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Another Noob from Canada - Ground floor of CM400 Project

This is a discussion on Another Noob from Canada - Ground floor of CM400 Project within the NEW MEMBERS READ HERE! forums, part of the Caferacer.net Forums category; Its taken me 500 miles on my XS and building up confidence on her to admit that she needs rear sets and the clip ons ...

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Thread: Another Noob from Canada - Ground floor of CM400 Project

  1. #21
    Senior Member Integra99's Avatar
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    Its taken me 500 miles on my XS and building up confidence on her to admit that she needs rear sets and the clip ons and top clamp lowering down - these are my next jobs of what will never be a finished bike lol!

    I had trouble with pods and fitted Ram Air filters (large) these have worked well!

  2. #22
    Junior Member YoungSonOfaGun's Avatar
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    Alright so I took the carbs off and over to my old neighbour's place and took them apart to clean them in the parts cleaner bath he has. Shined them up and ran a #69 drill bit through the pilot jet. Now I keep reading that the stock pilots were 72.. So I may upsize it slightly again but I must say, there has been a definite improvement in power, throttle response (partly due to tightening some slack on the pull cable), and the bog it would deliver mid-low rpm's is gone. It is still backfiring, very slightly, on deceleration and I checked and adjusted the valve clearances. What would you guys say to that? I'm thinking timing is off a bit. I've read up and it seems as though it's fairly common with these bikes. I was even told in the honda twin forum to toss the stock CDI unit for a programmable unit from Ignitech (Czech company who makes programmable CDI's and the like). Seems a little extreme for what I'll be doing, which is, using it as more of a daily drive/backroad burner. I also cracked and retightened the nuts to the header studs after the penetrant had time to seap in and the bike was warmed up a touch. 2 of these nuts weren't as tight as I'd have liked, any leak here could be the cause of my backfire but that was at the end of the day and I haven't drove it to see if it resolved the issue (I'm not too hopeful though).

    Summary and questions:
    -Maybe dumb question but is there a difference between buying a #72 jet and running a #72 drill bit through a jet?
    -Still backfiring slightly on deceleration, idea's?
    -Timing? It's next on the list of items to troubleshoot when I locate my dad's timing light. I have the specs, downloaded the shop manual (my old neighbour actually has an original copy in his stockpile containing dozens)
    -Sprockets need replacing, JT Steel makes them cheaper than Sunstar apparently from the same grade of steel. Any body buy from them before? JT Steel.
    -Chain is a joke, so finished. I've already learned my lesson once running a tired chain, didn't do much riding that day. What brands do you guys reccomend?
    -Push throttle cable was rusted and completely severed so.. I'm replacing both of those. Got a good price on both from Motion Pro, Any reviews?

    I have finally accepted that the stock airbox isn't going anywhere. I came to find out that these CV type carbs are able to adapt to changes in altitude and since I'll be diving it in the Rocky Mountains.. you get it. Everytime I read up on someone who put pods its the same story, they're fumbling around in the dark with V stacks, endless jetting changes, even modifying or replacing the needles and so on. I'm sure it's achievable in a lifetime but I want to ride the bike.
    Exhaust! I'm 6'1" so placing my feet comfortably for planned rearsets definitely interferes with the stock mufflers (which are busted and leaking). This has led me to desire either a scrambler style exhaust to avoid the interference or a 2 into 1 system so at least I'm only dealing with the issue on one side. Looking at making a 2 into 1 myself from the stock pipes and some exhaust pipe. Read bad things on MAC setups and others are pricey or they want to sell the package deal and the muffler looks like Fred Flinstone's club. Looking at a shorty pipe. Feedback welcome here, is it doable, making my own 2 into 1 system? Consider the welding ability a non issue in your reply, I'm looking for the technicalities. That and any links to decent systems.
    Bars, going to cut the stock ones and try to fab a Norman Hyde M style bar from them. If I fail, plan B is to at least confirm what style is comfortable for me before buying.

    Gotta get some sleep. Thanks in advance for input
    1981 CM400T - Cafe Project
    2006 CRF250R
    1979 185XR - I'll fix it in my next life

  3. #23
    Senior Member Geeto67's Avatar
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    Quote Originally Posted by YoungSonOfaGun View Post
    -Maybe dumb question but is there a difference between buying a #72 jet and running a #72 drill bit through a jet?
    No, but if you are running a #72 drill bit through a jet that isn't marked #72 then you are fucking over your future self or the next owner when they go to pull the jet and read it is a #69 and forgotten/didn't know you hogged it out to #72. Honestly, honda still stocks jets for these as does sudco, just get the ones you need. They are cheap.


    -Still backfiring slightly on deceleration, idea's?
    have you checked for exhaust leaks? That's what usually does it.

    -Sprockets need replacing, JT Steel makes them cheaper than Sunstar apparently from the same grade of steel. Any body buy from them before? JT Steel.
    -Chain is a joke, so finished. I've already learned my lesson once running a tired chain, didn't do much riding that day. What brands do you guys reccomend?
    use whatever works. I've used generic no name sprockets and chain I bought off a spool. Surprisingly enough for such a critical part it's hard to find bad ones.

    -Push throttle cable was rusted and completely severed so.. I'm replacing both of those. Got a good price on both from Motion Pro, Any reviews?
    I use motion pro for everything cable. They are great


    I came to find out that these CV type carbs are able to adapt to changes in altitude and since I'll be diving it in the Rocky Mountains.. you get it. Everytime I read up on someone who put pods its the same story, they're fumbling around in the dark with V stacks, endless jetting changes, even modifying or replacing the needles and so on. I'm sure it's achievable in a lifetime but I want to ride the bike.
    Now you get it. CV carb's sorta adjust to altitude...the jet sizes don't magically change, but as the air changes they react differently. Radical Changes in 3000 feet or more probably still require a re-jet if you are going to spend any length of time there (think months, not days) but for the most part because the CV carb responds to engine vacuum rather than a cable, the slide compensates.
    Last edited by Geeto67; 04-26-2017 at 08:28 AM.
    YoungSonOfaGun likes this.
    Ever tried. Ever failed. No matter. Try Again. Fail again. Fail better.

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  5. #24
    Senior Member Cyorg's Avatar
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    Quote Originally Posted by YoungSonOfaGun View Post
    Still backfiring slightly on deceleration, idea's?
    There is a valve on the side of those carburetors. It's usually referred to as an air cut valve. It's purpose is to stop the popping in the exhaust during deceleration. Did you remove them when you had the carbs apart? Sticking? Torn or leaking diaphragm?
    YoungSonOfaGun likes this.
    "Non urinat in ventum"

  6. #25
    Junior Member YoungSonOfaGun's Avatar
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    Thanks for the feedback Geeto, spot on as usual! I have a few things coming in the mail now. As for the backfiring, I think Cyorg might be onto something. The exhaust leaks it has are at the muffler, I think thats a bit far back there to be the culprit. I was really listening today and it sounds as tho it is backfiring through the intake valves and into the carbs. There was also visual evidence of this when I pulled them off, could have mentioned that earlier.
    There is a valve on the side of those carburetors. It's usually referred to as an air cut valve. It's purpose is to stop the popping in the exhaust during deceleration. Did you remove them when you had the carbs apart? Sticking? Torn or leaking diaphragm?
    I did not remove them to inspect, I'll try and do that tomorrow! I actually saw a replacement set at a decent price, I think on David Silver Spares site.

    Alright, PROGRESS. Lets play the name game: What would you guys call these bars we made up today?
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    They're a massive improvement from the stock setup. Took the bike for a rip and they're really nice HOWEVER, Note the front brake reservoir. Would you guys reccomend any particular lever/brake cylinder/reservoir that'll work for these bars? Seems as tho I'll be able to find a set on ebay fairly easily/cheaply. And also, in terms of cables, whats the best way to deal with the excess brake line hose/clutch cable/throttle cables??? What I think I'll do is buy cables/SS braided for a CB400 since the stock bars on them weren't so high like the CM. There may still be a bit of excess but it won't be as bad

    Next thing I want to tackle (other than the backfiring and jetting) is rearsets and the seat. Then exhaust. Which is something I am starting to consider pulling out the pesos for. I'll take the mufflers off so I can play with the headers and see just what all it entails to fabricate 2 into 1. If anyone has pictures of their homemade exhaust and/or some experience with it they could share, I'd much appreciate it.
    Thanks
    Attached Images Attached Images      
    drgonzo likes this.
    1981 CM400T - Cafe Project
    2006 CRF250R
    1979 185XR - I'll fix it in my next life

  7. #26
    Senior Member Geeto67's Avatar
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    They are clubman bars, that's what you call them because that's what they are and have been since the 1950's. I have to commend you on your resourcefulness and recycling.

    why can't you rotate the brake master forward? What's it hitting?
    Ever tried. Ever failed. No matter. Try Again. Fail again. Fail better.

  8. #27
    Senior Member Stephen J's Avatar
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    Neat work on the bars. The back angle on them looks a bit much for me but if it works for you good stuff.
    If you can't pick it back up, don't ride it.

  9. #28
    Senior Member Cyorg's Avatar
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    No guarantees that the air cut valves are the culprit, because as mentioned there are other causes. If you are running lean from an air leak or partially blocked circuit, then the air cut can't compensate enough. However, given the fact that their job is to stop the popping on deceleration, then definitely something to check out.
    Last edited by Cyorg; 04-27-2017 at 01:40 PM. Reason: Can't fucking spell and my grammar ain't no good.
    "Non urinat in ventum"

  10. #29
    Junior Member YoungSonOfaGun's Avatar
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    Right on, Clubman bars it is!

    why can't you rotate the brake master forward? What's it hitting?
    right there its hitting the small stub I left sticking out passed the weld. To get it sitting nicely I'll have to cut off the stub and some of the weld. I dont want to do that. The bars look real nice with the small stubs and my brake reservoir is old and brittle looking. Found a new Lever/master cylinder on ebay for $40, I think that'll do the trick.

    Geeto you talked about swapping the front end off a CX500 so I looked into it. Check out this guy's build:
    CM400 Re-Re-rebuild.
    In there is says that he the only difference between the forks is the springs and internals. The tubes, fork slider, they were the same. Thats with a 79 CX500 and an 80 CM. He mentions Honda changed the forks slightly in 81 or 82 on the CM400.
    I emailed Progressive Suspension and hopefully they are able to help me out. I am trying to figure out if I can rebuild the CM forks with CX springs and forkseal kit. Any one on here have experience improving front suspension on a CB or CM400?

    Also, I removed the Air cut valve cover on drivers side and the diaphragm had the smallest tear that appeared as tho it didnt go all the way through. Ordering new ones to replace, hoping it helps with backfiring.
    1981 CM400T - Cafe Project
    2006 CRF250R
    1979 185XR - I'll fix it in my next life

  11. #30
    Senior Member steveo's Avatar
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    Not that it makes a blind bit of difference, the handlebars look more like Ace Bars to me.
    I've used this brake reservoir from David Silver a few times, cheap as chips. Might work for you.
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    "You were only supposed to blow the bloody doors off"

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