28 mm PBHB carb conversion
Anyone know somebody who can set an Aprilla 125 PBHB RD carb up to run properly on a Lammy?
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carlos fandango
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I take it you mean PHBH ?
Ive converted a 4 stroke 26mm running on a std jet 200 engine.
Is your one a 4 stroke one and has it been converted?
http://scooterotica.org/forum/viewtopic.php?f=7&t=10032
Russ
Ive converted a 4 stroke 26mm running on a std jet 200 engine.
Is your one a 4 stroke one and has it been converted?
http://scooterotica.org/forum/viewtopic.php?f=7&t=10032
Russ
Last edited by carlos fandango on Sun Oct 31, 2010 7:57 pm, edited 1 time in total.
When i was young my Mom said "if you haven't got anything nice to say, say nothing at all " ..................... and people wonder why I'm quiet around them !
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Rich_T
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The current jetting on the RS125 Aprilia carb should be:
Idle 52, no change required
Main Jet 120, see note below.
Choke 70, no change required
Slide 50, probably no change required
Needle X25, need to look at this with the combination of the below.
Atomiser BN266, should be OK between 266-268 is usually normal for most Lambretta applications This number relates to the diameter of the atomiser hole 2.66mm etc so it is easy to work with. needles on the other hand are a pain, have a look around to find the dimensions of the X25 needle (standard needle on PHBH 26 is an X6)
You will need to block off the auto lube feed on the carb, this is the small brass pipe on the opposite side to the air screw. Also, depending on you aplication be aware that the adjustment screws are on the opposite side to a standard issue PHBH carb. This means that if your carb comes out on the R/H side the screws are easily accessed. If it comes out on the L/H side they may be a little obscured by the engine mount but this is just something you'll have to live with.
I have several of these carbs and plan to work out the jetting for use with GT kits in the future some time. As a basic rule of thumb the cubic volume of fuel air supplied in the RS125 install is similar to that of a 190cc GT kit so with the exception of the main jet i don't think it will be a million miles away. For a GT kit running this carb open I would start with a 102-105 main jet. Piston ported engines will usually require a bigger main, but again this depends wildly on their state of tune, pipe or box, open or filter etc etc. For a thirsty tuned piston ported 225 you may will have to up main and atomiser. The good news is spare are cheap for this carb by comparison.
Idle 52, no change required
Main Jet 120, see note below.
Choke 70, no change required
Slide 50, probably no change required
Needle X25, need to look at this with the combination of the below.
Atomiser BN266, should be OK between 266-268 is usually normal for most Lambretta applications This number relates to the diameter of the atomiser hole 2.66mm etc so it is easy to work with. needles on the other hand are a pain, have a look around to find the dimensions of the X25 needle (standard needle on PHBH 26 is an X6)
You will need to block off the auto lube feed on the carb, this is the small brass pipe on the opposite side to the air screw. Also, depending on you aplication be aware that the adjustment screws are on the opposite side to a standard issue PHBH carb. This means that if your carb comes out on the R/H side the screws are easily accessed. If it comes out on the L/H side they may be a little obscured by the engine mount but this is just something you'll have to live with.
I have several of these carbs and plan to work out the jetting for use with GT kits in the future some time. As a basic rule of thumb the cubic volume of fuel air supplied in the RS125 install is similar to that of a 190cc GT kit so with the exception of the main jet i don't think it will be a million miles away. For a GT kit running this carb open I would start with a 102-105 main jet. Piston ported engines will usually require a bigger main, but again this depends wildly on their state of tune, pipe or box, open or filter etc etc. For a thirsty tuned piston ported 225 you may will have to up main and atomiser. The good news is spare are cheap for this carb by comparison.
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Rich_T
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Oh, you'll also need the obvious, like a cable choke conversion as these usually get left behind on the bike and forgotten and remember the grey plastic bell mouth that screws onto the front of the carb. I'm not sure that a large GP air hose will fit but it is certainly easier to get soemthing to fit to that than just the plain thread out the front of the carb.
My mate ian had his done by al diablo...more than happy with the results.
I want to try one on my GT kit..i'll let you know.
I want to try one on my GT kit..i'll let you know.
randall ate my dog!!
no one likes us we dont care
no one likes us we dont care
Yeah I meant a PHBH, cheers for the replies. I do intend to run an SR or GT 190 kit so I'll look fwd to seeing your results.
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Rich_T
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Well, if you intend to use it on a GT186 kit with 30mm manifold I'd suggest starting at about 102 with a filter or 105 open. Lift the needle to highest position and give it a go, a 268 atomiser might be be an idea if it is a bit lean. The RS125 does have a cable choke so if buying from Ebay make sure you get this part in the purchase. This would be a fair base line to start from.