Hi there, I'm new to this forum and I'm here as this forum is my last possible help. I have this 15 year old bugger which is giving me a lot of grief. When I bought it, it was a right mess, rusted tank, only half the engine working, voltage regulator dead, pickup coil dead, cam belts dead etc etc. I started working on it, replaced the battery, voltage regulator, pickup coil, ht lead wires and the bike started running (for a bit) until it started to have the problem of the dyeing cylinder again. I managed to get a pair of good second hand carbs and fitted them in and eureka, bike was running, it was somehow reliable and it was finally a pleasure to ride it. I fitted in a dual 750 downpipe and installed two 50mm free flow termi cans and the problem came back. Me and my friend looked at it from every possible side, wire looms, coils, pickups, ICUs, lean/rich mixture and nothing. We can't get any conclusion whatsoever to overcome the issue of it killing the front sparkplug every 50 (or less) miles. Every time it dies, all I have to do is to replace the sparkplug for new and off it goes, like it never struggled before (for another 50 miles). I've ordered a 6sigma jet kit for it but it's taking weeks for it to arrive and from my experience with this bike I'm sure it won't solve the problem, it would be way too easy. Here is a list of everything which may relate to this matter that was replaced and still didn't seem to work in the end. HT coils (both+brand new) ICUs (one changed for second hand but they both work with the vertical cylinder) Pickups (both+brand new) Voltage regulator(brand new) Carbs (new mixture screws) Wires and connections looked at and partially redone where necessary. New oil and filter with oil flush thing (was told that maybe tiny metal bits are messing up the pickups) After these changes the only two things that are left as possible solutions are valve clearances and jets, but the colour inside seemed to be ok after looking at it through this mixture tester (Gunson Colourtune 12mm Sparkplug Tuner) Is there anything else I can do or is this bike doomed? Maybe someone had a similar problem? Don't tell me it's just a matter of installing a warmer sparkplug otherwise I'll just shoot myself...(although it shouldn't be the sparkplug as it is the "cooler" cylinder as it's set to the wind more than the other one). Please help me as I want to have the bike tested before the next season so I can peacefully ride it without worrying that it will die in the most inconvenient moment.
as you have already changed both pick-ups (and although you would tend to think the fault was electrical due to restored performance when you fit a new plug) a common occurrence is a valve shim closing down to zero clearance, usually the exhaust first. You could confirm this (although it doesn't have to be caused by just the worn shim) with a compression test.
Ebay doesn't seem to sell them, any clue what is the price of the new valve shims and where to get them from apart from a dealer?
Before you buy any shims it would be a good idea to see if you actually need any! Very often just the fitting of new 1/2 rings will be enough to bring the clearance back to specification. Would be worthwhile checking both cylinders compression with a compression tester to see what's going on as well before spending any money unnecessarily!
as said, best confirm what's wrong first and the good news is that if it is a closed down shim then you can reduce the size of the existing one by carefully grinding as long as you can do it yourself or know someone whose capable of doing it. If you don't then send me a p.m.
I wonder if the OP's problems are similar to what I had with my 750SS and the spitting back through the airbox at idle when openong the throttle up to and around 1500 - 1800 rpm.... I never really found a definite cause despite doing a lot with the carbs etc, and it will still do it occassionally until it gets warmed right up. Mine has always had a habit in colder weather of only starting on the vertical cylinder, and I have to wait for a couple of seconds for the horizontal cylinder to kick in.....perfectly fine once running. I have changed leads and plugs; substituted coils and CDI units; gone right through the carbs; etc etc etc.... But I also wonder if the OP should have a look at the air cut-off diaphragm in the offending cylinder carb.....they can cause all manner of issues (and al=though I thought mine were OK, they are the only thing I didn't change). Chris could well be right that a valve clearance is iffy......as the rockers wipe the top of the valve, the valve slowly rotates......so maybe there is a point when the clearance gets tighter and compression is lost.........I would think that the cylinder wouldn't die completely without some banging and spitting, but the OP doesn't mention any symptoms as it happens. AL
Me and my other friend had a look at it today, warmed it right up, for about 10-15 minutes it was running at idle with rags stuck in the pipes to eliminate the DBs as the neighbours would kill me. It was running fine, i stuck my hand against the "vertical" carb inlet to kill the cylinder and it kinda sneezed (returned a cloud of petrol through the inlet), I told the guy that this is exacly what happens when it stops running. I was advised to use the bike until the moment when it dies and keep a deodrant with me. I was told to block the inlet when it dies and let it go when after about few seconds to see if it will come back on, if not then to put some deodrant in there to see if it will run. Basically it's to see whether it's the carburation problem or the valve. I was going to check the compression but the tool I had was not small enough so it would'nt fit in the head.
See if you can check the air cut-off diaphragm on the offending carb......I'm beginning to think it may be split.... ..Unfortunately for you it is the one on the right hand carb stuck in the middle of the pair of carbs.....but you can get it off with a small crosshead bit and a small spanner to turn the bit, so you don't have to split the carbs. Forget deodorant......brake cleaner is better.......but I doubt if it will make any difference......Try putting the choke on instead, either it will kill the running cyclinder or the dead one might pick up again..... Does the cylinder die as the bike gets hot from cold or will it do it at any temperature? You can crudely check compression with your thumb in the spark plug hole (don't FFS push it right in!!) and compare with the other one......if the pressure blows your thumb off the hole, then it is probably OK.....but if you were losing compression I would expect to see some blue smoke from oil burning or a stink of petrol frm unburnt fuel with backfiring as well. AL.
Well, with the idea of the diaphram being broken; the thing is that two carbs were tested on this bike and the diaphrams seemed to be good, I can also remember that the guy that was using the "new" carbs had no troubles with them before and he only got rid of them because the mixture screw would'nt get out and he got a new pair, but after few days he managed to hammer in a thin screwdrived and got it out eventually. Deodrant, well i suppose it's not the best solution but its just to see whether it's something to do with the valve clearences because if it doesn't bring it back to live then that means that the valve isn't closing properly and it is the thing that is bothering my engine. I tried putting the choke on last times it was happening, it was only killing the other cylinder and I had to stick my hand on the air inlet to dry the plug so it would come back to life (we are talking about the left carb and the vertical cylinder which I hever had troubles with). The thing is that it only happens when my bike has warmed up so putting my thumb or a finger against a hot cylinder is probably the last thing I would want to do. Another thing, I remember a few situations where I would run the bike during the day, it would run and start normally and then after about two or three hours after I have turned it off (comming back from town and dropping my girl off to work after three hours scenario), it just wouldn't run on the vertical cylinder from the moment I start it. The other thing is that it doesnt consume oil and the exhaust fumes are clear so it's pretty much eliminating the issue of the lost compression on the piston rings or the cylinder, it looks as if it was the valve issue instead. Regards. I can try to swap the diaphrams tommorow as I've got the access to the top of the carbs as now the air box is taken out.
now you told us that it only cuts out when it's warmed up, have you tried rechecking to see that you have a spark on that cylinder? - just have a spare plug ready, remove cap then fit plug and rest on cylinder head to earth. I know you said you have fitted new pick-ups but if no spark when hot then you need to check all the way through that cylinders' ignition circuit. 'value' deodorant isn't such a bad idea if you've nothing else to hand and can be a lot cheaper than Bradex/carb or brake cleaner, it's only a quick test after all. Some of the air fresheners have 30% butane for the propellant and also work a treat. Just a long shot - this bike didn't come from near Torquay did it? and a 748 tank and seat unit fitted?
Don't forget that most deoderants contain a sticky powder...................don't want that getting in the air bleed drillings.... If you are worried about a hot engine burning your thumb, put a glove on or use a rag.... I'm not sure if the advice you have been given by your acquaintances is correct though......putting your hand over the inlet to dry a plug for example.....if you cut the air off from a cylinder you are effectively choking it and it will draw more petrol from the carb, thus more than likely flooding the cylinder.......therefore I am not surprised the engine dies when you choke with your hand. Out of curiosity, which carb did the previous owner have to bash with a hammer to get the pilot / idle circuit screw out? If the actual seat in the carb for the pilot screw is damaged there is a good chance it is letting more fuel through than it should be. If you need to know correct jet sizes for these carbs, I have the info here.....however, are you sure someone hasn't already fitted a Dynojet kit / needle / jets and not got the correct items? I think that if you have fitted 'open' zorsts, you really need to check the jetting out because the zorsts will in all probability make the problem worse if it is carburation problem, and BTW, has the top of airbox been cut about? AL
It does have the spark on that cylinder when it cuts of, I know that because I have removed the plug lead from the ignition wire and I've put it against the cylinder and it was sparking as hell. I heard sparking on between the plug lead and the plug when i have taken it of the lead but not far enough for the spark to be unable to jump from one to the other. It doesn't just die when it's warm, I also said that there were a few times when it just wouldn’t run a few hours after riding it. The whole ignition circuit was checked, cables were redone where necessary and the coils with wires were changed as well for brand new ones from electrexworld. I wouldn’t know where it was from originally, it was taken from near London by my cousin but because he had no experience with bikes i just bought it off him for myself. The deodorant I have chosen doesn't contain talc so it shouldn't be that bad as the ones which do contain it. The thing is that I can't really remember which carb it was; it might have been the one but only for 50%. Maybe I was wrong about saying that it will dry the cylinder, my other friend said the same thing that when it dies to put my hand against the carb on the good cylinder and it did work, only for a short while but enough to get me home without having to push it. The jet sizes are the same as the ones in the old carb, the old jets read 70 on the main jets (the bigger ones) and 128 on pilot jets (smaller ones which are held by this metal holder or whatever it is). This is why I've ordered this jet kit from 6sigma but I have to wait as its apparently something to do with customs... The airbox is not cut in any way, it's a totally stock thing.
You said " Every time it dies, all I have to do is to replace the sparkplug for new and off it goes, like it never struggled before (for another 50 miles)" Could it be that it's not a problem with the plug, but that you have been forced to wait 5-10mins whilst you change the plug out? And then off it goes again , so naturally you think it's the plug change that has cured your problem. How is your tank breather valve? Just a thought, maybe that's not functioning correctly, and it just so happens that the front cylinder is the first to show the effects of fuel starvation! Also how is your fuel filter?
The fuel filter was changed couple months ago when the bike started showing the illness; it wasn't a cure even after cleaning the carb. Do you think its to do with pressure building up in the tank and therefore the pump doesn't supply enough fuel? I have made sure that it wasn't the issue of the bike cooling down which solved the problem because I always try to run it before I fit the new plug, and it's never that it would run before I change the plug which when I do, cures the problem. The thing that makes me think the most is that there are occasions when I switch it off for two or three hours after running it normally and it wouldn't start which blows all the schematics from my head about when this problem occurs and leaves me with absolutelly no idea what is actually causing it, because why would it die when it's warm plus it wouldn't start when it's cold?
"Do you think its to do with pressure building up in the tank and therefore the pump doesn't supply enough fuel? " No, not pressure build up, the opposite- a vacuum If the tank is not vented to the outside atmosphere, as fuel get used up, unless air at atmospheric pressure can enter to tank to fill the space a vacuum will develop, which could effect your fueling.
"the opposite- a vacuum" Sorry, this is what I mean't. I really doubt it is the issue though because I had a situation when water got into my tank when the tank was closed so the seals musn't be allowing the vacuum to build up. I've checked the tank now, there is no water in it at the moment so it's not that as well.
Worth a check of your breather though, is it fitted round the correct way? ( with the tiny arrow pointing away from the tank)
And poke a bit of strimmer cable down the breather stub pipe that comes off the top of the tank...... BTW...to check the tank breather when riding only half fill the tank and just click the filler cap open before you start off (so it rests partly closed)...don't brake too hard. There is also a very tiny screen filter in the tee-piece where the two carbs join and the main fuel pipe is connected, pull the pipe off and you will see (or you should see) a white ring on the end of the tee piece.......stanley knife blade in the join to get it moving sometimes, then it just pulls out. OEM Carbs should be B156 OEM Main jet should be 132.5 OEM Idle / pilot jet should be 37.5 OEM Needle should be 5CJ1, third notch from the top OEM Emulsion tube should be Y6 OEM Starter jet should be 70 Why go Sigma and not Dynojet? Anyway, with open pipes and a jet kit (Stage 1 or Stage 2?) you will have to do something with the airbox......remove the rubber trumpets for starters. AL.
This is an unusual one for sure, and the feedback is helping. So closed-down valve clearance aside, it sounds like it has to be fuel if spark on hot engine straight after cylinder dies is as good as you say it is, and kind of rules out the plug tbh. It sounds like a full carb strip and clean wouldn't go amiss checking for any air leaks on inlet rubbers as you go.
