310-8 starves for fuel

[JIM W 1]

I have been nursing this 310-8 with the Magnum 10 magneto engine for decades.  I really hate to see it go but it’s got me beat this time.  The last time I mowed it ran normally until about 30 minutes in and then it started to act like it was fuel starved.  Playing with the choke kept it limping along for a while but it finally stalled and wouldn’t restart.

I was sure it was acting like it was out of fuel so I made sure the valve at the bottom of the fuel tank was flowing good and replaced the fuel line and filter all the way to the fuel pump even though fuel flow did not seem compromised.

The fuel pump was OEM and full of rust and crud and didn’t seem to be pumping adequately so I replaced it with one of the inexpensive plastic pumps from Amazon.

It would start but die after a few moments so I figured it must be dirt in the carb so I next replaced the carb.  The engine would then start but struggled to stay running as I played with the adjustments.  Once it stalled I just could not keep it running again. 

There was spark at the plug but it seemed pretty weak and, as the age of the plug was unknown, I installed a new one.  This was a few days later after the mower had been resting.  This time the mower started right up and I was able to mow for at least 30 minutes or so before it struggled and seem to run out of fuel.  But, it had plenty of fuel in the tank and in the filter.  When I unhooked the outlet from the fuel pump and cranked over the motor the pump was squirting fuel.  I reassembled and let the mower sit 30 minutes.  It would then start but only run a few minutes until it acted fuel starved again.

Usually, throwing parts at something like this works pretty well for me but this has me buffaloed.  Is it possible that the coil module on the flywheel of some other ignition component is failing as the motor heats up after 30 minutes or so?  I just don’t know what else to try. I appreciate any suggestions as to how to proceed.

[953 nut 51,993]

.The vent in your gas cap allows air to enter the fuel tank as gas is used. If the vent is clogged and no air can enter the tank the fuel being removed will develop a vacuum in the tank that your fuel pump can't overcome. Leave the cap loose and if the problem goes away then get a new cap for the fuel tank.

Edited October 20, 2023 by 953 nut

[JimSraj 344]

Are you getting good spark at the plug after it stalls?  Try an in-line spark check light.
I had a similar problem with my 1267. Turned out to be the coil. I replaced the coil, points and condenser. Runs great now. 

[WHX?? 46,941]

Be wary of the plastic pumps. I had a dead one right out of the box once. Intermittent problem to boot making trouble shooting hair pulling. For lack of a good metal pump replaced it with another cheapy plastic and problem went away. 

[JIM W 1]

I spent some time on the WH today.  After cranking a while it will start on full choke.  Push the choke in ½ way and it sounds good and strong.   The first time it ran five minutes and I started to get my hopes up but then it died.   Each time I start it after that it runs for a shorter and shorter time.  After a minute or so the motor starts to falter so I quickly pull out the choke and it perks up for a second or two until it starts to stall because it is too rich.  If I push the choke back in to ½ way it will catch and perk up but only for a few seconds.  I can keep it running another minute or so by working the choke in and out but soon it just seems to run out of fuel and dies.

If I then pull the output line from the fuel pump after it stalls fuel will run out so there seems to be fuel to that point.

Once I removed the idle jet screw completely and left it out.   The motor started and ran but soon stalled and acted no different from before.

I put the idle jet back it and then took the main jet screw and rod completely out.  It started right up and again ran as before (maybe a little fuel occasionally spit out the open hole).  I tried both jets 1 ½ turns out and settled on full 2 turns but they really don’t seem to make a difference.

I have a small engine spark viewer (cheap one) and I cannot see much of a spark even when the engine is running.  It could be the cheap spark tool or just poor eyesight in the daylight. The engine seems to have enough initial spark to start and run a few minutes.

I did think, at first, that it acted like it was fuel starved so I have tried a fuel cap from another mower as well as just leaving it loose but it doesn’t seem to make any difference.

BTW, The battery is pretty shot so all these test are done with the battery booster on and running so I should have continuous power.

Each time the motor stalls it seems to crank a while before it starts again as if I am refilling it with fuel.  I wonder if I can hook up a gravity feed fuel line to the carb and see if that makes any difference?  Maybe the new fuel pump is suspect but it seems like it has to either pump or not pump and would have no reason to pump sporadically?

I would say the new carb doesn’t work right but, for at least the first time I start it after a few days rest, it idles good and sounds strong and normal for a few minutes until the above symptoms all start again. Thanks for your suggestions.

 

 

[953 nut 51,993]

On 10/19/2023 at 6:07 PM, JIM W said:

The fuel pump was OEM and full of rust and crud and didn’t seem to be pumping adequately so I replaced it with one of the inexpensive plastic pumps from Amazon.

It would start but die after a few moments so I figured it must be dirt in the carb so I next replaced the carb.

If the replacement carburetor is one of the Chinese units being sold on  the internet you probably would be much better off buying a carb rebuild kit for the OEM unit you took off. 

[Tuneup 1,416]

I do hate what is happening to replacement Chinese parts the past few years. Now, OEM is becoming suspect. Yeah, if the adjustments do nothing, go back to a rebuilt original. I have used a PVC cap and nipple hanging from above the tractor to eliminate the pump and tank from the equation. Cheap way to go (also works for synchronizing old Honda 4 engines). Sounds like you've compounded the issue with those parts. Originally, sounded like a coil heat soak failure.

[JIM W 1]

Today I dug out my coffee can with a hose connection and hooked fuel direct to the input of the carburetor.  I took the hose that came from the fuel pump and fed that into a water bottle.

The engine started right up and ran great.  Idled good and seemed to take more throttle with no backfiring of stumbling.   The fuel pump was putting out a lot of fuel and could have filled the water bottle in just a few minutes if I left it go.

I kept the motor running several minutes and it seemed to run great but….  After only a minute or so I realized that the pump was no longer pumping fuel into the water bottle. The carb and engine were running great as long as I keep feeding fuel directly into the carb.

This was baffling as the fuel tank was open to air.  The only item in the fuel line was a new fuel filter.  The original filter was decades old and, although the little filter that came in the package with the new carburetor looked pretty cheap I figured I should change it when I changed the carb. I now removed that filter and spliced the fuel line together without a filter and then hooked the fuel pump back to the carburetor as it was meant to be. 

The mower started, ran great, and seemed to stay running so I proceeded to finish the mowing I started two weeks ago.  The motor ran great, never stumbled, and the carb seems to be working great, idled good and had lots of power.  I mowed 20 –30 minutes without a problem!

So….  Perhaps my old fuel filter was plugged and causing the low fuel issue all along?   Putting the new filter on didn’t cure the problem as it may have had a crack and was drawing air or was just junk to begin with!  Once all the leaves are all down I will put the mower to another test but it really seems I have cured the problem.

Boy, do I wish I had changed the fuel filter first before throwing new parts at this!!  Thanks to everyone that offered help.

[lynnmor 6,820]

1 hour ago, JIM W said:

The original filter was decades old and, although the little filter that came in the package with the new carburetor looked pretty cheap I figured I should change it when I changed the carb. I now removed that filter and spliced the fuel line together without a filter and then hooked the fuel pump back to the carburetor as it was meant to be.  .

 

Maybe I missed it, did you replace the old fuel line with new ethanol resistant?

[JIM W 1]

good question, i can't say for sure.  The auto parts store cut it off a big roll but never offered me a choice.  I would hope all they sell these days is ethanol resistant. 

[ineedanother 1,366]

On 10/23/2023 at 5:31 PM, JIM W said:

Boy, do I wish I had changed the fuel filter first before throwing new parts at this!!  Thanks to everyone that offered help.

That's not actually the best answer and most of us are guilty... - The right thing to do is to patiently diagnose before making an incision  

[peter lena 8,103]

@jimw  , have had  regular issues on used tractors , regular thing  I do , after dropping the carb bowl , for a clean out is to run it on a separate gallon of heavily treated fuel , letting run at fast idle , can of carb cleaner , linkage  check over , hand suck on running carb .  would not be surprised . if its fuel hose breakdown , crud in the tank , tank valve filter packed with debris . had all of that and more on   one I  sold months ago . just kept gaining on it , double fuel filters , one near tank , one near carb , fuel check valve . then electrical issues , yada . yada , pete