1978 XS400-2E Intro and Build

Wait, what? Gauze filter cover?

And yeah, mcrowell, I set the gaps to the minimum 0.012 inches or 0.3048 mm. The plugs are firing at exactly the right moment and at no other time. For now I am convinced the coils/condenser is bad due to he extremely high resistance I am reading at such a low temperature.
 
Well, it looks like my adventure is over for a while; I put the stock air filters back on and tried to start the bike again this morning. After having no success I pulled the plugs and found oil on them again. When I changed the oil I also saw plenty of metal glistening in it. I did another compression test for giggles and I am barely hitting 90 psi on either side.
 
keep trying, I believe you are backwards on the resistance to temp relationship, I remember hearing that it was backwards from what one would think.

Id venture to guess that the bike ran fine before it sat? therefore your electrics should be fine besides loose/rusted connections.

keep plugging along....
 
This bike never ran fine. When I got it it idled on choke. I have no idea if it was always running on 1 cylinder, but last time I got it to start it was. I did a compression test at this point and was able to hit 150 psi on both sides. I tore it open to adjust the timing after I could not get the right cylinder to fire. When I looked at the timing it appeared wrong. After adjusting it appears to be correct. When I tried to start the bike again it seemed to be firing at the wrong time and I got some smoke coming out of the crank case. I tore it open again and double checked the timing; I am quite confident it is correct. I just put everything back together this morning and my plugs are being fouled with oil and I cannot get more than 90 psi compression on either side. Oh, and when I drained and changed the oil it was full of microscopic metal shavings.

I have never rebuilt an engine before and I am worried about even trying. The parts look extremely difficult to find and any sort of surprise damage could quickly exceed the cost of what I paid for the bike to begin with. I can't imagine that having an engine re-bored is cheap...
 
metal shavings in the oil is normal in an old bike, expecially when you flush the crankcase with gasoline and losen those shavings up. There isnt anything you have done that could have damaged the internals. your loss in compression is probably because when the gasoline washed the rings they wont seal as well.
 
I'm sure if you're looking at medical school you don't want to spend a pile on your bike. Putting more money into things than they're worth is a luxury of the old retired farts like me. My current rebuild of this 78 model has already exceeded what I paid for the bike 33 odd years ago. If it ever gets done and runs and looks the way I hope it will it'll be worth it to me. Time will tell. Maybe I'll try to find a 650 that's been done the way I want it. I just like the twins, enough power, cheap to operate and light enough to handle.
 
I just spent all morning in the garage... with good news... it's running!

The first compression reading I got was wrong. My compression gauge, which has only been used once before and is new, was not sealing against the spark plug hole well. After a few tries loosening and tightening it I got 150+ psi on both sides.

Next I threw the stock air filters back on for giggles and taped the intake ports even smaller; the bike started to make some noises...8 or so turns out on the idle air screws and she idled for over 5 minutes until I shut it down.

Oh, and it looks like I set the timing right :) I am very happy right now. Time to jet! :thumbsup:

 
If you have the 78 carbs on that, by turning the mix screws out it leans. Try turning them in.
 
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I did try. It would start for 1 to 1.5 seconds on 0 to 3.5 turns out. I literally sat there and kicked 10 times for every half turn. It wasn't until 6+ turns out that it would even stay on for a short time. By 8+ turns out it was idling at 1200 fairly steady with occasional hiccups every minute or so.

Also, what confirms--to me--that I am running lean; If I shook/bounced the bike around it started much easier. Without tilting the bike from side to side and bouncing a bit on the shocks it would not start at all below 4 turns or so. It wont run off choke; It wont rev past 3 grand or so; It backfires; It hangs when you rev it; It surges at idle; I have a muffler with almost no back-pressure.

I can tell you that my carb boots are different; my tightening clamp is 1/3rd the size. Also my carbs have very few gaskets; just brass really. Also, the jets coincide with my vin 137.5 mains I think, and I have a 2g5.
 
That is messed up something is not right there:umm: how did the plugs look when you where at 3 turns out dry or wet? I think you have some other issues there 8 turns out with that carb and it should run very lean. Have you had the pilot jet out? I had a problem a few years ago with worn out needles that where like having them turned out 10 times. the bike would rev so bad it was not funny. Got some new ones and problem solved.
 
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Yes, I removed the pilot jets for cleaning. It's funny that the Hayne's manual recommends removing it by sticking a rod or something into it and pulling it out thereby risking enlarging the hole. All I did was unscrew them, turn the carbs upside down and tap the bottom; they popped out with no fuss. There is no need to shove anything in them. I did stick brass wire into the holes to clean them. I can't, however, guarantee that the previous owner didn't follow the Haynes removal recommendation. Most of this bike has been taken apart based on the condition of the bolts and such.

I did not look at the plugs. I am going to open the carbs again to confirm my jet sizes and order new ones. Once I have fresh jets I can confirm whether my existing ones were damaged or enlarged. I really wish wide band sensor kits were not like 300 to 500 bucks :(
 
Everything looks a little haggard from the previous owner. What should I look for on the front air jets? Everything has been removed and shows signs of aggression :p I have also never seen a front air jet for sale anywhere. Just to confirm, the front air jet is the jet on the air filter face of the carb pointing towards the rear of the bike? It is the passage directly leading to the pilot jet?

Oh, and I do remember that my plugs have always been dark in color upon removal; never yellowish or white; this would obviously be a sign of running rich, but I cannot be absolutely certain it is not some leftover oil in the cylinder (lol 5w30 leaks right in...). Since that incident I have changed the oil twice and allowed it to drain for 24+ hours each time, but it has not run long enough to burn the excess out of the cylinder. I have also used starting fluid a few times and even straight gas before I had starting fluid. I could buy new plugs and get a more accurate reading.

Oh, and my idle air screws do not have any kind of gasket or o-ring; is that normal? It's just a needle with a spring. The previous owner did smear them with graphite grease that I cleaned off.

And another thing; What are butterfly shaft seals made of? Are they easily damaged? mikesxs.net sells them, but they don't actually show them in the photo. I did not remove the butterfly valves to check, but they show signs of being removed previously.
 
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Mike sells the air jets as a small main jet. the butterfly seal are at the ends of the shafts in the carb not the butterflies. If there is a lot of damage to things as you said replace as much as you can with new. There was no o-ring on the mix screw.
 
I'll replace the small mains then; I am going to order right now and re-clean everything once things arrive. I'll make a manometer too and see if I can balance things.
 
Remember mikes bs34 mix needles are not the same as yours. just the jets and that is it. The graphite grease is good to have. Seals and lubes the threads.
 

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