Zbox New Carby-Fuel Starvation ?

[abbmota]

Hi all,
My first question here, most of my MB issues I have solved thanks to the MB forums.

But this probable fuel problem is new to me.

The set up:
ZBox 70cc, (new, not full run-in yet )
After market copper lead
NGK Plug Cap
NKG BP6HS plug (.025 )
After market Brass petrol tap/ in-line ZBox filter.
Standard kit fuel line.
Exhaust gasket port matched
Drilled holes inside muffler pipe tube.
Have not removed alloy inlet manifold to port match in-manifold gasket, yet.
No kill switch/wires soldered, no crimps. ( I don't want a kill switch)

Symptoms;
Will run well, then it will surge till I let off the throttle a bit, then it will run fine again.
At half throttle the surge does not happen.
At full throttle at less than 1/4 kilometer the surge will happen.
suspect fuel starvation ?

I have not yet taken apart, fiddled or adjusted anything on these ZBox "New Carbys",
but ther engine runs very well in comparison to those other standard carby, (no air leaks).
If I give it a bit of choke, it run much better to and did not seem to surge.

If this seems like fuel starvation, what can be done ?

Are there any threads specific on the ZBox "new carby" ?

Thanks

 

[Dave31]

This seems to be a common problem on all engine kits.

One, could be lose motor mounts that cause a vibration which will cause a fuel delivery problem.

Two, fuel valve on tank not flowing properly.

Three, filter screen inside tank plugged and not allowing proper fuel flow.

Four, gas cap not venting properly to allow fuel flow.

Five, carb float to low

Six, possible gunk inside carb

I'd start with that and then go from there.

 

[abbmota]

Thank for the reply and confirming my "suspects" fairracing31;

1:Engine mounts are fine
3: there is no filter inside the tank, it has an after market brass tap and inline filter.
6: All brand new, I don't think there is any gunk, but I'll check when checking bowl level.


Could be 2,4 and 5

Two, fuel valve on tank not flowing properly.

Four, gas cap not venting properly to allow fuel flow.

Five, carb float to low

I have posted a pic to show the setup

 

[wildemere]

Try it without the air filter, if it improves then get a better/bigger one.

I had issues with the stock filter on mine.

 

[abbmota]

Update
I started at the fuel tap. I have tried more expensive brass fuel taps that cost $25.00 each (AUD) and they work perfectly
This time I thought I would try the $10.00 brass tap

When taking these apart, it was obvious the "tunnels" the fuel travels through are too small.
All I could do was drill them a bit larger using a 3.5mm drill bit.
On test, 20km round journey there was a slight improvement, but still starved.
However the "recovery time" was alot quicker than before I drilled out the $10.00 fuel tap.
Also, there is no way knowing what is Off or On, the tap can spin 360 degrees.
I would rather spend the extra $15.00 and know it's right the first time and Made in Australia, mate...,

Ongoing...,
this may take a while to finish the process of elimination due to other teething things while running in.
Overall everything else is OK. Good pick up, smoother idling and no carby leaks at all.

 

[Norman]

getting plenty of fuel to the carb float not sticking or clogging off poo in the floats bowl?
did you check the dia of the main jet size it will make the engine surge if its too small. Here is the size 0.026" is where most are nice and round hole not wobbled out like some I've seen?
norman

 

[Nashville Kat]

Play play play with your petcock!

When I closed mine almost horizontal, but not all the way this problem goes away-

If you ran w/ filter off, you'll probably find gas spurting out the air intrake-

TOO MUCH GAS, not too little

Also- does even very slight closing of choke damp the motor?
Ten too much gas to air-

I thought the opposite too- not enough gas, but discovered accidentally the petcock thing when I went to run the fuel out of the line before taking the bike inside

I can't wait to get out again-
a couple of miles and playing with petcock confirmed it-

All the way open, and it still died at speed-

petcock only slightly open, and it runs better than ever-

Really relieved here,

but I think the carb is not so good and LEAKS like crazy- there must be other that would fit

I'm also going to install an inline filter, and see if that helps the fuel line surge

 

[abbmota]

Just a quick update, had stuff to do being Friday, this time 50Km round trip.
It worked well, postioning the tap at various minute locations, then all of a sudden, no go !.
I looked at the tap, overall engine vibration caused ot to turn slightly dowwards, to wards the Off postion.
I will simply replace the tank from the old bike that has the $25 petcock to rest my mind and then at least this piddly doubt is gone, and tune the rest of the bike as it is approaching towards the end on run-in. This carby I will buy again, no leaks whatsoever, no problems with choke and I don't need a kill switch anymore, I simply pull the chole lever to stop it.
This means less electrical restrictions and less wiring etc.
ongoing in a few days time, a bit busy now..,
Thanks for all who are putting in to this thread, I have noted it and checking all that is suggested.

 

[abbmota]

I believe the fuel starvation symptoms are solved.
The $25.00 Brass Pet Cock Wins. No leaks, No Fuel starvation and bike runs sweet.

The cheaper $10.00 brass version is a hassle and the aluminium standard kit version eventually they leak and is a eye sore anyway.

 

[Rockenstein]

25 dollars for shutting down the fuel flow?? Yikers!

I get my fuel flow stoppers 4 for a dollar at Dollarama...lol...yea I'm that cheap but hey they never leak

.

 

[abbmota]

25 dollars for shutting down the fuel flow?? Yikers!

The amount on money I have accumilated by not paying to run a motor car, justifies raising the quality on my motored bike.
It costs approx., $150 to register and insure a small 4 cylinder car for 3 months, plus on road cost and alll the rest of it. Lets assume $250.00 PLUS fuel and oil for 3 months.
$50.00 per week on fuel, 4 weeks = $200, multiply by 3 months is approximately $600.00 in fuel

$600.00
$150.00
$100.00
--------
$850.00 total
I would have had to fork out had I not built my motored bike.

Yeah, I can justify a quality made Brass Pet Cock @ $AUD25.00, the money stays here and the product is correctly engineered, works like it ought to, it's either On or Off and no 360 degree guesswork.
I save on fuel leakages, peace of mind and that is priceless.
Brass lasts almost forever.