1978 Yamaha XS650E running lean

[SigEpRider]

-1978 Yamaha XS650E
-Stock Mikuni BS38 carbs professionally rebuilt by OldSchoolCarbs with new shaft seals and float heights confirmed 24 mm. -Pilot jet upgraded to mikuni VM22/210 30. NOS pilot screws. Left side 2.5 turns out/right side 3.0 turns out
-New non-vacuum carb boots installed
-MikesXS non vacuum petcocks
-Tri-Spark ignition NGK 0 ohm spark plug caps
-New NGK BPR7ES spark plugs
-cam tensioner set
-Valves adjusted
-ignition timed (per Tri-Spark instructions)
-cylinder head exhaust gaskets replaced
-compressions - left side 135/right side 135

I’m at a loss. After all that work in tuning up this bike the right side cylinder is still running lean. Spark plug is white when removed.

I can only think of two things
1) the mikesXS non vacuum petcocks aren’t flowing as much fuel as needed and I’m thinking of returning to the vacuum petcocks and intake boots.
2) I need to get another set of carbs. Either another set of BS38s or some aftermarket knee. (I’d prefer to keep the bike as original as possible though)

What am I missing? Any help would be appreciated as I’m tired of chasing ghosts.

 

[5twins]

Have you changed the mufflers (freer flowing) and/or switched from the stock airbox to pods? If so, you probably need a bigger main as well (137.5 or 140). Also, you made no mention of the slide needle clip position. The middle slot (#3 from the top) is stock. If the clips have been moved (raised) to the #2 or #1 slot, that would make it run leaner.

 

[SigEpRider]

Stock airbox
Stock mufflers (exhaust gases are coming out of the drain holes on the bottom of the mufflers though. I suspect possible cracked mufflers but can’t get a clear answer as to whether or not exhaust should come out of the drain holes)
Stick headers - headers are not cracked (checked them when I put new gaskets)

I’ll have to check the needle clip position and confirm

 

[zrx1100]

have you checked the airfilter condition? check if there are any rips. check for the air leaks at the carb boots. use lighter fluid, WD40 out of a spray can and see if idle changes, or just inspect, tighten. Otherwise you may need to take your carbs apart and go over them yourself. Good luck. No doubt this is fixable

 

[JJames]

Not sure what other advice I could offer, but I wouldn't worry about the petcocks. The non- vacuum variety should flow plenty of fuel.

 

[SigEpRider]

Have you changed the mufflers (freer flowing) and/or switched from the stock airbox to pods? If so, you probably need a bigger main as well (137.5 or 140). Also, you made no mention of the slide needle clip position. The middle slot (#3 from the top) is stock. If the clips have been moved (raised) to the #2 or #1 slot, that would make it run leaner.

In checked the needles today. They are 502 with the clip in the 3rd slot.

 

[zrx1100]

In checked the needles today. They are 502 with the clip in the 3rd slot.

Keep going onto other parts. Air filters, leaks at carb boots, etc

 

[SigEpRider]

I did some quick checking and here’s what I discovered that might be causing the problem:

1. The right side carb has some chips where the slide diaphragm seats. I think this might be causing some air leak.

2. The carbs were out of sync despite me syncing them previously. As I synced them, the idle would jump up. Then I had to back out the idle screw. The screw barely opens the idle arm now. Yet the bike still idles close to 1500 rpm.

3. There is a lot of air trapped in the lines. I’m not talking about little bubbles. When I rode the bike today and got off I saw now fuel on the lines I have. Petcocks are open and no fuel is flowing. Is there a vent in the carbs that are supposed to allow air to escape the fuel lines? For the record I checked the fuel cover vent and even left the tank open. Fuel won’t flow.

 

[SigEpRider]

Here are the pics of the chips. I added some grease to see if it helped with sealing the diaphragms.

 

[zrx1100]

I don’t think this would cause your condition. If the diaphragm is in good shape it should still seal. The seal here is for the vacuum to lift the slide. You are having issues even at idle

 

[SigEpRider]

That’s what I figured. Plus when I did the slide test (covering air port and seeing if slides move at a slow pace) they passed that test. Just checking.

 

[zrx1100]

are you synchronizing the carbs with gauges?

 

[SigEpRider]

are you synchronizing the carbs with gauges?

Yes. I’m using a carb tune carb sync

 

[zrx1100]

to test the fuel flow, turn the taps off, pull the lines off, attach a piece of line to each tap to not get the fuell over the bike and open each tap to check. i am sure the flow is fine. the only issue that can happen is when there is something blocking the passages in the carburator itself. I had once carburators cleaned at a "shop" where they left the hose connecting the two caburators attached during the etch bath. the hose started to disintegrate and clogged up my carbs. the symptom would be sputtering as if the bike is running low on gas. it seems like you are very close. will the rpm go down at all below 1500? you may also check the ignition timing to make sure you are not too advanced at idle

 

[zrx1100]

Some more thoughts. Check your idle screw settings. Set each in the middle of of the numbers of turns that cause the idle to drop on the lean and on the rich side. Sync the carbs at the lowest idle that you can get to if you cannot reach 1100. Can you confirm that the air filters are in good shape and seal against the carburetors well? There should be metal springs that hold each filter against the air box. Make sure you have those