racing plug

[carryall]

After running the bike last weekend, and being very pleased with the results, I decided to start doing a little "tweeking" to the engine in preparation for a "Top-speed" run with it just out of curiosity.  I checked and needed to adjust the intake/exhaust valves which were slightly loose from .002 intake & .003 exhaust.  (Mind you, this engine is completely stock internally, and still has its governor installed and fully functional)  The only modifications I've made are to the intake and exhaust and the carb jetting.  The next thing I may do, is to install a "performance spark plug" (with indexing washers) to increase the stock compression slightly.  A Autolite AR3910X sparkplug will extend deeper into the combustion chamber to accomplish this.  Question...Anyone here have experience with these plugs in go-carts/mini-bikes, etc.?  (The karting sites claim approx. 3/4hp gain from them?) 

[kartjockey]

I am all for indexing the spark plug.  Have to do a little research as to which way to head it into the flame travel.  Not sure about that upping the compression much. But every little gain helps when you only have one piston!  I actually had over 9:1 in a 5hp flat head Briggs before but soon found there was more merit in helping the engine breath  then trying to pack it with gas that couldn't get in or out.

[carryall]

I'm running about as rich as possible with the stock carb (.036) and the 140 E-tube according to my plug chop tests, and the intake & exhaust I made using 1-1/4 pipe. (bigger I.D. than its ports)  I'm just curious how fast one can go with one of these budget engines without doing "real modifications" like bigger cam, better valves springs, gov. removal and aluminium flywheel, shaved keyway, pulse carb, decked head, etc...I.e on budget and keep it reliable/long lasting (or as reliable as a $100 engine can be LOL) 

[butch27]

I never thought much about indexing until a friend did his T bucket. Wow

[carryall]

I believe the theory is the open end of the electrode needs to point at the exhaust valve, (this engine is approx. 7 O'clock position) to assure complete combustion of the the fuel mixture.  I've never done it but, like we all know, every little bit helps when you're counting on a single cylinder for power.  Other than the valve lash being a bit on the loose side, I was happy to see both valves were seated properly and my compression tester read 110lbs with only 3-4 kicks, which tells me the rings are seated pretty well now.  BTW, For my "break-in" I ran regular oil for the first hour, varying speed constantly, then changed it again with regular oil for approx. another 2-3 hours of run time while slowly increasing speed and duration before finally switching to full synthetic Mobile 1. The addition of a Fumoto drain valve makes oil changes a breeze with NO MESS/DRIPS for anyone who mounts a HF engine to one of Waynes adapter plates because of the poor access to the factory drain plug.     

[carryall]

For lack of anything else to do today...(Ha, ha, like there's not enough chores/crap to do on a rare day-off) I figured I'd take the Servi out and see what the top speed is "as-is" after installing couple different "apps" on my phone to record top speed/speedometer.  After running it both directions (to/from like Bonneville... LOL) at WOT, using both apps, I averaged just a hair over 46mph.  Pretty good considering it's still governed and "stock configuration".  I must say, I'm really impressed with this engine and it's reliability and performance, considering it costs less than a $100 (HF 212cc)  Only 1 small issue on the day, and that was my kick-start arm.  I noticed it's developed a slight twist/bend to it, (from the longer, fold-up peg I adapted to it, I suppose) so I'll reinforce/gusset it this week at work, and it should be better than new (again).  BTW, I looked into maybe taking a couple days off to "go to Portland" but, our steel production schedule is so overloaded, unless something drastic changes with construction delivery dates, (new MN Vikings stadium) it's not going to happen...

[pd]

46 ain't so shabby .

Did you index the plug ?

Pete .

[carryall]

No...I stopped at NAPA for a AR3910X plug but, they didn't stock them so, I ordered one along with some index washers.  The "speed-run" I did was just "as-is" with the regular plug without indexing washers.  After I fix the kick start lever, I'll pick them up and maybe do a comparison using the new plug/washers, out of curiosity next weekend, if I have time.

[pd]

Be interesting to see any difference .

Pete .