BS38 Float Bowl Issues

[Kgreenhaw]

I recently rebuilt my engine and was having issues with one of the cylinders running rich at idle. I went through everything and finally found what the problem was. The float bowl. I swapped carbs from left to right and the rich condition followed the carb. I then swapped float bowls and the issue followed the bowl. to double check it wasn't the pilot jets i swapped those too and there was no change. Both carbs have #45 pilot jets.

My first thought was maybe the pilot jet wasn't seating all the way and was letting too much fuel through. I removed the pilot jet and saw that the seat in the bowl looked a little corroded/pitted. I found a drill bit that had the same angle as the pilot jet and gently "reamed" the seat to possibly help the pilot seal. Put everything back together and it made no change. I can turn the mix screw all the way in and it does nothing. I also tried a smaller pilot (42.5) and it ran way too lean even bringing the mix screw out multiple turns.

I thought about trying another bowl but when I search images I can't find one that looks the same as what I have. I'm stumped. there are no letter stampings and the hole along the front edge that lines up with a pickup tube is on the opposite side of the bowl...

I rebuilt the carbs before the engine, and got them dialed it. they sat for a few months while I rebuilt the engine and reassembled the bike. The carbs were soda blasted and cleaned. All passages were blown out with compressed air and brake clean. Since the issue started I disassembled and cleaned multiple times. I'm pretty much lost at this point...

 

[TwoManyXS1Bs]

Yep. Whutcha got there are the rare 70-71 carbs, with the enrichener pickup tubes on the opposite side from 72-on models.

I chased a similar overrich problem on mine years ago, caused by incomplete sealing of the critical center section, allowing extra fuel, or air, to wick alongside the non-sealing gasket. Caused by warped carb bodies, from PO floatbowl screw overtightening.

A way to check for this kind of seepage would be to put a thin coat of grease on both sides of the bowl gasket, reassemble, test. Use a toothpick to remove any grease from edges of bowl gasket orifices.

There's other things to check as well. Have a look thru my threads and albums for more info...

 

[Kgreenhaw]

Thanks for the reply twomany!

I had a look through your threads/albums, lots of good info...

Now with the grease method will this only make a temporary seal? I've pretty much ruled out the carb body being the issue since the problem also occoured when bowl was swapped..

I'm wondering what else I could look at as being the source. Are there air passages that could be blocked vs. Excess fuel passing through?

Also I haven't changed gaskets since carb rebuild and they've been on/off many times perhaps I should try a fresh one? I can see clear indentations on the top side of the gasket which would indicate a good seal, or so I would think.

 

[TwoManyXS1Bs]

The grease is just temporary, for diagnosis. I like cheep & easy tests.
New gaskets would be prudent. I believe those are 70-75 interchangeable.
There's a bit of a pitted area alongside the pilot mix passage in pic #1.
Check that bowl for flatness.

Edit: I'm concerned about your pilot jet seat. Not something to be properly recut with a drill bit.
Could try a thin coat of grease on the pilot jet's seat face, note changes...

 

[Kgreenhaw]

Yes, I realize the drill bit isn't proper. It's one I had for drilling plastic and happened to match the angle of the pilot jet tip. It didn't leave a perfectly smooth finish..

I noticed the pitting as well and Lightly block sanded the bowl to try and smooth everything out. Didn't seem to make a difference. I'll try the grease.

 

[gggGary]

What year are the carbs (supposed to be)
a comparo shot showing both bowls?
There is an orifice at the front for the idle/choke pic up circuit is it still factory size or might maybe gotten oversized during some cleaning work, yours or a PO?

 

[Kgreenhaw]

Tried grease on gasket, didn't change anything. I also used some valve lapping compound and ran that drill bit in reverse and it looked like it made the pilot seat pretty uniform...

Gary, the carbs are supposedly 1970. I will snap some pics today after work. I didn't do anything too invasive. Light media blast, soapy water rinse, compressed air and carb clean.

 

[TwoManyXS1Bs]

Well, if your next pilot jet tests show no change, I suppose you'll have to use some ingenuity to search for some sort of passageway cracks/leaks/voids, taping off holes, blowing thru hoses and such, similar to this overflow tube test:

 

[TwoManyXS1Bs]

Getting kinda obscure here. FYI, there were 2 float bowls for our early 70-71 carbs.
The W1 and E2 originals, used on early XS1s up to s/n 03629.
The E3 variant, used on later XS1 and XS1B after s/n 03629.

I have no data that identifies the differences in the bowls, just for the bodies.

Here's a closeup of my E3 bowl. Note the height/size/geometry of the pilot well.
Compare to your bowl(s). Your pic #1 in this thread looks a little different to me.

 

[grizld1]

If the problem doesn't resolve I have a dirty but unmolested XS1 float bowl that I'd be glad to send you. It's from a salvage carb set from a parts bike bought years ago for next to nothing that had been abused well past the point of no return. No charge, just pass the favor on to the next guy. PM your address if you want it.

2M, you may be able to give some input here. The donor bike in question was one of those early XS1's with needle bearings in the small ends of the rods, so the float bowl is probably the earlier series.

 

[TwoManyXS1Bs]

...2M, you may be able to give some input here. The donor bike in question was one of those early XS1's with needle bearings in the small ends of the rods, so the float bowl is probably the earlier series.

Hey, Griz! Welcome to the campfire. Pull up a log. Have a marshmallow.

Yes, the small end needle bearing changeover occurred about the same time as the E3 carb cutover.

1970 XS1 Engine change chronology by S650- serial number:

000136 - Add metal chainguide over shiftshaft, discontinue plastic protective sleeve.
001125 - Clutch worm now metal with nylon housing, new left engine cover, new right oil filter cover (o-ring changed to gasket).
001235 - Transmission mainshaft needle bearing OD change, new rev-1 cases.
001587 - Camshaft Endcover change, advancer side.
002487 - Change to front camchain tensioner bolt holes, new cylinder.
002515 - Carburetor change, from W1 to E2 (see bulletin #246)
003269 - Connecting Rod change, discontinue small-end needle bearings.
003430 - New Cases rev-2, longer left & right case cover screws.
003629 - Carburetor change, from E2 to E3 (see bulletin #246)
004130 - Oil Pump & sump screen change, from 4mm to 6mm rotor.
005830 - Change to kickstart shaft (see bulletin #300).

Those two serial numbers, 003269 and 003629, could possibly be accidental transpositions in the parts manuals. So, it's possible the small end bearing and E3 changes occurred simultaneously.

Either way, your needle bearing bike, assuming unmolested, should have either the W1 or E2 carbs with the earliest rev-0 W1/E2 bowl.

Unfortunately, I don't know the differences (if any) between those and the E3 bowls.
GggGary has an early set, maybe we'll have to compare bowls...

 

[Kgreenhaw]

Here's a few side by side photos, sorry they're not the best... (problem bowl on left)

They appear to be the same. I forgot to mention that I bought a set of "donor" carbs basically just for a float bowl. One of the carbs that came with the bike had a cracked bowl. I found the donor set on ebay and they claimed to be off a '71.

One apparent difference I noticed between my current set of bowls is that the pilot jet seems to be sitting lower in the problem bowl. may just be from my attempted "fix".

 

[Kgreenhaw]

Grizld1, That would be awesome. I very much appreciate the offer! I will keep that in mind if I cannot resolve this issue.

 

[TwoManyXS1Bs]

Downloaded your bowl pics, playing "where's waldo?", going crosseyed.

Next thoughts come to mind:

Compare pilot jets. Swap pilot jets?

There's some suspicious dings on the bowl edges, might mean something, so:
Make up a flat plate of some kind, aluminum or very flat hardwood plank.
Drill a 3/4" hole in it, attach some #180 wet-or-dry, cut out where it's over the hole.
The hole is for the overflow tube.
Paint the bowl's sealing surface with marks-a-lot, as an indicator.
Bowl on sandpaper plate, tube down in hole, do an 'orbital sander' pattern.
(Orbiting jitter plus rotate)
Check surface for marker removal, dark areas are low spots. Note their locations, and their influence.
Continue until all marker is removed.

Corrosion pitting in left bowl. Maybe more in the pilot well?

 

[Kgreenhaw]

I hadn't noticed that there was another jet that is permanently pressed into the bowl. This is for the starter or enricher circuit? would this have any effect on how the bike runs at idle even if enricher was not engaged?

 

[Kgreenhaw]

2M, I swapped the pilot jets in the first run of testing after I swapped carbs and bowls.

The corrosion you see is actually something on the surface and not pitting. It appeared mysteriously after the initial carb rebuild. It doesn't wanna come off with solvent/rag. Oxidation maybe??

I will try block sanding again using layout dye or something to that effect.

At one point I had tried a 42.5 pilot and it ran too lean. Wondering how this plays into the equation..

 

[TwoManyXS1Bs]

Here's 5twin's post showing the starter well in the bowl.
I'd expect rich idle problems caused by the choke to remain with the carb body, and not move with the bowls.

http://www.xs650.com/forum/showpost.php?p=435835&postcount=6

 

[Kgreenhaw]

Ok, I wasn't sure if that could effect the Idle circuit.. Choke definitely works and carb clean spays through passage just fine.

edit: I realize it would and does effect the idle circuit, but yes I meant isolated to the bowl. If that makes sense...

 

[TwoManyXS1Bs]

2M, I swapped the pilot jets in the first run of testing after I swapped carbs and bowls.

At one point I had tried a 42.5 pilot and it ran too lean. Wondering how this plays into the equation..

That makes this more difficult. With the only known (for now) difference being the seating depth of the pilot, I'm starting to wonder about the geometry of the aeration intermix zone. That area between the pilot threads and its seat, where bleed air comes down thru a diagonal passage, and 'percolates' thru the pilot jet's side holes. Changes in bleed air has strong influence on idle richness.

Could check the size and number of those admittance holes in your 42.5 versus the others.
I've seen pics of aftermarket offerings where the hole counts were different...

 

[Kgreenhaw]

Interesting... I will check this out. I did compare the 45's to the 42.5's last weekend and noticed a slight size difference in the air bleed holes and the fuel holes at the tip. The 45's were both larger, which is what I would expect I suppose. I didn't take note of the hole count.

While in the hardware store earlier today I came across a set of tiny drill bits. I had the Idea of making custom pilot jets, Haha.