mixture problems-advice needed

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ross46
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mixture problems-advice needed

Post by ross46 »

Hi all, i have looked through all the topics that i can find but none seem to be the same as mine and the ones that are havnt been resolved. anyway the problem(s) about 3 weeks ago i found a hole in my standard exhaust system on my l6 so i bought a stainless steel race system of ebay (unsure of make) with a yoshi can, swapped the yoshi back to my art can and sounds better. when i first fitted the system it still started and ran fine, power felt abit flat but i know thats because it will likely need jetting. as i its got colder my bike has started to run badly, when i accelerate it will sound like a twin throughout the rev range. if i roll on the throttle i can get it to run better up to about 10k when i have to wait for it to kick in with the power, feels like turbo lag sensation. i know it needs jetting to make it better but im looking for a starting point. over the weekend i stripped and cleaned the carbs, checked the mixture screws, floats, jets, diaghram and needle.
Mixture screws from left to right were-3 1/4 - 5 1/2 - 3 3/4 - 3 1/2.
I measured the float heights with the carbs at 45 degrees so the float needle was just touching, left to right (in mm)-10-10-12-10.
Main jets are all 90's
needles are n77
my question is where should i start to get in the ballpark so the bike rides ok enough to take it to the dyno for perfecting as at the moment it is dangerous. it wont idle unless its at around 3k and if i lower the idle it dies if you roll off the throttle and wont start again, it doesnt start easily from cold either. im looking at buying some 92 and 95 jets, are these a good start? another option im considering is dynojets? any experience with these anyone? i also need to balance the carbs again, i did it a while ago but they werent brilliant and close enough isnt good enough! i am still running the stock air filter, tommorow i am going to buy some new ht leads and spark plugs to help my old girl along.

any help would be greatly appreciated, i know im not going to get exact setups but i am needing some help getting it into the ballpark. thankyou very much

Ross
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Re: mixture problems-advice needed

Post by Robbie »

ok with out access to a dyno with airfuel mixture.Id start by trying to run it with the choke on at various amounts.if its better its running lean.if worse then rich.also try seeing if all the downpipes are routhly the same temp.you could run and try cutting it out while going at a decent speed revs up.then check the plugs u will find a guide online somewhere.
and i have a set of dynojet needles sitting here if you want them at a decent price.
cheers
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Re: mixture problems-advice needed

Post by banner001 »

get hold of some small m3 washers to use as shims for the needles, cheaper than dynojets and depending on your needs, might be enough to sort out your midrange and top end.
UK ZXR400 L3 (1993) - Fully restored and on the roads, my green beast!
JPN ZXR250 A2 (1990) - Revs to 19,200rpm... 'nuff said :smt003
ross46
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Re: mixture problems-advice needed

Post by ross46 »

thanks for the replys, will try the choke on my way home and i got some m3 washers of the guy i work with and hopefully they will work, il keep you updated as this seems to be a common problem as mine right now wont idle properly either
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Re: mixture problems-advice needed

Post by banner001 »

screwfix sell them for ~46p for 100 washers, though postage is about £5 :smt009
UK ZXR400 L3 (1993) - Fully restored and on the roads, my green beast!
JPN ZXR250 A2 (1990) - Revs to 19,200rpm... 'nuff said :smt003
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Re: mixture problems-advice needed

Post by ross46 »

there is a screwfix just up the road from me, does anyone have any suggestions for what main jets i will probably need to run with a race system and straight throuugh can?
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Re: mixture problems-advice needed

Post by banner001 »

ross46 wrote:there is a screwfix just up the road from me, does anyone have any suggestions for what main jets i will probably need to run with a race system and straight throuugh can?
probably +100's and 2-3 shims per needle? hard to tell though, but that might be ok for a ballpark...you would benefit from dynojet needles though, much smaller obstruction so more fuel for a given amount of venturi vacuum.
UK ZXR400 L3 (1993) - Fully restored and on the roads, my green beast!
JPN ZXR250 A2 (1990) - Revs to 19,200rpm... 'nuff said :smt003
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Re: mixture problems-advice needed

Post by ross46 »

Right on my way home I tried using the choke, it killed the bike when at low revs so under 3-4k revs, 4-6 the power was similar but with more popping and banging, above 6 it felt more powerful with less banging but still quite flat, and at high revs it was alot better, so im guessing lean out low down, so screw in mixture screws, increase float height, and richen needles and main jets? Still think dynojet would be a good investment, have pm'd you Robbie but not sure if it went through properly, what are the symptoms of an air leak? And is the airbox supposed to have a seal?
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Re: mixture problems-advice needed

Post by banner001 »

ross46 wrote:Right on my way home I tried using the choke, it killed the bike when at low revs so under 3-4k revs, 4-6 the power was similar but with more popping and banging, above 6 it felt more powerful with less banging but still quite flat, and at high revs it was alot better, so im guessing lean out low down, so screw in mixture screws, increase float height, and richen needles and main jets? Still think dynojet would be a good investment, have pm'd you Robbie but not sure if it went through properly, what are the symptoms of an air leak? And is the airbox supposed to have a seal?
air mixture screws are screw out to lean, screw in to richen. you might benefit from setting them all to the same value, as yours are fairly high, set them all to 3 1/2 turns out and go from there. also if you are running full system, look at a different air filter, this will also help to lean out your pilot/idle if you think you need it. after you get everything sorted balance your carbs, then you can start to tune the carbs, before a final balance.

increasing float height will richen your system throughout.

the carb to airbox plate should have a fabric/foam seal between it and the airbox.

air leak will cause revs to hang and might cause the revs to hang around 2-3k rpm...although a similar condition can also be caused by weak vacuum springs...slipping the clutch usually brings the revs back down to 1200.
UK ZXR400 L3 (1993) - Fully restored and on the roads, my green beast!
JPN ZXR250 A2 (1990) - Revs to 19,200rpm... 'nuff said :smt003
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Re: mixture problems-advice needed

Post by ross46 »

Might be an airbox leak then, I've had to keep slipping the clutch at traffic lights to get it down, I've got some carb cleaner to test for air leaks, will silicon sealant work to seal the airbox? And is there anyone near junction 13 of the m1 with carb balancers I could borrow? Thanks for all your advice, I will post the results
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Re: mixture problems-advice needed

Post by ross46 »

Right, thought my bike sounded like a twin, I actually had a zxr triple, one of the ht leads was arcing at the coil to the head, so stripped all the coils, sealed them with silicone to stop the water and cut the ends off, now it starts alot better but if I accelerate hard in lower gears it still coughs a bit, so I think next step is to balance the carbs and have a look at jetting
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Re: mixture problems-advice needed

Post by banner001 »

im up in coventry if you wanna come up one weekend?

i have a set of carbtune pro II gauges here.
UK ZXR400 L3 (1993) - Fully restored and on the roads, my green beast!
JPN ZXR250 A2 (1990) - Revs to 19,200rpm... 'nuff said :smt003
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Re: mixture problems-advice needed

Post by ross46 »

I may have to take you up on that banner, thanks, im at NEC this weekend but maybe week after, you said to try a different filter? Any recommendations? I've seen mixed reviews about k&n? Any advice welcome
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Re: mixture problems-advice needed

Post by banner001 »

ross46 wrote:I may have to take you up on that banner, thanks, im at NEC this weekend but maybe week after, you said to try a different filter? Any recommendations? I've seen mixed reviews about k&n? Any advice welcome
you will have to drive within 10 minutes of my place if you are going NEC, ill send you my number, i work every day so i will need at least a fixed date.

my k&n works fine, my bike was fairly rich at the bottom end with the replacement headers so that helped to lean them out a bit, i dont have a problem with them. you can get your bike setup well with whatever you have on it if you have the time/knowledge/cash.
UK ZXR400 L3 (1993) - Fully restored and on the roads, my green beast!
JPN ZXR250 A2 (1990) - Revs to 19,200rpm... 'nuff said :smt003
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