Dellorto PHBL 22 AS Jetting?
Posted: Sun Jul 22, 2018 9:47 am
Hi Guys,
After trying for ages to get consistent running from the original MB22B carb, I've finally caved and fitted a modern Dellorto PHBL22AS for my 175TSs. Eurocarb here in the UK were very helpful and provided a slight change to the standard jetting, based upon the original settings for the MB22B, to get me in the right ball park.
However, although I noted down the original settings as supplied and methodically worked my way through adjustment, I can't get the bike to fire and idle for more than about 5 secs tops and it dies immediately if you try to give it any choke or open the throttle. When it does fire, the plug is black an sooty and the engine often stops with it spitting back through the carb and a strong smell of fuel.
The best results (if that's what you can call them), are when the idle mixture screw is turned all the way in (thus weakening the mixture) and the idle speed screw turned out about 5 turns (just lifting the slide slightly), so I'm guessing that the 45 Idle jet is way too big.
My question is, what is a sensible amount to drop in idle jet size? I obviously don't want to order a whole bunch in single steps just for the hell of it, it'd be way too expensive and wasteful, but neither do I want to jump wildly about and go to the other end of the problem scale and make it too weak! So, is a drop down by steps of '5' too much? The idle jet fitted at the moment is a '45', so I'd be looking at a '40' and maybe a '35' to maybe get me in the right ball park.
By the way, I've checked that there is slack in the throttle and choke cable and that the timing and spark seem Ok. The jets currently fitted as supplied are:
Idle Jet = 45
Choke Jet = 70
Needle Jet = 268k
Main Jet 98
Slide = 40
Float Height = 24
Needle = D24
Any advice is greatly appreciated, this is the bike that just keeps on giving . . me grief that is
Cheers,
Jase.
After trying for ages to get consistent running from the original MB22B carb, I've finally caved and fitted a modern Dellorto PHBL22AS for my 175TSs. Eurocarb here in the UK were very helpful and provided a slight change to the standard jetting, based upon the original settings for the MB22B, to get me in the right ball park.
However, although I noted down the original settings as supplied and methodically worked my way through adjustment, I can't get the bike to fire and idle for more than about 5 secs tops and it dies immediately if you try to give it any choke or open the throttle. When it does fire, the plug is black an sooty and the engine often stops with it spitting back through the carb and a strong smell of fuel.
The best results (if that's what you can call them), are when the idle mixture screw is turned all the way in (thus weakening the mixture) and the idle speed screw turned out about 5 turns (just lifting the slide slightly), so I'm guessing that the 45 Idle jet is way too big.
My question is, what is a sensible amount to drop in idle jet size? I obviously don't want to order a whole bunch in single steps just for the hell of it, it'd be way too expensive and wasteful, but neither do I want to jump wildly about and go to the other end of the problem scale and make it too weak! So, is a drop down by steps of '5' too much? The idle jet fitted at the moment is a '45', so I'd be looking at a '40' and maybe a '35' to maybe get me in the right ball park.
By the way, I've checked that there is slack in the throttle and choke cable and that the timing and spark seem Ok. The jets currently fitted as supplied are:
Idle Jet = 45
Choke Jet = 70
Needle Jet = 268k
Main Jet 98
Slide = 40
Float Height = 24
Needle = D24
Any advice is greatly appreciated, this is the bike that just keeps on giving . . me grief that is
Cheers,
Jase.