Topic: 78 750 F2

[purveyor]

Good Day All,

Please,I need help with my carbs.
frame # CB750-2205594
engine# CB750E-3105608
carb KEIHIN #PD42A apgx c/w accelerator pump
new: points,air filter,fresh oil
running a 4 into 1 Dunstall exhaust
need 21/2 to 3 turns out on the pilot screws to get started
carbs have been synced
new intake boots

the dam thing does not like to idle at any thing less than 3000 rpm
and will increase at a stop

any help would be greatly appreciated
should i just sell it and purchase another one

ps.. I have had three mates look at it and they are stumped
my 73 500/4 runs like a dream what is the big brothers trouble.

[Wheelhorse77]

How far away are you, I will give you 100 bucks for the old junk LOL...

I noticed that you said carbs sync'd, may I assume that they have been completely disassembled and properly dipped in some caustic cleaner?

Have you adj valves?

Mike bike will idle a little rough until it is 100% operating temp.

[mikedialect]

are you running the right plugs with the correct gap?

I have a 78 F2 and I ran into what you are experiencing...

I did all of the tune up procedure in order and i runs like a champ now. If you do the valves, set the points gap, set timing (I went to a dyna), sync carbs and make sure all the boots are tight it should go away. If it doesn't I would say that it is your slow jets. Not sure on the turn out on the air screws, but I would run through all the tune up stuff and then set them all the way back and then put them where they are supposed to be stock. I thought I had it all nailed down, too, but a few of my boots were a tad leaky.

[Wheelhorse77]

We need an 77-78 red-headed-step-child forum for those of us who still manage to keep the F's on the road.

[miles nowhere]

..im having the same trouble with reving at a stop after the bike is hot..

[TwoTired]

With the info given, I would diagnose as plugged/restricted slow jets not feeding fuel during idle throttle positions.

They are pressed in, and the passages behind them get gunky/restrictive/ pluged, too.  Yank them and clean them as well and the entire slow passage system.

The slow jet is only about 0.016 in. in diameter. It doesn't take much to stop them up.

Cheers,

[yoomit]

have you tried turning down the idle mixture screw when the engine is fully warm?  this is the big brass-looking knob between carb #3 and #4.

my jets were clogged last winter.  once i cleaned them out the engine was definitely idling high.  a few turns of the knob and i was set!

[purveyor]

Thanx all,

I will try the yanking of the slow jets after the day gig and get back with an update.
That slow jet idea  is the only thing yet to try.
All the other ideas have been tried at least twice.

Other wise the first 100 bucks takes it.lol

Honda so smart in their own way.

off to the day gig

[Lumbee]

http://blog.360.yahoo.com/blog-Sg4KjsE8erQjVxgd6tTWVeKm_ww-?cq=1 

[Wheelhorse77]

Thanx all,

I will try the yanking of the slow jets after the day gig and get back with an update.
That slow jet idea  is the only thing yet to try.
All the other ideas have been tried at least twice.

Other wise the first 100 bucks takes it.lol

Honda so smart in their own way.

off to the day gig

I'll bid a 100.. LOL

[purveyor]

hey,
did not yank jets
just pushed wire up and blew air though
they are clear
no fire

i have not taken the whole carb apart
just spray carb cleaner in and though the correct spots

i had it running with high idle at stop before i put new carb boots on
now sounds like it wants to start but not
exhaust smells like gas

lost

[TwoTired]

If the exhaust smells like gas, hold the throttle open a nd crank or kick it till it starts to pop or starts.

Was your jet wire smaller than 0.016 inch?
You cannot properly clean the slow jets without removing them.  They have an emulsion tube on the blind side that can't be cleaned until it is accessible.

If you spray carb cleaner into the slow jet/ system can you you see it exit into the carb bore?  If not, you haven't checked it.

Cheers,

[TwoTired]

If you are getting no fire, check your run switch position.

[purveyor]

hey,
fired and ran at 1200
sounded wounderful
the rubbers on top of the air mixture screw were missing
now replaced

i hope that in the morning she will light up my life
thank thank you to all that have been very helpful

will report back in the am

[purveyor]

  hey,
no fire
so, i have purchased new carb rebuild kit
lucky for me Sirius is 15 min from my toy box,complete for $19.00 can x 4..also picked up a new haynes shop manual $25 can
am 1/2 done  on rebuild
one thing though,on the carb body there are what looks like pressed in rubbers
one is torn...this is trouble isn't it
can these be replaced??
off to sandman
thanx again agian all
ps..thinking of naming this one 100bucks

[purveyor]

hey all,

re build in the works
 all going well
should fire later today

thanx

[UnCrash]

Man o man I'm wishing you the best of luck.

I've got a 78 750 F2 as well.

You'll get a kick out of this... I bought the bike after it was stored outside all winter.  It hasn't seen maintenance in a LONG time...  So I've been bringing the old girl back around.

It has been very responsive, but going through all the steps makes sense to me so I thought I would try to balance the carbs.  Now she wants to die when I blip the throttle. I think she was harmoniously imbalanced before, and now that I'm bringing her back to specification  she won't be perfect until the last bit is done.


Best of luck with your carbs man.  I may need some tips from you in the future!   

Cheers mate!

[purveyor]

hey all,

i have fire
we are synced
timing is good
BUT...a blip on throttle kills her
i was very careful to do the rebuild correctly
had someone pretty much double check my work
but, i set the floats at 14.5mm and then once i get her installed  i read in to the "special" part on a 78 f2  that the floats are to be set at 12.5mm
so.. now redo and set floats for the sake of 2mm??

did these darn bikes ever run correctly??
off to market and then muck about some more

PS.. Sirius Consolidated Inc. for carb parts and other bits you need are excellent to deal with.
you might even get to chat with Harry for some knowledge
www.siriusconinc.com

[purveyor]

Good Day All,

I have a purring 2 wheeler.
this is what I have done:

new carb boots
new carb kit also new accel pump kit
clean everything
did not pull the pressed in slow jet- no replacement avail.
took my time and was methodical
set floats at 12.5 mm
1 1/8 turns on all air screws
plug that hose that the EPA people wanted that comes off beside the fuel line and feeds air to all carbs
new points and condensers and set those to spec
tappets set to spec.
purchase the Haynes manual and read the link further up in this post for some great input
use the choke to warm closing the choke as she warms

well that is it
I do not think that I have said or done anything special cept plugging that air inlet

will be in Port Dover on Fri. 13 /07
black 750 with veter wind screen

best of luck to all that preserve that classic two wheelers
PS.. still needs another 100 bucks..chain has tight spot

[UnCrash]

Congrats!

Ride her a little while before diggin in on that chain and you'll feel much better about it. 

My chain has a couple of tighter spots.  I loosened up the axle, slid the wheel forward and with some WD40 and about 45 minutes of working, got the chain into better shape. 

I'm prepared to get a new  chain and sprokets this winter for next riding season but for now, unless you think the chain is in real rough shape (or you are going on a 1000 mile trip), I would give it just a little elbow grease and enjoy her for the summer.

Great work.

Ben

[TwoTired]

plug that hose that the EPA people wanted that comes off beside the fuel line and feeds air to all carbs

You mean you plugged the air vent for float bowls?  That's not an EPA mandate.  That's physics.  For the float bowls to fill with fuel, it displaces air that escapes through that vent.  The vent also allows atmospheric pressure to push fuel through the metering jets when the carb throat pressures are lower than atmospheric.

The only reason why your carbs are still working, is because the overflow stand pipes in the float bowl are also providing vent duty (as long as they remain unplugged with fuel or debris).

Best of luck!

[Wheelhorse77]

Good Day All,

I have a purring 2 wheeler.
this is what I have done:

new carb boots
new carb kit also new accel pump kit
clean everything
did not pull the pressed in slow jet- no replacement avail.
took my time and was methodical
set floats at 12.5 mm
1 1/8 turns on all air screws
plug that hose that the EPA people wanted that comes off beside the fuel line and feeds air to all carbs
new points and condensers and set those to spec
tappets set to spec.
purchase the Haynes manual and read the link further up in this post for some great input
use the choke to warm closing the choke as she warms

well that is it
I do not think that I have said or done anything special cept plugging that air inlet

will be in Port Dover on Fri. 13 /07
black 750 with veter wind screen

best of luck to all that preserve that classic two wheelers
PS.. still needs another 100 bucks..chain has tight spot

Exhaust lash was set to .004? I believe honda recommended .003 and as later discovered on this board it is better to run .004-.005 for heat transfer. Hondaman coverst this in depth.

Also, besure to check your front sprocket for wear. I ended up replacing both sprockets--rear was fine, but the front had significant wear. I also stayed with the .630 0-ring through RK. I even bought the RK riveter and press... Darn classic bikes will suck you in. Out of all of my toys though, the F2 gets the most comments/compliments.

[purveyor]

Good Mornin',

500 miles on the weekend and still purring
i unplugged that breather hose..thank you
i forgot to mention that the points were set to 20 not 14 as one of my mates recommended

i put a good used 630 chain on..from a wreck less than 100 miles
i am looking at doing chain and sprockets this winter to lower highway rpm..5-7000 i feel is too high and noisy

now my lift is empty and i was wondering if any one in Southern Ontario Canada has a deal on a project bike for a preservationist that has time and no money

thanx again to all who helped this site is invaluable to the preservationist with time and little money

cheers