Advise Jetting for New Setup.

[Foximus]

So Ive searched through a couple threads but none would seem to apply directly to what I have done. Im putting together a totally new motor setup and I have NO idea on even where to start on jetting. For one, I have only worked on jetting dual 38s with a filled crossover.. My pilot was 65. I know 44s need a much bigger pilot but I have no idea how big....

Anyway, mysetup is this. 100% new to me so I have absolutely no baseline

Ported and epoxied 62t cases. I filled the voids and ported tunnels into the transfers. I also filled the finger and made the ramps. The transfer bowls have been previously rounded and blended on the inner edges.

Im also running a Tim Judge/Riva cylinder, Riva non girdled head, 35cc domes. 3*static advance. FPP limited SJ chamber.

OE 760 intake (filled crossover) OE 44s, ProK F/A's, 760 reeds (may move on to VF2's? Unhappy with Boysen Rads)


Other things that may relate, im running on a kawi 140 pump with a 9/17 hooker impeller, a TBM pump cone, RAD alum flywheel. I know these wont directly effect jetting... but perhaps somebody knows something I dont.


I know that without exact porting spec I wont be able to get perfect jetting, however the cylinder hasn't been delivered yet. Was just hoping somebody could give me a good idea of what to expect for jetting. Should I use 1.5 seats... 2.3? On my dual 38s I went for a 30psi popoff. Should these be more like 15-20psi?

As soon as the cylinder is delivered (hopefully today) I'll be able to take measurements and better pictures, and hopefully Judge himself will know what to tune to... but until then... I'm ansy.

 

[Foximus]

My cylinder just came in. I need to crack the head off to get some good measurements.... But damn this thing is beautiful.

 

[Matt_E]

I ran something similar on 2.0 N&S, 24psi popoff, 115 pilots, 122.5 mains.
No guarantee it will work, but maybe it's a place to start.

 

[Foximus]

Ok... cool. So main jetting is somewhat similar to 38s... At least mine. Lows are much higher though



Dunno... should I take measurements of the depth of all the ports or should I try and get a degree wheel and find the timing?

What would be the best way for someone to help with the jetting?

 

[orangefinger]

Here are my 760 Jetting specs Dont know if this will help

- Dual44mm OEM
-Ada girdled 180
-B Pipe
-Ported 760
-61 electrics with msd enhanc

Pilot 122.5 changed to 120
Main 135 changed to 130
H screw 1
L screw 1
1.5 N/S ( stock )
80 Gramm Spring
pop off forgot

Hope that might help

 

[Foximus]

Interesting.

This is a 61x cylinder. However it has some traits I'm not used to seeing. The intake side skirt has been narrowed, and in front of the transfer runners the sleeve has been... removed... similar to that of a kawasaki. It is no longer flush with the bottom of the cylinder.


Also the boost port is not raised, but is lowered about ... 4-5 mm or so.

Its still at a very steep angle, I believe stock is 60* or so, and this may be even steeper than that. The transfer port roofs are not flat the entire way like a stock cylinder, yet right before the sleeve and the sleeve itself are flat as a table.

If Riva is open tomorrow I will be calling them and see if they kept any porting notes on cylinder serial numbers.... this has some ID engraving on the side

 

[Matt_E]

I looked at the cylinder pictures.

There really isn't anything unusual about it. I used to port my cylinders similar to that (not nearly as pretty, no math behind it) and they didn't require weird jetting.

 

[Foximus]

Alright. What would be the difference between a 1.5, 2.0 and 2.3 N/S in this instance? I'm assuming that with to low of a popoff on 44s, with a larger seat, the carbs may leak at idle and overload to easy.


To small and it will have a crappy lean middle transistion, and to high of a popoff, it will do lightswitch?

 

[Big Kahuna]

Contact Tim Judge, he did the cylinders.


That your best guess.
Also, check the TECH FAQ section, there is a post that Randy at WATCON did that is a no brainer on Jetting and carb setup.

 

[Foximus]

Alright, Ive read the watcon writeup. I'll read over it again and get it all fresh in my mind.

I guess what I was really asking was, 44s are far more susceptable to N/S errors because of the lower pressure, unless 38s which seem to run fairly well on anything from 30-55 psi depending on your F/A. I always hear about people running 15-25 psi on 44s...

 

[orangefinger]

if i can recall the pop off was # 37 on my 44's

 

[Foximus]

So Tim told me the cylinder was ported by a guy named Scott Palmanofski or something of that sort of last name.

He recommended 20-25 psi popoff, a needle and seat of 2.3, a pilot of 115-120, and a main of 120 for starters.


Gonna try to get those in a bit.