LCGB Forums

PHBH carbs, whats the extra jet on the carb on the right I'm pointing to? The carb on the left has a similar hole but it is not tapped and is blank if you blow air down it.

Is it a power jet? never had one before on a Dellorto.

Whats the full name on the carb, it will say something like PHBH26CS or PHBH26CD ?

It's a power jet.
I had a read through the dellorto manual, pages 29/30 available here

http://bristollambretta.webs.com/dellorto_manual.pdf

Found another useful dellorto tuning guide here too, which anybody trying to set up a dellorto may find interesting

http://www.rotaxjetting.com/PDFs/Docume ... Manual.pdf

Nelly wrote:It's a power jet.
I had a read through the dellorto manual, pages 29/30 available here

http://bristollambretta.webs.com/dellorto_manual.pdf

Found another useful dellorto tuning guide here too, which anybody trying to set up a dellorto may find interesting

http://www.rotaxjetting.com/PDFs/Docume ... Manual.pdf

Thats ace Nelly thank you,

I've been running a 30mm PHBH with that internal powerjet for years. It means you can run a smaller main, but doesn't seem to make much difference to anything (including fuel consumption). For example on my piston port Rapido 225 engine I was running a 106 main rather than a 120 something that seems to be the norm. But my fuel consumption was comparable to others with similar set ups and there was no noticeable performance difference.
I've fitted it to my Rapido 230 with mini reed and run a 126 main.
Not sure if any of that is of interest.

Steve

I've been running a 30mm PHBH with that internal powerjet for years. It means you can run a smaller main, but doesn't seem to make much difference to anything (including fuel consumption). For example on my piston port Rapido 225 engine I was running a 106 main rather than a 120 something that seems to be the norm. But my fuel consumption was comparable to others with similar set ups and there was no noticeable performance difference.
I've fitted it to my Rapido 230 with mini reed and run a 126 main.
Not sure if any of that is of interest.

Steve

Re: PHBH carbs?
Post by steveg » Tue Jul 26, 2016 10:50 am

I've been running a 30mm PHBH with that internal powerjet for years. It means you can run a smaller main, but doesn't seem to make much difference to anything (including fuel consumption). For example on my piston port Rapido 225 engine I was running a 106 main rather than a 120 something that seems to be the norm. But my fuel consumption was comparable to others with similar set ups and there was no noticeable performance difference.
I've fitted it to my Rapido 230 with mini reed and run a 126 main.
Not sure if any of that is of interest.

Steve

My understanding of the ‘power-jet’ is that it allows a further level of controlling the upper range of the carburettor, usually being used as a boost to the main jet which can consequently be smaller.

My apologies as this may be getting ‘off topic’ but, what is interesting is that from a Rapido 225 with 106 MJ you now have a Rapido 230 with 126 MJ with a reed valve fitted.

It would appear that the MJ is bigger because of the reed functioning to ensure that the fuel charge is not getting loaded up twice as it fluctuates in the venturi, as is the case in purely piston ported.

Although you don’t mention it as a problem yourself, lately, there have been several mentions of reed valve manifolds being utilised where the owners are experiencing spit-back.

Perhaps I’m being naive in thinking that the reed valve serves mostly to eliminate spit-back, which is particularly prevalent @ the lower range of the carburettor.....

My PHBH is 28mm and fitted to an old school Suzuki 190 kit with an old Tino Sacchi Ancilloti from about 15 years ago. timing is 17 and static.

I jetted it as per Cam Lab set up for a 186 Mugello and it seems to be working fine! The main jet is probably a bit large bearing in mind what you said regarding the power jet and using a smaller main but I intend to do a bit more setting up the next couple of days. I don't need a racer, its just for local rides etc. I just fancied putting the old school top end on something to see how it would go.

Needs a couple of kicks to start cold and needs choke for a while, went up from 50-53 on the pilot and it was better but thinking of raising the choke jet now as the bottom end is good in normal riding and the hot starting is first kick perfect.

I've got a 26 PHBH carb also with a power jet and think maybe this motor would benefit from the smaller carb more. Just need to get a couple of parts for it.