Help with jets for 4 to 1 exhaust and short cone filters.

MB-5 Joined: Sep 09, 2014 Posts: 1 Location: NY

Hey everyone. Was wondering if someone could help me. I hear that if I have the 4 into 1 exhaust as well as short cone air filters on the carbs that it can be funny without the proper jets in the carbs.

So I guess the question is what jets should I be running? I'm not too sure what the set up is now but I'm pretty sure it's stock jets. Also I guess Im just curious about what constitutes the need for different jetting?

Posted: Wed Sep 10, 2014 7:51 am

Hi, I'm not an expert. I've just seen this question asked countless times on countless websites.

If you have aftermarket air filters on your carbs, that means you have an increased amount of air entering your engine. You need to maintain your fuel/air ratio to keep your motorcycle running well. In simple terms, since you have the increase in air, you increase the jet size to add more fuel.

This video helped me a lot to understand the basics of carb tuning.
https://www.youtube.com/watch?v=y836ZPjvoMI&list=UUp1dfLEBnxuor0JslvhC8rw

If you're riding basically any early 80's bike it probably has CV carburetors. CV carbs do not take modifications to intake or exhaust well AT ALL. If you're running stock carbs with pod air filters, you will most likely never get them running right and if you do, it won't give you the kind of power gains you're looking for. If you want a power increase, or you want to run pods for the look, I'd highly recommend switching to cable driven carbs, like mikuni VMs or Keihan CRs, a used set can be found for less than the price of getting your bike professionally dyno-tuned.

Posted: Wed Sep 10, 2014 11:12 am

Yes, stop what you're doing with those pod filters. Either put the stock airbox back on or switch carbs. When you say you "hear that if I have the 4 into 1 exhaust as well as short cone air filters on the carbs...." you won't ever hear that on this site, the home of this bike. Countless guys have been down that path, and honestly, only one guy claims to have conquered the CV carbs with pods, and even still, most are skeptical. You'll fight with it forever, when you could have reverted back to stock or gone aftermarket in the appropriate way. This is the advice you'll get from this site, sorry to disappoint you.

Hawk Joined: Dec 16, 2007 Posts: 371 Location: warwick,uk

Your 4-1 won't give you any trouble at all . . The pods can be a problem . . Do a search for REC carb mod . . You can get these to run without an air box . . But is work . .

Posted: Wed Sep 10, 2014 11:36 pm

The trick is vacuum demand of the airbox. it is not "free flowing",but has a "restriction".

CV type carbs need this to perform to put the carbs under vacuum. The slides are not direct but operate by the amount taken. The idle is controlled by the idle transfer and the air under the side,ie the slide does not move.

Any attempt to put K&N's on the bike results in the lack of consistency for the fuel so carb companies make them rich,some for the bike some for this lack,with resulting piss poor fuel mileage at steady state cruise.

Honda could have fixed this with "real" carbs,like everyone else had. Honda chose bigger,the smallest were 35mm on 750,37mm on 900,and 38mm on 1100,where everyone had 28mm or smaller.

Ditch the cone filters,get the 1100 airbox,it is best,and ride the bike. If it was rich it would "blubber" and lean would do the lean engine misfire. It does not.

Posted: Thu Sep 11, 2014 12:18 am

Pods or not.....it would help if we knew what bike you have Wink

Jebby

Posted: Fri Sep 12, 2014 3:47 am

here we go again. what you are killing with pods is
port velocity. that's why the air box has built in
"velocity stacks" and its not about restriction.
jetting is a science unto itself but, once understood,
makes a big difference in the way the bike runs !

Posted: Fri Sep 12, 2014 4:49 am

bobcat I wish you would just disappear,but since you won't how many of these bikes do you have?

You have ONE bike and done a whole bunch of wrong things to it and claim it is fast.

I have many,worked on even more and can make it work. It is the RESTRICTION of the airbox. It provides the restriction to make them work. Oh and all Hondas have velocity stacks inside the airbox. Want a thrill. Pull the airbox and gut it reinstall the velocity stacks and ride the bike. It will be screaming lean. Same carbs on CB750 were 120,then 115,then 110,finally 105. Gut the airbox,or cut it carefully and the jetting went to 120 and blew up. Pulled the output shaft out of the mortor.

Posted: Fri Sep 12, 2014 4:53 am

I'm running pods on my 900f with CV carbs with a yoshi 4-1.. Mine runs great, but that's only after changing jets among many other things, and even then I had to enlist my brother's help-- hes a pro Honda mechanic. It *can* be done well, but it isn't easy. I'm afraid I can't agree with Tdem, there's quite a few of us that have good running pods on here-- search on this forum and read up in technical/performance, you'll find all sorts of good info.

Here is a good thread to start with: http://www.cb1100f.net/modules.php?name=Forums&file=viewtopic&t=70514&highlight=rsc

Everyone here has good advice though, keeping the airbox is MUCH better than trying to enjoy bad running pod filters..

Posted: Fri Sep 12, 2014 8:05 pm

sonicrete wrote:

bobcat I wish you would just disappear,but since you won't how many of these bikes do you have?

You have ONE bike and done a whole bunch of wrong things to it and claim it is fast.

I have many,worked on even more and can make it work. It is the RESTRICTION of the airbox. It provides the restriction to make them work. Oh and all Hondas have velocity stacks inside the airbox. Want a thrill. Pull the airbox and gut it reinstall the velocity stacks and ride the bike. It will be screaming lean. Same carbs on CB750 were 120,then 115,then 110,finally 105. Gut the airbox,or cut it carefully and the jetting went to 120 and blew up. Pulled the output shaft out of the mortor.

I love you too mr. Bill Confused

Posted: Fri Sep 12, 2014 8:46 pm

bobcat7 wrote:

sonicrete wrote:

bobcat I wish you would just disappear,but since you won't how many of these bikes do you have?

You have ONE bike and done a whole bunch of wrong things to it and claim it is fast.

I have many,worked on even more and can make it work. It is the RESTRICTION of the airbox. It provides the restriction to make them work. Oh and all Hondas have velocity stacks inside the airbox. Want a thrill. Pull the airbox and gut it reinstall the velocity stacks and ride the bike. It will be screaming lean. Same carbs on CB750 were 120,then 115,then 110,finally 105. Gut the airbox,or cut it carefully and the jetting went to 120 and blew up. Pulled the output shaft out of the mortor.

I love you too mr. Bill Confused

Bob actually has three of them and he is correct in what he says......

Jebby

Posted: Fri Sep 12, 2014 10:55 pm

bobcat7 wrote:

here we go again. what you are killing with pods is
port velocity. that's why the air box has built in
"velocity stacks" and its not about restriction.
jetting is a science unto itself but, once understood,
makes a big difference in the way the bike runs !

Doesn't "port velocity" pertain to cylinder head ports? Not saying it isn't important, but in its place relative to other forces.

With "CV" (constant velocity) carbs, the velocity of the airstream passing through the venturi is (more or less) uniform. The throttle plate dams up the air stream so the reservoir of air behind it can be put to work. I know, the design has its shortcomings but whaddayagonnado?

Vacuum and volume change according to throttle position.

The airbox provides sufficient resistance that both vacuum duration and emulsification--wherein gas and air are premixed before exiting into the throat--are optimized for constantly changing conditions. This is a tall order for a paper accordion if you ask me.

Pod air cleaners decrease vacuum duration AND upset emulsification.

I would venture that anyone who reports success with pods has 1) good compression and 2) his valve clearances are in order. Yes, Virginia, it can be done.

Besides which, the phrase "it runs great" is rather subjective don't you think? Great compared to what? Hop on a 100% perfect engine done by a pro (like Prestotech), and then tell me.

OSC
Learning is everything. A cauliflower is a cabbage with a college education. Mark Twain

Posted: Sat Sep 13, 2014 1:38 am

I hate cauliflower.........

The air rushing through the throat of the carb causes a pressure differential between the throat and the area above the slide causing the slide to rise correct? So the faster that air flows the bigger the differential. The bigger the differential the faster the slide lifts. Could it really be that simple? (I already know the answer..........)

Oh yea.........port velocity explains it perfectly. Especially for this motor as it has 4 individual carbs feeding 4 individual intake ports (or runners).

Posted: Sat Sep 13, 2014 2:17 am

Jebbysan wrote:

bobcat7 wrote:

sonicrete wrote:

bobcat I wish you would just disappear,but since you won't how many of these bikes do you have?

You have ONE bike and done a whole bunch of wrong things to it and claim it is fast.

I have many,worked on even more and can make it work. It is the RESTRICTION of the airbox. It provides the restriction to make them work. Oh and all Hondas have velocity stacks inside the airbox. Want a thrill. Pull the airbox and gut it reinstall the velocity stacks and ride the bike. It will be screaming lean. Same carbs on CB750 were 120,then 115,then 110,finally 105. Gut the airbox,or cut it carefully and the jetting went to 120 and blew up. Pulled the output shaft out of the mortor.

I love you too mr. Bill Confused

Bob actually has three of them and he is correct in what he says......

Jebby

thank you Jebby.

Posted: Sat Sep 13, 2014 2:41 am

Lets see I had a 955,a 900,a 1100 that rode. A 1187,a 1187 and a 1220 that I drag raced,plus about that many of spares.

I had enough parts that I filled a 24 foot trailer and took 5 guys the entire Saturday to carry out parts. Want to compare?

The CBX that I saw was two of them and I built them with turbo chargers. Whole works down to the cases and built up with Carrillo rods.

Posted: Sat Sep 13, 2014 2:46 am

There are pods on the other three carbs...

Link

Posted: Sat Sep 13, 2014 3:08 am

I had a 750 once. The carbs have THREE large lift holes in the slides and heavy springs.

900 and 1100 have only two lift holes.

All this makes a difference.

Posted: Tue Sep 16, 2014 11:40 pm

Oh, Oldschoolcarbs, how your post made me laugh.. Yes, 'runs great' is very relative, you nailed that! Laughing

Thats probably the biggest reason nobody can agree on this. If any of you with 'perfect' running bikes or maybe well tuned CRs jumped on mine, 'runs great' might not be what you say. BUT, it accelerates very smooth, doesn't stumble anywhere in the revs, and gets around town or on the highway great. I've never dyno'd it, never taken it to the track or ran down the drag strip, and didn't really do any of this for performance, but it still runs great with no noticeable change to the power. Very Happy

Trying to quantify how well a 30 year old bike runs definitely causes interesting debates!