Miles By Motorcycle
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Suzuki S600 Bandit flat spot in throttleSubscribe to this blog RSS Feed
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    1 of 16
    6 years ago
    at approximately 6000 to 7000 RPM when you're on the throttle trying to read through the range more noticeable in the later years 3rd 4th 5th and 6th it has a lag and I can't tell if it's lean or Rich but it's a definite High dead spot and I'm not sure how to go about diagnosing it or not if I race out through first and second and keep the RPM's above 8000 it doesn't show itself but if I accelerate out of 3rd from say 4000 through that range up to redline when it hits about 6500 RPM it bogs or flat spots significantly for a few seconds before it catches up in about 8,000 RPM it wickedly takes off up to 12 500.
     this is my first bike although I have some minor motorcycle experience throughout my scrap my life and I am a ASE Certified mechanic but have never really dealt with motorcycle carburetors or for carburetors which must be synced together or really Carburetors in general because most everything f i now but I was wondering where I would start I'm going to build a homemade vacuum gauge to look at the synchronization of the four carburetors together but how would I tell if it's lean or Rich and then where to go from there?
    2 of 16
    6 years ago
    Coils breaking down?
    That was my problem. 
    3 of 16
    6 years ago
    Ben Mendis and I worked for ages trying to track down problems with his carbs. 

    To sync the carbs we used one of these:
    Link #54474
    6 years ago Motion Pro 08-0411 Syncpro Carburetor Tuner: Automotive

    Buy Motion Pro 08-0411 Syncpro Carburetor Tuner: Motorcycle & Powersports - FREE DELIVERY possible on eligible purchases
    (affiliate link)
    It's been a while. I no longer remember exactly how we went about setting the mixture. There's a black art to running the bike and checking the plugs to determine if it's lean or rich. There are a bunch of youtube videos on it. 

    I seem to remember at one point when we had the carb sync way out of adjustment that we also got dead spots. So I would definitely check the sync. If the bike has been sitting for any length of time, I'd suggest cleaning the carburetors if doing plugs, valve adjustment, and sync don't fix the issue. We ended up pulling the carb rail so many times that we got to the point we could pull the rail and reinstall it in under I think 15 minutes.

    To Goat's point, it could also be coils. 
    4 of 16
    Ben Mendis
    6 years ago
    In my case, we had a throttle jumping issue happening at a low RPM (just above idle). We probably went through every subsystem on the bike trying to track it down.

    Balancing the carbs helped, and really made it feel much better through the whole RPM range. Replacing the coils made no difference on my bike, but your symptoms are different so it's worth a try.

    Check your spark plugs. Make sure they're clean, and see if they give any hints of running running rich or lean.

    You can rule out a vacuum leak by inducing one to observe how the bike behaves with a vacuum leak vs without one.
    5 of 16
    6 years ago
    as far as the coil packs breaking down how would I test to make sure that there are within spec or is it just a buy it and replace it and see kind of thing?

     as far as that sync Pro thing that's pretty much exactly what I was going to build I watch the how to on YouTube that somebody built one and compared it to an actual manufactured one and had approximately the same result but it might be just worth buying a Quality Tool it usually is in my experience.

     now I have a general idea what I'm looking for is that the vacuum throughout Idol mid-range and wide-open should pull approximately the same vacuum if not exact but how exactly am I to go about syncing carburetors I don't really want to have to send it to a shop because I don't have the money for it and if I can't do it myself it bothers the crap out of me but I also don't want to get into a mess that's over my head as far as reading plugs white bad tan good black rich but yeah if anybody could give me a quick rundown on what I'm looking for in a carb sync that would be cool or maybe just a link.

     and what would I do to create a small vacuum leak remove a carburetor from the intake plenum slightly or pull one of the vacuum Port plugs off somehow like how much of a vacuum leak in my looking to create the kind of simulate the problem in a worse way to diagnose it.?

     and by the way guys sorry for the long and complex posts lots of questions all at once but I finally found a forum that people actually respond with helpful answers and not go buy an F4i as an answer
    6 of 16
    6 years ago
    Good point on simulating a vacuum leak, Ben Mendis. I had forgotten about that. 

    Tattoomike, do you have the Haynes manual for the bike? The carb sync procedure is pretty well described as I remember it. 

    As you suggest, you can remove the vacuum port plugs to get a sense of what the bike behaves like with a vacuum leak.

    Are you familiar with using carb cleaner to check for vacuum leaks? You have to be really careful though since carb cleaner is flammable. But the idea is if you spray around the boots and other potential sources of a leak while the bike is running, some of the cleaner will get sucked in and you'll be able to hear the idle change. Again, be very careful doing this. There are a bunch of videos on youtube.

    With a sync you're not looking at absolute numbers but relative. As you open the throttle you want all four carbs to pull the same vacuum so they are in balance. You end up hooking up your 4 port vacuum gauge to the vacuum ports and then adjusting the screws on the carb rail until they are more even. Ben probably remembers better than I do, but there's also a step involved of zeroing out your gauge before you use it so you get accurate numbers.

    It's a tuning process so as you change one the others will get affected. As I mentioned, there are youtube videos and the process is described in the Haynes manual. It's been too long since I've done it so the details are a bit fuzzy for me at the moment.
    7 of 16
    Ben Mendis
    6 years ago
    I don't (yet) know of a better way to testing the coil pack than just swapping in a replacement and seeing if the behavior changes. I'm sure there's probably a better way, like measuring the output using a multimeter. Actually, you might want to have a multimeter handy to check the output of your alternator. Are you seeing a voltage sag around the affected RPMs?

    As far a syncing carbs goes, I would recommend using a tool like the one Yermo linked to. They're inexpensive enough, and you want a tool that you can trust to be accurate. The gold standard seems to be a Tecmate TS-72, but they are prohibitively expensive. When I was going through the process, I considered building one of these DIY digital sync tools.

    The process is pretty straight forward. You're going to calibrate the tool so that the levels are all the same when they're plugged into one carb body, then connect the tubes across all the bodies and see if the levels are still the same at various RPMs.

    You'll need to have the tank off because the way you adjust the balance is by turning the screws between the carb bodies. There are three screws, one between the left pair that adjusts 1 & 2 relative to each other, one between the right pair that adjusts 3 & 4 relative to each other, and one in the center that adjusts the left pair relative to the right pair. You want to start by adjusting each pair separately, then adjust the center to bring the left and right into sync. It will likely take a few iterations (and some patience) to get everything synced up nicely. It doesn't hurt to periodically re-calibrate the tool (sanity-check), especially if the what the tool is telling you doesn't match with what you're hearing from the engine. As it gets more in sync it should sound more smooth, more even.

    As you get it into tune, try adjusting the idle speed screw (underneath the carb rail, between 2 & 3) to the lowest RPM where it still sounds smooth. Should be close to 1200 RPM I think. And I like to adjust the throttle using the throttle cable adjuster, it allows you to make small incremental changes and know that it's being held steady while you're taking a reading on the sync tool. 

    The easy way to create a vacuum leak is to pull the cap off of a vacuum port on one of the carb bodies. You can do that while the bike is running and instantly hear the difference, then plug it with your finger to control the size of the leak.
    8 of 16
    6 years ago
    yes I'm familiar with using carb cleaner to check for leaks around them. I do plan on grabbing a manual offline though because I found an original shop repair and maintenance manual for like $8 describing everything I don't know if it was a Haynes but I know it was a complete repair shop manual,

     however I've still got some other stuff I need to do I've got a new pinion sprocket and chain that needs to go on something bad so I might go ahead and just start with that because and most days driving it I don't ever get into the RPM range we're at lag so it's not too much of an issue at this point but I want to make sure that I'm not doing any damage to the engine if it's in a lean condition.

     I do think I'll go ahead and just buy a sink gauge instead of doing the DIY one because the price of the materials versus the price of the tool and then making sure that they're accurate makes sense to just get the right tool I never even thought to look to see how much a sink tool was I just figured they're really expensive.

     but anyway for now I'm going to start with the pinion and sprocket and chain at least get that flapping thing off there and get a new good chain on it and improve drivability.
     I really don't have a whole lot into the bike and it's in really great shape with very low miles it just needs some TLC I think so this is my intro to motorcycles and working on them even though I've worked on vehicles for 15-20 years their whole different animal
     so for the moment I appreciate you guys in the responses and I'm going to start checking into stuff and I'll be back if I have any more questions which I'm sure I will shortly thanks guys
    9 of 16
    Ben Mendis
    6 years ago
    My '97 Bandit 600 is my first, and also my intro to working on motorcycles. I bought it used in 2013 with just under 8k miles on it. Spent about a year working on it and training on it. Since then I've put over 20k more miles on this bike, including a trip from DC to Minneapolis and back, and then down to the Smoky Mountains and back. 

    Well maintained, it'll be a reliable workhorse whether you're looking for sporty riding or long-distance travel. 
    10 of 16
    6 years ago
    just out of curiosity how many RPM are you running approximately 60 miles an hour in 6th Gear because it seems like mine wraps kind of high almost about 6000 / 60 miles an hour
    11 of 16
    Ben Mendis
    6 years ago
    That does sound high. I'm out of town this week (not on the bike) so I can't test it at the moment, but I'm pretty sure 60mph would be lower than that. In top gear, at 60mph my gut feeling is you should be around 4.5k because I remember needing to downshift to accelerate at that speed on the highway. I'll have to check the next time I'm in the saddle.
    12 of 16
    6 years ago
    okay well I figured out the problem with my RPMs being so high at a cruising speed plus I figured out why my chain was so damn loose and why it felt like it was going to come off going down the road at that.
     so I got my sprocket pinion and chain all together and got ready to take it all apart I went and started looking at the pieces the chain was able to be lifted off the sprocket really easily so obviously it was too loose time to move to a new chain and gears and the wheel adjustment is all the way back so I could not adjust it anymore so I pulled the side cover off the transmission in found that somebody had a bunch of stacked washers and no large nut holding the pinion on to the transmission shaft just a little possibly 10mm bolt at the end with a bunch of washers they had about 3 in of play in the chain it was missing a tooth on the pinion and it was a 13 tooth pinion instead of a 15 and they were bent backwards look like a saw blade instead of gear I guess they call a shark finning.

     so I ordered original parts such as the washer in the large 24 mm by 1.5 nut to go on the end of that and a few other stuff that it was missing that wasn't original or in very good shape

     it amazes me that that the gear didn't come off while I was going down the road or something being held on by this teeny tiny Bolt and a 2in thick stack of washers.
     although having a 13 tooth front gear does explain why the acceleration was off the wall and I could keep up with accelerating with bikes that were almost twice its size
    13 of 16
    6 years ago
    so not knowing what's causing the flat spot I kind of wondered if it was rich or lean so I decided that if I wanted to try leaning it out I could just remove the exhaust and leave just an open header so that's exactly what I did it sounds great it's painfully loud but the throttle response torque horsepower acceleration every bit of it it runs better than ever which wouldn't make sense cuz most people say you would lose power by running an Open Exhaust and this case it increased it so I'm believing that I'm running too rich that when I wrap it up with the muffler on it there seems to be some a little smoke that indicates a rich condition because it was dark gray kind of black smoke therefore excess fuel

     so I'm guessing to control the noise but have an Open Exhaust I need a pretty much gutted pipe and I cut the baffle out of the back of the factory pipe but I couldn't get it out even with a slide hammer after I cut through both Wells it's like welded or it's really tightly pressed I could only get it out about an eighth of an inch before I gave up after 2 hours of slide hammering the baffle out of it so I think I might go ahead and just cut the can open get it some and then either use a band and rivets and put it back together or go to a welding shop and take it back together with a TIG welder
    14 of 16
    6 years ago
    even if I get back to a more restrictive exhaust the idea just hit me that I could also clean it out slightly if it needs to buy using for cone filters like K&N or Spectre filters instead of the factory air box but I haven't checked the air filter since I got it so it may just be clogged up there's no telling but I think I'm on the right track
    15 of 16
    6 years ago
    I’ve been away for several weeks. Hope you have found your answers. 
    Regarding how to test your coils.... I presume the right way would be to measure impedance. I have a R1150R, 2004, the bike broke down at higher rpm’s from the day I took delivery. BMW “mechanics” said they could not figure it out, and perhaps it would 
    16 of 16
    6 years ago
    So, a couple of thoughts...

    With your coils, in general if they're weak, you're going to notice that it happens above a certain RPM, as opposed to a flat spot, as demand on the coil to perform increases with RPM. So a weak coil will fail as you heat it up and increase demand.

    It used to be common for shops to have coil bench testers, though I don't know if that's still the case, and I can't imagine they'd charge you much of a bench test if you handed them a coil you'd removed from the bike. Alternatively, you might be able to find plans for a home brew tester, or find some "ohming out" procedures in the manual.

    Finally, one thought on the flat spot--you could try a plug chop test. This is very old school, but basically you run the engine in top gear up to the problem spot in the throttle range, hold it there for a few seconds, then cut the motor with a kill switch. Coast to the side of the road, pull your plugs, and then check the color. Tan is ideal, brown to black to rich, and light tan to white too lean. But this is a very crude and old school method which may not prove to be the best diagnostic...