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  1. #1

    Join Date
    Apr 2014
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    291

    Default Randomly decided to run on one cylinder

    So I was putting down the road the other day and after a solid 30 miles of riding, with the bike running tip top, it starts surging a little. Then it gets worse. And worse. Miraculously it dies in my neighborhood and I'm able to push it to the garage. I pulled the plugs and the right one was drenched. And, it's kicking back hard now when I try to start it, before it was an easy one kick and ran like a beast. And now when it's trying to start it's backfiring through the carbs sometimes. And then when it does start I have to crack the throttle open or it will "chug out."

    Here's what I've checked:

    • Replaced the igntion coils about a month ago.
    • Good compression on all cylinders
    • Pulled the pilot jets and blew them out with air
    • Battery is good and running over 12 volts
    • Checked for bare wires/grounds... nothing.
    • Spark all around
    • Verified fuel flow from the petcock to the carb.


    Basically, what the fuck? Why would it just start surging and running like shit for no reason? I have an electronic ignition so I know the points didn't shit the bed or anything. I feel like I've checked everything. My first thought was plugged pilots but I cleaned the Mikuni Round slides and that didn't help at all. The rest of it is a '66 Bonneville... which may explain some of it.

  2. #2
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    Backfiring through the carb and kicking back sounds like timing too far advanced for some reason. Verify ignition timing.

    Even electronic ignitions can malfunction. Which ignition (WHY don't people ALWAYS mention the BRAND and MODEL of relevant parts they are using?) are you running?

    I'd inspect the right carb to ensure it's not flooding.

  3. #3

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    Quote Originally Posted by farmall View Post
    Backfiring through the carb and kicking back sounds like timing too far advanced for some reason. Verify ignition timing.

    Even electronic ignitions can malfunction. Which ignition (WHY don't people ALWAYS mention the BRAND and MODEL of relevant parts they are using?) are you running?

    I'd inspect the right carb to ensure it's not flooding.
    Thanks, it's a Boyer Micro Mk. IV ign. I've never had any problems with that particular piece so far...

    I checked the enrichener seals too because I hear those go bad sometimes, but if it was a stuck float or a carb actually flooding, I assume it'd be coming out the overflow tube.

  4. #4
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    could be the ignition system. sounds like it too. after the bike cools down will it start back up fine? run it with a heat gun pointed at the ignition module if it dies after its hot, the module is overheating.

  5. #5

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    Quote Originally Posted by RichDodds View Post
    could be the ignition system. sounds like it too. after the bike cools down will it start back up fine? run it with a heat gun pointed at the ignition module if it dies after its hot, the module is overheating.
    That is the weird thing, I thought it could have been overheating too, but after letting it sit overnight I'm still having the same problems. Going to try to retard the timing tonight?

    Is it possible I didn't tighten the rotor on the ignition down enough and after lots of RPMs it loosened up on the tapered fitting? But I would think that would retard it, not advance it.

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    instead of retarding the timing how about verifying that it is timed CORRECTLY in the first place? Also check timing if/when it shits the bed. Do not wonder, do not speculate, test then know.

    Always do the basics first. If in doubt about rotor security, remove, inspect, reinstall. Basics, basics, basics.

  7. #7

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    Quote Originally Posted by farmall View Post
    instead of retarding the timing how about verifying that it is timed CORRECTLY in the first place? Also check timing if/when it shits the bed. Do not wonder, do not speculate, test then know.

    Always do the basics first. If in doubt about rotor security, remove, inspect, reinstall. Basics, basics, basics.
    Okay, I went through it and the timing was where I had it set and hadn't shifted. I had to advance the timing from the mark slightly because I'm due for a new alternator rotor, as its loosened up a little so the factory timing mark is off. But it was running perfect before.

    I also checked for stuck valves and they're all operational. Battery reads 12.73 volts.

    I can't get it to start, and I have no fucking clue why. All it wants to do is nothing most of the time, and then when something happens it kicks back HARD and backfires out of one of the carbs. Sometimes left and sometimes right. The mixture isn't burning but I checked and have spark, and the ignition appearance to be sending the spark correctly. These fucking coils are brand new nice British ones.

    I can't find anything that would explain why it randomly shit the bed and I also can't find anything abnormal that would explain the lack of combustion. Mix screws are where I set them.

    I hate motorcycles.

  8. #8
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    Describe how timing was checked, static or running. A hard backfire out the intake indicates firing way out of time so reality just took a runny shit over what timing marks may indicate.

    Now you have no joy with verifying timing to marks, you can infer the rotor shifted and it would be logical to retard the timing in SMALL increments to sneak up on a correct setting.

    You could verify ignition position relationship to piston position using a TDC indicator and a degree wheel if you have those, but first I'd move the ignition backing plate instead and time by ear.

  9. #9

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    When I got the timing right by ear I put a mark on the Boyer plate so I'd remember where to time it for next time. I probably did 200 miles like that since getting the bike on the road and haven't had any problems until now.

    I know you're right about it seeming too advanced, but there's enough voltage for the Boyer auto advance to work correctly, in theory.

    From there I tried retarding it, advancing it.... Nothing.
    Last edited by ScarTissue; 07-31-2015 at 4:27 PM.

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    Next step i'd try is swaptronics. Wouldn't hurt to have a points setup around for such things, they don't care what coils they are attached to. Trouble with electronic ignitions is there is no handy way to instantly check them. Points are in time or not and points switch open and closed, or not.

  11. #11

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    On something like this when ne plug goes bad, I put new ones in. Have you tried that? (Not cleaning them, but a new set, or at least a new for the bad one)

  12. #12

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    Well, I'm still not sure what happened, but I took the Boyer rotor out as well to inspect for damage and put it back, timed it and put it back... Now it seems to be idling and working like normal.... No idea what I did or what was wrong.

    Here's a general question, when fine tuning the ignition timing by ear, what are some signs that it's running too advanced, besides pinging? I'm pretty familiar with characteristics of too retarded timing.

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