1979 XS1100F Carb/Diaphragm Issues.

[cajun31]

Yamaha Xs1100 K&N for sale | eBay The YA-140 or YA-1400 is what you need for the xs1100s.

[DEEBS11]

"So I guess the question is now: What would cause an otherwise stock XS110 (with cheapo MAC or similar slash cut silencers) to not want to run with the stock airbox? Could the crappy silencers be ACTUALLY restricting flow? My experience with most Asian bikes is that changes in exhaust rarely effect anything other than the main jet circuit."

You are obviously running rich because something is not right. If it's not the float levels it could be an ignition issue and/or Chinese carb parts a previous owner installed. The exhaust muffler could possibly have a mouse nest inside. Did this bike ever run correctly in the past for you?

[LAB3]

However at very light throttle apertures it still sort of felt like it was "hunting"....the sensation you get when carbs are still just a little bit out of sync. At highway speeds, 55-65mph it felt stronger but still a bit sketchy on very light throttle apertures.

That "hunting" sensation would be telling me I'm still running a tad lean, have you tried the tape to cover the pod trick yet? In this case it isn't so much about the volume of air but it's velocity, if the incoming air isn't creating enough velocity then it can't atomize the fuel properly.

Learned about that while tuning in a single carb setup on my Goldwing, was using a cheap 5" paper filter in an aftermarket air cleaner housing. Took some tape and kept choking off the incoming air a bit at a time until it ran right.

[DEEBS11]

I agree that it could be a lean condition as well from the info that we have been given. However, airbox on = run bad & airbox off = run better indicates a rich condition.

These issues are hard to diagnose without having the bike in front of us.

[Radioguylogs]

I had a problem with "too rich" on my SF when I first got it going.

Turns out the pilot jet in the K&L kit is labeled correctly, but it is actually much larger than what it is labeled. Others had the same problem, and that's how I figured it out.



Do you know if your pilot jets are genuine Mikuni?

[Appie]

" It seems to me that if the slides are not opening up fully to where they should be corresponding to throttle position and rpm"

Ummm.....Lookey here and see wut constant velocity carbs actually do when they's wurking right. (^_^)

Under Load-

No Load-

As far as a quick test to see iffin the slides/diaphrams is ok or not? (O_o)

Just lift the slides to the top of their travel/limit, at the INTaKE bell cover the long "frowny" hole (like a mouth but NOT smiling....) wit yur thumb, and release the slide. (^_^)

The slides should stay UP cuz you've blocked the hole they need to draw the air in to drop. (O_O)

Iffin they pop back down fast you gotta tear in the diaphrams or a bad seal somewheres.... (⇀‸↼‶)

(Note- Kudos fOaR you iffin you drove yur bike down the road under load/no load and managed to get eyes on wut yur carbs were a doin w/o using a camera. )

I SECOND checking the fuel levels. Checking the float distance(s) from the carb/gasket body per the repair manual aint the same thang.
(●´⌓`●)

Larrym, checking my diaphragms/slides by occluding the intake bell, should the slides stay up indefinitely? Mine lazily settle down to the bottom slowly like they couldn’t be bothered to stay up. All 4 do this in the same way.

[Appie]

Apologies banzaibob, it’s off the topic of your thread!

[DEEBS11]

I had a problem with "too rich" on my SF when I first got it going.

Turns out the pilot jet in the K&L kit is labeled correctly, but it is actually much larger than what it is labeled. Others had the same problem, and that's how I figured it out.



Do you know if your pilot jets are genuine Mikuni?

I have also run into stock jets that were drilled. Total hack job for the next mechanic.

[cajun31]

Larrym, checking my diaphragms/slides by occluding the intake bell, should the slides stay up indefinitely? Mine lazily settle down to the bottom slowly like they couldn’t be bothered to stay up. All 4 do this in the same way.

They should stay up if they don't and drop on their own you have a leak somewhere on the atmospheric side of things. That is from the diaphragm up. Either you have holes in your diaphragms or they are not sealing properly against the top cover.

[Appie]

They should stay up if they don't and drop on their own you have a leak somewhere on the atmospheric side of things. That is from the diaphragm up. Either you have holes in your diaphragms or they are not sealing properly against the top cover.

Much obliged Cajun! ( and others) Back to my misbehaving carbs then 🤨

[Larrym]

Much obliged Cajun! ( and others) Back to my misbehaving carbs then 🤨

Cajun and I concure. Slides should STAY up as long as yur certain yur thumb ain't letting air get past and into the frowny hole. ๑(◕‿◕)๑

"Mine lazily settle down to the bottom slowly like they couldn’t be bothered to stay up."

Alrighty then... we knows wut that M E A N S but wut Next??? (O_o)

Here's the answer-

Like as shown in the vidya, I used "ThreeBond 1215" a "Liquid Gasket-Gray Solventless Silicone Sag Type" on my own diaphrams with a Q-Tip as the high tech applicator. (^_^)



No worries here on my end as we hijack the OP's thread... I mean in his approach he's eliminated the fuel levels as the problem and is way off in the woods chasing wild geeses everywhere and anywhere on his bike so's we can safely say this "thread" will likely go W a a a a y long wit lot's mOaR pages and pages. Yur minor intrusion will be buried and long forgotten in a few months. Plus by that time I'll have prob'ly reached my 100 posts per year quota and therefOaRs no longer be available till 2026. (O_O)

JUST-IN-CASE? (O_o)

We'll add fOaR his benefit that iffin his #3 carb slide ain't playing well wit' the others in a "One of these things is not like the others... one of these things just doesn't belong" kinda way? (O_o)

In the Diaphram vid Steptoe shows that the slides/diaphrams need to be installed in the proper direction and HOW to tell which direction is correct. (^_^)

Might be wuth the effort of the OP to check-n-see iffin #3 slide got put in 180 degrees backwurds by one of the many owneres befoAr him. (_Oo)

[Larrym]

Might be wuth the effort of the OP to check-n-see iffin #3 slide got put in 180 degrees backwurds by one of the many owneres befoAr him. (_Oo)

I wouldn't rule out #3 carb slide bein' the only one installed correctly and the OTHER ones put in 180 degrees backwurdz. (╯°□°)

I mean the history of who done wut and when/why on A N Y of these bikes before we got'em is a big question mork.... ( ◎_◎)

[Appie]

Cajun and I concure. Slides should STAY up as long as yur certain yur thumb ain't letting air get past and into the frowny hole. ๑(◕‿◕)๑

"Mine lazily settle down to the bottom slowly like they couldn’t be bothered to stay up."

Alrighty then... we knows wut that M E A N S but wut Next??? (O_o)

Here's the answer-

Like as shown in the vidya, I used "ThreeBond 1215" a "Liquid Gasket-Gray Solventless Silicone Sag Type" on my own diaphrams with a Q-Tip as the high tech applicator. (^_^)



No worries here on my end as we hijack the OP's thread... I mean in his approach he's eliminated the fuel levels as the problem and is way off in the woods chasing wild geeses everywhere and anywhere on his bike so's we can safely say this "thread" will likely go W a a a a y long wit lot's mOaR pages and pages. Yur minor intrusion will be buried and long forgotten in a few months. Plus by that time I'll have prob'ly reached my 100 posts per year quota and therefOaRs no longer be available till 2026. (O_O)

JUST-IN-CASE? (O_o)

We'll add fOaR his benefit that iffin his #3 carb slide ain't playing well wit' the others in a "One of these things is not like the others... one of these things just doesn't belong" kinda way? (O_o)

In the Diaphram vid Steptoe shows that the slides/diaphrams need to be installed in the proper direction and HOW to tell which direction is correct. (^_^)

Might be wuth the effort of the OP to check-n-see iffin #3 slide got put in 180 degrees backwurds by one of the many owneres befoAr him. (_Oo)

Thanks Larrym! Weekend coming up so I’ll watch that for sure unless the wheels come off at work. We don’t have 3Bond here as far as I know but what I do have is (hesitant to put it on this forum in case you block me) is…..Hondabond. There I said it! Worried my Yamaha will have an allergic type reaction if I put it on though.

[DiverRay]

Hondabond is sometimes easier to get, and a lot of us have used it. My bikes don't mind it, as it does what is needed.

[DEEBS11]

Only need a very thin film on a clean and dry surface. Let it cure before installing.