1200 carbs on a '76 - high end lack of power

[socrace]

Are you aware that running rich & lack of high rpm power with these carbs is very common, caused by leaking diaphragms? Something to check anyway.

[r.hesse]

.....you mean the diaphragms of the air cutoff valves?

[Toehead]

cv diaphragms?

[joedrum]

im following this rather closely to see if the outcome can get better for this setup on the the 1000 .....

[malte]

...before mounting i cleaned all parts disassembled with ultrsonic and checked all mechanic. the carbs are complete stock, clean and all parts in good condition.

but the diaphragm-hint is good. that means, when soften the spring of the cv-slider its going lean. thats easy, because i can open the carbs at this part without dismounting the whole carb-battery.

i will check that with spacers below the caps this weekend.

[socrace]

These are the diaphragms to check. Not exactly cheap to replace, though, which could be why some used carbs have this prob:
http://www.randakks.com/Carb%20Parts.htm#11B
A little more affordable, these look like they *may* work (just a WAG haven't tried them):
http://jbmindustries.com/KeihinVGinstructions.html

[malte]

so, today i took time and rode a longer distance. no change at the carbsetup. back at home i checked the sparkplugs... ...all four pretty clean with less coal-debris. the colour is difficult, but it doesnt look like rich... ....i´m worried now.
no more encouragement for moe changes today. its raining anyway...

[Whiskerfish]

Does anyone have the stock jetting values for the 1200 carbs?? Just for comparison values mind you.

I am going to move this to the unique Carburation Forum so it does not get lost in the shuffle here.

[malte]

the main jet was #102, I think. i am not sure any more that the problem is caused by rich-mixture...

maybe the powerlack correlates to an air-oscillation due to the shortened intakemanifold... ...but i´m not experienced enough by far for interpreting the enginebehaviour. may be an old car-tuner can help?

i should go in the basement, clean the 1000-carbs well, and just reassemble these... ....maybe....

....cruising up to 50-60mph is real good with the 1200-setup...

if there werent these decisions...

[Fred Camper]

I believe Alwing runs 1200 carbs on his 1000 and they work to readline I believe. It is well know that the smaller venturies produce less power at high rpm than the 1000 carbs, and some report not being able to run to redline with 1200 carbs. So without details on the power it makes at say 8000 rpm compared to 1000 carbs it is hard to tell if anything is wrong or just performing as expecting.