Vaporlock/run-on gone!

[Phils]

That electric pump is in its third and final mounting location: on the inside tub wall just fwd of the battery, under the gas tank, almost to the hyd filter. The hose is routed back under the tub 'lip' and then goes up to the carb at the right rear corner of the Robin engine.

Friday I was able to completely mow my entire yard without once being stopped because of vaporlock. I'm guessing it to be 3 or 4 sometimes steep and hilly acres and I've always been stopped by VL before the job was finished, making it a two or three session project (which hasn't been a problem as this could be considered a 'two-or-three-beverage' job). I'd still have it all done in two or three hours counting a lot of 'cool-down' time. This time I was finished in an hour.

Interestingly enough, I also have no more "run-on" when shutting down. Not even a little. During some other jobs Saturday I found the little "pop" when shutting down has almost disappeared too. If I let the PT engine idle for 1/2 minute or so before turning it off (after full power PTO operation), no "pop". I haven't had enough time to try all the combinations (ie - shutting it off at other throttle settings) yet. Before this fuel modification I got the pop or run-on no matter how I shut down, although I never tried letting it idle for more than a long minute as that really should be enough.

This indicates to me that the Robin-powered PTs suffer hot fuel problems because the fuel hose and pump are in such close proximity to the [very] hot exhaust. The engine runs lean (until it stops altogether from VL) which makes it run hotter, which puts more heat to those fuel components. Which makes the engine run hotter as the fuel mixture gets more lean. A vicious cycle.

But not a problem that would affect a PT powered by an engine with a rear exhaust and fuel hoses and pump away from those hot parts (like MR's Kohler, for instance).

Phil

 

[tracdoc]

Congratulations on your success!

</font><font color="blue" class="small">( This indicates to me that the Robin-powered PTs suffer hot fuel problems because the fuel hose and pump are in such close proximity to the [very] hot exhaust. )</font>

I agree with your assessment completely. It's interesting how two alternative approaches (fuel pump + re-routing vs. insulation + firewall barrier) to the same problem, viz., HEAT, come up with the same successful outcome. I still experience a single shutdown detonation on occasion, however. I believe that will be cured with a new exhaust header at some future point. /forums/images/graemlins/grin.gif

Another case of "persistence pays off." Thanks for sharing.

 

[BEK]

I'm new to TBN and a PT wanabe, I will probably purchase a 1445 this summer. I was reading the posts concerning the Kohler pop. run on and high operating temps and would like to let you guys know about the problems I had with the Kohler Command 25 on my Bunton ZTR. After trying various shutdown procedures with no success I was unable to eliminate the run on. My engine also ran very hot, the muffler glowed red at night. I started looking at the spark plugs. The Champion RC12YC plug is listed as a very hot plug in the Champion guide. While doing my spring tuneup I decided to install cooler plugs, so I put in RC9YC, (I wanted 7's but couldn't find them). I adjusted the idle mixture (the old way, best fast idle then 1/4 turn lean) and then set the idle speed,(again the old way, slow with out miss). I made these adjustments after the engine had run for 10 or 15 minutes under load to insure it was up to temp. The first time I shut it down it stopped dead, no pop, no run on. I have used it about 4 or 5 times since to mow between 2 and 5 acres each time and each time I shut it down I had no pops or run on. My Kohler now runs alot cooler, I do not have any temp readings but there is a very noticeable difference.

 

[MossRoad]

Welcome to TBN, welcome to the Power Trac forum and thanks for the tips! /forums/images/graemlins/grin.gif

 

[Spiffy]

Welcome to TBN! And looking at red PTs at that! /forums/images/graemlins/cool.gif

You'll love the sound of that 45HP Deutz. /forums/images/graemlins/smile.gif

 

[tracdoc]

I'll second MR's welcome to the Forum.

I guess that I'll just have to consider revisiting the heat range choice for the Robin 425. I looked into it last Summer, and found that the "OEM" plugs as delivered from PT were 2 heat ranges hotter than what was recommended by Robin. I said to self: "Eureka! Problem solved. I'll just go colder 2 ranges." We had a thread going on this topic for awhile {HERE}. I tried the colder plugs and did not see any improvment in the shutdown detonation. The colder plugs did make for harder starting in Winter weather, though as Jack Robin indicated. So, I switched back to the original plugs for Fall and Winter. Maybe for Summer, I should try even colder plugs than 2 heat ranges? /forums/images/graemlins/confused.gif

 

[ernemats]

Welcome! What part of Westmoreland County. I am 9 miles North of Ligonier and own a pt 422.

 

[BillCroasmun]

Tracdoc, Did you re-tune the engine after switching the plugs? If not the engine wouldn't have been optimized for your new plugs. I haven't switched plugs on the PT but I know on other small engines I have seen a huge difference after retuning when changing spark plugs/air filter types/etc. Basically anything affecting the air/fuel/spark combination.

 

[BEK]

I'm in Derry

 

[tracdoc]

</font><font color="blue" class="small">( Did you re-tune the engine after switching the plugs? )</font>

No,Bill, I did not re-tune. I don't want to veer off and hijack this thread, so could you PM me with your recommended procedure? Thanks.

 

[Phils]

Awww. Bill, c'mon. Please post it here or start a new thread! don't relegate such valuable info to a PM! I'm out of my warranty time now. After going through all I have on fuel problems I'd like to know a successful method of fine tuning the carb if/when it becomes necessary. I no longer have to fear the warning sticker. I am free.

Phil

 

[BillCroasmun]

Phil, This is your thread so you win I'll post instead of PMing. /forums/images/graemlins/smile.gif Actually BEK already explained it but I give my method with some explanation after each step as well.
1 Warm up your engine to normal operating temperature.
Carbs are picky about many things like temp/humidity/altitude/etc. so tuning your engine in the state that closest to it's normal operation will give best results.
2 Begin closing the idle mixture screw 1/4 turn at a time until you hear the engine drop in speed then open it back up 1/4 turn.
Some people try to set it in between this point and the factory setting by counting how many turns it takes to close it from the original setting and then counting how many turns it takes to close it from this new setting and then setting it in between. I find it best to go between this 1/4 back setting and an additional 1/4 back tuning by ear.
3 Adjust the idle speed screw 1/4 to a half turn at a time until you get the best slow idle without missing.
You can also look up your engine specs and set this with a tach to match the factory specified idle speed.

I'm no expert but it works for me.

And congrats Phil on the missing VL and run-on!