Advice on 1977 XS400 Jetting

[kshansen]

Took apart carbs to clean as bike has been parked a couple years and was being very hard to start it it would at all. Got a carb kit of Ebay from Japan back in Jan. and just getting around to this project.

First thing I noticed is that bowl gasket is a slight bit off but think I can work around that with a little trimming.

Real question is the main jet. The one in carb is a 137.5 and the one in the kit is a 142.5. What the thoughts on which to use? For now I am using stock air boxes and filters. Bike has stock header pipes with some kind of after market mufflers.

Took out butterfly seals and they are not broke or hard but think I should replace them just because.

This bike is going to be just for fun playing around and is in the final stages of getting a sidecar mounted up. Just want to have it so I can start with a few kicks, no electric start on this one.

Thanks for any thoughts. Ken

 

[drewpy]

with the aftermarket mufflers, I'd try the 142's first

 

[kshansen]

with the aftermarket mufflers, I'd try the 142's first

Will do. Just waiting for the butterfly seals to come in from Mike's.

 

[xschris]

If the bike runs fine with the sizes you have now I would keep what you have. You say the bowl gaskets don't fit well. Does your carbs have the tin tops or the aluminum ones. The gaskets are different from the 77-79 and 80-82 sohc carbs. They should fit without "trimming" but if the kit has any china made parts, other size stuff may not be so accurate. When it comes to jets use mikuni only Mikuni jets have a square within a square next to the size number stamped in them.

 

[kshansen]

If the bike runs fine with the sizes you have now I would keep what you have. You say the bowl gaskets don't fit well. Does your carbs have the tin tops or the aluminum ones. The gaskets are different from the 77-79 and 80-82 sohc carbs. They should fit without "trimming" but if the kit has any china made parts, other size stuff may not be so accurate. When it comes to jets use mikuni only Mikuni jets have a square within a square next to the size number stamped in them.

Well when I was able to start it seemed to run good, but then I only put a couple miles on the bike at that time. The tops of these carbs are the cast type not tin. Two problems with the gaskets. The post for the float are just a hair too fat to let the gasket fit easy. The other slightly off thing is the hole for the little brass tube that sticks down into the float bowl is slightly off to one side so screw holes don't quite line up, maybe 1/32 of an inch or less.

I'm hoping the needle/float valve works good as that was the main reason I pulled them back off, gas overflowing into intakes.

One other thing I noticed when taking them apart is someone was a little to heavy handed with the idle mixtrure screws as they have a definite groove in them from being turned in too tight at least a few times!

 

[xschris]

What kit did you buy? Make sure the parts look the same for the float valves. I would get some new idle mix screws before those break off.

 

[kshansen]

What kit did you buy? Make sure the parts look the same for the float valves. I would get some new idle mix screws before those break off.

Idle mix screws came in the kits and they look like the old ones with the exception of the grooves from overtightening. Float valve parts look the same as the originals.

These are the kits I got:

http://www.ebay.com/itm/131547738668?_trksid=p2060353.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

 

[xschris]

I have often wondered the quality of those kits. Now I guess that answered my qusetion. I know the non-mikuni stuff like needles are made with less than quality stuff. My guess is that the softer brass is the reason why your neeldes did that.

 

[kshansen]

I have often wondered the quality of those kits. Now I guess that answered my qusetion. I know the non-mikuni stuff like needles are made with less than quality stuff. My guess is that the softer brass is the reason why your neeldes did that.

Not sure I understand that comment. The needles that have the grooves in them are as far as I can tell the original NOT the ones in the kit.

 

[xschris]

I guess I misunderstood your post. The grooves could also be from being worn. When you put the aftermarkt ones in just be careful!!! They tend to break easy.