1978 xs400 WON'T START!!!

[jinxlovesmax]

hey guys, i have a 1978 xs400. been trying to get her to start for the past couple days with no success. first off i want to say THANKYOU to everyone that contributes to this site. it is such an amazing resource and i have learned so much from reading these forums as i have been since i got my bike last summer.

last summer i bought this bike non running. but this was not a bike that has been sitting for long, it was pretty damn clean and has minimal rust. 23,000 miles on it. fixed a stripped spark plug hole and got it to run very poorly (on 1 cylinder, had to have throttle open, backfiring) but at least running. i thought this was due to the carbs, which were atrocious. so i figured i'd put on a "new" set of carbs and it will be ok. but if i adjust the timing and valves with new carbs, it will be great! well no. i did that. and now its not working AT ALL.

i set the timing with a timing light (used tutorial from that youtube video) and timing is spot on. i also set the points gap and spark plug gap. (used specs from manual). points are in good shape.

i adjusted valves. intake to .004 and exhaust to .007, did that by aligning the LT/RT marks after i felt compression on my thumb over spark plug hole.checked for both rockers loose, and also used screwdriver to make sure piston was at the top when i did it.

cleaned carbs. completely disassembled, except for butterfly valves. soaked in simple green and cleaned in a heated ultrasonic cleaner. blew them out with compressed air. bench synched and set pilot mix screws to 3.5 turns out. set foats to 26mm from float bowl mating surface (or whatever its called). i was very thorough in making sure all jets were completely clean.

im getting spark at both spark plugs. tested by taking out plug and grounding it to engine.

Fresh gas, no rust in tank, rebuilt petcock, inline fuel filter.

Fully charged the battery and had it hooked up to the charger when i tired to start it.

I've been using the electric start mostly when i try to start it. not more than 5 seconds at a time. i have the wheels off the bike at the moment and i don't want to tip over when im trying to kick it!

the only thing i get when im trying to start it is the occasional backfire. had a poof of smoke come from the left side carb area once. no sound of "wanting" to start.

i don't know what to do except maybe trying to clean the carbs again. what do you guys think? Am i forgetting something?? ANY help is greatly appreciated!

 

[drewpy]

try putting some easy start in the bore, it sometimes takes a run to bed the engine in.

I remember working on a car engine and it took forever to start, after that, it fired first time every time!

 

[xschris]

Have you done a compression test on the engine.

 

[FUBAR]

switch the plug wires
check the gas cap for proper venting
check the banjo bolt holes where the fuel enters the carb

ez start in the plug hole as drewpy said

 

[jinxlovesmax]

Tried starting fluid, got nothing. Compression is the only thing i didnt check since i didnt have a tester. Went out and got one and i am getting about 60 psi on each side. DAMNNIT. does this mean new piston rings?

 

[xschris]

I would check your valves again. Then if that don't work put a little oil in the spark plug holes. If your compression goes up then its the piston-rings are bad. Compression should be between 120psi-160psi

 

[Drewcifer]

You can do the poor man's test. If you have someone kickstart /estart and place a thumb over the hole, you should see your finger blown off the hole by the pressure. If so, there's enough compression to combust fuel. After a thorough compression test of my bike I discovered that she had 60 psi, and runs really well, so no, it's probably NOT just that.

Gap your spark plugs! I didn't see you said you'd done that. For 6 bucks you get two new ones and ELIMINATE that potential issue.

Spark should ideally be fat, and bright blue in the dark. If it's thready and weak, clean off your points with sandpaper and electrical cleaner and GAP THEM! Mine were the cause of many issues. After I did gaps and valves my bike started first kick every time.

Have the battery tested at an auto store to see if it produces enough AMPS to start the bike. Volts are how wealthy the battery is, AMPS are how generously it spends that wealth. You need a battery with it's full amps to start your bike.