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1977 GS400X carb head scratcher

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Guest

Guest
I've looked at a few parts schematics and can't figure out if I'm missing something or maybe they were made this way.
I pulled the carbs off my bike to disassemble/clean and repair them.
The bakelite spacer that mounts against the head has no gasket/o-ring.
The rubber carb holders have no o-ring where they meet the spacer.
There isn't a groove for an o-ring either so I doubt someone left it out. I think this bike is a virgin. Only 6800 miles on it.
After cleaning & repairing and re-assembling the carbs, the engine runs at start up like it has an air leak. (needs lots of fiddling with the choke)
Anyone else have any experience with this situation?
Should I get out the RTV and start slathering it all around?
Thanks
Brad
 
I have a '78 motor [also had a '79 425] and the boots are typical rubber on steel with an o-ring groove; the spacer is aluminum with a gasket against the intake port. I've never seen a bakelite spacer, but maybe early production??, OR, somebody subbed in a Honda/Kawi/Yamaha part because they had it.

Every bakelite spacer I've run into has a gasket on each side. You can make them with some gasket paper [Fel Pro brand - auto parts store] by tapping the round end of a small ball peen hammer around the paper at the edges of the part. I'd use the thinner rather than thicker paper.

RTV is, well, don't get me started.

The usual original spacers and boots should be available on E bay, but 400 parts are getting scarce. I have a set if you can't find any.
 
OK, now we're on to something.
I see on the air intake schematic there is a gasket between the spacer and head that my engine is missing or it's melded with the spacer and I just plain missed it.
Still, nothing between the spacer and carb holder.
I'll go get some gasket material tomorrow
Thanks
Brad
 
John, Thanks
I just pulled the carbs off and looked again.
My black spacer has a black gasket on the head side.
I'll order 4 so I can put them on both sides of the spacer.
I'll bet my air leak goes away !!
 
I ordered them from Bikebandit for about $15 for four delivered.
Agemax, I bench sync'ed the carbs while they are off. (wire method) I'm sure that will help too.
I had to evict the mouse family living in the airbox before I started.
This old girl has been sitting for a long time but she'll be ready for Spring !
 
Last edited:
IMG_0119.JPGReceived and installed the new gaskets yesterday.
Cracked the spacer tightening down the bolts. Carbs off, epoxy the spacer back together.
The engine started right up but idled on the opposite cylinder from before . (runs on two, idles on one). ****er.
Let it sit over night and tried again in the morning.
A minor adjustment to the pilot screw and balance screw got both happy.
I'm ready to ride!
Thanks for the help.
 
Last edited:
A friend (mechanic) in Phoenix used a Twinmax for his work (BMW shop). I'm looking around for one now.
A neighbor has a manifold, many gages model but I'm concerned about syncing all those gages.
Your thoughts?
 
Last edited:
So, I bought the vacuum gages and set the balance and I'm back to idling on one cylinder again. I think the low speed circuit is plugged up on one carb. I have an ultrasonic cleaner coming on Thursday. More carb cleaning coming up.
the rest of the bike is coming along nicely!
 
Took the problematic carb apart in anticipation of an ultrasonic bath. Gave the pilot jet the "can I see light thru it ?" check and it was dark as the bat cave.
A little carb cleaner, a few strands of soft copper wire and voila! Light! Reassembled everything, gave it a few kicks and it was firing on both sides.
These Mikuni's seem a bit more sensitive to overall hygene than the Keihin's
 
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