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Hey guys I just picked up an '80 cm400t and it has been running OK, not able to get past 60mph pegged though! I think I finally found the problem, the right carb boot/insulator was leaking pretty badly and when i took them off it was completely disentigrated (sp?) from the rubber back portion, so I ordered two of these and the needed o-rings..heres my questions:
Would replacing these probably stop the low top speed and occasional backfiring? Also I sprayed carb cleaner through the drain valves in the float bowl and this is how I realized they were bad, carb cleaner came pouring out the bottom of the carb boot...

Also when I put the new ones on (expensive!) do I need to use any kind of gasket sealent or anything with the new o-rings?

And one more question, when I took the boots off I saw that there is a LOT of sludge in the head is it ok to spray carb cleaner and try and get all the carbon build up off or slide it down into the cylinders? The same question goes for the EGR valve I believe its called, on the top of the head...

Thanks a lot you guys, and its been really fun around town, even if i can only go 60

I'm not the expert here though I have done a complete carb rebuild on my old honda. Why don't you do a complete carb clean while you are in there? My experience says if you have any gunk in there, go ahead and take them off and clean them right or you might end up chasing your tail for a while. Doesn't take much to make them go wrong but once they are cleaned properly that'll last many years if you run the bike and store it properly when you aren't using it,.

Thats the thing, I just got the bike and the guy I bought it off of said it was fully restored literally EVERYTHING has been rebuilt within the last two years and he said this included the carbs, it seems one of the only negelected pieces was the carb boots as they had looked like they tried to be repaired (he used orange rtv where it was leaking) guess he thought it would hold? But nothing dirty came out of the floats and the only gunk is inside of the head right after it gets sucked in, the carbs appear to be sparkly clean, and there was no gunk in the boots...
I asked if they needed to be rejetted or anything and he said "ooh just a little spray in the float bowls and it should be fine" but I think the problem was the leaky boot the whole time, the carbs really look brand new! I hope the same goes for everything in them that I cant see

I'd take them apart (and leave them linked if there are two), but that's just me. Maybe you do need new boots?

Would replacing these probably stop the low top speed and occasional backfiring?

The new boots (intake manifolds) will likely cure your problem. A friend of mine had the same problem on his CM400. You don't need any sealant on the new o-rings.

And one more question, when I took the boots off I saw that there is a LOT of sludge in the head is it ok to spray carb cleaner and try and get all the carbon build up off or slide it down into the cylinders?

I don't think you want it in your cylinders. I'd try to get as much out as you can.

I'm with Joe. The new boots should cure the backfiring problem. That's caused by an overlean condition when you back off on the throttle. The old boots were letting too much air in. The problem is very common on 80s bikes with the original boots.

Yes to above advice

Don't mess with the carbon build up in the head. If you are really concerned about it, get some sea-foam, or some other type of fuel injector cleaner and put it in a low tank of gas, then fill up w/ gas. That way the bike will clean itself while running!

Thanks you guys I should be getting the parts this saturday from fedex...hope I can ride this weekend!

Thanks you guys I should be getting the parts this saturday from fedex...hope I can ride this weekend!