Carb cleaning and power problems...

Steve1066 · Post by **Steve1066** » Tue Sep 21, 2004 1:53 am

Hello everyong - I`m in a bit of a situation.... I`ve recently been forced to keep my bike outside. It was running fine (is a little rich) until one evening when it run really rough. Power was well down, vibey and sounding strange. This I suspect was a dud plug, as a header to one cylinder was a lot colder than the rest. It picked up and started firing OK when I put in a new plug. At the same time I took off the carbs and performed a strip down. I must admit I`ve only stripped down one other set of carbs before. I found these were really gunged up with nasty nasty varnish coating the needles and lying in the float chambers. I did notice two of the float chamber screws were really munched up - probably indicating that some hacker has messed about with them - more on that later... I cleaned these by spraying liberal amounts of aerosol carb cleaner through all the jets and visible holes. I soaked the jets for about 10 mins and poked through with a bit of wire. I did not however check the float heights. I also did not 100% clear out all the varnish in the chamber - I did clean the needles well! Putting the carbs back on everything went smoothly, but when I was putting the throttle cables back I noticed something very concerning. There is a small brass tube external to the carbs going from somewhere near the float chamber to somewhere near the carb slide top. This was snapped off just by the float chamber. Any one got any idea what this is for? How would the affect the fuelling? On or off choke there was no sign of fuel leaking out... I proceeded to balance the carbs back on the bike which was quite easy. It started after a bit of persuasion and reved nicely in neutral. All cylinders seem to be firing (well all the headers get very hot). Power low down is all there, great... however when I give the bike more than 1/4 of the throttle the engine sounds retarded, acceleration noticeably drops off and this happens all the way through midrange and up to top end. Wow - sorry for the long post but I need........... HELP!!! Best Regards, Steve

flyingcircus68 · Post by **flyingcircus68** » Tue Sep 21, 2004 5:59 am

Well, First off I would try to avoid using wire to clean out jets. Try to use carb cleaner and an air hose. if you need to persuade some stubborn deposits try to use a piece of nylon bristle. You didn't mention the year/model, but your description is thorough enough for me to venture an educated guess on the problem. Brass tubes are used as vacuum signal lines and to move fuel to different points on the carb body. It appears, through your description, that the brass tube is supplying vacuum to the slide diaphragm. Since it is disconnected, the slide is not functioning correctly, or at all, and at higher power levels that particular cylinder is running excessively rich. You need to repair it either by gooping epoxy, or soldering it. If your goop epoxy, make sure that you fit the tubing together with minimal gap, to prevent it being clogged. If you choose to solder it, first disassemble it to remove all the polymer parts. I would personally choose the solder repair. Don't forget to use a little anti-seize or low strength thread lock on the screws. <img src=http://www.ezboard.com/images/emoticons/pimp.gif ALT=":hat">

Steve1066 · Post by **Steve1066** » Tue Sep 21, 2004 11:11 am

Thanks for your replay! I think I`ll give gluing it back together a try - I can probably do that without removing the carbs. Is it important to remove all visable varnish deposits when cleaning the carbs? Thanks again for your reply... Steve

flyingcircus68 · Post by **flyingcircus68** » Tue Sep 21, 2004 1:26 pm

no, it's not. You need to clean the orfice of each jet, blast out the passage ways and anywere it might impede movement. I would think that you still need to remove the carbs, or the epoxy/glue will ooze away.

Steve1066 · Post by **Steve1066** » Thu Sep 23, 2004 11:11 am

Hi Again, Apart from fixing the tubing problem, I reckon I could have incorrectly set float heights. The float needle - this can be placed back on the float tab in two different ways, rotated by 180 degrees. I saw the mounting 'wire' is not symetrical, so can this affect the float height? Regards, Steve...

cvhjkdis · Post by **cvhjkdis** » Thu Sep 23, 2004 8:06 pm

The external brass tube is for choke/cold start fuel transfer. It might let some fuel out on the engine when hot, It's more likely to let dirt in. The float pivot pins can go in either way, with the head to the outside you can remove the floats with the needle valve in place to adjust the float height tabs. Installed to inside, they are captive by the jet casting, and the whole float assembly (with needle valve) has to come out for any adjustment. Kind'a hard to tell what affect your adjustments are making that way. Good luck, Bob. Welcome, from the land of cheesy puffs.

exupjon · Post by **exupjon** » Fri Sep 24, 2004 4:15 am

float height is 12 to 14 mm fule height is10.5 to 11.5 mm and this must be your lucky day ive got 2/3 of thm tubes in my shed somwhere if u need one let me know<img src=http://img.photobucket.com/albums/v209/ ... Cheers.gif ALT=":cheers"> <img src=http://img.photobucket.com/albums/v209/ ... Cheers.gif ALT=":cheers">

Steve1066 · Post by **Steve1066** » Sun Sep 26, 2004 9:08 am

Yikes! I just checked the fuel level in th carbs.. Each one was set to 18mm above the float chamber line!! The Haynes manual says it should be 6.8mm to 7.8mm above the line! I`m thinking that as all of them are equal I`m not getting a leaking Needle valve? Would this way to high level cause my bogging down at full throttle probelm? Cheers!

exupjon · Post by **exupjon** » Sun Sep 26, 2004 9:39 am

haynes sez what we are talking 1000 exup arnt we???

Steve1066 · Post by **Steve1066** » Sun Sep 26, 2004 10:46 am

Ah maybe I should have mention its a YZF750r 1996.... Thanks to all who have helped out in this thread so far - much appreciated <img src=http://img.photobucket.com/albums/v209/ ... ock_On.gif ALT=":rock">

flyingcircus68 · Post by **flyingcircus68** » Sun Sep 26, 2004 6:12 pm

Get out the rope boys - it's time for a lynching........... You are very correct Bob, the brass tube in question is the fuel supply line to the choke valve. Since no particular model/year was mentioned, I deduced the purpose to the line based on its described position. This was a very open thought process that led me down the path of wrongfulness. I thought about it some time after my posting and came to the realization that the tube being described is exactly like the type found on the 94 yzf 750 carbs that I upgraded to.<img src=http://img.photobucket.com/albums/v209/ ... ng_sad.gif ALT=":sad"> Speaking of float heights, does anyone know what the float height spec is for 94 carbs? I have mine set to be right on the float chamber marks and it appears to be a little rich on the pilot/needle transition point. I would guess that the fuel level should be some specified distance below the cast in mark, possibly somewhere between 4 - 7 mm below.

djalbin · Post by **djalbin** » Sun Sep 26, 2004 8:40 pm

94 FZR750 carb fuel level is 7.3mm - 9.3mm 94 FZR1000 carb fuel level is 10.6mm - 11.6mm Don

djalbin · Post by **djalbin** » Sun Sep 26, 2004 8:48 pm

BTW - the fuel level measurement is above the float chamber line. You measure the distance between the line on the float chamber/carb body and the top of the fuel level in the tube/gauge. This distance is the fuel level. Don

flyingcircus68 · Post by **flyingcircus68** » Mon Sep 27, 2004 5:48 am

I apologize Don, but I am a little skeptical about the fuel level measurement being above the float chamber line. The reason that I am is because I have the 1987 fzr1000/750 and 1998 R1 Yamaha shop manuals and in each case the measurement is below the cast in line. Can anyone else verify that the level should measure above the float chamber line?

exupjon · Post by **exupjon** » Mon Sep 27, 2004 9:35 am

ive got the yam 1000 exup 89 ,90 manual states above the line and all exup 1000 use the same carbs<img src=http://www.ezboard.com/images/emoticons/eyes.gif ALT=":rolleyes">

flyingcircus68 · Post by **flyingcircus68** » Mon Sep 27, 2004 6:27 pm

Thank you exupjon, that proves that the specification is not consistently above, or below the cast in line throughout the various models that were offered. The specification is very dependent on how much the carb assm. is tipped from vertical. Obviously, this is not a problem on the stock bikes, since there is no adjustment to cause confusion. My frankensteined set up has them pitched at 9 deg (stock for 87 model) from vertical, can someone grab a protractor and level to verify what the yzf carbs are pitched at? (strictly at your leisure, of course). I could then use this to make a valid comparison of my present level to the stock yzf level.<img src=http://www.ezboard.com/images/emoticons/ohwell.gif ALT=":\">

djalbin · Post by **djalbin** » Mon Sep 27, 2004 8:31 pm

Paul, The above the line measurement for the FZR models came from the manual. Thanks for pointing out the fact that some bikes/carbs are measured below the line. <img src=http://www.ezboard.com/images/emoticons/happy.gif ALT=":D"> Don

Steve1066 · Post by **Steve1066** » Wed Oct 06, 2004 12:47 pm

Hi All, thanks to everyone for there help! Last weekend I got my 'spare' set of carbs out (eBay last year for 20GBP)... Gave these a thorough clean and blow through. These went on to the bike yesterday and it started surprisingly easily, with a slight tweak of the idle speed I was off...... It ran smoothly out of my drive and on to a back road. Took it easily until I was on the main road and gave it a wrist full........ OMG!!! The front went light, my heart raced, mouth dry - a huge smile spread across my face.. The bike is better than it has ever been, by a long way! Steve...

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Carb cleaning and power problems...

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