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  1. #41
    CB750 Addict Wez_'s Avatar
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    Just watched your utube vieo posted above. It appears your top end is full of carbon. I understand you want the bike to run without going too deep into the motor, but from the color of the exhaust during the revs, it appears there is carbon build up. When you rev the motor not under load, I would expect to see white smoke (briefly in your video), not browninsh. With the headers off, you can look into the exhaust valves and see their condition. The intake valves will likely be in the exact same condition. If those bad boys are all gummed up, then that could be why you have higher compression (excess carbon causing a better "seal" around the valves. This is not ideal. Also, with the condition of that gas tank, it's likely that gunk got in the carbs and the poor efficiency of the motor built up excess carbon deposit. It's not ideal to gauge a motors condition from a thermal test of headers on an air cooled motor neither. Ideally, you dont want an air cooled motor to idle like that no longer than 5 minutes ( not enough time to heat up properly) use compression and leak down tests aside from visual inspections. Try the scrubbing the exhaust valves with SeaFoam brand spray from the parts store. Get one of those air gun cleaning kits and use the brushes to brush down the valves from the outside of the motor with the headers removed. if you are really handy, you can make a shop vac hose attachment out of a soda bottle and tape it with gorilla glue tape to be a nice and small cone shape. put it on the end of your shop vac and suck out all the carbon and Sea Foam spray to clean the valves the best as possible. My heads came off as soon as I saw the condition of the exhaust valves. Even AMC told me to just do a compression test. I don't like running that crap in my motor. Clean that top end and you might have the improvements your looking for. Aside from that, a few trips around town might blow some of that out.

    My heads before
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    My heads after disassembly/cleaning
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  2. #42
    CB750 Addict pidjones's Avatar
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    Could be, but a lot of that smoke on first start was from fogging oil that I had sprayed in the tank once I had cleaned it to prevent flash rust. It is much better now (although still spitting nut hulls). Still needs two things before being ridden; a chain (I through the stiff, rusty one from it out) and tires (these are over two decades old).
    Last edited by pidjones; 12-16-2018 at 01:20 PM.
    "Love 'em all.... Let GOD sort 'em out!"

  3. #43
    CB750 Addict pidjones's Avatar
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    Carbs back on. Never really found anything, but pulled all of #1 jets and blew cleaner through them and all passages again. Built a fuel cell to feed them with, without mounting the tank - so now the carbs can be balanced (although all cylinders need to be working for a balance to really mean anything.)
    "Love 'em all.... Let GOD sort 'em out!"

  4. #44
    CB750 Addict Wez_'s Avatar
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    This is what I used for a "fuel cell" it doesn't take much fuel to fill the bowls and keep the bike running. Attach this to the fuel line and set it upside down on the frame. Either position it nicely or tape it. It will likely need a few squeezes to keep the bowls from starving but these bottles are cheap and readily available at hardware stores.

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    What do you mean, "still spitting nut hulls"??

  5. #45
    CB750 Addict Wez_'s Avatar
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    Quote Originally Posted by pidjones View Post
    but no. #1 plug wet but not overly so - so why isn't it firing?

    Haven't pulled anything apart on the carbs yet. Checked choke, butterfly, and piston freedom is all.
    You will likely need to do a major overhaul of your carbs. If your valve clearances are truly within spec, the varnish is likely plugging up a circuit. I disassembled my carbs, dunked them individually in a gallon of carb cleaner from the parts store, baking soda blasted them, and cleaned them in the dish washer. Carb cleaned and compressed air numerous times and they were spotless!! it wasn't until I read through the below rebuild that I found out that my carbs were only marginally clean compared to what is expected. I had a clogged accelerator pump nozzle that required almost every bit of engineering I could muster up to un clog. Ultimately, CLR soaking overnight ate away at the solid varnish clogged in the accelerator pump nozzle. The only way I discovered this was from reading the below write up in its entirety and checking every check the author said to check leaving no stone unturned. A simple bowl clean with carb cleaner and compressed air is not enough on a carb that has varnish damage. There were a few other clogs that I overlooked also prior to following this rebuild. If you finish this rebuild, you bike will have no choice but to run nicely

    Professional Overhaul .pdf

    http://www.cb750c.com/publicdocs/Sea...anual_revG.pdf

    My rebuild thread.

    http://www.cb750.com/threads/4812-Carburetor-Rebuild

    Spark plugs should be tan and dry. Wet with fuel to me means a valve is not sealing completely. If the valves or heads are damaged then that will likely cause wet plug symptoms. A leak down test should be done on your heads. The leak down tester uses two gauges. One to set the supply air pressure, the other gauge reads the connected cylinder pressure after being filled. Let it sit for a few minutes and watch the "leak down" from the gauge # 2. Ideally the pressure should only drop marginally. You can find articles and videos on the test. But once its done, it will give you overall analysis of valves, piston rings and cylinder head condition. Oh yea, cylinder must be at TDC. Anyways, do a leak down test on each cylinder and go from there. Varnish carbs are deadly bro. fully disassemble them and make sure those accelerator pumps are all squiring a nice solid squirt of fuel onto the center sliders when done. I had 3 of the 4 squirting after completing the above overhaul that included soaking each piece individually, soda blasting and carb cleaning....Once I got that last AP Nozzle cleaned, I confident that she was ready and whala....like new. I know its hard take on these long projects, but they aren't impossible tasks, they just take some knowledge, tools, guidance and courage to accept you have a problem that needs fixing.
    Last edited by Wez_; 12-17-2018 at 02:27 PM.

  6. #46
    CB750 Addict Wez_'s Avatar
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    My baby

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  7. #47
    CB750 Addict pidjones's Avatar
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    Quote Originally Posted by Wez_ View Post
    What do you mean, "still spitting nut hulls"??
    When first started, it spit a BIG shower of nut shells out of the exhaust - no doubt ruined some critter's winter hideaway. They still come out at times. Hope I've blown all from the airbox.
    "Love 'em all.... Let GOD sort 'em out!"

  8. #48
    CB750 Addict pidjones's Avatar
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    Got a little more checked (or really, re-checked) today. Did the ignition test with screwdriver on the pickup coils - good hot spark on old plugs with the gap opened to ~ 3/16". Voltage test on spark units in spec. Buttoned that up and pulled the valve covers. checked the valve clearances again. Tightest is .003, loose one was .006 inch. Need a couple 295s to get any closer to the .004-.005 I'd like to have. Spent a lot of time getting RTV off of the valve cover from a PO putting it on the gasket. Now, I believe in tacking the gasket on the cover to make it more convenient, but not squishing RTV out everywhere. Anyway, cleaned that up and tacked the gasket to the cover with Indian Head.

    Then, while digging out the RTV from the head I noticed something that I had not seen before. Right end intake cam holder is broken. This thing just keeps getting worse! Anyway, found a full set on eBay for $40 and ordered them.

    Finished up my aux fuel cell. Presently using a 1/2 liter isopropyl bottle for the reservoir. Can go bigger if ever needed by just getting a bigger bottle to put the nipple in the bottom of. I like this one because I can just cap the bottle when I'm done with it and take it out to the shed, drain it in a tractor.
    "Love 'em all.... Let GOD sort 'em out!"

  9. #49
    CB750 Addict pidjones's Avatar
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    A good test this afternoon. Backed her out of the garage and hooked up to the aux fuel cell. Fired as soon as I touched the start button, and came off of the choke a lot faster than before. Reved up fast, not lethargic as before. All pipes are getting warm (~50F outside today)! Didn't bother with balancing carbs yet. #3 float must be sticking as it was overflowing (I put clear drain lines on this time). But it is firing on all 4 finally!

    Holiday duties will be keeping me busy soon, so when I bring it in (have to leave it outside to air out so the wife doesn't complain as much about the exhaust smell) it will be pushed aside for a while to make room for getting the Hunley prepped for a show mid-January. Guess it is time to order a chain for it, too. Still won't be able to ride it as the tires are too old to even ride up my driveway, but at least it can be taken through the gears on the center stand.
    "Love 'em all.... Let GOD sort 'em out!"

  10. #50
    CB750 Addict pidjones's Avatar
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    "L" cam holder is broken pretty badly. Could have been over-torqued, but I really suspect they just rammed in a too-long screw for the valve cover (only had a couple proper valve cover bolts when I bought it). Also, this is not the first holder to need replaced. As I looked at the others to see if they were damaged, I found a J in position for an F (far left end of intake cam). And yes, there is a J in the J position. Guess this one need to be Plastigage checked and also check oil hole alignment, too.*

    I was going to see what I could do to fix up the tail section on the seat as it seemed to have a lot of repair fiberglass under it. Turns out, almost the entire tail is packed with Bondo and fiberglass, which is all separating from the remaining ABS part which is the top part. Need to figure out what to do with it. I could just glue it back together with ABS cement, but it weights 3.4 pounds with all of this Bondo packed in it! Think I'll check forums and ebay for another. Cracked/broken doesn't matter as I can always glue with ABS cement and reinforce from below with fiberglass cloth, but all of the bottom/back of this one is missing.
    *
    Last edited by pidjones; 12-20-2018 at 09:58 AM.
    "Love 'em all.... Let GOD sort 'em out!"

  11. #51
    CB750 Addict pidjones's Avatar
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    Honestly, I need to stay away from this bike for a while. But, parts are supposed to be in this afternoon, so.... Good thing, too because I decided to check that J cap in an F position. They had jambed screws in the cross-drilled supply holes in the cap, and RTVed the bolt holes. And of course, broke one of the cap bolts off. I was able to remove the broken bit with little drama, then spent time picking out RTV. Bolts are supposed to be included with the caps I bought, so hopefully things will get better.
    "Love 'em all.... Let GOD sort 'em out!"

  12. #52
    CB750 Addict pidjones's Avatar
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    Swapped in new (used) F and L caps after first Plastgage testing them - both between .003 and .004 inch. Measured with both cylinders on respective side with lobes away from lifters. Final assesmbly with assembly lube on the bearing surfaces. New chain came in too, but it will wait for tomorrow or Monday for installation. Good weather forecast for next week, so hopefully there will be a chance to run it through the gears to make sure that is all fit.
    "Love 'em all.... Let GOD sort 'em out!"

  13. #53
    CB750 Addict pidjones's Avatar
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    Chain is now on!

    Merry Christmas from East Tennessee! What a great gift it would be, if people would live in harmony - or at least tolerance of each other. Just how hard would it be?
    "Love 'em all.... Let GOD sort 'em out!"

  14. #54
    CB750 Addict pidjones's Avatar
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    Rolled it out this morning, hooked up the aux fuel cell with ~ 1/2 liter real gasoline, and fired it up. Once warmed enough to take off the choke I ran it through all 5 gears (on center stand). Clutch engages/disengages well, all gears work and sound pretty good (chain is hitting the plastic chain guard some, so need to adjust that). Then shut it off and hooked up the mercury sticks (old MotionPro unit). Balanced the carbs, lowered idle, balanced again. Have not touched pilot screws - all set at 3 turns open. Aircut valves are disabled.

    Guess the next thing other than fixing the seat rear cowl assembly is tires (ouch$$). Thinking maybe getting a bunch of wrecked Honda plastic from the dealer and gluing it together to patch the existing cowl assembly now that I've pried 3 pounds of Bondo off of it..
    "Love 'em all.... Let GOD sort 'em out!"

  15. #55
    Moderator dirtdigger's Avatar
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    Watch the oil for metal as you run it more. Those caps are machined as part of the head from the factory. No two are exactly alike and you really should not use caps from another head. Yes people do it and get away with it. you may have bearing clearance up and down as you checked but the clearance at the parting line(side to side) could be shifted to where when it is running the cam can contact the bearing on either the cap or the head depending on how much misalignment there is. If it seems like the engine is running hot or oil gets really shiny from metal stop running it and take the caps off and inspect for damage.

  16. #56
    CB750 Addict pidjones's Avatar
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    Yep. I don't expect problems with the F cap that was replaced. You could see that the bore left margins at the split on both sides, leaving extra clearance there. The L cap checked Ok at three places. Just have to hope that the oil wedges are symetrical at sustained speeds. A lot of the "luck" in this is the wear tolerances in their machines that bore and ream the dowel holes as well as those that do the line bore. I always check drained oil for wear particles, including dredging it with a magnet to find gear train wear. I only have ~1.5 liters of fuel through the engine so far. Winter plus ancient tires will keep it from being ridden for a few more months. Presently running 15W40 diesel rated lube, same as in my older GoldWing. I run 5W40 Rotella 6 in the GL1800.
    Quote Originally Posted by dirtdigger View Post
    Watch the oil for metal as you run it more. Those caps are machined as part of the head from the factory. No two are exactly alike and you really should not use caps from another head. Yes people do it and get away with it. you may have bearing clearance up and down as you checked but the clearance at the parting line(side to side) could be shifted to where when it is running the cam can contact the bearing on either the cap or the head depending on how much misalignment there is. If it seems like the engine is running hot or oil gets really shiny from metal stop running it and take the caps off and inspect for damage.
    "Love 'em all.... Let GOD sort 'em out!"

  17. #57
    CB750 Addict pidjones's Avatar
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    Ordered new Kenda 657s for the '79 CB750F rat bike. Not in a hurry for them, as it will be a couple months before decent riding weather, and I have a showw in a couple weeks to get the GL1000 ready for, plus rides scheduled for the GL1800 (weather permitting).
    "Love 'em all.... Let GOD sort 'em out!"

  18. #58
    CB750 Addict pidjones's Avatar
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    The Kendas are mounted and wheels back on. That's about as far as the weather and my health could take her this week. Came down with a cold that knocked me out until yesterday, when I went to the funeral of a high school classmate and then to see a cousin in a nursing home that is not doing well at all. I still need to drain the fuel from the tank into my waste gas jug to get rid of the fogging oil and storage spray grease that I'd put in the tank and never flushed out. I'm sure that is a major cause of the smoke that she displayed before, because she doesn't smoke on the auxiliary tank. The weather has turned its typical East Tennessee January/February crud. Maybe the middle of next week it will settle and I can at least try to ride around the neighborhood.
    "Love 'em all.... Let GOD sort 'em out!"

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