Topic: 1971 CB750K1 #2 Carb not getting fuel to cylinder

[Duke McDukiedook]

Clean out passages on #2 again (with air) and check your float level.

[Johnie]

If you decide to do a bench sync when you have the carbs off, go to the FAQ section and search sync or bench sync and there is info there. Pretty easy to do.

[Old Scrambler]

The backfire and fouled plugs indicate you have poor ignition......check for a fresh battery at full power.........then check valve clearance and timing..........then for spark leaks from the coils to the plugs.  Sometimes the spark is there when cold but is grounded when hot.  With this condition you often will find that the idle is affected by the weak spark. Check one thing at a time.

[dharris324]

Purchased an oem float from ebay today for #4 carb.  Also took a chance on an oil pressure sensor from a 1980 cb750K.  Hope it fits my bike (looked the same as mine).

Bike will not start until I get that float in.

[ekpent]

Did you buy another brass float?

[dharris324]

I think so...  The photo on ebay just shows the plastic bag (bubble wrap with red sticker).  Says it comes with float and pin.  Orig Honda OEM parts.

[dharris324]

Here is the link on ebay.

http://cgi.ebay.com/ebaymotors/Honda-CB750-CB750F-CB750K-Float-Pin-OEM_W0QQcmdZViewItemQQhashZitem587e9f0379QQitemZ380081472377QQptZMotorcyclesQ5fPartsQ5fAccessories

[dharris324]

See if this link works.  This is the first time since 1977 that this bike ran.  Kicked it over twice and it started right up.  It ran and idled great.  Since this video (about 3 weeks ago) it started running bad.  Only thing I can think of is the light rust inside the tank.

http://www.facebook.com/video/video.php?v=1279935193062

[Duke McDukiedook]

I think brass floats only went on the K0. Everything after was plastic.

[dharris324]

Mine are all brass....  If I receive a plastic one in the mail would that be a bad thing?

[Duke McDukiedook]

It should still work, I guess after the K1 they went to plastic. It might have different buoyancy than the brass one so it may open at a different height than the brass one.

If it is the same number as the fische partfor your K1 it should be brass.
Would've been nice to show a pic of the actual part.

[Kevin D]

Are you running it with the airbox off? Runs better with airbox on.
Are you riding it or just running it in the garage? It will do better if you ride it.
Do you have a meter that you can check your spark plug caps?  5000 ohm resistor inside.
Do you have another set of new spark plugs?
 FWIW, I got one replacement black plastic float to go with my other 3 non-leaking brass type and it works just fine. I also have just the least little bit of rust in my tank, and it has not caused me any jet plugging problems. I might be wrong about this but I would venture to say that the fine mesh screen in the petcock is much finer than any jet or carb orfices. Just the same you should try and get the tank as clean as possible. There's lots of threads here an tank cleaning and de-rusting. If you keep the petcock off of "reserve" you will only catch floating crud, as the heavier stuff will be on the bottom of the tank.
Be patient and hang in there dharris, its gonna work out. Fresh gas and a new battery goes a long way, but not always all the way.

[dharris324]

Thanks Kevin,

It does have a new battery and the gas is also fresh.  Have cleaned the tank out by sloshing the gas around and pouring it out several times.  Been cleaning the petcock every so often to see if it still has crud in it.  It is getting cleaner every time.

I am running it with a set of pod filters i purchased recently.  Cranking and running it in the garage and also taking it out on a short block long spin every now and then  (when it decides to run fine that is).

I have a second set of spark plugs on the way.  The set that are in the bike are new as well (probably fouled right now).

Glad to hear the plastic float works with the brass.

[dharris324]

Installed the new spark plugs today.  Fired right up but runs rough.  Still waiting for the new Float.  Right now it pees on the floor (baaad bikey).

Also Installed another oil pressure switch.  Stopped the leak from the crankcase!

[Kevin D]

Right now it pees on the floor

Just like a dog marking its territory.

 

Make sure the float hinge pins are clean and smooth.
No cracks in the overflow tube
Gas shuts off when float is raised.

pod filters i purchased recently

Another thing that has to be sorted out. I've never been down that road, but theres others here who have.

[Spanner 1]

My K1 with the original Gold tank like yours was really, really rusty but I was determined to use/keep it !
Did the toilet cleaner de-rust x3 times and went ahead and put it on the bike...first day the bike quit with a rust filled petcock and no gas flow  !!
Then I came across a trick... a bar magnet ( two bucks @H.D.) zip tied to a length of coat-hanger and' fished' into the tank to rest beside the petcock intake....leave it there in the tank with the wire below the gas cap. Take it out every day and wipe off the rusticles stuck to the magnet , after a week it's all gone. Worked a treat for me, the magnet is still in my tank, trapping any rust that would get sucked down to the carbs......

[dharris324]

Good info!  Thanks.

[Johnie]

My K1 with the original Gold tank like yours was really, really rusty but I was determined to use/keep it !
Did the toilet cleaner de-rust x3 times and went ahead and put it on the bike...first day the bike quit with a rust filled petcock and no gas flow  !!
Then I came across a trick... a bar magnet ( two bucks @H.D.) zip tied to a length of coat-hanger and' fished' into the tank to rest beside the petcock intake....leave it there in the tank with the wire below the gas cap. Take it out every day and wipe off the rusticles stuck to the magnet , after a week it's all gone. Worked a treat for me, the magnet is still in my tank, trapping any rust that would get sucked down to the carbs......

That really is a great idea spanner. Those zip ties will be OK in gas?

[dharris324]

Well..... Got the new float in today.  Cranked until by leg and battery were dead.  Couldn't figure it out until I looked guess where (in the tank).  There was no go juice to be found.

After addind a gallon It cranked rught up.  Firing I might add on all cylinders.  No sputtering and popping.  Took it down the road and back and bout froze to death.  But the icicles on my teeth are a trophy to me!

Thanks all for the advice!  Wil tacle the dreaded 2nd gear at a later time.  Just happy It woke up.

[dharris324]

By the way.. The float was the plastic variety.  But if it works,  it works.

[ekpent]

Don't worry on the plastic. I have your twin over here,replaced them all. One had a leak and the other fell apart. When you get ready for some gears put a shout out-lotsa help and maybe some cheap parts------Eric

[dharris324]

WOW ekpent!

You cornered the market on old Honda's!   Very nice bikes there.  Love that color.  Wish mine were running better.  Spoke too soon about the #2 carb.  It decided not to work again yesterday.  It popped and spit out flames and smoked a lot when it was trying to work.

Will be too cold to tinker on it today.  Besides,  my Mother is having breast cancer surgery today.  Say a prayer for us.

[dharris324]

It is cold outsise!!!  Just finished cleaning the carbs and reinstalling them.  Used better air pressure this time.  Purchased a air nozzle for my compressor to build up enough pressure to blow the passages out.

Here is a video:

http://www.facebook.com/home.php#/video/video.php?v=1296494607037&ref=nf