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xj 650 maxim sputtering on acceleration

Discussion in 'XJ Technical Chat' started by Dstrong77, May 8, 2018.

  1. Dstrong77

    Dstrong77 Member

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    1981 XJ 650 Maxim
    The other day I was riding and noticed that the bike had started sputtering upon acceleration. The bike has pods (I know) and a 4 into 1 with a straight pipe, It has been rejetted and has #42 and #116 jet set up. I did the valve shims late last year so they should still be in good shape probably only 500 miles or so. I thought maybe I had a stuck float. I pulled the carbs and the #2 carb pilot jet was lose and no longer seated it was just floating around. So since I had the carbs off I went ahead and cleaned them. I did not split the rack as I also had done throttle shaft seals late last year.

    One thing I did try on one of the needle jets was to polish it with a metal polish pad. It is similar to a scotch brite pad but made specifically for metal. So when I did that I saw that I did change the finish from smooth to a somewhat "less smooth" state. It went from shiny to a cloudy color. I stopped and didn't do anymore with that pad. I did wipe it down with liquid carb cleaner and put it back in. I didn't think I did enough to make it not operate normally.

    I soaked all metal parts in carb cleaner for an hour. I did not soak the carb bodies or diaphragms in carb cleaner. I know it doesn't like rubber. I reassembled everything bench synced. The bike fired right up and then I vacuum synced. Bike still sounded sputtery. mostly when I rolled on the throttle. I had probably 40% less power. I went to the manual and checked for spark -yes. checked both sides of the coil. One coil was testing at about 11000 ohms and the other coil was at around 15000 ohms. I swapped out the coil with another coil that I had on a parts bike. Both coils now tested at 110000 reassembled and went for another test ride. Still sputtering.

    Before I cleaned the carb and noticed the jet was loose I did have gas on the floor. I couldn't tell for sure where at on the carb it was leaking from. I assumed when I cleaned the carb that it was the pilot jet being loose and not letting the float to operate properly. However now that I have reinstalled the carb with everything tight I can see that it is still leaking gas and it is coming out of the # 2 pod filter. So I am wondering if running it wi9th that jet loose for about 10 miles home flooded the engine oil with gas and or caused piston damage. I do not have a compression tester and I am going to pull the carb again and replace the needle jet that I "polished" I will clean it all again and blow air through the passages and bench sync and vacuum sync.

    Would anyone have any other ideas? I am going to do an oil change just to be sure there isn't gas in the oil tonight as well. Also would a loose pilot jet on one csarb cause piston failure if ran for 10 miles or so?
     
    Last edited: May 8, 2018
  2. Chitwood

    Chitwood Active Member

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    Did you wet set your float levels?
     
  3. Dstrong77

    Dstrong77 Member

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    Not this time. I did about three weeks ago when I tried to switch out #42 pilots for #41 pilots. I didn't like the way it sounded, so I went back to #42 then set float height. That was three weeks ago, I did not do it this time, but I put the floats back in the same carb and didn't do anything with the tangs on the floats to change the height when I had them out. Carb is coming back off tonight though so I will recheck them to see if they have changed any. I suppose that loose jet flopping around in there could have affected the float setting especially with the bike running.
     
  4. Chitwood

    Chitwood Active Member

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    That was just the first thought I had about fuel coming out of the #2 pod
     
  5. Dstrong77

    Dstrong77 Member

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    Ok disassmbled the carbs again and drained oil. The oil smelled like gas.put new oil in checked compression. everything was low but then I read that if you put oil in the cylinder then it will give you different results. I did that and the all compression was at 155 except cylinder 2 which was 180. I think I may have put a little more oil in that cylinder. Anyway, I know that 180 is high but it shouldn't be the cause of my sputtering.

    I had a friend over that knows these carbs and we did quite a lot of adjusting on the float arms. we have them all measured equally and not sticking at all. We would find that after a few taps on the needle that they would sometimes stick. I also found a pretty small rip in one of the rubber diaphragms. It's very small and we went ahead an put a drop of gasket sealer on it. I think it will be ok. I reassembled the carb. I have not wet set the fuel height yet and will do that tonight.

    I am going to go ahead and stick new plugs in it and this thing should be in pretty good shape. I might check the valve shims to see if they tightened up any since last season. I will report back with how it turns out.
     
  6. cruiserlover

    cruiserlover Member Premium Member

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    I sure would like to know the end of this story
     
  7. Dstrong77

    Dstrong77 Member

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    I will update it. I do think that I may have had a diaphragm not seated properly. There was one that had a little bit of a crease in it and I got that straightened out. ITs hard to tell if they are seated properly when you're pushing the spring-loaded hat down and screwing the screws back in. When I push up on the carb slides they all operate similarly. I think I had one before that was not sliding like the others. I assume because of the diaphragm not properly seating. Anyways I feel pretty good about it now and will report back if its fixed.
     
  8. cruiserlover

    cruiserlover Member Premium Member

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    carbs to me are extremely hard to get right.I never have done a good job with them.
     
  9. Dstrong77

    Dstrong77 Member

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    I have been guilty of this myself and last night after a little more tinkering I found that my diaphragm on the creased section was still not seating properly. I went back to "church" and read that had I put some vaseline on the grooves where the diaphragm seats it would stay when reinstalling the carb hats.

    To whoever took the time to write out : the In The Church of Clean https://www.xjbikes.com/forums/threads/in-the-church-of-clean.14692/ , The Information Overload Hour https://www.xjbikes.com/forums/threads/the-information-overload-hour.27544/, and the-ultimate-relay-switch-sensor-and-diodes-guide https://www.xjbikes.com/forums/threads/the-ultimate-relay-switch-sensor-and-diodes-guide.27543/ , as well as the experienced moderators on this site and Chacal. Hats off to all of you. Sharing this information is keeping these bikes on the road a hell of a lot longer than our Yamaha shops. And you have done so in such a way that makes even the nobbiest noobs get it.

    buy bike- do valve clearences-take carb to church- vacuum sync- color tune No shortcuts-then come at us with your questions. Its hammered into all the threads. But it is absolutely necessary. Thanks for keeping these bikes going
     
  10. Chitwood

    Chitwood Active Member

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    Did you get your sputtering issue resolved?
     
  11. Dstrong77

    Dstrong77 Member

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    I didnt get everything put back together. I got a 4-1 exhaust and I took off the exhaust to change the oil filter. When I removed the exhaust I had 2 header gaskets to replace so I am waiting on that. But summarize how my problem came about here is what I believe has happened
    1. Tried to step down 1 pilot jet size 3 weeks ago. didnt like it so I moved back to what I had. when reinstalling I didnt get one of the jets tight. During riding it came losse and jammed the float in the bowl flooding engine
    2. When i opened carbs back up after that problem I must not have seated the diaphragm properly. It was creased on a small section instead of rounded all the way. took it out for ride and had sputtering. But this sputtering was caused by poor vacuum and not loose jet. Assumed I had a bigger problem. Not knowing about diaphram not seating. So I drained the oil. Yes it smelled like gas and I did loose some gas.
    3. Tested coils removed one that was slightly testing out of spec and installed other coil off parts bike that was closer to normal Ohm out put.
    4. Completely tore down carbs except breaking rack. New throttle shaft seals last year so didnt want to mess with them. Carb zestfully clean and bench synced
    5. New Oil, Filter and Plugs
    6. Carb reassembled with vaseline in grooves for the diaphragm seating.

    Now waiting to get the gaskets for header and then gonna fire it up. Then I will vacuum sync. Not gonna count my chickens yet but very hopeful of a smooth running lil yamachopper next week.
     

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  12. Chitwood

    Chitwood Active Member

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    Dude! Nice! You gotta think about going to this! There is a group of about 7 people that I know of that will be there. Love to get the numbers up. Not that we are the only ones there, but it's not a huge turnout
     

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  13. Dstrong77

    Dstrong77 Member

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    I would consider that. Thanks! Des Moines to Dubuque is a good ride on a hardtailed 650 but hey I just tuned it up right!
     
  14. Chitwood

    Chitwood Active Member

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    Mine is only strutted right now, eventually once I get the 750 on the road it will go in for backbone surgery and get hardtailed. Rode from Fort Atkinson WI to Dubuque IA and back last weekend. It was a good ride other than hwy 11 being rough as a cob
     
  15. Dstrong77

    Dstrong77 Member

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    Man I just dont know. This thing is driving me crazy. Now it's acting like it has throttle shaft seals going out. Roll on the throttle and nothing. then all the sudden take off like a rocket. More so after a minute or two of riding. came back, It idles just fine. I start the bike up and it runs great in the garage. throttle responds pretty well on start up. Get going and then its like its dead at a stop light. barely rolls through a stop then it shoots off. All 4 plug wires are testing at 12.5k ohms. Brand new spark plugs. fresh oil, premium gas, bench synced and vacuumed synced carbs. Took the new plugs out. #1 carbon fouled.#2 bright white #3 and #4 looked fine. Cut the plug wires back 1/4 inch and reinstalled boots. I am going to upload a pic of the #2 plug. It looks like its abnormally lean right? This looks like a combustion issue right? I know the plug sparks I pulled it out and grounded it to the motor. Bad TCI? I know the carbs are clean. I am unsure if the gasket sealant on the pinhole in the diaphragm held. I know they were all seated. I set the floats and they were all within 3mm of the of the top of the float bowl (gasket area). It runs pretty good at speed. It just is a complete dog taking off from a dead stop. it would take me 3 or 4 seconds for the power to kick in. Then I would shoot off like a rocket...Please Help

    The #2 cylinder compression is 180 PSI. That is the same cylinder with this lean looking plug. All fuel air mixtures are at around 2 turns out. Course thread screws. This feels exactly like throttle shaft seals as I had that problem 1 year ago. I dont see how they could have failed again...
     

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  16. Chitwood

    Chitwood Active Member

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    Do yourself a favor and order a colortune plug from xj4ever if you don't have one already. Mine bike ran "ok" after complete carb rebuild, valve clearances corrected, new battery, etc, etc. After I put the colortune plug to it, it made all the difference in the world. I know I need to up the size of the pilot jets by a size but I'm still well within an acceptable range. Colortune, synch, colortune, synch, rinse and repeat. It may seem like a bunch of small little changes but when you add them all up it equals a sweet running XJ!
     
  17. XJ550H

    XJ550H Well-Known Member Premium Member

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    gasket sealer is not what you want to use to seal diaphram

    180psi #2 is high but that could just be the tester what did the other cylinders read
    650, 750 air-cooled engines:
    Minimum: 128 psi
    Standard: 156 psi
    Maximum: 171 psi
    Max. variance between lowest and highest: 14 psi
     
  18. XJ550H

    XJ550H Well-Known Member Premium Member

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    check your charging system output voltages
     
  19. Paul Howells

    Paul Howells Active Member

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    I have often read about using oil in your cylinder to help check the compression. My understanding is that your compression psi is tested without oil in the cylinder. Adding oil does not help you get an accurate reading. Adding the oil will only indicate if your low compression is due to rings or valves. If the psi increases when oil is added then it is your rings. If the psi does not increase then your valves are the problem.
     
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  20. jayrodoh

    jayrodoh YimYam Premium Member

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    Have you checked for vacuum leaks on the intake manifolds? Sputtering off idle and taking off is a pretty good indication of lean off idle situation. I will admit I had an old Kaw I was riding that did exactly that. Cleaned and adjusted the carbs multiple times, only when I checked the manifolds I realized they were leaking badly and replacing them solved the issue. You can spray brake cleaner on them and the gasket at the cylinder head when running and see if the idle increases. I've never had much luck with the propane test.
     

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