Author Topic: L side Firing Inconsistently  (Read 382 times)

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Offline jdbushnell

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L side Firing Inconsistently
« on: October 23, 2021, 05:46:20 PM »
Restoring a 1970 Mk II SS 200 for over a year now. Nearly done but for the life of me I cant get the L side to fire as well as the L side. New battery, new coils with new wires/caps, fresh fuel without ethanol, rejetted carbs dozens of times, checked timing over and over, changed plugs several times, replaced carbs with new, pulled engine apart and checked timing marks/installation of rotary valves, etc. I am at my wits end and just dont have any more thoughts. Anyone else out there ever have this problem? Anything else I can check? I can start and even ride the bike but the L side is very wet, pops and doesnt run smoothly like the R. I even get fuel dripping from muffler joints on the L after running it for a while and the L side exhaust header and cylinder head are less than half as hot as the R side so I know that the fuel isnt burning completely. Feels to me that maybe its only sending a spark to the plug 1/2 the time. Thanks! I am losing interest in this project as a result and would really like to finish it.

Offline Old BS Guy

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Re: L side Firing Inconsistently
« Reply #1 on: October 24, 2021, 01:21:08 AM »
How far apart have you had the engine? What are the current compression figures for both sides? Have the points and condenser been replaced? Have you looked at the exhaust baffle on the problem side for potential blocking? Have you set the o.i. pump, and do you know for sure the check valve for that side is working properly? If not, it could be drooling oil after shut off and picking it up when restarting. Your problem may not be as much fuel related as oil fouling.
'65 BS Homer 50, '69 Mach II RS 200, '67 GTR,(2), '70 GTO,'79 Honda CBX, '80 CBX '82 Yam 650 Turbo, '74 RD-350, '70 Triumph 500 Trophy, '64 Honda CL72 250 Scrambler, 67 Honda CL77 305 Scrambler. '67 Kawasaki A1SS Samurai

Offline AlanJohn

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Re: L side Firing Inconsistently
« Reply #2 on: October 24, 2021, 06:21:04 AM »
l recently done a simple muffler change and the bike wouldn’t run right after ld fitted it l couldn’t work out why it didn’t make sense so l took the muffler back off and away it went the muffler was blocked something had been nesting in it and that was the reason cleaned it out problems solved
« Last Edit: October 24, 2021, 06:28:02 AM by AlanJohn »

Offline czmike

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Re: L side Firing Inconsistently
« Reply #3 on: October 24, 2021, 06:25:11 PM »
Hello JD,

Sorry to hear you are having so much trouble with the 200 but two stroke twins can be very troublesome sometimes.

The ignition needs to be proven good first.
Buy two of these and install them:
https://www.2fastmoto.com/Lighted-90-Degree-Spark-Plug-Cap-Clear_p_190.html

They are great for quickly sorting problems with ignition systems.
If you have an ignition misfire the light output will flicker or go dull, instantly indicating a problem.
You should be seeing flashes of light from each cylinder with identical brightness at low speeds and two identical, steady glows at higher speeds.
The brightness will fall at the higher speeds (due to the fixed Dwell Angle) but they should both be the same brightness, with no drop-outs.
You are lucky you have one good cylinder to compare things against.
The lamp brightness relates directly to the electrical energy (milli-Joules, or mj) of the spark!

I have high-tech equipment for testing ignitions but I always reach for these little gadgets first when I get troubles.
They literally show you the ignition's performance.

Good Luck & let's know how you get on please.


Best Regards,

Mike Munday,
Melbourne, Australia

Offline jdbushnell

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Re: L side Firing Inconsistently
« Reply #4 on: October 24, 2021, 07:54:16 PM »
Thanks for the feedback. I hadnt thought of the oil pump. Its been adjusted per the service manual but I can take the one way valves off and test them. I will try the 2fastmoto products as well. I like the idea there. I pulled the generator yesterday and sending it to Rex's Speed Shop for rebuild and electronic ignition if they can fit one so it'll be a couple months before I get to try it again. That's gets the points out of the equation. Exhaust is clear but excellent thought.

Offline Old BS Guy

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Re: L side Firing Inconsistently
« Reply #5 on: October 24, 2021, 09:24:59 PM »
Another quick way to validate that would be to disable the o.i. and run it on some 32:1 premix just to see if it cleans up and runs. (After you get your dynamo back). if memory serves, there's a drain plug under the crank cavity on each side. You might want to pull the one on the problem side just for kicks to see if there's any big residual amounts in the cavity. It's a good tattle-tale. Again, all this assuming compression is strong and equal. Good luck with it.
'65 BS Homer 50, '69 Mach II RS 200, '67 GTR,(2), '70 GTO,'79 Honda CBX, '80 CBX '82 Yam 650 Turbo, '74 RD-350, '70 Triumph 500 Trophy, '64 Honda CL72 250 Scrambler, 67 Honda CL77 305 Scrambler. '67 Kawasaki A1SS Samurai

Offline OldSwartout

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Re: L side Firing Inconsistently
« Reply #6 on: October 25, 2021, 08:58:36 AM »
Here's my instructions on adding an electronic ignition to a 350. The same instructions apply to later model 175/200s, plus there are instructions for early model 175s elsewhere. If you search this site for  "electronic ignition" you'll find other electronic ignitions referenced also. No need to reinvent the wheel.

https://bridgestonemotorcycleparts.com/index.php?topic=3645.msg19684#msg19684
« Last Edit: October 25, 2021, 09:17:40 AM by OldSwartout »
Karl Swartout
Mooresville, IN
BS175 Roadracer. BS200RS, BS175HS
BS350 GTR

Offline jdbushnell

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Re: L side Firing Inconsistently
« Reply #7 on: Yesterday at 09:05:16 PM »
Karl, that conversion looks excellent. If Rex's doesnt have a solution I will use yours. Its taking a long time to get the generator rewired so may be another month before I can get it back to try this. Thanks

 


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