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7 Posts
Discussion Starter #1

I ride a '83 Suzuki GSX400E, restyled as a true cafe racer (though not by myself). Its my first bike, and I absolutely love it. But I have encountered some issues.

Since weather in Belgium has been terrible so far I haven't been able to ride as much as I'd like. I just did a small tour (+-50 km) which was basically the third time or so I rode the bike properly. I have noticed some issues that I wanted to share because they can get quite annoying I think.

First up: when the engine is warmed up properly and I have to stop at a red light, the engine's rpm start climbing pretty radically. During the first 5 seconds or so after coming to a hold everything's fine. But the the idling speed starts climbing up to the point that it's nearly too much. At first I tried to counter this by loosening the clutch somewhat so the rpm's would drop again. But after the 5th time I thought I'd just check how far it would go. It's not completely unbearable but still pretty high. Since I don't have a revcounter I'm afraid I won't be able to give accurate numbers. Sometimes, not always, after reaching a peak in rpm the speed starts declining again to a normal ratio. But it's not stable.

Second issue: when I've come to a complete stop and try to shift the engine in neutral, this will be either very, very hard or plain impossible. It sometimes helps to slightly loosen the clutch untill the bike is about to start rolling again, but only like 20% of the times I try. However, when I anticipate and shift down while slowing down towards a red light or so, it's not a problem to find neutral gear.

Third thing: when I need to start again in first gear, the clutch releases not smoothly at all. When loosening the clutch lever, it's nearly impossible to release it smoothly. Instead of releasing tension on the clutch cable in one swift motion it sort of jumps, as if the cable itself is sticky or something like that. So whenever I start again at a red light I kind of look like a complete rookie (well tbh I definitely still am a rookie) since I accelerate in a jumpy, uncontrolled way. If you know what I mean...

These problems are not making it impossible to ride, but I was hoping someone could try and explain or figure out what I can try to resolve these!

Thanks a lot in advance and hopefully the issues are somewhat clear to you :)


1,661 Posts
Second issue: when I've come to a complete stop and try to shift the engine in neutral, this will be either very, very hard or plain impossible. It sometimes helps to slightly loosen the clutch untill the bike is about to start rolling again, but only like 20% of the times I try. However, when I anticipate and shift down while slowing down towards a red light or so, it's not a problem to find neutral gear.
You just described every Ducati ever made.

Doesn't help solve your problem but at least now if you ever do buy a Duc you'll already know how to find neutral on it.

53 Posts
1. Put a tach on, could be an air leak. What happens if you turn the choke on while this is happening?

2. Sounds like the clutch is dragging.
How is the clutch freeplay?
When was the oil last changed?
What condition are the cables in?

3. See #2.

Sent from my iPhone using Tapatalk

29 Posts
I'm no pro but I would check the throttle cable, see if turning the throttle back past stop gently with your wrist pulls it down. I had a KZ1000 that I bought a nice set of grips for and they were rubbing and keeping the throttle pinned just a bit. I would also check to see if your carbs are returning to idle through the linkage when you are in fact at idle. If it has always done this then someone may have tuned the carbs to high on idle, this is very common when someone tunes the bike when cold instead of NoT. I will also ad that a dragging throttle cable will also keep the carbs opened.

1,512 Posts
if the bike sat for long time and this is common
exposed to seasons and weather over a year or ten
can allow the steels of the clutch pack plates get a bit rusty
this rust makes the plates stick together like glue many times
it will not happen in nice dry storage in one season may take several seasons in ''dry''storage

the steel plates are then like almost a friction the steel driven ones where they must be very smooth and precicely flat to act normal
the frictions, smooth steels and oil all work in harmony wiith the coefficient of friction that they have as an assembly to work with no drag and very little wear at all
of course old enginwe oil has corrosive acids that speed up the rusting
it really only should cost you an oil change and a clutch cover gasket to inspect clean and gently scrub the steels on a flat glass with 220 grit sandpaper
it isnt a metal removing concept just gettingn the fluffy shit off the steels
you can use the glassd and 220 to very gently deglase the frictions
no need usually for new plates unleess they are burnned or badly worn
do not get the frictions water wet ! it can ruin the bonding of the frictions to its plate mostly the bonding agent is oven cured water solluble compound
factory service manuals will have service limits for plate thickness of frictions
even just .1mm wear on each friction adds up tp a mm with 10 plates !
this causes slippage inadequate plate preload
to make sure the clutch has good grip with the veryn slightly worn used frictions,the springs can safely have a bit more preload in most cases from stock
common method was a ring washer under each spring maybe 1/2mm a new sparkplug washer,if it sits nicely under spring is a perfect solution
also if the steels are of a thin dimension anyway like 1mm - 1.5mm or less you can sometimes add 1 steel to the clutch pack giving same inntended extra preload
if left unserviced eventually the clutch may start slipping badly and soon after that it is money for all new plates
so its a thing to do whenever you getn a bike used and have no history about it
fix clutch look for airleaks
thottle needs to havwe a small amount of free play
badly routed cables can cause issues with ghost throttle on high angle steering inputs
clutches are very sturday lots of people throw awaynmoney on all new when a sim-le solution is possible
the money could be better spent on tires brakes riding gear,limo rentals,hookers red headed ones or justn loose women, kentucky bourban whiskey, cigarettes ,chrome 45 automatic pistols,1000 feet of detcord to cut down trees for firewood and to play with expolosive plasma cladding of dis-simillar metals and explosive forming of cafe racer parts like gas tanks and expansion chambers to keep sharp reflexes and prevent poor judement a few handy salt shakers full of booger sugar..
why waste money ?
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2,559 Posts

4StrokesSite AdminPosts: 1229Joined: May 02, 2016[h=3]Carb Jetting Tricks & Troubleshooting[/h]
Postby 4Strokes » Fri May 06, 2016 6:26 pm
Your engine is basically an air pump, and your carb meters how much air and fuel are sucked into that pump. Even though they may differ wildly in size, shape and design, all four-stroke carburetors have the same basic parts or circuits. Your slide cutaway (or throttle valve) needle and needle jet will all affect your bike's acceleration from one-quarter to three-quarters throttle, and this is the most important area for off-road riders, since we spend the most time at these throttle settings. Due to the hassle of making changes to these circuits, these are the most neglected areas of tuning. Too rich jetting (too much cutaway, needle positions too high, too large a needle jet) can make your bike lunge and hard to control. If it's too lean in this area, the bike will feel really flat and down on power, but will respond quickly to changes in throttle position. It may detonate (ping) under a load too. Pinging can also be caused by too little octane or winterized fuel (oxygenated, blended with additives), so keep in mind any fuel changes if your bike suddenly starts detonating in otherwise "normal" conditions.

Your main jet is probably the most talked-about circuit, and it's as critical to get it right on a four-stroke as with a two-stroke. The main kicks in at half throttle and takes over metering duties as you hit full throttle. If your main is too rich, the bike will sputter and surge as it tries to burn all of that fuel. Too lean, and the bike will run flat or have a flat spot in the powerband. A severely lean main will cause your bike to seize just like a two-stroke. It's better to be slightly rich on the main than slightly lean, because it will run cooler.

Yamaha's new 400s have an accelerator-pump circuit. This system squirts a stream of raw fuel into the carb venturi every time you wick the throttle. Think of it as the four-stroke's PowerJet carb - it richens the mixture to run best at lower engine speeds, yet allows a leaner top for more over-revs. If you radically modify your engine (flowed head, hot cam, etc.), you may have to richen this circuit slightly, but it's otherwise not something you mess with for mere weather or altitude changes.

Your pilot jet (or slow jet) controls the idle circuit, or from zero to one-quarter throttle opening. The pilot jet and airscrew control the amount of fuel and air going into the engine at slow engine speeds. It's very important to tune these circuits because they control throttle response and starting. The pilot circuit has a major affect on how well your four-stroke starts -or refuses to start - after a fall. At every event we attend, there is always some four-stroke rider who comes into the pits with his bike revving wildly. Invariably, this rider will say that his bike is hard to restart after a stall, so he turns up the idle adjuster so it won't die.

That's like jumping from the frying pan in to the fire. Thumpers are only hard to start when they are jetted poorly or when the wrong technique is used. The rider who turns up his idle is only perpetuating the myth about thumpers being hard to start. Most manuals (and this magazine) tell you that you should not touch the throttle when you kick a thumper. Well, turning the idle up is mechanically opening the throttle, right? You will make, your bike even harder to start. You have to fix the problem, not the symptoms of the problem!

Geaneral Carburetor Jetting Tricks
Your bike's owner's manual is a great source for recommended jetting and tuning tips. If you bought your thumper used and don't gave a manual, get one. Set the idle speed as per your manual. If it won't start easily using the manual's technique, your pilot jet is the likely culprit.

Whether your bike is air or water cooled, you should start it and get it up to race temperature before tuning the pilot circuit. A hotter engine will run leaner than an old one, so failure to properly warm the bike will result in a too-rich setting. With the bike up to temp, adjust the airscrew so that the bike runs and responds best to slight throttle movements. Now, kill the motor and see how many turns out you have on the airscrew. Less than one, and your pilot is too lean. More than two, and it's too rich. Install the next-size pilot and repeat the test.

Most off-road bikes are jetted lean to meet emissions standards, so you will likely want to richen these circuits, especially if you have gone to an after-market pipe, air filter or even removed OEM baffles (pipe and/or airbox). If you remove the muffler diffuser, you should toss the airbox stuffer too, or the airbox won't be able to draw enough air to feed the engine. Most aftermarket companies will give you recommended jetting, so use this as a baseline.

Under most conditions, about the only time you will need to go leaner on an EPA-legal four-stroke is because of altitude. Air is thinner at higher altitudes, so it contains less oxygen, and your jetting will be too rich. You will want to go down a size on the pilot, one or two on the main and lower the needle a position (raise the clip).

Cold air is denser than warm air, so it holds more oxygen. On cold mornings, your jetting will be slightly rich, but thumpers are less susceptible to changes than two-strokes. Where you might change the pilot on a two-stroke when it's really cold, an airscrew adjustment will suffice on a thumper.

The same is true for barometric pressure. As the barometer rises, the pressure compresses the air, and your jetting will be slightly lean. A falling barometer causes a rich condition, but thumpers don't care about the weather as much as two-strokes.

Four-Stroke Carburetion Troubleshooting
Overall, the Yamaha YZ400F is jetted almost perfectly from the factory; however, it is very picky about its air filter. Do not over-oil the filter, and do not expect it to start immediately after oiling the filter. Let it sit overnight (not in the cold) to allow the carriers to evaporate. Better yet, keep spare filters in a plastic bag so that you never put a freshly oiled filter in the bike on race day. Modifications throw stock jetting out the window, so this troubleshooting guide will apply to the 400F as much as any other four-stroke.

Bike Won't Start After a Crash
- Pilot too lean
- Idle set too high
- Improper starting procedure
- Bike wants hot-start button (KTMs and 400Fs)

Bike Runs-On or Won't Idle Down When Throttle is Chopped
- Idle set too high
- Air leak in intake or engine
- Pilot too rich (when bike is hot)

Bike Wont Start When Cold Temp Outside
- Pilot jet too lean
- Air filter over-oiled
- Motor oil too thick for temperature

Bike Sputters / Wont Clean Out at High RPM
- Main jet too rich
- Air filter over-oiled
- Spark plug has debris on electrode

Bike Coughs & Stalls in Slow Turns
- Pilot jet too lean
- Idle set too low
- Valves set too tight
- Decompressor is set too tight, so turning the bars engages release slightly

Bike Hesitates or Bogs Over Deep Whoops or G-Outs
- Float level too low
- Carb vent tubes blocked
- Main jet splash shield not installed
- Float level too high, gas is trapped in vent tunes (install T-vents)

Bike Starts But Wont Take Throttle Without Sputtering
- Pilot jet too rich
- Water in fuel
- Debris in main jet

Bike Suddenly Starts Sputtering / Gas Flows from Vent Tubes
- Stuck float check valve
- Debris in gas or carb

Bike Runs Hot / Feels Slow & Flat on Straights
- Main jet too lean
- Fuel octane too low, causing detonation

Bike Coughs & Stalls When Throttle is Whacked Open
- Needle too lean
- Slide cutaway too lean
- Pumper circuit blocked or too lean

Article reprinted from Dirt Bike Magazine, May 1998. Submitted to by XR4DEZ (Chris of Imperial, CA).


2,559 Posts
Clutch check your cable for damage poor routing. As far as cable action I generally would disconnect both ends and make sure the cable moves freely by hand. Lube if stiff but clean replace if rusty and or frayed.

1,512 Posts
almost none of that applies to his bike
some of the worst advice i havev ever seen anybody give a novice who should not be on a pitifully molested ''cafe racer'' death trap in the first place
he should be grinning not cringing
ffs he thinks he has gotten a sweet ride
mattjiz run away from that piece of shit !! pay somebody to remove it from your life
get a reliable stock motrorcycle and have the fun of your life,buddy
right now you are doing it exactly wrong
actually you should take the bike back to the theifb who stole money from you !!and shove it up the mother fuckers ass (well at leat the throttle side bars)who told you it was a killer cafe racer after you seduce his mom and pee in her bunghole on his front lawn at noon easter day

your bike has much more sophisticated instruments mixing the air and fuel
has altitude/air density diaphram cv carbs that jet themselves within a reasonable range as long as the engine intake and exhaust are in the extremely well designed stock condition
carburetor tuning is one of the most time consuming things top learn and it takes a real genius tuner to get good at it
suggesting he needs to change the tune of his first mc's carburetors will end up makling him hate motorcycles
it takes careful regimented exacting testing to tune carbs not too mention a few hunddred dollars in sparkplugs brass and worst of all trying to feel up yer girfriend stinking of mid grade gasoline
well that dog wont hunt
he needs to be riding and learning basic mainrtainance enjoying the motorcycle
few even gpood mc wrenches can tune carbs its the worst most expensive and time devouring thing in the whole scheme of wrenching except for the erv kanemotos and don vescos i suppose
all anybody could do is just make the carbs be stock like new, same with the exhaust and airbox but its way too late for that it is a parts bike not even safe to ride
srsly whoever sold it too you should be beaten to a bloody pulp ,after the mom thing
buy a stock reliable 5 or 6 yearn old well tajken care of fine running motorcycle with a reputation for being near best in its class
go ride and have fun you may not even like it at all
but do not dont try to tune the carbs,you made a mistake its ok i have done far worse
do not fall in love with this fraud bike.period you my friend have been robbed

2,559 Posts
Guy already likes the bike sounds like simple issues keeping it from running well enough. Bad cable or poor routing could be the whole of the clutch issue.

Tell your wife what to do she might listen.
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