First start in 14 years. What's that sound?

Discussion in 'Airheads' started by Slicky, Apr 8, 2021.

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  1. Slicky

    Slicky Adventurer

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    R80RT '86 had been sitting for 14 years, most of that outside. So far I've cleaned resealed the gas tank, cleaned and rebuilt the carbs, new petcock filters, fuel filters, cleaned petcocks, new plugs, valve adjustment, oil change, trans fluid, and battery. I'll be looking at setting the timing this weekend. Starts up ok, I can get it to idle about 1100 rpm but it constantly has a sputter or misfire. Video should show that.

    Where should I start with diagnosing this?

    #1
  2. Plaka

    Plaka Brevis illi vita est

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    start by giving it a full tune up, and double check the valves. i don't try to do sounds unless i have the machine in front of me.
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  3. Motopsychoman

    Motopsychoman Not a total poseur Supporter

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    Welcome n00b!
    Sounds like a nice project.

    Airheads are pretty simple beasts, but some problems can be a PITA to isolate. I spent months figuring out a faulty coil years ago, because it seemed to behave just like fuel starvation.

    Like any IC motor: air, fuel, fire makes it run.

    A few basics:
    Do you have a shop manual, Clymer, Haynes, etc.? Some of the specs seem to vary a bit between sources.

    What does it sound like when you open the throttle some?
    Does it sound like it could be backfiring out the carbs (too lean) or detonating out the exhaust (too rich)?
    When you rebuilt the carbs, did you inspect/replace the diaphragms? They develop pinhole leaks.
    Are the chokes in the right way around? Are they on the correct sides?
    Did you replace the float pivot pins? They get flat spots and the float can stick.
    Correct jets and needles? Genuine Bing parts or some aftermarket?
    Did you set the float heights?

    Does this bike have the original ignition (bean can) or something aftermarket?
    What spark plugs did you install?
    How about the spark plug leads?
    Original Bosch P.O.S. coil? Many of them developed cracks which produces bad behavior.
    Have you cleaned all the electrical connections from the bean can, ICU, coils, etc.?
    You set the valves, so timing would my next step. You might attach the timing light to both of the spark plug leads to see if one side may be missing occasionally. The wires do get old and fail.
    Check the timing advance. The pivots for the weights in the bean can can get sticky. You can get at them through the little plugged port on the side of the bean can.

    After that is carb adjustment. What tool(s) were you planning to use to set the carbs?

    So, more info helps.
    #3
  4. thetubespoke

    thetubespoke Long timer

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    I think it's running on one side, I think the left. The other will fire occasionally, it sounds like it speeds up a hair, then back down to what it was.

    I'm guessing idle mixture isn't right. You should be able to tell a difference and figure out which side it is, then make adjustments on the side that isn't firing.
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  5. Pokie

    Pokie Just plain Pokie.

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    If the bike has been parked for that long, you NEED to check for nests in the starter and air filter areas. Mice really like to move into these spots. Watch for mud dauber and wasp nests under the gas tank.
    #5
  6. boxermoose

    boxermoose Regressive airhead Supporter

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  7. Slicky

    Slicky Adventurer

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    Great info! I have some more info to share but to answer your questions first.

    Do you have a shop manual, Clymer, Haynes, etc.? Some of the specs seem to vary a bit between sources.
    Not really, I have a PDF of a GS BMW Manual. Probably worth buying a shop manual any recommendations?
    What does it sound like when you open the throttle some?
    It bogs down a dies when I open the throttle quickly. Slowly it can rev up to 3k but rough
    Does it sound like it could be backfiring out the carbs (too lean) or detonating out the exhaust (too rich)?
    Hard to tell
    When you rebuilt the carbs, did you inspect/replace the diaphragms? They develop pinhole leaks.
    Replaced, all new rubber components except for the butterfly valve o-rings
    Are the chokes in the right way around? Are they on the correct sides?
    Oriented correctly and on the correct side. Unless they are 360 degrees out, is that possible?
    Did you replace the float pivot pins? They get flat spots and the float can stick.
    I did not replace the float pivot pins, no flat spots were noticed
    Correct jets and needles? Genuine Bing parts or some aftermarket?
    Cleaned the jets and needles that were in in the bike. Did not replaced them
    Did you set the float heights?
    Checked float height, opens at perpendicular. Fuel flow in both carbs is plenty

    Does this bike have the original ignition (bean can) or something aftermarket?

    Original
    What spark plugs did you install?
    NGK BP6ES
    How about the spark plug leads?
    Original
    Original Bosch P.O.S. coil? Many of them developed cracks which produces bad behavior.
    Yes
    Have you cleaned all the electrical connections from the bean can, ICU, coils, etc.?
    I have not

    Your suggestion with altering the timing light is great, ill certainly do that. Before staring the bike up I check for sparking by putting old plugs in and grounding them. On both sides I as getting spark.
    #7
  8. Solo Lobo

    Solo Lobo airhead or nothing Supporter

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    I'm with tubespoke... running on one (occasionally two).

    You should get your hands on some kind of balancing tool, but you find the gremlin when you do that

    One other thing to try is to unscrew the spark plug caps, cut off a bit, and thread them back on.
    #8
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  9. Slicky

    Slicky Adventurer

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    :clap Bingo. Not sure how you were able to notice this via the video and I wasn't when I was standing right there. I'm impressed. Must have been the excitement of starting the bike up for the first time. I started the bike up again and it was clear that the left cylinder was not pulling its weight. The exhaust seemed the same but it was clear that it was pulling less air through the carb. I could almost fully cover up the carb with my hand without any effect on the idle. On the right side the bike would quickly bog down and die. I compression tested both cylinders. See video below ~60-65 psi on both. =( Added some oil to both cylinders and similar results. The left intake valve looks to have a sealing issue.




    Left intake valve looks like its not sealing to me based on the attached pic. Surprised the right has such bad compression and is running.
    20210410_145615.jpg


    Given this added info. Anything else I should try before taking it apart?

    Pics of the plug
    20210409_192929.jpg 20210409_192937.jpg

    Attached Files:

    #9
  10. Motopsychoman

    Motopsychoman Not a total poseur Supporter

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    Your compression tester has a problem. The check valve is bad. It shouldn't leak down. Plus, if it is like the similar one I have, the compression is really about 20% higher than it reads due to the large volume of the plug adapter.
    Mine read about 108 PSI. When I used my older Sun gauge, it read 128 PSI (which I believe). G/S is a low compression airhead.

    But sucking more air through one side sounds like an indication of imbalance. Could be valves, could be stuck rings (are you seeing grey/blue smoke?).

    How many miles on the engine?

    I'd spray some carb cleaner in the intakes and see if any of that scum comes off.

    From the plugs, definitely looks like one side isn't firing at all. One header should get hot fast and I'd bet the other is cold. Wave your have by them. Then swap the wires and see what happens.

    Manual: I like the Haynes, but others like the Clymer better.
    #10
  11. thetubespoke

    thetubespoke Long timer

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    Ah, great! Glad it was that one side.

    Sometimes running a motor, especially under load, will help in a case like that. There might be some gunk under the valve. In general though, it looks kinda like there's an oil leak maybe through the valve guide or something on that side. That plug is really oily.

    If you really don't want to tear into it, I'd try going for a ride and see if it gets better. Maybe be sure to change the oil first since it's been sitting that long. If not, taking the head off and working at the valve should help. Combination of cleaning and then inspecting the valve and valve seat.

    It does look like further inspection is warranted either way.

    I've never tried this before, but I suspect there's a chance as well that without spark on the left side and without the carburetor, you might be able to spray in a strong solvent (carb cleaner, starter fluid) while it's running and possibly free something up. Gasoline is a great solvent, but I assume the bike was put away with the valve looking like that. Which would be another point towards pulling it and looking it over.

    Even if you need to do a bit of a valve job it's probably not too hard to clean it up and lap the valve/seat with some lapping compound. I haven't done it myself, but I've seen it done often on Japanese bikes.
    #11
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  12. Slicky

    Slicky Adventurer

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    Agree about the rubbish compression reading. Ill try and find a new gauge today and retry. If I have decent compression Ill focus in on the ignition.
    #12
  13. Motopsychoman

    Motopsychoman Not a total poseur Supporter

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    Also, you might want to go back into the carbs and replace those o-rings on the shafts. When I puilled mine apart 2 years ago, those fell out in about a dozen pieces. Replace the little brass screws in the butterfly plate at the same time (don't want one falling into the cylinder).

    @thetubespoke is right. If you can get the motor just running enough to take it out and get the thing hot, crap may break free and start running looser.
    #13
  14. Solo Lobo

    Solo Lobo airhead or nothing Supporter

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    Switch the carbs to side to side and see if the issue follow the carb or not
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  15. Cogswell

    Cogswell Road General

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    How does it run and idle with the air box on the bike ?
    #15
  16. Slicky

    Slicky Adventurer

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    Update:
    Got a new compression gauge and both cylinders checked out at 100 psi. Nice
    Bike is pretty far from being road ready, so no joy rides of now.

    Ran the bike again. Same behavior, right carb can audibly sucking in air and bike dies when I cover it. Left doesn't seem to be pulling as much vacuum, can cover without bike stalling.

    On a cold start the right side get hotter faster but the left still gets hot. Certainly wouldn't say its cold.
    Lifting each carb throttle individually a little this is what happens. Left, idle rises. Right, bike start to bog and die.

    While the spark plugs both had spark I took the tank off and to check out the leads and coil. Both lead checked out at 5k ohms. One of them was stuck in the coil and in my infinite wisdom I yanked it, ripping of the plug going into the coil from the wire. Had to mangle the plug to get it out of the coil socket. Bummer
    Ill solder it up and reform it today. Maybe it will be salvageable for continued testing

    Looks like I have the crackomatic ignition coil. Coil is 1.8 ohms between the 1 and 15 screw terminals. No continuity from the secondary spark plug sockets, 4a and 4b. I'll double check this with a better meter today.

    20210411_171138.jpg
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  17. Slicky

    Slicky Adventurer

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    This will be next up after I fix the plug wire.
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  18. Slicky

    Slicky Adventurer

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    Still in the process of cleaning out the airbox and repainting. 20210228_115403.jpg
    #18
  19. Pokie

    Pokie Just plain Pokie.

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    Are you sure that bike wasn't involved in a flood? It's not often you see the inside of the air box that bad.
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  20. noman

    noman Long timer

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    this isn't uncommon :D
    [​IMG]
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