A35 Polini + 19mm PHBG Race Questions

Breece McConnell /

So, I am in the process of rebuilding and restoring my a35. It has the 64cc Polini kit and the 19mm Dellorto PHBG Race carb, but It has never run as good as I think it should. It sat for a long time before I bought it and I bought it from someone who was the third owner of the bike. I have no idea who built it originally, but it needs some love. It is currently completely disassembled and being rebuilt (gaskets, seals, bearings, cables, brakes, tires, cleaning carbon build up in engine and exhaust, etc) while the frame gets powder coated.

I was reading through the PHBG wiki and came across the section about the "metal disk" in the PHBG carbs. I checked mine, and it was still there. So, I removed it. The bike immediately ran better, but not perfectly. I then read the section about the AN ( 4 stroke) vs AU (2 stroke) atomizers. It turns out that my carb has the 4 stroke atomizer and bushing. I understand that with the a35 reed block setup it is not necessary to replace the AN atomizer with the AU, but I am going to do it since it is a relatively cheap and easy thing to do. I also found out that the stock Tomos throttle has probably not been fully opening the slide on the 19mm race carb. I have ordered a new short pull throttle as well.

My question is this: since the carb was tuned with the disk between the jet and atomizer, the 4 stroke atomizer, and the stock throttle, how should I adjust the jets to compensate for all of this change?

I have noticed on the Tuning Spreadsheet that similar setups are running 100+ main jets. My current carb setup is a 70 main jet (if I'm reading it correctly see pic below), a 60 starter jet, a 45 idle jet, a W9 needle (on the lowest clip), and a 30 slide.

(Edit: Also the pipe is a technigas.)

I fear that this will be far to lean when I am able to fully open the slide with the new throttle and the other additions. Any advice for me? Thanks to anyone who read my novel!

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(edited)

Re: A35 Polini + 19mm PHBG Race Questions

u can dremel the stock throttle so it opens more, id feel better in the 80 range of jets. yours main probably drilled out. temp gauge might help w tuning.performance exhaust?

Re: A35 Polini + 19mm PHBG Race Questions

Breece McConnell /

The main being drilled out would explain why I have been able to get away with such a lean jet. Yes, the exhaust is a technigas.

Do you think I should start with a 100 and work my way down after I finish the rebuild? Or should I start lower? I ordered a trail tech vapor with a temp sensor so I should be able to keep an eye on the temps.

I am trying to go all out with this build.

Re: A35 Polini + 19mm PHBG Race Questions

With the flat 2 petal a 100 sounds like a good place to start. With a 4 petal I would try a 105

Re: A35 Polini + 19mm PHBG Race Questions

Probably going to want a w7 needle but w9 should be able to get you in the ball park.

Yea start high then work your way down. Not going to hurt anything running a fat main jet.

Those metal disk will make your bike run lean! Make sure you have the correct bushing and its facing the correct direction.

Re: A35 Polini + 19mm PHBG Race Questions

Breece McConnell /

I ordered the bushing as well! Hopefully they won't be too difficult to install. Why would a W7 needle be better? Will that make me run richer or leaner?

Also, is the 30 slide the right size?

Thanks for the reply!(edited)

Re: A35 Polini + 19mm PHBG Race Questions

> Breece McConnell Wrote:

> -------------------------------------------------------

> I ordered the bushing as well! Hopefully they won't be too difficult to

> install. Why would a W7 needle be better? Will that make me run richer

> or leaner?

>

> Also, is the 30 slide the right size?

>

> Thanks for the reply!

These carbs can be confusing so you should really start at a good base.

https://www.mopedarmy.com/wiki/How_To_Tune_PHBG_Carburetors#Out_of_the_Package

I'm think you need a number #40 slide btw

Crazy Wayne is there to hold your hand & tell you exactly how to install the bushing.

When you search phbg on google the first thing to pop up is the mopedarmy.com tuning page,probably has been open more then the float bowl.(edited)

Re: A35 Polini + 19mm PHBG Race Questions

Breece McConnell /

That page is a great resource. The person who built this bike seems to have tuned the carb very strangely. I guess I will order a 40 slide and a W7 needle along with 90-100 main jets to start tweaking.

Does anyone have any recommendations on starter jets or idle jets? Or should 45 and 60 do the trick?

Re: A35 Polini + 19mm PHBG Race Questions

> Breece McConnell Wrote:

> -------------------------------------------------------

> That page is a great resource. The person who built this bike seems to

> have tuned the carb very strangely. I guess I will order a 40 slide and

> a W7 needle along with 90-100 main jets to start tweaking.

>

> Does anyone have any recommendations on starter jets or idle jets? Or

> should 45 and 60 do the trick?

Idle jet is probably somewhere in between 40 and 50 and your choke jet is always 60!!!!

45 seems like a good start but if you have the money I would definitely buy more sizes like 42,48,50

Re: A35 Polini + 19mm PHBG Race Questions

Breece McConnell /

Ok, I will by a range of idle jets in the 40 to 50 range.

Also, going from a W9 to a W7 will make it leaner right? Since a 7 needle is shorter overall than a 9? Based on this site.

Or am I thinking about that wrong?

Edit: Actually that makes it richer i think. Shorter needle is richer right?(edited)

Re: A35 Polini + 19mm PHBG Race Questions

Breece McConnell /

That would make sense to have a richer needle. Because when I am at WOT (even though the slide isnt all the way up with the stock throttle) and i let off the throttle after being at wot and then i try to give it half throttle while the rpm is still high it bogs. Then I have to crank it all the way open to get it to go again. That means the needle is to lean to keep up with the main jet right after WOT right?

Re: A35 Polini + 19mm PHBG Race Questions

IMG_1170.PNG

W7 Is over-all leaner! It's a fatter needle so it lets less fuel thru the jet.

Also the w9 first clip is like being on w7 last(edited)

Re: A35 Polini + 19mm PHBG Race Questions

Breece McConnell /

Ok, so do you think the symptoms I described are a result of having a needle that is too rich? The W9 needle in my carb was set to the very bottom notch.

When I put in the W7, should I start out at the middle clip notch with a really fat main jet?

Re: A35 Polini + 19mm PHBG Race Questions

> Breece McConnell Wrote:

> -------------------------------------------------------

> Ok, so do you think the symptoms I described are a result of having a

> needle that is too rich? The W9 needle in my carb was set to the very

> bottom notch.

>

> When I put in the W7, should I start out at the middle clip notch with a

> really fat main jet?

I think your symptoms are based on that fact that the carb was never properly modified to make it tune-able.

It had the wrong slide

Worng bushing

It still had the metal disk

& your needle was okay

What happened properly is the guy that built the bike didn't know jack about phbg.

Just get a solid base & go from there. With out the base you'll be Throwing what ever at it like the guy that built the bike

Re: A35 Polini + 19mm PHBG Race Questions

Baron Von Hamilton /

W9 has a leaner taper. You can tell it is fatter in the picture. I get a better tune out of a W9 then a W7. W7 seems to sometimes have a lean spot on the transition from pilot to main. So you can be rich on idle and rich on main, but get a lean spot on the transition. It always seems like when I am doing a group ride that is always my throttle position.

Re: A35 Polini + 19mm PHBG Race Questions

> Baron Von Hamilton Wrote:

> -------------------------------------------------------

> W9 has a leaner taper. You can tell it is fatter in the picture. I get

> a better tune out of a W9 then a W7. W7 seems to sometimes have a lean

> spot on the transition from pilot to main. So you can be rich on idle

> and rich on main, but get a lean spot on the transition. It always

> seems like when I am doing a group ride that is always my throttle

> position.

The w9 looks thinner too me. To Be honest I believe they are the same size but the w9 will let more fuel in at the same position

Re: A35 Polini + 19mm PHBG Race Questions

i think both you guys know what you are trying to say but the way you are saying it is somewhat confusing

the w7 needle has the transition point lower than the w9 so it adds needle jet fuel mix at a larger throttle opening.

if you go back and look at the chart of what tuning parts are affecting what range of throttle opening- the 'straight shaft' portion of the needle blocks almost all of the fuel flow through the needle jet orifice until the taper kicks in. Up until the throttle is open on that taper, all the fuel flow is coming through the pilot jet, via the atomiser holes and being controlled by the air bleed screw.

once the slide is up far enough to hit the taper portion, it opens up that needle jet orifice and fuel begins to flow.

if you are getting a dead spot before it hits the transition point- like eric is talking about- you can go from the W7 to the W9 and it will add more fuel. or vise versa if it is kicking in too soon.

it all depends on how progressive your setup is and the airflow for a relative carb size. Get your pilot jet adjustment as good as you can for the 0-1/3 throttle condition, then adjust your needle jet to start kicking in. If you have a smaller carb you'll be getting a stronger pressure signal whereas a larger carb wont get as strong of a pressure signal (which pulls fuel from the pilot jet) and might need more flow being added mechanically from the needle.

Lots of bikes that other people have tuned that i ride have this screwed up, Eric is dead on when you are riding with a group and trying to modulate throttle, this will drive you crazy if you dont get it nailed down.

Re: A35 Polini + 19mm PHBG Race Questions

One of us is wrong so there is no way we both know what we are trying to say. And I think we started to over educate the kid with info. Just keep it simple and get a good base!

Yes your right w9 will allow more fuel to enter at the same Throttle position and your main jet will kick in sooner.

Also running w7 on the bottom clip position is almost like a w9 on the first clip position but they are different.

Re: A35 Polini + 19mm PHBG Race Questions

Breece McConnell /

I appreciate the detail on the needles! That info will be useful for diagnosing problems when I complete the rebuild. I want it to be really dialed in.

Do any of you guys know what this amber build up is on my case?

I am tempted to just chip it out but it crossed my mind that it looks like some kind of epoxy? Maybe placed there on purpose? It doesn't really look like carbon build up.

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Re: A35 Polini + 19mm PHBG Race Questions

Dude that is some whack shit... looks like somebody case matched to the polini but then... went too far? had second thoughts? And tried to like epoxy it back up. Do the cases match the polini transfers better with or without that shit? Either way in my mind that has to go, because it looks like it's already been eroding away and entering your crankcase

Re: A35 Polini + 19mm PHBG Race Questions

I totally agree with Mike^ .

If it does need build up there , you might try alumiweld .

https://www.alumiweld.com

Amazon or Harbor Freight .

Re: A35 Polini + 19mm PHBG Race Questions

Breece McConnell /

Yeah, its maybe the bunkest thing I've ever seen. It might match better with the epoxy. it's hard to tell. What do you think?

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If I remove the epoxy and it doesn't match up anymore, will there be issues?

Re: A35 Polini + 19mm PHBG Race Questions

Breece McConnell /

Damn this rebuild is turning into a nightmare. I really want to find whoever built this hack job.

Re: A35 Polini + 19mm PHBG Race Questions

Removing epoxy and running it might create a strange transfer turbulence . Likely you'd never tell the difference . But , it should run as long as there are no base sealing problems .

Re: A35 Polini + 19mm PHBG Race Questions

Breece McConnell /

If I remove it and try to replace it with alumiweld, do you have any tips for getting it to match the transfers? Are there any tricks that people use to line things up?

Re: A35 Polini + 19mm PHBG Race Questions

take pics with the cases split, showing the transfers lined up on either side to the kit transfers

Re: A35 Polini + 19mm PHBG Race Questions

those are A55 cases not A35, which is good. you have more sealing area around the ports.

get rid of that epoxy junk, if the case transfers are bigger it wont matter

its a moped, don't overthink it.

Re: A35 Polini + 19mm PHBG Race Questions

Breece McConnell /

Shit.. what makes you say it's an a55? I've been thinking this was an a35.

Re: A35 Polini + 19mm PHBG Race Questions

Breece McConnell /

I will snap some pictures when I get home.

Re: A35 Polini + 19mm PHBG Race Questions

Breece McConnell /

I thought a55s don't have reed. This engine def has 2 petals.(edited)

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