some assistance please...(lenghty)

[Anonymous]

good day to all of you...havent been here in awhile. I need help w/ my '78 gs750, back on thanksgiving, I was going to ride down to my cabin(perfect weather), the bike would not rise above 1300r's, #4 cylinder was cold to touch on the exhaust side.decided to replace points and condensors(all O.E).So, now after all of this plus new intake o-rings, and a valvecover gasket, and new air filter, it's still not firing...AT ALL!!!


P.S: not firing at all as in all 4 cylinders...and yes the points and condensors are wired correctly

PLEASE HELP ME!!!!!

P.P.S: just found out about jojo, my condolences...R.I.P

 

[Jethro]

Ok, what have you checked so far? The engine only takes two things to run, spark and fuel (getting them right can be a bigger problem). Try to fire it up and then immediately take the plugs out and check if they are wet. If they are wet, then check for spark at the plugs. Have you checked this yet?

 

[first timer]

try cleaning your carbs, if you have spark on all 4 plugs then it probly is dirty carbs.

-ryan

 

[Anonymous]

carbs are clean, i'll get spark every 6/7 time i bump the starter, i get a huge backfire, but thats it, occasionally it will start to turn over, but just piss out after about 3 sec :? , battery is @ full capacity, it just wont run :evil:

 

[Anonymous]

try putting the old condenser back in . i always look at the last thing i touched before looking for new problems

 

[first timer]

how clean is clean, can you safely say for sure that every little hole is void of dirt and gunk. what is the condtion of your tank, do you have a inline fitler. i say these things cause when i first got my bike i had the carbs cleaned by a mechinic and the bike worked good for 60 miles then all this dirt from my tank dumped into the carbs and cloged everything, and i thought my carbs were clean untill i cleaned and dipped them my self. then i knew they were perfectly clean. i then installed a inline filter and creemed my tank so this wouln't happen agian.


i'm just saying this cause it seems like you have spark on all plugs, are the plugs new that helps big time too when finding a problem.

what kind of filtration system are you running when you try to start the bike pods, factory air box with filter installed or no air filter installed. this matters too.

did you clean the resitor caps on your spark plug boots? take a flat head screw driver and stick it in the boot then unscrew the metal tab the spark plug slides into, you will find a little metal disk a spring and 1/2" long ceramic like rod, take some emery cloth and remove any burn, rust or corostion on all these parts that make contact with each other, rember you want the electricity to flow as easy as possable from the coil to the plug. make sure to clean the contact point inside the spark plug boot too, i used a little wood rod with a little sand and just twisted the rod around inside the boot till i saw copper again. after all these are clean use some brake cleaner to rise everything.

put this all back together and see if that helps at all, you should get a stronger spark.

are you sure your timing on the points is set correctly, when you cleaned the carbs did they get staticly synced? take a small drill bit and put it inside you carb throat and open the slide let the slide close on the smooth part of the bit and adjust the slide so it barely holds the bit in place, repete this to all the rest of the carbs so they all open and close to the same exact hieght when you turn the throtel. give yourself a bit of play using the igle knob the moves all slides at the same time so you can increase how much all the slides are open or close them more then the size bit you used, this will help you set a idle that you want.

hope these things help, these are some of the routes i explore first when trying to find the problem.


check your carb boots and o ring behind them for cracks and seperations, they get mad when you try to move them when it's cold and they are old they love to crack maybe your turkey day ride seperated some of them.

also check your carbs to these specs and see if something if off

1978 GS750E

Specs in mm.
Carb Type- Mikuni VM26SS
Bore Size- 26
ID# - 45030
Idle r/min - 1050 +/- 50
Fuel Level - 2.5-3.5
Float Height - 25-27 mm
Main Jet - #100
Main Air Jet - 0.7
Jet Needle - 5F21-3
Needle Jet - O-6
Pilot Jet - #15
Bypass -
Pilot Outlet -
Valve Seat -
Starter Jet -
Pilot Screw -
Pilot air jet - 1.6
Throttle Cable Play - 0.5-1.0


-ryan

 

[Anonymous]

Are the right points firing the right coil?

 

[dpep]

Check your throttle and throttle cable. Make sure there is slack at all of the carbs. I once put on some new handlebars and slid the throttle back on wrong; the cable was catching and effectively I was traying to start it with the throttle tiwsted open. It exhibited the same symptoms you describe.

 

[Anonymous]

thanx for all of the suggestions so far...but i think what has ultimatly happend was the bike jumped timing, will check for sure tomorrow, i.e, the breaker plate was cooted about as far back as it could go

 

[Anonymous]

you initially said you had backfire..... this points to firing order , intermittent coil operation or a loose connection with the thin wire attached to the coil.
I suggest you check the small wire fittings then the firing order.
It is possable to dislodge the connectors when removing the fuel tank.. very frustrating as it is hard to notice.
Best of luck

stay upright