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Problems with 1981 Seca xj750

Discussion in 'XJ Technical Chat' started by RusteeGold, Jun 1, 2015.

  1. RusteeGold

    RusteeGold Active Member

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    Hi

    I'm fairly new to this forum and I hope I can get some help. After looking for 3 years I found the bike I just had to have - a 1981 Seca 750 with the touring package. I live in California and the bike was in Michigan so I flew to Michigan last week with the intent to ride it home. I had some mechanical problems on the way home and I was forced to modify my trip after 1400 miles (New Mexico) and uhaul the bike home. So now the bike is home but it doesn't run well at all. It will start and idle but has no power. If I let the clutch out in first gear it dies.
    Here are some facts about the bike:
    I cleaned the carbs and I am getting fuel. I'm getting spark to all 4 plugs. I tested for compression and I have 130 to 135 psi in all cylinders. The coils both have 2.5 ohms on the primary circuit and 25,000 ohms on secondary. My manual indicates the proper amount of ohms should be 11,000 on secondary but I have a 1982 Seca that runs well and the ohms for the secondary on that bike is 22,000.

    I'm stymied with this bike. It should run well BBB asked on all the numbers and it did run well when I bought it. What could be the problem?

    Thanks in advance
    Steve
     
  2. hogfiddles

    hogfiddles XJ-Wizard, Host-Central NY Carb Clinic Moderator Premium Member

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    How did you clean the carbs? What did you set your idle mixture screws at? Did you flush the tank? Service the petcock? Check the gas cap to make sure the vent works? Did you do a bench sync? Running sync?

    Did you adjust your shim clearances first?

    What were the mechanical problems you had?

    Dave
     
  3. RusteeGold

    RusteeGold Active Member

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    HI Dave,

    Here are the answers to your questions:

    How did you clean the carbs?
    When I first picked up the bike in Michigan is would get up to about 70 MPH and then it would start to stutter if I applied any more throttle. I know the bike had been sittin gin a garage for about a year and I suspected old gas and varnish in the jets. I ran 2 bottles of Seaform over teh course of the next 1000 miles and it didn't seem to help - in face the performance of hte bike got worse. I decided to clean the carbs on Memorila day in New Mexico. I boght th e toosl I would need and pulled the carb rack off the bike and dis-assemebled all the jets and used 3 cans of carb cleaner in the process. It took me about 4 hours to complete the process. A local car garage owner allowed to use the tailgate of an old pickup as my bench. The inside of the carbs looks a little dirty but I found no blockages in any of hte jets or passageways.

    What did you set your idle mixture screws at?
    I did not touch the mixture screws. Apparently the bike ran well before storage and I did not think the mixtures screws needed to be adjusted.

    Did you flush the tank?
    I did not flush the tank. The gas in teh tank was old - probably a year old. I ran that gas through the bike and ran 8 more tanks through the bike. I assume that by now the gas in teh tank is good gas even if it was bad gas to start with.

    Service the petcock?
    I did not service the petcock. It seems to be working fine.

    Check the gas cap to make sure the vent works?
    I have tried to run the bike with the gas cap un-locked - so that air can get into the tank. It makes no difference.

    Did you do a bench sync? Running sync?
    I did not sync the carbs - again, it was running well a year abo and I am assuking the carbs were in sync then.

    Did you adjust your shim clearances first?
    I did not adjust the shims. I have not checked the valve clearance.

    Mechanical problems: After a day of riding, my top speed was about 60 P MPH. Any additional throttle wold cause the bike to stutter and actually lose speed. Going through Oklahoma I ran in a lot of rain. The bike strated bogging down bad - top speed of about 30 MPH. I stopped and determined the 2 outside cylinders were not firing - teh exhaust pipes were cold to the touch. I found a motorcycle shop and then found a crack in the left coil which was liklely the cause of the cold exhaust pipes. They blew water out of the coil and dried it the best they could then sealed it up with JB Weld. The coil started to work - I had spark to all cylinders so I continued on my journey.

    The next day I was going through Amarillo, Texas and my top speed had dropped to 45 MPH. However, all cylinders were firing. I bought new plugs but didn't seem to help.

    On Memorial Day I was in Tucumcari, New Mexico. I decided to clean th carbs that day (see above desciption). After cleaning the carbs, it made no difference. I decided to try to make it to Albuquerue because there was a bike shop there. It was 175 miles away. After spending an hour riding, I had only gone 30 miles. I decided to return to Tucumcari, however I did not make it back. On the return trip the bike kept losing power. Finally it got to the point that the bike would idle, but did not have enough power to move itself forward at all. It would die when the clutch was engaged. I called a tow truck and that's how I got back to Tucumcari.

    Now the bike sits in my garage. It has 135 PSI comptession, spark and gas. But I can't get it to run. It ran before I bought it and it seems unlikely that the carbs fell ot our sync of the timing got messed up or the valves fell out of adjectment just by sitting for a year.

    But I'm open to any ideas - I really want to get this bike running. It's a great bike.

    20150521_194752.jpg
     
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  4. MattiThundrrr

    MattiThundrrr Not a guru

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    It is a good looking bike! Lots of potential there. All that plastic is getting harder and harder to come by, and yours looks pretty clean! You just need to remember that it is 30 + years old, and you must assume that everything the last owner did was wrong. "THe Church of Clean" thread should be your next stop. These carbs are filled with tiny tubes, and spotless is the best way! Also, have you checked the valve clearances? there is a link in my signature... If the valves are out, every other adjustment is futile. Also VERY important to look for a date code on the brake lines, they may be 28 years past life expectancy! Rear brake shoes are prone to delamination, with possible fatal results. Take care of this bike, and you will love it for years!
     
  5. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    +100

    You have a sick bike. The only cure is a thorough going through to attend to all of the maintenance that was likely never done. Making assumptions will leave you stuck on the side of the road ( as you have found)
    In addition to the church of clean, I recommend that you visit The Information Overload Hour link
    In my signature and read it front to back
     
  6. hogfiddles

    hogfiddles XJ-Wizard, Host-Central NY Carb Clinic Moderator Premium Member

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    So you tried to ride it home that far on dirty carbs with old gas in the tank, not knowing what the clearances are.... Or if there even is any-----

    Well... Your home now--- start reading and cleaning. All you did was make a few parts look sort of clean.

    Got a fuel filter to catch anything from the tank ?

    You have a long list of things to attend to before your bike will be ready. BUT... You have a BEAUTIFUL ride sitting there, so take you time and do it RIGHT. You'll be rewarded..... Just have the patience of Job......
     
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  7. mwhite74

    mwhite74 Member

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    Holy frig, wonderful looking and probably pretty rare blue edition. Is that a full stainless supertrapp system too? Sounds like something got wet if you were missing on the outer cylinders, that or some dirt in the tank which impacted fuel flow. That being said, take it from the valve clearances onward to make sure all is in spec and all should be OK. Jaysus, nice looking bike...
     
  8. lush90

    lush90 Member

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    Great looking bike, I admire your nerve in flying out and attempting to ride it back across half the country! Quite the adventure even with the hiccups. If you take your time and follow the maintenance advice on this forum, you'll be one lucky and happy Seca owner. That is a great color.
     
  9. RusteeGold

    RusteeGold Active Member

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    Thanks for all the positive feedback and the suggestions. It will take a while to go though everything that has been suggested so I'll get started and let you know when it's on the road again.

    Thanks,
    -steve
     
  10. luvmy40

    luvmy40 Member

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    35 year old coils and one's cracked? I'd say that is the majority of your issue. Len sells excellent replacement coils and mounting kits.
     
  11. Toomanybikes

    Toomanybikes Well-Known Member

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    How about the air filter?
     
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  12. bstig60

    bstig60 Member

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    Good looking bike, Steve. Does the engine die when you put it in gear or when you put load on it. If its the latter, check for pin holes in the diaphragms and/or sticking slides. It would be a good idea to check the air jets as well. There may be multiple problems here.... A cracked coil will surely cause a loss of power. I agree with others that starting at the basics is a good idea. BTW: nominal compression on these engines is 156 psi. Compression should be checked with a warm engine if possible and with all plugs removed and grounded and the throttle wide open.
     
  13. chacal

    chacal Moderator Moderator Supporting Vendor Premium Member

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    First off, beautiful bike. PLEASE do the right things, in the right way, so you can get that puppy purring (do puppies purr?) the way that it should.

    4 hours is about the time needed to pull the carbs off, give them a quick visual, play around with some spray cans, and re-install. To do a proper rebuild on 30+ year old carbs, plan on about 20 hours if it's your first rodeo, about 12 hours if not. If you don't believe me, ask Dave (the fiddles), he does rebuilds for a meager living and can do them with his eyes closed and two toes tied behind his back......

    Recommendation:
    - check valve clearances, adjust as needed.
    - pull carbs and rebuild completely, throttle shaft seals, fuel pipe O-rings, the whole enchilada....including:
    - wet-setting the fuel levels. This is the part everyone hates, do it once and do it right and you won't have to fiddle with this task for another few years or more.
    - vacuum synch the carbs as soon as they go back on the bike.
    - colortune the mixture screws using, you guessed it!, a Colortune Visible Spark Plug. After you do this procedure, vac-synch the carbs again.
    - do all other routine maintenance (plugs, filters, etc. including ALL fluid changes, even the air in the tires and forks since air is, after all, a "fluid", technically speaking)
    - inspect the brake system, rebuild and replace as needed.
    - inspect the fork system, rebuild and replace as needed.
    - added bonus: upgrade to a blade-style fusebox, the original fusebox was a weak point when new, and it didn't get better over time.
    - ONLY THEN DO YOU GET TO RIDE AGAIN!

    Sounds like a lot of work. It is. You're making up for 30+ years of previous owner's neglect, ineptitude, and incompetence. Once it's done you can ride it at redline all day long and impress your friends to your heart's contentment.
     
    Last edited: Jun 5, 2015
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  14. Xjrider92117

    Xjrider92117 Active Member

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    That's a SWEET bike. Take the advice and it will run great for a long time.
     
  15. Bushy

    Bushy Active Member

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    That is a fine looking seca 750. Do all the catch up maintenance as recommended, I did, and it will be very reliable. Good luck with it.
     
  16. RusteeGold

    RusteeGold Active Member

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    I wanted to give an update on my bike. I took the advice that was given and checked the valve clearance. They were all with in spec:
    Cylinder #1: intake=.006/ exhaust=.007
    Cylinder #2: intake=.005/ exhaust=.008
    Cyliuder #3: intake=.006/ exhuast=.007
    Cylinder#4: intake=.006/ exhaust=.007

    I chedked the compression on each cylinder this morning:
    The caburetor was off the bike when I did this test so there was no chance of having the throttle partially closed
    Cylinder #1: 150
    Cylinder #2: 145
    Cylinder #3: 145
    Cylinder #4: 150

    I have new plugs. The plug gap is set at .028 Each plug fires with a blue spark.

    The coils both test to be in spec - I have 2.8 ohms across the primaries and 11K ohms on the secondary (coils only - the plug caps are removed.) Each plug cap has from 5K ohms to 8K ohms so total resitance from plug cap to plug cap is 22K ohms on one coli and 26K ohms on the other.

    The carburetor is clean based on the Church of Clean. Just to validate that the carubetor is not the problem, I have another Seca - 1982 xj750 that is in working order. I removed its carburetor and installed the carburetor from my new bike on it. The old bike ran fine with this new carburetor so I have eliminated the carb as a problem.

    I previously took the TCI unit from my old 1982 Seca and installed it on my new 1981 Seca - it made no difference.

    I hired a mobile mechanic last week who went through all the things I have listed above. He suggested I had a vacuum leak in the carb boots that connect the carbs to the head. I argued that the symptoms did not support that theory. The boots pulsated when the bike was idleing but when we sprayed starting fluid on the boots there was no change in idle speed (I would have expected some change if there was a leak.) Still, he convinced me to spend $412.00 on new OEM boots and gaskets. He came back today and installed the boots and it made no difference. To his credit, he worked on the bike with me for a total of 4 hours and did not charge me a dime.

    We used new gas to try to start the bike. After minutes or cranking, the bike will occasionally start to idle, but it idles poorly. Any throttle movement causes the engine to die.

    I'm planning on buying a leak down tester today mainly because I have run out of ideas. But I've got decent compression so I don't know what I will learn by running a leak down test.

    Any ideas what I could check next? The only thing I can think of is to pull the head and visually inspect the rings, valves and cylinder. The mechanic suggested there could be excess carbon build up on the piston or that the cylinder walls could be glazed - But I'm not sure why either of these conditions would cause the symptoms described above.

    Thanks,
    Steve Gold

    1981 Seca XJ750
    1982 Seca XJ750
    1982 Virago XV750
    1982 Virago XV750 Cafe Racer
    1990 Virago XV1100
     
  17. chacal

    chacal Moderator Moderator Supporting Vendor Premium Member

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    Does the engine run with a bit of choke applied to it?
     
  18. hogfiddles

    hogfiddles XJ-Wizard, Host-Central NY Carb Clinic Moderator Premium Member

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    You said you cleaned the carburetor---

    Which one? You still have three more to do. You also have the bowls to do, and you must make sure the tubes are clear, and the jets are in the right spots.

    Did you bench sync them? Running sync? Valve shim clearances checked?

    Just how did you clean everything?
     
  19. RusteeGold

    RusteeGold Active Member

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    Chacal - the engine does NOT run with a bit of choke.

    Hogfiddles - I cleaned all four carburetors. I took all the jets out and cleaned each one according to what I read in the Church of Clean. I verified the emulsion tubes were clean and blew compressed air through all passages. I did a visual bench sync. I was not able to do a running sync because I cannot get the bike to run. Also - I installed this same carburetor onto a different bike (my 1982 Seca) and that bike started right up and ran like a chanp. So I am confident the carburetor is not the problem. I also checked the valve shim clearances - I mentioned that in my previous post and the clearances are in that post.

    I know it's tempting to say "well - this new guy didn't clean the carbs right - he doesn't know what he's doing." But I have followed all the advice I've gotten from this forum and I appreciate it. I have 4 other bikes - all Yamahas. One Seca and three Viragos. I've been into the carbs and engines on the other bikes and I keep them on the road, running well. I have a basic understand of engines. My carburetor works on bike #2. I have 150 pounds of compression on each cylinder. The valves are adjusted according to spec. I have a blue spark - new plugs. Coils have the correct resistance.

    Compression - Fuel - Spark - I've got them all. What am I overlooking?
     
  20. hogfiddles

    hogfiddles XJ-Wizard, Host-Central NY Carb Clinic Moderator Premium Member

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    Ok, then in light of that, let me go back and read through everything again see what I may be missing
     

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