CB 900F Kehin carbs

Posted: Sun Sep 18, 2016 11:26 pm

FYI..It is possible that draining my carbs at the end of each ride is messing them up.

I had posted some time ago that upon turning the petcock on, one of my carbs would leak a little gas out the drain tube and then stop.
As if a float would stick and then start working.

Well today after not riding for a couple weeks, I turn the gas on and 3 of the carbs are running non-stop out the drain tubes after the bowls have filled up.
Did a quick about face on the vehicle and took the 71 Bronco instead. But the carbs have to come apart to see if a film is building up on the float pin or something when they dry out?

Posted: Sun Sep 18, 2016 11:49 pm

Tap the bowls with a plastic mallet, should fix it.

Posted: Sun Sep 18, 2016 11:58 pm

Tried that and it wouldn't stop flowing. All the parts in there are new within the last couple years so something is buggering up. I'll pull them apart and check the float pins. Thought that draining them would be good but now, not sure?

Posted: Mon Sep 19, 2016 1:32 pm

ethanol fuel? if so. yes then draining after each ride maybe be drying out the rubber bits.
as we all know, it's becoming a real issue.

I don't drain after each ride, but I am rethinking my strategy for end of year draining as well. I may consider adding 2 stroke oil to the fuel for winter storage and try to keep things from drying out.

no good answer it's seems anymore. ethanol fuel issues has me real agitated. I am having more problems with all my power equipment too.

try leaving the carbs wet and then drain just before the ride to get fresh fuel in the bowls. that's what I used to do 20 years ago before the fuel got so shitty.

Posted: Mon Sep 19, 2016 4:17 pm

I never drain during the riding season since I like to believe the fuel hose and needle valve tips shrink when dried out and swell again when exposed to fuel (which is why you usually see a fuel joint leak stop after a while).

Posted: Mon Sep 19, 2016 5:07 pm

Buna-N (Nitrile) does grow in fuel and shrink when dry. Throw an o-ring in some gasoline for a few days and then look at it.

Posted: Mon Sep 19, 2016 7:03 pm

genesound wrote:

Buna-N (Nitrile) does grow in fuel and shrink when dry. Throw an o-ring in some gasoline for a few days and then look at it.

That's why almost every float needle made is VITON tipped, not Buna-N. But, certainly there are exceptions.

I run my carbs dry after the day's ride and highly recommend doing so.

Leaving fuel in for extended periods is worse for the parts than not. And I suspect Rick is riding his bikes more than most so, the fuel never has a chance to evaporate fully.

Theory is, if you leave fuel in the carbs to the point it evaporates out and dries my itself, the residue will clog the primary jets which, I've seen hundreds of times. Then the bike won't idle.

If you run the carbs dry, there isn't anything left to leave behind to do damage.

If in fact you have Buna-N o-rings and bowl gaskets like the carbs came with (and was OK for yesteryears gasoline), it's not OK for today's fuel (no longer can be technically called gasoline) then, you need to replace those components with viton pieces such as Randakk's sells in his kits.

BTW, when/if I need to replace float needles, I only source Keihin components from several aftermarket companies or the Honda dealer. Everything else is junk (IMHO).

Posted: Mon Sep 19, 2016 10:34 pm

When I rebuilt those carbs last summer I am pretty certain the pilots were OEM. The rest may have been rebuild kits supplied by the Honda dealer which probably weren't OEM. Sounds like everything dried out? Float needles I am not sure but I know I replaced them. I figured the pins that hold the floats in place may need to be wiped shiny again but it sounds more like something dried out from the responses here. Wont know till I pull the float bowls off and if the floats move up and down as they should then I may be looking for some new rubber stuff.

Posted: Mon Sep 19, 2016 10:36 pm

Not one comment on the Bronco?..come on guys LOL

Posted: Mon Sep 19, 2016 10:46 pm

Looks lonely, or no one dares park near you and embarrasses their own ride.

It would look better if you loaded up the 900f in the back instead of leaving it at home though.

Posted: Mon Sep 19, 2016 10:54 pm

Did you happen to start the bike? If not wonder if the vibration of running would help seat them pesky needle valves.

Not to rub it in but if you kept your automatic fuel valve it would not start leaking until it started or you cranked it a long time. Very Happy

Or let the bowls fill and then let them sit in gas for a bit and hope it fixes itself.

Posted: Mon Sep 19, 2016 11:59 pm

That's one clean machine Greg, a classic for certain.

Posted: Tue Sep 20, 2016 12:04 am

That’a pretty nice my friend! I’d love to take that thing to the beach.

Posted: Tue Sep 20, 2016 2:27 am

I will fill the bowls up and then shut the gas off. Worth a try Rick..thanks

Posted: Tue Sep 20, 2016 4:27 am

I found with mine it was the floats were a little sticky on the pivot pin. First start was interesting, fuel pouring out of all four drain tubes!

Posted: Tue Sep 20, 2016 5:50 am

Yep, very nice Bronco alright! Mr. Green

Who transplanted the 351W into it?

Will a bike even fit in the back?

Posted: Tue Sep 20, 2016 11:40 am

Bronco is a cracker, I'm sure I have seen it before

Posted: Tue Sep 20, 2016 7:02 pm

J.R., I've had my bike since 2008, I have not touched the stock carb setup. At no point have I EVER drained the float bowls. Even last winter when I stored the bike in a heated shop, all I did was top it right up with SHELL 91 and added a half bottle of Seafoam. It started up in the spring with out too much fuss.
I have never had an issue with these carbs.

Chris

Posted: Tue Sep 20, 2016 7:32 pm

CDN1100F wrote:

J.R., I've had my bike since 2008, I have not touched the stock carb setup. At no point have I EVER drained the float bowls. Even last winter when I stored the bike in a heated shop, all I did was top it right up with SHELL 91 and added a half bottle of Seafoam. It started up in the spring with out too much fuss.
I have never had an issue with these carbs.

Chris

Great! Not everyone can be as lucky as you.

Seafoam or any other stabilizer definitely helps for the long term storage along with a heated building.

Additionally, I find that folks that ride their bikes often (like you and Rick) have less problems than those that only ride once in a while, like the fellow on the tech page.
The constant flow of fuel through the carbs keeps them clean inside whereas the folks that don't, allows the fuel to sit in all the passages and do things that hurt performance.
If whatever you're doing has worked for you in the past, than who am I to argue?

That said, if you turn on the fuel and the leaking stops after a while when the o-rings swell, then you're only prolonging the inevitable.

Posted: Tue Sep 20, 2016 7:44 pm

That Bronco is one sick machine! I love it and I love the color too. I'd trade an F for it!

Tom

Posted: Wed Sep 21, 2016 1:13 am

Thanks Tom, That is a nice compliment!

Maybe an old Sting Ray Schwinn will fit in the back Gene or two to 3 people.

The paint is Ford off white and Ford Grabber Blue. I tweaked the blue a bit removing some of the black to lighten it

Posted: Wed Sep 21, 2016 1:35 am

Hondo57 wrote:

Not one comment on the Bronco?..come on guys LOL

It's a beaut........considering there are about 3 or 4 left in the whole state of Michigan....mighty rare.
These started rusting on the car carrier on the way to the dealer.........

Jebby

Posted: Wed Sep 21, 2016 1:37 am

BTW....if you leave the bike sitting for extended periods.......store with Torco or VP race fuel......
It will keep for quite a long time.....

Jebby

Posted: Wed Sep 21, 2016 1:37 am

Ha ha.. you got it. I got lucky with this one

Posted: Sun Sep 25, 2016 4:09 pm

Update on the carbs...
You are spot on again Rick. I filled the float bowls as you suggested on Friday night. Now, by mid day Sunday they are not leaking any more. Time to go for a ride!! Thank you:-)

Posted: Sun Nov 06, 2016 10:49 pm

Sad to say...I have left fuel in the float bowls since this thread started and thought all was well. A beautiful day today and worthy of a last ride for the year. Turned the gas on and one of the carbs started to overflow out the drain tube again. I also tried my best to start the bike on and off till the battery ran out. Almost started but wouldn't stay with it. Just decided to winterize and in doing that, pulled the plugs to check. Of course they were wet and black. Sometimes over the years I have wanted to blow up these CV carbs. When they are good they are good but it always gets to the point of a rebuild no matter what. Well, the bike is tucked in for the winter, all chrome is wiped down with WD40, sprayed WD inside the exhaust pipes as usual and put a spoonful of Marvel Mystery in each cylinder. Gas tank is filled up and stabile is there for the duration.

Posted: Mon Nov 07, 2016 1:21 pm

Did you try tapping on the bowl of the leaking carb?

Posted: Mon Nov 07, 2016 1:53 pm

say good night gracie Smile

Posted: Tue Nov 08, 2016 10:40 pm

I did try that Russ. I have not ridden the bike much this summer. It sat a lot with the bowls empty and that is what started the problem I think. The rubber dried out. It was working for awhile as I went out for 120 miles a few weeks back. I did not drain the carbs but just shut the gas off. I thought all was well but this time when I flipped the petcock a couple started to overflow again. I'll just strip them this winter. I have a new ring kit from Cary that I'll put in too