So in the process of putting my newly serviced H89 'head back on, I snap the front bolt of the rocker shaft at 19nm (Aren't they supposed to be tightened to 25nm?), and decided now would be a good time to take a look at my carbs. They are covered in muck and white stains.

I'm pretty careful about cleaning them as I've heard they need to be handled extremely carefully. I have no fund to spend on them at this moment, but this is the ideal time for maintenance on them.

Any suggestions or advice on this matter would go a long way for me as this is my first pair of Hitachis. Where do I start? How full do I fill them up? Is sewing machine oil correct? My father suggested cleaning the inside with penetraing oil and not fuel, is this correct? Can I clean the outside with fuel?

I appreciate any advice in advance!

the most important thing to do, is to open one carb at a time. never open both at the same time, because the carb slide/piston is machined fit with the dome. in other words, the slide is paired with the dome.

most people i know use sewing machine oil for the dashpot. i use engine oil, 40 monograde to be precise, for thicker "accelerator pump shot".

and the float level is crucial. set float level correctly. more than 1mm tolerance, and it's impossible to tune them

Rocker Shaft bolts torque spec is: 2.0 - 2.5 kg-m (15-18 ft.lb.)

20.3nm - 24.4nm got it! Just curious at to why it would snap at 19nm =/ Think I might have turned the torque wrench too slowly for it to alert me...

bakat, by monograde you mean something like SAE 40? Doesn't this have an impact on the carb's function?

thickness of oil affect your 'accelerator pump shot'. those hitachis don't have accelerator pumps, they rely on dashpot oil to provide extra fuel when you slam the gas. thicker oil means the fuel provided when you open up is richer, vice versa for thinner oil. i use that 40 oil because of convenience (my engine use same oil). theoretically any oil can be used. some use auto fluid, some use sewing oil. you have to experiment which is best for your application, considering your weather, engine mods et cetera.

plus by quantity, sewing oil is much more expensive for me. LOL

I see...So if my common sense serves me well, thicker oil slows the plunger movement? But doesn't that mean its slower both ways?
.
See they're ment for an A15. Temperature around here is 22-27 degrees celcius on average. Humidity and atmospheric pressure ....well, we're a few kilometers from the coast.

Also, what can I clean these with?

i used carb cleaners generously. thicker oil resist the movement of piston upwards. to make them drop faster, adjust spring rate.

you may find what you need here: http://www.ratdat.com/images/posts03/HJL38W.pdf

Thanks for the info!
Thanks to the advice, I left out of bed, went down to my cave and finished them! Strapped them straight onto my brother's A14 and they worked beautifully.Hopefully I'll have finished my A15 by tomorrow and then I get to see if they really perform =D

Thanks Once Again!

I used fuel to clean mine. My father helped me when we cleaned them.
The dome and slide thing inside we polished with some brasso to get it perfectly clean and they must have a very smooth movement. Try to do everything in a very clean environment.
I have used ATF but found I have to frequently topup as it uses it up quickly.
Through research I found a british company on the internet who restores SU carbs.
They suggested a 20W weight oil. Locally I could'nt really find it so I noticed my old scrambler shock oil is a SAE 15W. I used this oil and it is working great. Car is driving smoother and also is better on fuel economy.Also don't have to topup so often.