www.zxrworld.co.uk

Interesting reading. Thanks for all the ideas (I know I'm late to to this thread) Being in Sydney its bloody hot even in October. I've been getting hot start problems. Had removed the hoov toobs but now I'll put em back. Me bike bloody hates running out of fuel (ie getting lower than full tank) and if its hot, not a chance of starting. Ran battery down and had to give it 4 pushies to start. Not much fun in 30 degrees and 80% humidity.

I have been trying to determine possible causes, ultimately I don't think there is one sure fire fix or one sure fire fault.

From day one I have ran the bike with hoover tubes , FCR's and meshed funnels with a full size heat shield underneath. Although I don't experience the hot issue all the time and indeed I can still count them on both hands it is there

So while our day time temp was still above 30'c I had a wee experiment.

On a 500m stretch of road I opened the throttle wide and shut it off rapidly for about 10 times , when I stopped up at the traffic lights it wanted to cut out and was only firing on 2 or 3 cylinders , keeping the rev's up I managed to take off when the lights changed but it soon konked out while moving !

Sat at road side and attempted to get it going again - no joy.

The purpose of this was the theory of fumes accumulating in the area and making the air mix too rich , if you've ever watched FCRs or TMRs being cracked wide open you know how much vapour comes out the funnels so doing it rapid for 10 times would have filled that area right up.

10mins later I tried again but it still wasn't having it, I eventually took it into a car park with a slope and bumped it, it caught but again was only firing on a few cylinders. About 400m down the road it konked out again I sat for a couple of min's and tried starting it and it fired on all 4 this time and ran perfect all the way home.

On other occasions where I have had this issue I believe I had been "charging" rather than cruising so again it's likely that the area around the carb's was heavy in fuel vapour.

Once I find it in my storeroom I am going to rig up a 150mm 12V cooler fan from a PC onto a switched live and mount just behind the carbs and get it sucking the fumes and blowing them out the rear , I will then try the full throttle treatment again on the same stretch of road and see what happens.

After that I will then decide on fitting additional foil heatshield onto my existing Nylon one to see if that helps, I also noted that HRC call these airtrays on their race bikes that run open meshed carbs rather than a heatshield and they also look to channel air from the front across the carb's.

What I have noticed is that High Octane fuel with a fully charged battery will make the bike start no problems regardless of the temp, so in the summer months it might be a good idea to keep the battery in peak condition.

MM!

Mate you are dead set the ZXR Whisperer!

Believing the Hot start issue is a combination of elements I have now tried out testing on the battery.

I removed the battery from the race bike and put it into the ZXR , this has got to be quarter of the size so a huge weight saving However the amp hours are not the same - my onboard volt meter wasn7T showing any apparent increase in regulator output and on start up voltage was showing constant each day.

Initially the bike fired up fine and almost instant too - it is after all anew battery with full kick

However, it wasn't long before I couldn't get it to fire up after only a 7 mile journey, bike was well warm though as the final mile or so is a dual carriageway so it got used Day time temp was 25~28'c

Shop came out with their booster pack and off it went.

Next time I had been using the bike for around 50miles and it was a cow to get going and the other day was the last straw as day temp was only 25'c and bike was only at 70'c coolant & 67'c oil and I hadn't been thrashing it - almost killed the battery trying to get it going but gave up and got a bump start - fired up instantly.

My conclusion is, your battery does need to be in tip top condition - this may be further surmized if you consider that brand new bikes didn't have a recall with starting problems, owners must of had at least one year of trouble free motoring with them unless your a one owner bike and can verify you did have this issue from new but wasn't entertained under warranty ?

So as the bikes get passed around, either poorly maintained batteries or cheapies have been the order of the day or like what I done fitting something that just works rather than is the proper item.

Have now got the pukka battery back in and my next few outings should almost replicate what I have done over the past weeks , I am expecting no problems but you never know !

MM!

So far so good, have done a 200mile blast , city stop starts and short stop thrashing and the bike is firing up fine.

With the FCRs you give the throttle a 1/4 twist as you press the button and it catches quicker , if you then hit the kill switch and then try again it will fire up with no throttle utilizing the residual fuel in the down tracts.

Of course day time temps have dropped somewhat but have had the cooling fan come on several times after thrashing it or sitting in traffic so it's been plenty hot.

Oh, I've fried another clutch

So you reckon the battery is the key.....
Was thinking that the 12 volt fan was a good idea. Plenty of room behind the carbies.
Am going for a thrash this weekend. Will see how it goes. Have charge me battery good n proper.

Still going to fit the fan myself - I have one hiding in the cupboard so might as well put it to use, don't race the bike so what little weight it is could be worthwhile.

Seen a rec/reg with one siliconed on it but bolting it under the muddy would be cheaper

MM!

Here's another take on this issue. A recent discussion about the fuel pump has cleared up that this is a full pumped system with a check valve which prevents gravity feed. I suggest that the hot starting problem could be caused by the fuel in the float bowls evaporating - it can't be replaced with the ignition off. Then when you come to start the bike the carbs are empty and it takes up to 30 seconds (as if you'd run the bike dry) to replenish them. 30 seconds is a long time, by which time some people try to bump the bike which 'cures' it. Or they try turning the ignition on / off and fiddling with the starter. The fact the bike then fires up indicates the cure has been found but in reality the cure is patience, just give the fuel pump time to refill the carbs.

If this is right then turning the fuel tap off when you stop will make no difference - the carbs can't flood through the pump.

The 'cure' would seem to be to turn the ignition on and wait for 20-30 seconds before thumbing the starter to give the pump time to fill the carbs. Simple as that. A preventative cure would be fitting heat shielding to keep the carbs cool - this was one cure suggested to me recently by a tuner who had experience with hot starting issues, so this also fits in.

The empty float bowls seems to be the cause. Hot starts are a pain if stalling at the lights cos no end of jamming the starter gets it going. After 20 secs you can hear the first couple of cylinders firing and then it runs. Classic symptoms of fuel starvation.

I don't have a heat shield yet but working on it.

I think that there has been an incorrect assumption in one of the replies. Assuming the carbs are empty of fuel, just turning on the ignition will not cause the pump to energise. This can easily be confirmed by turning the petrol tap off while the engine is running. When the engine stops because of lack of fuel, turning the tap on again will not cause the pump to run, even though the ignition is still on. The pump will only operate continuously when the starter button is depressed. Once the engine is running the pump will energise spasmodically to top up the float chambers as fuel is consumed. The Kawasaki handbook does say that if the bike runs out of fuel on the main tank, switching to reserve will require at least 20 seconds depressing to fire up the engine again. A few years ago DynoPro racing rebuilt my engine, and when I took the complete bike back to them to run-in and set up the carbs, they used a short piece of wire to short the red wire to the black/blue wire on the relay to activate the pump and fill the float chambers. I'm sure they would just have turned on the ignition and waited 20seconds if the pump ran immediately.

Interesting point. This would explain all the more why once the carbs are dry you need to spin the motor for a (seemingly) long time to get them full enough to fire. And possibly why the problem is exaccerbated if your battery is poor by the time the carbs are full the battery is too low to spin the motor enough and produce a good spark for ignition. So, combination of old battery and hot engine is not good.