I need jetting help....

[StuJohnson]

Thanks you rock.
One more quick question that I forgot.
The air fuel mixture screw
I am about 1 3/4 turns out ....
What are the basic guidelines in setting it?

Also what is with the plastic idle screw.? Is the thought process here that the plastic won't back out from the vibrations ?

[Jakobi]

Air screw is for idle mix and off idle. If you close it the bike should stall. If you open it past 2.5 turns you're better off moving to a smaller pilot. Ideally when the bike is up to temp and cleared out you should be able to adjust the air screw for the best (highest idle). Signs of being too lean is that the bike will bog when cracking the throttle quickly from idle. Too rich you'll have a lot of burbling.

The idle screw just lifts the slide up. Plastic/brass is used so that it doesn't damage the slide. Plastics cheap The spring is to stop the vibes from backing it out. Quick hint - open the throttle up when adjusting the idle to reduce strain on it.

[n_green]

Fitted Jake's 38mm to my bike and fired it up for the first time today. Used 42p, N3CJ #3, 178main as recommended by Jake and pretty much every other GG rider with a 38mm carb that rides in Australia.
I dunno whats wrong with my bike but something isn't right. I left the AS at 1.5 turns and warmed her up, cracked the throttle and there was a massive lean bog right off idle. Crack the throttle and BUH nothing, almost stalls then clears and comes good, thought ok had a play with the air screw wound it right into 0 turns and it still ran for a fair while.
Put in a 45 pilot which was then too rich and the air screw didn't have too much effect at all.
Put in a 40 pilot for comparison, lean bog is back but with air screw at .5 turns out is pretty much gone but definitely still there. Threw the 42 back in and best setting seemed to be .75 turns but again the bog is still there.

Threw in a N3CW #3, the air screw actually started working with this needle and the 42 pilot, best air screw setting seems to be about 1 turn out but whilst the lean bog has all but gone riding it round the back yard its obvious it lacks torque.

Weird thing is the bog is the only sign of being lean, there is no hanging idle. Regardless of where the air screw is set it actually seems to settle quite nicely to a decent idle.

I'm confused for two reasons, firstly the above info and secondly the fuel my bike seems to desire, how is it possible it requires so much more fuel then any other Gasser in Australia?

So what could cause the lean bog just off idle I've suddenly developed?

[Jakobi]

I could always get mine to hesitate slightly when cracking the throttle fast from a very low idle, if not entirely up to temp. Its the trade off for the clean bottom end. I could have run a larger pilot to act as an accelerator pump.. Never any issues with torque for me though. With the 40 N3CW 178 I could chugg around in 3rd gear at walking pace all day long, and easily loft the front off band in second from a stand still.

Strangely enough, the Smart Carb is giving me the exact issues you're having..

What effect does raising the idle have on the hesitation?

[Jakobi]

I was also thinking last night. Have you ever checked the overlap on your transfer ports (case to cylinder). I wonder if its possible your cases are further out than everyone elses and restricting flow.

[n_green]

Not sure but I've decided to do the top end on it and while I'm at it check/replace all the gaskets to rule out an air leak anywhere. Doubt this is my problem as its only affecting bottom end jetting and no where else. Ill go over the port clearances while I've got it apart.

[n_green]

As Jake says "you can't jet around an engine issue". Thats true as I found out. I had a leaky stator side crank seal and also suspect reed cage gaskets. Replaced them and its a better bike.

I still found I'm having to run the W diameter needle with the 42 pilot as the J diameter is too lean on the straight section but it has been pretty cold here lately (avg 10-15 deg C). I stuck a N3EW #3 in the 38mm carb with a 42p and 178m and the air screw works well now. The best setting is right on 1.5 turns out.

Quick squirt up and down my street tells me I'm in the ball park, I reckon I'll have to play between the N3EW and N3CW for the best setting but I'll do that when I'm on the dirt and can really play with it.

[n_green]

Had a good ride on Sunday in what could be called ordinary conditions. Was a 14k loop and it was bloody hard work in the wet. 90% of it was first and second gear low throttle openings with a small stretch of 3/4 gear on the pipe trail.
At the beginning of the ride I threw the N3CW #3 in. It's still rich off the bottom, you can hear it burbling away at low throttle openings. The transition onto the pipe was pretty smooth and dull too which makes me think its rich throughout. I was too busy trying to stay upright to tinker so rode it as it was. Fuel economy was crap - 5.5l of fuel for 30k's of riding.

The jetting headache continues.


http://youtu.be/Oh0WY1-U6jY

[Jakobi]

Try N3EW#2 and ride again.. That slow muddy slopfest chews fuel.. While your front wheel did 30kms I bet your rear did a whole lot more!

[n_green]

Originally Posted by Jakobi

Try N3EW#2 and ride again.. That slow muddy slopfest chews fuel.. While your front wheel did 30kms I bet your rear did a whole lot more!

Good point. Never really thought of that haha.