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I was able to unblock the 2 seized needles in my carbs by heating them up slightly with a heat gun and then pushing the needle pieces back through using a piece of a sewing needle glued to the upper jaw of some Channellocks. I got this idea from a post on this forum by @Greasy Fingers. You can...

OK, I'm going to have to look at this thing!

I can understand the sealed beam with reflector and bulb in one sealed unit...after all, cars had them for years. It's the adding of the ring and mounting bits that strikes me as odd, because that makes it proprietary and complicated. Or maybe proprietary is what they were going for.

Thanks @clegg...so, it's soldered in there? I thought the reflector back was glass. Need to inspect!

Thanks @BBS360. Amazing to me that they did it that way. Luckily, the current bulb is still going, though seems to be about 1 candlepower. I *might* think about the whole cut and fit an H4 thing while keeping an eye out on ebay.

I'll shorten my question. Is that the "normal" light assembly? With the bulb, lens and mounting bits all permanently joined together, how do you replace? Or is there an aftermarket reflector/mount combo that allows an H4 bulb or something?

I've looked through some of the headlight threads, but my question is more basic than "I want more light" etc. I'm not sure I understand what the hell I've got on my 79 400F--it doesn't appear to be the same as the Yamaha parts page. The headlight "lens assembly" in my case (see the pic)...

Just to close out my end of this thread by getting back to the exhaust.. just in case this hasn't been said before, @xschris knows all! I checked around the header to exhaust bell joint and there's a pretty good leak happening on the left side, as you suggested. Mostly answers that mystery. Now...

Sounds like a plan, Chris. Borescope showed plenty of carbon in there!

Ok, well, I've squirted some Seafoam in each cylinder and cranked it over, and for fun I might take a look inside with my cheap borescope. After tomorrow, I'll try to put some runtime on the engine and see how it fares.

Reporting back, and with some puzzling results. I tested both cylinders dry again, WOT, but using the starter instead of kick: #1 = 170 psi, #2 = 180 psi! Of course, I suspected the accuracy of my Mityvac gauge, so I attached it to my compressor and the Mityvac reading matches the output...

Thanks as always, xschris. I feel good about the valve clearances. I had done them a month or two ago when I got the bike, but I rechecked #1 a few days ago to make sure. I think I'll first do a new cold dry test using the starter (alas, I have a jump trigger but not here). I want to see how the...

Thanks Chris. Before I saw that I went out and did it the more work way. So, what is the compression supposed to be? Doing it cold, wide open throttle, both plugs out, I got 145 psi on the left and 160 psi on the right.

OK, prepare for some dumb questions, because I haven't done a compression test before. Plugs are out, carbs have been drained, Ignition fuse removed. But I can't use start button without the ignition fuse...will kick starting provide enough force? If not, I don't want to hurt the ignition...

I'll be doing a compression test this weekend. I didn't want to suspect that the cause could be mechanical underperformance in cyl 1--was hoping for something like "Oh, they all do that!" ;-)

Synced with a manometer, yes. Have done no compression tests yet. I hadn't thought of exhaust leaks as a possible cause. Given that it was sitting in a barn for 17 years, maybe I should make sure there isn't some mouse nesting material up in the header. :-)

That is, I have stronger exhaust coming out of the right side than the left. Is this indicative of a problem in cylinder 1? The bike, a 79 XS400F, starts easily and idles nicely. But even at idle I can feel a marked difference between the two sides. I can't answer much about how it is on the...

I had never heard of fuel med Rx. I'll give that a try.

I noticed it seemed to flow at that position but I wasn't sure it was full flow. No worries...my slightly stubby handle looks fine. I might go the continual full tank route when I get the XS on the road, but I didn't want the tank full until I knew all was well. I see you have multiple bikes...

The straight fitting looked a little crowded to me (although it looks fine on yours). As it was I had to cut the end of the handle off a bit to clear the edge of the tank when turning to reserve. The petcock screws had no washers, only lock washers. I assume the tapped holes in the tank didn't...