B12 Problem - possibly carbs.

[ptitza]

Suddenly my '98 B12 started behaving wierdly.
When I open throttle beyond some point (like > 1/3 throttle), exhaust noise changes to something that resembles farting and immediate loss of power occurs.
Spark plugs are new (<1000km), and I`ve cleaned air filter recently.
I`ve got a feeling that this might happen because of clogged carbs, so I`ll take them off and clean them.
But before I do that - might that be any other problem?

[rider123]

What air filter do you have? If you've just cleaned it but haven't added oil(depending on filter) it's going to be lean which would give you the "farting". It shouldn't be that lean though I'd check that the air filter is fully seated and any extra air is getting in there by mistake. Check and tighten all boots, re-seat the air filter and oil it if nessesary then see. Try the cheap stuff first. Sound like you're a little lean in that rev range. Is it stock? Or is it jetted with a pipe? Did it run well just before the air filter cleaning? For fun try some  "carb cleaner" or "gas treatment" in the gas tank and take it for a long highway ride after you've checked every thing, that should clear it out.

[ptitza]

What air filter do you have? If you've just cleaned it but haven't added oil(depending on filter) it's going to be lean which would give you the "farting". It shouldn't be that lean though I'd check that the air filter is fully seated and any extra air is getting in there by mistake. Check and tighten all boots, re-seat the air filter and oil it if nessesary then see. Try the cheap stuff first. Sound like you're a little lean in that rev range. Is it stock? Or is it jetted with a pipe? Did it run well just before the air filter cleaning? For fun try some  "carb cleaner" or "gas treatment" in the gas tank and take it for a long highway ride after you've checked every thing, that should clear it out.

Air filter is K&N, stock replacement.
Jetting is dynojet stage 1, and exhaust is made by Arrow.
Filter was throughly oiled after cleaning. I`ll re-check it's seating, but anyway it should not give me such kind of problems.
The bike is not able to pass 60mph when slightly uphill,at 5th gear and at the 3/4 throttle.
I`ve cleaned the filter some 3000km ago, and, considering the fact that this is K&N high flow one it should not be cleaned again so often.
I'm trying to use this "gas treatment" stuff already, anyway there is no way I can get to removing the carbs before friday.

[rider123]

Did it run ok before you did the servicing? What could have happened is that the bike was tuned before you got it to a dirty air filter so was leaned out. When you cleaned it, did the bike suddenly run lean? Do you have for fun the stock air filter kicking around? It doesn't breath as well, you could pop it in for fun to see the difference between the two. I know that here the general concensus is that the K&N stock replacement cause more problems than they solve at least on the newer 2001+ Bandits. You could also try running the bike on prime. If the petcock diaphram is a little weird, or the air breather hole in the top of the tank is clogged it will starve the bike of gas. You could let the gas get down to half tank and then drive with the tank lid open to eliminate that source of the problem. I can't see how you would see such a dramatic loss in power with slighly clogged up jets. Did you store the bike over winter and forget to put fuel stabilizer in there?

Could you please explain a bit how it happened? Were you running down the road all happy then suddenly "bang" no power? Or was it running fine then you cleaned the air filter and now no power? It sounds like it's fuel starved so there is only 2 things that may be happening.

1. It's not getting enough fuel from either the tank, or the jets are clogged. But if it was running great before you did the air filter cleaning then I doubt that this is the problem.

2. After cleaning the air filter its now getting too much air. Either it's not seated, too little oil, or it was jetted when the filter was super dirty and leaned out to run with a dirty filter. No dirt--->More air---> lean condition--->loss of power.

If it started after you cleaned the air filter I doubt that there is a serious problem. It may just not be seated correctly, too little oil, jetted with a dirty filter, etc. Can be fixed quite easily.

If you want to test the "too much air" theory. Temporarily block up some of the air filter with masking tape and see if it starts improving after you've determined its not air blockage in the tank or a fuel delivery problem(jets)

[ptitza]

Did it run ok before you did the servicing? What could have happened is that the bike was tuned before you got it to a dirty air filter so was leaned out.

It did run ok before the servicing, and it did run ok afterwards:)
As I`ve told, I`ve serviced the bike about 3000km ago, so I can hardly beleive that this problem is a result of something that went wrong during the service

Do you have for fun the stock air filter kicking around?

No. The stock one hase been replaced by the previous owner.
I generally avoid doing perfomance mods when I`m happy with power I got, and my previous bike was Kawi`s  Vulcan 500:)

You could also try running the bike on prime. If the petcock diaphram is a little weird, or the air breather hole in the top of the tank is clogged it will starve the bike of gas.

First thing I`ve done. No result whatsoever.

You could let the gas get down to half tank and then drive with the tank lid open to eliminate that source of the problem.

That`s a good idea. I`ll do that first thing at the morning.

I can't see how you would see such a dramatic loss in power with slighly clogged up jets.

Me too. But only one another idea I got takes me to spark plugs. I`ll check them anyway,maybe they are way dirty (that dynojet stuff results in very rich mixture). Anyway,I`ve changed them when I`ve done servicing 3000km ago.

Did you store the bike over winter and forget to put fuel stabilizer in there?

No:)
I ride all the year.

Could you please explain a bit how it happened? Were you running down the road all happy then suddenly "bang" no power?

Yep. The only thing I`ve done before it happened was refuelling.
Which leads me to "crappy fuel" possibility. This is going to be checked out tomorrow, as I`m supposed to be hitting reserve soon.

But.
I haven`t cleaned the carburetors since I`ve got the bike (10000km ago), and I don`t know when the owner done it last time.
So,I`m going to check the fuel supply issue tomorrow morning and then we'll wee what to do next.
I would also like to get rid of the dynojet kit. It gives quite low fuel mileage (160 km before reserve - while driving very calmly!).

[rider123]

It could be very possible be then the "crappy fuel" as you suggested. I would fill up with some premium just for the hell of it and see what happens. Could you fill up some now? Theoretically if you were filling up as a tanker truck is filling the storage tank at the gas station some sediments and crud got into your tank as they get swirled around when the tanker is refilling the stations storage tanks. Try the gas cap off for fun but I think you may have hit it on the head. 160 kms before you hit reserve? That does seem a little low it's around 30-32 mpg.

As a replacement for the Dynojet/K&N setup you have you could try an Ivan's kit or Holeshot, well proven. The concensus here is that Dynojet and K&N are a little wonky on the Bandit series for some reason. Just make sure the Dynojet didn't make you change your emulsion tubes otherwise I think you can't screw in standard jets due to the threading. I'm not sure on G1 Bandits though. Unfortunatly for you the previous owner chose the 2 most wonkiest parts to get running correctly when rejetting his Bandit. You might want to forgoe jumping to a new jet kit and just lean out what you have slightly to get it a little better milage when you're back up to normal.

One guy here who had an Ivan's said if he went up one needle notch on his Bandit he could get it to wheelie in 3rd gear!! However his milage went to someting like 27 MPG. If he left it stock he got around 32 MPG. So what he did is drop the needle down one notch, lost a little power but is now getting 42 MPG. I think you can tune out your bike to help a bit with the milage. I would go that route since it's free and the Dynojet emulsion tube/standard jet issue. Hypothetically you buy a stock filter which will make you lean out your bike more anyway to compensate and is less wonky than the K&N filter.

[ptitza]

It could be very possible be then the "crappy fuel" as you suggested. I would fill up with some premium just for the hell of it and see what happens. Could you fill up some now?

Now I`m going to sleep, as it 22:25 here and I need to get up early:)
But I`ll try to fill 98 octane tomorrow morning - just to try

160 kms before you hit reserve? That does seem a little low it's around 30-32 mpg!

Actually, its around 23-25mpg.
I can even see the hole in my pocket:)

As a replacement for the Dynojet/K&N setup you have you could try an Ivan's kit or Holeshot, well proven. The concensus here is that Dynojet and K&N are a little wonky on the Bandit series for some reason. Just make sure the Dynojet didn't make you change your emulsion tubes otherwise I think you can't screw in standard jets due to the threading. I'm not sure on G1 Bandits though.

I was thinking about getting back to stock jetting for starters(price is an issue too).
As far as I can get it, I need stock main jets, needles and springs.
Unfortunately, local dealer don`t have those springs in stocks.
I wonder if it is necessary to replace dynojet springs with stock ones.

[ptitza]

One guy here who had an Ivan's said if he went up one needle notch on his Bandit he could get it to wheelie in 3rd gear!! However his milage went to someting like 27 MPG. If he left it stock he got around 32 MPG. So what he did is drop the needle down one notch, lost a little power but is now getting 42 MPG. I think you can tune out your bike to help a bit with the milage. I would go that route since it's free and the Dynojet emulsion tube/standard jet issue.

Ok.
Accepted.
I`ll lower the needles one notch,and I also think that I should tweak the air/fuel screws.
BTW, dynojet instructions for stage 1 kit installation on G1 bandit do not have anything regarding drilling (except for air-fuel screw cover).

[rider123]

No sorry for the misunderstanding, there is no drilling, what the deal is with the Dyno jet setup is they make you change the emulsion tubes and somehow this changes the threading from standard Mikuni threads to "Dynojet" propriatary threads. I can't find the posts right now but I'll try. Basically Dynojet wants people to buy their main jets instead of the $5 mukuni ones. Whether this is just to get your money or that they are actually superior, I don't know, someone with more Dynojet experience can help you. You might want to go to their site. If you look at their kits they usually get you to change the emulsion tubes to the Dynojet ones as I believe they are superior and wear out less. You might want to check it out before you buy main jets take the carbs off and then can't screw in the jets. One guy on this board had that problem when doing the same thing as the previous owner got a Dynojet kit. He tried to screw in standard Mikuni jets and they wouldn't screw in to the Dynojet emulsion tubes.

I figure if your bike is running well(when fixed) it might be a safer route to try and lean it out a little with what you have. Sometimes getting into jetting can get a little frustrating. To tweak it out a bit is free and then if you don't get what you want, well at least you tried, and you can go from there. For example I gained about 7 MPG just by turning in my mixture screws 1/4 turn and a bit, as I do mostly in city driving(alot on the pilots). I imagine with your setup working properly you must be getting crazy power!

There are alot of experts here better than I to help you tweak it a bit. I went from total hell stock jetting to fairly nice(for stock) with some help from the guys here. You obviously sound like you know what you're doing, let us know how you make out.

[ptitza]

Well.
Open gas cap - no result.
Better fuel - no result.

I'm going into stuff that requires disassembling this weekend.

[chupacabra]

I'd try draining the float bowls first and then check the plugs, make sure their not loose or fowled, clean and regap, or try a new set, gap and install.
Look into the gas tank with a flash light, checking for water or rust and dirt.    Good luck!

[ptitza]

I'd try draining the float bowls first and then check the plugs, make sure their not loose or fowled, clean and regap, or try a new set, gap and install.
Look into the gas tank with a flash light, checking for water or rust and dirt.    Good luck!

Sure thing:)
I`ll check the spark plugs and air filter first, if that won't help I'll get to the carbs.
Thanks.

[solman]

I've had more problems that seemed like carb problems, but 95% of the time turned out to be a spark problem.

81 CB750K:  Ran bad above 5K.  Result:  Tore out the carbs 7-10 times trying to fix it.  Fix:  New spark plug wires

03 B12 Ran bad during lower rpms and suttering problems.  Result:  Tore out the carbs a couple of times.  Fix:  New spark plugs.

Once again 03 B12:  Stuttered on accels and overall ran bad.  Result:  Tore out carbs and shimmed needle.  Fix:  Removed and installed spark plugs.  On this last fix, I think that one of the plugs was getting a bad ground and by removing and reinstalling the plugs, it gave it a better ground.

I am not saying that it is a spark problem, but if you can't find a fix by looking at the carbs, consider buying a new set of plugs.

[ptitza]

I am not saying that it is a spark problem, but if you can't find a fix by looking at the carbs, consider buying a new set of plugs.

I think that the carbs deserve their annual cleaning anyway, but I agree that spark plugs are most likely to be the source of the problem.

[rider123]

You may have something there pitza, especially if the bike's been re-jetted and is running a little rich. I've had spark plugs go on my bad jetting experiments in as little as 3000 kms. Just for fun throw a new set in there if only to eliminate that source of a potential problem.

As far as the crappy fuel is concerned you may have rust particle contamination, draining the floats may be a good idea and fast to try.