Hot weather engine performance

[disassembled]

Hi guys,

I took my zx9 out for a quick run this morning and noticed something odd...

My bike is running better, accelerating faster... tuning issue? Could this mean its underperforming in cooler weather? Of course this could just be my imagination too, but it seems to be far too substantial a difference for that.

Any ideas?

Cheers,
Mick.

[wackyrider]

It probably overheard you saying that you were gonna rip off all the fairing off and is just soo happy about it that it's running much better now

[pav69]

thats a weird one my zx runs like shit in the hot and loves the cold is it stock or modified.

[pav69]

second that less weight and more wind in your face just feels good.

[disassembled]

Wacky, that met well be true.

Pav, it stock except for a full exhaust system and the carbs have been re-jetted.

[disassembled]

...may well be true. Stupid phone

[evilkarl]

Often means the bike is running lean in cooler conditions. My dragbike is the same, have to up the jetting in the colder months.

[Dynomutt]

If the bike runs better when it is colder, then it is usually running a little rich when warm, if it runs better when warm than when cold then it is usually running a little lean which gets worse as the air temp goes down. My 650 with TMR carbs runs two different size jets for winter and summer, 152.5 summer and 157.5 winter, not much difference but enough to be noticable. If you are going to remove the fairings from a ZX9R C model onwards then you'll need to run a short pipe from each of the flaot bowl vents into the airbox, a couple of inches tall and slash cut 45 degres facing forwards, this will sort out the problems when the ramair is removed and ensure the float chambers get the correct air pressure. I've done a few on the dyno and they run great on the roller but once on the road and above about 50mph they run lean and fuel starve, with the vent pipes routed into the airbox they run fine on the road, as the carbs rely on outside air pressure to equalise the pressure in the venturi, in a similar manner to a pitot tube on a boosted bike..

[80s freak]

Dyno does this negate the need to run the silly looking extentions on the air ducts where they go through the frame?

[80s freak]

Just thought of this, what if you're running pods?

[disassembled]

Should I be using an ego sensor (obviously my bike doesn't have one) and afr meter to sort out the mixture or can this be done 'by feel' if you follow me here.

Actually I've also noticed recently that if I use too much throttle at lower revs that instead of waiting to build up revs/power, the bike bogs right down. I don't remember this happening before. It feels to me like she's over fueling. Shouldn't the fuel flow be governed by vacuum?

[Dynomutt]

If you run the float vents into the airbox as described you can get away without running the air intakes out of the front of the frame.
If you look on the airscoop under the headlamps you'll see the small diameter pipes which are connected to the float vents, by doing away with all of that crap, and just cutting two small holes in the airbox between carbs 1&2 and 3&4 and running about 3 to 4 inches of pipe off each float chamber vent into the airbox and slash cutting it at 45 deg to face forwards, you make the bowls get the same pressure as the venturi. Once you have done that you can just leave the air intakes into the airbox flush with the frame, or trim them back a little so they aren't really obvious.
Get the bike set up on a dyno, and do this airbox/float vent mod, and it will run fine on the road.I've done a few of these over the last couple of years to allow the bies to run correctly on the road. It's not a problem that shows up on the dyno very easily as it only occurs over about 45mph on the road due to the airflow. I found it on a customers ZX9R the first one I set up without fairings on it, and no air tubes sticking out of the frame, it ran fine on the dyno but not good on the road over about 45mph, a few minutes arse scratching and I sorted it as described.
If you are running pods then you don't have the same issues of the venturi getting a slightly higher pressure than the float chambers.
The ZX9R with stock carbs doesn't like running with pods though, it's far better to retain the airbox, and fit a K&N filter inside it.
Unless you are fitting Keihin FCR and stacks or better still Mikuni TDMR with stacks. I'm currently building a bigbore motor based on the 06 Z750 bottom end with 05 Z1000 cylinders and head JE drop in high comp pistons, ZX9R cams, ZX9R Dyna2000 ignition, and Mikuni flatslides instead of the injection.

[BANDITROD]

http://www.streetfighters.com.au/forum/topic.asp?TOPIC_ID=1396&SearchTerms=Ram,air, there is some more info on the subject here aswell mate

[Dynomutt]

That essentially outlines the issue, and shows another way of dealing with it, although I think it is easier and quicker to use two small tubes, to the vents rather than splicing them into one and going through the filter. But he is correct as far as identifying the problem, although the chap with the SRAD and K2 engine is suffering from a completely different issue. This problem only afflicts carburetted bikes not FI bikes.

[Redmohawk]

Even pods can benifit from balance tubes being fitted in hard to tune cases, depends alot on where your legs are in relation to the pods/frame of bike etc. Esentially if your legs make a dam for the air to build up pressure near the pods this can effect tuning. On two bikes I have fiddled with a bit over the last 7 months you can see the difference in the air fuel ratios on my oxy sensor one bike at speeds over 120 kph can vary as much as 1.5 just by moving your legs from pegs to pillion pegs. Running the balance tubes into the base of each pod facing the sealed end sorted this issue to the point of not being able to see the same effect on a wide band oxy sensor after mod.