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1982 Yamaha Seca 750 Loping Idle, Needs Choke to Run

Discussion in 'XJ Technical Chat' started by Mark Wyzgala, Jun 3, 2021.

  1. Mark Wyzgala

    Mark Wyzgala Member

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  2. Toyobaru866

    Toyobaru866 Active Member

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    You're absolutely right I think. Just looked at my spare set of carbs. IMG_20210605_220121.jpg IMG_20210605_220105.jpg
     
  3. Toyobaru866

    Toyobaru866 Active Member

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    Took me a while to picture this but I get it now, learning curve... Thnx!
     
  4. Mark Wyzgala

    Mark Wyzgala Member

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    Found that test online after having a carb problem turn out to be a slipped diaphragm.
     
  5. Toyobaru866

    Toyobaru866 Active Member

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    I discovered it by accident, sitting on the couch making love to my beautifully rebuilt carbs :)
     
  6. Mark Wyzgala

    Mark Wyzgala Member

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    I’ve rebuilt these carbs half a dozen times. They don’t do nothing for me.
     
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  7. XJ550H

    XJ550H Well-Known Member Premium Member

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    that will lift the slide what you are doing is "inflating " the diaphram from the underside.
    that portal is to feed air to the airjets
     
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  8. Mark Wyzgala

    Mark Wyzgala Member

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    Yes
     
  9. Rooster53

    Rooster53 Well-Known Member Premium Member

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    Try removing the pickup cover and rotate the engine until the reluctor is adjacent to the bottom pickup. If that doesn't do it then rotate the reluctor until it is adjacent to the upper pickup.

    I really think it is a bit irrelevant since you have verified spark on all four and verified all pipes are getting hot. Now I suppose it could be marginal on the 2, 3 side, but the only way to really test a TCI (excepting special test equipment) is to try it in another bike to see how it performs over RPM range.
     
  10. Mark Wyzgala

    Mark Wyzgala Member

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    OK, thanks Rooster. I thought this may be an indication of a failure in the TCI. But you’re right, all cylinders were running so it must be firing when running. I’m getting an ignition test light tomorrow and can confirm proper fire of all cylinders. This TCI is literally the definition of a black box that’s impossible to tell what goes on inside.
     
  11. Jetfixer

    Jetfixer Well-Known Member

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    I have a TCI That has an issue , when I plugged it in bike idled higher and would quit running after a short period. So took cover off was corroded on the circuit board . Needless to say it is in my stache of parts . You might pull the cover and make sure it is not corroded, you can spray it down with contact cleaner .
     
  12. Mark Wyzgala

    Mark Wyzgala Member

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    Thanks for the idea. I’ve already cleaned all the TCI contacts, then took the cover off, inspected the solder joints and reflowed one that looked bad. It was not corroded inside tho. Didn’t help.
     
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  13. Jetfixer

    Jetfixer Well-Known Member

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    Okay I bought a another set of carbs off of eBay so I have a spare set , you could always buy another set off of Dave Fox ...sure he would have a good set he would part with . I know the feeling of WTF is wrong, trying every trick you can think of , almost tempted to pour two gallons of gas and a match and torching it ( please realize it is sarcasm). Sometimes it is something simple , that is overlooked. I once had an airbus A320 that had half of the power bus INOP, I swapped out the power panel, did countless power resets , I had 9 years of experience and had tried everything we could think of , we grounded the aircraft and towed it off the gate , a co worker was sitting in the cockpit, he had his hand on the glare shield , he pushed the master reset switch out of habit with his thumb ....and everything powered up ...we looked at each other and had a shazam moment ...the switch had been pushed in my Mr. Copliot to hard and it was stuck in ...we replaced the switch and no more problem. My long winded story is this is similar it is always the little things ...even if it sometimes the little things . Cheers
     
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  14. Mark Wyzgala

    Mark Wyzgala Member

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    Thanks, Jetfixer. I was getting very frustrated after a year of putzing with this. My Father was a truck mechanic, so I grew up working on cars. So I’m sure I can fix this if I just think it through. I remember when I rebuilt the variable valve mechanism on my old Maxima. When I was done I tried to turn over the engine manually and It wouldn’t rotate very far. It was an interference engine and I thought I had the timing chain on wrong and bent the valves. I just sat down in front of the engine and stared at it for a half an hour. Finally had a flash and realized it was still in gear. Put it in neutral and it spun freely. I’m hoping for one of those flashes of inspiration here.
     
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  15. Rooster53

    Rooster53 Well-Known Member Premium Member

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    Is it running so poorly you haven't even put it on the road lately? The point is at least with my Seca (may not be right) is that too many cold starts / idle time with choke and not getting it on the road can actually foul plugs. It starts with choke and is a little lumpy on startup but just once through the gears it smooths right out.
     
  16. Mark Wyzgala

    Mark Wyzgala Member

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    Yes, I can’t get it to stay lit. I can only get it to idle with the choke on, but I wouldn’t take it out on the street. Besides my driveway is somewhat steep and I don’t want to try pushing it up the driveway. And yes the plugs are fouling with all of the idling. I don’t rev it much when I’m trying to run it at idle. However this isn’t new. I remember before I put it up for storage, plugs 3 and occasionally 1 would foul during normal use.
     
  17. Jetfixer

    Jetfixer Well-Known Member

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    For shits and giggles you might try putting in new plugs , try a set of Autolite Ap63 or 63 these are equivalent to NGK . Change plugs but try to run it out riding , letting it idle especially with choke on can definitely cause plugs to foul out and , cleaning with a wire wheel might and might not save plug. I do have a question for you when you had carbs off did you clean the float bowl enrichment jets ? If one or more is plugged it can cause a only one or two carbs to run cold this could be a possibility and would mimic a loping idle . I once had a Honda CB750 ( never should have sold it but that is another story) number two cylinder you could hold onto the exhaust header at the cylinder, turned out the plug cap was toast .
     
  18. Mark Wyzgala

    Mark Wyzgala Member

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    Yes, when I had the carbs apart I followed Lens advice, got a wire and made sure they were cleaned out. A pipe cleaner was useful to clean the port down in the bowl. I made sure
    I got a strong, straight stream out of each enrichment tube, and could see light through them. Unfortunately I also made sure to blast carb cleaner and air through the pilot circuit passages. I plugged the idle mix port and air jet port with Q tips and made sure I got a good jet of fluid out of all three idle ports in the throttle throat when I squirted into the pilot intake. Perhaps something loosened and went down stream after I reassembled the bike.
     
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  19. Mark Wyzgala

    Mark Wyzgala Member

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    Ok, I think I’ve solved the idle issue. I’ve pulled and disassembled the carbs yet again and found that there was black globs of assembly lube clogging the bowl inlet screens. Apparently the assembly lube doesn’t dissolve in gasoline as I’d expected, but just beaks up and embolises downstream to clog up everything. And I used this assembly lube because I was afraid the silicone lube would embolise and clog things.
     
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  20. Andyam5

    Andyam5 Member

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    Pilot passages, just sayin'
     

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