Technical (non Paso) 1990 900ss

[giocast]

well it ain't the carb! - quite cold here in England this evening, but despite that, and only having one hand at the moment, I couldn't resist trying a second carb I picked up recently. It was quite difficult overhauling as you can imagine - put carb body between knees to undo/do up screws and jets! so I will try and forgive myself for overlooking accelerator pump circuit in full anyway, persevered with the churning and even checked spark - a lovely fat one now, and then I hit the sweet spot and it was trying every time again bless it's heart. Symptoms almost identical, but kickback everytime now.. ran on 3 occasions for 2 to 10 seconds.. ah well, time for another regrouping session. My 900 almost got a little sister yesterday - a 1989/1990 750SS came up on UK Ebay, hardly needed anything and low mileage - went for £780 approx.

[higgy]

Have you checked for good compression?

[giocast]

Yes I have Higgy, but I guess that will be my next thorough port of call now... not that it was too low, but wonder about the opposite. My compression tester is quite old now but I don't see any reason to doubt it. I think it was around 130 p.s.i. and I remember being pleased that it was even. I might do a short wet test with a 2nd low capacity battery linked up to see how high it gets with a decent cranking speed. (both plugs will be out of course). Something you could help with maybe Higgy as I see you are a Weber lover (me too! - I have 3 of these brand new (42) ready for a project) :- I notice that 'they' (Cagiva) played around with the air intake/ram height as the spare carb, off another Paso or SS of similar year, had shorter studs so plastic spacer omitted intentionally - unless this was the difference between 750 set-up and 900? You mention that one of the crucial mods is to obtain and fit the longer auxiliary venturis, I have the shorter ones at present so maybe something for the future (when/if it ever runs properly!)

[giocast]

Think i've finally cracked it.. stumbled on a long thread where some other poor sufferer has been trying for ages to solve identical problem also with a 900 - has Kokusan as std but just fitted High Comp pistons. answer was to retard static by 2 deg (I know graph starts at zero advance) and it worked. I'm scratching my head as to how to achieve same with single timing sensor without heavy machining but it looks like my only simplechoice is to convert to Kokusan to achieve same. I will peer into spark plug hole to try and confirm pistons maybe.

[higgy]

I notice that 'they' (Cagiva) played around with the air intake/ram height as the spare carb, off another Paso or SS of similar year, had shorter studs so plastic spacer omitted intentionally - unless this was the difference between 750 set-up and 900? You mention that one of the crucial mods is to obtain and fit the longer auxiliary venturis, I have the shorter ones at present so maybe something for the future

a 42 would have a different jetting than the 44 as well as a smaller main choke. You could swap out for a larger main choke assuming you can find them,main chokes, emulsion tubes and auxiliary venturis are getting hard to find.
Most of the 750 came with either a 40 or a 42. The 904cc engine as far as I know all came with the 44.
The plastic block was to improve flow and increase torque mainly by changing the sonic properties(tuned length) to limit short circuiting between the two sides of the carb. Sonic properties can cause a cloud of fuel to float over the top of the carb which alternately can get dumped down one side or the other of the throats. Gives you an unintended leaning and then sudden richening of the mixture. Many autos these days have intakes that change the tuned length at different rpms to take advantage of the same effect improving response,economy and torque.

[giocast]

Thanks Higgy Both carbs are 44 and I will wait a while before even looking at jet sizes etc - baseline is a good place to start until I learn what pistons are fitted etc. I appreciate the theory behind varying intake stack height, I remember when Ferrari/Fiat introduced variable tract length on road cars and F1, was doing some consultancy work for a couple of teams at the time - what i wanted to know was, does the 'spacer fitted' set-up on a 900 actually show a worthwhile improvement in terms of performance or tractability or both?

[higgy]

does the 'spacer fitted' set-up on a 900 actually show a worthwhile improvement in terms of performance or tractability or both? :beer

Yes,both. It would be a simple thing to leave it out and prove it to yourself.........Once you get it running

[giocast]

does the 'spacer fitted' set-up on a 900 actually show a worthwhile improvement in terms of performance or tractability or both? :beer

Yes,both. It would be a simple thing to leave it out and prove it to yourself.........Once you get it running

Ha Ha.. loving your humour - no, really!

[giocast]

Kokusan it is.. for this cure, when I am well enough. Will pick up this thread in a couple of months all being well. Thanks again everyone

[angelix]

Kokusan it is.. for this cure, when I am well enough. Will pick up this thread in a couple of months all being well. Thanks again everyone

QUESTION

what if the FLYWHEEL got loose and the key is missing or broken?

you will always read 0 dregrees (or whatever is the "fixed" value), but it will be out of phase so, starting would be extremely difficult.

its a long shot, but i remember seeing a couple of flywheel keys broken (not mine, I saw them in a garage) still forth checking

for the Kokusan set up, you will need:

- KOKUSAN modules; once started and running I STRONGLY suggest you swap them with a programmable IGNITECH unit

- Pick-ups and bracket

- coils, Black version, alternatively a set of Dynacoils 5ohms; do NOT buy the grey ones because the plug cables are NOT replaceable.

everything can be salvaged from any M600-750 or SS 600/750

[paso750]

coils, Black version, alternatively a set of Dynacoils 5ohms

unless the Ignitech needs something different the correct ones would be the green 3 ohms Dyna coils

G.

[angelix]

coils, Black version, alternatively a set of Dynacoils 5ohms

unless the Ignitech needs something different the correct ones would be the green 3 ohms Dyna coils

G.

Ignitech can work with either of the two.

the original Ducati ones are 3.5-5.5 ohms (aproximately) so if you use the 3ohms with the kokusan, it is more likely the moodules will fail (eventually)

the difference between the two is the size: the 3ohms are smaller, but the disadvantage is that they will absorb quite a lot and the electrics could be an issue plus the fact that they heat up substantially more therefore they will need to be fitted away from heat sources.

The problem i found with the 5 Ohms is the size, they are 20-30% bigger that the stock ones and I had to make a special bracket to fit them ; they fit a little tight but they do.

3ohms should be better for performance at HIGH rpms, but could cause the ECU to fail for heat too much causing misfires

the 5ohms should be more kind to electrics and electronics, but at high RPMs could be less performant.

having to chose i decided to go for the 5ohms as i have them fitted under the tank.

[paso750]

3 ohm coils from Dyna, Andrews etc are just fine, nothing will happen. Every Duc shop or parts supplier sells them.
The only ones that are known to sometimes cause damage are the ones from Nology as their 3 ohm coils vary and some actually have a lower resistance.
I did run 2,7ohm coils from Silent Hektik for many years with the original Kokusan units although I wouldn`t recommend anyone to do so as these should only be used with their own programmable CDI unit. Still, I personally never had a problem.
the 3ohm Andrews coils are the yellow ones if I remember well.

G.

[paso750]

QUESTION

what if the FLYWHEEL got loose and the key is missing or broken?

you will always read 0 dregrees (or whatever is the "fixed" value), but it will be out of phase so, starting would be extremely difficult.

I had a similar suspicion as longer time one or two guys posted about starting problems which were caused by a previous belt change. Either the engine was turned over during belt change or not all pulleys were set to their marks when doing the job. But, according to giocast that´s all ok.
I really wonder what the real problem is.

G.

[angelix]

3 ohm coils from Dyna, Andrews etc are just fine, nothing will happen. Every Duc shop or parts supplier sells them.
The only ones that are known to sometimes cause damage are the ones from Nology as their 3 ohm coils vary and some actually have a lower resistance.
I did run 2,7ohm coils from Silent Hektik for many years with the original Kokusan units although I wouldn`t recommend anyone to do so as these should only be used with their own programmable CDI unit. Still, I personally never had a problem.
the 3ohm Andrews coils are the yellow ones if I remember well.

G.

Honetly when it was time of chosing ythe coils i just took my Ohmeter meadsured 5.8 ohms from my old perfectly working coils and decided to get the 5.0

the reason why everyone sells the 3.ohms is Just because they are the ones preforming slightly better at high RPMs, ie when you are pushing at 9000or over (Baynes Racing used to push the old 750s over 11000 rpms) on a long straight.

In my (our case) I am not racing, therefore i believe the 5 is better for an overall street usage.

I wil in any case look for a "cheap set" on ebay amd run a comparison, as you are making me curious...