Carburetor Drippling

[Smith]

Looking for some ideas and feedback

I have a set of blackjack 44s on a Dasa 950 that has a 4mm stroker crank

I have rebuilt the carburetors including the needle and seat and the rear carburetor is still drippling fuel

What causes this?

Been reading up on tuning and contemplating trying to increase the pop off pressure, seems like some have had success with this.

Any suggestions or recommendation for carburetor settings?

 

[Freakie]

double up on the anti syphon valve under the little removeable kidney inside the carb chamber as a start ....that works for most situations.....thee is an upgraded kidney that came out in later carbs that also solves this problem due to how the fuel flow is changed.

 

[JetManiac]

Is drippling like dripping but a little more?

 

[Smith]

Sorry I am newer to this carb style -what is the anti-siphon? is the anti-siphon the clear plastic plate screwed down on the backside of the kidney piece? looking at the mikinu manual - is it part #12, the checkvalve on the back of the kidney piece?


the drippling is not enough to make a droplet but when running you can see a small stream/residue falling down from the hole above the venturi. this is the hole where the primer fuel is shot in when priming. when engine is runnning its like a tiny water fall down the side of the carburetor. For some reason only does it on the 1 carb closest to the pump?

 

[JetManiac]

Sorry I am newer to this carb style -what is the anti-siphon? is the anti-siphon the clear plastic plate screwed down on the backside of the kidney piece? looking at the mikinu manual - is it part #12, the checkvalve on the back of the kidney piece?

Yes.

 

[Smith]

I disconnected the primer but looks like the fuel is coming out of the small
ports around the venturi

 

[Quinc]

Contact Art at jetworks and ask him. (Art is one who builds and sells blackjack carbs.)

 

[stefan]

double up on the anti syphon valve under the little removeable kidney inside the carb chamber as a start ....that works for most situations.....thee is an upgraded kidney that came out in later carbs that also solves this problem due to how the fuel flow is changed.

x2 on this one

 

[DylanS]

I had cool fella on here send me a sheet of plastic once, about twice the thickness of the standard check valve plastic.
He cut out his own check valves and I did the same and it worked better than stacking valves imo.
Also the gp800 kidney blocks are the ones you’ll want I believe.
You can also bump your pop off and raise your low speed jetting a little.

Low pop off pressure, high fuel pressure, worn needle tip or sides/defect in seat, worn check valve, etc can all cause this but most times it’s low pop off pressure coupled with the violent shaking from the motor.

 

[Smith]

Thanks for all the ideas and input.

Tested my pop off pressure both are close to 26psi. Should I raise this up to a higher pressure?

I doubled up on the anti-siphon check valve

Has new needle and seats 2.0 size

I'm at a lose, not sure what else to try, is there anything else to replace or adjust to help correct this

 

[DylanS]

Thanks for all the ideas and input.

Tested my pop off pressure both are close to 26psi. Should I raise this up to a higher pressure?

I doubled up on the anti-siphon check valve

Has new needle and seats 2.0 size

I'm at a lose, not sure what else to try, is there anything else to replace or adjust to help correct this

You shouldn’t be having this much of a issue at 26psi
Have you checked your fuel pressure?

 

[Smith]

I have not check fuel pressure, is there any specific way the is best to due this?

 

[DylanS]

Good info here
Should answer your questions

importance of the correct return jet sizing

I recently discovered after spending countless hours on here searching for advice and trying every logical jetting combo known to man I started to see a lot of people post issues similar to the problems I was having and struggling to get their ski tuned properly and it always seemed to ended up...

www.x-h2o.com

 

[Smith]

thanks

 

[fastgtfairlane]

Good info here
Should answer your questions

importance of the correct return jet sizing

I recently discovered after spending countless hours on here searching for advice and trying every logical jetting combo known to man I started to see a lot of people post issues similar to the problems I was having and struggling to get their ski tuned properly and it always seemed to ended up...

www.x-h2o.com

Exactly what I was gonna suggest. Check your return tee for a main jet on the outlet side to the tank. I'd imagine that most blackjack carbs have the returns drilled out so the fuel pressure can be adjusted

 

[Smith]

Thanks for all the info,

Am I understanding it correctly? that you can place a restrictor inside the carburetor or on the return line to the tank?

Either works?

Does anyone know if the blackjack carbs are typically drilled or have any restrictor modifications?

Where do people typically install an inline restrictor?

 

[fastgtfairlane]

The internal restrictor inside the carb is not adjustable, drilling them makes the fuel pressure adjustable by changing the jet that us tapped into the outlet side of the return tee. This will equalize the fuel pressure between both carbs making them easier to tune.

 

[Wetbuffalo]

I had cool fella on here send me a sheet of plastic once, about twice the thickness of the standard check valve plastic.
He cut out his own check valves and I did the same and it worked better than stacking valves imo.
Also the gp800 kidney blocks are the ones you’ll want I believe.
You can also bump your pop off and raise your low speed jetting a little.

Low pop off pressure, high fuel pressure, worn needle tip or sides/defect in seat, worn check valve, etc can all cause this but most times it’s low pop off pressure coupled with the violent shaking from the motor.

Any idea what this material this plastic was?

 

[DylanS]

Any idea what this material this plastic was?

@cudaben was who sent me it, I can’t remember what exact plastic but it was a blue sheet.

 

[Smith]

Looks like my problem is most likely fuel pressure, my returns are not drilled

Got some jets on the way, any suggestion on what size to start with?

The return line off the carburetor is always the upper?