'78 XS1100E, '80 carbs low rpm funk

[gtem]

Is it possible that the buggered threads have prevented the main/needle jet from resting in the proper spatial relationship with the needle?

No the main jet snugs up and pulls the needle jet into the correct position thankfully. It's only #2 where the threads are a bit chowdered up and not that bad, I put a bit of PTFE tape around the main jet threads yesterday just as a bit of a precaution but I doubt it was actually a problem.

The '80 carbs sat overnight with gas in the lines and I have barely seen the level drop (beyond an expected amount of evaporation). I wonder if a better simulation of the amount of fuel pressure in those lines would be to suspend a larger volume of fuel over the carbs for some more "head" to test how well the float needles are sealing before I can fully be satisfied and move on to trying out my experiment with increasing pilot air jet size (or stepping down to #40 pilot jets even). I still think it's rather odd that my '78 with stock airbox/filter and a (presumably freer flowing?) 4-1 exhaust would need LEANER than stock jets?

[DEEBS11]

gtem, another thing to check is jet needle position. There is a plastic washer holding the needle that has a protrusion on it. It must fit into a hole that is provided or it will sit too high and cause a rich condition off idle. Make sure the spring is also in the correct position.

[DEEBS11]

BTW the last picture does not show the position correctly. Its just to show you what the parts look like (somewhat, its a 78 part). The plastic piece fits down in the slide first. Steel washer on top of plastic. Spring on top of steel washer. Yours has screws holding down everything. Some have a circlip (early). Just make sure that needle is as low in the hole as it's supposed to go. That will prevent a rich condition.

[gtem]

Thank you very much Steve, I will definitely double check this! I definitely messed with this a bit when I first got the bike, I was convinced that fat plastic "donut" washer should go on top of the circlip/washer not under it, and then looked at parts diagrams and put it back to the way it was. I will double check this. A mistake here would 100% make sense with where I'm experiencing a rich condition.

[gtem]

Ok here are some close-ups of my '80 needle setup.

[gtem]

Well, I've honed in on a *potential* problem: I'm missing the washers (#30 in diagram). Investigating the way things are sized and stacked up, it's concievable that without the washer in place to hold the spring securely against the circlip, the spring could instead by pressing along the outer edges of the plastic "donut" and the needle could conceivably push up relative to the plastic donut (and the slide), causing the low RPM rich condition!

[DEEBS11]

Is that the protrusion facing up towards the circlip circled in yellow in this picture?

[DEEBS11]

The protrusion should face down and it inserts into a small hole in the slide. Spring on top. This orientation would keep the needle as low as possible curing a rich condition just off idle.

[DEEBS11]

Another issue I see is the condition of the needle. Looks rough. Rich. Emulsion tube must be worn as well.

[gtem]

Yes I noticed the wear there as well, definitely less than ideal, not sure how tricky/expensive it might be to source a new set of correct emulsion tubes/needles (actually I wouldn't mind finding the more "linear" Venturer/Standard setup). What you have circled in red is actually just looking at an angle where the circlip opening is. My plastic "donuts" don't seem to have these protrusions at all.

I modified some washers to put on top of the circlips and reassembled, just waiting on a new float valve for carb #1 (some leak and pressure testing showed it to leak a bit). Will update the thread once I have carbs back on the bike and do a test ride!

[LAB3]

Great job with the pictures and the explanations guys, good stuff!

[gtem]

Great job with the pictures and the explanations guys, good stuff!

No kidding this forum and community is nothing short of incredible! Thank you so much to everyone who's chimed in with ideas and advice!

[skids]

Note that the airboxes are different for 78's and 80's. The nipples are plugged for the 80's because the inlet bells for that year have breather holes. Put screws in those or plugs if they are open. 78's must breathe and the hoses from the upper Tees can go to a crankcase filter or something but they can't be blocked off, if they are blocked, the carbs will overflow. Leaking fuel out of the air jet is pretty crazy (is that what you said?) Sticking float pivots, broken orings at the fuel valve seat, sticking float valve pivot needle, holes in float, wrong float heights?

[gtem]

Note that the airboxes are different for 78's and 80's. The nipples are plugged for the 80's because the inlet bells for that year have breather holes. Put screws in those or plugs if they are open. 78's must breathe and the hoses from the upper Tees can go to a crankcase filter or something but they can't be blocked off, if they are blocked, the carbs will overflow. Leaking fuel out of the air jet is pretty crazy (is that what you said?) Sticking float pivots, broken orings at the fuel valve seat, sticking float valve pivot needle, holes in float, wrong float heights?

Yep I have the holes in the '78 airbox capped off. It's not a flowing leak I can just see a bit of wetness/fuel forming in the hole of the smaller pressed-in main air jet (I misspoke saying it was the larger pilot air jet) after the carbs sit with fuel in the bowls and "head pressure" from additional fuel in extra fuel line suspended above the carbs. I've tested the float valves extensively for leaks around the seat o-rings etc, seems like just a worn seat/needle interface so I ordered up an OEM replacement valve and seat for about $25. Carbs 2/3/4 seem fine. Likewise on the '78 carbs the float valves needed some attention, I had leaks from 3 of the 4 carbs in this same way (minor wetness at the main air jet), in that case 2 of the 4 just needed a tightening of the seats (screw in type with that orange gasket), and one was leaking from the valve/seat interface so I ponied up for a new OEM replacement there as well.

Plan is to see if the jet needle stack/washer issue and new float valve sorts out the '80 carbs and I'll probably just keep running them if that all works, and keep the '78 set around as a spare (for another '78 1100E I'm hopefully picking up).

[gtem]

I just wanted to update this in case anyone ends up stumbling across this thread in the future with similar symptoms. My low-rpm stumble has been cured!!!

I ended up setting up all of the needles correctly with shims on top of the circlips to keep that spring from pushing directly on the plastic donut, I also did some leak testing of my float valves by applying (light) air pressure to the fuel rail and monitoring for any leakage by spraying some WD40 on the valves and watching for any bubbling etc. The float valve on Carb #1 was leaking slightly. Bought a new OEM float valve assembly on Ebay. Buttoned everything up last night and went for a ride: hallelujah! Pulls nice and evenly right from idle, nice smooth roll-ons from 3000rpm where I used to have issues.

Thanks again to everyone for the help, DEEBS11 in particular, you asking about the needle setup is ultimately what lead me to "crack the code" so to speak.