Topic: 79 CB750 Just won't start??

[Bluenose]

Hi...my cb750 has me stumped...the carbs were rebuilt by a pro 1.5 years ago. I have checked all electrical per service manual..ok...getting good spark on all plugs. Took the carb out and checked the bowls...everything clean but did not clean them this time. It will turn over good but just not fire or start except for the odd burp. Checked plugs and they are wet. Just can't figure this one out. Any help or ideas is appreciated.

I just joined today and hoping to ride before the snow hits! Thanks

[Pinhead]

Try with starting fluid? Honda went to DOHC in '79 so your bike is different than most on this forum. If the plugs are wet they may need to be replaced. I would try with a small shot of ether to see if it'll fire up, and then maybe the "burn" will clean your plugs. Don't give it too much, though. That's a good way to blow a hole in an engine.

[crazypj]

Has the bike been run in last 1.5 yrs? The three jet carbs block up quite easy if its been sitting with gas in it.
 The other thing to check is the ignition timing.You could have plug leads on wrong plugs. Coils are for 1:4 and 2:3, you'll have to check wiring to coils, frequently its backwards so no 2 fires when it should be 1
PJ

[Bluenose]

Thanks for the hints...bike was running great until 2 weeks ago and just went bad on way home..loss of power and a little coughing...I thought maybe electrical and even replaced the spark units as the epoxy was all melted out. Had the coil checked at the honda shop..ok...I have checked and checked the coil/wire numbering on various days to make sure I didn't screw up. Even stepped back a few times and had a rum and coke, second thought or two going thorugh the procedures.

I am going to try the the quick start, new plugs, check the rubber gaskets from carb to engine...after that push it to the shop which just kills me!! I'll let you know.

Thanks again.

[crazypj]

I have seen same thing happen once on a CB900.
 As the ignitor units got overheated there is a possibility the trigger units may be damaged.( hall effect sensors)
Bike still sparks but if you put a timing light on it the spark is retarded too much to allow it to run.(not a stuck advancer,it may be worth checking that as well though) Check the trigger unit resistance and the wiring to ignitors.
Sorry I cant be more help.
PJ

[Bluenose]

Ok...took carb off again...really cleaned them and blew them out...also out and in with the pilot screws counting the turns....put all back together and the thing fired up. It is now running too fast and surging....in fact the surging is quite prononunced. Any thoughts or advise?

[eurban]

Did you gauge, or at least bench synchronize the carbs?