Topic: Do I need smaller jets?

[slowjo]

This past spring I took my carbs of my 1972 K1 CB750 and cleaned them pretty good as per instructions in Hondamans book. Now it runs really rich. The mains are 120 with 40 slow. You can actually see gas spray out the mac 4 into 1 pipe at start up. I am running the stock airbox but have been thinking about turning to pods. Would changing to a smaller jet help with this? I did do a fresh tune up this past summer. Reset the valves and checked the timing. But it still runs real rich. Anyone have any solutions that might work? 

[yozuri54]

Honda Spec Guide:
105 main - carb 086A, 657B
110 main - carb 657A
105 main - carb B750A, 7A

all carbs use #40 slow jet

needle position 3rd from top - carb B750A, &a
needle position 4th from top - carb 086A, 657A, 657B

Float level 26.0 mm
Idle mixture - I turn out (basic setting all carb models)
Check all that stuff out - but it sounds like raw gas is pouring in - make sure float needles and seats are in good condition - they may need to be replaced. Also make sure the gas is being filtered properly. If you can't rely on the inside tank filter - connect an inline one. Good Luck!

[grcamna2]

I hope your carb floats aren't soaked/filled with fuel...that would sure make it Rich.

[scottly]

Check the actual fuel levels in the float bowls with the "clear tube method". Jets alone should not cause raw fuel to spray out of the exhaust. You most likely have a float issue.

[Danno]

120 for a mac four into one pipe unless the baffle has been opened up it too rich i would not go any richer with the main than 110 because the mac pipe gives near stock resistance without modification  but still if you have a s much gas as you say coming out than there is another problem with the carbs

[david 750f]

+1 , carb issue. Is your gas tank clean? Petcock filter intact? Sounds like your carbs are over flowing (filling)..

[slowjo]

After a short ride the plugs are black, I mean pitch black. The floats do float. I soaked each one of them overnight and they did not sink. I set the floats the best that I could at 26mm.

[bollingball]

I have had better results with clear tube gas level 2 mm below gasket all the same. Getting them the same made a huge improvment in mine.

[78whiteorbs]

do they look like this


have a similar issue I am investigating to see if I need to jet down myself. Are all four of yours fouling simultaneously /evenly?
 Checked compression?

cool thing is you can change jets without removing the carbs ,big big plus-   I have an open exhaust running 4-2 and you would think that will stock jetting it'd be running lean if you have a stock airbox and just run a straight exhaust but me myself I am wondering about the size of my jets- fortunately I can just drop my plugs into the ultra sonic and they are as good as new!

[Frostyboy]

Not knowing the procedure from Hondaman, did you remove the emulsion tubes when you cleaned the carbs? I found mine blocked considerably. The holes in the tubes is where the air comes from to mix with the fuel, if they're blocked up you'll get an overly rich mixture. Just tryin' to help. 

[dave500]

check the plug caps resistance,and the coil primary resistance,a lot of these irks turn out to be feeble ignition,but everyone likes to #$%* with carbs.

[dave500]

Ride it fairly hard to six grand to make sure the mains are operating in a good situation???


six thousand revs aint nothing,ride it very hard all the way or your just pussy footing around here with plug "chops".

[Spanner 1]

I wouldn't mess with jets until....... +1 on the clear tube fuel level check, takes 2 mins./carb to do !
Also+1 on the slow and main emulsion tubes AND just as important their air bleed passages, check 'em for clear.  Good luck 

[slowjo]

The plugs are black like the picture posted. I will post a actual picture of mine. I did clean and drill out the emulsion tubes as per Hondamans book. This was my first carb cleaning I have ever done so I might have to do it again. I did replace the spark plug caps with new ones from NGK because the original ones were way out of range. Thanks for all the help. 

[dave500]

youll need some full throttle loading.