88cc Engine Rebuild Question

Discussion in 'Tech Area' started by PurplePackFan, Feb 2, 2020.

  1. PurplePackFan

    PurplePackFan New Member

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    Having a bit of trouble getting my '71 CT70 HK0 engine running right after rebuild and adding 88cc big bore kit.

    As background this is my third build and second using an 88cc kit. My first was a '72 K1 which I kept stock displacement and it runs great with new CHP carb. The second is a '71 Candy Blue K0 with big bore kit and new carb. It runs well but I just finished it in Decemeber and haven't had chance to ride it due to it being winter here in Wisconsin.

    This third engine was rebuilt using the 88cc big bore kit, new CHP stock carb, clutch plates, shift forks and pins, valves, high volume oil pump and new gaskets and seals. Cam gear installed with "O" at 9:00 on head and at "T" on flywheel; points set at 0.016" with flywheel at "F" position; valve lash at 0.002" at TDC.

    Engine runs on stand but will bog and run rough when trying to give it some throttle. It won't accelerate.
    I'm thinking carb. I have the main jet needle at lowest groove setting(rich) and have bigger jets available to install.

    Any recommendations?

    Thanks

    John
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  3. OLD CT

    OLD CT Well-Known Member

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    Set the points at the T, not the F.
     
  4. racerx

    racerx Administrator
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    If resetting the point gap doesn't correct the problem, try swapping the carb from your other 88c tune. If that fixes it, the problem is in the new carb. If nothing changes, then it's either cam timing or low compression. You made no mention of doing a valve job. Low compression can cause this but...that usually results in hard starting and weak idle.
     
  5. PurplePackFan

    PurplePackFan New Member

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    Thanks for the feedback. I'll reset points at "T". The valve were replaced with new ones and they were lapped in the head but the seats were not cut.

    Is there anything I should look for with the centrifigul advance on the "H" engine/flywheel? The 3 speed doesn't have the advance so there is nothing to change.
     
  6. allenp42

    allenp42 Well-Known Member

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    Just a tip on something I just recently experience first hand.....points. Depending on the brand - OEM Honda, Daiichi, K&S, K&L and many others - you may have to clean the points with your cleaner of choice -and- lighting sand with 600 grit sand paper and then clean again.

    The problem I was having? Nice spark up to about 2000-2500 RPM and then hit or miss or nothing at all. My normal routine of cleaning the points with contact cleaner was not working.

    Don't know what protectant lube is being used on some points (K&S and various NOS Japan mfg), but it has been taking more work than usual or expected to get 'em clean enough to work properly.
     
  7. PurplePackFan

    PurplePackFan New Member

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    Good tip, I'll try that also. Thanks for the reply.
     
  8. kirrbby

    kirrbby Well-Known Member

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    X2^^
    Good tip Allen.

    600 grit?? I think...even my buttcheeks are rougher than that.
     
  9. Texan

    Texan Member

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    Air leak maybe? I see you do not have the Carb Insulator in place.
     
  10. allenp42

    allenp42 Well-Known Member

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    Funny, mine too. But my butt is way to big to fit between the points. I did not have any 400 grit at the time, which is probably better, but since "clean, sand, clean" is working, not going to change for now. Honestly, kicked my butt for a couple of hours. Only after I swapped in a set of used OEM Honda points did I figure it out. The points looked good, measured good, but flaked out at higher RPMs. Took way more cleaning than normal. Made no difference if I used CRC electrical contact cleaner ("technician in a can") or Brakeleen. Still had to clean, sand, clean. I just was not going to let a set of points kick my butt.
     
  11. racerx

    racerx Administrator
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    Lapping, without cutting...or at least verifying condition...of the valve seats, bad idea IMHO. It can work out for the short term, too often it doesn't even last that long. If there's any pitting in the valve seats, compression will bleed-off. If there's any size/angle mismatch between seat and valve, then either sealing will be a problem from the get-go...or will become one far sooner than normal. The contact band, on the valve face, doesn't have to be perfectly centered and the perfect width but, achieving that with a rebuild gives the best shot at a long service life.

    You really should check compression. At the minimum, turn the engine over via the kickstarter, by hand. Full compression should stop you dead when the compression stroke is reached. If it's hard to figure out when the compression stroke has been reached, compression is way down.

    It doesn't take much to foul points. In my experience it doesn't usually take much to clean them either...a few passes with 600-grit and cleaning solvent. There has been one constant, though...weak, yellowish, spark. If you're getting nice blue-white spark with audible snap to it, I seriously doubt the point contacts are fouled.
     
  12. allenp42

    allenp42 Well-Known Member

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    That pretty much describes what I was seeing....until it went to sporadic spark and then to crickets. I haven't had any problems with OEM Honda ($$) and Daiichi (when you can find them). Mostly where I've experienced a problem is with all others. Honestly, I cleaned/sanded/clean a set of K&S (I think) 2-3 times before I had a nice white/blue spark. On one in particular, I changed the condenser to OEM Honda thinking that was the problem. I ended up back at the points. Sure fooled me.
     
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  13. racerx

    racerx Administrator
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    Oh yeah, I went through this for the first time back around 2006...only I tried cleaning cleaning the points first, which instantly corrected the problem. The only point I'm going for is that fouled points will manifest as a weak spark...and that's easy to check.
     
  14. PurplePackFan

    PurplePackFan New Member

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    Well first of all, thanks for all the input. I ended up sanding/cleaning points and re-gapping them. No luck. Now I have no sparke at all. I decided to pull the head and have the valve seats ground and valves matched at machine shop to make them right. That will take a couple weeks to get them back. Now I am looking at going with a CDI ignition. I did some searching here on the forum and some have used the kit from "xrarespares" on ebay. Is this kit any good?
    https://www.ebay.com/itm/HONDA-CT70...991935&hash=item5409c28e8c:g:2qUAAOxyhS9TfchT
    Otherwise there is the kit from DrATV: http://dratv.com/ctsl64.html
    This is a 1971 HK0 so I am finding differant comments for this 4 speed conversion compared with the 3 speed. Any feedback is welcome. Which do you guys recommend? I am tired of dealing with 50 year old points ignition.

    Also, with the big bore kit, how should the carb be jetted? Should I increase the main jet size? I have some in stock just in case. I also ordered the heat insulator for the carb.

    Looking forward to your feedback.
    John
     
  15. OLD CT

    OLD CT Well-Known Member

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    Buying a cdi kit for a 4 speed is a gamble. It might not work. Lots of folks purchased them and were pissed when it didn't work. I have used the cdi kit on a Hitachi 3 speed and it does work but the wiring needs reworking, too short and the wrong connecters.

    Come spring time I am going to test a kit from a different seller in Malaysia on a Mitsu flywheel and report back, sorry I can't let you know any sooner as the bike is buried and sleeping for the winter.
     
    #14 OLD CT, Feb 6, 2020
    Last edited: Feb 6, 2020
  16. Gary

    Gary Well-Known Member

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    Well you should never use sandpaper to work on points - it leaves behind grit which in-beds into the surface of them causing problems. There are files made for that use called ignition point file. It is my understanding that today since very few engines use points anymore that rather than using solid tungsten for the contacts they have switched to tungsten plated ones which if you file you remove that plating. Probably a good idea to use genuine Honda sets if you can get them,my original set on my 50 went with out any adjustments up until the 90's when it needed a valve job anyway.
     
  17. allenp42

    allenp42 Well-Known Member

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    OLDCT is correct. Now there are several sellers on e-Bay selling the kits, all made of parts from the same supplier. But as I understand, it's up each "seller" to support the kits they sell. I am familiar with 2 of the sellers on e-Bay.

    I have tested both the Hitachi and Mitsubishi versions. The wiring was too short on both and it took a little experimenting on the Mitsu version to get the lighting/charging coil to work correctly. Ignition/spark was fine. I also made it clear that it was going on a US CT70, needed longer wiring with a 4 pin plug but received the same kit supplied to everyone else. I have the Mitsu version on my HK0, but other than verify it will run and the lights work, that's it. Will be another month or 2 before I give it a workout.

    On the Hitachi CDI unit I tested, it worked out of the gate on a K0 and HK0. However, I did have to use my wire stretcher on the harness.

    To Gary's point, I think I just found the cause for my recent issue. As I stated, I normally use CRC Electrical Contact cleaner. Encountered the problem again today and I decided to give Brakeleen a try on a new set of aftermarket points as my first step. It worked. No sanding. I suspect that whatever the protection lube used on AFT points I have, CRC will not remove it. I agree that sanding on new points should not be necessary and may leave some residue, which is why I clean them again after sanding.

    I have never had a problem with OEM Honda points, and until recently, minimal problem with aftermarket points.
     
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  18. lukelaw1

    lukelaw1 Active Member

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    I have 2 kits from "xrarespares" on my 108 stroker builds with a Mitzi flywheels and both have worked great for me. I did remove the advancers, spring and etch on both flywheel/magnets.
    Yes the wires from the stator are to short to reach the main wiring harness. I didn't want to hack up the original CT70HK1 wiring harness so I went to cycleterminals and bought the correct barrel connectors and 4 way plug and made a short sub harness. On my CL70 I just needed to lengthen the wires with the proper terminals.
     
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  19. allenp42

    allenp42 Well-Known Member

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    On the Mitsu flywheel, did you just remove the cam?
     
  20. lukelaw1

    lukelaw1 Active Member

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    Resized952020020795122526.jpg Resized952020020795122900.jpg

    No I took the two screws out and removed the small angle brackets. I'm pretty sure this allowed me to remove the cam. Then I removed the e clips on the studs for the weigh bobs.
     
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  21. allenp42

    allenp42 Well-Known Member

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    Gotcha. Thanks for sharing the pics. That explains what I need to know.

    FYI - On my HKO with a mitsubishi flywheel, I did not remove anything. Once I saw that nothing was close to touching the coils, I left everything in place.
     

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