legendary yamaha
IG:ne_caferacer_club
My bike is 1977, and the carbs are Mikuni bs38
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need help with my '77 xs650 Not idling and blinkers stay solid
- Thread starter legendary yamaha
- Start date
My bike is 1977, and the carbs are Mikuni bs38
If the bike has been modded (pod filters, freer flowing exhaust), then there's a good chance the carbs have been re-jetted. But, that doesn't mean it was done correctly. These carbs usually require more than just changing the main jet size. You usually need to change pilots and the needle clip setting too.
These carbs differ from most others in that the main and pilot jets are mounted into the float bowl, not up into the main carb body in the normal fashion. This makes access to them easier. You can just remove the float bowls using a stubby screwdriver, carbs still in place. The mains are mounted under the drain bolts on the bottom of the bowls so you can actually change them with the bowls still in place too.
These carbs differ from most others in that the main and pilot jets are mounted into the float bowl, not up into the main carb body in the normal fashion. This makes access to them easier. You can just remove the float bowls using a stubby screwdriver, carbs still in place. The mains are mounted under the drain bolts on the bottom of the bowls so you can actually change them with the bowls still in place too.
legendary yamaha
IG:ne_caferacer_club
It was running /idling good for a while until I changed the ATU springs, since it was idling at 3k after warming up.
I removed the carbs from the bike already, I have them in the side.
legendary yamaha
IG:ne_caferacer_club
And yes it has pod filters, I guess I will have to wait until I open to see what is going inside.
You may need to re-visit those ATU springs. The replacements from Mike's are often no good, too weak right out of the box. Many times all that's required is a good cleaning and lubing of the advance rod that runs through the head. It's often all dried out and sticking. That makes the timing stick in the advanced position and that causes the high idle.
When you clean your carbs, take only one apart at a time. That way, you always have a reference point.
The bowl gasket can usually be reused if you take care in removing it.
The bowl gasket can usually be reused if you take care in removing it.
I don't usually completely remove the float bowl gasket. When you take the bowl off, the gasket will usually remain stuck to it or the main body. I leave it where it is. I do wipe down the surface of the gasket and the corresponding metal surface on the other part it mounts to, basically a gentle cleaning. When re-assembling, I wet the gasket down with some light lube like WD40 or something. I like to think this softens it up a bit, helps it seal up better, and hopefully prevents it from sticking so it will come apart intact next time. I never put stuff back together dry.
legendary yamaha
IG:ne_caferacer_club
thank you for the advice, actually that's what I am afraid of , the gaskets breaking, I don't know if it has rubber or kind of paper material(whatever its called)
legendary yamaha
IG:ne_caferacer_club
That might also be the case, but now Im having problem of not idling at all, it just shuts down, not reeving at 3k anymore.
legendary yamaha
IG:ne_caferacer_club
IF I want to clean only the main jet and the pilot jet, is it necessary to remove the diagram and all the parts apart or not?
If you just want to clean the main and pilot jets then you can just pull the float bowl off and clean them separately. But if you're going to be spraying any carb cleaner on the main carb body and through it, you'll need to remove the slide/diaphragm assembly. The rubber diaphragm will shrivel up like a used condom if you get carb cleaner on it, lol. Honestly, it's no big deal removing the slide/diaphragm, you just take the carb top off and lift the thing out. Then set it off to the side, far off and away from all the volatile cleaners you're using.
You may just need to clean the pilot jet as maybe it got plugged, but if dirt got past it, the passageway into the main carb body may be plugged too. That would require blowing carb cleaner through the carb body.
You may just need to clean the pilot jet as maybe it got plugged, but if dirt got past it, the passageway into the main carb body may be plugged too. That would require blowing carb cleaner through the carb body.
legendary yamaha
IG:ne_caferacer_club
Thank you
It sounds similar to experiences I’ve had with small debris in the fuel lines and then the carbs.
The tank cleaning, petcock replacement, in-line filters, and carbs on and off repeatedly. All could easily dislodge small debris in the fuel lines.
Old fuel lines ? Anyway, it is good to be able to both drain the float bowls, flushing the bowls say, And even having the ability to drop the bowls in a pinch to clear the needle and seat and clean jets if needed. Carbs in place.
I’d flush em again..
The tank cleaning, petcock replacement, in-line filters, and carbs on and off repeatedly. All could easily dislodge small debris in the fuel lines.
Old fuel lines ? Anyway, it is good to be able to both drain the float bowls, flushing the bowls say, And even having the ability to drop the bowls in a pinch to clear the needle and seat and clean jets if needed. Carbs in place.
I’d flush em again..
legendary yamaha
IG:ne_caferacer_club
I cleaned and sealed the tank, new petcock, new fuel filter but still have old fuel lines, I should go and buy new ones before I put my carbs back.
It sounds stupid to do all that job with the tank and keep the old fuel lines.
Na, wasn’t implying that at all. I’ve reused old fuel lines, just making a point as to a possible cause. The fuel line length and routing nicely as you know by now is cramped. If you trust your petcock screens as I do you could just take the in-line filters out of the equation for now? IDK but flexible 6mm fuel line is what you’re after either way. You’ll get it all clean and flowing.
Hang in there with the BS38’s and you’ll probably really like tuning them in the end.
If you need new brass parts for your carbs DON'T buy Mike's knock offs. You can buy genuine Mikuni brass from several online sellers. I have bought mine from Niche Cycle. Jets R Us is another good place. They sell the good parts for about the same price Mike's sells the knock offs.
With a bit of shopping you can find good gaskets you need for less than a kit you can't use most off.
If you follow the carb guide mentioned earlier in this post, you won't have much problem with your carbs.
The only real problem most have is getting the idle passages clean. If plugged very much they can be a PITA.
I don't think your should be too bad. They have not been plugged very long and should clean easily.
Leo
With a bit of shopping you can find good gaskets you need for less than a kit you can't use most off.
If you follow the carb guide mentioned earlier in this post, you won't have much problem with your carbs.
The only real problem most have is getting the idle passages clean. If plugged very much they can be a PITA.
I don't think your should be too bad. They have not been plugged very long and should clean easily.
Leo
legendary yamaha
IG:ne_caferacer_club
I was thinking about it, since everyone is saying will not need the jets and stuff maybe is better to have just a pair of gaskets, but was looking online and was finding only as kit not gasket by themselves.
Here's some .....
https://www.ebay.com/itm/2-Float-bo...74AAMXQ~6VQ47-3:sc:USPSFirstClass!14075!US!-1
But if you're careful when taking the bowls off, you should be able to save and re-use what's on there. The original float bowl gaskets are very robust and can last darn near forever if you don't break them. I still have the originals on both my '78 and '83. When you pull the bowl off, do it slowly. You may find the gasket sticking to both sides in some spots. Carefully free it up off the less stuck side using a small sharp knife. Don't just yank the bowl off, you'll most likely break the gasket doing that.
I cleaned up a set of carbs for a guy several years back. Following my usual routine, I was able to save and re-use the original gaskets. Then the guy let the bike sit for nearly a year and the carbs got plugged up again. I told him he had to take the float bowls off and clean the carbs out. He promptly broke both gaskets doing so, lol. Needless to say, the guy's a putz and really shouldn't be allowed to even use tools.
https://www.ebay.com/itm/2-Float-bo...74AAMXQ~6VQ47-3:sc:USPSFirstClass!14075!US!-1
But if you're careful when taking the bowls off, you should be able to save and re-use what's on there. The original float bowl gaskets are very robust and can last darn near forever if you don't break them. I still have the originals on both my '78 and '83. When you pull the bowl off, do it slowly. You may find the gasket sticking to both sides in some spots. Carefully free it up off the less stuck side using a small sharp knife. Don't just yank the bowl off, you'll most likely break the gasket doing that.
I cleaned up a set of carbs for a guy several years back. Following my usual routine, I was able to save and re-use the original gaskets. Then the guy let the bike sit for nearly a year and the carbs got plugged up again. I told him he had to take the float bowls off and clean the carbs out. He promptly broke both gaskets doing so, lol. Needless to say, the guy's a putz and really shouldn't be allowed to even use tools.
legendary yamaha
IG:ne_caferacer_club
Im surprised he had tools
The first time I went over there to help him with his bike, I saw he had a nice 2 car garage with just the bike in there, and a couple of those big rolling toolboxes. I thought "Oh, this will be great .....", that is until I had a look in those toolboxes. Most of the drawers were half empty and what was in there was all jumbled up. The rest of the tools were scattered all over the place, laying on the floor where they had last been used, in cardboard boxes with parts, a real mess. I don't help that guy much anymore, he doesn't deserve it. Let him pay a shop for repairs.
