Topic: 1974 CB450 - High Idle

[Kenzo1979]

Ok, I posted this on the twins forum too, but I feel like I get more input here.


Bike:
It's a CB450 K7. Cam chain tension is set, valve clearance adjusted, stock carbs and carb parts cleaned with cleaner and compressed air (gone through them twice, no prob there, pistons pass the "straw" test). Float levels set, air screws turned out 1 full turn. New spark plugs and resistor caps, getting spark on both sides. Stock air filters. Petcock is clean, tank is clean, gas is new, fuel lines are new. Throttle cables are new. Cables and carb throttle springs open and snap back fine, no problems with the cable routing. Static timing set, fooled around with the timing while it was running and it just revved higher or died completely. (I did recently monitor the points and right side is sparking like crazy, bad condenser?)  Battery is new and fully charged. About 20k on the bike.

Problem:

Start it up and the RPM's shoot to about 3.5/4K. If I start backing off the idle screws it stays high even with the idle screws completely off, there is no vary. Sprayed starter fluid and wd-40 (seperate times) around the intakes to see if they was a leak - no difference. Got it to run at near "sputter/die mode" by holding throttle a bit, popped it in gear and rode it around the block a few to see how it behaved. It was really wonky. Kind of between running and sputtering and would also seem weak then kick in with super-balls, then sputtery, and on and on. Going bananas over here.

Got some advice from hondatwins.net and ruled out the carbs.  So now I'm wondering if it could be the spark advance?  The condenser?  The coils?  Something else?  If anyone's got a solid theory, I'm all ears.

[fendersrule]

What throttle cable are you using?

[Kenzo1979]

Motion pro 02-0000.  Which did not have enough freeplay, but i took them apart cut the housings down and recrimped.

[grcamna2]

I'd say it's either throttle cables(make sure to properly service the spark advancer first w/ both springs evenly & Correctly  tensioned...)or the carb. slides are dirty.
The carb. slides on those early CB450 twins are Very sensitive to Any hint of dirt,varnish, or even dust sometimes ! Pop them out individually and super clean them & their bores as best you can w/ Gumout spray,assemble & then go from there...

[fendersrule]

I had the same issues with the motion pro cables on two of my CB450s. The cables are simply too short. Motion pro cables do not fit the CB450, even if they say that they do.

Maybe try disconnecting the throttle cable and then starting up the bike.

[Kenzo1979]

Yup, the damn cables!  Really thought I was around that problem.  Tell me what cables can I get that work?

[Kenzo1979]

Ordered the honda ones up from the local honda shop.  Banged me for $47!!!  I swear they just hate dealing with any bike prior to 1990.  Pricks.

[fendersrule]

Yep. Go with the original honda cable.

Someone should really contact motion pro and tell them that their throttle cables do NOT fit a CB450. We can't be the only ones with this issue. It's pretty obvious after you hook them up, loosen them all the way, and see that the throttle plates are lifted a 1/4 of the way...

I ripped off the SL350 throttle cable and put it on my girlfriend's CB450 and it fits like a glove.

[Kenzo1979]

So I got a reply fro Motion Pro:

...We strive to ensure our applications are the most accurate and complete in the powersports industry.
We reviewed our applications for 02-0000 and we do not list 02-0000 for use on your  1974 Honda CB450K7.
We went as far back as our 2008 applications and that application list does not show a throttle cable available for the older CB/CL 450’s.
Unfortunately, we do not control what applications other companies list for our products...

I went to Motion Pro's website, and it's true.  If you do a make/model/year search for any CB450 from 68-74, it does not offer a replacement throttle cable.  He did let me know that they can make a custom cable if given the specs, which may actually be cheaper than Honda, but as far as how quick it can get to your doorstep is another question.  So, really it's the vendors selling this cable, and listing CB450K's as an appropriate application, that are at fault.  Hopefully this helps others in the future.

[fendersrule]

That's good to know that they don't make a cable for the CB450, but I'm wondering most venders that I've seen lists that as an applicable CB450 cable? Even my local honda dealer ordered it, straight out of their catalogue I believe.

Anyhow, Motion Pro always tries to sleeze out of things. I had a horrible experience with their custom cable process. They messed up (sent me the wrong cable), and now they won't respond back to fix the issue, even after admitting blame. The only good thing to come out of it is that I decided to buy shorter bars, and their cable that they sent "works", but could be a tad bit shorter.

I'd be interested to know if there are other alternatives to throttle cables besides the Honda one. I'll need to be ordering two soon.