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Discussion Starter #1
ok, i have a 1981 CB650C that im fixing up for a comfortable ride. i feel that it would be more better for longer rides than my drag bar equipped CB350. its gonna be a while before i can get it back on the road, so i may need to open another project thread.

anyway, how the fuck do you get the airbox back on the carbs? its like the frame was made around the carbs/airbox/filter housing...its like there is 8 pounds of shit crammed in a 5 pound sack between the motor and the frame right in there...any tips?
 

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Are the carbs on now? I'm pretty sure the box has to be in there before the carbs go in. Even then its a huge pain in the ass. Trying to shove them in there without screwing up the rubbers isn't fun. Then once they are in there its hard to get the old rubber around the carbs.
 

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Discussion Starter #3
yeah, the old hard rubber is a hindrance. im on the lookout or a set of intake boots as we speak, because i think thats part of my sporadic running problem, and they are so hard that its hard to get the carbs to seat into them. i had to use a rubber hammer and beat the carbs into the intake boots because they wouldnt slide in. would it be easier to leave the intake boots attached to the carbs and slide them onto the head? or leave the boots attached to the head and slide the carbs into them from there?
 

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Try a little lube. Leave the boots attached to the head, Just my guess because your having clearance issues.
 

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Hit the engine to carb boots with some heat from a heat gun. That will soften them enough to allow the carbs to slide back in pretty easily.

As for the carb to airbox boots, same deal.
 

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I haven't worked on a CB650 since around 1979 but the airbox had to be fitted before carbs.
Leave out mounting bolts and use bungy cords to hold it back as far as possible
If exhaust system is off bike, remove all but lower rear engine mounts and allow engine to tilt forwards.
Fitting carbs to CB500,550, 650 sucks but still not as bad as 400f ;)
 

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IIRC the airbox on that (and many other) bikes can only be removed to the rear, and in two pieces. This would require the rear wheel and inner fender to be taken out to allow you to access the airbox. Now, my memory is a bit cloudy on this, much like PJ's, but having the rear wheel off (I know, PITA) should allow you a straight shot at putting the airbox back in.

Then again, I could be recalling some other bike.
 

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First off - don't use a hammer to try to jam carbs on to the motor. Most folks use a combination of lube and sometimes a heat gun to make the mounts soft enough to allow the carbs to be installed. Sometimes you have to angle the carbs on to the mounts.

The airbox will either have enough room or not to be installed after the carbs are in place. This all depends on the bike and the frame design. If there is not enough room to install the airbox after the carbs are in place, then you have to position the airbox into place (loosen any part of the bike that might be in the way from allowing you to have room between the airbox and carb), mount the carb to the motor then slide the airbox on to the carb. Again, if the rubber mounts are old and hard then you have to use lube and sometimes a heat gun to make the mounts soft enough to expand and fit on the carb.

If the rubber mounts are that old, check them for cracks especially on the mounts that go between the motor and carbs. If there are cracks then you will have an air leak and the motor will never run correctly. At that point you have no choose but to replace the rubber mounts.

Most of this fitting and mounting is basically a combination of experience, mechanical skills and patients.
 

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Emit R Detsaw, your thinking of a different bike.
CB/CM400 can only be fitted from rear with wheel out (and a couple of others from mid 80's)
CB650 was developed from CB550 and has similar frame/airbox.
 

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Discussion Starter #10
its the custom model, if that matters. right now the carbs are off (bought a new rack, waiting for them to come in) and the front half of the air box (the box that attaches to the carbs) is off. the box that has the air filter in it is still on the bike. when my new carbs come in im gonna heat up my rubbers to hopefully help with the ease of installation. i have a bunch of RTV to skin them if i have to just to get it running.
 
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