Topic: boggy

[TwoTired]

I am running 110 mains and 135 slows (pressed in)

I believe you are mistaken with the slows. They should be #35 as that is book value from Honda.  A #135 would be larger than the main jet and would run way too rich at idle, if at all.  Consider this.  The earlier carb had the same venturi diameter and slow jets that were #40.  Although, the air jet may have been different, too.

I dont believe putting needles with "clip" possitions in is the answer. Honda put a lot of time in these bikes and if they needed clip possitions they would have them.

Believe what you will.  However, the same design carb from one year before did have needles with extra grooves for adjustment.

I'm not certain, but I think 78 was the last year of the manual slide carbs for Honda.  They went to CV types after that, as they were easier to get Emissions compliance over a wide operating range.  77 and 78 were transitional years where even though emission laws weren't in place yet for motorcycles, they were in place for the auto industry.  And, "lean burn" engines were quite vogue for the time.  The 77-78 carbs were Honda's attempt at making these earlier carb styles "lean burn".  And, just as auto manufacturers were puting anti-tamper devices on cars to keep people from changing their cars into poluting vehicles, Honda incorporated some anti-tamper items into the the 77 and 78 carbs, notably the pressed in jets, and in 78 needles with only one groove.  This was done to discourage changing the bike's tune from the stock, minimal poluting, configuration produced by the factory.  Later, the idle mixture screws received a special winged cap to limit how far from factory setting these screws could be adjusted.

You are right, though, Honda did put a lot of time getting everything setup correctly.  And, as long as every bit of the bike is still in factory configuration, no extra adjustments are needed.  But, if you change the way the engine breathes from intake through exhaust, you'll likely need an adjustment range outside of the factory selection.

Good luck.  I hope you get things sorted to your satisfaction.

[Buffo]

yes yes...35... a miss type.

Maybe the carbs or more restictive to tuning than I realize but even with the K$N and the header that I am running my bike seems real close to being spot on.

Twotired...I take it that your bike(S) have the carbs with the needles that have multiple clip slots in them. Would you happen to have any used ones that you replaced from an overhaul? I will pay you for them. I would need 4 of them of course. If I can't get the settings correct with the idle set screw and the pilot screws adjusted I would like to try a leaner clip setting. It would be an interesting experiment at least.

Don

[TwoTired]

Maybe the carbs or more restictive to tuning than I realize but even with the K$N and the header that I am running my bike seems real close to being spot on.

Well, yes, they can only get close with changed bits.  (chuckle)  That's why they call it tuning, so they can become spot on.   

Twotired...I take it that your bike(S) have the carbs with the needles that have multiple clip slots in them. Would you happen to have any used ones that you replaced from an overhaul? I will pay you for them. I would need 4 of them of course. If I can't get the settings correct with the idle set screw and the pilot screws adjusted I would like to try a leaner clip setting. It would be an interesting experiment at least.

Sorry, I have no spare needles.  But, my CB750s are F models.  The jetting, needle taper, and settings are different than the K model  because it came with a 4 into 1 exhaust instead of a 4 into 4 exhaust system.
It is an interesting notion though, to use F carb set up data on a K model fitted with a 4 into 1.
I don't have complete set up data for 78 K and F models, but the shop manual does list that data for the 77 K and F:

 Item -  K7/F2
Main Jet No. - #115/#105
Main Air Jet No. - #150/#120
Slow Jet No. - #35/#35
Slow air jet No. -  #150/#150
Jet Needle Setting -  F2D51E-1/F2051F-2
FLoat Height- 12.5mm/14.5mm

Note the needles have different numbers and the dash following is the clip position on the multi-groove needles.  The different numbers indicate a different taper profile for the needles.  This would yeild different mixtures for the various low to midrange throttle settings. Also, the main air jets are drilled into the carb bodies.

Something to note, though, is that the F2 has different valve timing than the K7.  And, CR of the F2 is 9:1 and 9.2:1 for the K7 and K8.  This will alter the engine breathing characteristics, too.  But, I don't know what part of the Honda carb set up was affected by that.

Were it me, I'd buddy up to a machinist or a model steam train enthusiast with a lathe, and get them to cut extra grooves in your existing needles with the spacing equal to the existing groove width.  That way, you can experiment and go back to the original position if it doesn't yield pleasing results.

Cheers,

[Quail "Owner of the comfortable k8"]

I know I jumped onto this thread but there is some good info for us redheaded stepchild 77-78k owners.  Well I got my floats set and I used a hose to check them.  The level seems high to me but the bike is running very good.  The level is almost to the top of the bowl!  1/4 inch down from the gasket max!  It does not load up and the plugs looked good after a 70 mile ride.  The idle is much better and I was able to set my timing correctly because the "bogg" is almost all gone.  Only if I snap the throttle full open do I fell it hesitate for an instant.  (It was throwing me over the handbars then running over me.)  My thanks to Eldar and every one that had the answers.

Ok now for a funny.  I could not get # four to fill the bowl no matter how I adjusted the float.  Then I remembered these floats look like they are upside down when installed properly.  Yes i had put #4 in upside down.  Fliped it and adjusted it and guess what it worked!  Those little guys in Japan were smart.