Connecting Carbtune Manometer to Inlet Manifold

[JonnyP]

Hi all, please can anyone advise how a Manometer (such as a 'Carbtune') can conveniently be attached into the rubber inlet manifold?
I've noticed that the Startgomma items that I am using do not have any pre-punched/ sealable access points for this connection.
I'm reluctant to punch a hole in the rubber, in case it is not easy to reseal. I've also read somewhere that some bikes feature a balance pipe between the carbs. My 500 does not have any such pipe, the only thing shared between the carbs being the petrol feed pipe.
Thanks for any guidance or feedback!

[72degrees]

Being the bodger that I am, I just drilled holes in mine on the 375 that uses PHBH carbs with no balance pipe. Sealed with a stainless steel dome head socket head screw. M5 if I remember correctly - I can check. The OEM rubbers had natty stepped 'plugs' but I assume these are unobtainium.

The drill needs to be small enough that the screw actually has to be screwed in rather than just pushed (they sort of cut their own thread). Surgery performed too long ago to remember the exact size drill I used.

Never had any problem with them working loose or leaking air and the adapters that came with my (modern) Carbtune work well in the 'holes' too.

Others may have employed a more elegant solution.

[JonnyP]

Thanks for your reply. That approach did cross my mind, but as you say, it's something of a fudge. It may be that it's the only option!

[72degrees]

Thanks for your reply. That approach did cross my mind, but as you say, it's something of a fudge. It may be that it's the only option!

To which I can only respond "It works for me", including using the setup for years competing in speed hill climbs where it spent most of the time 'WFO'.

[3potjohn]

I find with a bit of care you can get very close to throttle slides lifting together by ear and feel. The main thing is sufficient slack at the carb top adjusters then gradually reduce it (but not so you can here the motor rev.)
I do use a carb balancer on my bikes but it is never far out.
I have balance pipes so no need to go via the manifold rubbers.

[72degrees]

A picture is worth 1000 words. Definitely M5 - drill hole smaller than you would for tapping in to metal though.

I find 'close but no cigar' by ear and feel. Good enough for sure, but when you get those carbtune columns dipping together perfectly given a whiff of throttle I reckon you can feel the difference on the road.

You can probably drill more accurately in to the centre of the 'boss' than I did. I'm not a great one for immediate appearance over underlying form

inlet-plug.jpg (494.05 KiB) Viewed 3544 times

[72degrees]

Aha. That photo reveals some incipient cracking of the rubber. Almost certainly due to having no air filter box, S&B cone filters and big zip ties to take the strain. One day I will get some proper high tech supports made. Then I dare say this set of rubbers will "see me out"

[norbert]

I´ve done that the same way as 72 degrees and it worked without any problems for years. Just make sure that the screw does not enter in the manifold canal. If I rememer it well, I´ve added an O-ring underneath the head of a simple allen screw.

There are some special "plugs" to seal the hole in the rubber. But I prefered the solucion with the screw

k-DSCI0030.JPG (29.05 KiB) Viewed 3538 times

The cracks in the manifolds for not fixing the carbs when not using the normal air box normaly begin in the fold where it is put on the cylinder head. They advance from inside to outside, so you cannot see it from the outside by the right time. Normaly you notice it because it´s not posiblle to achieve a correct idle. Then it´s time to have a look at the iside of the manifold.

Using a tube between the underpresure points between the carbs/manifolds can simpify to adjust idling.

[72degrees]

Can you buy those plugs anywhere these days?

Since I changed the idle jets, treated it to new Iridium plugs and checked the carb balance mine is idling very well. Perhaps a bit fussy to start when hot (1 size too far on pilot?) but I'm learning the required technique and it warms up much quicker in cool weather now. Progression also seems much improved and very little suggestion of the dreaded flat spot. Bear in mind this is all on a much modified engine, so usual disclaimers apply.

['It must be a .....']

Hi, Scottoiler have M5/M6 vacuum connection spigots and a spigot for rubber manifold connections

https://www.scottoiler.com/shop/spares- ... al-spigot/
https://www.scottoiler.com/product-cate ... em-spares/

[JonnyP]

Thanks to everyone for your replies.
I think I'll buy a 5mm leather punch and drive a hole through the rubber manifold. As shown in your pics above, Morini conveniently provides a 'boss' for this moulded into the rubber. I can use this to temporarily insert the brass fitting for the Carbtune.
Afterwards, I will seal it with a 6mm rubber blanking plug (thank goodness for ebay...)
Hope it works... thanks again, it's great to have this Morini community!

[bigred]

Norbert. Where did you get the aluminium clamp rings for the rubber manifolds?
cheers Paul

[norbert]

If would prefer drilling. If you use a 5 mm drill, the hole in the rubber will be quite less than that 5 mm. It will be dificult to enter a M5 screw or adapter. But it will seal very well. I don´t remember well but think that at the end I had to use a bigger drill than the thread of the adapter

[norbert]

Norbert. Where did you get the aluminium clamp rings for the rubber manifolds?
cheers Paul

Years ago one guy of the german comunity has made some of them. I regret having bought only one pair of them Especially the one for the cilinder conection is very useful.
I´ve had a lot of broken 501 manifolds for years (only the 501 ones, no problems with 350), with a 350 airbox. I guess because the used snorkels from a 500 fitting on the PHBH 28 produced a certain tension on that manifolds. It´s very important not to overtight the clamps!
Dulcinea wears Polini filters and I´ve cought them with stainless steel stripes > manifolds last a lot longer than on Rocinante with the 350 air box. If you don´t catch the carbs using pot filters, you´ll be in trouble for sure!

k-DSCI0006.JPG (134.35 KiB) Viewed 3475 times

[72degrees]

If would prefer drilling. If you use a 5 mm drill, the hole in the rubber will be quite less than that 5 mm. It will be dificult to enter a M5 screw or adapter. But it will seal very well. I don´t remember well but think that at the end I had to use a bigger drill than the thread of the adapter

Thanks for that. I still can't remember what size drill I used. Probably best to get it working with the carbtune adapters first and then find a suitable screw for blanking.