Flat spot at 1/4 to 1/2 throttle?

[swbarnett]

I have a problem in that for the past 20,000k or so my bike has had a couple of issues when it comes to twisting the wrist. At between 1/4 and 1/2 throttle it dies until I open the throttle further. The second thing is that if I hold the throttle above 3/4 it splutters for a bit and at its worst won't go past about 8,000rpm (redline's about 11,500rpm).

The bike has Yoshi pipe that was put on about 70,000km ago. Nothing else was done to the bike at the time (i.e. no carb tuning or the like). I was told that this was not required and can attest that until recently this appears to have been correct.

BTW: The bike has just past 110,000km.

Any suggestions as to what might be going on and how to fix it? I've had a mechanic look at it. I'm just after a second opinion before I go ahead with their suggestion.

[Akzle]

its fucked. You know my offer.

[haydes55]

Sounds like carbs need a clean/balance. Could be anything from a sticky butterfly valve or slide or what ever you have in there. Or a partially blocked jet.

If the timing slipped, bearings are collapsing or anything else internal has fucked out, you would be having worse symptoms at a greater rev range.

Carb strip and clean, if that fails then look at electrical connections, could be due to at certain revs it rattles a loose connection enough to fuck an earth until the revs smooth out.

[skippa1]

Electrical.....maybe earthing issue, coils breaking down under load, plugs fucked, HT leads need replacing
Fuel.....crap in fuel, shitty in line filter, carbs shitty need clean and balance, shit in tank, water in tank or bowls

most unlikely it runs good for 70,000kms with the pipes then all of a sudden needs jetting

[swbarnett]

Sounds like carbs need a clean/balance. Could be anything from a sticky butterfly valve or slide or what ever you have in there. Or a partially blocked jet.

A mechanic has had a look and the carbs are clean as a whistle and working fine.

If the timing slipped, bearings are collapsing or anything else internal has fucked out, you would be having worse symptoms at a greater rev range.

That's what I thought. Other than the two niggly little problems it runs fine.

Carb strip and clean, if that fails then look at electrical connections, could be due to at certain revs it rattles a loose connection enough to fuck an earth until the revs smooth out.

I had the tank off last weenend and everything looked OK but I didn't specifically check the connections. I'll have another look this weekend.

I had another bike that used to cut out completely, then run for a while, then cut out etc. It turned out to be a worn throttle cable earthing on the cylinder.

[swbarnett]

Electrical.....maybe earthing issue, coils breaking down under load, plugs fucked, HT leads need replacing
Fuel.....crap in fuel, shitty in line filter, carbs shitty need clean and balance, shit in tank, water in tank or bowls

Plugs are brand new as of last weekend. Made no difference. Carbs, as above are evidently clean and working.

One thing I have noticed is that it runs better on Caltex than all the others (haven't tried Mobil yet). Runs worst on Gull.

most unlikely it runs good for 70,000kms with the pipes then all of a sudden needs jetting

That's what I was thinking. I even had the pipe repacked to return it to the original airflow. Didn't do anything noticeable but definitely sounds better than it did.

One thing I forgot to mention is that it runs perfectly without load. Revs like there's no tomorrow.

[unstuck]

Coil or coil packs?

[buggerit]

split in carb boot?
oval emulsion tubes?

[swbarnett]

The really weird thing about this problem is that it only happens at higher speeds. I can take off from a standing start and gently progress through the throttle with no problem.

[Ribit]

http://www.kiwibiker.co.nz/forums/sh...run-GSXR750-K7

Beginning to sound like theres a common fault with this era zoom(less)zuki

[flashg]

My 2005 FZ1 ran like that on 95 octane. Put it onto 91 octane and it came good. Dealer said handbook says 91 only. He said there's been many problems with plugs (it stuffs them)many twins don't like it either. Other bikes I've owned love the stuff

[Drew]

Hmmm, till you said it happens when the speed was higher I was thinking battery voltage. But that usually presents at lower revs when the throttle is opened. Once the revs climb the load is lessened.

Got me fucked, take Akzels $5 and bag of chips.

[spanner spinner]

It will be worn needles and oval emulsion tubes, all Suzuki's with the type of carbs your bike has have this problem at some stage. I am surprised you made it this far they usually start giving problems around the 70,000k mark, maybe the pipe works with a slightly rich mixture better than the standard exhaust. You are talking wear in the 0.01mm range so it is hard to see with a eye-ometer.

[Drew]

Time for a set of flat slides!

You'll get better fuel economy than currently, but maybe not as good as when it was new.

Upside to the extra power...You get to listen to them go chikka chikka chikka at idle.

[swbarnett]

It will be worn needles and oval emulsion tubes, all Suzuki's with the type of carbs your bike has have this problem at some stage. I am surprised you made it this far they usually start giving problems around the 70,000k mark, maybe the pipe works with a slightly rich mixture better than the standard exhaust. You are talking wear in the 0.01mm range so it is hard to see with a eye-ometer.

Interesting. So the fix would be to replace the needles and emulsion tubes, yes?