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Discussion Starter #1 (Edited)
97 carb. Up until a week ago this bike ran like a Swiss clock. Went out one eve and it ran fine. Half way home stopped at a junction. Pulled away again and the surging started............From stone cold it's perfect....After approx 4 miles the bike starts to surge on a partial throttle. Say 2500rpm and up. At wot it pulls like a train. Until its warmed up the bike is like silk but the hesitancy / surge appears to be getting worse the hotter it gets. Albeit it never cuts out it feels as tho someone's pulling on the grab rail slightly. It idles perfect at about 11 - 1150rpm. So far, Carbs balanced, Tank cleaned and fresh fuel, New fuel filter, New petcock diaghram, New fuel supply lines and vac pipe. All vac ports have their plugs in No leaks at carb inlet rubbers (tested) Carbs stripped completely and cleaned. Stock carbs. No bent needles or wear. All diaghrams are perfect. Jets are whistle clean. Factory setting on air screws. Carbs are stock factory to UK settings. Floats all good and in spec, no wear marks. New air filter, Air dams in place in front of air filter intakes both sides. Plugs are new and iridiums, not fouled. Ht leads are 5k ohms on the caps and contacts are clean. Coils are 2.9 and 3 ohms at primary windings and 33k at secondary. Continuity from cdi to coil leads. Continuity from ignition pulse sender to cdi. Ht leads are also in spec, 5v present at tps. All header pipes equal. With bike running on idle if I pull any cap there's a noticeable change in engine noise ie cylinder out. This is driving me crackers. To the point I've had enough with it unless someone can shed fresh light please?Thanks!
 

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Re: Surging when warm ??? Out of ideas!! Help

hi rocket, sounds like carbs could do with a strip and clean,have you checked tank vent pipe ?
 

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Discussion Starter #3
Re: Surging when warm ??? Out of ideas!! Help

Carbs have been stripped completely. All vents renewed and checked. Even ridden it with cap open to double check.
 

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Re: Surging when warm ??? Out of ideas!! Help

Random thoughts here ...

Works fine cold ....... Fuel system seems to have been gone over thoroughly,

Electrical break down when warm .... coils, leads, plugs, RR, stator/alternator.

Battery Leads tight? ... Earths clean and tight?

Starter motor?

Do any of the electrics play up when the surging happens?
 

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Discussion Starter #5
Re: Surging when warm ??? Out of ideas!! Help

No electrics play up. Rev counter and speedo are spot on. All dash lights work. Starts on the button hot and cold. Coils and leads are spot on at resistance readings. Just have peak voltage left to check. Can't foresee reg rec giving it grief. Charging is fine, can be left for a week and starts first hit. No issues with whether lights are on or off makes no effect. All cdi connections are clean and in good order. Checking batt earth to frame earth shows no resistance and good continuity. Primary coil resistance is 2.9 - 3 ohms. If I heat a coil with say a hair dryer forn10 mins resistance goes up to 4.5 ish.... Any effect there?Thankyou so far.
 

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Re: Surging when warm ??? Out of ideas!! Help

Hmmm ... I'm guessing you don't have a spare set of carbs or mounting rubbers?

If .. the electrics are fine it can only be fuel/air .... something expanding or sticking when warm?

Have you tried running it without the air box on .... ? It will be a bit boggy but might help point to the problem ...
 

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Re: Surging when warm ??? Out of ideas!! Help

Where did you get your last load of fuel? Water in the fuel will make it behave like you describe.
 

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Discussion Starter #8
Re: Surging when warm ??? Out of ideas!! Help

Hi guys thanks so far. I can replicate the fault at idle. Holding a steady throttle in neutral. Increase rpm to approx 2500 and hold it steady. Bike hunts either side by about 3 - 500 rpm. It's not a continual or rhythmic hunt infact quite random but only when hot. Fuel is good. Have tried it on stand with an aux fuel tank and fresh fuel. I'm stuffed on this one !
 

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Discussion Starter #9
Re: Surging when warm ??? Out of ideas!! Help

Hmm interesting. I took both of the coil feeds off both coils today. The black/orange 12v wires which feed back to the cdi were checked. These initially showed 22ohms from Coil to coil wires. Playing with the kill switch for 5 minutes reduced this resistance down .01 ohm. (Probes from black/orange on right coil to black orange on left coil, probes on spade connectors of wires with wiring disconnected from coils.) I've yet to run the bike out but how important would this 22 ohms be to / against its running?Thanks
 

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Re: Surging when warm ??? Out of ideas!! Help

Do you routinely use the kill switch when shutting the bike down? All the hydro for "run" conditions go through that right hand throttle/kill switch block. I'd pull it apart and check for carbon arc patches on the contact points (if you can get at the contacts, I'm not sure what you'll see in there). If the fuel system is good (and your work so far seems to indicated that all is/should be well there) then it must be an electrical issue, at least in my mind.

Tony
 

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Discussion Starter #11
Re: Surging when warm ??? Out of ideas!! Help

Thanks tony. I've split the switch this morning. Sprayed some contact cleaner in there. Didnt take the whole thing apart for fear of a million springs or such like going everywhere. I can't really see the surge being down to the switch? Or does your view differ?New fuel supply hoses going on this aft to give a drop more room under the tank. Ill try it this aft when done see if the switch has made a difference. Literally as I operated it I could see the 22 ohm resistance drop each time. It's never used but I visited a friend on it. Bike ran perfect there. He had a nose around the bike as others do. He may have on / offed the switch when he was looking as it was the ride back that the surge started. If its the switch ill go nuts I've pulled the carbs over 10 times now !!
 

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Re: Surging when warm ??? Out of ideas!! Help

Hmmm, this is a tough one. Some thinking out loud here. Is it possible that the ignition pulse generator or ignition trigger plate might some how be at fault? A loose/bad/heated ignition pulse generator or connector damage? Could not be a trigger plate (right side crank cover area) that could be loose or somehow giving bad info to the ECU. I'm wondering if your seeing a bounce in the ignition advance part of the system that might cause the rpm swing in some form or fashion. The advance is all controlled by the ECU so any faulty signal might cause some sort of bounce and surge condition perhaps. This would be difficult to check I think. The trigger plates do not wear out but if it were loose (which is doubtful) it might cause an advance or timing bounce of some sort at rpm. Not only that but the trigger runs rather close to the pulse generator/senor so you could end up with parts contact and very bad things happening. If the pulse generator were on the way out (heading to failure mode) is it possible to think that heat soak conditions might play a part in the failure mode? Maybe or maybe not me thinks. The generator does not run in a oil bath like the older CB-F DOHC motors of old, so engine oil temp does not come into play here, but there will be some engine case heating of course. And you note that the idle is steady when engine is running it is only under rpm loading that the surge comes on..hmmm. Tough one to crack for sure. There is one way to go but it is costly,..start replacing parts until it stops doing what it's doing. Not the perfered method of course. Pulse generator is about $50.00 (MSRP) depending on vendor. Is there a way to change out the ignition coil set and test if this is part of the issue? Ramble mode off.

More ramblings: Check ignition pulse generator connections. Check all connections/plugs in the ass end of the bike at the ECU,..ensure the ECU is securely mounted. Go through all the fuses and ensure they are all good. How bout checking ignition switch connections etc? Clean and check all battery ground and hot side connections, the ECU system is electrical power sensitive. If power is not at or above the required number it may bounce the system and produce variable performance.

Non-electrical: You state the carbs have been off 10 time or so. It is possible that the carb boots can be cracked and thus you have an air leak that present at higher rpms, perhaps. That does not explain why this started in the first place though when you had not touched the carbs or boots, does it?

Another test you might try: Pull the body panels down so you can get at the motor ignition coil area's but still allow the bike to run. Disconnect the headlight (you do not want extra light for this test). What until dark and then start the bike while in the dark and do rpm pulls while watching for spark arc's to ground from the ignition system and related wiring. Spark plug wires can arc to ground through failing insulation if they are cracked or old etc. In the dark you will see arcing and a light show of sorts if this is the case.

That's all I've got at the moment, most likely of no help but.... I'll keep thinking on it.

One more thing carb related: Choke function is normal and correct? Don't know how or why this could be the cause but just thought I'd ask. First start of the day requires choke operation, yes? or no?.

Tony
 

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Discussion Starter #14
Re: Surging when warm ??? Out of ideas!! Help

TonyThankyou again. I currently have a new set of coils and ht leads inbound. I cannot see any arcing and I'm wondering if I have a coil breaking down under heat or the same for an ht lead. Ground/earth thru the bike is bang on. Stator etc producing correct voltages. Battery is on the nail. All fuses pulled and are clean. Ecu unit is firmly mounted and shows continuity to all associated circuits. Carb boots are fine. Leak test performed and no issues. Pulse generator has been swapped out and is good. One other thing of note is the tps makes no difference whether connected or not but does show full continuity. Grateful so far, thankyou
 

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Re: Surging when warm ??? Out of ideas!! Help

Greetings Rocketeer,

I know a whole lot about nothing and a lot about something.
With that being said I had an outboard motor that would do the same thing when the throttle was in and area that was used a lot.
The TPS was worn out in that particular spot.. Found it by ohming it out with my meter. Changed it out then all was well.
Stex
 

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Discussion Starter #16
Re: Surging when warm ??? Out of ideas!! Help

Thanks Texas. I have the honda meter inbound to check it this weekend hopefully. It runs exactly the same with or without it connected. Hmmm
 

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Re: Surging when warm ??? Out of ideas!! Help

Re: TPS; Did you do the WOT check and the Fully Closed (throttle position) check on the TPS? Sort of following ST11XX lead here. If the output from the TPS does not change from Wide Open to Full Closed, then it may be an issue. Semi related,..my Ford Ranger 98 model year lost the TPS and the motor would high rpm on me for no good reason. I guess the fail safe position was something well above normal idle speed so that you might be able to limp the thing home.

How many miles on the machine, btw?

Tony
 

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Discussion Starter #18
Re: Surging when warm ??? Out of ideas!! Help

Tony roughly 30k. Until the meter arrives I can only check for voltage at the block connector just prior to the carbs?
 

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Re: Surging when warm ??? Out of ideas!! Help

Would there be a variable resistance indication from a multi meter, dependent of throttle position, from the TPS? The FSM shows a WOT and Closed Throttle test, but I'd think the output (resistance) across the TPS would change with throttle position, but that's just a guess on my part.

Tony
 

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Discussion Starter #20
Re: Surging when warm ??? Out of ideas!! Help

Hmmm the plot thickens. I managed to insert a pin on the centre cable on the tps multi block. The voltage climbs steadily to a wide open throttle in general. However there are significant drops in the climb. For instance it will go 1.22 1.34 1.35 0.8 1.45 1.55 0.7 0.6 1.66 etcI am lucky enough to have a spare bank of carbs I use for spares. I plugged that bank in to the sender and operated the throttle by axle by hand. This tps shows a far far smoother scale 1.22 1.23 1.24 etc all the way up with no drops. This is a fluke meter so we could be into something I think. Would a tps play such a vital role on a carb xx?Thanks again
 
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