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Motorcycle Forum / General / Sportbikes / October 2005fouling plugs
I have a 97 1200 Suzuki Bandit. Lately it fouls plugs, but runs great after plug replacement. My thoughts are that the ignition coil/wire combos are broken down and I need to replace coils. The wires can't be replaced separately on these coils. The bike doesn't get ridden much, but doesn't sit long enough for gas to gum up. I have double checked my jetting and carb circuits to make sure I'm not dealing with carb gum. Is this a common problem with Japanese bikes? The pipes for cyls 1 & 3 read cooler than 2 & 4, so I think I am on the right track since one coil fires 1 & 3 and the other 2 & 4. I want to make sure because there is an ignition ignitor that I have no way of checking. TIA---------Alex  SignatureMy 2¢ YMMV > I have a 97 1200 Suzuki Bandit. > Lately it fouls plugs, but runs great after plug replacement. My thoughts [quoted text clipped - 7 lines] > The pipes for cyls 1 & 3 read cooler than 2 & 4, so I think I am on the > right track since one coil fires 1 & 3 and the other 2 & 4. Are the EPA anti-tamper plugs drilled out? They may be on top of the carbs or underneath. If you can see slot headed brass screws in holes downstream of the throttle butterflies, that's the idle mixture screw and if you can see it at all, the EPA plugs have been drilled out. If the idle mixture screws are underneath the carbs you may need a mirror to see them. What happens is that shade tree mechanics have no clear understanding of how CV carbs work, or which way to turn the idle mixture screws. The shade tree guys think that the idle speed will increase as they turn the idle mixture screws counterclockwise. After a certain point, the idle speed does not increase, the exhaust sound just gets dull and muffled from the excessively rich idle mixture and the idle speed actually slows down. So the shade tree guy will turn the master idle knob up and when he does that, the idle mixture transition ports downstream of the butterflies are uncovered. If the shade tree guy really screws up, he has some carburetors richer than others and it's not surprising that some spark plugs carbon up and the exhaust pipes are closed while other carbs are too lean and and run hotter. And maybe the shade tree guy thinks that the problem is really carb synchronization, so he turns up the idle speed on some of the carbs that are running too rich. If the idle mixture screws can be seen, I recommend turning them all the way in until they seat lightly, open all the screws half a turn, set the master idle knob so the idle RPM is according to the manual spec and then synch the carbs and reset the master idle knob to spec again. If you got the idle mixture correct, the engine will start from cold with just the full "choke" and you won't have to touch the throttle handle at all. The engine will warm up quickly and you won't need to keep messing with the "choke" lever to keep the idle RPM from getting too high. I jetted the bike when I first bought it. I think I got best mixture and part throttle response at 1 & 3/4 turns out. The carbs come very close to balancing with them all just off flat against the stops. I thought I could hear a faint snapping like a wire is grounding out, but I couln't see anything. I wish I could just replace the wires. I am going to ohm out the secondary leads on the coils, and if they check OK, I'll revisit my jetting. This did happen after the bike sat for a while, and I thought it might be due to varnish in the carbs, but I didn't find any. There are some very small circuits in there though. My first thought is that it just wouldn't run like a top if I had a plugged circuit in a carb. I didn't really check the float level very carefully since my set up worked so well. Thanks for the advice. I'll report back what finally does it. Alex >> I have a 97 1200 Suzuki Bandit. >> Lately it fouls plugs, but runs great after plug replacement. My thoughts [quoted text clipped - 51 lines] > keep messing with the "choke" lever to keep the idle RPM from getting > too high. > I jetted the bike when I first bought it. I think I got best mixture and > part throttle response at 1 & 3/4 turns out. Well, it sounds like you may be the source of your own problems then. I'd would guess, without actually looking it up, that your idle jet is around #40, #42.5, or even #45. With a huge idle jet like that, your idle screws were probably originally set about 1/2 or even 1/4 of a turn open from the factory. >> I jetted the bike when I first bought it. I think I got best mixture and >> part throttle response at 1 & 3/4 turns out. > > Well, it sounds like you may be the source of your own problems then. You missed the part where I said the bike ran well with my set up for years. It's a 97 > I'd would guess, without actually looking it up, that your idle jet is > around > #40, #42.5, or even #45. With a huge idle jet like that, your idle > screws were probably originally set about 1/2 or even 1/4 of a turn > open from the factory. Nope. Stock jet 37.5 was about 2 turns out stock. Factory jet kit gave me # 35 and recommended more turns out. I actually got best mix at 3 turns out. > "skimmer" <rynchops_niger@yahoo.com> wrote in message > > I'd would guess, without actually looking it up, that your idle jet is > > around > > #40, #42.5, or even #45. With a huge idle jet like that, your idle > > screws were probably originally set about 1/2 or even 1/4 of a turn > > open from the factory. > Nope. Stock jet 37.5 was about 2 turns out stock. > Factory jet kit gave me # 35 and recommended more turns out. I actually got > best mix at 3 turns out. Conventional wisdom on idle jets in CV carbs is that if you have to turn the idle mixture screw out more than 2.5 turns, the idle jet is too small. I wonder what they were thinking of, supplying a smaller jet than the already small stock idle jet. The diameter of that tiny jet's orifice is less than 0.014 inches. It's always going to be susceptible to gum and varnish. When you're riding down the highway at cruising speed with 1/8th of a turn on the throttle, you're running on the idle jet mostly, the jet needle hasn't come up out of the needle jet enough to get onto the taper. You'll hear the exhaust sound going piffle-piffle-SNAP! as you roll off the throttle. That tells you the idle jets are getting plugged up. >> > screws were probably originally set about 1/2 or even 1/4 of a turn >> > open from the factory. [quoted text clipped - 20 lines] > You'll hear the exhaust sound going piffle-piffle-SNAP! as you roll off > the throttle. That tells you the idle jets are getting plugged up. Well, the kit supplies the 49 state jet, as well as different needles and slide return springs. This is typical of what a California denutted carb is like. Due to the spring and jet combo it spends more time on the low speed circuit, so the jet is actually a little bigger. The slide doesn't lift as it would for optimum performance and they don't want it to. This bike in stock form would flatten out at about 6 grand. They really force people to modify them by denutting them so much. They did the same crap with carburated cars. Every Ca. car with a V-8 had a 4 barrel carb. The secondaries would just suck air and the engine would flatten out at rpms. They don't want you revving it. > This bike in stock form would flatten out at about 6 grand. They really > force people to modify them by denutting them so much. All inline-4's with 4-into-1 exhaust systems have a flat spot between 5K and 7K. It's a bad interaction between the exhaust pipe and the cam timing that allows the returning pressure wave from the header to go back through the valves at overlap and push air back through the carburetors. The airbox and crossovers between the exhaust pipes help the flat spot out though. > I have a 97 1200 Suzuki Bandit. > Lately it fouls plugs, but runs great after plug replacement. My [quoted text clipped - 10 lines] > no way of checking. > TIA---------Alex Clean the carbs, and take it out for a blast with some fresh plugs, and beat on it a little. Next time you park it, put some stabil in the gas. Yes, maybe theres a problem with a coil, but take care of youe fuel system... http://www.i4at.org/surv/sta-bil.htm Signature1984 RZ350 >> I have a 97 1200 Suzuki Bandit. >> Lately it fouls plugs, but runs great after plug replacement. My [quoted text clipped - 15 lines] > Yes, maybe theres a problem with a coil, but take care of youe fuel > system... You were right. When I pulled plugs again the # 3 didn't even look like it had ever had fuel on it. I pulled the carbs off and very carefully cleaned the low speed circuits, retuned and resynced. I had to carefully study the carb diagram to be sure I got all the circuits clear. All is well now. As it turned out it wasn't a fouled plug at all. I don't know why it ran good for a bit after I initially changed plugs, but I guess I'll try to ride it more than 800 miles a year! Alex > http://www.i4at.org/surv/sta-bil.htm >>> I have a 97 1200 Suzuki Bandit. >>> Lately it fouls plugs, but runs great after plug replacement. My [quoted text clipped - 26 lines] >> >> http://www.i4at.org/surv/sta-bil.htm LOL! Glad it was an easy fix, but when you do ride it, maybe throw some gumout in the tank, and pound on that baby! Signature1984 RZ350 I put about a pint of naptha in it and gave it a well deserved flogging :) >>> Clean the carbs, and take it out for a blast with some fresh plugs, >>> and beat on it a little. Next time you park it, put some stabil in [quoted text clipped - 15 lines] > Glad it was an easy fix, but when you do ride it, maybe throw some > gumout in the tank, and pound on that baby! |
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