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View Full Version : Qustion from a newbie----Flat Spot



2wheels in Red Beach
10th October 2005, 20:58
Any ideas...... I will be cruising along 100 or so k's start to excelerate then hit a flat spot to the point of decelerating then all of a sudden the power will kick in again. would this be something obvious.

marty
10th October 2005, 21:02
could be anything - a flat spot on the tx curve maybe. i trust your not asking your 250/4 to accelerate from 100 in 5th/6th gear?

2wheels in Red Beach
10th October 2005, 21:11
It can do it fairly comfortably, but lately seems to stuggle.

marty
10th October 2005, 21:13
how bout that 30 knot head wind you've always got up there on the peninsula?

2wheels in Red Beach
10th October 2005, 21:23
lol....yup. i do get that as well but that has a different feel to it. the engine all of a sudden picks up quickly from the flat spot.

Any way wot ur saying.....ur saying I got a slow bike or wot.....

SuperDave
10th October 2005, 21:45
My 250 accelerates from 100kph in 5th or 6th quite comfortably up until 170kph - but then again, acceleration is all relative, to me my 250 is relative to my old FXR150 :laugh:

I felt a flatspot similar to this once when I was test riding the ZXR, I believe it had to to with trying to fling the throttle open wide very quickly though. Just easing off the throttle and then trying to reopen it seemed to fix the problem fine. Have yet to have it happen to me since.

2wheels in Red Beach
10th October 2005, 22:04
I have tried easing off the throttle and then tried to reopen it slowly
I have tried easing off the throttle and then tried to reopen it fast
I have tried easing off the throttle quickly and then tried to reopen it quickly and repeated a few times as if revving.
It just seems to make it's own mind up to put gas on again.

It's not good when I have some idiot in a cage right up my arse :argh:

Gremlin
10th October 2005, 22:38
What revs are you running when you try to accelerate? My zzr has a big flatspot about 4-5k, and speaking to JSG (who has a zzr) he also has it.

Two solutions I've found:
1. Run a higher gear. Accelerating from 6-10k is no effort besides twisting the wrist
2. Depending on the gear (mine seem to have different ways of behaving) some, if you gently open the throttle and allow it to build, you might be able to minimise the effect.

Riding a 250 (even a quick one like the zxr or cbr) you have to, have to use the gears. Big bikes have power from 2-3k I believe. I have most of my power beyond 9k.

For fast acceleration, drop 2-3 gears, then go :chase:

TwoSeven
10th October 2005, 23:39
What rpm and gear is it doing it in ?

2wheels in Red Beach
11th October 2005, 05:42
It is doing it in 5th gear (top) at around 10 rpm. but not always. (although seems to be getting more frequent) is it ok to drop down to 3rd at 100-110 k's? Sorry for any silly questions.

SuperDave
11th October 2005, 06:54
I'm no expert but I believe that dropping down to a too lower gear whilst still going fast then trying to rip the throttle open is gonna cause valve bounce (?) which is bad and can screw up your engine. Someone correct me if I'm wrong.

thehollowmen
11th October 2005, 07:08
I'm no expert but I believe that dropping down to a too lower gear whilst still going fast then trying to rip the throttle open is gonna cause valve bounce (?) which is bad and can screw up your engine. Someone correct me if I'm wrong.

Yes I'd say that's about right but you'd have to go over the redline to do that.

2wheels in Red Beach
11th October 2005, 07:40
My redline is 18 i am only at 10-11 when in fith. maybe i will only drop down one gear then. to try and get some more power.

Hitcher
11th October 2005, 08:24
Most four-cylinder 250s, in my experience, have a flat-spot somewhere in their power range. Some worse than others.

Gremlin
11th October 2005, 09:11
My redline is 18 i am only at 10-11 when in fith. maybe i will only drop down one gear then. to try and get some more power.
yep, the cbr and zxr rev very high, your power is high up in the rev band. Before you accelerate, just drop a gear (maybe two, depending on your revs) and then roll it on and grin :devil2:

bugjuice
11th October 2005, 09:15
when were the carbs last checked and reset? And checked the plugs etc? Agree with Hitch, that there are flatspots all over the show on some bikes and others. But on occasion, you can iron them out by making sure the engine is running at it's best for it's time in life.

Also, whacking the throttle wide open can cause a slight flooding effect of fuel, so the flat spot would be the engine trying to get rid of that, then it'd pick up the power as more air gets in to replace the fuel you've just dumped in there.
See about getting the carbs checked over and cleaned. Might help some

TwoSeven
11th October 2005, 11:51
Dont wack the throttle open on a cibby. You need to lean to chase the power with the throttle. Its a 1/4 turn throttle and if you respond too quickly it will lean out/ then richen the engine too quickly causing it to bog - eventually you'll kill your plugs by fouling them.

Also, cibbies require being reved 7-10k all the time. Flat spot is 4.5-5.5k rpm, there isnt another one. To me it sounds like the bike is beeing run in too high a gear for the speed/rpm and the plugs/carbs need a tune.

enigma51
11th October 2005, 12:23
Had similiar problem with a bike of mine once and ended up being a plug lead that was broken so what would happen that all the cylinders would spark until a certain rev range one would die and kick in after a while but because the rev where high already the only thing you would see is the rev climbing quickly drop down a bit (no engine splutter as the revs are high) go up slowly and then all of a sudden it will be fine again.

How I found out it was the plug lead was more a mistake than anything else I pulled the tank off to balance the cabs and accidently pulled out the plug lead and noticed a "kink" in the lead so decided to change the leads etc and the problem went away. So have the leads checked. Its not an easy problem to spot as it only happens at high revs so simply taking the plug out and checking for spark will not help you actualy have to take it to someone with the proper tools.

2wheels in Red Beach
11th October 2005, 18:19
I thought I would try a couple of things on the way to work like dropping down a gear, do ya think i could find the bloody flat spot. Probably the best ride home I have had in ages. Fantastic weather and not a flat spot for the whole 50k's home. :2thumbsup

It will probably be back tomorrow. :angry:

It's probably time I got it serviced anyway. :clap:

marty
11th October 2005, 20:12
my RS250 would do similar, accelerate from 100 (5500rpm) to 115 in 6th, then struggle - just at the bottom end before the pipe came on song. if i dumped it into 4th it would come right, but if i went into 3rd it would climb happily (in 3rd) thru to 170ish before running out of puff

nudemetalz
11th October 2005, 20:25
When was the last time you cleaned out the fuel flow (ie fuel filter) and cleaned/replaled the airfilter ?
Could be related.

2wheels in Red Beach
12th October 2005, 06:19
When was the last time you cleaned out the fuel flow (ie fuel filter) and cleaned/replaled the airfilter ?
Could be related.
If they do that with a service 6 months ago, if not i have had the bike for two years and not had it done at all.

nudemetalz
12th October 2005, 09:35
If it had a service then that would (should) have been checked.

2wheels in Red Beach
12th October 2005, 18:32
OK......riding home tonight started to lose power 115-120 ks kicked down to 4th gear and started to pick up fine (in fact it felt quite good :niceone: ) then at around 16rpm 'ish I went back up to fith gear and immediately felt the power loss. :argh:

vfrboy
12th October 2005, 19:52
I had a similar prob with my bike when I got it, would go great sometimes then not others no matter what gear I was in. I eventually tracked it down to the 4 gauze filters in the fuel bowls of the carbs were blocked with crap. Would probably be a quick check on your bike, can't be any harder than a bastard VFR to work on. Also check filter in tank as has been previously suggested, try new plugs and leads. Good luck. :2thumbsup