78 bs38 carb replacement parts?

YammieBruh

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Hey all. I have a new to me 78 that I've been trying to get back on the road. I've managed to get it to the point that it will fire and idle, but only with the choke on. As soon as I turn the choke off the bike dies instantly. During my carb cleaning and videos I've watched I've come to the realization that I'm missing some parts I believe. First, on the idle screws I dont have springs or flat washers on either carb. I do have the oring on the screws themselves. Also I'm assuming I'm missing a plug as seen in the pic right below the idle screw on the right side of the bike. Does anyone know where I could get those parts?

I'm hoping these missing parts is the cause of most of my problems
 

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Here are some places to find your parts off the top of my head.
In no particular order:

Sirius Consolidated Inc They ship from Canada or New York.
XS650 Direct Since you're in Ontario
Jets R Us They offer genuine Mikuni parts
650 Central Outstanding service. You have to call Michael and he's in California.
Niche Cycle I haven't used them, but they come recommended by people I trust on this forum.

I hope this helps.
 
Because of that missing plug screw, you have a massive air leak. It's the same as this flat headed, straight blade screw on the outside of the other carb .....

K8kd2K5.jpg


Yamaha still sells them, and what looks like an aluminum sealing washer for it, but they're pretty expensive. It's just a short normal M6 screw though so you could use any that would fit. I put short stainless button head Allens in one carb set.

The spring for the mix screws could be a problem. It's not available from Yamaha anymore. But, it fits on the inner end of the screw and often remains stuck in the carb when you take the screw out. So, take a good close look in those mix screw holes, maybe the springs are still in there.
 
on the idle screws I dont have springs or flat washers on either carb.
1978 doesn't have flat washers under the idle screws, those are only on some later year carb sets.
I can give you the missing proper M6 screw and sealing washer, along with the idle screw springs that you need, for a few bucks, but shipping to Canada will be $12 USD.
 
Yes, no little washer on the '78-'79 BS38 mix screws, just the o-ring and spring. That little flat washer was used only on the later carb set's mix screws, the BS34s from 1980 on up.
 
hey thanks for the info guys. thanks Dogbunny I will try to source those parts up here, if not I guess we'll be in touch . I've seen carb kits with the springs in them i believe. I'm just wondering though, if there is no flat washer at the end of the spring what is the purpose of the spring. Just to put a force on the screw so it doesnt vibrate loose?
 
Yes, carb kits usually have the springs. I also think xs650direct.com sells replacement idles screws that come with springs. I think the kits might also come with the aluminum sealing washer that you need for the M6 screw. If not, you could probably find a copper sealing washer or make a gasket out of gasket material.
Yes, the purpose of the spring is to keep the idle screw from vibrating loose.
 
The mix screw is spring-loaded mainly so it holds the adjustment you set it to. It wouldn't be much good for tuning if it didn't.
 
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