frankenstein carb talk.

[WaveDemon]

I didn't want to junk up the carb specs thread so....

Brand = Riva / Mikuni
Model = Powerbomb 48
Size = 48mm
Quantity = 1
Pilot Jet = 117.5
Main Jet = 132.5
Needle/Seat = 2.5
Spring = 114g
Pilot screw = 1-1/4
Main Screw = 1-1/2
Return line restrictor = 60 main
- - - - - -
Gas Octane = 93
Altitude = Sea level - 700ft
Main type of riding = Freeride
Would it pass the 10 second WOT test = YES!
Powerband = Bottom, midrange, top
Motor type/setup = 760 Frankenstein (62T cyl/61X case), heavy homemade cylinder porting, case porting, 175psi head, Factory "mod" B Pipe, Stock ignition, lightened stock Flywheel, stock F/A.

what pop off does that give you?

Spring should read 115g. Gives approx. 19psi.

Always verify the popoff pressure with a gauge. The springs can be very inaccurate.
This past weekend, I double-checked popoff in my 48 Full Spec. I had 2.3 N&S and 115g spring - this should give 22psi.
Two 115 g springs gave me 26-27 psi, and a third one gave just below 20.

thanks. I'm using a guage. I've got some low end problems with my frankenstein I finally got running this weekend. I'm using a 120 pilot with 15 psi pop off. I'll raise my pop off to be a little above yours to see how that works out for me. my main is way bigger 142.5 I think. my big hit is missing so I'm probably off there too..

 

[Matt_E]

What carb?

 

[WaveDemon]

46 buckshot. (formerly an oem 44)

 

[Matt_E]

Can't say for sure. Smaller diameter carbs should generally need smaller jets than larger carbs, and higher popoff.

But jetting itself can be quite a bit different.
Example: I run a single Full Spec 48 on an engine very similar to the Frankenstein. It's jetted at 22psi, 135p, 145m. The Riva is at 19psi, 117.5p, 132.5m
Phill ran a 61X @ 84mm on X cases with OEM 44 @ 130p/150m

 

[WaveDemon]

Brand = Riva / Mikuni
Model = Powerbomb 48
Size = 48mm
Quantity = 1
Pilot Jet = 117.5
Main Jet = 132.5
Needle/Seat = 2.5
Spring = 114g
Pilot screw = 1-1/4
Main Screw = 1-1/2
Return line restrictor = 60 main
- - - - - -
Gas Octane = 93
Altitude = Sea level - 700ft
Main type of riding = Freeride
Would it pass the 10 second WOT test = YES!
Powerband = Bottom, midrange, top
Motor type/setup = 760 Frankenstein (62T cyl/61X case), heavy homemade cylinder porting, case porting, 175psi head, Factory "mod" B Pipe, Stock ignition, lightened stock Flywheel, stock F/A.

OK, my new powerbomb should be here in a couple of days. I'm going to order/pick up the jets for it today. where does the inline restrictor go?

 

[Phill]

Matt has mine right after the return line fitting comming off the carb....something like an inch away.

 

[WaveDemon]

Matt has mine right after the return line fitting comming off the carb....something like an inch away.

is it just a main jet shoved into the return line or is there some kind of fitting it is in?

 

[Phill]

I cant remember for sure....it seems like he has a fitting in there too. I guess I should look at that kind of stuff..... He should be online soon....I'll let him explain......

 

[RoyalFlush@PCB]

is it just a main jet shoved into the return line or is there some kind of fitting it is in?

They make a fitting for it that the jet screws into. I believe RIVA carries it. :cool2:

 

[RoyalFlush@PCB]

Here ya' go, Tim: http://www.rivayamaha.com/RivaStore/product_page.asp?Category=Fuel Line Return Restrictor

 

[Matt_E]

I simply use a male-male hose barb. Put a 1-2 inch long piece on one end, put the jet in that, and put it on the return line.

Or, get fancy and get that bling Riva fitting. Somehow I don't think that's you, Tim. :fingersx:

EDIT: Just looked at the Riva piece. My, what a surprise. :lmao: male-male hosebarb. Except theirs is threaded. And costs $14.99.

 

[WaveDemon]

I couldn't get a 60 main jet for the return line. they had 50 should I use that or drill it bigger or get a real 60?

 

[Matt_E]

Can you get a 55, 57.5, 62.5, or 65?

You could get a 0.6mm drill bit for the 50 main

 

[WaveDemon]

Can you get a 55, 57.5, 62.5, or 65?

You could get a 0.6mm drill bit for the 50 main

there jetting box sucks. the other 2 jets were pretty close.

 

[WaveDemon]

after some restrictor problems and Tom21's slick jetting hone on a welding tip the new carb rips!

Thanks for the specs Matt!

 

[Matt_E]

:biggthumpup: Glad it works for ya.

What carb did you run before? Big difference now?

(I ask because I never ran a different/lesser carb on my Frankenstein)

 

[WaveDemon]

I ran a buckshot before but that was before case porting. It had a huge sudden hit before now it’s more smooth. I’m not sure if it’s more smooth because of better tuning, porting or the carb its self.

 

[RoyalFlush@PCB]

I ran a buckshot before but that was before case porting. It had a huge sudden hit before now it’s more smooth. I’m not sure if it’s more smooth because of better tuning, porting or the carb its self.

All that matters is it's better...:biggthumpup:

 

[JustinB]

I didnt want to start another thread, so I'll bump this old one. I need some help jetting my new Frankenstein build. It is a stock 760 cylinder, with stock 61x cases and 44mm carb. I will be using a Protec "A" pipe with either a stock 61x manifold, or I may buy a Protec manifold. Anyone have any ideas where I should start?

64x cylinder and head
61x cases
stock 44mm carb
Protec A pipe
61x electronics

Jetting I got from Protec for the pipe with a 61x cylinder is as follows:

main=135
pilot=120
spring=65
needle and seat=2.3
high adj=2 turns out
low adj=1.5 turns out