Need help tuning MK2 Race with 19mm Dellorto.

[icecruncher]

I have a 2004 zuma with a 70cc mkll bbk and 12mm wrist pin stage6 hpc crank with the stock woodruff key, 19mm stage6 dellorto carb that came with a #92 main and #50 pilot. Stock airbox with snorkle and stock exhaust. Green malossi clutch springs.

The accelleration is extremely slow and it bogs up any slope. The idle screw sounds best when it is over four turns out. I am at sea level and I think it is far too rich. I tried changing the contrast spring to polini medium and using both 5gram and 4gram rollers with the stock variator without much difference. I am using a brand new Athena bando belt.

It would be of great help if someone could tell me what range I should expect the jets to fall into? I also need to know if putting in extra variator shims is recommended because the belt seems to ride to the top just fine but it has a hard time staying low (I think) or is the current jetting making that big of a difference? It also dies when I left off the gas right away making me think the pilot jet is way to high.

I am using three head base gaskets with sealent between each one and the o ring on top with sealant. The bike feels like it has great compression because you can feel it really compress air when I try and turn it over by kick start. I will be doing a carb cleaner test after I put sealent all around the intake and air filter box.

Please any advice pointing me in the right direction would be greatly appreciated. I am scared to sieze the engine.

[tsimi]

Get some pilot jets sometime like 37, 38 or/and 40 and a main jet kit for example the Stage6 5mm jet kit #70-92 you want to be around 85-88 with a stock airbox with the snorkel in place.

Start with the mixture screw 1.5 turns out.

Needle W7, 2nd from top position.

Set it up like that and tune from there. Always start with larger number jets and work your way down till she feels crisp and has good response.

Regarding the jets treatland has a wide variety and any spare parts you might need for your PHBG carb. Also get the 36mm airbox adapter to be able to fit the stock airbox easier on the carb.

[icecruncher]

Oct 10, 2017 17:06:02 GMT -5 tsimi said:

Get some pilot jets sometime like 37, 38 or/and 40 and a main jet kit for example the Stage6 5mm jet kit #70-92 you want to be around 85-88 with a stock airbox with the snorkel in place.

Start with the mixture screw 1.5 turns out.

Needle W7 2nd from top position.

Set it up like that and tune from there. Always start with larger number jets and work your way down till she feels crisp and has good response.

Thank you. I should menti9n that the porclin on the spark plug is very white and there was a small clump of carbon on the top of the hook that goes above the electrode.

[tsimi]

White? That would indicate that you are lean or you haven't driven it long enough or the plug got flushed with fuel because too rich.

It is always recommended to tune the main jet first. Go for a couple longer WOT (wide open throttle) runs and check the plug again. I suppose you got at least a BR8 spark plug in there right?

Once you got the main jet set tune the lower throttle positions, 1/4 and 1/2
The pilot jet will affect the tune up till WOT. But only slightly. So once you start to tune the pilot jet you should check again the main jet just to be sure.

Yeah, I know tedious work and those PHBG carbs can be a pain to setup but once you got the right spot they are great.

[moofus02]

That's a nice combo of parts on the motor. The bbk is on the high strung end of the spectrum for a stock pipe. A sport kit with stock pipe is great but that is more on the higher end and a mismatch for a stock pipe. Being rich and the combo might well be why it feels off. If you pull the snorkel out of the airbox it will lean things up slightly. I would be looking for something like a c16 pipe to wake that motor up

[icecruncher]

I am pretty sure the plug was being flushed with fuel. The stock exhaust is only temprorary for a few months. I was thinking of going with a Yasuni R pipe because it aparently has a deeper quieter tone than other expansion chamber exhausts and it will allow me to get past 10,000rpm. Most of my power will be closer to 20,000rpm.

I jet my jet kit today or tomorrow and someone on zumaforums recommended that I go to a 45 pilot and an 88 main so I will try that.

[tsimi]

Sounds like a good plan even though I think 45 pilot might be still a bit rich. But better start rich and work your way down.
Regarding the pipe a Yasuni R is a good pipe looks and sounds nice.
A C16 would be a perfect match but you'll have to remove the center stand to make room for it.
Then there is the Yasuni C16.07 aka. City 16. That pipe is between the R and the C16. You can keep the center stand, she looks identical to the R and comes closer to the performance of the C16
I run the City16 on my Malossi MHR Replica setup and I am more then satisfied with the pipe.

[icecruncher]

Apparently I did not do a proper plug chop but it still has been determined I am way too rich. I need a "quiet" and reasonably affordable expansion chamber exhaust. Is the Yasuni city quieter than the c19? I want to remove the centre stand either way.

[icecruncher]

Okay so after recieving my parts today I installed the proper jets and got it runing good enough that it is a better than stock. Now I will need to take out the snorkle and tune the transmission. Thanks for the help I think I can manage from here.

[Corrosion]

#1 You have a mid-race cylinder 8k to 10k power scheme. With a factory muffler, not a perfect match.
#2 Pull the snorkle from the Air box. Bike need more unrestricted air.
#3 50- pilot is large for an Air box, IMO.

Is ths a true Dellorto, or a clone. A true dellorto comes in 2 or 4 stroke configuration. The needle bushing and atomizer are of different design. A 4 stroke Dellorto will have a different / heavier float too. The float does not seem to mater as much as the correct needle bushing and atomizer.

Here is a photo of the bushings to verify it. Also a link to a decent article on PHBG.





If you have a Clone, I would go over the whole carburetor, check float setting. Also check for correct Bushing & Atomizer. They often have off float setting, and combination of parts that won't work well together.

I would start with a 40-42 pilot jet, and a 82-90 main jet, W-7 needle in middle. snorkle out, of factory Air Box, proably need some additional air holes drilled in air box inlet side, when, or if, you eventually pipe it.


Moped Army has some infomation on the AU budhing & atomizer. I have tuned 4t phgb's to run fine, it is harder but not impossible. The idle and slow speed adjustments are not as precise.

link Moped Army / AU bushing explanation

[moofus02]

Should probably be looking at some up gears. The 04 had 14.64:1 gears and will limit your top speed or require some extreme rpm for fast speed