Tuning dual 44's - couple of questions

[Matt_E]

I am in the process of putting my ski & motor back together. I am working on the carbs right now.

For reference, my setup:

61x @ 83mm bore, FS porting (std port heights, exhaust widened, bottom modified for more flow, intakes roughed, exhaust polished
62T cases, ported
35 cc domes, about 190psi compression
MSD TL, about 30 deg initial advance
B-Mod
VForce 2 reeds, reedspacer
Dual Mikuni SBN 44s on Riva Manifold
Concord 13/16 cutback 3mm

The carbs are currently jetted at 125 low, 122.5 high, and 2.3 N&S. I am not sure what the springs are - but I checked the popoff with the Mikuni gauge last night.
Waxhead recommended about 15-17 psi popoff with that setup. I checked, and it is currently at roughly 22-24 psi in each carb.
Can that difference (5-9 psi) be compensated for without changing springs?
Also, the pop doesn't happen like a clean pop - it sort of opens, and stays open until the pressure bleeds off a bit. It always pops at the same point though.
Any ideas?

 

[Mile9c1]

22-24psi sounds better to me. When you check popoff, put some lubricant on the N/S so it can make a good seal (spray some WD-40 or fogging oil on it, that's what I do).

I'd drop the pilot jets down a bit but that's just my opinion.

 

[Matt_E]

Yeah, I kept the N&S lubed with WD40 during testing. BTW, N&S are brand=new, maybe one hour of use.

 

[Mile9c1]

Your popoff and your low speed jet work together. So if one's too lean, you can make the other rich to compensate. I don't see why you'd need such a low pop-off though (under 20psi).

 

[SuperJETT]

I'd keep the popoff in the 20's also. mid teens is racer stuff and your bottom end will never be clean/crisp.

 

[SUPERJET-113]

not to threadjack, but I rode Butch's new blue boat yesterday with Pauls dual OEM 44 jetting suggestions and that thing hit great with a smooth powerband through out. That ski rips for stock porting/pump gas/stock flywheel with Enhancer. I was very impressed! Oh yeah that Solas pump is very sweet too Mile.

I am learning from all this too. I am no carb guru at all!!

Carry on!

 

[Mile9c1]

Oh yeah that Solas pump is very sweet too Mile.

Kick ass :cheer:

 

[Matt_E]

Good stuff...I'll give it a try.

 

[waxhead]

your high is way to big for my liking i would go for a 100-105 high
i have tried 20 psi pop off and found the ski didnt hit off the bottom like i wanted it to , but try 23 then try 15-17 and see what you think

If your n/s are driblling replace them they are stuffed

the mod chamber has less down low than a limited chamber so it will more than likely need more fuel to get it off the bottom
but then again 30 degrees will help it come off the bottom as well

 

[Matt_E]

Thanks Jared. The N&S are brand-new. The leaky popoff was caused by not enough lube on the needle tip.
I measured both again - right at 24psi.

 

[Matt_E]

Another question: I am pretty certain I do not have a restrictor in the return line.
That would be inside the fuel line, and not inside the carb, correct?

Both return lines are teed together. Would the restrictor then be downstream of the Tee? (Just one).
What size do I run?

 

[Mark44]

Matt,
I am currently running 44's SBN on my Magoo port 62T with glass reeds. I am running a 117.5 pilot 2.0 NS and a 95 gram spring that is giving me a pop off at 29 PSI. I started with a pop at 19 and the increase to 29 worked very well. I am installing a 115 gram to try this week should run the pop to 35-37 on my gauge. I have a slight hesitation right of throttle that I just can’t seem to get out with the pilot jet. If my 115 works out I will then try the 95 gram spring again with a 115 pilot just to see how that performs.

I am also playing with different restrictions on the carbs such as screens don't know what kind of elements you are running but I see possibilities there also.

Your restrictor is integrated into the carb if you are running Mikuni SBN.

Mark44

 

[SuperJETT]

The carbs have a builtin restrictor from Mikuni. Aftermarket carbs have it drilled out so you can run an external one.

If you pull the fuel pumps, you can see it.

 

[Matt_E]

Thanks...that answers the restrictor question. :smile:

I am running a 117.5 pilot 2.0 NS and a 95 gram spring that is giving me a pop off at 29 PSI. I started with a pop at 19 and the increase to 29 worked very well. I am installing a 115 gram to try this week should run the pop to 35-37 on my gauge. I have a slight hesitation right of throttle that I just can’t seem to get out with the pilot jet. If my 115 works out I will then try the 95 gram spring again with a 115 pilot just to see how that performs.

Wow...that's quite a bit different than mine. My 2.3 N&S and 95g spring give me a clean 24psi popoff.
Additionally, the combo of my 122.5 pilot jet and 24 psi popoff make for an even larger overall difference compared to your 117.5 pilot and 29 psi popoff.
Now I am stumped.
Out of curiosity, what's the rest of your setup (motor, pipe, igntion, etc)
What was your jetting starting point?

 

[Mark44]

I am running a limited factory B pipe with MSD CDI on a ported magoo cylinder stock bore a mild port on case. 190 comp.

This thing hits bad azz, never felt a motor hit so hard. I started my pilot with a 117.5 went to 120 then back down. I will have to check my main I can’t remember what it is, I have it wrote down at home. Pop off I started with around 19 now at 29 and increasing for another test. If this pop off increase removes my hesitation I will then be trying 95 gram spring again and 115 pilot just to make sure I am set correctly. Also started with 2.0 NS.

Mark44

 

[Mark44]

I checked my notes last night.
My main jet is 112.5 I started 110 and had to bump it up one. I was running lean at wide open throttle.

Mark44

 

[Matt_E]

I just talked to Paul about my jetting. :smile:
I think I was mistaken about having 2.3 Needles & Seats.

Paul suggested right about 25 psi popoff - which you should get with 2.0 N&S and 95g spring.
I get 24psi popoff, and we both think it's unlikely I would get that number with a 2.3 N&S combo. (I cannot check right now)
He suggested I try 110 Mains and 117.5 Pilots. That setup is almost identical to yours, Mark.
I'll give it a shot.

Thanks Paul! Helpful as always.

 

[Mark44]

That is where I started at just had to bump up the main one size and still working on the low. I am increasing the pop just to see what I get but I may need to go down one jet on the pilot and decrease the pop back to 95 gram after my 115 gram test.
Just can't get this hesitation out but when it hits.........DAMN.

Let me know how you turn out.

Mark44

 

[Blaster94]

Mark is that the set I sold you?

 

[Matt_E]

That is where I started at just had to bump up the main one size and still working on the low. I am increasing the pop just to see what I get but I may need to go down one jet on the pilot and decrease the pop back to 95 gram after my 115 gram test.
Just can't get this hesitation out but when it hits.........DAMN.

Let me know how you turn out.

Mark44

I don't know much about carb tuning, but what happens when you lower popoff? Does it feel any different? The hesitation may be from a too-high popoff.