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I've read most/all of this thread, but may have missed the answer to this question: Has the bike, in its current trim, ever been able to pull redline in 5th gear? If so, what has changed immediately before the symptom?
I think it's a slow fuel supply..... normally you don't spend much time in 2, 3, and 4 th. gears. Just run up thru' them to get to 5th. and so don't run the fuel levels down far enough to effect acc. in those gears. I guess the test would be to hold the bike in, say, 4th. @ 4-5K rpm for some distance and see if the fuel levels/fill rate can keep up.....
I may have dreamed this up (so be nice), but I think i might have read somewhere on here about a bike that had a similar weird problem. Because of the position of the overflow tubes, above a certain speed the pressure of the air flowing up the overflow tubes was causing a back pressure that was preventing the bike from reving past a certain point. I think all they did was move the tubes a little or something. Again, be nice
Quote from: knowsnothing on May 15, 2012, 02:11:07 pmI may have dreamed this up (so be nice), but I think i might have read somewhere on here about a bike that had a similar weird problem. Because of the position of the overflow tubes, above a certain speed the pressure of the air flowing up the overflow tubes was causing a back pressure that was preventing the bike from reving past a certain point. I think all they did was move the tubes a little or something. Again, be nice I remember that thread. It was forum member: Johnie and his 750 K1 that was struggling to get over 50+ MPH. The problem turned out to be the carb overflow tubes.http://forums.sohc4.net/index.php?topic=68898.0
If it's running out of gas, the plugs should be bleach white when you plug-chop it at 7k in 5th. (Hit the kill switch, pull in the clutch, and coast to a stop.) It bears considering that 7,000 rpm's in 5th gear, with stock gearing, is around 105mph.
Quote from: Doctor_D on May 15, 2012, 04:02:39 pmIf it's running out of gas, the plugs should be bleach white when you plug-chop it at 7k in 5th. (Hit the kill switch, pull in the clutch, and coast to a stop.) It bears considering that 7,000 rpm's in 5th gear, with stock gearing, is around 105mph.at 7000rpm in top gear with standard gearing 18/48 im only doing 82mph ill go for anther ride this arvo thanks russ
Quote from: BIGRUSS58 on May 15, 2012, 04:24:56 pmQuote from: Doctor_D on May 15, 2012, 04:02:39 pmIf it's running out of gas, the plugs should be bleach white when you plug-chop it at 7k in 5th. (Hit the kill switch, pull in the clutch, and coast to a stop.) It bears considering that 7,000 rpm's in 5th gear, with stock gearing, is around 105mph.at 7000rpm in top gear with standard gearing 18/48 im only doing 82mph ill go for anther ride this arvo thanks russBear with me here, but we need to get on the same page with what is possible and what's not. It's not possible for you to be going 7000 rpms in 5th gear with stock gearing and only be going 82 mph. Either the tach is way off and your going about 5500 rpm and 82 mph. Or your going 7000 rpms and the speedo is way off and your going Dr. D's 105 mph.In your scenario Russ, one of your instruments is lying to you. And they don't have to be balls on accurate. A little off is OK, you still can't have the scenario you described.
Also, is the airbox a K2 type for sure... look at the parts fiche for your bike and compare.....
Hey Russ, welcome! Are the clocks off a different SOHC than a 750?
it definatley gets a full throttle opening?
ok cool,we can swap bikes if you like,i know some dead straight long roads here on the gold coast for speed tests,,we do one up and down pass all legal and check for cops first,then we have a play drag race then swap bikes,you keen?
sweet,ive been dying to embarrass a 750 with my 550!
im only joking,well have a look at yours and feel it out im sure.
Quote from: TwoTired on May 15, 2012, 11:16:44 amQuote from: dave500 on May 15, 2012, 03:02:55 amill get flamed here,the float height isnt dead critical,,what happens inside the bowl of fuel when your accellerating or cornering or going up or down steep hills and rough roads,,its all over the place inside like a washing machine.I'm not flaming or insisting that the bowl fuel level is the problem. I will explain that the fuel must be lifted to the carb throat from the bowl, and the longer the lift the more force is needed to lift it. Further, the amount of force needed, relates to the volume of fuel that can be lifted.This is why setting fuel level in the bowls has an optimum fuel metering.I'd still like to see pics of the spark plugs after a plug chop during the exhibition of the problem. A lean mixture should show if fuel starvation is the fault..........It could also be fuel tap restriction. Or, fuel line restriction.One way to tell, is to do a variation of the plug chop, only with the fuel valve. Get the machine to exhibit negative symptoms, turn off the fuel valve, then hit the kill switch, and pull in the clutch. Coast to a stop and pull off the fuel bowls to check fill level. If the fuel level is below the point where the pilot jet tube extends, you've found the problem and can chase down the source.Which reminds me...Some pilot jet aftermarket parts distribute a pilot jet physically shorter than what was stock length (28mm O.A.L., I think.)The bowl fuel level could be low under high power demand situations, and that would surface as a fuel deficiency, even though such a small pilot orifice is providing little mixture augmentation.The pilot jet tube inlet is normally positioned high in the fuel supply than the main jet. But, how high is significant.If the fuel valve needle spring pins are stiffer than stock, the bowl fuel level will be low. If the pilot jet tube is shorter as well, you have a recipe for fuel starvation under high fuel flow demand situations..........Or, it could be that the the coils are not recharging fast enough to provide reliable spark. But, then I'd expect sputtering/engine misses near the transition point between running well and a power level plateau limitation. Spark gaps in high pressures under max load in the engine cylinder do require more spark voltage. Have the stock coils been tried?Just an idea...thanks for your help . i will try all the things you have suggested and get back to you and send some pics of plugs , i have done it but not exactly the way you told me the plug was black on the threads and white on the electrode part and porcilin was light brownish cheers russ
Quote from: dave500 on May 15, 2012, 03:02:55 amill get flamed here,the float height isnt dead critical,,what happens inside the bowl of fuel when your accellerating or cornering or going up or down steep hills and rough roads,,its all over the place inside like a washing machine.I'm not flaming or insisting that the bowl fuel level is the problem. I will explain that the fuel must be lifted to the carb throat from the bowl, and the longer the lift the more force is needed to lift it. Further, the amount of force needed, relates to the volume of fuel that can be lifted.This is why setting fuel level in the bowls has an optimum fuel metering.I'd still like to see pics of the spark plugs after a plug chop during the exhibition of the problem. A lean mixture should show if fuel starvation is the fault..........It could also be fuel tap restriction. Or, fuel line restriction.One way to tell, is to do a variation of the plug chop, only with the fuel valve. Get the machine to exhibit negative symptoms, turn off the fuel valve, then hit the kill switch, and pull in the clutch. Coast to a stop and pull off the fuel bowls to check fill level. If the fuel level is below the point where the pilot jet tube extends, you've found the problem and can chase down the source.Which reminds me...Some pilot jet aftermarket parts distribute a pilot jet physically shorter than what was stock length (28mm O.A.L., I think.)The bowl fuel level could be low under high power demand situations, and that would surface as a fuel deficiency, even though such a small pilot orifice is providing little mixture augmentation.The pilot jet tube inlet is normally positioned high in the fuel supply than the main jet. But, how high is significant.If the fuel valve needle spring pins are stiffer than stock, the bowl fuel level will be low. If the pilot jet tube is shorter as well, you have a recipe for fuel starvation under high fuel flow demand situations..........Or, it could be that the the coils are not recharging fast enough to provide reliable spark. But, then I'd expect sputtering/engine misses near the transition point between running well and a power level plateau limitation. Spark gaps in high pressures under max load in the engine cylinder do require more spark voltage. Have the stock coils been tried?Just an idea...
ill get flamed here,the float height isnt dead critical,,what happens inside the bowl of fuel when your accellerating or cornering or going up or down steep hills and rough roads,,its all over the place inside like a washing machine.
Quote from: Doctor_D on May 15, 2012, 04:02:39 pmIt bears considering that 7,000 rpm's in 5th gear, with stock gearing, is around 105mph.at 7000rpm in top gear with standard gearing 18/48 im only doing 82mph ill go for anther ride this arvo thanks russ
It bears considering that 7,000 rpm's in 5th gear, with stock gearing, is around 105mph.
