Alright, who wants a challenge?

popojijo4 · Last edited by popojijo4 on June 28, 2009, 7:44 pm; edited 1 time in total

So, I've got a 79 xs650-2F that I've gotten to the point of starting ONLY when the choke is applied (bs38 carbs). I can flip off the choke, and it'll drop down to the correct 1200 rpm, but after about 30 sec of running it just dies. 30 sec it dies regardless of if I leave the choke on or not.

I've rebuilt these carbs probably... about 10 times now. Carb cleaner, blown with compressed air in every passage I can see and have read about.. even those microscopic 3 little pilot circuit holes by the butterfly valves-- with a thin wire and cleaner and air.

In addition, within those 30 seconds of running, if I try to rev up, it seems to always die at around 2200-2500rpm. Makes me question whats the range handled by the pilot circuit? I'm running 27.5's for the pilot jets (which IIRC is the stock size). The main jets are a bit difficult to read the number off of, but I believe it also the stock sizes of 135.

Important to know is that I had accidentally cracked the original float bowls, by screwing in the float bowl drain plugs too tight, so I had bought a new set of '78 carbs off ebay (was impossible to find just float bowls). So I swapped on the float bowls from the 78s after several thorough cleanings. I swapped in all the jets from the cracked bowls (I trusted them more). Is it possible that the float bowls don't fit like the old cracked ones? The only thing I was thinking was that maybe if they don't mate the same, the needle wouldn't fit the same way in the jets....

As far as other things go, I have great compression.. and the pamco iggy kit, new dual output coil-- good spark.

I can keep taking my carbs apart over and over, but really... I don't even know what to look for anymore at this point. Confused

kingwj · Posted: June 28, 2009, 7:25 pm Post subject: Re: Alright, who wants a challenge?

Clogged petcock filters?

popojijo4 · Posted: June 28, 2009, 7:26 pm Post subject: Re: Alright, who wants a challenge?

Additional info: Taking a look at the plugs they do look a little blackish rather than tan, so maybe running rich somewhat? Sometimes one of them is a little wet. I always clean them up after a plug read.

popojijo4 · Posted: June 28, 2009, 7:28 pm Post subject: Re: Alright, who wants a challenge?

Well I'm definitely getting gas into the float bowls as when I undo the drain plugs they each let out approx. the same amount of fuel. Good to know the float bowls each hold about a shot glass's worth lol.

xjwmx · Posted: June 28, 2009, 7:47 pm Post subject: Re: Alright, who wants a challenge?

Adjust your valve stem clearances if you haven't. Easy to do, and might have eliminated the last 9 carb cleanings, or all 10.

AMT82xs650 · Full Member Joined: Dec 22, 2007 Posts: 17

Grasping at straws here...

Check for a blockage in the fuel line causing the float bowls to drain faster than they can fill.

aybe gunked up fuel strainers or petcocks resulting in the same thing?

popojijo4 · Posted: June 28, 2009, 8:10 pm Post subject: Re: Alright, who wants a challenge?

xjwmx wrote:

Adjust your valve stem clearances if you haven't. Easy to do, and might have eliminated the last 9 carb cleanings, or all 10.

I like easy.. any tips on how to go about this?

xsleo · Posted: June 28, 2009, 8:13 pm Post subject: Re: Alright, who wants a challenge?

I'm not sure just when they did it. they changed the way the pilot jet mixes the air and fuel. In one the mix is from the top of the jet the other below. i think it was in mid 78. So if you had the one style pilots and the new bowls have the other style. They don't interchange well. Try using the pilots from the new bowls.
One of the carb guru's can explain it better than I can, maybe one of them will help out.

xjwmx · Posted: June 28, 2009, 8:20 pm Post subject: Re: Alright, who wants a challenge?

popojijo4 wrote:

I like easy.. any tips on how to go about this?

Yes. Download the official manual and follow the official instructions Smile

popojijo4 · Posted: June 28, 2009, 8:24 pm Post subject: Re: Alright, who wants a challenge?

xsleo, there is this section in the ""XS650 garage Carb Guide":

"From 1970-1975 (XS1 through XS650B), the BS30/96 pilot jet was used. In this jet, the tightest restriction (metering orifice) is located toward the barbed end of the jet, opposite the
threaded end. The VM22/210 jet was used from 1976-1979 XS650C-XS650F). In this
series, the metering orifice is located toward the threaded end of the jet. Either series
will thread into the carb body, and installation of incorrect jets is common."

Is this what you are referring to?

borjawil · Posted: June 28, 2009, 8:31 pm Post subject: Re: Alright, who wants a challenge?

I had the same problem. Has to do with the carbs if your getting gas flow to them and its not the petcock.

I rebuilt mine twice. the realized it was the jets. Got new ones and bumped up the sizes on them i believe. After the new jets ran fine.

jayel · Last edited by jayel on June 29, 2009, 4:15 am; edited 1 time in total

here's what mikesXS has to say about the jets the bowls should interchange between 78 79 tho' the 77D 78E and 79F all used the same type pilots

popojijo4 · Posted: June 28, 2009, 8:41 pm Post subject: Re: Alright, who wants a challenge?

jayel wrote:

here's what mikesXS has to say about the jets the bowls should interchange between 78 79 tho' the 77D 78E and 79F all used the same type pilots

Exactly why I thought I was safe bidding on those '78 carbs. Depending on prices of jets, wondering if just ordering a new set of pilots & mains + a set thats one size up might be a good idea. The thing that kinda gets me is the cutoff at 2500 thing... Is that when the main jets take over? Or is it not at all related?

xsleo · Last edited by xsleo on June 28, 2009, 9:25 pm; edited 2 times in total

That's what I was talking about, one jet is different than the other, you should use the jets that match the bowls.
I have some bowls here. The one on the right side is from a late 78-79 carb, the one on the left is from a 73 carb. the right one has the slot cut from the top of the pilot over to the hole. This mixes air and fuel above the jet.
The jet for this bowl has the orifice in the top of the jet and has a solid body
The left one doesn't have the slot. If you look close you see a dark spot in the edge of the hole, this is an air passage to the bottom of the pilot jet.
The jet for the this bowl has the orifice on the bottom, with holes in the sides of the jet.
The air travels down the passage, thru the holes and mixes with the gas.

gordo · Posted: June 28, 2009, 9:03 pm Post subject: Re: Alright, who wants a challenge?

Popo, jet's are cheap.Question. Do you have the pilot jet's from both set's of bowl's? Do they look to be the same type, other than maybe different oriface size?And yes, a couple of set's of jet's to find the right mixture is a damn good idea. Most motercycle mechanic's, at dealer's, have a wide selection for tuning preferance's. At least that's how it used to be, but most bike's today are fuel injected. No carb's.And one thing more, what position are your slide needle's in? There are 5 slot's, numbered from the top, the top slot being #1, next one down #2, ect.These jet's don't come into play until the slide's start to lift, usually about 2500-3000 rpm under load. Carb's can be very frustraighting, but once you understand where & when thing's happen, it get's alot easier, trust me. Oh, if the pilot's are all the same,get a good magnifier and read the size's, then you can purchase the size's you desire.Let us know how it work's out,,,Gordo Smile

Retiredgentleman · Posted: June 28, 2009, 9:34 pm Post subject: Re: Alright, who wants a challenge?

This is a picture of a float bowl on my 78SE. Notice there are a few drilled passage ways that allow fuel to go from the bowl to the main jet, and from above the main jet to below the pilot jet. Check to make sure these passage ways are fully clear.

xsleo · Posted: June 28, 2009, 9:36 pm Post subject: Re: Alright, who wants a challenge?

The Yamaha factory manual has a series of pics that show how the fuel and air travel thru the carb at idle and at different throttle settings. A very good read. It helps you understand just what is going on inside the carbs.

popojijo4

xsleo: Of the pics you posted, all the bowls look like the one on the right.. so should be compatible. Same as what Retiredgentleman posted. I have the Clymers manual, so hopefully a decent explanation of how things flow and when will be there.

Gordo: Both sets of pilot jets appear identical. All say 27.5 so I assume all same orifice size. All I cleaned out with cleaner/air/thin wire. Currently trying to check which notch the needle's on but how the heck do you remove the clip that holds the needle assembly? Do you need a special tool? Super fine tip pliers?

Retiredgentleman: Currently in process of checking those drilled passageways you indicated.. particularly the one from the above the main jet to below the pilot jet.

Everyone: Thanks for the super speedy help! This 650 community rocks!

popojijo4

Gordo: So got the needle out somehow, and it's on the 3rd notch (center). Needle says 502.

popojijo4

think I may have found a problem: I buffed up the main jets so I could read the numbers better, and the ones that came with the '78 bowls read "145" fairly clearly. The other set I could read a "35" and just a "5" on the other one... but I can only be left to assume they're both 135? I think I'm going to use the alleged 135's and see how that works.. 145 is def too large for what is mostly a stock bike (save mike's pod filters, but I hear that doesn't affect it too much on bs38's-- would still run mostly I would think)

tacoswild

You're getting lots of good advice already, I just have a comment on one thing you mentioned, the dark plugs. If the bike isn;t running well enough or long enough to go for a 20+ minute ride you can't can "read" anything from the plugs. They're always going to be dark because they're not reaching their self cleaning temperature.

popojijo4

good to know thanks

jayel · Posted: June 29, 2009, 4:18 am Post subject: Re: Alright, who wants a challenge?

I suppose it would have helped if I had posted a pic

yamaman

I would have thought that checking float height should have been top of the list after cleaning..........What are your floats set at?

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