New to mopeds. Carb help

Hello all,

I picked up a project moped a couple weeks ago. Someone had a 1979 Honda pa50 that they started years ago and lost interest. It was in boxes. I have it all together and am running into issues getting it to start so I can try to start tuning in.

It’s a 1979 Honda pa50 with a lot of new mods all at once. I know, not the best idea but that’s how it came. Since it was torn down years ago it has a dr 70cc kit. A trick 6 variator and a delloroto phbg 20mm carb. Along with a lot of new seals cables etc. so I have it together and am getting good spark. I’m really just trying to figure out a rough initial setting on carb ( idle and mixture) to get it to start. At first idle screw was backed out all the way and I could only get a few pops of it trying to fire with some throttle. I have it in most of the way and still get some trying but not much. I have fuel on the spark plug now so maybe getting too much. Not sure? Anyway it’s 90 deg and humid the last few days so I’ve lost a lot of sweat pedaling this beast. Let me know if anyone has any recommendations.

I have the stock carb if anyone thinks it’s worth it to put it back in for a shot.



Re: New to mopeds. Carb help

Ya gotta ask yourself why it is in pieces.

1. is the compression good

2. did u change the seals

Re: New to mopeds. Carb help

It's not the screws man, It's the jetting. Pull your jets, post what they are and somebody will let you know a good starting point.

Re: New to mopeds. Carb help

Yeah I feel like an idiot now. I didn’t even check the compression. I thought I could be lazy and throw the engine in trusting the prev owner assembled it correctly and it would run. Yeah I only have like 35psi compression. I guess I better just tear it down and go through all the seals and check everything.

Re: New to mopeds. Carb help

trust no one but yourself

Re: New to mopeds. Carb help

Michael Branscombe /

fix compression and put the stock carb back on until you get it going

Re: New to mopeds. Carb help

Okay have the compression fixed. Put all new seals. Bike started right up. I have it idling good but it wants to die as soon as I give it any throttle. I believe too rich but I’m not smart with carbs. Doesn’t seem to make a difference with choke on or off. If I give it throttle extremely slow I can get the rpms up some but still will not allow me to really get it up and running. Any help is appreciated. Should I pull jets out first and see what is in there. The brass mixture adjustment screw what way does what on this. It doesn’t seem to make much of a difference when I’m moving it. I’ve only made small adjustments though.

Re: New to mopeds. Carb help

stock carb or phbg? probably lean down low unless its blowing tons of 2 stroke oil

Re: New to mopeds. Carb help

If still using that 20 Dellorto PHBG you need to know what parts you have in there in order to tune. Disassemble and make note of:

Main Jet number

Idle Jet number

Starter Jet number

Needle number

Slide number

Atomizer and Bushing number/type

Re: New to mopeds. Carb help

Correct still using the 20 carb. Just pulled her apart. Here is what I have now.

Main 88

Idle 40

Start 60

Needle W2 ( set on second clip down from top)

Slide 30

Atomizer 260AN. 4 stroke type

Let me know how this all seems. Thanks

Re: New to mopeds. Carb help

numbers sound usuable and should be able to rev up. What sound strange is your choke has no effect, I've seen it where the plunger doesn't seal up on the tip, make sure it goes all the way down.

The w2 needle has a small tip, u want something with a big tip, the 2 stroke atomizer and bushing.

u can try dropping that needle all the way down and screw the idle adjustment screw all the way in, both to lean out your off idle low end but take a peek at your choke first.

also, did the reeds look good and did u put the piston in the right direction?

Re: New to mopeds. Carb help

Sounds good. Will check on all.

Reeds did look good. They were a two reed type replacement that came with the bike. I do have the original single reed one here too.

I hope I did. The arrow pointed toward the frame? The cutout in the piston seemed to match up.

I will report back tomorrow with my findings. Thanks. I owe you all a beer or two.

Re: New to mopeds. Carb help

Arrow on the piston crown should point to the exhaust . The direction of flow .

Re: New to mopeds. Carb help

Kevin Bishop /

That’s the only way the exhaust knows where to go. EXIT ==>

Re: New to mopeds. Carb help

Well now I’m second guessing if I didn’t screw that up. I’ll see if I can pull the spark plug and take a peek without pulling the head off.

Re: New to mopeds. Carb help

Piston is installed correctly, whew.

When i pulled the plug it does look like it has been running more rich then lean. Def not white or hot looking.

I’ll try moving the needle down to see if that helps.

Re: New to mopeds. Carb help

What exhaust pipe are you using? What air filter?

Re: New to mopeds. Carb help

Proma circuit pipe and no air filter right now.

Re: New to mopeds. Carb help

Okay back at it again with this beast.

I have checked the choke. It is operating correctly and sealing. I did play with it more and when I turn the choke on it increases the idle and I can get closer to being able to rev up. It still Boggs down at around 1/3 to 1/2 throttle.

I decided to start back at the beginning with checking timing. I verified tdc and gap is perfectly in spec. I got a timing light though and it is firing almost too the tdc mark. Well past the fire mark on cover. I don’t see any way to adjust this? Could this be contributing to my issue. It is firing between fire mark and tdc mark.

This thing fires right up with just 1/2 a pedal every start and idles great though. Just get get much past that.

Re: New to mopeds. Carb help

Hepatitis J [OFMC] /

You should try to nail down what your timing really is in degrees/mm btdc, don't always trust the case/flywheel marks. That being said, I've never had an issue running the stock ignition setup with the cam on key. I guess you could check and make sure that your woodruff key isn't chewed up.

As for jetting, I ran a 98/100 main jet with a setup very similar to yours. The humidity might drop your jetting some from that but i figured I'd throw it out there.

Re: New to mopeds. Carb help

Finally got parts and have been trying a lot of different things with no positive outcome. I’m lost as of where to go from here as I still think it’s carb setup but would think by now it should be able to at least get this beast at more than an idle consistently.

So to recap it’s a 79 hobbit pa50I. Dr 70cc kit. Proma cuircuit pipe. PHBG 20 carb.

I just checked timing again. It’s a hair before the stock fire line and points gap is good.

I just checked compression again now I’m getting 112psi with a cold engine, so a little low PWR the manual but shouldn’t affect it much right?

Originally the carb had

88 main

40 idle

60 choke/start

4 stroke atomizer bush

260an atomizer

30 slide

W2 needle

With the above carb setup it would fire up with a half pedal every time and idle great. Once I started bringing throttle in around 1/8-1/4 it would bog down and die unless I let off throttle quick. I believe it was rich at idle and lean at throttle but I’m not smart at this stuff.

I ordered some parts and have tried a combo of things that I have not progressed much past the above and now doesn’t idle as good and Boggs down immediately at throttle. Plug looks very rich. Also now only likes choke on.

Currently have

97 main

40 idle

60 choke / start

2 stroke atomizer bush

262au atomizer

40 slide

W7 needle set on second clip down.

I have main jets 88, 90-110

30 and 40 slide

W7 and w2 needle

2 and 4 stroke atomizer bush

262au and 260an atomizer

Parts to play with now and if anyone thinks I need to order something different to try I will. I just don’t want to keep throwing money at this guessing.

Let me know if anyone has any good ideas

I’ve also checked for air leaks as much as I can at idle with carb cleaner by crank seals and all intake areas with no changes in idle.

I also have stock carb I can throw on and try I will prob just have to order a larger main jet correct? I also don’t have the stock throttle cable so would have to get one too. I think that’s where I’m heading unless anyone chimes in with other ideas.



Re: New to mopeds. Carb help

Also running 25:1. I figured it would be better to break it in with this. But is this too rich and causing issues too?

Re: New to mopeds. Carb help

Any ideas where to go from here.

Re: New to mopeds. Carb help

Maybe run 50:1, pour that other shit out. W7, 98, 40, third clip. Don't run the AN atomizer, tune with the AU everything. Make sure that those two rubber things are still on your carb holes. 🤷🏾‍♂️

Check and make sure that you don't have air leaks around your carb since you've been messing with it so much. There's a full on phbg tuning performance guide that I'm not gonna link but that you should look up and read. I don't know the most about these things but I have a better understanding after reading.

Hope this does something for ya. I'm currently working on my phbg tuning right now, trying to switch the bushing out.

Re: New to mopeds. Carb help

I am running a mikuni right now and in the exact same boat. I have it idle fine, if I creep up the throttle I can get some momentum, but it definitely bogs and dies quick at WOT. My numbers wont be anywhere similar but the results of this will help direct me in my tuning.

Please keep sharing the progress sir!

Re: New to mopeds. Carb help

Any luck on your end. I’ve been busy with work and haven’t touched mine in a while. Going to get back at it next week.

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