I'm about to throw the XS in the lake...

Faniman57

XS400 Enthusiast
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I've been lurking around the forum since I got my bike a few weeks ago and have learned so much, so thank you for sharing your know how on this machine.

And here we are today. When i bought the bike, it ran good but topped out at 65 and would flood easy. The cylinders would fill with fuel and I couldn't get it to start. After countless hours searching and learning on this forum,I bought new plugs, needles and seats, and bowl gaskets.I also set my float height to the manual spec, 32mm. My floats don't have holes in them and my carbs were cleaned in an ultrasonic cleaner. The bike is a 1978 XS400 special with 6k original miles on it. 170 pilot, 132.5 main, screws turned out 3.5 times. Stock air boxes, brand new air cleaners from Mikesxs, looks to be original exhaust. Can't find any air leaks, sprayed starting fluid around the boots and plastic intake H pipe. IM STILL HAVING FUEL IN THE CRANKCASE and flooding out, so much that it runs great for a bit then it gets hung up at around 3000 rpms and I have to switch the key off. Try to start it again and the plugs are soaked. I've changed the oil 3 times now, I'm tired of wasting money and there's a nice lake nearby that this can spend the rest of its life at the bottom of. Help. Please.
 
Hello, don't throw the Bike into the Lake, simply leave it in Front of my Garage ;)
Seems you still habe a carb Problem. Your carbs are supposed to Stop the fuel from pouring into the Motor. Check float valve and the petcock, These are the Problem.


Viele Grüße aus Deutschland, Uli
 
You did the right thing by asking before you dumped the bike! Do as Drewpy says and that will help. The fact that your engine is filling with gas is a sure sign that it is a significant leak or something way out of spec (like the float bowls as Drewpy pointed out) so see what happens when you fix the floats and see whats up!

And if it doesn't work out, sell the thing and get some money (and keep an XS alive!) instead of feeding the fish's motorcycle addiction
 
I pulled the line coming off the petcock to the left carb and the petcock doesn't leak. I'll do that 26mm float height and put it all back together. If that takes care of my crankcase filling with fuel, I'm throwing the manual into the lake instead.
 
After the floats are set sync the carbs with a manometer. Have you set the valves, points and timing yet? If not do that also:wink2: Your pilot jet should be 42.5. The 170 jets are air jets. What mufflers and air filters are you using? Post some pics of the bike so we can see what you have:)
 
Not sure how to post pictures, tapatalk tells me I can't and I don't have a computer to do it on.

Xschris- stock air boxes, new OEM style air cleaners from Mikesxs. I have not adjusted valves or set points and timing. I just got the carbs back together after the ultrasonic clean and waiting for new needles, seats and bowl gaskets.
 
Well I set the float height to 26mm and it's still flooding out. With dry cylinders and plugs, the bike fires in 3-5 kicks(nothing happens when I push the electric start button, don't care). Idles beautifully, but when I rev it up it takes a while for it to go down back to idle. After about 5 or so minutes of idling, if I rev it, it hangs up on the rpms and doesn't come back down to idle. I have to turn the key off to stop the motor. Then if I try to start it again, nothing happens so I pull my plugs and there soaked. When I cleaned my carbs in the ultrasonic cleaner, I disassembled them and tied the floats down to the basket with a paper clip. When I removed the parts, the floats were still floating so I don't think I have a hole in the floats.

Float height is 26mm, carbs ultrasonic cleaned, new needles and seats, new bowl gaskets, petcock doesn't leak. I'm lost and that lake is looking nice and deep.
 
Make sure all the other tune up stuff has been done. Check compression in the motor. Make sure you have the assembled correctly. You can find a blowup in the manual. Sync carbs with a manometer. It would also be a good idea to replace the butterfly seals. If you have a 78 make sure the idle mix screws have not broken off in the carb bodies.
 
ImageUploadedByTapatalk1429548210.959104.jpg 78 XS400 all stock besides clubmans.

ImageUploadedByTapatalk1429548268.389653.jpg
I pulled the carbs off the bike and this is what my screws look like. That right side looks a little worn. Could that be the culprit?
 
sounds like you have an air leak somewhere. the worn needle would help in this case as it allows more fuel in. try the 3.5 turns out and recheck the jets for blockages
 
I would replace those before they snap off. When they are that worn, is usually when it happens. What setting do you have the needles set at? These are the ones in the diaphragms. Should be on the third clip down from top. Also you need to sync the carbs.
 
Thanks gents, I'll replace those.

Just for shits, I put the floats under water last night while I slept. Pulled them out before work and I can hear water in the float when I shake it. I probably should have checked that when I pulled them out of the ultrasonic cleaner. I assumed they were good because they were still floating. I ordered new brass ones from Mikesxs and I'm hoping that will fix that issue. I'll report back when they are installed.
 
Like xschris keeps saying, set the valves, timing and sync the carbs. It all really matters even if you think you have a particular problem you can't know for sure until it's all done.

I'd also check the valve seat assembly, the valve and seat controlled by the floats.

17225667995_fec802e36c_z.jpg


If that is worn it can leak and let the fuel past the carbs. An easy way to check them is to take them out, carefully remove that little filter screen, place the seat on a paper towel or rag, set the valve in the seat and fill the remaining space with gas using a syringe. Leave them sit overnight. If the gas level has gone down, you have a leak so they should be replaced.
 
I already bought new needles and seats. They weren't the issue. My float has a pinhole in it. That was the issue. I ordered new floats.
 
Well I've installed my new floats and set them at 26mm. The bike no longer floods, but still gets hung up at around 3k and won't come back down to idle once it's warmed up. I rode the bike around the block and pulled plugs when I got back. They look to be white on the tip so I'm assuming lean condition. Screws are still at 3.5 turns out and no tips are broken off. What's my next step?
 
Go up one on the pilots jets. Have you synced with a manometer? Did you replace the butterfly shaft seals? Check to see if they are pulling air if you did not. Carb spray around them and if the rpm's change they are bad.
 
Sprayed carb cleaner in/out/under/around/top/bottom/left/right of everything from the boots to air box and nothing changed. I'm just bringing it to a bike shop, I'm getting frustrated now and I'm losing riding time.
 
I did ride around the block and I noticed that if I slow the bike down to nearly a stop while I'm in first gear, then I pull the clutch in right as it's about to stall it idles normal. If I pull in the clutch while rpms are still high, it wants to run at 4k while I'm stopped
 
My only guess is, still lean, out of sync carbs or a hole in one (or both) of the diaphragms. Did you replace those worn idle mix screws?
 
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