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  1. #1
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    Default 750 Honda SOHC - The Imp

    Look what came to my house



    for a visit. It's not mine, but I'm lending the garage space, tools, and my helping hands to a friend. I've been wanting to build one of these into cafe racer, so the opportunity to learn on someone else's bike is very welcome.





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    Mock -up on the Imp begins...



    Pull it out of the corner and get to business.


    Put the stock battery box in....


    "Oh yeah," he says, "I was going to use this oil bag set-up." The wings gotta go though.


    About this much.


    Here's a bonus pic of the swing arm extension that he built.


    To the shed and the cut-off wheel.


    Dress it with the grinding wheel.


    Cut off the other wing.


    Clean off the last of the burrs with a file.


    Big boy James and mostly grown-up James mock-up the oil tank.


    Take some measurements for the oil mounting braces.


    The tank needs to come up a bit so that the petcock will clear the carbs.


    The stock key has found it's new home.


    The wires on the switch had a big pinched spot that needs to fixed.


    Cut off the crappy part off and call it a day.

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    Figuring out the wiring and oil plumbing



    Looks like we need a brake light switch that will fit that.


    Let's roll the bars foward so we can get at the wires that are already in the bars.


    Ohm check to see what is what. A manual might make this easier, but we have no idea where these handlebars came from.


    Trying to figure out the left side is completely fruitless, so...


    We'll take a peak to see if can figure out the colors from the back of the switches.


    Now we're making progress, so I'll take some notes and make some labels.


    Okay, two things are kind of wierd. This on-off switch on the right grip. We're guessing headlights, but we can't find a 750 wiring diagrams on-line with this switch even the earliest ones. The other wierd thing is wires going to the clutch lever. I have seen safety switches on clutch levers, but again not in any 750 wiring diagrams on-line.

    Labeled and ready to go. Now we need to plan the rest of the wiring and built the harness.


    Now to the oil bag. It has four threaded bungs. Two with snorkel tubes and two at the bottom of the tank.


    The holes in the bottom are the gravity feeds to the engine. Not sure why there are two, we will only use one. One snorkel should be longer that the other. The short snorkel is the feed back to the tank and the long snorkel is a vent. We tried to use a mirror to find the long snorkel, but...


    we couldn't see them, so will filled the tank with water. The short snorkel should flow first. Amazingly both of the snorkels appeared to be the same length. So I guess either fitting could be either oil line.

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    Love that tank!

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    Mounting the oil bag and coils



    Now to figure out this front oil bag mount.


    Here's the strap for the crosspiece.


    Tick marks for our knotch cuts.


    Make a cardboard piece to the same size and shape to check fit our plans.


    Looks good.


    Wow, check this out. The bike traveled cross country in a trailer just fine, but the I-40 crosstown knocked it over in the trailer and bashed the points cover.


    Luckily, the points still look okay.


    Bierkan hammered the dent back out., mostly.


    We need a bend in these to fit the headlight right.


    Fastfoward a day or two, and Beirkan took the oil bag front support to a band saw and cut the knotches.



    Set it in.


    Bierkan studies the welder's set-up charts, then set every to MAX. I think.


    Time to get to it.


    Try to tackt it in place.


    That didn't work well because of all the paint still on the frame. D'oh.


    Now it seems to work.


    Tacked in place.


    The little seatpost support piece won't fit, but we don't really need it. Mark the spot for the tank.

    Center punch the center of the mark.



    Center drill the center punch mark.



    Drill it.


    Hey, let's cover those carbs and the alternator area so we don't get more chips in them.


    Now let's finish the hole.



    Perfect.



    Bierkan pulled the tank and finished the full welds for the bracket.


    Now to the back supports. The plan is to use all-thread to support the back end. Two five inch sections should do it. This is how I cut all-thread to length. Double-nut both sides of the cut line.


    Then cut it. I used angle grinder, but I have used a hacksaw to do it before. Taking the nuts off helps to clean up the threads at the cut, too.



    Two nice 5 inch studs. We'll see if this works out later.


    Mount the new coils and dump the old ones.


    hhmmm...


    I believe this under the stock mounting bracket, but the spade style terminals were interferring with the stock bracket and this way seems to fit, okay.
    Last edited by JPWilliams; 01-23-2011 at 9:43 AM.

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    Quote Originally Posted by JPWilliams View Post
    Okay, two things are kind of wierd. This on-off switch on the right grip. We're guessing headlights, but we can't find a 750 wiring diagrams on-line with this switch even the earliest ones. The other wierd thing is wires going to the clutch lever. I have seen safety switches on clutch levers, but again not in any 750 wiring diagrams on-line

    The clutch safety switch on my CM was tied into the headlight switch. I don't remember exactly how it went, just that one of the powers for the light went thru the clutch switch.

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    Yeah, I working to this...


    This someone showed me this and it seems more accurate...


    but I doubt there will be any clutch related things in the custom harness. The on-off, hi-lo, horn, and off-run-off be used and some form of front brake light switch will be used for sure.

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    Back of the oil bag

    Chase this hole with pipe thread tap.


    Smoke these fittings down.


    Looking good, but we are still short a plug for the last hole.


    Now to plan our all-thread studs for the back of the oil bag.


    Center punch...


    Center drill...


    Drill...


    This one doesn't line up, but other side did. We had to put the hole in the frame in this location, so something is not quite even, either the frame or oil bag, no surprise either way.



    Make a new hole for it.


    Now we can put the nuts on the mounts and cut the all-thread to length. I love my right angle attachment and EZ Lock cut off wheels for my Dremel.


    We'll need more nuts, washers, and red loctite , but otherwise we're good to go. Plumbing the oil lines and running the wires will be next.

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    750: We have spark!



    Getting really close to trying to kick off the 750. The oil lines are run.


    The wiring is pretty much temporary using the stock harness. The goal is to check out the how solid the bottom end is and see if the rebuild top end will hold together and run.




    We kick it through and we have spark! So the next time we will add some gas and see what happens. There's no air box and straight pipes with stock jets, so it won't run right, but we'll know how much more effort should go into cleaning things up and making it streetable.

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    750 fires on all four, now



    Okay, we couldn't get spark to the inside cylinders. We tried every kind of troubleshoot only to be more confused about it. We swamped the condensors to see if one was bad. That's when Bierkan realized that the green wire to the condensor on the suspect point set was on the outside connector and not the inside connector. He swapped the wires and now there's a spark on all four. Not sure when it got crosswired, but we should be running next week.

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    I have a simple wiring diagram for "chop style wiring - charging, lights, signals… if you need it. also I love the gas tank!

    jb

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    Dont plug that forth hole on the oil tank. Run a straight barbed fitting with a short length of hose and a plug and zip tie it somewhere to your frame. Makes for very easy oil draining for oil changes.

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    750 Oil lines revisited



    Okay we didn't have the oil lines correct and that was causing out oil tank cap to blow off. Big thank to FXRSBIGBORE on the Shovelhead.us board. This is the correct oil line set-up.




    We had the bottom crankcase vent going to the air and not connected to the tank.

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    Odds and ends on the Imp



    We've been mostly picking at this, but making progress.

    Shortened and cleaned up the spark plug wires.




    Fresh battery.



    Trying to figure out how to make the three phase alternator work with a regulator/rectifier from a late model Vulcan. This will let us mount one unit instead of the two piece regulator/rectifier that was stock on the 750.




    hhhhmmm....




    The wire colors from 1500 Vulcan manual don't match.



    But the 800 manual shows the colors we have in hand.




    So the three yellows from the 750 go to the three blacks.

    A 750 green wire(ground) goes to the black/white.

    750 black(key-on) goes to black/red.

    The black/blue from our rectifier goes straight to the battery positive.




    Time fix this over flowing carb.



    Float needle and seat are okay, but not great.



    The float tab is way different than the good carb. So we adjusted it to match. We didn't pull the carb and properly set the height, so hopefully we're close.



    New throttle cable.



    New throttle sleeve.



    This broken screw is stuck. So we soaked in WD-40.



    Bierkan want to swap the sprocket back to stock. I forget the teeth counts one these, I think 38 and 45 or so.




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    750 Imp - Electronic Components



    Spare aluminum, 1/4-20 all-thread, nuts, and the left over softail mounting bracket from the oil tank, that's all you need to mount the battery, starter solenoid, and Vulcan rectifier. Some fab work is required, too.


    Cut the tab off.




    Cut the aluminum to length.



    Time to test the free Lenox blade.



    Yes, it does cut well.




    File the edges for safety.




    Transfer the holes from the bracket to the aluminum.



    Drill.



    Something like this is the plan. These holes are tapped and ready to use.



    Cut the 6ft section into something manageable.





    The threads aren't too messed up, so that's good.



    Starting to look like something.



    I need holes in the battery box now.



    I had to unmount the oil tank to get a drill to where I need the holes. It was full of oil, but I didn't have to empty it or disconnect the lines to get at it.



    Actually had to clamp up the aluminum to bottom of the battery and and transfer drill up.





    Mostly fits, the studs are too long and interfere with the frame on the right side.



    I need to mount things to the under bracket. Two holes for the rectifier.




    Two holes for the solenoid.







    Bolts, nuts, and red loctite.




    Cut down the studs to final length.



    Looking good.



    The solenoid and rectifier are under there now.



    Bierkan loves to use adjustable(aka crescent) wrenches just to annoy me.



    Time to wire it. Here's Beirkan's plan.



    Coil wire routed up the front down tube.



    Time make the alternator work with the rectifier.



    Tear it up!






    Solder it all together.

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    Outstanding attention to detail guys! Makes me not want to rush my 550.

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    Got any pics?

    Seriously though thanks for taking the time to detail everything. Lots of useful info for sure.

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    750 wired and starter working

    Okay, still working on a wiring. The key switch is place and wired with the 30 amp breaker behind it, mounted to a existing frame tab.




    Ground wire to the frame, to green wire from the harness, and to yellow/red for the starter switch.


    12V+ one to the starter relay, and one through the circuit breaker and to the key switch.





    Here's the circuit breaker.



    Starter button.



    Back of the starter button. It takes a ground to low side of the starter relay. The key switch is the high side of the relay.




    Seems to work. Vierkan does the honors.



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    750 Frame help
    Vierkan had cut the frame tubes that run from horizontally from seatpan to the front downtubes, then discovered that the frame section at the front of seatpan section was weak and had porous welds. So Nguyễn the weldor stopped by to fix things up. He smoothed off the old welds and cleaned off the paint.


    Then down to business.


    All welded up.


    We didn't care, but Nguyễn wanted things to look good.


    Now to stiffen to the back end a bit. The seat support behind the shock mounts will be coming off soon too. A little pipe right here should do.




    Tacked in place.


    Nguyễn does the full weld to the tube.


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    Wow talk about documentation!

    Good work so far on the build.

    If I can suggest anything, consider relocation or at least protection of the Coil wiring on the downtube, between two headers is a very hot place.

    Also, you need to do something about the backbone, really it needs to be cut out and replaced with a heavier wall thickness. The 2 Side rails have been cut out, just leaving the single backbone. This was pretty common in the 70's, but that doesnt say its a good idea. Honda frames are made out of pretty thin wall, poor quality tubing.

    Here is a simple solution to strenghtening the backbone without cutting it out. And dont forget the gussets where it joins the seat area.

    Thick wall pipe that is a fit over your existing backbone (EG your backbone may be 1 3/8" O.D. tube, you would use 1 3/8" I.D. pipe)




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