Here's another carby question

stevo707 · Post by **stevo707** » Sun Jan 23, 2005 3:18 am

OK guys i just put KN air filters on my bike pulled the old air box completely out. The bike is a FZR750RU 1988 model the problem now is give it a boot full and she breaks down around 8 to 9000rpm and then comes out of it same with second as well etc, but if you screw the throttle on slowly the bike will go all the way through without breaking down, but feels a little bit dead on pick up. Ok well its obvious its getting a @#%$ load more air down its throat so my questions are bigger jet sizings,shift the needles or go straight to the dyno guys the main jets are 105's or any other advice or questions you would like to ask before you answering just ask away. Your help on this matter would be appreciated before i go any further. thanks guys. stevo707

dragracer1951 · Post by **dragracer1951** » Sun Jan 23, 2005 8:26 am

it's not your main jets. too low in the rpm range, you're still in the midrange. Raise the needle and you may want to give the pilot air screw a quarter or half turn out Let us know if that helps Jim

stevo707 · Post by **stevo707** » Tue Jan 25, 2005 3:11 am

OK this is what i have done so far i have raised the needles they are now at the second bottom setting i have put 110 main jets in as well and gave the air screw 1/4 turn out it has definitely helped. The old girl sounds not to bad, but it is raining here and i am unable to take it out and put it under load to see how she performs i think in all honesty i should go higher in the main jets say to 112 or 115's but i will wait and see, now what do use guys think? Also can use guys tell me as well how expensive jets are to buy over in the states like the mains for mikuni they're bloody expensive here. stevo707

dragracer1951 · Post by **dragracer1951** » Tue Jan 25, 2005 9:20 am

one thing you didn't mention, Steve, is if this bike has a jet kit in it. I'm thinkin gthat it does as you can adjust the needle position. If I am correct then th emain jet size is NOT a mikuni number and can not be thought of in terms of mikuni numbers..... also the carbs slides (needle) are not controled directly by the throttle but are controled by vacuume so the point at which they transition from running on the needles to the mains is dependent upon rpms and load..... Just something else to think about Jim

Matt at PSB · Post by **Matt at PSB** » Tue Jan 25, 2005 12:12 pm

I say the fello would have been better off with his stock airbox. Unfortunately I see this all the time. Individual pod filters are generally more hassle than they are worth unless you have switched to aftermarket race only carbs. I advise my customers to not go beyond a stock replacement K&N air filter element & a stage one jet kit. There are very definite limits to what you can ask the stock CV carbs to do. Nobody believes this and it takes about twenty years, unless you own a dyno and/or have a big budget, of owning & tuning the same bike to figure it out. So, the great myth of pods & stage 3 jet kits lives on always catching new young players. Worse thing is once someone crosses the line & buys pods it is almost impossible to get them to reverse direction. CV carbs are very limited induction devices. There is only a little bit of tweakage available with them then you have to move on to smooth bores. Matt at PSB Edited by: <A HREF=http://p072.ezboard.com/bexupbrotherhoo ... atpsb>Matt at PSB</A> at: 1/25/05 10:12 am

dragracer1951 · Post by **dragracer1951** » Tue Jan 25, 2005 1:29 pm

Amen!!! <img src=http://img.photobucket.com/albums/v209/ ... odpost.gif ALT=":goodpost"> Jim

stevo707 · Post by **stevo707** » Wed Jan 26, 2005 2:32 am

Well ok i have posted some pics below of a Haynes Owners Workshop Manual and if you own 1, refer to chapter 5-2 FZR750 (US) Carburetor type for the BRAND of the carby, the main jet standard size quoted only and chapter 5-17 for Carburetor exploded view go to number 13 on this page and see if you can see the main jet and what it looks like, mine is the same as the book states and they have their size marked on top of the jet eg 105,110 ect and i do realize they are vacuum carbys and no i havent got a stage 1 kit in it. Matt i do hear what you are saying about the air box but answer this for me then. Two puny holes in a standard air box dosent allow it to draw very much air at all does it,for a hyperformance bike like mine? Now a friend of mine made his own air box by using a Hyundi air cleaner out of a car yes thats right Hyundi air cleaner out of a car,his bike is a FZR 1000. The air box's out of the 750 & 1000 are the same standard. Now he achieved 16 more HP at the rear wheel by doing that. If any one wants Prof of the dyno that was performed on his bike i should be able to get it, he generally keeps all that type of stuff. Seems to me, like a bit of an incentive to try for a few more HP doent it? If he can achieve that with a car filter lol. Also i have been riding motor bikes for more then a few days more like over 20 years and have tinkered with them pulled them down and put them back together again so i must say i am not young or new at this. But if i can not get the carbs to settle and run sufficient i will humble my self and be the first to admit it was a wrong move BTW the twin air pods cost me $20 US in good condition. I apologize if i offend any of use guys by saying what i just said. sorry Stevo707 i dont mean to sound harsh just stating the facts. <a href="http://img.photobucket.com/albums/v504/ ...  <a href="http://img.photobucket.com/albums/v504/ ...  <a href="http://img.photobucket.com/albums/v504/ ...  Edited by: <A HREF=http://p072.ezboard.com/bexupbrotherhoo ... tevo707</A> at: 1/26/05 1:00 am

dragracer1951 · Post by **dragracer1951** » Wed Jan 26, 2005 9:44 am

Steve I was certainly not trying to impugn your ability. I was not aware that the 750 had a needle with multiple grooves from the factory, and thus thought you had a jet kit in there.... If you are running pods with the stock jets then I would certainly think you are running lean. I think jets over here are about $4 or $5 apiece for the mains and I think the pilots are about the same HAve you tried to go through Sudco? They are a HUGE source for Mikuni parts Jim

stevo707 · Post by **stevo707** » Wed Jan 26, 2005 1:17 pm

No worries Jim i didnt mean to sound so harsh either sorry. Have you got a website i can go through for Sudco or some way of contacting them thanks. stevo707 its still raing here its our wet season now so the bike might stay indoors for a while before i get a chance to sought the problem.

dragracer1951 · Post by **dragracer1951** » Wed Jan 26, 2005 2:26 pm

<a href="http://www.sudco.com/">www.sudco.com/</a> Edited by: <A HREF=http://p072.ezboard.com/bexupbrotherhoo ... cer1951</A> at: 1/26/05 12:28 pm

Matt at PSB · Post by **Matt at PSB** » Wed Jan 26, 2005 4:29 pm

I was only offering free advice based on my experience. I was not questioning anyone’s abilities. CVs PLUS PODS: The CV carb depends on the pressure differential between the airbox (vacuum) & the atmosphere to hold the slide open. The slide lift holes in the bottom of the slides "see" the airbox vacuum. The other side of the diaphragm "sees" ambient air pressure. In an airbox set up there are four evenly spaced induction pulses to open & hold open the slides. With 4 individual pods 75% of those slide-lifting pulses are absent. With dual outlet pods 50% of those slide-lifting pulses are absent. If the slides do not get lifted than all the re-jetting & slide needle changes in the world are of no avail. CV carbs are the bastard stepchild of a bad marriage between British carmakers & the EPA. Prior to motorcycle emissions controls in 1979 all the successful performance oriented bikes had mechanical lifted slides without throttle plates in their carbs. All the performance oriented bikes today also have carbs that are: 1) Non EPA compliant. 2) Have mechanically lifted slide carbs without throttle plates. CV carbs are the Bastard Stepchild rammed down our throat by the EPA. They are improvable though tuning tweakage, but only to a very limited extent. Pods on CVs falls outside these limits. Many would have me stoned for saying this; it is never the less the truth. CVs need a common airbox, smooth bores do not. BTW, I'm a dealer for www.sudco.com. at PSB Edited by: <A HREF=http://p072.ezboard.com/bexupbrotherhoo ... atpsb>Matt at PSB</A> at: 1/26/05 2:34 pm

750muppet · Post by **750muppet** » Fri Feb 04, 2005 12:24 am

beautifully said, I never stop learning.THanks

KontoBoy · Post by **KontoBoy** » Fri Feb 04, 2005 10:33 am

I alway like reading your posts Matt because when it comes to bikes you seem to know what you're talking about. But don't buy your spin on EPA and regulations. CV carbs were around long before the EPA got around to regulating motorcycle emissions in the 90's. I had them on my CB450 back in the early '70s before EPA and the Clean Air Act even existed, and they were on common on Japanese bikes at least a decade before that. At the time they were promoted as providing smooth throttle response and improving carburetion by maintaining constant airflow through the entire RPM range. That smooth response was actually the moment it took for the vacuum slide and diaphragm to adjust to pressure differentials between the venturi and ambient environment. No doubt EPA regs contributed to the increased use of CV carbs in the early 90's when the Clean Air Act started looking at motorcycles--they were simply cleaner. But EPA never mandated CV's. The multi-year public rulemaking process, designed to balance the environmental and economic costs, simply set emissions standards. It's was up to the motorcycle manfuacturers to decide how to meet the new standards. Fuel injectors surpassed CVs as a cheaper and more reliable solution to lower emissions long ago. Automakers made the wholesale jump to EFI in the 80's, while motorcycle manufacturers dragged their feet and didn't commonly adopt EFI until a decade later (even some modern street bikes are just switching over). So yeah, my '97 Yamaha track bike got stuck with crappy CV's, a 40 plus year old technology. I live in a high pollution area that has upwards of 30 bad air days a year. I run in it and I ride in it. On a Code Red days the news reports tell us to stay inside. I can smell it and feel it burn my eyes and lungs. I see the haze of pollution hanging in air as I ride to work in bumper to bumper traffic on my bike flanked on four sides by SUVs. And there is no significant industry here--it's virtually all from cars. So I for one appreciate the cleaner air the auto emission regulations have brought even if it means running EFI and a catalytic converter on my street bike. Of course I'm biased--I've worked for EPA for over 20 years--but I would welcome even more environmental regulation. I've got nothing to complain about--even with all the regs, I can still buy an out of the box street bike that will go close to 200 mph. And if I'm not happy with 150 mph straightaway speeds or I want to race, I can still buy FCRs for my "YZF750" and play with the carb settings all I want. That's when I'll be relying on guys like you for your for help and expertise. Kontoboy

exupturbo · Post by **exupturbo** » Fri Feb 04, 2005 12:40 pm

I've been trying to get my bike to carburate properly for nearly 3 years on CV carbs <img src=http://www.ezboard.com/images/emoticons/embarassed.gif ALT=":o"> Some depressing reading. <img src="http://img.photobucket.com/albums/0703/ ... ynojet.jpg" style="border:0;"/> Piolt Air correctors don't seem do do a damn thing my bike and I'm trying FZR600 pilot jets to try and and lean out the bottom end. Mark

dragracer1951 · Post by **dragracer1951** » Fri Feb 04, 2005 2:09 pm

I have a couple bikes with Dynojets in em...Why? I'm not sure. But the fact is that I have removed the air correctors (HA!!) from the carbs on all of em to make them run not so freekin pig rich on the bottom..... Your milage may vary Jim

Matt at PSB · Post by **Matt at PSB** » Fri Feb 04, 2005 6:47 pm

CVs evolved from the SU carbs that first appeared on British cars & Volvos in the mid to late fifties. The EPA never mandated CVs. They were just the easiest & cheapest way for the motorcycle manufacturing industry to use then existing technology to meet emission standards that came into effect for the first time on motorcycles engines, in the USA, during the 1979 model year. I had no intention to denigrate the EPA in particular or environmentalism in general. I was merely stating a factual time line. I know better that to denigrate anyone’s sacred hypocritical cow. I did intend, however, to denigrate CV carbs. Simple put they suck. They sucked on a 1968 CB450T Black Bomber and the suck on a 1997 YZF1000. CVs or SUs sucked on an MGB & they sucked on a 122 Volvo. They were so bad that Volvo became one of the first car manufactures to convert to fuel injection, albeit that awful Bosh mechanical fuel injection system that first appeared as a Bendex system on the 1957 Chryslers, and MG went tits-up in the early eighties. CVs do not work near as well as smooth bore carbs, but they are much more idiot proof than smooth bores. I am made keenly aware daily of the value of semi idiot proofing in today's world in which the meek are rapidly inheriting the earth. All of the above really misses the point of my postings in this tread though. I was trying to help those who might fall into the Stage Three Jet Kit & pod air filters in conjunction with CV carbs trap. No problem; I understand that if you want or believe in something enough no amount of informed advice is going to save you from yourself. In the spirit of this I am able to supply Stage Three Jet Kits & several types of pod air filters to my customers that insist that my advice is incorrect. Just please do not ask me to do any tuning work on your bike after you go to this set up. With the best rubber diaphragm CV carbs I say stage one & an OEM replacement K&N air filter element in a stock airbox is the best you can do. In the diaphragmless Keihin metal slide piston CVs you cannot even do this with screwing everything up. I spent twenty years actively experimenting before coming to this perhaps over simplified conclusion. The laws of physics made be different where you live. It is like what Paul Simon said about twenty years ago: “I know what I know. I say what I said.” Matt at PSB Edited by: <A HREF=http://p072.ezboard.com/bexupbrotherhoo ... atpsb>Matt at PSB</A> at: 2/4/05 4:48 pm

EXUP Worldwide

Here's another carby question

Here's another carby question

Re: Here's another carby question

Re: Here's another carby question

Re: Here's another carby question

I disagree

Re: I disagree

Re: I disagree

Re: I disagree

Re: Here's another carby question

Re: Here's another carby question

Re: Advice is free

Re: Advice is free

Re: Advice is free

Re: Advice is free

Re: Advice is free

Re: Origin of the species