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'82 Seca 750 Refresh Project

Discussion in 'XJ Technical Chat' started by Nuch, Aug 24, 2019.

  1. Nuch

    Nuch Well-Known Member

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    Hello my friends.

    I thought I’d start a thread for the Seca 750RJ that followed me home from the 2019 CNYCC that is hosted by our gracious host Hogfiddles. I had mentioned this new addition in the clinic thread, but as I continue to clean, sort and organize things I figure I’d share some details and progress (who doesn’t love before and after pictures?) and ask questions as they arise. One in particular at this point… but I’ll get to that down the thread.

    Day 1… On the trailer. Really good bones in need of a cleaning.
    750RJ-01.png
    750RJ-02.png
    750RJ-03.png
    750RJ-04.png
     
  2. Nuch

    Nuch Well-Known Member

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    One of the first things I did was deal with the fuse box. There were some funky things in there with a previous upgrade.
    750RJ-05.png
    Additionally, I found that the old girl had some furry dinner guests.
    750RJ-06.png

    Here is the clean up I did. Wire colors are not exact, but I made sure the gauge matched. Donor wires came from my old Volkswagen wire stash.
    750RJ-07.png

    For the clearances, I had to remove the valve cover of course and found the source of my oil leak. A home made gasket! Only 1 shim out of spec, so that got swapped out with a new one… Clearances in spec now… Thank You Len! The cover gasket and bolt “doughnuts” were dealt with accordingly as well.
    750RJ-08.png
     
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  3. Nuch

    Nuch Well-Known Member

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    Then on to more cleaning up and polishing of things as I waited to place the order, then receive the carb rebuild kit from Len.
    750RJ-09.png
    750RJ-10.png
    750RJ-11.png
    750RJ-12.png

    Carb rebuild kit came lightning fast from Len (of course) and on to the teardown, clean and rebuild of the carbs… The first stage of breakdown...
    750RJ-13.png
     
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  4. Nuch

    Nuch Well-Known Member

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    Hey, Give a girl some privacy while she’s taking a dip!
    750RJ-14.png

    Clean #3… Dirty #4!
    750RJ-15.png


    Here’s #1 all dressed up and waiting for for the family reunion…
    750RJ-16.png


    Almost there… Orange Juice caps make nice carb caddies!
    750RJ-17.png

    All back together… Benched Synced, Leveled in my home made carb rack holder, Wet Set and ready to go!
    750RJ-18.png
     
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  5. Nuch

    Nuch Well-Known Member

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    After reinstall, of carbs, she fired right up… It was awesome. She screamed up to +6k quick, but when I backed off the idle adjustment screw, the idle came back down.

    More Info...

    - I set the air mixture screws to 2.25 turns from soft seat position.
    - Brand new plugs
    - Did a vacuum sync and got everybody playing nice together
    - Using the Colortune, I was getting a nice blue on all cylinders (or so I thought... feel the question coming here?)… Did not touch the mixture screws at this point.

    Here’s the problem/question(s)…

    I can’t keep her running... seemed ok at first, but I believe as the plugs quickly began to get dirty, it got worse quick... plugs are deep black sooty now… not wet.
    750RJ-19.png


    Seems like things are getting worse… probably as the carbs continue to build carbon…

    Here is the color tune working in #4… at this point it was seemingly running a bit better in this video.


    I guess I’m having trouble “reading” the color tune. Seems like a good blue in the window, but it’s a bit misleading as there is the actual spark from the metal prong which can be seen only momentarily in the video unfortunately… Hard to differentiate between the spark jumping to the collar of the color tune and the overall explosion of blue… I’m not sure I’m being clear here… I apologize.

    Here’s another video of #2 color tune. In this one it is a better view of the actual spark… not just the explosion… Am I seeing purple? I’m so confused….


    Where I’m at now is that I have a low popping sound that can be heard in this video…


    What are your thoughts on next moves here?
    Quarter turn clockwise on the mixture screws?

    It’s tough to keep her running at this point to even try to get the vacuum sync up and running. With the increasing popping at throttle, I’m scared to break something!

    I’d love to hear all thoughts.

    Thanks…
     
    Last edited: Aug 24, 2019
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  6. Polock

    Polock Well-Known Member

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    2.25 is lean, it don't cost nuthin, try 2.5 or more. that plug never got hot, it might look rich because it only fired every third or forth time and then just went poof
     
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  7. Timbox

    Timbox Well-Known Member

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    Nice work! Think of changing to a different type of plug? Are the coils as hot as they should be? You seem to have taken care of all that needs to be done to make her fun like she should. Coil wires are okay? Have you looked down the cylinders to see how much if any, carbon is on the pistons? If there is a lot in there, cleaning them up might help?
     
  8. Nuch

    Nuch Well-Known Member

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    Hmmm. I was thinking it was rich because of the black color. Opening it up a bit is a good idea.
    Still, the colortune (which should be the answer to getting the mixture correct) baffles me...

    I put NGK BP7ES in there.

    Resistance? That's a good question. I have a "cheapy" Harbor Freight meter... though perhaps I put it on the wrong setting...
    voltagemeter.png
     
  9. Polock

    Polock Well-Known Member

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    put the colortune away for now and tune for peak rpm. turn a mixture screw in or out 1/4 turn, if the idle goes up leave it there if not put it back and go to the next one.
    first pass don't try to make it perfect, just better. second pass go by 1/8 turns, higher rpms is better. now do a running sync again.
    make another pass over the mixture screws again. the process is easier if you start on the rich side and lean it as you go.
    take it for a ride get it good and hot and make one more pass over the mix, if it was stumbling on take off open the screws 1/8 turn
     
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  10. XJ550H

    XJ550H Well-Known Member Premium Member

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    you can add some heat shrink to the exterior of the color tune if that is where the spark jumps from
     
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  11. k-moe

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

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    Soot is an indication of an incomplete burn, either rich or lean. Follow Polock's advice.[/QUOTE]
     
  12. Nuch

    Nuch Well-Known Member

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    Update:

    I pulled the plugs, gave them a quick brushing and reinstalled. I also turned the screws out to 2.75 turns as a starting point. I then followed Polock's instructions and did a pass across all 4 screws. Then I did another vacuum sync. Not perfect, but much better... Here's what I have now.



    No test ride tonight, and tomorrow is booked, but I plan to get it done on Tuesday. I'll update again.

    Thank you so much my friends.
     
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  13. Polock

    Polock Well-Known Member

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    go over the screws again after a ride while it's good and hot. getting it up to full temp makes a difference
     
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  14. k-moe

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

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  15. Nuch

    Nuch Well-Known Member

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    Curious about the indications on the sync as well... Am I looking for a specific number when at idle? Or is it just more important that all four are doing the same thing at the same time?
    screen-shot-sync01.png
     
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  16. XJ550H

    XJ550H Well-Known Member Premium Member

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    same thing same time
     
  17. Nuch

    Nuch Well-Known Member

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    Update:

    I'm glad I not only recorded video of a decent idle, I posted it as proof... Why? Because when I went out there today to start it up and giver her a run... I was back to the popping, stalling, can't keep her running issue.

    Rats!

    I literally did not do anything to it after that running video. I shut everything down, and left everything as is... sync gauge and all.

    After fiddling with it for a while, I decided to check again if the bowls were getting fuel... Source on PRI, loosened the drain screws, it seemed like it didn't refill as fast as it could have... #4 actually drained completely and it took a wrap of the screwdriver handle to apparently get the refill going. Perhaps this was just coincidental...

    I decided to shorten the fuel line to the tank that I had sitting on the toolbox maybe there was too much slack I thought. This resulted in the fuel filter breaking!

    Rats Again!

    With no other way to connect fuel source to carbs, I used a clear-ish bic pen body so I could see the fuel supply. My set up...

    fuel-delivery-tune01.png fuel-delivery-tune02.png

    When all connected, (again, at PRI position) it doesn't seem to allow fuel AT ALL into the carbs without a massaging (pinch, squeeze, etc) of the line. When it finally starts to trickle down, It never exceeds the level that you see in the close up. After start up, the level disappears and never returns...

    Enter stage left, the popping and general unhappy-ness (both me and the bike!).

    Cap on the tank is OPEN by the way.. so now I'm thinking that if indeed my issue is a lean condition, the fuel level in the bowls is getting too low and not able to recover... When I we set the floats, I left the carbs for a few days with fuel on prime connected... no leaks, no change in level.

    Perhaps I have a petcock problem. I don't have one of those nifty (Expensive) auxiliary tanks used for tuning so that I can rule out fuel delivery as a possible problem.

    Given my makeshift set up, shouldn't the fuel "fill" the pen body? I'd think so, but if not, at least keep a consistent level after startup? Interesting...

    My next move is to get a new fuel filter and alternate source for the fuel. This may take a bit as I'll need to cobble something together... Unless I can borrow one from a certain semi-local fellow XJer (cough, @saftie , cough, cough).

    Until the next update... and again, thanks for all of your problems solving considerations, and of course willingness to share your years of XJ experience.

    Update to the Update:

    Skip the petcock issue for now... With my limited knowledge, I feel like it is a lean issue. Just tried again, She will start and run (all be it miserably) with the choke on. Once I back it off, she starts to pop and things get worse. All screws are at 3 turns counter clockwise from seated.

    Maybe my float levels somehow changed. They were "dead on" when level on the bench. Now they read slightly lower on the bike, but I think that is to be expected as once carbs are installed, they are not level anymore.
     
    Last edited: Aug 27, 2019
  18. XJ550H

    XJ550H Well-Known Member Premium Member

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    I use a lawn mower gas tank as a fuel supply. How much fuel do you have in your tank( happens a lot being to low)?

    if your floats drop so low that the needles bind or does not drop enough to drop needle there is a second tang that hits the float pin post it was set at factory for factory needles, after market are about a mm longer. could be po messed with them. look at the droped float level see if they are all even.

    the carbs on bike are slightly angled. which would account for slight lower level if measured at rear of bowl. bike on center stand also affects level some bikes the manual says to raise the front tire
     
  19. XJ550H

    XJ550H Well-Known Member Premium Member

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    XJ650G manual base manual for all 650 and 750 bikes

    upload_2019-8-27_17-50-43.png
     

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  20. Nuch

    Nuch Well-Known Member

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    Just came in from garage again. I actually found a fuel filter replacement locally at advance auto parts. Filter fills and stays full. So I think that is sorted out.

    Still, the problem exists and it is the same across all cylinders. I pulled, cleaned and reinstalled again. At 3 turns out. Same condition... only seems to run on choke, and not well at that. Plugs look very black and sooty.

    The thought had occurred to me that perhaps I still missed some grime in the cleaning/rebuild... but on all four? And apparently the same way?

    Air box is clean. It does however have one of those stupid UNI filters. I guess a stock paper one should help bring back the airflow to what it should be.

    She’s kicking my butt!
     

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