Back in the fold: '79 XS1100F

[DEEBS11]

I have filled rim lock holes with JB Weld steel putty and never had an issue.

[cajun31]

My first interesting find: mismatched 10k resistor caps on the outside two cylinders, 5k resistors on the inner two cylinders, coupled to BPR7ES plugs. I am planning on getting a matched set of non-resistor caps and BPR6ES plugs (finding the BP6ES has gotten to be a real pain, I assume no longer produced).

Yambits : for Yamaha bikes

[gtem]

Finding good quality non resistor caps of that long reach style to retain the stock plug wires turned out to be trickier than suspected. The "path of least resistance" ended up being finding some BP6ES non resistor plugs via partzilla (Kawasaki and Honda still have them listed as factory part numbers, the Honda ones are $2.96 a piece), as well as two NGK 5k resistor long reach (OEM style) caps, also a Kawasaki factory park number assigned to an NGK part on partzilla ($4 a piece or so). So for future reference, at least for now, that looks to be a good source of these obsolete parts (NGK discontinued production of non-resistor plugs, and all of their phenolic plug caps).

[LAB3]

As mentioned, you can easily convert your resistor caps to non resistor, a Google search should turn that up easy enough.

[gtem]

Latest updates:

Got my BP6ES plugs and NGK 5k caps installed. New Shinko 230 Tourmaster tires mounted (kept the tube in the original front rim, converted the rear to tubeless by sealing the rim lock holes with 1/4 NPT plugs).

A test ride in yesterday's cool afternoon weather confirmed that she's still breaking up at mid range (around 5k) at high throttle/load at higher speed. Down low she's smooth and strong, absolutely dead-on. I will be taking a closer look at the coil pickup wires, that's my #1 suspect. But I have experienced a very similar cutting up on a different bike when I had an airbox leak that leaned it way out at higher speeds but the bike ran perfect down low and lower speeds. When I took the old BPR7ES plugs out it looked like cyl 1/2 were a bit darker, #1 was a bit damp and smelled a bit gassy (leaking vacuum petcock)?. #3/4 were a really nice very light grey. Also, my tach is definitely reading a bit low. 3k rpm at 60mph in 5th, that's off by a fair bit. At low RPM it seems fine 1-2k rpm. That's a new one for me. I haven't pulled plugs yet after yesterday's ride.

[DiverRay]

If your carbs are off, for whatever reason, you will not get a smooth climb up the RPM mountain. I would verify the plugs, and try to find and fix the problems. The petcocks only let fuel flow when the engine is running. The carbs have the needle and seat to cut off the fuel when the float bowl is full. If you do not have Mikuni parts in the carbs, you WILL have problems. I've spent many hours learning that lesson!

[gtem]

Hi Ray, oh I am all too familiar with the need to use high quality OE or mikuni parts in these carbs. This bike as a whole is thankully very stock and unmolested aside from the exhaust that the original owner installed at some point. I haven't been inside the carbs yet to see what all is going on in there. I did pull the #1 plug at lunch today and it looked good and clean, perhaps on the lean side of things, but none of the wetness I had seen before (the bike did a lot of sitting prior to me getting it, float valves and vac petcock seals may just needed to be "exercised" a bit.

I'm going to try and eliminate any possible ignition culprits and things like leaking airboxes/boots before I go into the carbs. The good news is I have a full set of '78E carbs that I had rebuilt with nice new OEM parts before realizing the idle mixture screw holes were damaged on the carb bodies so I have an excellent source of high quality replacement jets, float valves/needles, etc if needed.

[jkorn]

I know it’s a PITA, but take the time. Pull the carbs. Completely dismantle them, keeping the parts and jets separate and knowing into which carb they go. Get carb cleaner and spray the heck out the million little passages. Check the float levels. Synch the carbs. Adjust the idle mixture.

Then start looking at spark.

[gtem]

Jeff, from my very recent experience, I went down the rabbit hole of carbs and it turned out most of my issue was in an incorrect plug/wire combo. So that is why I'm going over the basics there first. I'm no stranger to Mikuni BS series carbs at this point.

[gtem]

Well, I've got the bike running *GREAT*

I pulled the carbs off this weekend to compare them side by side with my spare set of '78 carbs to see if there was a difference in how well the slides hold vacuum, etc. Nothing of note. I then popped the bowls off, and was greeted by the sight of #150 main jets! I swapped the 137.5s off my spare carbs, checked float heights and polished float valve needle seats, quick leakdown testing, then reinstalled back on the bike. Oh, I also swapped the K&N filter that was in the airbox for an emgo dry element style. Eureka! She runs spectacular! I ended up doing an 80 mile ride yesterday afternoon after a quick rotella oil change. No idea why the PO put such oversized main jets on a stock bike with a baffled 4-1 exhaust.