gmkieran Posted July 2, 2010 Share Posted July 2, 2010 Greetings, all!!! Been lurking around for a few weeks and have found a bunch of helpful information, already, so thanks for that!!! I'm in the process of reviving a hybrid ('80 XS400SG motor in '79 XS400F2 frame) into a cafe-styled streeter. The bike sat in *my* garage for 15 years and in someone else's for an unknown period before that. It ran decently before I put it away... So, questions - I want to put a '78 XS750 triple tank on it, but the tank's not local, so I can't measure it first. Anyone know how well the 750 tank matches up to the stock 400? It *looks* similar enough to convert easily if there's a small difference. Main concern is that the petcock being so far back on the 750 tank will put it in the path of a frame member on the 400. This is the tank, the petcock is all the way to the rear on the left side: http://i796.photobucket.com/albums/yy248/Mrfixit-Surplus-Cycles/6-15007.jpg"]pic of the 750 tank Second question - the bloody thing won't run! I've disassembled the carbs down to their component parts, verified that fluid and/or air flows unimpeded through EVERY passage, even pulled the emulsion tubes and cleared them. I replaced the floats and needle valves (and their seats) as well as all related rubber and adjusted the float-height to manual spec. I can get it to fire, by judicious application of starter fluid, and run for about 20 seconds with the throttle 1/8-1/4 open on no choke. At the end of that run it makes a loud, unhappy noise (more than just the pop you get from starter fluid running out) and dies. Oh, and I tried searching the forums to see if anyone had posted anything about the tank conversion in the past, but the search engine doesn't like me. Thanks in advance! Grafton Link to comment Share on other sites More sharing options...
Moderator drewpy Posted July 2, 2010 Moderator Share Posted July 2, 2010 Grafton there is a xs400 with an xs750 tank on youtube wurth was his name http://www.youtube.com/watch?v=Owwd19VDbpg #2 have you tried the petcock on prime position and fuel is flowing? Link to comment Share on other sites More sharing options...
gmkieran Posted July 6, 2010 Author Share Posted July 6, 2010 Thanks for the video, Drewpy! I believe that's the very tank I'm looking it. Have to dig a little further and see if he says how he mounted it. In fact, the only way the bike would run was on prime. However, since I originally posted, I have gotten the bike running at least partially. I replaced the inline fuel filter, cleaned the petcock assembly thoroughly and ran the idle screw up to max. Once those things were done, it started first kick every time (as long as I had no choke on - won't run on choke). Rode the bike around for about 10 minutes when it started racing at idle - dropped the idle screw back a couple turns and it stopped racing, but then wouldn't start again the next day. I believe I have determined that only 1 carb has a functioning idle circuit at the moment, so I'm going to have to go back into the other one and figure out what's blocked. Apparently I will need to replace the tank sooner than I'd thought, since neither the petcock nor inline filters seem to be stopping enough stuff to keep the carb passages clear. Link to comment Share on other sites More sharing options...
Moderator drewpy Posted July 6, 2010 Moderator Share Posted July 6, 2010 front mountings will be the same, the rear with need a little fabbing methinks Link to comment Share on other sites More sharing options...
bznchris Posted July 7, 2010 Share Posted July 7, 2010 I have a 750/850 tank on mine. It needed some easy modification to the tank mounting point, and also a little to the frame, because of the petcock. There are two different 750 tank designs though, and mine is the Special version, if I remember. It's the same as the 850 or European version. Link to comment Share on other sites More sharing options...
gmkieran Posted July 7, 2010 Author Share Posted July 7, 2010 front mountings will be the same, the rear with need a little fabbing methinks actually, the front mountings are reversed (the tank I picked up is the boxter style with the squared shape and cut-outs for the knees). The tank has cups to catch the bushings it expects to be on the bike frame (where the 400 tank has the bushings on it that slide into cups on the frame). So, I will end up with cups on both sides and need to fabricate a means of holding the two together. The rear attachment is a single point, just like the 400 tank, so I don't think it will require any mod at all. I was concerned about the possibility of needing to modify the petcock/frame interaction, but this was too good a deal to pass up, so I guess I'll figure it out. This is the tank: Link to comment Share on other sites More sharing options...
Moderator drewpy Posted July 7, 2010 Moderator Share Posted July 7, 2010 I'd leave the tank alone and mod the frame, use the old tank mounts and grind off the old frame mounts . weld on the new mounts to the frame after careful measuring Link to comment Share on other sites More sharing options...
gmkieran Posted July 8, 2010 Author Share Posted July 8, 2010 I'd leave the tank alone and mod the frame, use the old tank mounts and grind off the old frame mounts . weld on the new mounts to the frame after careful measuring Hoping to find a solution that doesn't involve welding, as I'd have to pay someone to do it. since they're not load-bearing, it's mostly a matter of finding a solution that will keep the tank from bouncing around. I'm hoping (but not counting on) there'll be enough clearance between the 2 sets of receivers that I can just fill the space with a couple pads. Won't know 'til the tank gets here, tho. Link to comment Share on other sites More sharing options...
gmkieran Posted July 19, 2010 Author Share Posted July 19, 2010 Finally got the new tank! It's better even than I'd hoped (at least in terms of looks). think I've figured out how I'm going to do the mounts - no welding, but it will involve grinding the old catchers off the frame and some drilling. Has anyone else mounted a '78 XS750E tank on a '79 XS400_2F frame? I'm running into clearance issues with getting the rear of the tank to fit down onto the frame and wondering if any one has suggestions. Although it occurs to me I may want the tank to set more level than the old teardrop did, so suggestions on how to mount the tank with the back end raised would also be welcome! getting petcocks and a cap to go with it - should have those soon. Something else that's beginning to bug me - the electric start won't work. I've pulled the cover and replaced the chain. both sprockets appear to be in good condition (teeth aren't worn or broken) and I've verified that the clutch engages correctly, but the chain just spins past the teeth on the main sprocket and doesn't turn the engine over. Kick starts fine (when the carbs aren't clogged with rust from the old tank), so I know there's no issue there. I've been trying to track down a starter-side sprocket with more than the stock 13 teeth, but haven't had any luck. Anyone else ever encountered this? Or have a source for 15-17 tooth starter sprockets that will fit the XS400? Link to comment Share on other sites More sharing options...
johnsnownw Posted July 19, 2010 Share Posted July 19, 2010 Finally got the new tank! It's better even than I'd hoped (at least in terms of looks). think I've figured out how I'm going to do the mounts - no welding, but it will involve grinding the old catchers off the frame and some drilling. Has anyone else mounted a '78 XS750E tank on a '79 XS400_2F frame? I'm running into clearance issues with getting the rear of the tank to fit down onto the frame and wondering if any one has suggestions. Although it occurs to me I may want the tank to set more level than the old teardrop did, so suggestions on how to mount the tank with the back end raised would also be welcome! getting petcocks and a cap to go with it - should have those soon. Something else that's beginning to bug me - the electric start won't work. I've pulled the cover and replaced the chain. both sprockets appear to be in good condition (teeth aren't worn or broken) and I've verified that the clutch engages correctly, but the chain just spins past the teeth on the main sprocket and doesn't turn the engine over. Kick starts fine (when the carbs aren't clogged with rust from the old tank), so I know there's no issue there. I've been trying to track down a starter-side sprocket with more than the stock 13 teeth, but haven't had any luck. Anyone else ever encountered this? Or have a source for 15-17 tooth starter sprockets that will fit the XS400? How about this one? http://www.bikebandit.com/jt-steel-front-motorcycle-sprocket?m=8261&t=1&td=1 Link to comment Share on other sites More sharing options...
gmkieran Posted July 20, 2010 Author Share Posted July 20, 2010 How about this one? http://www.bikebandit.com/jt-steel-front-motorcycle-sprocket?m=8261&t=1&td=1 Unfortunately, I'm looking for the starter sprocket, not the front drive sprocket. Sorry if I wasn't clear on that. Thanks, though! Link to comment Share on other sites More sharing options...
johnsnownw Posted July 20, 2010 Share Posted July 20, 2010 Unfortunately, I'm looking for the starter sprocket, not the front drive sprocket. Sorry if I wasn't clear on that. Thanks, though! Sorry about that. Here you go: http://compare.ebay.com/like/200487196029?ltyp=AllFixedPriceItemTypes&rvr_id=&crlp=1_263602_263632&UA=%3F*F%3F&GUID=9e1f996c1280a0e669345774fffce626&itemid=200487196029&ff4=263602_263632 Edit: Never mind, only has 13 teeth. Link to comment Share on other sites More sharing options...
Moderator drewpy Posted July 20, 2010 Moderator Share Posted July 20, 2010 not sure why you need to change the spec of the starter sprocket! maybe the chain has worn past its use by date or the guide is worn? Link to comment Share on other sites More sharing options...
gmkieran Posted July 27, 2010 Author Share Posted July 27, 2010 not sure why you need to change the spec of the starter sprocket! maybe the chain has worn past its use by date or the guide is worn? Chain's brand new - I replaced the old one thinking that might be the problem, but the new chain (which looked and measured exactly the same as the old) still slips past the main sprocket teeth without grabbing. Initially it had more tension than the old chain (1/2" of play v 1.25"), but after the first run at starting the bike the new chain was back to 1.25" of play and there's no bloody tensioner in '80 400. Neither sprocket nor the chain guide appear significantly worn, so I was hoping the added diameter of a couple extra teeth would tighten things up enough to get the chain to grab. Link to comment Share on other sites More sharing options...
gmkieran Posted July 27, 2010 Author Share Posted July 27, 2010 I have a 750/850 tank on mine. It needed some easy modification to the tank mounting point, and also a little to the frame, because of the petcock. There are two different 750 tank designs though, and mine is the Special version, if I remember. It's the same as the 850 or European version. bznchris, what did you do seat-wise when you changed over to the 750/850 tank? I'm trying for a cafe look and I'm almost done with the frame mods to get the tank in place, but it's either going to end up sitting lower than I want it to or interfering significantly with the stock seat. Trying to figure out a) what I can do with the stock seat so I can ride until I can track down a cafe-style seat that will properly fit with the tank wherever it finally ends up. Thanks! Link to comment Share on other sites More sharing options...
johnsnownw Posted July 27, 2010 Share Posted July 27, 2010 bznchris, what did you do seat-wise when you changed over to the 750/850 tank? I'm trying for a cafe look and I'm almost done with the frame mods to get the tank in place, but it's either going to end up sitting lower than I want it to or interfering significantly with the stock seat. Trying to figure out a) what I can do with the stock seat so I can ride until I can track down a cafe-style seat that will properly fit with the tank wherever it finally ends up. Thanks! If you haven't looked, MikeXS has a cafe seat for the 650, not sure how much of a difference there is between the 650 and the 750 tank. Check it out: http://www.mikesxs.net/products-17.html#products Link to comment Share on other sites More sharing options...
Moderator drewpy Posted July 27, 2010 Moderator Share Posted July 27, 2010 Chain's brand new - I replaced the old one thinking that might be the problem, but the new chain (which looked and measured exactly the same as the old) still slips past the main sprocket teeth without grabbing. Initially it had more tension than the old chain (1/2" of play v 1.25"), but after the first run at starting the bike the new chain was back to 1.25" of play and there's no bloody tensioner in '80 400. Neither sprocket nor the chain guide appear significantly worn, so I was hoping the added diameter of a couple extra teeth would tighten things up enough to get the chain to grab. its there in the fiche, no 3 Link to comment Share on other sites More sharing options...
gmkieran Posted July 27, 2010 Author Share Posted July 27, 2010 The parts finder lists that as a chain guide rather than a tensioner. I was hoping, when I first got into the case, that it was actually a tensioner, but there's no adjustment to it. It's just a piece of hardened rubber that lays along a section of the case and keeps the chain from making a racket. I was referring to the idler gear like the 850 has (part 1 in the image) when I said tensioner (sorry if I used the wrong term!). Link to comment Share on other sites More sharing options...
Moderator drewpy Posted July 27, 2010 Moderator Share Posted July 27, 2010 the guide/tensioner is unworn? i had to renew mine and it took slack out of the starter chain. I can't belive that your chain can jump after renewing the chain and an unworn guide/tensioner. its a very simple system! Link to comment Share on other sites More sharing options...
gmkieran Posted July 29, 2010 Author Share Posted July 29, 2010 the guide/tensioner is unworn? i had to renew mine and it took slack out of the starter chain. I can't belive that your chain can jump after renewing the chain and an unworn guide/tensioner. its a very simple system! I can't, either, but there appears to be no significant wear on the guide. If I can track one down, I'll replace it, just to see what that does (can't hurt and it's cheaper and easier than anything else I can do). Link to comment Share on other sites More sharing options...
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