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'82 Seca 750 Refresh Project: Now Scooby's Bike

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

  1. Minimutly

    Minimutly Well-Known Member

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    Why did you split the chain?
     
  2. scoobydew

    scoobydew Member

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    Trust me, I didn't want to. But since the valve fell into the cylinder, the engine couldn't be turned over. So I couldn't turn the cams, get access to the sprocket bolts, take the sprockets down from the cams and take the chain off the sprockets.
     
  3. Dave in Ireland

    Dave in Ireland Well-Known Member

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    You don't need any special tool to install a new soft-link. Just insert the main part, close down the flat piece over the protruding pins and you'll feel them fit together nicely when the flat piece sits down properly on the shoulders of the pins.
    At that point you could use a pair of fine-nosed pliers to make sure they're seated properly.
    Once you're sure that's happened, take a 2lb hammer and use that as an anvil behind the chain, while with a 1/2lb hammer knock the ends of the pins down on the flat piece. Don't over do this part, you don't want the soft ends of the pins being too deformed and breaking off, but they must be deformed and spread out enough to prevent the flat piece from moving outwards, and lock it in place.
     
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  4. scoobydew

    scoobydew Member

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    long time no see.
    I'm fixin' to install new valves and springs myself. I handed it off to a shop but its been months and they haven't even touched it. I just feel like the likelihood of installing the spring crooked is high with my primitive spring compression tool from Amazon. Anyone else have any experience with re-lapping and installing valves?
     
  5. Minimutly

    Minimutly Well-Known Member

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    Yes, loads. Its easy, you can do it and undo it over and over until youre an expert. Fine lapping paste should be all you need.
     
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  6. scoobydew

    scoobydew Member

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    Took a while but the bike is finally "done". I synced carbs the best I could though not perfect, I didn't colortune yet though. I'm still a bit confused if all mixture screws must have the same amount of turns out or if each mixture screw has a unique amount of turns for that blue flame when colortuning. But I was able to get the bike to ride, starting up needs some throttle, that might be because of the carbs? Needs new throttle cable, I see some strands poking out of mine.

    For some reason I'm always sitting around 4-5k rpm when in fifth gear. Rode around the block a bit, when I got back home I noticed some smoke and checked for oil, there is this little hole on the coil governor cover on the left hand side of the bike. Looks like some oil dripped out of it. What is it? This looks factory made, not a crack or anything

    My rear brake seems to not even work. I stomp on it and i dont notice much. My front brake does all the work. I've never used drum brakes before. Maybe its just me

    Not gonna lie. I'm not the biggest fan of this bike compared to my DRZ400. mainly because of its size. Just seems big and clunky, and syncing those 4 carbs... so annoying. I never rode a bike with more than 1 cylinder. It's a beautiful bike though. It's comfy but when I take off, I feel like my butt is gonna slide off. Not sure how to ride it, maybe more in a laid back style like a Harley
     

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    Last edited: Sep 10, 2022
  7. Jetfixer

    Jetfixer Well-Known Member

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    The color tune , you set the synch screw indepently for each carb IE one might be two turns while another might be three turns out . As long as you have the four vacuum gauge or Morgan Pro four synching carbs is relatively easy . Ideally the theory is for all four carbs function as one three are slight variations that can change over time valve clearance is one factor. You bike looks good once sorted the Seca has plenty of power 86 Hp so it is no slouch, mine I can ride all day out of all the bikes I've owned it is one of my favorite . Years ago bought my first new bike after owning just used bikes got my first "Thumper" a 2003 Buell Blast 500 supposedly 39 hp , I had a Kerker pipe on it so loud I had to wear ear plugs to ride . Cheers
     
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  8. Franz

    Franz Well-Known Member

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    Remove the cover where the pick up coils are. If oil is coming out of that hole you have a leaking crankshaft oil seal.
     
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  9. Franz

    Franz Well-Known Member

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    @scoobydew did you fit a new crankshaft oil seal during the engine rebuild? If you have one fitted without the lip that slots into the crankcase Chacal has the seal you can fit from the outside. Worth checking with him if yours is gone.
     
  10. scoobydew

    scoobydew Member

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    Hey Franz,

    I don't remember if the seal had a lip or not but I replaced everything in the engine, most likely I ordered those parts from Partzilla... before I knew about this site so the parts took MONTHS to ship to me. There was only a few drops when I came back from a ride. So I took the coil governor off, cleaned it up and put a bit of Yamabond. I Idled it to 200 degree F, rev bombed a little. Doesnt seem to leak. at idle When the weather permits then I'll go for another ride and see whats up.
     
  11. Franz

    Franz Well-Known Member

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    Hope it seals it.
     
  12. scoobydew

    scoobydew Member

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    Hey ya'll

    Been riding the bike around, sealed up any oil leaks but there's been a lack of power. I attempted a colortune but two of the cylinders have an issue. Cylinder 1 goes dark when throttle is blipped rather than orange meaning not enough fuel is being sent in and Cylinder 4 is always whitish blue no matter how many turns out the mixture screw is. So I went to check for vacuum leaks with carb cleaner. Checking what the PO did to the carbs, I assume he replaced throttle shaft seals etc. when he tore down the carb. Everything is sealed up tight. No changes in idle when sprayed down.

    So I pulled the carbs and found two issues. Carb 1 has the needle sticking up a bit? I posted a picture of it and another Carb for comparison. And Carb 4, the butterfly valve isnt completely sealed. There's a slight gap, you can see right through the bottom of the butterfly valve which would explain why the colortune never goes orange. How would I fix these issues? Do I have to break the rack to fix the butterfly valve?
     

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    Last edited: Oct 23, 2022
  13. Nuch

    Nuch Well-Known Member

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    Each butterfly will look different based on tuning… some with more/less light than others…

    You shouldn’t have to break the rack… the adjustment screws will open/close the butterfly.

    That rack has been rebuilt completely with Len’s full carb kit complete with throttle shaft seals.

    The needles sticking is a completely different issue… each should “clunk” down nicely and completely when you push up with your finger…

    Also make sure that no pinholes appear in the diaphragms… hold each up to the light to make sure. When I had that rack open, everything was A-Ok…
     
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  14. Minimutly

    Minimutly Well-Known Member

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    A lack of power?
    Please explain - anything to do with synching and idle mixture will only be effective at idle or setting off. Real power is open throttle and 5000 rpm and above - it’s important to differentiate.
    You should be able to fully close each butterfly before setting the synch - if not you need to slacken off the butterfly screws and reset.
     
  15. scoobydew

    scoobydew Member

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    It feels like I'm riding a smaller CC bike at the moment. Getting to 30 mph takes some time and a change of gears. Granted, I never rode an XJ750 with a solid running engine/carb so I can' compare but I do ride a DRZ400 and currently that bike takes off way faster and has a higher top speed than my XJ right now.

    For sure the real power comes from higher RPMs. It does take off if you wide open throttle but it takes some time to get there. Just at the moment, I have idle screw all the way backed out and yet sometimes when the bike is warm, it goes to around 1400 rpm. After throttle blip, the RPMs drop a bit below 1k like it's going to stall then come back to around 1100k. There's no popping or backfire.

    The carbs are synched according to my manometer, I used the blanking tool as well. The color tune isn't working right for two cylinders, I assume it's because of the two issues I mentioned, esp after Nuch confirmed he rebuilt the carbs.

    I'm going to try bench synching them with a paperclip, try to close that butterfly valve so it's sealed and fix the stuck needle.
     
    Last edited: Oct 23, 2022
  16. scoobydew

    scoobydew Member

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    Well, I'm a fool. The butterfly valve is like that because it was synched with the others. It should only be an issue if it wasn't synched. So something else is causing the mixture issue.

    I popped open the float bowls and a main jet fell out, that's why the needle was falling out As for the carb that is always lean, to be honest, I'm not sure. The jets look chewed up though they aren't dirty, you can see through them. I'll check the float level and maybe move up from 120 to 122 I think? Not sure, been reading a bunch of info on here. I have an aftermarket exhaust, I think it's MAC 4 into 2, the stock exhaust was rusted out.
     
  17. hogfiddles

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

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    It wouldn’t be the first time for a jet to get loose either.... first carb clinic I ever attended— they had a rack that was giving nothing but trouble— Couldn’t sync, Couldn’t colortune......One of the guys finally caved in to open the rack....yup, a jet rolling around in the bottom of the bowl.
     
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  18. scoobydew

    scoobydew Member

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    Indeed, if all else fails. I could bring this carb over to the clinic.

    Though that's a while away. I'm confident I can finish this before next riding season. Although, it's been a headache of a project, feels good to dial in on some of the issues by just tinkering with things
     
  19. scoobydew

    scoobydew Member

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    Good news,

    Removed those old jets with new nice ones. Synched the carbs, colortuned as best I could and took her out on the highway. Runs great!

    Finally finished after about 2 years or so. It was a trip, a huge pain in the butt when I fixed one thing and another thing broke but I'm glad I took on the project. I may not be an expert on motorcycles but I know this one in and out after taking her apart so many times. Just wanted to thank everyone for chiming in, giving some advice and information while I was stuck on an issue.

    Appreciate ya'll, gonna see if this bike can make it to Michigan and back
     

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  20. Huntchuks

    Huntchuks Well-Known Member

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    If successful, next stop = Carb Clinic.
     
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