HELP.. ZXR400 PROBLEM

[jamkwak]

Anyone have any ideas please.....!
Engine wasn't idling, had to keep the revs up or it died, at low revs it sounded like a cylinder was off, so this is what I did........
Engine out... stripped carbs ( very dirty ) completely cleaned them and fitted Stage 1 Dynojet kit with 96 main jet and pilot screw out 1.5 turns,reset float heights, cleaned and re-oiled K&N Filter
Next... camshafts badly pitted, replaced with good used ones, No2 cam cap broken.. replaced it. New camchain and tensioner bar, all set up and lined up perfect. New cylinder head gasket, left out the cylinder block to crankcase gasket to increase combustion.
Next checked valve clearances and set to race spec ie inlet 20-25 and exhaust 25-28 (new shims). Replaced Fuel Filter, new Iridium Plugs,Oil Filter and filled with fully synthetic engine oil.

After 5 weeks work ( on and off, not constant, wife wouldn't allow it ) turned the bike over and would only start on full choke, if you touched the throttle it died. Reset the pilot screw 2.5 turns and still had to use choke ( not as much ) but was now able to use throttle. Below 2000rpm engine died, wouldn't idle even fiddling with idle adjuster still no good, had to keep revs high but still sounded like it was labouring in low revs. Sounded good at high revs. Still have to use choke to start..won't start without it
Does anyone have any idea what it would be, ignition system...? fuel system...?
Any thoughts would be welcome.. doing my head in

[Tyrant]

Sounds like the problems I was having recently.
Mine was down to a dodgy connection in the ignition switch that meant the battery wasn't charging properly but also a broken fuel pump relay that meant the pump wasn't working all the time. Worth checking the pump and voltage across the battery.

I found the PDF on this site great for fault finding on my charging system-http://www.electrosport.com/technical-r ... -guide.php

[jamkwak]

I was thinking it might be more of a fuel pump or relay problem, I'll check them tonight... I'm hoping that I haven't overlooked a possible valve seat problem, don't fancy a complete strip down again....

[zimm]

not directly related, but the valve clearances in the kit manual are on the silly side of excessive,

aim for .20 EX and .15 IN

mine's at the kit clearances, sounds awfull till fully up to temp, and a couple of bhp down due to lost duration and lift the rest of the time.

#96 mains sound a bit small, (my almost stock H1 is on #105's and still so lean that the airbox intake has been restricted with gaffa tape to correct the mixture) whats the rest of your setup ? exhaust ? tuned at all ? what clip position are the needles on ? are your air corrector jet blocked off ? (has the bike previously run ram-air ?)

all your pilot jets nice and clear ?

[jamkwak]

I was going by the Kit Manual for valve clearances thinking due to race temperatures this would allow room for expansion... in your experience if you think that is excessive then I'll try the clearances you suggested.
I fitted a Stage 1 Dynojet kit with needles on the second setting down.. the kit came with #92 and #96 main jets recommending #96 with aftermarket pipe.
I have a K&N filter fitted and a Scorpion end can so I went for #96. I know the head has been skimmed but as far as any other performance work, I have no idea. I have a set of #97.5 jets which I haven't tried....

[jamkwak]

One other question... the vacuum pipes at nos 1 and 4 cylinders had been blanked off.. is this recommended or will I connect the two with vacuum pipes ?

[zimm]

i did mine almost to the kit clearances, and then spoke to a couple of respected tuners about it who said to tighten them up a bit, so im just passing it on, thinking about it, if you were racing in F3, in SE asia, with full works support, its going to be a damn sight hotter than it is here, and the bike will be properly up to temp the whole time, so maybe under these conditions you may well want massive clearances..

i didnt get time to re-do mine for oulton, just left her ages to warm up, but without a thermostat or tape on the radiator she was running cold again by lap 2 .. (plus, .. um .. im a bit slow)

try dropping the needles right down, its where they normally seem to end up for a crisp midrange, and IMO anything less than a #100/#102 main jet is going to be lean with a tuned engine, our zx4 is bog stock and running #98's

course it's all guesswork to a degree, best thing to do is get it idling and put it on a dyno for a few hours. But you know that already.

I dont know wether its preferable to have the vacuum pipes linked, or blocked .. as long as they arent open to atmosphere it should be ok though.

[MillaMeter]

Hi,

I found that the dynojet kits aren't 100% I installed my stage 1 by the manual and it was totally bollox, I had 3 mahoosive flatspots. I tuned my own carbs my way and it now runs spot on with no flatspots or idling problems. I've put the bike on the dyno and is kicking 62bhp at the rear nicely.

Try this:

On the needles, put the E clip on the very top groove instead of what the manual says, second 1 down. Make sure you put the 2 washers on top. THis will give you the perfect WOT midrange.

Install the 92 main jets (i know the manual says about 96's with aftermarket can and filter) I have both can and K&N installed on my bike and runs perfect with 92's, plus you'll be saving fuel. You can always change them back to 96's if the 92's don't agree with your bike. But because you got the head skimmed, you'll have to see which 1's work best between the 2.

Set the idles/mixture screws to exactly 3 turns out.

Check that all 4 slides move freely up and down and go right to the top.

You might also wanna check the fuel pump and relay.

I'm not sure about the vacuum pipes but personally I would link them back up just to be on the safe side.

Regards

Rich

[jamkwak]

Thanks for that Rich, so many conflicting ideas ... all a matter of guess work I suppose...I'll try the needles on the top groove with the #97.5 jets with the pilot jets at the present setting of 2 turns and take it from there.
I checked the plugs earlier tonight and No2 cylinder was running very rich, all the rest were fine...
Ta
John

[zimm]

pay close attention to the float heights, these bikes are VERY sensitive to them, a mill out can be all it takes to utterly screw the midrange..

needle height and jets wont fix the not idling though, my guess is a blocked pilot jet, or WAY out of balance carbs,

try setting the carb balance "on the bench" with a 3-4mm drill bit/allen key as a guide just to get the butterfly's somewhere near each other

[MillaMeter]

I checked the plugs earlier tonight and No2 cylinder was running very rich, all the rest were fine...
Ta
John

Hi,

You're welcome.

Have you tried a new set of plugs? could be a weak spark. Like zimm mentioned, the floats are very sensitive so make sure they're spot on
Correct me if I'm wrong, I think the float heights are 11mm?

1 thing that fooked my idle 1 day was very very leaky carb holders. Replaced them with the later type from a L3 from trusty Cradleys for only £70, that's everything, holders, o-rings, VAT and postage.

Regards

Rich

[zimm]

11mm +-2mm iirc ?

i normally set to 12mm as the needles are usually on the rich side anyway

[jamkwak]

Thanks Guys... going to spend a few hours Saturday double checking float height, sync etc. Lifted the needle to the top groove as suggested and it is now ticking over albeit at 3000rpm, if I adjust idle down it drops suddenly to 1000 for a few seconds then stops, if I increase the throttle as it drops, it splutters for a bit but does increase the revs again to 3000rpm... something ain't right.... it ain't gonna beat me.....

[will#224]

throttle cables are moving freely yeah?

just an idea

[jamkwak]

Yep.. cables all ok... needs the choke everytime to start though....!