Moby polini av10 build having issues

Reaching out for maybe a dumb tip to help get my bike right. This is my first french build to this extent. The issue I'm having repeatedly is I can get about 1/4 mile down the road about 0-53 mph then I'll fuel starve regardless of float height, gas cap on or off and jetting.

My set up is polini av10 race cases

Factory 4 petal

21 phbg matched intake

Artek crank

Parmakit 74cc air cooled

Gianelli 97mm pipe

Ere clutch less variator

Ere clutch less pulley

Le parti at 1.1 btdc

Red engine spring

With an inline on off 1/4" fuel shut off

Fuel is flowing, I have no air leaks, everything on the build is fresh, I've tried 3 different carbs, 2 complete different ignition set ups new out of box, different plug boots, different coil wires, played with float heights, played with jetting and filters as well as no filter. Is a fuel pump something I should try? Any other recs i should try? I'm just tryna rip this bike. Any tips are appreciated.

16483191627314045249949711721795.jpg
16483192013143018546840599189445.jpg
16483192446194482971609713930339.jpg

Re: Moby polini av10 build having issues

Totally normal JBOT /

Are you sure the petcock flows fast enough?

I’ve had probs with partially clogged filters in the petcock that gets worse once riding cuz debris is still in tank.

Try a aux tank with no petcock and see what happens

Re: Moby polini av10 build having issues

Conan shifty smo G /

That's a good idea, I'll give that a shot. Fuel seems to be flowing just fine, no fuel filter. When I feel it cutting out I've just come to a stop and let the float fill back up and the. Turn around to the shop and it just does the same thing

Re: Moby polini av10 build having issues

Totally normal JBOT /

I have had this issue with my hobbit with stock tank. On top tanks with only an inline petcock I’ve never experienced this issue. Fuel flows fast and easy

Re: Moby polini av10 build having issues

It's been a long time since I had a Moby w/ PHBG, but I remember a couple of tips I heard to improve fuel flow. Moby 70cc+ engines tend to be very 'buzzy" with vibration so the spring loaded needle was recommended to me and I think it did help my build.

Also the "metal disk" mentioned in the Wiki is another potential factor. Try removing it if you are using it, or if you are not using it maybe try opening up the holes and running it to see if there is a difference.

"It sits between the main jet and diffuser tube. It was designed to break up air bubbles in the fuel when high vibrations cause foaming within the carburetor Bowl. This help prevent air bubbles getting trapped within the fuel metering system which would cause an extreme lean condition under high throttle power demands. Many have removed this disk because the new fuel which has been developed has different properties of tension thus it tends to trap the air bubbles underneath the apron causing extremely lean conditions under high vibration modes at full power or close to it. By enlarging the holes in the disc will allow the air bubbles to flow through this mod must be done especially if you're running fuel with any alcohol in it and most new fuels due to the difference in the chemical blending from when this device was originally designed to work with the fuels properties of tension.

I have found that running carburetors that suffered from heavy foaming that by reinstalling the disk with larger holes assisted greatly with breaking up the bubbles and causing them to move away from the main jet pocket under the desk."

Re: Moby polini av10 build having issues

On my "thirstier" bike I jumped up to 1/4" exit petcock and 1/4" fuel lines and the 24mm+ carbs typically have 1/4" inlets. That's always my first attempt before I'd go fuel pump. Vacuum operated fuel pump would be pretty simple to rig up though, and could be necessary to get fuel flow stabilized on that particular step through setup.

Sometimes step through frames have a hard time pushing fuel nicely.

Could totally be vibration/fuel foaming issue aswell.

Have you tried a polini CP carb? Those have a nice anti-foam setup built in.

Re: Moby polini av10 build having issues

Dirty30 Dillon /

Similar setups have known foaming issues as stated above, which cause breakup under load/throttle, then ride just fine.

Re: Moby polini av10 build having issues

> Mike Boyd wrote:

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

> It's been a long time since I had a Moby w/ PHBG, but I remember a

> couple of tips I heard to improve fuel flow. Moby 70cc+ engines tend to

> be very 'buzzy" with vibration so the spring loaded needle was

> recommended to me and I think it did help my build.

>

> Also the "metal disk" mentioned in the Wiki is another potential factor.

> Try removing it if you are using it, or if you are not using it maybe

> try opening up the holes and running it to see if there is a difference.

>

> "It sits between the main jet and diffuser tube. It was designed to

> break up air bubbles in the fuel when high vibrations cause foaming

> within the carburetor Bowl. This help prevent air bubbles getting

> trapped within the fuel metering system which would cause an extreme

> lean condition under high throttle power demands. Many have removed this

> disk because the new fuel which has been developed has different

> properties of tension thus it tends to trap the air bubbles underneath

> the apron causing extremely lean conditions under high vibration modes

> at full power or close to it. By enlarging the holes in the disc will

> allow the air bubbles to flow through this mod must be done especially

> if you're running fuel with any alcohol in it and most new fuels due to

> the difference in the chemical blending from when this device was

> originally designed to work with the fuels properties of tension.

>

> I have found that running carburetors that suffered from heavy foaming

> that by reinstalling the disk with larger holes assisted greatly with

> breaking up the bubbles and causing them to move away from the main jet

> pocket under the desk."

I have always wondered what that disk was for, very good info here!

Re: Moby polini av10 build having issues

What's up with the motor mounts? Is it a washer with a conventional rubber mount or did you do some kind of custom aluminum hard mount thing?

Motor mount issues can make the foaming really bad. Usually spigot mount carb it's not a problem so much, but who knows. Every kit, crank, variator, intake is going to have a different vibration.

Re: Moby polini av10 build having issues

> Graham Motzing wrote:

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

> What's up with the motor mounts? Is it a washer with a conventional

> rubber mount or did you do some kind of custom aluminum hard mount

> thing?

>

> Motor mount issues can make the foaming really bad. Usually spigot

> mount carb it's not a problem so much, but who knows. Every kit, crank,

> variator, intake is going to have a different vibration.

He has a washer over the rubber bushing, I do this sometimes as well, it gives the rubber less area to rip away on big vibrating kits

Re: Moby polini av10 build having issues

Putting the big washer over it basically negates having a bushing still all. You’re gonna snap those rusty motor mounts off that frame for sure.

Re: Moby polini av10 build having issues

> Daniel '' wrote:

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

> Putting the big washer over it basically negates having a bushing still

> all. You’re gonna snap those rusty motor mounts off that frame for sure.

I've never snapped a mount (I have built probably 15 Mobys), the washer shouldn't be flush on the frame, it just helps the engine bolt from ripping the rubber

Re: Moby polini av10 build having issues

What helps the rubber not rip is setting the correct preload on the engine bolt. You know, just because you have built a bunch of bikes doesn’t mean you know what you’re doing. I have worked on thousands of mopeds and still learn new stuff every day.

Not saying I’m above sketchy fixes, but with mobys, especially tuned ones, you have to dampen all the vibrations. Like even using silent blocks to make a support for the spigot carb mount to mount to the case and rubber hose to mellow the spring rattle, don’t forget to lock wire every nut too! Otherwise you end up with a buzzy-rattle trap that’s main purposes is ejecting hardware and foaming fuel. (edited)

Re: Moby polini av10 build having issues

Looks like the original stock petcock! It’s a fuel delivery issue end of story unless the motor was built wrong. The float bowl can’t refill quick enough. Have you tryed just going reallly slow, if it only happens at wot then it just can’t refill quick enough. (edited)

Re: Moby polini av10 build having issues

put a polini cp carb on so much easier to tune. and that is the strangest variator weight set up I've ever seen but hey if it works. I also set the le partie at 1.5 and higher rev bikes normally need a colder plug i run a ngkb9hs. now go tinker have fun hope it helps

Re: Moby polini av10 build having issues

Conan shifty smo G /

I'm pretty well versed in the phbg, but yeah maybe I'll try that carb, I haven't touched this since the post was made. But my french friends helped with the variator set up, and it do be variating good, and I set timing tight cause I been told the big kits don't really be doing them high rpms, and when I set it at 1.8 it blew up in like a mile, but could have been other mistakes causing that

Re: Moby polini av10 build having issues

Oh fuck 1.8 is a lot of timing, I usually start around 1.1mm. If you’re using the included parmakit head too the compression ratio is bananas, you’re gonna need to turn it out and get that compression down to about 140 or so.

Re: Moby polini av10 build having issues

The CP carb is a lot lighter, and it's got a nicely designed fuel retainer disc in the bowl so it might be quite a bit better with fuel foaming. That was the first thing I noticed when I got it, lots of nice touches that should be great for french bikes.

In my experience it hasn't been great to tune but I really haven't put much time into it at all, it's still fuck off winter in my neck of the woods.

Re: Moby polini av10 build having issues

todd amundson /

I have solved the same issue on many bikes by:

1: I install a new plug

2: Remove and remount the exhaust. Nine out of ten times a slight leak at the header opens up at higher speed dropping back pressure and killing the revs. It feels as if you run out of gas but once bike is brought back to idle, you can start riding again until pressure builds then drops off.

3: Increase your variator weights

Want to post in this forum? We'd love to have you join the discussion, but first:

Login or Create Account