Only running on cyldrs 3 & 4
#11
06-27-2018, 12:48 PM
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Timbuctoo - it's a 1991FM.
My thoughts about timing/valve clearance confirmed - thank you.
It's cyldrs 1&2 (or maybe just 2 now) that are the problem ones so I think it's unlikely to be the coils (1+4/2+3) - although at some point I might get round to that stick coil mod I've been reading about on this forum.
Petcock is vacuum operated and flow is good so no problem there either.
Your comment about the foam air filter is a new one on me. I was wondering only yesterday what that little black plastic cube was as it seemed to go nowhere other than the breather. Well now I know! I've just taken a look and it was absolutely fine and in tact - right up to the point I touched it when it completely fell apart in my fingers! I'll be doing something about that (thanks for avoiding another potential carb cleaning not very far down the line) but as it was OK until I touched it, it's probably not the cause of my problem. But in any case if/when the carbs do come off again, debris of any kind will get sorted.
I asked earlier whether the hitherto completely untouched pilot screw could be contributing to the issue. I'm inclined to think not, but do you have a view? Thanks again for (all) the input.
My thoughts about timing/valve clearance confirmed - thank you.
It's cyldrs 1&2 (or maybe just 2 now) that are the problem ones so I think it's unlikely to be the coils (1+4/2+3) - although at some point I might get round to that stick coil mod I've been reading about on this forum.
Petcock is vacuum operated and flow is good so no problem there either.
Your comment about the foam air filter is a new one on me. I was wondering only yesterday what that little black plastic cube was as it seemed to go nowhere other than the breather. Well now I know! I've just taken a look and it was absolutely fine and in tact - right up to the point I touched it when it completely fell apart in my fingers! I'll be doing something about that (thanks for avoiding another potential carb cleaning not very far down the line) but as it was OK until I touched it, it's probably not the cause of my problem. But in any case if/when the carbs do come off again, debris of any kind will get sorted.
I asked earlier whether the hitherto completely untouched pilot screw could be contributing to the issue. I'm inclined to think not, but do you have a view? Thanks again for (all) the input.
#12
06-27-2018, 02:18 PM
Super Moderator
Agreed. I think a good first step would be to confirm fuel flow to all four carbs
If fuel confirmed, suspect pilot jets, or maybe go back to spark as TimBucTwo suggested
If no fuel, suspect strainer, bad vacuum, or floats/valves
If you're running without a fuel filter, it's definitely possible that you've kicked some debris free, and now it's migrated somewhere it shouldn't be. (Probably want to get one on asap)
Good luck. Keep us posted
If fuel confirmed, suspect pilot jets, or maybe go back to spark as TimBucTwo suggested
If no fuel, suspect strainer, bad vacuum, or floats/valves
If you're running without a fuel filter, it's definitely possible that you've kicked some debris free, and now it's migrated somewhere it shouldn't be. (Probably want to get one on asap)
Good luck. Keep us posted
#13
06-27-2018, 02:23 PM
Super Moderator
Sorry, didn't see your other reply. If you're worried about the pilot screws, you could run them in, counting the number of rotations. Write those numbers down. Then go back to factory setting (check your manual, but I think it's about two turns out from seat)
It will adjust the a/f at idle, but won't have any effect at higher rpm's, so if it won't run at any speed, it's unlikely to be the main cause
It will adjust the a/f at idle, but won't have any effect at higher rpm's, so if it won't run at any speed, it's unlikely to be the main cause
#14
06-27-2018, 05:04 PM
Timbuctoo - it's a 1991FM.
Your comment about the foam air filter is a new one on me. I was wondering only yesterday what that little black plastic cube was as it seemed to go nowhere other than the breather. Well now I know! I've just taken a look and it was absolutely fine and in tact - right up to the point I touched it when it completely fell apart in my fingers! I'll be doing something about that (thanks for avoiding another potential carb cleaning not very far down the line) but as it was OK until I touched it, it's probably not the cause of my problem. But in any case if/when the carbs do come off again, debris of any kind will get sorted.
Your comment about the foam air filter is a new one on me. I was wondering only yesterday what that little black plastic cube was as it seemed to go nowhere other than the breather. Well now I know! I've just taken a look and it was absolutely fine and in tact - right up to the point I touched it when it completely fell apart in my fingers! I'll be doing something about that (thanks for avoiding another potential carb cleaning not very far down the line) but as it was OK until I touched it, it's probably not the cause of my problem. But in any case if/when the carbs do come off again, debris of any kind will get sorted.
#15
06-28-2018, 02:24 AM
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Tentacleslap mentioned a couple of things that I'd like to clarify. I've been looking at the service manuals available on this forum - (one for the 87 model and another for the 93 model, mine's 1991FM UK model) - and noticed something. The 87 manual has the same carbs as mine combined with an inline fuel filter, whereas the 93 has different carbs with no filter in the line. My 91 seems to be a mixture of the 2 which has the carbs of the 87 model but no inline filter. It's a UK model so I'm wondering whether this kind of bastardisation is "normal"(?).
Having looked again at the carb strainer situation, the diagrams in the service manual seem to suggest they're located inside the seating of the float valve and hence require that seating to be removed to access them. Is my interpretation correct?
How can I check the fuel flow is good to ALL 4 individual carbs? I know the fuel flows well from the tank (checked that), but I get the impression that the only way to check whether fuel is flowing into carb 1 and/or carb 2 is by dismantling the carbs (which I'm not too enthusiastic about). Or am I missing the point?
I'm going to steer clear of the pilot screws for now. Don't want to risk creating another problem without being certain that the action I take will solve an existing issue!
Finally, I like very much the idea of fitting an inline fuel filter (once my existing problem is resolved) but my fuel line route (which seems to be different from the 87 models which are built with filters fitted) seems to offer very little room to fit one. Is the "suggested" fuel filter to be used the same as that found on CBR1000's that are built with them, and is there in fact room to fit one? Also, I just wonder whether putting a filter inline with a vacuum (no fuel pump) operated system would tend to starve the fuel supply by adding additional resistance in the line(?). {I remember seeing some discussions on fuel filters elsewhere on the forum but I'm currently trying to focus on my specific problem so don't want to go searching at the moment}. Apologies for keeping going on about things but, well, I guess that's the nature of the beast. Thanks, thanks, thanks...
Having looked again at the carb strainer situation, the diagrams in the service manual seem to suggest they're located inside the seating of the float valve and hence require that seating to be removed to access them. Is my interpretation correct?
How can I check the fuel flow is good to ALL 4 individual carbs? I know the fuel flows well from the tank (checked that), but I get the impression that the only way to check whether fuel is flowing into carb 1 and/or carb 2 is by dismantling the carbs (which I'm not too enthusiastic about). Or am I missing the point?
I'm going to steer clear of the pilot screws for now. Don't want to risk creating another problem without being certain that the action I take will solve an existing issue!
Finally, I like very much the idea of fitting an inline fuel filter (once my existing problem is resolved) but my fuel line route (which seems to be different from the 87 models which are built with filters fitted) seems to offer very little room to fit one. Is the "suggested" fuel filter to be used the same as that found on CBR1000's that are built with them, and is there in fact room to fit one? Also, I just wonder whether putting a filter inline with a vacuum (no fuel pump) operated system would tend to starve the fuel supply by adding additional resistance in the line(?). {I remember seeing some discussions on fuel filters elsewhere on the forum but I'm currently trying to focus on my specific problem so don't want to go searching at the moment}. Apologies for keeping going on about things but, well, I guess that's the nature of the beast. Thanks, thanks, thanks...
#16
06-28-2018, 02:57 AM
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Just had a thought about the "checking fuel flow to the individual carbs". I guess if I crack open the float bowl drain screws and fuel continues to flow through the drains whilst a fuel supply is still connected then that'll show there's a continuous fuel supply to each carb.......Off to check that right now as it'll eliminate one aspect straight away. In fact, I think it was Gronkfries who first mentioned the "banks" of carbs and fuel supply to them. This is better teamwork than some of those guys trying to play football (or should that be soccer) in Russia at the moment!
#17
06-28-2018, 04:24 AM
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Latest - just been running the engine from a temporary fuel supply and it's definitely only cyl 2 that's the problem. I've opened the carb drain screws and fuel flows from all of them; stops when I remove the fuel supply (no surprise there); and restarts when I reintroduce the fuel. So my conclusion is the fuel supply to all the carb float chambers is good. I'm now narrowing things down to the float/float valve of cyl 2, or this strainer thing which I haven't yet clapped eyes on - can someone please confirm I have to remove the float valve seat to get to that. When I had the carbs opened 2-3 weeks ago I remember the "resistance" of one of the float valves (maybe cyl 2) feeling a little less "springy" than the others and maybe that has something to do with the problem - but I don't see any float valve "spring" shown in the service manual. Is there an explanation why it might feel different like that and what I should do to rectify it. I checked the float heights (as best I could) last time around and they seemed "about right". Finally, if I find I need floats valves/floats etc does anyone have a supplier in mind????
#18
06-28-2018, 10:28 AM
Super Moderator
Yes, you need to remove the valve seat to access the strainer. You pull the floats, along with the float needle, and then unbolt the seat itself. I think it's 10mm hex, could be 12. Been a few months since I was in there
But if we've confirmed fuel, the float valve is working. That puts us back at the pilot jet
I'm thinking that debris has bypassed the strainer and wedged into the tiny orifice on the pilot jet. It's the smallest opening in the carbs, and a common problem. As before, you need to remove the jet, and use a piece of thin wire to poke through the opening, then blast with solvent, and chase with compressed air before reinstalling. Guitar string works, and I had good results using a bristle from a rust wheel. Could probably also use thin mig wire or whatever else you have lying around, but if you use guitar string, the slinky stuff can actually file away at the opening, so just a light touch if you go that route. Ox/Acy torch tip cleaners will be too big. Sounds like you've already cleaned them out, so this'll all be pretty familiar territory
Fuel filter should be a requirement for older bikes. There would be a length of fuel line from the petcock to the common carb fuel line, so would think it's just as simple as buying a fuel filter (OEM or aftermarket, just size for the fuel line diameter) and then cutting an inch or two out of the fuel line somewhere where the line is relatively straight. Jam the filter in and secure with a couple wire clamps. They are unidirectional, so make sure you don't install it backwards or else you won't get any fuel
What's interesting is the older carbs. Do you think the bike might have been modified? That could have implications for tuning since you won't have a fuel pump, making it a bit lean on the high-end when these things really guzzle. If a previous owner tried to put a jet kit in it it might have made the problem worse. There would also be some vacuum trickery since the later years petcock uses a vacuum line that doesn't exist on older years. Anyway, it's all academic until you get it running
One other thing about the '87 carbs is the aircut valve. This infernal contraption is a small diaphragm underneath a circular plate on the side of each carb. Prone to failure, and will cause massive problems at idle if one of those diaphragms rips. They are easy to remove, and I understand that you just need to block off the vacuum source for the aircut, but I don't know that process since mine came pre-removed. There's also aftermarket kits (one of the few carb parts commonly available for the '87) but they're not great quality. Before removing the carbs, you could pop the aircut covers off and check for bad diaphragms
This is the first hit I got on the subject. I think these are a definite suspect, but I do think you're probably looking at a clogged pilot jet
https://www.motorcycleproject.com/te...alve_more.html
But if we've confirmed fuel, the float valve is working. That puts us back at the pilot jet
I'm thinking that debris has bypassed the strainer and wedged into the tiny orifice on the pilot jet. It's the smallest opening in the carbs, and a common problem. As before, you need to remove the jet, and use a piece of thin wire to poke through the opening, then blast with solvent, and chase with compressed air before reinstalling. Guitar string works, and I had good results using a bristle from a rust wheel. Could probably also use thin mig wire or whatever else you have lying around, but if you use guitar string, the slinky stuff can actually file away at the opening, so just a light touch if you go that route. Ox/Acy torch tip cleaners will be too big. Sounds like you've already cleaned them out, so this'll all be pretty familiar territory
Fuel filter should be a requirement for older bikes. There would be a length of fuel line from the petcock to the common carb fuel line, so would think it's just as simple as buying a fuel filter (OEM or aftermarket, just size for the fuel line diameter) and then cutting an inch or two out of the fuel line somewhere where the line is relatively straight. Jam the filter in and secure with a couple wire clamps. They are unidirectional, so make sure you don't install it backwards or else you won't get any fuel
What's interesting is the older carbs. Do you think the bike might have been modified? That could have implications for tuning since you won't have a fuel pump, making it a bit lean on the high-end when these things really guzzle. If a previous owner tried to put a jet kit in it it might have made the problem worse. There would also be some vacuum trickery since the later years petcock uses a vacuum line that doesn't exist on older years. Anyway, it's all academic until you get it running
One other thing about the '87 carbs is the aircut valve. This infernal contraption is a small diaphragm underneath a circular plate on the side of each carb. Prone to failure, and will cause massive problems at idle if one of those diaphragms rips. They are easy to remove, and I understand that you just need to block off the vacuum source for the aircut, but I don't know that process since mine came pre-removed. There's also aftermarket kits (one of the few carb parts commonly available for the '87) but they're not great quality. Before removing the carbs, you could pop the aircut covers off and check for bad diaphragms
This is the first hit I got on the subject. I think these are a definite suspect, but I do think you're probably looking at a clogged pilot jet
https://www.motorcycleproject.com/te...alve_more.html
#19
06-28-2018, 10:48 AM
Super Moderator
Nevermind. I looked up on the fiche and it looks like those are the correct carbs for that year, and it's meant to run without a fuel pump, just on vacuum. Cool stuff
Apparently, 93 was when they rolled out the newer, better carbs. I always thought it was '90
That said, I'd check out the aircut valves, but you're probably removing the carbs to do another cleaning of the pilot jets. While you're in there, you can do the strainers
...that and the fuel filter. Whether or not it came installed, you should put one on pronto
Just my 2c
Apparently, 93 was when they rolled out the newer, better carbs. I always thought it was '90
That said, I'd check out the aircut valves, but you're probably removing the carbs to do another cleaning of the pilot jets. While you're in there, you can do the strainers
...that and the fuel filter. Whether or not it came installed, you should put one on pronto
Just my 2c
#20
06-28-2018, 11:45 AM
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Tentacleslap (and others) - just been to look at the externals of the carbs after reading your latest posts (thanks). The carbs are the ones that appear in the 1987 service manual (with 4 securing screws holding on the diaphragm cover) BUT the aircut valve doesn't exist. The carb housing casting looks the same as that which could have accommodated an aircut valve (and hence that in the 1987 service manual) but that part of the casting is completely sealed as part of the original casting process and definitely not an after market modification. It makes me wonder whether there were in fact 3 different models of carb (maybe this was just for the UK market) and mine is the 1987 version minus the aircut valve?? Anyway, at least the absence of the aircut valve eliminates that as contributing to the problem!
Tentacleslap - I hear what you say about the pilot jet (again) potentially being the prime culprit (and tend to agree - although it pisses me off knowing it was genuinely pristine just 2-3 weeks and only 200 miles ago) but I'd just like to be clear about the fuel flow situation and conclusion. Fuel readily flows continuously through the drain plug when the carbs are connected to a gravity fed temporary fuel supply. Do you think that means that the float/float valve/strainer combination is working properly and is not clogged? I don't want to mess with it and create a problem if it's clearly not the cause of my current situation.
Tentacleslap - I hear what you say about the pilot jet (again) potentially being the prime culprit (and tend to agree - although it pisses me off knowing it was genuinely pristine just 2-3 weeks and only 200 miles ago) but I'd just like to be clear about the fuel flow situation and conclusion. Fuel readily flows continuously through the drain plug when the carbs are connected to a gravity fed temporary fuel supply. Do you think that means that the float/float valve/strainer combination is working properly and is not clogged? I don't want to mess with it and create a problem if it's clearly not the cause of my current situation.