Accidental XS1100 Horse Conversion

[Lars Helly]

My 1979 XS1100 special gallops like an old horse. I have no idea why, I’ve tried everything, and nothing changes. Mid throttle (or really any level of throttle) surges and lags and ridiculously jolts forward when I try to accelerate. It clunks and bounces, and feels like constantly about to stall. It also won’t idle unless I’m on the throttle. It somehow seems to be running both rich and lean at the same time.

It all started when I took my project out for the first time and it was idling high. Messed with the mixture screw, nothing happened. Figured it was lean so I ordered bigger jets. 45 and 147.5. Now before you make comments on the jets (which I’d still highly appreciate feedback on), the problem started before I even installed them. While waiting on them to arrive I took the bike out again and it started doing this weird galloping, which was a huge change from the loud high revving lean it was doing the few days prior. When the new jets arrived, I installed them, and nothing changed whatsoever, which was highly concerning seeing as they’re a few sizes over stock. The same exact unridable surging and jolting and weakness. After that I realized something was seriously wrong or broken. I checked my slide diaphragms, slightly cracked, so I replaced them. No change. Blew compressed air through all passages. No change. Break cleaner test for vacuum leak. No change. All 4 spark plugs are sparking, but fouling quickly. I adjusted the needle, no change. One of the T connectors is leaking fuel, so I ordered another and am waiting on it, but it doesn’t seem like that would cause such extreme symptoms.

It feels and sounds like I’m riding a V-twin. Not even actually, more like a V-step siblings, because none of the cylinders seem to be related in any way besides being stuck in the same engine block. I’m extra confused because it started happening without me changing anything. I feel like I’m losing my mind and i just cannot figure out what’s going on. Any advice is welcome and thanks for reading my rant.

[cajun31]

Questions rather than answers at this point. What is your level of expertise/experience with working on motorcycles? Where are you located? Other than the things you mentioned is the bike still stock or not? Meaning does it have the original airbox and original cartbs etc.? You stated you changed some carb parts. Where did you source the parts and are they genuine Mikuni? If not can be a source of your problems. No where did you mention anything about synchronizing the carbs. On these bikes that has to be done. Not doing it can cause some of the symptoms you are describing. Normally I would advise to never change more than one thing at a time but seems you are past that point. Do you still have the original parts that you replaced? What all did you do to clean the carbs? You mentioned you replaced the diaphragms. Where did you source those and further what brand are they? If you are running the original carbs the mixture screw tips are prone to break off at the tip and get stuck in the carb blocking your pilot circuit. You can check those by removing them and inspecting them. To do that you will need to slowly turn them in until very lightly seated and write down how many turns for each screw then remove them to inspect. That will give you a good starting point when you reinstall them. Check out the maintenance section on carburetors and there are a lot of good tech tips to guide you along. Depending on your answers to my questions others will chime in.

[DEEBS11]

While this certainly could be carb issues, the abruptness could be caused by broken pick up coil/advance wires.

https://xs11.club/forum/repairs/battery-electrical-aa/631-pick-up-coil-wire-repair

[Radioguylogs]

I was thinking same as Deebs.

If you can get the bike to idle, you can pull on those wires while it is running to see if it affects the status.

[Lars Helly]

This is my first bike, I’m in Michigan, and it’s about as far from stock as it could be, except the engine and carbs. I’ll attach some pictures. Jets are genuine, diaphragms are Chinese off ebay, but feel relatively high quality. The other parts that I changed were just from a mid-quality carb kit but I’ve ridden the bike on those for a while without any issues. I used an ultra sonic cleaner and an air compressor to clean the carbs. I set float hight correctly and everything was working fairly well. The pipes are stock 4 into 2 but with no muffler (not because I’m a hoodlum but because I can’t afford the mufflers). I have 4into1 brand foam pod filters (not yet in the pictures). I got the bigger jets because of the open pipes and pods. I will check the mixture screw tips. I will also check the pickup coil wires. I am definitely a beginner making beginner mistakes, so I appreciate any feedback and advice.

[cajun31]

Well to begin with I am not disagreeing that you need to check those wires as Deebs pointed out. Once you verify that then if the issue ends up being the carbs then you would need to use this tip as a guide on your jet sizing. Jetting Recommendations - XS11.club Forums. We always ask this question when it comes to the pod filters. Have you verified that the lip where they mount is not blocking any of the inlets? Did the diaphragms have for lack of a better word ears on them so that they align properly? What I mean is along the edge of the diaphragm on the originals they have a slight bulge on them that match the carbs to ensure alignment. When you installed them were you careful to make sure you maintained that alignment? It is important. At least you sound eager to dive in which is good. Do you own a set of synch gauges? If not would be a good investment. I recommend Morgan Carbtune. Morgan Carbtune - carburetor synchronizer for balancing motorcycle carbs. You may also be able to find them on Ebay. There is also a tech tip that walks you through bench synching them that will get you very close but the gauges will help you get them spot on.

[jetmechmarty]

Those pod filters are suspect. There’s likely a lip in there blocking the ports on the back of the carburetors. These carburetors aren’t so friendly with pods in the first place. The wrong pods are impossible.
These XS Performance pods from MikesXS work as well as any. Just order the proper size. Uni pods also work. Order by intake size. MikesXS has them too. Get the longer ones if they’ll fit.

[cajun31]

Looked at those pictures you posted and tried to zoom in to see the carbs but the pictures are not close enough to see anything. That bike has been modified from the original to say the least. That always presents a host of other issues depending on how everything was handled. Where is the TCI mounted and is all the wiring solid? Have you checked all the connections and grounds? How is the carb venting being routed/handled? If you could take closer pictures of the carbs that will help us determine issues for you.

[Lars Helly]

Just took the mixture screws out and I think I found the problem... The top set is what I was trying to use. All missing tips, one completely bent. The bottom set is what I took out of the bike when I bought it. I'm looking at a new set but I can't find any that match what I have here. Everything on the bike when I bought it was either wrong, missing, or broken, so I am suspicious that they were never the right part and that I replaced something that wasn't even supposed to be there in the first place. Now I'm just wondering what to buy and if anyone has any idea on how to fix this. Carb picture for model reference.

[cajun31]

If you look up in the carbs close the butterflys you will see a small hole. Take a flashlight or whatever bright light you have and shine it down the pilot screw tunnel and look to see if you see the light from the holes below. You just want to make sure there aren't any broken tips still in those holes blocking air flow. If there are tips in there a tech tip is available to remove them without destroying them. The screws themselves never live in the carbs fully seated so the screws you have may still be good. Did you also notice a small spring, washer and rubber o ring in each one?

[Lars Helly]

I have the springs, didn't notice any washers or o rings, but can take a closer look. The newer set I have I doubt can't be reused because the one is so bent. The older set maybe but I'd have to do some crazy tuning since theyre broken off so high. Would I be better off replacing them? All the ones I see online are a much different style and I'm just confused on what to buy. I will also check for shards left in the holes. Thanks.

[bikerphil]

The older type carbs as pictured don't use the washer and o ring in the tunnel as the later carbs do.

[cajun31]

The older type carbs as pictured don't use the washer and o ring in the tunnel as the later carbs do.

thanks Phil. I have never owned those.

[cajun31]

Sorry for the confusion Lars. These should be what you are looking for. Yamaha XS1100-E 2H7 Carb Carburetor Mixture Screws 1978 1979 #72 ACP21 | eBay

[Lars Helly]

Sounds good. Those are the ones I was looking at so I appreciate the confirmation. Just ordered them and will hopefully get the bike back out on the road in the next few days after a much needed tune. Thanks a ton for all the help and advice!