Bs38 carbs dumping gas out of intake

[Hankoldboy]

Hello all. I’m new here and also fairly new to these bikes and honestly motorcycles in general. I’ve been working on a 79 and I just got it running riding and stopping. At the moment the issue I’m currently trying to address is with my carbs. I’ve rebuilt the 2 times now with the same issue every time. As soon as I turn the gas on at the Petcock gas starts pouring out of the intake. I’m not sure if my floats are hanging or what but after a while it stops. The choke is a real pain to flip on and and off as well. I’m not sure if this is part of the problem or not. Any help would be much appreciated.

 

[5twins]

Sounds like your float needles and seats aren't sealing properly. When you rebuilt the carbs, did you use aftermarket kits? If so, the float needle and seat assemblies in them are often bad right out of the box. Best to use Yamaha originals, expensive yes, but you know they will be good. And this is something you should only need to replace once, it should last longer than you'll have the bike.

 

[Hankoldboy]

It was an aftermarket kit. I figured it was something to do with the needles. I was going to try and put the old ones back in and see if that helped. I’ll find an oem kit and get it ordered

 

[Hankoldboy]

Sounds like your float needles and seats aren't sealing properly. When you rebuilt the carbs, did you use aftermarket kits? If so, the float needle and seat assemblies in them are often bad right out of the box. Best to use Yamaha originals, expensive yes, but you know they will be good. And this is something you should only need to replace once, it should last longer than you'll have the bike.

Any suggestions on the choke lever? It’s really hard to move with the switch. If I take the switch off it operates very smoothly just turning it with my fingers. Also when I luck it over with the choke engaged it goes straight to a very high rpm. Is that normal?

 

[5twins]

Yes, try the original float needles and seats, they may still be fine. I'm still using the originals in my '78 and in many of the extra carb sets I have. Yamaha doesn't sell complete carb rebuilt kits, just the individual parts. Most of the time you don't need much anyway as the original parts are very high quality and long lasting. All I usually replace are the o-rings and the jets. There are only 2 o-rings in your carbs, one on the needle jet and one on the mix screw. We have figured out the sizes so you can use generic o-rings (much cheaper).

For jets, I only use genuine Mikuni ones. My bikes are mildly modded (pipes and pods) so I need larger than stock sizes anyway.

I'm not sure what's going on with your choke. It may be improper assembly of the lever and linkage. Got a better, close-up pic of the area? Maybe we can spot something that's off. Yes, the bike will idle high with the choke on initially but should drop down rather quickly (in warm weather anyway) and start running rough. That's an indication that you can turn the choke off.

 

[5twins]

I use Partzilla for parts look-ups mostly because I find their parts diagrams easy to navigate .....

https://www.partzilla.com/catalog/yamaha/motorcycle/1979/xs650f/carburetor-xs650-e006501-f

But once I find the part I'm looking for, I usually go to Part Shark and buy it there because it's cheaper .....

https://www.partzilla.com/product/y...?ref=cae0656d0675a58c87f92a61ab74a2fd6b99c501

https://www.partshark.com/oemparts/p/yamaha/168-14190-20-00/-valve-seat-assy-20

 

[Hankoldboy]

This is extremely helpful. I’ll give these suggestions a try and when I get home I shoot you some photos of the choke. When I got the bike the carb didn’t have a choke lever and I could find a whole lot of options for purchasing one. The one I found and purchased just bends when I try to flip it on or off. I have to use 2 hands to get it to do anything.

 

[5twins]

Sounds like you may have the wrong lever, or maybe you're missing some of the special mounting parts. There's a stepped spacer the lever fits onto then a small fender washer under the mounting screw. There's also a small spring washer in the assembly to keep tension on the lever. Here's a couple of pics of a correct lever .....

 

[Wingedwheel]

Yep if your choke lever was missing chances are that stepped spacer was also. Really gotta have that.

 

[Hankoldboy]

It looks like the piece that holds my throttle cable is pretty bent as well.

 

[Hankoldboy]

The stepped space is there as well as the small fender washer. Could it just be too tight possibly?

 

[Wingedwheel]

Did you get a new choke lever assembly? Looking at the pics it appears that spacer is there

 

[Hankoldboy]

Did you get a new choke lever assembly? Looking at the pics it appears that spacer is there

I did. I purchased the only one I could find for these carbs.

 

[Wingedwheel]

Beat me to it lol. Perhaps it’s too tight but see if loosening it a little makes a difference. The screw has to be tight enough not to fall out.

 

[Hankoldboy]

I’m about to pull the carbs again and put the old float needles back in. I’ll loosen the screw as well and get back to you guys with results soon. Thank you for your help.

 

[Wingedwheel]

Should look like this.

 

[5twins]

Yes, your throttle cable holder is badly bent. But, it does look like you've got all the correct choke lever parts and lever. Maybe the linkage is hitting that bent cable holder? I'd straighten it out and see if that helps. Heck, just trying the choke once that bent bracket is removed should tell you if it's the issue.

 

[Hankoldboy]

Ok. Here’s the verdict. The old float needles fixed the gasoline waterfall issue I was having. Bless you 5twins for that tip. I polished the old seats and needles with a q tip in the chuck of my drill dipped in brasso then cleaned everything with carb cleaner. Fixed it right up. The choke lever however was not as straight forward. The end of the lever assembly was starting bottomed out in the slot in the choke rod so it had no where to slide. If that makes sense. The pin on the choke lever that moves through the slot had no room to move. With a little grinding and a little bending I was able get that pin positioned back to where it would work properly. It’s still a little sticky but I can operate it with one hand now. 80 percent improvement. That you guys for your help. The first image is before repair second is after. Third photo is a reference for the bend I put in the choke lever to get it to work.

Now to sync them and try and get rid of as much of the popping as I can. Fixing the carb issue helped the popping but I think it may be running a bit lean now.

 

[Hankoldboy]

Sounds like your float needles and seats aren't sealing properly. When you rebuilt the carbs, did you use aftermarket kits? If so, the float needle and seat assemblies in them are often bad right out of the box. Best to use Yamaha originals, expensive yes, but you know they will be good. And this is something you should only need to replace once, it should last longer than you'll have the bike.

Do you have a recommendation for getting parts for these carbs? I’ve fixed the gas dumping issue with the old float needle but now I’m in need of new jets because the bike is running lean.

 

[Wingedwheel]

nichecycle.com
Try these guys.