Bike almost there, slight fueling problem though. Thoughts?

[Taipan]

I have a set of carbs on my bike which have a Dynojet set up in them. Set up is as follows;

DJ136 mains. 17.5 pilots. DJNeedles 2nd clip and with the oem washers fitted as per DJ recommendations. Mixtures 2.75 turns out. BMC street filter. Standard headers. Scorpion street extreme (baffle in) slip n can. I haven't checked float heights.

Bike runs fine overall and pulls hard and power feels nice and linear. My problem is 1/8 to 1/4 throttle cruising. Bike will dip or stumble if you open the throttle after cruising at this throttle opening. Trying to deliberately ride along for any distance at the most minimal throttle opening in say 2nd or 3rd gear will result in the bike stumbling about and even cut out if you pull the clutch in. Backing the mixture screws in to 2.5 turns improved things greatly but the problem is still there in a lesser severity.

I balanced the carbs using my carbtune but aren't convinced its 100% as my gauges are worn and the rods seem to stick. but switching over vacuum tubes to the different columns makes me think I'm as near as damn it? They were definitely out according to my gauges though and there was certainly a very noticeable improvement in the bikes performance for the balance!.

So any ideas on what could be causing this stumble at just off idle? Is it jetting/needles or could it just be my worn balancing gauges? Could this sort of stumble be in keeping with unbalanced carbs?

[Spanner Man]

Good afternoon.


It sounds as if you have a little too much fuel entering the cylinders when you open the throttle. I have noticed this on a lot of bikes that have been Dynojetted.
You can try winding the mixture screws in still further, & see if it helps. However, if you have them too far in, the engine will idle erratically, due to the mixture being too lean.


Cheers.

[yorkie_chris]

Sounds like a needle issue, has it had dynojet needles in it for any length of time?

[Taipan]

Originally Posted by yorkie_chris

Sounds like a needle issue, has it had dynojet needles in it for any length of time?

Supposedly not but cant guarantee it. The DJ needles wear the emulsions tubes dont they? I have some other needles in the box with a symbol I cant read on and 6E 38-54 on. Are they the standard needles? Better off with them in?

[Taipan]

Well I did move the needle to the middle position and it seems to have more pick up and grunt and the stumble is lessened. But part throttle cruising is still all over the place. 2nd gear 3-4k and its really lurching about. The more you back the throttle off the worse it is. Overall the bike just doesn't seem very smooth or crisp, although its better (or less noticable?) at higher RPM?

[yorkie_chris]

Steady state is on pilot screw, much higher rpm cruise it will transition to jet needle part

[Taipan]

I'm going for one last balance and needle height adjustment and then I'm going to just refit a standard set of carbs with shimmed needles and different MJs. What MJs do folk use for such a set up?