Topping out at 110mph

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banner001
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Topping out at 110mph

Post by banner001 »

...now before you start to direct me to Rob's derestriction posts a few things...
Bike is UK L4, so no pink restriction wire to the clocks.
Bike has a M CDI on it, and in 1st, 2nd and (i think) 3rd gear it revs fine to ~15,000 rpm

However, 4th gear it revs to just over 13000rpm and stops (true 110mph, clocks were showing 125mph), and in 6th gear it gets to 110mph (measured with GPS)...but no more, i think it was 10-11k rpm.

I have no other electrical gremlins to speak of, but i am convinced that it must be electrical. Before the bike went to Roger Middleton it made 54.14bhp on the Jordans dyno, after having new front and rear sprockets, new chain, can chain replaced, cam chain tensioner (which was broken) replaced, new semi-synth oil, new downpipes (minus holes) and having the valve clearances done it re-measured at 54.15bhp...an increase of 0.01bhp.

Hence why i am thinking it must be electrical, also if you check out my dyno trace (viewtopic.php?f=168&t=13188), it just goes nuts at ~110mph, like it is trying to dampen itself down??

So im wondering if anyone has any ideas...im thinking its got to be electrical, some kind of feedback, but what i dont know? Could it also be a bad CDI unit? I have no idea when it was changed to an M unit, is there any way to check that its working correctly other than swapping it for one thats known to be perfect? Also i assume that thi bike didnt come with an M cdi to start with, would anything electrical need to be altered (wires going to different places, resistors inserted etc...) to convery a standard UK bike to the M CDI.

I have tried looking for, and talking to RedexRob, about this, am waiting for his reply whilst im still stumped, also the fact that the forum wont allow you to search for 3 letter words like CDI limits me as well...

Thanks
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JPN ZXR250 A2 (1990) - Revs to 19,200rpm... 'nuff said :smt003
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Re: Topping out at 110mph

Post by banner001 »

also, if it is likely to be just a dodgy CDI, and someone has one lying around that they know is fully operational, i.e. will pull to more than 13k rpm in 4th gear, so over 110mph...any chance of you putting it in the post for me to test before i mail it back to you. of course, if it is a true spare and you dont mind selling it, if it works on my bike ill have it off you for a fair price.
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Re: Topping out at 110mph

Post by cargo »

I'm not getting into a long wind explaination of ZXR restrictions..............................

but in this case.......your speed indicated or other wise is nothing to do with it. Your speedo is not connected to the CDI

And given that you bike revs to 13K then it is NOT a restriction problem that you have becasue a restricted CDI with no speedo connection is restricted to 10K revs regardless of speed or gear

there could be some merit in your suggestion that you have a faulty CDI

Equally there are any number of other posibilitys
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Re: Topping out at 110mph

Post by banner001 »

Such as? My thoughts is the cdi is faulty, but it seems odd that its only faulty at the top end. Might see if an ebay special sorts it out? What else could it be? Weak sparks? Would you guess its electrical rather than mechanical?

Cheers for any suggestions
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JPN ZXR250 A2 (1990) - Revs to 19,200rpm... 'nuff said :smt003
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Re: Topping out at 110mph

Post by CaNsA »

My money is on air/fuel mix.
@110 the bike is running lean.
tape up 1/3 of the snorkel and give that a shot.

either that or the wrong size jets.
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Re: Topping out at 110mph

Post by Tirpitz »

You're not making much power TBH. Your model L should be making 65ps at the crank which will give a hell of a lot more than 54ps at the rear wheel on a dyno. My stock L4 (apart from can) makes 62-3ps at the rear wheel and it will hit the limiter in every gear up to 5th. I haven't tried it in 6th but the way it keeps pulling I have no doubt it will get there given a long enough road. So, why isn't it making much power?

Looking at what you have already done, have you cleaned the air filter?

I have seen on the internet a few people moaning that Sandy Bike Spares headers dropped their power (not ZXRs). Headers are part of the tuning circuit so an alteration, if inferior, will have a detrimental effect. They don't have balance linking pipes on them.

Have you cleaned the carbs or have you at least added some cleaner to the fuel and let it run through - main jets could be partly gummed up.

Have you balanced the carbs?

Check the fuel lines for kinks which could be causing fuel starvation.

Check the tank breather is clear - test by trying to open the cap immediately after a fast run. If there is a vacuum in the tank the breather is blocked.

Just a few thoughts for you to try.
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Re: Topping out at 110mph

Post by banner001 »

Looking at what you have already done, have you cleaned the air filter?
Yes, cleaned with alcohol and oiled correctly.

I have seen on the internet a few people moaning that Sandy Bike Spares headers dropped their power (not ZXRs). Headers are part of the tuning circuit so an alteration, if inferior, will have a detrimental effect. They don't have balance linking pipes on them.
My old pipes didnt have balance pipes on them, i think thats only H models. Plus they were making the same power with the old pipes that they do with the new ones now, so i dont think thats the cause.

Have you cleaned the carbs or have you at least added some cleaner to the fuel and let it run through - main jets could be partly gummed up.
Not cleaned the carbs yet, i have run several tanks of petrol through with 50ml redex per-tank. Looking at my dyno trace fueling is spot on on the main jets, although its rich on the pilots, this shouldnt affect the top end should it?

Have you balanced the carbs?
Yes, to within 1mmHG, i think they pull ~12mm on tickover and ~14mm at ~2-3k rpm...does this sound reasonable?

Check the fuel lines for kinks which could be causing fuel starvation.
Fuel lines are fine.

Check the tank breather is clear - test by trying to open the cap immediately after a fast run. If there is a vacuum in the tank the breather is blocked.
Not checked, but will do. Might just take the pipe off and run some water through it, that should also tell me if its blocked or not.

I do still have the problem with a small amount of oil leaking from my carbs, i think this is down to the airbox not sealing correctly, i have bought an airbox from a breakers, will buy a gasket from cradleys today as the old one is soaked in oil...that might still be the problem, if the airbox is not pressuring correctly?

When i did the carb balance i also tried to look for air leaks around the carb rubbers, couldnt detect any, but i cant be sure i managed to spray carb cleaner over all the carb rubbers...its a bit hard to see where you are spraying that stuff, but i got no detectable RPM increases.

I will also try to block off 1/3rd of the snorkel, see if that helps. As for what needles are fitted i have never taken apart carbs before. I dont know if mine are 32mm or 30mm carbs either, might have to pick some up from ebay and have a play around, dont fancy doing carb work for the first time on my only set of carbs.
Last edited by CaNsA on Tue Jul 24, 2012 5:05 pm, edited 1 time in total.
Reason: To make for easier reading.
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Re: Topping out at 110mph

Post by Tirpitz »

If you eliminate fuelling then I don't think it is the CDI as you say it revs out in 1st to 3rd. So we have to come down to why it's not making enough power. I'd be looking at a compression test next as you may have worn rings / bores and simply be blowing power away. Do you burn much oil between services? Reason I wonder about this is you say you have a lot of oil coming from the carb gasket. This might suggest you are getting blow-by into the crankcase which will escape through the crankcase / airbox breather. This will be hot, oily gas which may be what you are seeing.
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Re: Topping out at 110mph

Post by banner001 »

Tirpitz wrote:If you eliminate fuelling then I don't think it is the CDI as you say it revs out in 1st to 3rd. So we have to come down to why it's not making enough power. I'd be looking at a compression test next as you may have worn rings / bores and simply be blowing power away. Do you burn much oil between services? Reason I wonder about this is you say you have a lot of oil coming from the carb gasket. This might suggest you are getting blow-by into the crankcase which will escape through the crankcase / airbox breather. This will be hot, oily gas which may be what you are seeing.
bike doesnt eat hardly any oil, its not a lot of oil just a small drop hanging on the edge of the carb that sometimes falls off, but its more than should be coming out. What do you mean by blow-by? is that gas leaking round the piston ring into the crankcase? this gas then escapes up the breather pipe?

if so i will have to look at getting a compression tester. i do usually have a small amount of water in the breather pipe, and it usually smells of (im guessing) oil and a tiny bit of petrol? i take it there should be nothing in here usually?

i know when i got the bike the inside of the pipe looked a bit corroded so i bought a new pipe, might be summat to investigate. two of my mates here in cov run garages, im sure one will show us how to do a compression test. ill report back...
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Re: Topping out at 110mph

Post by Tirpitz »

banner0012 wrote:What do you mean by blow-by? is that gas leaking round the piston ring into the crankcase? this gas then escapes up the breather pipe?
Yep, you got it.

It doesn't sound from what you say that you've got a massive problem, you're not burning oil and a tiny bit of stuff in the airbox drain pipe is perfectly normal, you will get condensation in the box and a bit of oil off the filter element. It's just that you've got eliminate methodically where that power is going. If the fuel is right and the sparks are right then you have to look at the compression. A compression test wouldn't cost you much.
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Re: Topping out at 110mph

Post by banner001 »

have sent a mate of mine a message, ill see what he says when he gets back to us.

also ive bought a set of 32mm zxr 400 carbs, would like to see how to work on them before tackling the ones on mine, you never know, mine might just be jetted wrong or the top end? might not be able to draw enough fuel in?? also mine are really rich at low revs, and you can feel it, the bike is very sluggish until ~4500 - 5000 rpm, so that will need sorting at some point as well. plus starting the bike makes the air smell of petrol...which im sure it shouldnt do?

carbs will be here in a few days, tirpitz, you have an L4 same as me, to the best of your knowledge are your carbs jetted like in the manual?
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Re: Topping out at 110mph

Post by CaNsA »

Did you try the tape thing?
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Re: Topping out at 110mph

Post by Tirpitz »

banner001 wrote: tirpitz, you have an L4 same as me, to the best of your knowledge are your carbs jetted like in the manual?
I can guarantee that my carbs are absolutely stock as I've owned it from new and no-one has ever messed with them. What I would say to you is that my bike also ran noticeably rich and boggy with the standard can on but now my fuelling is near as damn it perfect with the A16 can on. I think the OEM can stifles the bike at low revs and leaves it rich to get through the noise test. The A16 can, whilst still road legal, is freer flowing and leans it out. When I fitted the can I took it to the dyno with the intention of having the jetting tickled to suit but it didn't need it. This suggests to me that it deffo runs rich as stock as it pulls much better now with no 5-6k flatspot.

However, I would also say that I saw 130 on the clocks in 6th on the Mountain Mile in the IoM on mine with a stock can (which would probably be 120 in reality). So yours should be pulling better than it is.

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Re: Topping out at 110mph

Post by CaNsA »

If we are on about top speed, I get 135 out of mine with a bit more in the wings but ran out of road.
I've got 130 out of it fully packed.
Image

If i pulled the rev 14.5k limiter off i would easily get 140/145
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Re: Topping out at 110mph

Post by banner001 »

Gonna try the tape today, with us having olympic football matches on there are loads of police. Need to find a quiet day.
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