my bike is running terrible some times i have spark other times i dont

[tim4891]

I recently bought a bike that had sat for over 3 years ,its a 1977 xs 400 i worked thru most of the issues but there are still some problems i need help with. The bike picks and chooses when it will run on both cylinders some times it will only run on the left cylinder others only on the right cylinder and very rarely do i get both i have cleaned the carbs, adjusted and cleaned the points, and both cylinders have spark atleast the times i have checked. Also when the bike is running the carb is doing this weird back fire just air no fire or bang is this normal? Could this be a timing issue. When i rode it back from my brothers today it was acting like it was starving for fuel and was only running on the left cylinder most of the time and stalled while doing 55mph more than once and at stop signs and no take off power at all other times it will go like a raped ape i dont get it any help with this would be great! I am thinking i am going to have to buy new points or rewire from the coil to the points this is just hard to diagnose for me cause the problems can be stemmed from many things

 

[FUBAR]

pull the plugs 1 at a time leve it plugged into the boot and hold the spark plug body to the engine, kick it or turn over the engine with the start button.

do this to both sides to verify there is infact a spark.

if so and you have infact cleaned the carbs well and shot air down every little hole, then check the fuel cap for a rotted gasket or somthing, sounds like its not getting fuel cause you got a vaccum in the line. run it with the fuel cap off.

if that dont work switch the plug wires and re try

start with 2 turns out on the air/fuel mixture screw and full choke no throttle

 

[tim4891]

i checked both have spark but it is eratic, i also noticed with the point cover off that im getting sparks between the gaps could this be cause the issues im am having?

 

[FUBAR]

trace the 3 colors i mentioned back to the TCI box and check theyre not frayed or crushed, stick a ttest light in the prongs of those colors on the plug and they should have power when the keys on, make sure the tci and reg/rectifiers are grounded tightly and no corrosion.
sand the tip of the spark plug and the metal plug tag . its gotta be somewhere in there man

 

[drewpy]

Fubs, i think you will find that he has points, no TCI.

sparks on the points is not good, try earthing the condensors/clean connections and "dress" the contacts flat to get good connection.

If it still sparks, you need a new condensor

 

[226dark]

First thing I would check is look very closely and make sure the bottom end of the points, the cam follower(?) is against the cam. The breaker points assembly may have rotated so it is not riding the cam.
After that is fixed make sure you have the gaps right, will probably be way too wide after getting the bottom end of the assembly against the cam and big arcing. After alot of messing with the points eventually you can eyeball the gap without using feeler gauge.
After gapping is done, then with the points closed, my method of "dressing" and cleaning is to cut strips of fine (400 or finer) sandpaper or emery cloth, open the points with fingernail or flathead screwdriver and pull the long narrow strip of emery cloth across them. Turn the paper upside down to clean other contact. Use a business card or just folded piece of paper to do same thing after the emery cloth.
Then time it by turning engine by hand to see points open at LF and RF (or just a bit sooner). Or turn the key on and ground spark plug against motor and look for the spark at those timing marks. Or use a tester light and ground one end, other end aligator clip to one of the points spring bands (?) starting with left. Light should turn on right at LF mark (or just before). OR if it is running and you are careful with not grounding out things with the screwdriver, use the timing light.
Work from there and if problems with arcing, possible condensor issue - mine was good but the wire started coming out of the plastic connector.

 

[tim4891]

i messed with timing a bit tonight but the points are not opening on the right marks they are the light is turning on a lt and just past rt i tried adjusting the timing by moving the ignition plate how it shows in the repair manual but the description is pretty vague and even when i tried adjusting no matter where i moved the plate the light wouldnt turn on close enough to the right marks how do i adjust the points to open at the correct time i have never messed with timing on a bike b4 and his has me totally confused

 

[226dark]

i messed with timing a bit tonight but the points are not opening on the right marks they are the light is turning on a lt and just past rt i tried adjusting the timing by moving the ignition plate how it shows in the repair manual but the description is pretty vague and even when i tried adjusting no matter where i moved the plate the light wouldnt turn on close enough to the right marks how do i adjust the points to open at the correct time i have never messed with timing on a bike b4 and his has me totally confused

I think what I was trying to describe is called the heel (i think) which should be pushing (riding along) against the cam before anything else.
With the spark at Top Dead Center the bike won't want to run very good. Near LT (TDC) the plate has to be turned to the right but there is a limit to how far you can turn it so points may need replacing. Maybe. The points gap will also affect the timing. If they are just barely opening right now - barely gapped - firstly that may cause the intermittent spark (or dirty, or number of things). But also as the gap is adjusted wider it affects the timing in the more advanced direction - minutely wider gapping (but still close to spec limit) will flash the timing light closer to the LF and RF 10 degree advance marks. If you widened the gap for example on the left breaker points, it will affect timing to be more advanced not just for left but both. If you widen gap for both you will get even more advance (without going too wide on gap of course).
If they have been arcing make sure they are "dressed" and closing flatly one against the other. If badly pitted sometimes better to use a nail file or small file from hardware store. Or the wife can get one from the salon

You said how it shows in the repair manual, don't go by the picture. If you still have room to move the plate clockwise and it is at LT (TDC) do so.

 

[tim4891]

sweet thanks for the help man i picked up new points today and i am goin to install them tomorrow and mess with the timing some more ill let you guys know how it goes and if i have anymore problems

 

[tim4891]

bike is running way better now thanks for the help guys

 

[226dark]

Nice work! I was afraid you would have problems with installing new points. My bike's po claimed he put new points in and still wouldn't run (it had bigger problems, like a stuck valve etc.) When he put new points in he had the right side terminal grounded and not inside the plastic insulating washer. Also it's necessary ( i think ) to remove the plate to more easily and properly install the new points.
Nice job on that!!

 

[tim4891]

yeah thats how i installed the new points is taking the plate off... the bike is running way better but i am still having issues with the bike cutting a cylinder out after i have been riding for 10 minutes or so and pops back in every once in a while for a brief second i also noticed that i still have sparks between the left contact point would replacing the condenser fix this? the only other thing i can think of is possibly carbs out sync not getting enough gas to the left cylinder any thoughts

 

[DanMach]

I'd wager money on valves being too tight.

Oh geez just realized he fixed it already.

 

[226dark]

yeah thats how i installed the new points is taking the plate off... the bike is running way better but i am still having issues with the bike cutting a cylinder out after i have been riding for 10 minutes or so and pops back in every once in a while for a brief second i also noticed that i still have sparks between the left contact point would replacing the condenser fix this? the only other thing i can think of is possibly carbs out sync not getting enough gas to the left cylinder any thoughts

From your original post it sound like you are practiced in the adjusting points - gap .30 -.40 mm - and so is it arcing like this?
[URL=http://i1038.photobucket.com/albums/a469/gxfade/arcing.jpg][/URL]

Or is it just an occasional spark you see at the points? Is it still missing just one cylinder or either / or like before? With gap adjusted (and points heel riding the cam) and points cleaned then make sure condenser is well grounded to the frame and check each of the two connections in the condenser plastic connector, make sure bullet connectors from points and from coils are all clean and tightly connecting, not just a loose fit.

 

[drewpy]

I think its more like this

 

[tim4891]

the points were sparking between the gap maybe 1 time every minutes or so... but i took the carbs of tonight and boiled them in lemon juice thru them back together and so far so good going to take it for a long ride tomorrow ill let you know how it goes

 

[226dark]

the points were sparking between the gap maybe 1 time every minutes or so... but i took the carbs of tonight and boiled them in lemon juice thru them back together and so far so good going to take it for a long ride tomorrow ill let you know how it goes

For the points. . . that is normal as long as it doesn't resemble the above video Good luck