running to see if you have a damaged seal, there should be no RPM change. If RPM jumps then you have a seal bad. Ebay you can probably find a motor. I have not seen a short block for the 4.75 hp LB.

I had the same mower for probably as long as you did. My son filled with gas when I was out of town, did not know I filled with fresh gas but normally had mixed in can. I bought a duraforce in replacement. You can find them on craiglist readily and you can also get short blocks for around a 100.00 which is crank and cylinder assembly. That is what I did, bought a donor mower for 25.00 and put a new short block in.
 

lewb

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When I took the muffler off the other day I was inspecting the crank shaft seal area and there wasn't anything unusual there. No gas/oil moisture or anything that might look like blow by . I really believe that i have a issue with the air-vane not operating correctly.

I'm going to put back together and hopefully get it to run long enough to maybe manually hold open the air vane from the closed position. maybe install a new spring or fiddle around with the governor collar. I have never touched either in the 21 years I have owned it so I don't know why it would be off now. If that isn't it then i'm done. I'll have a LB for sale for parts.

The vane is a governor, the more load on engine the more it opens up throttle. Your spring is probably sacked out or something is binding which is why no difference in throttle change rpm. To replace the spring you have to remove the throttle plate/butterfly (looks like a penny) Just use a needle nose and pull it, The spring has a tab the sits in the dial adjuster and the other end goes into throttle. To set it clockwise each click is 25 rpm at full throttle, want 3000 to 3200 rpm. I have done in the past is tie up the safety handle and start mower, you can turn the vane by hand to run throttle up and down. You should be able to do this to see if you can get it to stay running.
 
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