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Discussion Starter · #1 ·
Hello all, after closing around the forum for some time i finally decided to join... I bought my cm400a from a guy for $400... he had previously just had it sitting for about three years and wouldn't start...I kno it probably wasn't the best financial decision but I really feel in love with this bike. Plus I'm a beginner s.o i kno it's a good bike to start on and i figured i can learn as i go...so far I've replaced the battery, throttles cables(push cable was completely frayed, but decided to order and change both), ordered new shocks, oil filter kit, ignition switch... the biggest issue in having is finding a carb kit specially for my year or any interchangeable parts from other bikes...I've been able to get it to start but it won't idle, so I assume it could be a carb issue... I've pulled the carbs to inspect and clean and by general first look they don't look too bad, BUT haven't pulled any jets or other parts out yet because I'd be lying if I said I wasn't nervous about getting everything back to proper adjustments...
 

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Not the worst ever but it would be a good idea to make sure they're clear while you've got them off. You do have two carbs that should be very similar other than the accelerator pump (note where all the o-rings/rubber bits go). Disassemble/reassemble one at a time and you shouldn't have too much trouble. Also take pictures at every disassembly step and try not to do it over multiple sessions to minimize the chance of forgetting how things go back together.

The adjustments are probably already not perfect and it's easy to get them fairly close. One other thing to make sure you have is compression, but that can wait until the carbs are cleaned and back in
 

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Completely rebuild the carbs with Honda kits, including the accelerator pump, (take your time and get them really clean), sync the carbs and go up two sizes on the primary jets. This is what I did to my 80 CM400T and it runs like a champ. Good luck. Scott.
 

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Discussion Starter · #9 ·
So after cleaning every crook and crany and adjusting, I put the carbs back in place, now she idles but really low...also whenever I give it a bit of gas, it cuts off completely, so it's almost the complete opposite of what I was feeling with to start off...I also sorta fixed my sticking throttle situation, it doesn't stick but it doesn't snap back either...
 

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The black knob below the left carb adjusts the idle speed. Clockwise is faster.

Carbs-b3.jpg

After adjusting speed you'll need to adjust the idle mixture screws and sync (balance) the carbs. Any questions on how to go about that?
 

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Have you adjusted the idle up to 1200ish using the knob between the carbs?

Also throttle snap back is usually related to adjustments, the nuts at the carbs and also the one at the handlebar control that
 

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I've merged the replies in your member intro thread into this one since discussing the same issue in two different threads just confuses the issue. Let's keep the fuel discussion in the fuel section.
 

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Discussion Starter · #13 ·
Yea sorry about that boss, I honestly don't kno why I posted in two different threads... but to answer your question, yes I've tried the screw adjustments and got it to sorta of a stronger idle but it's not a solid idle, sounds like a little bit of puttering... but now there's a new issue(not surprising), my bike is smoking a little from the exhaust connection to the cylinder in the left side... so maybe too much adjusting??
 

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Probably need to replace the 2 exhaust gaskets where the pipe meets the head. There may be a couple of them in there so scrape them out until you see aluminum.
 

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It looks like there's been some kind of attempt at a repair of the exhaust studs there. I notice there is a double nut on the exhaust flange indicating some kind of repair.
 

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Discussion Starter · #16 ·
@LDR ok I will check that out tomorrow morning, I had to go to work... And yes that was the PO's handy work... He also almost completely stripped a couple screws on the carbs which were a pain to remove... and before I forget I wanna say thank you to all for the help so far, it's really appreciated...
 
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