jetting a big bore

[350xorbust]

K...I know the 425cc bigbore kit, on a 350x, is a pretty common one, so someone out there should be able to help me. I may be doing this kit, along with a low to mid range cam, a K&N filter, and probably a DG or supertrap exhaust. I hope to be around the 10-10.25:1 compression...a good trail bike combo.Sorry right now I cant be more specific. My question is, with the stock carb, what jetting range should I be starting with?

[JasonB]

Are you talking about for a 350x?

[jays375]

I would suggest a 39mm FCR carb.No lid on the box and remove intake tube from the frame.Another thing that has to be done is get the rockers hard faced.If you swap out the cam.

[350xorbust]

I would suggest a 39mm FCR carb.No lid on the box and remove intake tube from the frame.Another thing that has to be done is get the rockers hard faced.If you swap out the cam.

As far as the hardened rockers, that will be up to the builder to decide, but I was just wondering if there was any jet size that would allow me to keep the oem carb?...Sound like a no...What company is FCR??

[DohcBikes]

The manufacturer of whichever big bore kit you buy, should you decide to, will be able to give the best recommendations for their particular setup.

[6speedthumper]

The FCR is a carb that is used on MANY dirtbikes, and the earlier carbed 450 sport Badass carb right there! I have one on my built Warrior, and have one waiting to go on my 350x, once I get the engine back together. Great carb.

[barnett468]

I was just wondering if there was any jet size that would allow me to keep the oem carb?Yes there is

[barnett468]

POST CORRECTION

Sorry, all my text didn't copy.

I have no edit button.




I was just wondering if there was any jet size that would allow me to keep the oem carb?

Yes there is however I doubt that many would know what that size would be. This is because, in my experience, most people that install big bore kits, do so to increase performance, and since in general, a big bore kit requires more air than the oem carb can provide, people run a carb that is larger than stock to get the extra air the big bore will require to achieve its optimum level of performance.

Running a stock carb on a big bore kit is similar to installing an intake restrictor plate on a Nascar engine. Yes it will still run, however, the amount of restriction in the plate [carb size in your case], determines the amount of reduction in the potential power output of the engine etc.

The cylinder head ports are also potential restrictors when doing other mods like increasing displacement and/or cam size. Installing a big bore kit and/or bigger cam without doing some porting, might prohibit the engine from reaching its optimal potential.

A cam that is bigger than stock also requires more air flow than a stock one to perform at the maximum of its capabilities.
Imo, the bottom line is, until, or unless, a larger carb is installed on a big bore kit that also has a cam that is bigger than stock, it will, in technical terms, most likely run like a P I G.

[350xorbust]

The FCR is a carb that is used on MANY dirtbikes, and the earlier carbed 450 sport Badass carb right there! I have one on my built Warrior, and have one waiting to go on my 350x, once I get the engine back together. Great carb.

Just after you mentioned it, I went on ebay and found a few. They all had some sort of electrical pigtale comin out of em...whats that for...electric choke or what??

[350xorbust]

The manufacturer of whichever big bore kit you buy, should you decide to, will be able to give the best recommendations for their particular setup.

And yes I agree. I hope who ever I choose will point me in the right direction as too size and jetting. Again...just tryin to save a buck and rebuild and reuse the oem carb. ...Too small???

[barnett468]

Just after you mentioned it, I went on ebay and found a few. They all had some sort of electrical pigtale comin out of em...whats that for...electric choke or what??Power jet.

[350xorbust]

Power jet.
What the he** does that do?? Sorry Im old school.

[350xorbust]

POST CORRECTION

Sorry, all my text didn't copy.

I have no edit button.





Yes there is however I doubt that many would know what that size would be. This is because, in my experience, most people that install big bore kits, do so to increase performance, and since in general, a big bore kit requires more air than the oem carb can provide, people run a carb that is larger than stock to get the extra air the big bore will require to achieve its optimum level of performance.

Running a stock carb on a big bore kit is similar to installing an intake restrictor plate on a Nascar engine. Yes it will still run, however, the amount of restriction in the plate [carb size in your case], determines the amount of reduction in the potential power output of the engine etc.

The cylinder head ports are also potential restrictors when doing other mods like increasing displacement and/or cam size. Installing a big bore kit and/or bigger cam without doing some porting, might prohibit the engine from reaching its optimal potential.

A cam that is bigger than stock also requires more air flow than a stock one to perform at the maximum of its capabilities.
Imo, the bottom line is, until, or unless, a larger carb is installed on a big bore kit that also has a cam that is bigger than stock, it will, in technical terms, most likely run like a P I G.
So do I rebuild the oem carb or not. I cant afford to throw away $, even if it is only $15 on a rebuild kit. Or do I wait and invest in a FCR carb???

[barnett468]

Again...just tryin to save a buck and rebuild and reuse the oem carb. ...Too small???That depends on what type of performance you want, however, I would install a larger one.

Since you are trying to save a buck, why would you want to spend money on another cam?

Did your current one get rusty also or is it damaged?



...in my experience, most people that install big bore kits, do so to increase performance, and since in general, a big bore kit requires more air than the oem carb can provide, people run a carb that is larger than stock to get the extra air the big bore will require to achieve its optimum level of performance.

Running a stock carb on a big bore kit is similar to installing an intake restrictor plate on a Nascar engine. Yes it will still run, however, the amount of restriction in the plate [carb size in your case], determines the amount of reduction in the potential power output of the engine etc.

[barnett468]

So do I rebuild the oem carb or not. I cant afford to throw away $, even if it is only $15 on a rebuild kit. Or do I wait and invest in a FCR carb???

I did not see this post before I posted.

Providing all your parts match properly and the carb is properly jetted, an inexpensive, standard, old school, round slide Mikuni will perform perfectly, and is EASY to jet.

An Electrified, Titanium, Octoport, Air Stroker, Mombo Stealth Dragon Slayer carb will also likely work too, but I'm a simple person and like simple carbs that don't require a physics degree to jet.

[DohcBikes]

Maybe its a good idea to start a thread called "350x bench racing". Then instead of starting a new thread every time you wanna discuss the POTENTIAL use of a single part on your 350x, you could go in there and ask about it, instead of starting a thread to discuss each individual part on an engine build that will likely never happen. This way people will also be aware that they are spending their precious time giving technical advice to somebody that has changed his mind 8 times about what he wants.

Yup, another harsh reality post. Don't get me wrong, I wish the best to you, but all these questions could be in one thread. You have also started multiple threads posing the same questions, and have also completely disregarded the advice of several good techs on this site. A couple of your threads have started major arguments here, and its mostly because you don't know what you want yet, you're just throwing darts and hoping they stick.

Several people on this thread have told you that a stock carb is not in your best interest for a big bore, so your answer is NO. NO.

As I said before, IF you decide to get a big bore kit and put it on a 30 year old bottom end, ask the people you buy it from what they recommend.

No person on this site can CORRECTLY suggest the carb that will work BEST for an engine that hasn't been built yet. As Barnett suggests, spending money on a big bore and then putting a stock carb on it is a WASTE of money.

So again, your anwer is NO. Now cmon and hate me for telling it like it is guys.

[oscarmayer]

get a eBay Mikuni and be done. new they run around $100 for the size you need. as mentioned tons of jet kits for them and easy to work with.

[350xorbust]

Ya my cam and rockers were both beyond reusage with damage, but I told Tom and Mickey that this was to be a trail machine only so to only make the cam work well with the cc,s and not so much for all out performance. I just want a cost effective reliable rebuild, that I can trail ride on Sundays...lol
What size is the stock carb, and with that info, what size do u figure would work as a all around carb?

[350xorbust]

Maybe its a good idea to start a thread called "350x bench racing". Then instead of starting a new thread every time you wanna discuss the POTENTIAL use of a single part on your 350x, you could go in there and ask about it, instead of starting a thread to discuss each individual part on an engine build that will likely never happen. This way people will also be aware that they are spending their precious time giving technical advice to somebody that has changed his mind 8 times about what he wants.

Yup, another harsh reality post. Don't get me wrong, I wish the best to you, but all these questions could be in one thread. You have also started multiple threads posing the same questions, and have also completely disregarded the advice of several good techs on this site. A couple of your threads have started major arguments here, and its mostly because you don't know what you want yet, you're just throwing darts and hoping they stick.

Several people on this thread have told you that a stock carb is not in your best interest for a big bore, so your answer is NO. NO.

As I said before, IF you decide to get a big bore kit and put it on a 30 year old bottom end, ask the people you buy it from what they recommend.

No person on this site can CORRECTLY suggest the carb that will work BEST for an engine that hasn't been built yet. As Barnett suggests, spending money on a big bore and then putting a stock carb on it is a WASTE of money.

So again, your anwer is NO. Now cmon and hate me for telling it like it is guys.
Hey A** ,its called being on a strict budget. Ever heard of it? And ya, sometimes when on this kind of budget unfortunately some sacrifices have to be made. Im desperatelly trying to build my childhood dream bike, as cheapely, reliabely and as smart as budget allows.And Im sorry if people with a disposable income dont get it and get pi**ed off. I simply cant get through to people like that, and they dont understand my view, and cant handle it. Nothing I can do bout them. And no, This is not a "Bench Racer". I am already close to putting everything back together...the engine being one of the last (and most expensive) hold ups. I realize I cant keep everyone happy here, but when money is no object, its easy to give advice!!!!!

You know what...Im done with this site.Thought these forums were a place to get and give HELP, not comdenation...SEE YA

[DohcBikes]

How can you be close to putting it back together when you just spent the last three days on here asking about which topend parts to use,and where to get em? So what you are saying is that you already had the parts, you just enjoy wasting our time. OK.

By the way, when people are discussing the POSSIBILITIES of using performance parts, combinations of performance parts, and making conjectures about how it will perform in the real world, that's the DEFINITION of bench racing. Nothing wrong with it either, as long as everyone knows that's what's going on.

[DohcBikes]

not so much for all out performance. I just want a cost effective reliable rebuild, that I can trail ride on Sundays...lolhuh, I thought we were talking about big bores:wondering

If not, my apologies. Since we are now talking about a "cost effective" "reliable" rebuild that you can "trail ride on Sundays", then my suggestion is the you leave the highly capable 350x stock. SEE YA.

[250rRoostmaster]

What's disposable income?? :wondering

[jays375]

Big bore equals big $,no matter what.I am sure Tom and Mickey both explained things to you.Neither one of them would have liked the idea of not splitting bottom end.It is just impossible what you are trying to acheive.Maybe you should try picking up a take out motor.Cost would be around $1000-1200.As budgets go,double it.Just how it works out.Just getting a trike in good riding condtion is costly.Price of bearings,cables,chain and sprockets,tires,good brakes.Not talking a restore,just dependable.Just figure that dollar value.That's why it is cheaper to buy the best machine you can.You have been given the info you requested.

[barnett468]

You know what...Im done with this site.Thought these forums were a place to get and give HELP, not comdenation...SEE YAFYI, According to Cartman, the appropriate phrase is "Screw you guys...I'm goin home.". Since it is HELP you seek, and HELP is what we are happy to offer when we can, the proper spelling of the word "condemnation", is in fact, "condemnation". If a word is possibly misspelled, the site will automatically underline in red.


It appears that some are becoming a little frustrated in their efforts to help you, which imo is understandable based on what seems to be your resistance to take some very intelligent peoples advice, such as at least splitting the cases to do an inspection. You also wanted to grind away a ton of aluminum with the engine assembled, ok, maybe not the best idea, as was stated multiple times on your other thread.

Imo, some of your comments make think of a person that has an ailment and goes to different doctors until they get one that agrees with their own diagnosis. In my experience, this is typically not the most prudent thing to do.

EVERYONE here simply wants you to achieve the best possible outcome, and I’m sure they are appreciative of the costs vs long term success. NO ONE here wants you to take your ball and go home. Imo, they simply want you to be receptive to their suggestions.



I’m just curious, have you ever ridden a 350x?

What is your skill level?



Imo, for someone to want more power for basic non race type riding than a stock 350x has, is commendable, but also a bit extreme. This is NOT a Wussy bike. If one simply increases the compression, installs a 2mm bigger Mikuni, and replaces the stock muffler with virtually ANY non spark arrestor type, it will be more than most people can SAFELY handle.





Im desperatelly trying to build my childhood dream bike, as cheapely, reliabely and as smart as budget allows. I just want a cost effective reliable rebuild, that I can trail ride on Sundays.

I’m desperately seeking a date with a Victoria's Secret model but am confident that exceeds my budget and may therefore have to settle for one of those girls that spins the signs on the street corner directing me to a newly opened cholesterol laden eatery.

You implied your budget is so tight that even spending a mere $15.00 on a rebuild kit for a carb that you might not be able to use due to its small size is a concern. Ok, we understand. I suggested simply getting a custom piston made. This is your cheapest option as far as I know. Instead of doing this, you are wanting to spend around 2 1/2 times more money on a big bore kit which should also have a bigger carb and cam to optimize its performance potential. You need a cam anyway so no big deal there.

I have never posted info on big bores or custom pistons on the site before because I never saw a need to. Some others know just as much or more than I do on the subject. Between EVERYONE's info, you have WAY more info than I have seen any one person here get on this subject. One suggestion I have at this point is for you to simply review ALL the info provided and decide what the best option for you is.





What size is the stock carb, and with that info, what size do u figure would work as a all around carb?The stock carb is 31 mm and it has either QA05A or QA10A cast into the side in tiny font.

My guess, based on the info provided, is that a 34mm carb would be the ideal size for a big bore with a slightly larger than stock cam.
You already have a few varying opinions on which carb people would use. If you buy a Mikuni, I suggest part number VM34. See some Mikunis and Kehins in the link below.

http://www.carbparts.com/mikuni/mikuni_atv.htm





Ya my cam and rockers were both beyond reusage with damage, but I told Tom and Mickey that this was to be a trail machine only so to only make the cam work well with the cc,s and not so much for all out performance.If you do not get a suggestion on cam size, I suggest looking at the cams below for your app. Both sites also hard weld rocker arms.

55-731 = strong low end. adv dur 252, dur @ ? 228, .350 lift.

55-741 = slightly less low end but stronger mid range power. adv dur 260, dur @ 236, .362 lift.

http://www.webcamshafts.com/index_blank.html?pages/vehicle_search.html


162-00 = possibly inbetween the two cams above. dur @ .040” 234, .333 lift.

http://www.megacyclecams.com/catalog/Page27.pdf





Big bore equals big $,no matter what. You have been given the info you requested.




PS – What became of your Nikasil [or similar] plating idea?



Here, have a cold wet Heini;

:beer

[barnett468]

Hello 350xorbust;


If you buy ANY camshaft, and find you want either just a bit more bottom end performance at the expense of a bit less top end performance [less peak rpm] or vise versa, I suggest you buy an adjustable cam gear. Advancing the cam timing will LOWER the overall operating range slightly, and retarding it raises it. The maximum recommended amount of advance or retard is 4 degrees imo.


Here's some more cold wet Heini's for you.

:beer