Topic: CB750 still not running (pending).. what's the next step..

[oldhondarider]

well.. crap... I bought a 75' 750f as a spare bike while I was rebuilding my 550.  It ran for a couple of days ( I know....the start of a bad story) then it wouldn't turn over and it mysteriously it developed a leak on the shifter side... SO I threw a blanket over her and marked it for another day to get to the problems.  Well....2 1/2 years later.... I'm getting to her..LOL

I changed the gasket on the shifter side...  that fixed the leak.
changed the oil filter, oil...etc..   kicked it 30 times to get the oil moving...
replaced the battery...  
lights on...starter works...  but it still won't turn over.
tried kickstarting it.... no good
checked the plugs ( that #3 is a beeeaaachhh to get to) they're black and sooty.   ( is there an easy way to get to #3 and #2?)

pulled the tank and drained the gas..  looks very dark ( dark amber)...

Christ I just wanted a quick run around bike.... LOL..

Now it looks like I have to pull the carbs and clean them....  There goes some of my vacation...

[flybox1]

Christ I just wanted a quick run around bike.... LOL..

I'm looking for one of those too 
I'm not TOO far north of ya!   I'll gladly take it off your hands.

Be sure to 'wash' the inside of your tank with some clean gas before completely filling it.
Have a fun 'cleaning' weekend, and remember...gas and fireworks dont mix 

[oldhondarider]

hmmmm....
welll I pulled off the carbs...  no fuel in the 2 of the bowls... a little in the #1 and a little in the #4..  yellow/amber gas.

So I gave them the dip in Simple green, cleaned the bowls out.  I followed some advise and didn't pull the carbs apart..just let soak in simple green and the a good cleaning with carb cleaner.  I put it back to gether, w/ new hoses for the fuel lines to the bowls.  Replaced the air filter and reinstalled.
(BTW....getting the carbs on a 750 is a hella lot hard than on a 550.)

Still not running.
The starter works....just no kick over... I pulled off the #4 plug wire and jiggled it..the engine sputterd a bit but still no turn over..

Suggestions?  Should I buck up and pull the carbs completely apart?  or is there something else I'm missing.

What's the 3 things again....  Fuel delivery, Power delivery....and

Thanks in advance for your help.

[Scott S]

 Fuel, spark and air.

 Did you check the float bowls again to see if they had gas in them? Your floats and/or needle valves could be stuck.

 Jiggling the #4 wire is an interesting statement. Do this: Remove one of the end plugs and put it back in the wire. Hold it against the engine and crank the bike over. Do you see spark?
  Doing the outside two plugs only tells you if one coil is working, though. To check the other coil you'd have to do one of the inner plugs (2 or 3) or use a multi-meter.
 Check for fuel and spark first.

[oldhondarider]

Thanks Scott S. for the help.

well, I pulled off and checked each plug...sparks on each one...  Next step I guess is to check the bowls for fuel.

[TwoTired]

It's not hard to remove the bowls and then take out the pilot and main jets for cleaning.

Does require some dexterity and patience, though.
2 1/2 years of old gas has likely gummed them up.

[oldhondarider]

Thanks TwoTired... I'll flip the latches on the bowls this afternoon and work on the jets.

[oldhondarider]

well the bowls were filled with fuel.. not to the rim.. about 3/4 of the way down...  gonna work on the jets now.

[oldhondarider]

On my way home to pull the jets out and clean everything.  I just cleaned them a little, did the simple green soak and then reinstalled... I guess I missed the point of cleaning out the jets...  However, I still hadn't planned on pulling the carbs completely apart unless this is some essential reason.  I've read a few areas that you don't need to pull apart the individual carbs...  Is this bad info?

I did notice that when I dunked my carbs ( without the bowls) in the simple green bath...along with a little scrubbing... the slides got a little sticky going from closed to the full open position.  A bit of carb cleaner sprayed around and they started to slide again... not sure if that is pending doom? .

while i was doing the teardown, i was going to do the camchain adjustment.  I'm going to follow the FAQ's on this... Is there any other information that will help me?  Always looking for the latest tips....

FAQ: "How do I adjust my camchain?

Each model engine has its best method. The 750 is the easiest. It is done without the engine running. Simply turn the crankshaft to TDCC #1, then turn it about 15 degrees farther (in the running direction). At this point, the mechanical advancer's spring retaining pin will be close to the crankcase mark. Loosen the cam chain tensioner locknut and bolt, then carefully retighten both."

[Silverback]

Just stopped running years ago? Hmmmm, have you checked out the points? Were the new plugs wet when you pulled them again?

[oldhondarider]

I stopped running and I didn't think a lot about why... the oil leak put it on the back burner as I was trying to rebuild my 550 at the same time..  The plugs were dry but black and sooty.

I did find something interesting...  I've never pulled the jets out of a 750 before.. not sure what these are called...I doesn't appear that they were completely clogged but it couldn't have helped.   
but they had a bunch of gunk in the filters and in the cavity.










Cleaning out the jets tonight...  guitar wire...is that what i need to use on the slow jets?

[CB750Ken8]

I believe that's your slow jet.

[laser145]

I think the guitar wire can be handy but risky... you don't want to scar the passages or enlarge them in the slightest...

Compressed air or carb cleaner is good to use.

[TwoTired]

I believe that's your slow jet.

No, what he is holding with the screen on it is the float needle vale seat.

I agree with the guitar string warning.  Steel is hard and may gouge brass.  Yes, it can be used.  But, like many tools, some skill is required.  In this case being carful to not alter the jet orifice hole size or ramps leading to the orifice.

You carbs look clean enough that the aerosol carb cleaner can blast away or soak then blast most crud out of the jets.  The slow jet will have the smallest orifice (about 0.016" diameter).  It's the brass thing shown in the carb body with the slot across the end.

Cheers,

[oldhondarider]

gotcha..  this thing.


I got them out... they were seated pretty good.  I sprayed carb cleaner over them...and will do the air can technique tonight.  I tried to just put the nozzle of the carb cleaner on the jet (screw side)...but nothing would come out the other end.

[TwoTired]

gotcha..  this thing.


I got them out... they were seated pretty good.  I sprayed carb cleaner over them...and will do the air can technique tonight.  I tried to just put the nozzle of the carb cleaner on the jet (screw side)...but nothing would come out the other end.

Soak them in the carb cleaner for a half hour or so, and give it another flow test.  When done, you should be able to see light through them.  Soak them several times, if necessary.  Blast with the nozzle both directions.

If they were hard to remove, don't put them in as tight.  They like to snap off.  I don't know what the torque spec is except just-enough-to-keep-them-vibrating-out.

Cheers,

[oldhondarider]

Thanks TT!   

[oldhondarider]

well... got everying cleaned at put back in place... blew everything out with air...everything looks pretty good.

I  had to run a few errands this weekend so I couldn't put it back on the bike....  I did have a curious question... are these markings related to a factory stamp...or is there some greater meaning?

[oldhondarider]

well...crap..

got the carbs back on... and the airbox.. hooked up the gas tank......

nothing... still not starting....  I have spark... just doesn't kick over..

and now I have bowl #1 and 4 leaking... I just I didn't think I had to measure the bowl floats everytime....


sob..sob..sob

[ron.cieri.313]

Maybe take a quick look at your main fuse...sometimes these blow due to corrosion built up over time and won't let you start it.

[MRieck]

well.. crap... I bought a 75' 750f as a spare bike while I was rebuilding my 550.  It ran for a couple of days ( I know....the start of a bad story) then it wouldn't turn over and it mysteriously it developed a leak on the shifter side... SO I threw a blanket over her and marked it for another day to get to the problems.  Well....2 1/2 years later.... I'm getting to her..LOL

I changed the gasket on the shifter side...  that fixed the leak.
changed the oil filter, oil...etc..   kicked it 30 times to get the oil moving...
replaced the battery...  
lights on...starter works...  but it still won't turn over.
tried kickstarting it.... no good
checked the plugs ( that #3 is a beeeaaachhh to get to) they're black and sooty.   ( is there an easy way to get to #3 and #2?)

pulled the tank and drained the gas..  looks very dark ( dark amber)...

Christ I just wanted a quick run around bike.... LOL..

Now it looks like I have to pull the carbs and clean them....  There goes some of my vacation...

Use a 12" 1/4" extension with a 1/4" swivel on the end. Attach a 1/4" to 3/8" adapter to the swivel and then your 18 mm socket. Stand on the right side to get to #2, left to get to #3

[worlddrum13]

checked the plugs ( that #3 is a beeeaaachhh to get to) they're black and sooty.   ( is there an easy way to get to #3 and #2?)

^ basicaly what he said 
i dont know how much diffrent this is for the F, but on my k6 i figured out that u can take 12" extention and a pivot thing.(i dont know what the're called but the thing that looks life a driveshaft linkage) and the deep socket and it works great. i need to pull my tank off and there is a V in the frame that i stick the whole socket assembly down from the front and it goes right to the plugs. alternating sides on the frame will allow you to get to the other plug. a little hard to explain without lookin at it but it makes sense..trust me...  

[oldhondarider]

Maybe take a quick look at your main fuse...sometimes these blow due to corrosion built up over time and won't let you start it.

ok... dumb question time..  where's the main fuse... I've replaced all 4 of the fuses on the fuse box....

[oldhondarider]

wait... hold up... I'll go look at the manual first..    Don't want to get blasted for not checking first..lol

[KB02]

wait... hold up... I'll go look at the manual first..    Don't want to get blasted for not checking first..lol

 

Should be one of the four in the box.

[ron.cieri.313]

Even after you replace the main fuse, as soon as you turn the switch it will blow again and you'll still be left wondering wtf.

Are you getting your display lights on (neutral and oil lights)?  Have you checked your battery with a volt meter?...I'm told all old Honda mechanics say "start with the battery"...and then work your way to the starter motor if the battery is good by bypass the solenoid with car batter cables, and see if the starter motor turns.

[oldhondarider]

Even after you replace the main fuse, as soon as you turn the switch it will blow again and you'll still be left wondering wtf.

Are you getting your display lights on (neutral and oil lights)?  Have you checked your battery with a volt meter?...I'm told all old Honda mechanics say "start with the battery"...and then work your way to the starter motor if the battery is good by bypass the solenoid with car batter cables, and see if the starter motor turns.

Are you getting your display lights on (neutral and oil lights)?   yes sir.
Have you checked your battery with a volt meter?.  no sir.. new battery.. have not checked it but I will
and then work your way to the starter motor if the battery is good by bypass the solenoid with car batter cables, and see if the starter motor  starter motor turns..  the engine just doesn't kick.

[oldhondarider]

wait... hold up... I'll go look at the manual first..    Don't want to get blasted for not checking first..lol

 

Should be one of the four in the box.

yup... all have solid filaments.

[ron.cieri.313]

and the starter motor turns over nice and strong...hmmm, doesn't seem like an air flow problem as if its not getting enough, it seems it would start and then choke itself off...so gas or spark.

Did you check your volt reading at the end of the spark plug?

...and if you're good there, have you ruled out plugged jets?...I don't think float level would prevent starting unless the were set so low it was preventing jets from dipping down into the pool of gas.

[oldhondarider]

Did you check your volt reading at the end of the spark plug?
 hmmmmmm good question... I haven't checked the volts at the spark plug.  do I just ground the black lead and then touch the red to the end of the exposed coil wire?  leave the setting on 20v and hit the starter?

and if you're good there, have you ruled out plugged jets
I thought I rulled out plugged jets... I pulled them all, cleaned, nice soak in carb cleaner and a compressed air shot for good measure, new gaskets.   but I could still have something buggered up.  ( didn't pull apart the carb assembly...just the bowl/jets/gaskets...

My guess on float level being off was that after about the 7th time on the starter ... I paused....and saw gas coming out of #4 and then eventually #1.

[TwoTired]

Many standard voltmeters will be damaged with too high a voltage.

Expect a voltage of about 20,000 at the spark plug, and that is a short duration pulse, not a DC level.
Make sure your test equipment can handle the voltage and type of electricity before you just probe about willy-nilly.

Since a good spark can be seen, you don't normally need to actually measure it to make is visible.

[ron.cieri.313]

Go with what Lloyd says...

It would seems it would seem fuel is the problem then...at some point, the fuel flow is not making all the way up into carbs.

What do you think Lloyd, make sure gas is making into the bowls and if so, would seem the carbs need a good cleaning?