Differnt carbs and jetting questions?

[JOHNDOE83]

Ok, im not %100 sure on why these carbs are so different with jetting?

Fcr, 450r, stock...etc.

I realized this issue just recently, and dont have all the info on why it is the way it is.

With my mods, and a 450r carb, depending on temp, humidity...etc...I can be anywhere from 190 to 220 on my main jet sizes.

I noticed Steve, has a 450r carb 416 bore and a 168 main jet, but a 170 in a stock carb.

Nacsmxracer, has a 175 with a fcr carb, 452 stroker motor.

ericcrip, has a 155 with a fcr, and a 440 with more mods then I do.

I know all machines are different, I can build two identical bikes at the same time, and one will need different jetting then the other.

But heres the weird part, bigger carbs need more fuel, more mods need more fuel and air.

So if honda2003400ex needs a 170 with a stock carb and a 416, but nacs needs a 175 for a 452 stroker with a fcr, but ericcrip only needs a 155 for his 440 and fcr, and I need 190+ for a 440 with a 450r carb, what are the issues that would cause this?

Nacs just got his dialed in with a 175, and honda2003400ex has his dialed in with a 170? So these are actually good jetting settings for these bikes they are perfect for their setups.

So why would nacs need only a +5 increase for a 452, and steve need a 170 for a 416? Just like ericcrip has a 440 more modded then mine, but only running a 155?

So basically, what are the issues involved that would cause eric to need smaller jetting then me, nacs to have only + 5 from steve, and me to need 190+???

I know temp and elevation plays a role, different bikes need different things even with the same mods.

So what am I missing here? Its confusing the hell outa me?

Is the fcr with its setup designed to put out more power at a lower jett setting? why would it need smaller smaller jetting then a stock carb? with my stock carb, I could leave it at 220 main no matter what temps were that day, but with my 450r carb, its sensitive to temp changes?

Is it the slide, needle and accelerator pump that make it different with jetting, I feel kinda lost at the moment?

Carb basics tells me that the bigger the carb needs the bigger the jet would have to be, which works on mine, but it seems its not the same for others that have the same?

Can someone clear this up for me?...trxracer1 and steve Im looking in your direction...lol.

Am I missing a simple explanation here?

[bkelley]

I run a 165-168 main in my 450r carb with a pretty much stock engine. Just thought I'd share.

[honda400ex2003]

alot of variables. too many different pressures, temps, humidities. imo. different engines can be more efficient using smaller jetting than others too. My 450 carb is more efficient than my 400 carb was with my machine. the carb engine combo doesnt work so hard thus requiring less fuel. i could run a 178 in my 400 and have it run fine. I did for a few weeks until i got it tuned. it is all in how it rides. I just have it jetted there so it is performing at its peak hp and best f/a ratio it can be. Now it is rich for the summer. if it was cold, it would be lean and i would have to jet to something different. I have been told every 10 degrees is 1 jet size so every 20 would theoretically require a new jet to stay where it needs to be. im not going there though. these engines can be so different with so many aspects, porting, how rough the intake ports are to help mix the mixture ( no pun intended lol) how much turbulence is created inside, how smooth it flows, how ground the header pipe is, how much goop is in the header. how much packing is in your exhaust, if there is an arrestor on it. too many things to think about imo to get something completely right ever. your thread makes a point for them to do it on their own instead of having a suggestion which is great. the person can go until it doesnt run good, then go down a bit. I am not denying that this is a good method to do it. I am denying that it is the best method for getting the most out of an engine. I am not out to have big jets as we have discussed in the past. I need to get good mileage for when i trail ride. thus i like to keep it on the border of where it runs most efficient. it runs cool(by cool i mean 200-240F oil temps in the tank) all day long. I can put 100 miles on it in a day if i prefer and not have to worry about running out until about the 80 mile mark if i am riding hard. I get on ave 35 mpg most of the time and occasionally get 40mpg. that is great! If i was running a 178 it would be a much tougher sell to get 40 out of it. I can run either cam i want to, either exhaust i want, it doesnt matter. my t-4 is the better of the two i have since it flows better and it jetted to it. the q4 richens it up a bit. even better for trails. just too many variables to decide on one suggestion or anything. when i suggest a jet size, i try to take into consideration what mods are done, what elevation it is, everything i can to make a judgement. my suggestions are hardly ever the same for any application. unless it is a slip on and filter. ill go with a 150 or 152 every time depending on the exhaust. This is still a judgement call. I hope i didnt ramble too much, i am starting to get tired so sorry if i did. im off to bed. steve

[JOHNDOE83]

Would compression be a BIG factor here?

I think it would, higer compression would need higher octane fuel, but wouldnt the jetting need to be slightly smaller to compensate? would kinda explain erics situation?

Being that the fuel ignites quicker and needs less room to create combustion? could that be why? or is that backwards?

Because I have low compression, but use much larger jetting then most others, like Bkelly just added his jetting on mainly stock motor, stock is low compression and his jets are close to steves 416 jetting.

Nacs has a stroker, and eric uses high compression, could that be why they run lower jetting sizes?

Kinda like dalejiw has a 440 stroker with a 190, but im usually 190 or higher? with a basic 440 cylinder kit not a stroker?

Does this sound like a good explaination? or am I a lil off track here?

[gt400ex]

ZRpilot, dosent come on here much anymore, seemed to be a carb god on this subject. If you read through his install thread he states that because the 450 carb is bigger and set up different that the vacuum signal is much different from the stock 400 carb. When you start tossing in things like different cams, compression, exhaust, intake and everything else you are making that vacuum signal change that much more. None of these bikes in your examples are set up very close to the same set up so the air they are pulling in is probably much different then the other. At least this is my take on why everyone is so different. And just for comparison I have a 440 stroker with open intake, head welds ground and an old E series and Im running a 175 right now at the coast.

[JOHNDOE83]

Exactly, but I have less mods then some of these guys and use much larger jetting.

Mines not a 440 stroker, which would lead me to believe you have a 426 with a stroked crank? which Might need smaller jetting?

Would that be why you need smaller jetting? Mine is a true 440 piston without the crank, and have a lower compression, could that be the factor in why my jets are larger, thats wht im kinda leaning towards now, I guess this is one of those questions that cant be answered easily.

Thats why I would assume that higher compression might need lower jetting? but there is still 440 strokers out there using 190 main jets, so im still kinda stumped?

The compression thing makes sense, but im not 100% on that, Ive also seen 416 and 426 guys with mods like mine in the 200s like me, and only after going into the 200s they saw a massive gain.

LOL...Im still confused, it seems like I start to get somewhere with this then prove myself wrong?

Maybe I should consult with a big engine building company like duncan or trinity on this? to try to clear up some confusion.

im running all most 13.1 comp. and my port looks smoth so the fuel will flow faster. if you need a pic let me know ill post it. also your close to water. im over 3 hours away from the water now. that plays a big role in it to.

johndoe 83 is your head ported? if not get it done. you will love it. and if you have the money go +1mm on the vales that my next step on the heads.