Runs rough when hot

[KE4AVB]

Good thought...I have heard of choke problem with the thermostat chokes but all the 09P engines I have seen so far have been the primer bulb system.

[bgsengine]

Actually that just reminded me ..last year I did a warrant on a briggs 09p carburetor (thermoplastic ones) because the non-replaceable inner venturi was not properly welded at the factory - was not even noticeable until taking the carburetor completely apart to fully inspect fuel system to find the problem, remove the main jet and then while turning carburetor over, the venturi fell out... Symptoms ere different though - acted like it was starving for gas but it was one of those . bought new, starts right up, ran 10 to 15 minutes and started running weird and then died" complaints - almost would have thought "bad fuel" except after it sat a while and it repeats - runs just fine for the first few minutes,,

But does make one wonder if there might be other possible design issues with the plastic composite carb that might lead to an over-fueling after it warms up...

[plpitts1]

Alright. Received the new coil. No change. Tried new (3rd) plug. Pinched off gas again, took about 2.5 minutes to start sputtering and surging which lasted about 30 seconds before it died. The mower runs perfectly smooth for about 3 minutes, then starts acting up. Gets a little air puff or misfire through the muffler randomly about every 5 to 10 seconds, rpm's drop just slightly when it happens. The rpm's are set at 3060. I have let it run for 10 minutes and it does not get worse, just continues. Might be ok under load?? I can't take it home and use it though. Choke is open completely, and disassemble carb and cleaned in ultrasonic cleaner just cause I had time.
Thanks,
Pat

[bgsengine]

I seem to recall a service bulletin about certain thermoplastic carburetors where the main jet had a problem and needs to be replaced with updated version.. gonna have to check the power portal next chance I get and see if applies here.. I think it was specific to choke equipped (I think?)

[KE4AVB]

BGS, I think you're referring to DSB1060 where they moved the idle jet lower to prevent gumming and it was this idle being high that was causing erratic operation. This does require the changing of the complete module assembly. Other than I haven't seen any other bulletins relating to carburetor internals. One thing note don't over tighten the fuel bowl screws as they will strip out easily.

I have copy of DSB1060 in the Briggs Advance Service Info sub directory of the Briggs Service Info download directory.

Also note as most us do know but all the these engine runs off the idle passages except when loaded so this could the cause.

[bgsengine]

BGS, I think you're referring to DSB1060 where they moved the idle jet lower to prevent gumming and it was this idle being high that was causing erratic operation. This does require the changing of the complete module assembly. Other than I haven't seen any other bulletins relating to carburetor internals. One thing note don't over tighten the fuel bowl screws as they will strip out easily.

I have copy of DSB1060 in the Briggs Advance Service Info sub directory of the Briggs Service Info download directory.

Also note as most us do know but all the these engine runs off the idle passages except when loaded so this could the cause.

Yeah - fuzzy memory -I have yet to ever see one of those come through the shop,so details faded over time. just the one warranty I did , other than that most of the issues I came across so far were simply bad gas or dirt in fuel.. nothing that ran fine until warmed up on those versions,so I can only take guesses. But as noted in my warranty comment if coil did not do it perhaps try swapping out carb with a new or known good - it could easily be a separated thermoplastic weld somewhere in the carb causing the issue as it warms up.

[KE4AVB]

I agree that we don't ever know everything. It will always to something new that requires taking an educated guess at until we know better. I have over the years had even customers show me new things. I good example is the time I was working on perplexing electronic problem on a calculator when operator asked what item was on the circuit board. Behold it was exactly what was wrong with it and she never has a day's training in electronics; I felt dumb as can be but I have learn things like this happens and not to be embarrassed by it.

I don't like guessing either but sometimes all we got to go on is our previous experiences and gut feelings. On top this with these push mower engines we are not seeing them in the shop like we once did due to low cost of the equipment where the operator are just tossing them and buying new equipment.

Once this problem we discussing get resolve it will benefit all of us in the long run provide the info is provide to us.

[plpitts1]

I will try new carb, I believe I have on. Although doesn't seem like that would be the issue seeing that it runs fine untill warm. Other than that I will have to send it off.
Thanks for the replys, I will post when we resolve it.
Pat