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Thread: R100RT firing on 1 cylinder.

  1. #1

    R100RT firing on 1 cylinder.

    Hello all,

    I have a 1984 R100 RT. It has the Seibenrock Power kit. I've been running into a few gremlins and looking for ideas and what to check.

    The bike would not rev beyond 5000 rpm. In neutral, it would go past but stumbled from 4500 to 6200 then picked up again after. After noticing the bean can was in dire need of servicing, I decided to swap to the Alpha v4 ignition (Hall sensor and ignition module). After, the bike was revving nicely and I got the carbs sync'd. The next morning, went to take it for a ride, would not start. Stumbled and would only fire on left cylinder. Removed right plug, noted plug wet with fuel. Tested the ignition coil, showed open, replaced both coils. I have compression on both cylinders, within 3 psi of each other. Removed front cover, made sure timiing mark were correct. Reassemble, still does not fire on right cylinder. Removed cylinder head and inspected, nothing out of the ordinary present. Swapped carbs left to right to check if possibly a fueling issue. Would not fire on either cylinder. I have spark on both cylinders when the plugs are grounded outside the cylinders.

    I disassembled the carburetors and removed all the jets and brass fittings, soaked overnight and then used wire files to make sure there was no varnish or clogs. I never quite trusted the plain spray type cleaners. I have fuel refilling the float bowls and the floats move freely. When I raise the floats, fuel stops. The diaphragms are new as well.

    So to recap:
    Carbs cleaned when engine was assembled (600 miles ago.)
    New Plugs
    New NGK Wires
    New Alpha v4 Ignition system
    New Bosch Ignition Coils
    Timing set
    Valve clearance set
    Compression checked

    I'm at a loss here as it seems like the spark is being snuffed somehow. Perhaps too much fuel? I tried to lean it out and still will not fire. I am leaning towards an issue with the carburetors themselves but, my experience with them is rather limited.

    Thanks in advanced!

  2. #2
    Liaison 20774's Avatar
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    Welcome to the forum! Thanks for the write up...you've been very thorough. I find myself saying something like "change the plug wires" and then check your list and see that you did that. "You need new plugs"...ooops you already did that. So, I'm still scratching my head. I think the issue points to electrical.

    An after thought...with the bike running on one cylinder, have you tried spraying carb cleaner into the throat of the right carb. That would ensure that it is getting something to burn in terms of fuel.

    Also, where are the settings for the carb in terms of mixture, idle speed, throttle cable tension. For a starting point, the air-fuel mixture setting should be at about 0.5 turns out from lightly seated. For idle speed, the knob on the underside of the carb should be turned until it just makes contact with the slide and then turn the knob one full turn. Cable tension should be such that when you pull on the cable at the carb, you should see about 1mm of slack in the cable with respect to the ferrule on the carb.
    Kurt -- Forum Liaison ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  3. #3
    I did try starting fluid and it will sputter but, never "catch" so to speak. I do have the idle speed screws 1/2 turn from seated. I have the mixture screws 2 full turns out on both carbs. With the increased compression, it won't idle on one cylinder for me but, with the one plug removed, it will for a while. Cables are equally adjusted, around 1-2 mm pulling the ferrule from the carb.

  4. #4
    Liaison 20774's Avatar
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    BTW...what are the carb numbers? The Bing manual shows 0.5 turn out for the idle mixture and I suggested one full turn for the idle speed. Maybe we're not talking the same thing. But if you are 2 full turns out on the mixture, that's probably way too much...could be over richening the mixture for start.

    How have you checked timing if it won't run all that well? I guess you could see the timing using an inductive timing light on the left spark plug wire when running only on one cylinder. What would happen with the timing light if you were to move the inductive pickup to the right hand plug wire? Does the light still flash?
    Kurt -- Forum Liaison ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  5. #5
    As far as checking it, I pulled the front cover, made sure the marks were lined up. I thought perhaps I could have been off a tooth. Unfortunately, not off there. If you mean setting the advance, obviously it needs to run right to do that but tweaking the advance to get it to start is simple enough. I usually start in the middle and nudge either direction based on how it's cranking. I've heard it can be technically set static but, haven't seen a reliable way that works better than my current method. It the manual, it recommended 1.5 turns for the adjustment on the bottom of the carb then increase as necessary. When the carbs were syncd, and even prior to the ignition issues, that was were I had them. Regardless, I have tried going in by 1/4 turn each and try to start with no luck yet. The 1/2 turn I have for the idle speed. Not sure if you're referring to the same thing. I will double check that when I get home.

  6. #6
    Liaison 20774's Avatar
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    If you can, tell us the numbers on the side of the carb. 64/32/xxx or something like that. I would go with Bing settings. Somehow I feel we may be talking about different points of adjustment. I'm more familiar with my /7 carbs and where the adjustments are...they may be different for your bike.
    Kurt -- Forum Liaison ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

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