Hello, I have been a lurker for a year and have received lots of good ideas from this forum. I would appreciate a bit of specific help on my new kit. This is a '01 Tomos Sprint, with stock carb, tecno bullet pipe, #60 jet, B8HS plug, open intake, Airsal 65cc kit with new reeds. I took the time to clean up the kit before installing, polishing ports, gapping both rings & deburring the edges of stuff. It runs pretty good with about 10 miles on it so far, using premium with regular 2T oil at 35:1 ratio mix. Plug chops look good, though I am only going 3/4 throttle (about 33 mph). After riding for about five minutes, the bike gets noticeably slower, yet also much smoother/quieter in vibration. I'm guessing it's heating up & something is getting real tight, but I check and there's no evidence of a sieze. Any ideas?
Loss of power on A35 Airsal kit at top end
Re: Loss of power on A35 Airsal kit at top end
does it start with no choke?
Re: Loss of power on A35 Airsal kit at top end
Maybe too much oil in the gas... You might be able to upjet more as well.
Re: Loss of power on A35 Airsal kit at top end
Use a hotter plug.
Re: Loss of power on A35 Airsal kit at top end
Yes, it does. It didn't used to when I had the stock cylinder on it & #58 jet. I tried this morning (pretty warm day in LA) and it took a few kicks, but definitely started. I have noticed while riding that it four-strokes pretty easily if I am coasting at certain speeds, mostly lower (25-28). At about 29 I have a "Sikorsky shuddering SH*thouse" condition until about 32 mph.
Re: Loss of power on A35 Airsal kit at top end
I started with 32:1, and noticed lotsa smoke; checking the exhaust port it was just wet with oil. Went down to 35:1 and it's better, but maybe a 40:1 until I finish break-in is OK? I normally run full synthetic at 50:1.
I started with a #66 jet, it four-stroked real bad. #61 wasn't much better. #60 is still four-stroking more than I would like while coasting at lower speeds, but I tried #58 and it bogged at first-twist.
Re: Loss of power on A35 Airsal kit at top end
Yeah, the kit came with a BR9HS, I tried it but then read something about a resistor plug not being good on A35 because the Bosch CDI already has a resistor wire? Anyway, I had a B8HS that was way too cold for my stock head, thought I would try it and noticed some small improvement. Why would a hotter plug work better when the engine is warmed up?
Thanks for all the good advice, this 2-stroke stuff is a little new to me. Only had 4-stroke up until now, not counting a jetski.
Re: Loss of power on A35 Airsal kit: piston!
Discovered something that's probably important; after running it the plug gap is getting squashed! I tried Double's suggestion of going to a hotter plug, and right away noticed that the gap was real small. Immediately pulled the head, but can't see any damage to the piston...phew! Just because I'm stupid, I did it again and confirmed that the plug gap is getting smooshed somehow during engine operation.
Gotta get one of those index washers, I guess. Funny, the piston is domed, but not that much. It seems really odd that the piston is slapping the plug, but it has this little nipple sticking up right in the middle, maybe a casting error...can I sand that thing off?
I've read that a thicker gasket below the cylinder might be beneficial, but I checked my port timing and the exhaust port is barely full-open @ BDC .
Re: Loss of power on A35 Airsal kit: piston!
OK, put an extra washer on the plug, no more problem with the pistion changing spark plug gaps. Now, the vibration that starts around 29 mph continues to about 32 mph but my top end is retained (though I haven't gone WOT yet, only 37mph since I am only 50 miles/6 cycles into the break-in.)
My compression in 150 psi, warm. Is that good? I am concerned that there are threads exposed to combustion, since the plug does not go all the way into the cylinder now. I did note that since torqueing everything, the last piston check looks like it actually drops below the bottom of the exhaust port, by maybe 1 mm.
Re: Loss of power on A35 Airsal kit: piston!
Try a Champion L86C or Autolight 425 it may have a shorter reach of the thread thus eliminating your squish problem. There are many different thread reaches in various plugs. Use the right one! NGK are not be all and end all, even though some people think so. Also make sure you are using a non resister plug and spark plug cap on your bike.
Re: Loss of power on A35 Airsal kit: piston!
OK, bought a Champion plug, compared it in the store and it's definitely a little bit shorter. However, on the ride home (longest ride since adding the extra washer to the plug, about 10 minutes each-way from Kragen's) the Tomos did it again! I had been waiting at a light for awhile, then while accelerating past 34 it suddenly lost power just like before, and got quieter and smoother. Max speed now 29 mph.
Now I'm thinking the reed block needs adjustment. I noticed while installing that there were very tight tolerances; the gasket actually would hold the reed open until I shaved the gasket. Could that have swelled up or expanded during operation enough to stay open, and cause the power loss? Full tear-down tonight!
Re: Loss of power on A35 Airsal kit: piston!
The reed block is not square. You probably had the gasket on up side over. lol
Re: Loss of power on A35 Airsal kit at top end
OK, checked out the reed block, looks like I installed it right & there's no sign of sticking. Kinda makes sense, since I never lost low-end power or throttle response.
Thought maybe I am just fouling plugs: dropped oil ratio to 40:1, went to B7HS plug, gapped to 0.25", rode around for awhile, seems to top-out at around 37 mph. Plug chop looked perfect. Pulled the head and saw a funny burn pattern, like the air coming in was a blowtorch. Picture shows the weirdness, but the clean notches near intake almost feel like the piston on either side got melted.
The head shows no sign of carbon deposit or overheating. Cylinder walls still look great, you can see the cross-hatch all the way around, with just some very small vertical streaks.
Re: Loss of power on A35 Airsal kit at top end
personal opinion to much heat. i would guess because of to much oil.
Re: Loss of power on A35 Airsal kit at top end
You are not getting enough air for your fuel mixture ration I think..your stock carb and intake are restricting you, so lighten up on the oil some maybe 45:1 or something.
Try 2.9oz per gallon or figure out your own mixture Here
Re: Loss of power on A35 Airsal kit at top end
I think I was just lean. Temps dropped from my first break-iin ride in the low 80s to the 30s! I never went WOT until last week, and the plug came out white with a #66 jet. Went up to a #72 jet, and it looks "creamy" (see attached photo). I think one more upjet oughtta do it.
Thanks everyone for your advice. I'm up to 46 mph and now just need better brakes LOL.
re: Loss of power on A35 Airsal kit (pic)
Oops forgot the pic
re: Loss of power on A35 Airsal kit (pic)
still looks kinda lean to me
re: Loss of power on A35 Airsal kit (pic)
OK, a kinda weird experience. Went up to 72 jet and ran much better, but only "creamy" plug chop, as reported in earlier post. Took the whole thing apart to inspect while waiting for jets; found the intake bolts were a bit loose, and saw some leakage on the exhaust header. Tightened, etc. and reassembled. Started with the #71 jet, and had to go down to #68 before it would not 4-stroke! Last plug chop (attached pic) came out red, of all things. I musta had an airleak? but my top speed is down to 40; do I need to loosen the intake bolts to get 46 mph again? ~
re: Loss of power on A35 Airsal kit (pic)
engine mustve liked the air leak a little bit. now its all sealed up youre getting less air and needed to downjet accordingly. if you wanna get back up to speed maybe pull your air box or replace it with a performance airfilter and upjet accordingly.
maybe.
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