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Discussion Starter #1
Hello.

I just bought an old '74 cb450 the other day. This is the first bike I've owned and the first one I plan to work on myself. The bike does not idle. It runs fine keeping the throttle moving but I can't let go otherwise it just quits. The seller tells me he recently cleaned the carbs and says the problem is in the timing.

Is this a common problem? Is it very difficult to fix?

I've been searching these forums today and have already printed out a few of your carb cleaning and syncing posts in order to just try them anyway, but if these actually do fail I'm going to have to try my hand at fixing the timing problem.

Any info is helpful.

thank you,

Jeff
 

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Sensei
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Sounds to me like the pilot jet is clogged OR the advance unit springs are weak.....Both are common on the 450's....
 

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Quick tip -

If your mixture or "air" screws seem to have little or no effect (3/4 turn out to start), or they don't pass the "straw" test, then you need to tear down the carbs and clean them.
But they are brutally simple carbs - there's a post here in the 450 section about it.
 

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Discussion Starter #5
Ok I will check using the straw test and the other things you mentioned. I plan to do it this weekend (was going to try this evening but with the rain here I won't have a chance...my work area is outdoors.)

Thanks for the help!
 

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Discussion Starter #7
66Sprint said:
Sounds to me like the pilot jet is clogged OR the advance unit springs are weak.....Both are common on the 450's....
I'm not even sure what the "advance unit spring" is? My clymer manual doesn't describe it anywhere I can find (at least in the index).

Been trying to work out the problem and I think it's past my capabilities at this point. I can't get any idle whatsoever it's super frustrating.

So far I have:

cleaned carbs (twice now) and checked float levels
checked points and gap (cleaned and fixed gap distance)
cleaned the air filter (has nothing to do with this though)
tried my best to adjust timing, but I'm at a loss here.

Bird76Mojo said:
Welcome aboard from a fellow 1974 K7 owner! :D

GB :mrgreen:
thanks, good to be here. Will be great once I can actually ride my bike.
 

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OK -

Let me take some photos out in the shop today, I'll post a thing on ignition timing later tonight.
It should get you timed up properly, real quick.

You also never mentioned if you checked the compression readings??
Do it and post results. All this other stuff is irrelevant if the compression is bad, and you're making yourself feel bad for nothing.
 

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Discussion Starter #9
I wish I had a gauge to be certain (or at least access to one.) Going by "feel" which is never a good thing, compression seems to be ok. I will see if I can find myself a gauge to work with.
I must mention that the bike, when running, loves to backfire, especially from the right side. So I'm guessing the carbs are not nearly as synced as I though and perhaps I should re-re-take them off, clean them, and sync them again.
 

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Discussion Starter #11
thanks. Luckily I just received a timing light and a test light from the mechanics that work where I work. They will be very useful considering the test light I had was not very good.
 
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