|
|
123
|
|
This post was updated on .
OK had some free time to mess with the bike again. I pulled the plugs to check them for gap and then also to check to make sure I had spark because at this point I don't think its my carbs. So i'm glad i did this because i now know that i'm not getting spark out of the ignition coil on the right side of the bike (1 and 3..i think, but which ever respective cylinder they fire) So before i ran inside to part search i decided to make sure it was bad by swapping the leads with the other side.
So my new problem now is that the live wire that connects to the right side isn't providing power anymore...when i swapped the ignition coil the one that wasn't firing the plugs will fire them and vise versa. i tested the leads with a simple light pen thing but right side will not light and the left side will light.
I can see the wire colors at the connector are a black w/ white stripe, solid yellow, solid blue. the solid yellow in my case is now dead. it connects to a bundle that goes into the headlight and then to the rear towards the battery(?) but i cant see any wires that match what is on the connector.
So any ideas where i should look and try to figure out why it isn't giving it power now?
82 CB750 SC - Lincoln CA
|
|
|
Try swapping the spark modules under the seat. If the fault moves then you have found the problem. Replacements are easy enough to find. Procomm do some new upgraded modules.
1980 CB750F S/S
1979 CB750F
York
England
|
|
|
Went out this morning to mess with the bike, wasn't getting spark from the coil pack on the right hand side of the bike still so as suggested swapped the modules under the seat to see if it followed. It did not i was still only getting spark from the left hand coil pack and not the right. So then i hit up the service manual and checked pulse generator. when i touched the left steel core to the generator was getting spark out of the left coil pack, perfect. When i was trying to get the right steel core and rotor to make a good contact at first i had no spark and then after i'm guessing the tip of screw drive scrapping away some possible crud i had spark on the right side again.
I buttoned everything back up, reconnected fuel, and magically it turned over in about 3 pushes of the start...and seems like all the issues i was having are now gone. I let the bike warm up and checked my sync made a small needed adjustment to #4 and then I was only able to take the bike around the block in my neighborhood a couple times today.
Nothing to fast, might of gotten it up to 30 mph but everything ran really smooth, nice idle, nice shifting, no stalling out (even with the mixer screws set at the bench sync setting, so i will monitor my plugs and adjust them if needed) just rides really nice. With that i plan on taking it out letting it warm up and take it through some paces to ensure its running good tomorrow.
I did notice some frothy sludge on the bottom of the pulse generator cover, is this normal or this a sign of more maintenance i need to look into? Also, i noticed an oily residue all over the pulse generator, is this normal as well, looks like the crank is behind it an all but i'm thinking of it like a distributor cap on an older car, i know when moisture got into those you could have some problems.
Again thank you all for the help with all my issues on this so far!!
82 CB750 SC - Lincoln CA
|
|
|
So happy you got it fixed. Glad your riding it instead of fixing it. Good work enjoy them nice rides ahead. Also if youre still having trouble with the spark issues I suggest you read about switching the coils to cbr f2 coils. Its considered an cheap upgrade and its pretty cheap on ebay. I just got mine for about 30 bucks. Haven't put it on yet because Im trying to fix an oil leak from the Ignition/timing cover. Kinda pissed off right now. lol
|
|
|
I have just rebuilt my 1979 CB750 and she won't draw fuel, any ideas...tank is clear
|
|
|
Petcock maybe? I only rebuilt my carbs and had issues but only fuel issue I had was if I didn't have enough gas in the tank when I had it up on a ladder trouble shooting. Doubt that's your issue though...
Sent from my iPhone On May 27, 2014, at 2:25 PM, "munster [via Honda CB750'S]" < [hidden email]> wrote:
I have just rebuilt my 1979 CB750 and she won't draw fuel, any ideas...tank is clear
82 CB750 SC - Lincoln CA
|
|
|
I have thrown fresh fuel in around half full, I have blown through the petcock with compressed air. I have tried running it with the float bowls manual filled with fuel via an oil can through the jets and it runs until they run dry, but it still wont draw down from the tank.
|
|
|
Have you plugged the vent? The plastic T should have hose comeing off it, that is open to atmosphere.
|
|
Administrator
|
OK, this is a stretch, but since you mentioned the 79 model:
Is there a fuel vacuum manifold control between the petcock and the carb assembly? It has a vacuum line going to one of the carbs, and controls fuel flow: on when the engine's running, off when it stops. If there's no vacuum, there's no fuel flow.
If there's no control in line, disregard this message.
Do a search for "spawn of satan" or "SOS" at the homepage, and see if that might help.
Luke M
Used to have a 1979 CB750L, sold it as a parts bike, now riding a slightly modified 1984 VT700C. Network/Field Engineer. Central OH, USA, Earth, Sol System, Milky Way Galaxy, Universe.
|
|
|
If you have the SOS like LukeM mentioned that could do it for sure, I had one and removed it long ago. So now it's just petcock to fuel filter to carbs. On my bike when I turn the petcock on/reserve I can visually see fuel run into the fuel filter, bike running or off. Could also check your inline fuel filter see if that's clogged up.
Sent from my iPhone On May 28, 2014, at 2:31 AM, "munster [via Honda CB750'S]" < [hidden email]> wrote:
I have thrown fresh fuel in around half full, I have blown through the petcock with compressed air. I have tried running it with the float bowls manual filled with fuel via an oil can through the jets and it runs until they run dry, but it still wont draw down from the tank.
82 CB750 SC - Lincoln CA
|
|
|
Thanks to all for getting back, it has the air vent hose from the T piece between the carbs...it has a standard non vacuum petcock...it has the vb42 a carbs...its one of the last spoke wheeled DOHC 750k.
I have tried raising the tank to around 10 feet above the bike and still no joy.
There is a new accelerator pump on the way for it and carb gaskets...Would the accelerator pump draw fuel in to the carbs?
|
|
|
Just to add that the bike ran ok around two years ago, I have replaced the cylinders as the cam chain eat into the case.
|
|
|
That's the part that's confusing me, mine will flow fuel when the petcock is turned to on or reserve, no need for the motor to run. Have you tested to see that fuel flows out on the respective setting? Then also of the fuel filter is clogged that would stop flow also, and if you have a SOS that isn't working correctly would prevent flow.
Sent from my iPhone On May 28, 2014, at 3:08 PM, "munster [via Honda CB750'S]" < [hidden email]> wrote:
Just to add that the bike ran ok around two years ago, I have replaced the cylinders as the cam chain eat into the case.
82 CB750 SC - Lincoln CA
|
|
Administrator
|
put the tank on the bike, like it's supposed to.
take the fuel line off the carb rack, while still attached to the petcock.
or cut it half way.
turn the petcock on.
if fuel doesn't come running out, it's got to be the petcock, or something in the fuel line.
hell, just take the fuel line off the petcock and turn it to on, with half a tank, fuel should flow.
if it still doesn't, gut it with a drill and ride while you wait on a new one or replacement.
|
|
|
Fuel flows fine from the tank, is the 750 Dohc gravity feed or does the accelerator pump play a part...did this model have an auto petcock?
|
|
|
The "auto" petcock is the square vacum box the sits between the tank and the carbs. On an older bike like ours the diaphram stops working and will stop fuel flow. Get rid of it and get into the habit of manually turning the petcock on and off (good practice to be in anyways). I have mt current CB and had a 82 Virago, both had these vacum switches and both were nothing but a pain in the a  .
It's only illegal if you get caught.
If at first you don't succeed, use more lighter fluid
95% of Harley Davidsons ever made are still on the road... The other 5% made it home.
New Baltimore, Va '82 CB900c, 1980 CB985F/K 'Mutt"
|
|
|
thanks for getting back...my CB750 doesn't have the Auto petcock. I cannot figure how it was OK before the build?
|
|
|
Mine is gravity feeding now that i took off the SOS(autocock?) I turn my fuel to off when i pull into the garage and leave the bike running so it usually empties the inline fuel filter by the time i get it situated. So next time i go to ride, before starting it, when i turn the petcock to on(or reserve) i can see the inline fuel filter fill back up with fuel. The accelerator pump should play in when twisting the throttle as it should spurt fuel into the carbs to stop the bike from stalling out from low idle to a higher idle.
If fuel is going from the tank- through the petcock- through fuel filter- but not into the carbs..i would think next place is the brass T that the fuel line connects to might be clogged.
82 CB750 SC - Lincoln CA
|
|
Administrator
|
from what I understand munster, the pump is just here for when you twist the throttle.
on my 79, there is a rod that is pushed by a lever that sticks into a kind of diaphragm
on I think the number 2 carb, squishing it down so it squirts a shot into all 4 carbs
when you grab a handful.
if you have fuel flowing to the carb rack, take one of the float bowls off, or all 4 of them,
the floats should fall to where the bottom of the bowl was, and fuel should gush
out of the fill valve, the hole where the pointy thing that gets pushed up by the floats is.
you sure you didn't put the floats in upside down?
|
|
|
Thanks for that I will check it out...quite possible
|
123
|
Locked
