bs 38 carb rebuild

easytravel · Posted: October 3, 2008, 11:18 am Post subject: bs 38 carb rebuild

What's that saying....something about beating a dead horse? O.K. simple question...as there is no doubt that my '78 carbs need a rebuild and cleaning, could someone tell me of the best kit (if one exists) to install and what jets to use for shorty pipes? Any tips would be appreciated as I've already cleaned them once (thought I did anyways!) and the problem went away for the first start but not the second, yes I have a spark and fuel to the carbs. Problem is it just won't start without draining the bowls (?). Thanks in advance

weekendrider · Posted: October 3, 2008, 11:46 am Post subject: Re: bs 38 carb rebuild

easytravel wrote:

Problem is it just won't start without draining the bowls (?).

This would be flooding? Have you checked the fuel level of the bowls?

5twins · Full Member Joined: Aug 05, 2006 Posts: 1616

Your float needles and seats may need replacing as well. They may not be sealing and the bowls are over-filling as a result.

As far as rebuild kits go, I don't usually buy them but rather just get any part I need individually. If you do need all the stuff in the kit then, yes, it is cheaper to go that route. Usually you don't though. Most of the stuff ends up sitting in the bag. If you've done mods and need to re-jet, stock size jets included in some kits will be of no use to you.

Your '78 carbs came with the largest mains ever put in a 650, #135s, so re-jetting for one change like pipes shouldn't need to be too radical. I'd go up one size to a #137.5. If the bike handles that OK without any break-up through the midrange, you could try 140s. The mains bleed over into the upper midrange. As you keep increasing their size, eventually they will make that upper midrange too rich and stumbling or break-up will occur under heavy throttle applications. The "fix" is to lower your needle (raise it's clip) to lean the midrange out. When you do that, it also leans the upper part of the idle or low speed circuit and a larger pilot jet may be needed.

easytravel · Posted: October 3, 2008, 2:41 pm Post subject: Re: bs 38 carb rebuild

Thank you genemen,(5twins and weekendrider) I will order the rebuild kits, main jets, float needles and seats. Once I recieve them I will take the carbs off and do a thorough cleaning. Wouldn't you know...I've already had to drill and tap for stainless screws as I forgot how soft this material is (potmetal?). Funny thing...I find taking apart a carb, putting all the pieces in pie pans, cleaning with solvents and then reassembling these parts very relaxing, must be the solvents! Oh...check out my bike on youtube at mark58mark, thanks again.

5twins · Full Member Joined: Aug 05, 2006 Posts: 1616

Check the contents of the rebuild kits. Many times they come with float needles and seats so you wouldn't need to get them separately.

easytravel · Posted: October 3, 2008, 3:42 pm Post subject: Re: bs 38 carb rebuild

Does the rebuild kit from mikesxs have the float needle and seats? When they say "comes with float valve assembly" I'm assuming it comes with the seat and needle yes? Thank you, Mark

5twins · Full Member Joined: Aug 05, 2006 Posts: 1616

Yes, it does.

weekendrider · Posted: October 3, 2008, 3:57 pm Post subject: Re: bs 38 carb rebuild

Yes, the needle and seat are the "valve" part of the assembly.
It could be your present one just needs adjusting.

easytravel · Posted: October 3, 2008, 7:46 pm Post subject: Re: bs 38 carb rebuild

I have the manual, (haynes or claymor, I'm not sure which, red bike on the cover) is it explained how to adjust the float valve inside? You know ...this bike is in beautifull shape but it will not start every time and when it does, after a few miles, it wants to stall and I have to keep feeding it gas. Oh well...I'll order the parts and keep you posted on my progress. Thanks again

Retiredgentleman · Posted: October 3, 2008, 9:45 pm Post subject: Re: bs 38 carb rebuild

easytravel; If you want your bike to run well, I'd recommend you take your time and do a thorough cleaning of the carbs. I think to many guys rush the job and end up disappointed when the bike still doesn't run well. Its very difficult sometimes to actually see if the small orifice in the pilot jet is fully clear. I have a magnifying glass with a circular fluorescent light around the mag glass. I know what you're thinking..............no, my eyes are just fine Smile

If you want an accurate float bowl level, you should use a clear plastic tube connected to the float bowl drain. Find a spare drain plug or buy a bolt with the correct thread, and drill a hole through the bolt. Use some small brass tubing to make a barb, and connect the plastic tube to the barb. Check that the carb is level when you set the floats.

easytravel · Posted: October 4, 2008, 10:47 am Post subject: Re: bs 38 carb rebuild

thanks retiredgeneman, yes I agree. I now know to take my time on the next cleaning. I'm sure it's a case of not cleaning the pilot holes with a guitar string, again ...much appreciated.

raincrow · Posted: January 2, 2009, 3:56 pm Post subject: Re: bs 38 carb rebuild

hello, I am in process of cleaning the carbs on a 79 xs sf. After setting 20 plus years, they are in pretty good condition. My first step is cleaning the bowls. I've gotten everything thoroughy clean, but my fuel bowl has a hole to the side of a tower cast in the center of the bowl, opposite of the starter circuit passage. It seems to be a blind hole, but i'm not sure and can't make out enought detail in the drawings i've seen posted. Any help here will be appreciated, taking me to the next step. Thanks.

Retiredgentleman · Posted: January 2, 2009, 5:35 pm Post subject: Re: bs 38 carb rebuild

raincrow;
Here's a picture of my 1978SE BS38 bowl. I've labeled a few items.Yes there is a blind hole to the left of the 2 jets. Appears that it was cast for some function but is not used on this model.

5twins · Full Member Joined: Aug 05, 2006 Posts: 1616

On '77 and earlier carbs, that blind hole had a brass overflow tube stuck in it. It led to the nipple and hose on the bowl bottom and drained off fuel if the level got too high. I'm not really sure how the '78-'79 BS38s accomplished that since the tube and nipple/hose on the bowl bottom were eliminated.

raincrow · Posted: January 2, 2009, 8:02 pm Post subject: Re: bs 38 carb rebuild

Thanks RG and 5twins, good to know. Will continue my cleaning and could very well have more questions. Again thanks and Happy New Year

xsleo · Posted: January 2, 2009, 10:41 pm Post subject: Re: bs 38 carb rebuild

i think on the 78-79 carbs the over flow was elimanated because the epa decided that the gas overflowing would cause to much pollution. i guess that they thought that having the gas overflow into the engine or out the air cleaner would be better.

jayel · Posted: January 2, 2009, 10:54 pm Post subject: Re: bs 38 carb rebuild

xsleo wrote:

i think on the 78-79 carbs the over flow was elimanated because the epa decided that the gas overflowing would cause to much pollution. i guess that they thought that having the gas overflow into the engine or out the air cleaner would be better.

that and with the never-fail vacuum operated petcock it wouldn't,couldn't, shouldn't over flow anyway.....

xsleo · Posted: January 2, 2009, 11:08 pm Post subject: Re: bs 38 carb rebuild

we all know just how perfect the epa makes things work.

5twins · Full Member Joined: Aug 05, 2006 Posts: 1616

yep, now the government wants to tax cow farts ......

brookiedc · Posted: January 3, 2009, 3:28 pm Post subject: Re: bs 38 carb rebuild

easytravel,

I've had my 650 for about three years, worked on the carbs a ton. I basically rebuilt them twice, and I was still having problems. I went by the Haynes guide, but this last time (this summer) I went full bore and followed the 650 garage carburetor guide. Incredibly comprehensive and easy to follow:

xs650temp.proboards29....rd=carbfaq

It requires setting up an account for that forum. I'm still no expert, but now my bike is running far better than it ever has. I still need to do some jet adjustment, but that's the real fine tuning. I can't recommend enough that you read this guide several times, then read it as you're cleaning your carbs. You will be glad you did.

What Happened to 650rider.com?

Yamaha xs650