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SOLVED! Honda CBR 600f 1999 possible Rectifier problem


Noble Dave
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I'd be tempted to give it a flush...OTOH, has the bike always done this (overheat at low speed) since you have had it? If so, have you looked at the radiator closely - it could be partially blocked, or even worse, have had some of the cooling galleries purposely crimped shut (a la fastbob) because of a hole or bad leak in it. If someone has put radweld (or mustard or an egg) in it in an effort to stop it leaking, this could also have caused a partial blockage.

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Looked at it from one side as not taken it out, no leeks and temp gauge stays below mid point when travelling, when idle it starts to rise then or ofc filtering slowly, when the bike is moving even at low speed ie 15mph it dont cut off only when idleing after a lil ride and sitting at lights, starts up straight away though but if dont start moving the bike revs stutter fan stays on and cuts again, had x2 mechs looks over bike also and test all the loom and looked at carbs etc all came back well and like new all electrics came back reading perfectly apart from old rec wernt giving off enough charge!

Guessing next thing to do it flush rad and refil it and test that, also see about comp fan on rec?

Know coolant plays a role in keeping engine cool but surly even if not changed in say 5 years wouldnt cause this issue or it would overheat rapidly without really going anywhere?

Im not bad with mech and sparky stuff but still learning by tinkering, not had much play with with rads and coolant.

With old rec bike when from cold would stutter revs never sounded solid, with new rec she purrs nice and all stable, only now when she gets really hot and sitting there the fan comes on spinning hard and loud and the revs bounch getting lower and lower until she spits her dummy out and shuts off, but will start again instantly then if not moving off she gets bored and shuts off again.

When open back up and hit 30mph+ the temp drops and stays at half or below and rides perfectly.

Edited by Noble Dave
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So have you got any idea what the coolant temperature is doing? Is there a temperature gauge anywhere on the bike? Can you borrow an IR thermometer to see how hot the hoses are getting?

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This is the temp gauge on bike, she usually sits at 50mph+ below half, 20-30mph mid or just above, idle-15mph keeps rising but never gets near top, about 3/4 up the fan kicks in hard, then revs stutter and then she shuts off.

Usually have her idle at 1800 rpm

20190317_221312.thumb.jpg.518a2fa523c53c40e16454a7fe2b2565.jpg

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But she dont always shut off when sitting there idle, it seems to be after about a 30 min ride that the idle goes crazy and temp rises, thats what made me thing the new rec is hot by then and starts to struggle due to poor ventilation and heat from what its produced?

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Could also be a stuck thermostat (stuck partially open) or water pump going west. I think the engine temperature will be the key to all this. .....there again, often been wrong in the past.....

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Aye thermostat pain to get too, water pump maybe but once again if the pump was bad would always be overheating no matter what speed I would have thought? No expert mind, could be thermostat I really dont know, if its just old coolant thats the issue that be great but aye defo something with engine temp either...

Rec overheats and then cant produce enough volts for spark and fan to be on why keeping engine ticking over running fuel pump

Old coolant not enough to keep engine cool but would have thought it would always overheat even when riding?

Could be stuck thermostat intermittent but on big trips she is laughing would it just happen when idle and filtering at slow speeds? As when the engine cools down she is absolutly fine again for abit u til come to abunch of red lights again

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Is your oil clean or is it milky? Is there oil in the coolant? I know this sounds a bit off-base, but a leaky head gasket can cause overheating as well.....

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Literally just changed the oil today and filter, was a lil bit of cream that came out very miniscule but rest of oil was still near clear! Not black and dirty at all and a lil around cap once again not alot at all like have seen on some cars in past where its covered, guessing just from condensation but never seen any leaks on engine or on deck, so unless its all internal, best thing would be to drop the coolant and have a look at it me thinks see if its contaminated.

Edited by Noble Dave
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Could be worth replacing the 20yo rad when change coolant but £80 is a steep price for something that may be absolutly fine!

...Yeh, but you'll never know unless you check it - I still think it's something to do with a flow restriction. Is it very difficult to remove the radiator on this bike?
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X4 hoses and x2 rubber grommets at top x1 bolt bottom, possible wheel and forks off which could be a pain as dont have a garage nor have I done it before, is a chance I can undo bolt on bottom and slide it off the grommets at top, disconnect hoses and slide it out hmmm if I did take it off though what would that do how would I rest it as if the dmg or blockage is inside how would I find it?

Whats best to use coolant wise, Putolin coolant for aluminium rads with distilled water?

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Something that will be compatible with whatever was in there originally.....there are 3 principal types, inorganic acid technology (IAT), organic acid technology (OAT) an hybrid organic acid technology (HOAT).....more info here https://www.autoguide.com/top-10-best-engine-coolants


If you don't do a thorough flush, mixing the various types of coolant can produce precipitation of sludge, that can lead to blockages. If you can get the radiator off, you can check to see if it looks as if it's partially blocked......but be careful. Old radiators can be very delicate..... :shock:

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Aye the front of it facing front wheel the small bars/vents are crumpled in some areas mainly near bottom and very soft! Tempted to just buy a new rad and throw it on with new coolant in it, possibly have a garage do it so I know its flush right, only issue is I dont trust garages... Generally do all work meself but no experience in this.sure can remove rad and replace it may be abit fiddly without even removing front end, but more flushing out all the crap thats is the tubes going into the engine!

Would rather sort someone out on here to do it haha

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Righty tested coolant and had rad off all fine, kept bike running idle for ages until bike got really hot and fan came one, only then when fan kicks in does the bike starts to have issues,


Ran bike, got hot no where near red and fan comes on, cools bike abut revs stutter only a little still stable...


Fan goes off bike runs fines again...


Fan comes on again about 30 secs later then revs stutter and bike cuts out, changed rec and made it fun alot better, fan works and thermostat works so guessing when fan on bike dont have enough power to run fuel pump, sparks and fan and lights and that why cuts out..

I thinm it could be the battery now a garage did put one on a new one but could have been a cheap lousy thing, if ai put a decent bty on you thinm that may solve it? Coolant system fine its a power loss when fan is on that does it, could be Stator will have to have a gander again

Edited by Noble Dave
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UPDATE :

Tested rec perfect

Tested stator perfect

Tested bty, bike off 12.75V turn bike on dont drop below 12V so perfect

Why idleing 14.35V so working fine and shows stator and rec work...


Now the issue which found, you turn lights off or just use side lights bike stay on when when hot and fan going all stable, as soon as ye put headlight on the revs bounce, voltage drops on bty to 12.05V and bike dies...

Run bike side lights on fine turn headlights on revs bounce turn quickly back to side lights and all goes stable again!


So its the headlight being on when fan and rest is on that kill bike, engine temp is normal not even near red just over half way, so.... There is the issue headlight doing it!

So if I now just run with side lights on all will be fine and at night headlight as be nk traffic to filter past done! Anyone have any idea why headlight is doing it? Ta be nice to figure it out haha well chuffed though.

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So.....you think its electrical. Could well be. I reckon from what you've said that there is either a dodgy connector or a bad earth somewhere. The electrical system on your bike should be able to handle running with the fan going with the lights on. Check the fuses in the fan circuit to see if they've been replaced with mad big ones. Also (your SO won't like this, but.....) when the main lights are on, have a sniff in the headlight shell and up the main loom to see if there's any burny-burny smells.

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  • 4 years later...

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