What carbs to run on my engine?

RSKI

RSKI

Location
Oregon
masterblaster said:
good choice,I have a sim able motor to yours and have run almost every carb on them. 46 black jacks 46 d booster novis,48 and 49 full specs,oem 46s and 44s. All worked well,but 46s made the best power to fuel use ratio for surf riding. That motor rips on tl and bpipe hard in surf,way more than most would expect
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Masterblaster, can you share jetting specs when you had 46's on that engine? I don't have a good idea on where to start.
 
KTM434

KTM434

Jamie FN Hickey
Location
Palm Coast FL
My ski is 200psi on pump gas with zero deto and I do ride WOT sometimes while listening for deto and it's always good but it's for fairly short bursts but that's a carbon hull. I've also ridden Jetmaniacs ski which runs good with no deto on pump gas and his engine is loaded by a 148 mag pump so proper tuning can do a lot for your setup
 
ProSouth

ProSouth

Seriously, Don't be a dick.
Location
kawasakis suck
Waveblaster785 said:
Amazes me the compression some people run on pump gas. I guess for flat water and surf it's fine but damn. Even 210 on AV gas is crazy to me.

Then again I hold my ski open whenever I can.


Sent from my iPhone using Tapatalk
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i generally cant do that on my bob, but ive done wide open runs on my fixed steer with that high of compression on AV fuel
 
wanderer1

wanderer1

Location
Cruising Around
So spend big $ on hull and motor but dont wanna run 110 or VP because of cost? Ok. Detonation can occur and not show symptoms on piston/dome but can really shorten crank bearing life. You want power,thats why we buy big ported motors with pipes big carbs and advanced timing, good fuel makes more power. Just limiting power with lower grade fuel imo. Y'all have fun
 
OCD Solutions

OCD Solutions

Original, Clean and Dependable Solutions
Location
Rentz, GA
Exactly how much more fun do you figure you're having for all that extra money spent on premium fuels and oil?

Articles like the following speak of an extra 5-10 HP gain for over double the fuel cost. Add to that the extra cost of premium oil as well and you have what I believe to be one of the most expensive mods with the least amount of return. Please correct me if I'm doing the math wrong.

http://www.rc51.org/fuel.htm

We've pretty much done the homework for you when it comes to testing various grades & brands of race fuels in the RC51 (or any other motorcycle for that part)
In hours & hours of dyno testing & Powercommander map building several key points were discovered some we intentionally set out to test others just came about on their own:

1. Standard Race Fuel (VP C12, C14, Sunoco 104, 100LL AvGas even high octane pump gas 96 or 100) ran straight on a stock RC51 motor will actually lose horsepower.

This is argued by many because the throttle response becomes crisper & is often mistaken for more performance when in truth the bike is making less power on the dyno sometimes by as much a 4-6hp. Many race fuels are designed for higher compression engines >13.0:1 & simply do not perform well in low compression motors like our RC51 (10.8:1). As has been noted many times on just about every sportbike forum on the net more octane does not mean more power! It simply means more resistance to detonation. If a higher octane fuel happens to make more power in a motor it is because of the additives in the fuel having the potential for more energy not just because it is higher octane.

What can be beneficial, but not always so is a blend of about 25/75 of race fuel & pump gas (1 gallon of race fuel added to 3 gallons of premium pump gas) which has been shown to consistently yield a horsepower or two. However I strongly urge you to stay away from the race fuels on a street bike if for no other reason than the extra contaminants it will leave in your motor. For me the cost of premature wear on the motor is not worth the negligible horsepower gains.

2. Oxygenated Race Fuels (Nutec #4, VP MR1 etc) can add 3-5hp without any fuel or mapping changes at all & 5-10hp sometimes even more on a stock motor with proper mapping & lots of playing around with the ignition timing. Some oxygenated fuels benefit from retarding the ignition while others benefit from advancing it.

The catch is that A. the stuff is really expensive usually about $15-$20 a gallon & B. it is highly corrosive & must be drained from your tank after each race weekend to keep it from eating parts of your fuel system. There are also many true horror stories of racers getting a bad batch of Nutek & ruining a set of carbs or throttle bodies due to a varnish that settles onto the components that is basically impossible to remove. I have actually witnessed this myself once & could not believe how bad it actually was.

There are some newer oxygenated fuels out now such as VP MR9 & Ultimate 4 which is claimed to be much less caustic to fuel system components (o-rings, gaskets etc..). I have sampled the MR9 & was very impressed with the performance & the Ultimate 4 is just plain awesome even in a stock motor, but as the cost of gas soars, $16 a gallon is pretty hard to swallow. I've been mixing it about 50/50 on my stock engines with excellent results. Not as powerful as the MR9, but nowhere near as expensive either.

3. In testing various grades of pump gas I consistently found that 87 octane fuel makes 1-2 more horsepower than those exact same bikes ran on Premium 93 octane. We tested five liter class motorcycles (97 CBR900RR, 02 Honda 919, 2000 RC51, 2000 GSXR750 & an 02 R1) & only the R1 seemed unaffected by the octane of the fuel. Now I am certainly not going to tell you to run less than the recommended octane (92) in your RC51 as the specific needs of the motor dictate that a higher octane fuel is needed, but the results are blatant in that more octane does not mean more power.

It is only fair that I note that when testing the pump gas on some of the 600's (Yamaha R6 & the GSXR600) the inverse was true in that they did lose a little horsepower on the 87 octane vs the 93 octane. Most likely because of the higher compression ratios of the smaller motors, however the CBR600F4i gained a little horsepower.

Additional notes (not tested on the dyno): Never add any type of octane boosters or fuel system cleaners to your motorcycle tank. Additives sold in auto stores are designed to treat anywhere from 16-22 gallons of fuel from one small bottle of concentrate & more often than not those chemicals are very hazardous to your motorcycles fuel system especially if the mix ratio is not absolutely perfect. I cannot tell you how many carb jobs I have done over the years because some yahoo dumped half a bottle (or more) of octane booster into his fuel tank. The bike runs great for awhile but within a day or two a varnish starts to set up on the fuel system components & it just gets worse from there. Run quality fuels & stay away from the additives period.
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Disclaimer: The article only covers the scenario of using high octane fuels in lower compression engines. It does not show how much more power can be extracted from an engine specifically built and tuned to get the absolute most power per CC. In other words, a full blown competition series engine that most people simply do not own.
 
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ProSouth

ProSouth

Seriously, Don't be a dick.
Location
kawasakis suck
Every one of my motors have been 190-220 psi on cheap ol sbt cranks. I agree with wanderer on the fuel octane to an extent. I ran 93 on the motors from 190-200 and anything over that I ran the AV/93 mix. I agree I'm not getting full potential as I would with race fuel, but I also don't have to spend $10+ a gallon. I pay 6.50 for the AV fuel. I ran the race fuel and just about went broke doing it. I felt no power loss when I went to AV, but that was in a heavy ass ski and just a lightened flywheel, so there could have been a difference to be felt in a light ski and aftermarket ignition.
 
wanderer1

wanderer1

Location
Cruising Around
OCD, I guess I want as much as I can get after spending the money. I prefer the "peace of mind" too. Detonation costs more than the fuel in my experience. If you are happy running 91 then go for it, but "super unleaded" in 1 area is not the same as others. Fuel octane/RON can vary by region and the data is accessible online. My B1's ran great in Texas on pump 93 at 185psi and a lot of fun. In AZ on pump 91 not so much fun. The term "pump" gas can be misleading. Just part of the big picture imo, but if a $40 jug versus a $20 makes or breaks it for ya after the purchase of the high end ski/engine then run the $20 jug. Your above quoted info does apply to my B1's since I lowered cranking compression to 165 but hardly applies to my DASA/stroker at 220psi as stated in the disclaimer. When I get back to riding I'll be the "sucker" buying the 110. Smells good with the overpriced oil too.
 
OCD Solutions

OCD Solutions

Original, Clean and Dependable Solutions
Location
Rentz, GA
Although I am responding to your post, my comments are not directed towards you specifically. I believe guys like you are in a different class than most though since you truly understand and are building specific platforms. The average rider is buying an off the shelf engine like my SS865 and making the choice between premium pump gas and racing fuel.

Fuel choice alone is a small piece of the puzzle that most don't understand and my comments are meant only to make others ask better questions and not to disregard your knowledge in the least. For every pro posting in these threads, there's at least 20 novices reading and soaking it in.

There is a growing trend here where all advice seems to be geared towards all or nothing. Shades of gray are no longer good enough. Call me silly but I want new riders and guys just starting to build to know that there are different levels to this sport and that they don't have to spend $8K on a hull, $2K on carbs and $10/gallon for fuel. I miss the days when a $1500 ski was acceptable.
 
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RSKI

RSKI

Location
Oregon
Thank for all the info guys, like Boyer said some of us are noobs relying on the knowledge of all of you to help us make better informed decisions. I really do appreciate it.

I don't know crap about carbs other than my oem 38's, and I'll be the first to admit it. I took the plunge on 46 mikunis, but they're still in DAG's possession because I'm too clueless on jet sizes to tell him what sizes to ship with the carbs. Any ideas?

Setup:
Carbon footrocket
144 skat mag
771 Able 4mm stroker, 82mm bore
Stock electronics with msd enhancer
B-pipe limited chamber
1800 ft elevation
 
OCD Solutions

OCD Solutions

Original, Clean and Dependable Solutions
Location
Rentz, GA
If you haven't read thru the carb database thread yet, I urge you to take some time and do so.
http://www.x-h2o.com/index.php?thre...-of-any-kind-props.129250/page-4#post-1503837

I went thru it one night and entered all the data into a spreadsheet to do some comparisons and it was surprising how repetitive it became. Slight variations from ski to ski but total jetting (pilot + main) was usually very similar for any given carb size and configuration.

Another good exercise is if you are going to run 46's, go thru the database and write down all the different specs for 46's and I bet you see a trend. Even with a wide variance of mods, the total jetting stays surprisingly consistent making a starting point pretty predictable. That's why a database like this is so valuable.
 
W

waxhead

wannabe backflipper
Location
gold coast
As much as it pains me to say this as I know it will bring the retail price back up. The std 760 carbs are awesome and just plain work. There is nothing to be gained by running after market 44s over these carbs. 46s are better again and after that its novi all the way.
Remember you have to feed the horses if you want them to perform
 
RSKI

RSKI

Location
Oregon
OCD Solutions said:
If you haven't read thru the carb database thread yet, I urge you to take some time and do so.
http://www.x-h2o.com/index.php?thre...-of-any-kind-props.129250/page-4#post-1503837

I went thru it one night and entered all the data into a spreadsheet to do some comparisons and it was surprising how repetitive it became. Slight variations from ski to ski but total jetting (pilot + main) was usually very similar for any given carb size and configuration.

Another good exercise is if you are going to run 46's, go thru the database and write down all the different specs for 46's and I bet you see a trend. Even with a wide variance of mods, the total jetting stays surprisingly consistent making a starting point pretty predictable. That's why a database like this is so valuable.
Click to expand...

I have read the database a while ago, and I will go through it again. I actually forgot about it. Thanks man.
 
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