Topic: Is this Normal? K8 carbs

[frostypuck]

Ok, K8 750. 4-2 exhaust, all the rest is stock. New air filter, points/ condensers, plugs (D7EA), etc. Just rec'd this bike a few weeks ago, so I don't know the history of it, but Here's how it goes. I start the bike, (starts instantly with choke full on). If I open the choke up immediately, the bike will run, but not well. IF I leave the choke on, and ride off after a minute or two, it will go ok, but soon the engine warms up and I have to push the choke cable in a little, then a little way down the road, it won't pull past ~4000RPM, push the choke in a little, and it's good for another 3 minutes, then it won't pull past 4000 again, push choke in some more, etc.
Basically, it's a 19 step process, taking more than 15 minutes at in-town speeds. Every so often opening the choke a hair until it's fully open. Plugs look acceptable, timing is spot on, choke is operating as it should (when I looked at it with the air box off) and acc.pump rod seems to be moving ok.
I'm going to drop the bowls today and have a look-see at the jets and floats, but, is the just the nature of the beast? I had one other K8 a few years ago, and although it was pretty heavily modified, it really didn't run any better than this, but I attributed it to the drag pipes and pods.
Perplexed,
Chris in Boston

[dpen]

"The Rat" is a K7 - same carbs as yours & has no trouble. I don't use the choke as, since it has an accelerator pump, a couple of twists of the throttle & she starts. I set a fast idle on the idle adj. wheel & let her go for a few minutes & she's right to ride.
I know this doesn't solve your problem but it shows they're not a problematic? model.

[Cvillechopper]

I'm pretty sure you've got the wrong plugs in her.  I've got D8EA's in mine and I've read tons of places that this is the right plug.  The D7EA is a cooler plug so you'd never get up to the right temp (assuming I've understood everything I've read here).  That really should fix the slow 19 step process.  After that, pulling the jets and giving them a real good soak may make a difference.  You may need to get some larger mains with the 4-2 set-up if it's not already been done.  Plenty folks in here can give you guidance on which ones to look in to.  Have the carbs been synched?  The red-headed step child of the SOHC can be tough to get parts for, but I love my engine (as only a parent can)

Hope that helps
James

[frostypuck]

Yup, sorry, D8EA's that's what's in'er. Also, in an effort to make it run a little better, I removed the p.o.'s inline fuel filter.
As for the K7 running good, I understand the '77/78's are a breed unto themselves,(stylistically)  but I usually see the K8 listed separately from the K7, with the F2/F3 in terms of performance and am wondering if it is even a little bit more removed from the family. Maybe the red-headed step-child's brother-in-law or something.
The K8 is actually going to be my wife's ride, because I prefer my '76K THAT runs well.
Chris in Boston

[dpen]

Funny thing the K7 & K8 thing. Mine is a June '78 build which I thought at first was K8.
An old Honda parts man in Sydney swears blind that it's a K7 as no K8s came to Australia.

[frostypuck]

UPDATE-
I used a digital tach, and went "by the book" setting the pilot screws. AHA! Much better, now. But falls real flat when cracking the throttle open from idle, so more investigation needed.
Chris in Boston

[eldar]

Yeah the idle screws will do that. I need to do this work with my bike as well yet. I need a new choke cable as mine does not stay since it is worn out, new plug caps since I still have the originals. I am getting these then I will sync carbs and do idle screws.
I still do not take as long to warm up but it still feels like there is power waiting to be tapped but tuning is just not at par yet.

Have you replaced your accel pump at all? It could be worn out. Is it adjusted right?

[78_SaltLick]

i got a 78K, have to pull the choke to get it started, and have to leave the choke on for about a minute after that you can take it off and the bike will idle on its own. It takes a good 5 minutes before its fully warmed up and ready to ride. Until then, if you push the throttle in will try to die on me, so i just leave it be for 5 minutes til its warm. I always thought it was just cold blooded.

[eldar]

Well you can drive with the choke on. That is why they make the tension adjustment. You set it so the choke stays where you want. You can then start to drive and adjust choke as needed. Miine takes a couple minutes with choke, then I can open it and it will run but I have to finnesse the throttle.

saltlick, I say dont sell your bike. Stick it out. Someday, you will think, " I am glad I kept it". Sure they are a lot of work and parts can be scarce but also remember that we dont need to monkey with jets so much and our engines are the best of the years in reliability and in many cases, power.

[Buffo]

I have done a lot of tuning work on my carbs on my 1978 CB750K8. I have come to find that making ABSOLUTELY sure the carbs are clean makes a huge difference in how it runs. I had to clean my carbs in berrymans chem dip twice and clean out all the air jets and the slow jets many times.

I after a sync if it still bogs or hunts when slamming the throttle from an idle start turning your pilot screws out a 1/4 turn at a time...you will have to back the idle set screw off as you do this...if turning the pilots dont make a difference after 2 - 2 1/4 turns your slows are clogged to some degree....

FyI...I am putting bigger slows in mine but for now I have my pilots turned out so far I cant remember how many turns they have. Just keep turning...but the bike needs to be at full opporating temperature...1 1/2 turns is just the starting point to get the thing running so you can tune it....I bet your bike runs ALOT better at about 3500 rpm's than below...it most likely hunts and skips a little at low rpm speeds...after it is fully warmed up and no choke

I have a lot of posts on the k8 carbs...start a readin 

Buffo the Magnificent

[dusterdude]

buffo the magnificent?