Aprilia RS 125 | Dellorto PHBH28 Carburettor Basics Explained Part 1 - Clean and Assembly.

Hi and thank you for watching my channel, Tom Did It.
This video is Part 1 of a 2 Part series where I service, clean, reassemble and tune the Dellorto PHBH28 carburettor. This Dellorto PHBH28 carburettor comes standard on the later models of Aprilia RS 125 2 stroke.
In this video I clean and reassemble the Dellorto PHBH28 carburettor and share my basic understanding on how it works.
My jetting setup is as follows:
Main Jet 125. Pilot Jet 60. Emulsion Tube B40. Needle X2. Choke jet 70. Mixer Tube BN266. Float Needle 250. Fuel Screw 2.5 turns out (approximately)
Thanks for watching!

[@rdom4256]

Thanks for these videos Tom they are really well made and very informative! i've just got my first RS125 and your videos are a massive help, thank you! Looking forward to the next video!

[@tomdidit4216]

Hi there R&D. Thank you for the nice comment. I’m glad they are of some use to you👍 Congrats on your purchase. The RS is great bike. I’m sure you’ll like it. I just released a suspension video, so look out for that. More videos on the way. Regards Tom

[@rdom4256]

@@tomdidit4216 Thanks Tom, my RS125 is not quite as mint as yours but i'm using your videos as guidance to restore mine to her former glory :-) i rebuilt the carb from your video and she started for the first time yesterday! I watched the fork rebuild last night and you've given me more food for thought :-) Thanks again for taking your time to make and upload these videos they are genuinely inspiration for me to rebuild my bike!

[@tomdidit4216]

So glad to hear that. It’s the reason I make the videos. Good luck with the maintenance!

[@afonsocarneiro]

Amazing video! could not bee more detailed. thanks a lot.

[@aphexs-2-fynixs]

Thx Tom! (again) for this advice. Happy new year. 👍👊

[@tomdidit4216]

A 1am (Sydney time) Happy New Year to you Patrick. Wishing you the best of luck for 2022. Cheers Tom

[@hyundaike011]

Thanks for helping me with this video!! Verry good explain ✌️

[@florianaicher785]

Very nice and precise explaination...Thanks to you and go on

[@tomdidit4216]

Thanks for your comment Florian.

[@JaapGrootveld]

I have a 34mm on my bike. It,s a full power,1995 version and it consumes gas like a ship's crew in the desert. The 34mm gives a little more torque in the middle. With te 28mm, the bike runs more economically with the same top speed. I'm looking forward to the tuning video.👍

[@tomdidit4216]

Hi there Jaap. I heard great things about the 34mm carb. I may invest in one. It would be interesting to see the difference on a Dyno run. Wish I had the RS 1995 version, they look awesome! Thanks for the support mate👍

[@JaapGrootveld]

@Paul Mickiewicz Hi Paul, I think at best I get 14 km from 1 liter of petrol. It's a little richly tuned. 1 liter 98 costs here $2.10 that's about $3.30 (Australian dollars) It's not a touring bike and I only use it to let off steam after work. Or if the wife talks too much, because I don't have a dog to walk. So a few cents more or less doesn't matter. Every now and then you should consider a 28mm for longer distances 🙂

[@att49356]

Hello Tom! Fantastic videos, I really like your calm and precise method. Have you thought of a power upgrade? 34-36 flat valve carbs can do a lot, especially when paired to a Selettra or PVL ignition system. Yes it prevents the engine to feed all the electrical components, but this problem can easily be solved with a small secondary wiring loom and a lithium battery so you can still ride on the road within the rules. I'll be doing the same in my RS 50 2005, but with its original Minarelly AM6 engine. Euro 2 ignitions are not the best sadly. Lots of limitation and very weak sparks.

[@tomdidit4216]

Hi Roger. Glad you like my style of video. Thanks! I think the 34mm carb will be the next meaningful upgrade I will do. Also I’d like to compare Dyno results…. I probably won’t modify the he bike too much more after that as I’m planning to keep it as stock as possible👍 I hear Zeelteonic make a great CDI box that can add a bit of HP. Have you heard of these? Tom

[@att49356]

@@tomdidit4216 If you have a dyno available it's a great help for your Zeelteonic. Yes, I've heard good words about those CDI. I don't know if you get all the connectors needed with the CDI itself, so you might have to check that on the website, otherwise you can either modify your original wiring loom or get another RS loom and modify that instead (much better, so you have yours tucked away and safe that it's working perfectly). I suggest you to ensure that your bottom end can withstand the increased power! Otherwise, you should renew your crankshaft bearings and cranshafts rod.

[@tomdidit4216]

I’ll have to do a bit of internet searching to find a local Dyno who will also professionally tune the carb for maximum HP. But let’s see. I agree with you Roger, more HP adds stress you the engine. Checking the bottom end is a must. Luckily my bike has only done 5,000kms and I checked the bottom end along with my top end rebuild. All is well.👍 Thanks for your opinion on the CDI units and ignition systems. Hopefully others will read your comments👍

[@att49356]

@@tomdidit4216 Please be very picky on the tuner! Let it do to who's surrounded by two stroke engines 😄 Also consider buying a steering dampener, they really make the difference and also a great safety measure. Stay safe and see you in the next video. Ciao!

[@tomdidit4216]

Cheers pal

[@grierson2008]

Super professional video Tom. My 07 py Rs 125 is Rev Hanging when I stop at traffic lights at like 4k rpm for 15 seconds, just wondering if you would have any ideas to rectify, Iv tried the air screw and needle clip to no avail. Original settings on carb 128MJ Full arrows so decat and sls gone which is the cause.

[@Vega_Mad]

Hi Tom, this video is brilliant and has helped me out alot Ive got a issue where if i rev my rs 125 too hard itll splutter then stall but if i slowly bring it though the rev range its got no issue at all. i believe this could be due to the air/fuel screw being too tight restricting fuel which also may be the reason my bike dosent like to start. What do you think? Thanks

[@davidbates247]

Great stuff Tom lovely quality of pictures on your video I'm running a 28 are you on a standard air box? I've got a pod on mine thinking of up jetting the main currently on a 124 thinking of going up to 126 I think standard is a 120

[@tomdidit4216]

Hi David. I’m running a 28mm carb with PiperCross air filter. I have also removed the snorkel from the air box to free up (a bit) of air flow. I’m running 125 main jet in the carb. Summer time here in Australia so I may need to go down a main jet size as the weather warms up, but let’s see. I hope to release the Part 2 carb tuning video soon - pending work commitments etc. Thanks for your message and support. Tom

[@tompenny1638]

Great vid. Do you have a diagram of where all the pipes go, especially the ones from the tank (there’s two) guessing a main feed and an overflow? Thanks. Also Tom ha.

[@Олександр-я9к5р]

Дякую брате👍

[@YorchQBerengario]

Muy buen video amigo! Tengo un porblema con mi 28 phbh, esta todo limpio, pero con el jet secundario a 62 se me revoluciona mucho en 3000 rpm, tengo que quitarle el jet pulverizador y poner en el jet secubdario un 75 y asi va bien, puede saber lo que puede ser? La moto esta recisada de todo y no tiene entrada de aire, tiene cilindeo 140cc gracias amigo!

[@tim3437]

hi great vid - thanks. Question - I just bought a nice rs as have wanted one for years - runs and rides but when it sort of warms up when you pull the throttle back it sounds like its running out of fuel, won't accept full throttle / tick over. I knocked the guy down quite a bit and decided to take it on. It sounds like the jets are gummed up - what do you think?? Its a full power 2012. just got an arrow end can. He hasn't ridden it for 8m and the fuel was yellow. Any help is appreciated! (also it seems to run fine on choke on start up)

[@tomdidit4216]

Hi Tim. Thanks for your comment. It defiantly sound like the carb and jets. I’d suggest clean the air filter, change the oil and clean the carb.

[@Sulfaseb31]

Good morning, a question, at the bottom of the conduit on the tank side of the starter nozzle there is a small hole, what is it for please?

[@conker3637]

Could you tell me what your idle screw was set at was it seated all the way in or backed all the way out? Cheers 😅

[@MacaulayHowells]

I am running the same carb but having an issue with the revs not revving high enough.

[@RonaldPuruleski]

What year is your bike? I know some got the PHBH28 and some got the VHST28. 2008-12 get the VHST28 if I recall correctly? Also do you have a good idea what the differences are between the two? I know you upgraded to the 34 so it’s a moot point for you, but I’m having trouble finding resources for the reasons to change models of carb.

[@fluffymat1]

Hi mate, I have a honda crm 125, it runs perfectly a part from cold, I put the choke on and it fires up straight away, as soon as I drop the choke off it stalls and cuts out, I have to warm the bike up with choke full on for around 4/5 minutes before it will tick over, once it does warm up it’s absolutely fine will start and tick over, it’s just on the cold starts, like it isn’t getting enough fuel on tick over when cold, it uses the PHBH 28 carb, do you have an idea on what’s happening? Thank you

[@tomdidit4216]

Hi there. From what you’re saying the bike seems to be operating ok. The choke will richen the fuel mixture to start a cold bike. I usually use the choke for about 2 mins until the engine gets quite warm. If the bike only runs on choke then I would assume the pilot just is clogged - clean the carb. Cheers

[@nikolaus2206]

on my carb the two breather hoses you were talking about at 7:37 are just connected to eachother via a single hose, also my bike doesn't like to idle, could that be why?

[@tomdidit4216]

Greetings Niilo Thank you for watching and leaving a message. I have reviewed my video around 7:37. These are breather hoses that keep the float bowl and atmospheric pressure and allow the float bowl to fill. To answer your question - I would use two separate hoses. Make sure the hoses are clear and do not restrict air flow. Lastly you mention that your bike doesn’t idle - in my experience, the main cause for a bad idle is a blocked small pilot jet. I would clean the carb then try again. Good luck👍 Cheers Tom

[@riccardocasali2196]

Hi Tom. I need some help with my Cagiva Mito which has the same carb as the RS 125. What’s the best way to ask you a few questions? Cheers

[@liamjackson3030]

would most of this information apply for a 2 stroke aprilia rs50?

[@tomdidit4216]

Greetings Liam. Thanks for your comment. To be honest I don’t know. I would assume it would be loosely similar, but probably not identical. Tom

[@angeldevil6177]

Can you please help me with ways to recognize and distinguish Delorto PHBH 28 BS carburetor. For this type, how to know and distinguish between 2 and 4 types..???. I have a Phbh 28 Bs. But I don't know if it's 2-stroke or 4-stroke, and it's missing components. I'm thinking of buying parts for it. But I don't know if it's 2 stroke or 4 stroke.

[@tomdidit4216]

Hi there. I’m sorry I’m not familiar with this carb. Is it installed and an Aprilia RS?

[@kampanopoulos_official]

because main jet 125 ?I in my own wear main jet 118

[@tomdidit4216]

Hi there. Thanks for your comment. There are allot of different factors to consider when choosing the main jet👍 If your bike runs fine on the 118, then stick with it😎

[@kampanopoulos_official]

@@tomdidit4216 Hi, I recently drove a Dyno and got 28.50hp at 11.500 on the rear wheel, I'm wearing a gianneli exhaust, another filter panel, and it has been porting to the cylinder,and spark plug Iridium BR10EIX,crank wossner and piston prox 53.96mm,16/40 gears and Did VO chain

[@tomdidit4216]

That’s a nice setup! I’m thinking of Running mine on a dyno soon👍. I’ll be able to compare HP. May I ask, what is your name?

[@kampanopoulos_official]

@@tomdidit4216 My name: kampanopoulos official You?

[@tomdidit4216]

@@kampanopoulos_official Hi Kampanopoulos, my name is Tom. When I make my Dyno video, would it be ok if I reference your current setup and HP? My bike is standard compared to yours, so I assume my HP should be a bit less (I think). If you are not comfortable, I respect your privacy and will not mention you or your bike👍 Cheers.

[@drz7787]

I have dellorto phbh28 but im not have fuel air mix bolt Can you please tell me why? I have 1999 rs125 Thank you Dellorto phbh28 을 가지고 있습니다 제 carb에는 공기 연료 믹스 bolt가 없습니다 혹시 왜인지 알려주실수 있나요? 저는 1999년식 rs125를 가지고 있습니다 감사합니다