Hi Guys, My little ZX2R project is on the road now and despite setting carbs to where they should be for air mix i.e. 1.5 turns out from what was running ok at 2.25 turns out she wont rev out beyond 12500 rpm in 3rd+ when under load i.e. me. Managed to see 16500 on clock when in neutral........ Any ideas what this could be ? Will a later SP CDI cure this or are we talking something more fundamental ? Your wealth of experience is appreciated! Cheers Min
Hi and welcome. I'm thinking fuel problems. How is the air cleaner? Try removing it and see if you can get the revs. Does it run rich and splutter to get full revs? Does it run lean, ie go better if you pull the choke half on? If so it may be float heights. Join the premium members and look in the manuals section for the specs.
Welcome, Further to Murdo's request for information, what RPM are you getting in all gears before it starts to ... actually... what is it doing? Is it spluttering, just stops revving, feels like an electronic cutout? Have you done a compression test on the engine? Is there good spark from all plugs? These engines rev happily to 19,000rpm when it good tune, so you're a long way from home.
Out of curisoity , can you post your engine number ( the first 8 digits) , Im curious if you have an A or C engine as we have had a few A model bikes with C model engines and they wont rev over 16k
definetly looks like a zxr engine, balius engine are blinged out more, i think kiffsta might be onto something, someone had the same problem on here.
The rocker cover Is the same as the balius if you look closely, but most likely Is zxr engine I was just throwing it out there. The engine numbers will be good to see.
One of those people (with the 16,000rpm problem) was me. The fact that Minimata's bike won't rev past 12,500 makes me think it's something else.
Great threads guys! It's an A2 according to frame number but granted it has had a C swinging arm fitted. Can't find an engine number......vin is 010910-zx250A Interestingly the Cdi unit is 21119-1290 M and I think perhaps it's needing a less restrictive CDI like a 21119-1271 A which I can get for £40 used... No compression test done but healthy spark on all 4 new plugs I fitted. Carbs have been jetted up to 32 & 28. Initially 2.5 turns out on air mix screw.......now 1.5 with no running difference. Great up to 12k. Playing with gearing too......have been running 14/40 but going 13/40 now as not so flat round here! Cheers Min
Min, When you say main jets are 32 and 28 I assume you mean 132 and 128. Like Murdo, I think your problem is fuel. It sounds like the bike isn't getting enough of it. 1.5 turns out seems not enough. Your CDI is fine, unless the unit is out of tolerence (check to recommendations in the manual). From what I understand, all the 21119-12** series of CDIs are usable on the A model's loom. Only other thing I can suggest is you check the vacuum hoses are intact and clear. Cheers
Cheers Frankster. Jets are x3 132 and x1 128 from what i had available. Perhaps replacing all mains with new 134, 136 or 138 + any thoughts on size ?? I had carbs at 2.25 out on air mix with no notable difference. Surely i don't need to go 3 turns? I will have a play running on choke to see what this does too. Vac tubes and seals good thanks to self amalgamating tape. Air filter housing just has a bit of scrunched dacron for free flow. I am determined to sort this one way or tother!
Well that can't help, the inner 2 factory should be 128 and the outer 2 should be 125. Going back to a stock setting may help to rule that out.
What he said ^ You have a random set of main jets and some random air intake. top RPMs are controlled by the main jets set it up stock and take it from there
I will see if the stock jets are serviceable, try that and let you know where that gets me......... Would I be right that higher jet number means bigger hole and more fuel so theoretically more power and revs ? I am even confused about what lean or rich means now.......?lean on fuel or air.... Whatevs this gives me an excuse to fettle and experiment which is half the fun of bikes! Min
When talking of rich or lean we mean the amount of fuel; ie too much fuel is rich. I would also suggest that you go back to the standard jetting as too much fuel (rich) will lose power. Also what is the aircleaner? 'scrunched dacron'? In a lot of cases (I don't know your particular bike) the air filter is used to smooth the airflow into the carbs, allowing all 4 carbs to 'suck' evenly from an area of still air. Running no airbox (or them silly little pod things) will cause disturbed air to the carbs and will be an absolute nightmare to try and tune. Go back to standard jetting and filter to give you some where to start from.
Have to agree with Murdo, Fiddling with jets and air mixtures can only worsen the situation. What in fact is occurring is the overall balance is being upset ie: air / fuel mixture which in essence does not produce more power. I think the Jap engineers at the time had done the hard work and gotten some great result power wise, that's why using the air box on the bike is vital in getting the correct continuity of air flow, couple this with the correct jetting should get you to a better place, only my 2 cents worth. Good carburation is a fine balancing act, air to fuel ratio.
Definitely agree I always say to mates who lower cars and all that jazz is the r&d put into development is extensive and if not racing it y change it they spent $$$ and time getting it right!!! Return to stock and check mate
Wise words........that is where I am headed. On another front the cam chain slaps rocker underside on when revved beyond 10k in neutral. Otherwise no signs of it when riding bike. As you can see from the pic below there has been some superficial grazing. I am now running a manual CCT and have dialled in just about right with no noticeable effect upon tickover, so no undue resistance in the system. I guess it is new cam chain time sooner than later ?
Min - two seemingly unrelated problems may be the same thing! First, my fizzer (fzr250). Brought it with pod filters, with duct tape wrapped round them. This is not a joke. Ran okayish but not great. Took the tape off, it would hardly run at all. Went back to standard airbox - magic all cured. Any deviation from standard on these tiddlers seems to ruin their running. I can't agree more with your decision and everyones advice to go back to standard. However, cam timing that's a bit out can mess things up too, and whatever you've got going on with your chain and tensioner cannot be right. Even if you chain is a bit long because it's worn, the chain should still be tensioned in order to stop it flailing out and hitting the cover. Unless your tensioner has used all it's travel then it needs to be tighter. There's quite a lot of force trying to chuck the chain off the sprokets. Think about it, the chain's heavy and even at the half engine speed it rotates at, here up to 10,000 rpm, there's loads of centripedal force trying to pull it off. That's why spring loaded tensioners have a ratchet system, the spring alone is not enough when the revs get up. Fizzers have a steel cover with a big nylon block inside it in the area between the cams to help as well. Anyway, let's imagine that you've got your exhaust cam set up perfectly, and at standstill your inlet cam set up perfectly. When the motor gets some revs on the peice of chain between the two cam wheels is lifting and hitting the cam cover as you report. Even if the exhaust cam timing stays correct, the chain lifting off will advance the inlet cam, which is clearly not what you want. If it gets really extreme you may even get pistons hitting valves. I'd sort this sharpish, you may find it improves your not revving out problem,...either that or compliment yourself on inventing a very simple vairable valve timing system!!!
No denying there are two jobs looming...carburation and cam chain. What cam chain replacement methods have folk used ? Running on a split chain, full engine strip down or some other cunning way of introducing an endless chain ? I am not in too much of hurry to make 19000 rpm with the cam chain as is, that's for sure!!