right piston lacks performance...hmm

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LC Cnd
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right piston lacks performance...hmm

#1 Post by LC Cnd » Thu Jul 13, 2017 2:48 am

Compression on both pistons is 120 on my LC. Premix 40:1. Just adjusted the carb needles to stock position cause it was boggying out when I cracked the throttle - was on 2nd lowest fm the tapered end. Tonight put stock pilot jets (new), new 230 mains in becuase of Micron exhausts (as recommended). Idles at 1200rpm and air screw set at 1.5 turns. Pipe between the Mikuni vm26s connected. New plugs properly gapped. Fired up. Noticed the right piston exhaust felt like it has half the compression to the left which just crackles. Left pipe smokes fine; right hardly note any exhaust. Go for a ride and felt the right piston just bog out & stops, and noted I was running only on the left piston. Not a seizure. Stopped, waited 2 minutes and fired her up again on both both cylinder for the ride back home. Leak down test - passed. Suspect this problem is a spark (right jug) issue that I should be examining.

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two-stroke-brit
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Re: right piston lacks performance...hmm

#2 Post by two-stroke-brit » Thu Jul 13, 2017 1:51 pm

Sounds like a bad plug/cap/lead to me
350LC,Athena 392 big bore,stock porting,swiss cheese air box,stock reeds,spec11 pipes.(now TSA big bore pipes)
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1982 YAMA RD350LC
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LC Cnd
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Re: right piston lacks performance...hmm

#3 Post by LC Cnd » Thu Jul 13, 2017 9:36 pm

Well replaced the plugs and bought new caps from Yambits. Whats the best way to test the ignition coil right lead? Possibly a crack in there. I do have a spare coil but a new banshee coil would be the best replacement.

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Re: right piston lacks performance...hmm

#4 Post by Jessy » Fri Jul 14, 2017 8:56 am

Swop the leads over, if the problems moves to the other side it could be your coil.
Jess

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Re: right piston lacks performance...hmm

#5 Post by silverstrom » Fri Jul 14, 2017 9:48 am

Jessy wrote:Swop the leads over, if the problems moves to the other side it could be your coil.
Jess

It doesn't work that way. On the RZ350 the coil fires both plugs at the same time.

LC Cnd
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Re: right piston lacks performance...hmm

#6 Post by LC Cnd » Fri Jul 14, 2017 9:48 pm

Suspect its the same on the RD nes pa?. Can I do a meter test to determine if the right lead is defficent?

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Re: right piston lacks performance...hmm

#7 Post by silverstrom » Fri Jul 14, 2017 10:45 pm

The resistance values are in the manual for the coil, leads, and caps.

Make sure you are using resistor plugs, caps, and leads. If not, RF interference will play havoc with the ignition/CDI.

As far as electrical problems go that affect only one cylinder; a faulty lead, cap, or plug would be the possibilities. The exception to that would be coil damage affecting only that output post at the coil. That would be a very rare occurrence. I doubt many people have seen it happen.

Replace the spark plug every time you have cylinder ignition problem. They're cheap and it's always the weak link.

It's worth checking your reeds as well. A broken or stuck reed petal will cause similar symptoms.

Right cylinder problems can also be traced back to plug fouling caused by a right crank seal failure and the ingestion of gearbox oil. Monitor your gearbox oil level if you see oil on your spark plug or see other than 2 stroke smoke from the right pipe. The performance result will be exactly as you describe. If you put a plug in and the bike runs fine...until it doesn't, and you can repeat that, you know where to look next.

It's worth doing a leak-down test at some point.

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Re: right piston lacks performance...hmm

#8 Post by LC Cnd » Sun Jul 16, 2017 11:26 am

Replaced the plugs (r's) and caps. The problem still persisted. Noted that ignition, in the right cylinder, appeared to intermittantly ignite/fire when I pulled down on the throttle. Ck's both carb bowls and each had fuel come out of the drain plug. The crank case oil level is still full from when I 1st put it in - will monitor however. Ck'ing the reeds next.

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Re: right piston lacks performance...hmm

#9 Post by LC Cnd » Thu Jul 20, 2017 1:46 am

Pulled the reed (right) and it appears to be fine. When I fired up the engine prior to pulling out the reed, I did note an odd exhaust noise right side. There was a hissing (or missing?) sound when I gave some throttle. The hiss happened several times. The left would not produce this noise. Next right crank case seal - this means splitting the case correct?
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Re: right piston lacks performance...hmm

#10 Post by silverstrom » Thu Jul 20, 2017 3:07 am

You said your leak-down test was good?

Typically if you have a right crank seal failure you'll see the smoke and you'll see a fouled plug.

What do you feel when you put your hand over the end of the exhaust left and right? No suction...just pressure? Put a clean white cloth over the end of the pipe and see what it looks like. Different colour left and right?

Is your coolant level ok? No chance of a head gasket leak on the right cylinder, although the compression test should have picked that up if it was bad.

Are you absolutely certain you aren't really chasing a fueling issue.

Your reeds look to be solid, but are they opening properly? Those 2 stage reeds have a tendency to stay stuck together and not open properly, especially at low RPM. Over-oiling with pre-mix can exacerbate the problem. If they're Boyesen, they suck. Throw them in the garbage. A single stage carbon reed would be a better option.

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Re: right piston lacks performance...hmm

#11 Post by LC Cnd » Thu Jul 20, 2017 9:22 pm

When putting the reeds back in, decided to try putting fuel resistant gasket sealer on the reed valve assembly and both sides of the valve seat gasket. Yes it will be messy when I have to pull it apart but now both pipes have equal pressure coming out. However did note that the right does throw a bit more oil out the end on the towel. Lighten up on the fuel mixture (45:1) and the boggy sound has been reduce. Took her for a ride and she pulls and at one start the front tire did lift sightly when on the pipe. I will monitor the plugs colour and crank case oil. So far its promising.

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Re: right piston lacks performance...hmm

#12 Post by silverstrom » Thu Jul 20, 2017 10:11 pm

That's good progress.

Always seal reeds and use gaskets/sealant on both sides of the cages/blocks. Permatex MotoSeal is what I always recommend. Use it for the case halves, reeds, etc.

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Re: right piston lacks performance...hmm

#13 Post by LC Cnd » Thu Jul 20, 2017 11:24 pm

Thats exactly the product I used actually. Good stuff and I'm glad I wore latex gloves. The next challange is timing which I've never done but will give it a go. Thx for your guidence John - cheers Scott.

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Re: right piston lacks performance...hmm

#14 Post by JonW » Fri Jul 21, 2017 1:18 am

could also be a sticking fule inlet valve in the carb, Ive seen bikes tick over and run quite happily with only 1 cyl running, tap the carb on the non smoking side and wow, 2 cyls. worth a check if you ever have an issue.
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Re: right piston lacks performance...hmm

#15 Post by LC Cnd » Fri Jul 21, 2017 3:24 am

Good pt Jon. When I pulled the reed out, I pulled apart the carbs and inspected the play in the float needles (functional) and ck'd float levels while I was at it. Well, learnt 2strokes are unforgiving when it comes to the balance/beauty regarding sum of it's working parts. Discovered that today when I felt the power band kick in and I had to grab tank with my thighs while my shoulder sockets began to stretch. I kept thinking ooOH YA.... and it not fully tuned yet! Smiling now.

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