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Discussion Starter #1
Symptoms: Bike stalls on start first few times. Will warm up with choke on. After normal warm-up period, if choke is switched off and any gas given, bike stalls. After warming up longer than usual, will run but is really choppy off idle in neutral or in gear. Lots of afterfire during warmup and while riding at constant RPM. Runs ok on highway at higher rpms.

Any ideas?
 
N

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Is it running on both cylinders? At idle, are both header pipes equally hot?

A bum plug or loose plug wire (...or bad coil) or a vacuum leak would cause similar symptoms.

:)
 

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Discussion Starter #4
well, just pulled the plugs. front is light tan, rear is whitish-tan. plug boots look ok. can't seem to locate any loose vacuum hoses. going to pull the tank, carbs and hope i don't screw all of this up.
 
A

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A vacuum (air) leak usually results in the engine racing like a . . . well you know. You'd be looking for that kind of leak around the carb boots, usually, or maybe a leaky head gasket. I doesn't sound like a head gasket or a vacuum leak to me, although you could spray some carb cleaner around the carb boots and see if it makes the engine race at all, that would be an indicator of an intake leak. It does sound like it's not getting enough gas, though. Could be a strangled or partially detached fuel hose, a plugged jet (how old is the bike, has it sat for a while, have you been through the carbs)? Also, a simple test is to throw in a new set of plugs. How long since you've had new plugs in there? This often produces miracles!

Good luck.

Ari
 

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Discussion Starter #6
Thanks Ari

I'm putting the new plugs in now. Bike is three years old, usually sits all winter but I do put fuel stabil in it. I just sprayed some cleaner down the throat of the TBs. Going to hook it all back up, check the fuel line, and fire it up. See if anything changes.

Would I have to pull the carbs off the bike to clean them? What is usually involved in a cleaning?
 

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Discussion Starter #7
I forgot to mention, this appeared gradually and got worse over time. When I had the bike initially tuned for the pipe I put on, it was rock solid all of that season.
 

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Discussion Starter #8
Well, so far I have

Changed plugs
Checked that both cylinders were running
Checked and found no vacuum leaks
Sprayed carb cleaner into the carbs
Checked the fuel lines
Drained the float bowls

Still running exactly the same.
My only ideas are:

Carbs out of synch (unlikely)
Plugged jets
Tuning went off?
Bad timing

At this point, the idea of trading in on a fuel injected vehicle sounds wonderful to me.
 
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OK- back to the basics: fuel-compression-spark:

Fuel- gas: it sounds like you've have "probably" eliminated the carbs as your suspect, since it appears to be affecting both cylinders.

Fuel- air: have you tried running it with the tank up and the air cleaner off? Could the air filter be dirty/ oil soaked, or could the soundproofing under the tank have come loose or mouse nest in the airbox?

Compression: if it sounds normal while cranking you can "probably" (quotes again!) rule this out. On this topic, you should make certain that the exhaust is not blocked in some way (mouse nest, overly helpful toddler...).

Spark- intensity: with a plug removed but still connected, ground it to the cylinder head and crank the engine (hold it by the spark plug cap so you don't get a 25KV zap!). The spark should be bright blue and fat. Repeat for other cylinder.

Spark- timing: for this you should reference the service manual. Possible problem areas are wiring (as always!), the pickup and the igniter box itself.

A head scratcher ya got there...

:)
 

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Eliminate timing. Timing is fixed by the crank trigger. Not adjustable. You could look to see if the crank trigger is still attached properly. Plugs and wires are strong possibles. It sure sounds like misfiring. Water in the tank would be my second guess. This usually occurs right away and doesn't get worse.
 
A

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" (mouse nest, overly helpful toddler...)." I love that, I still remember my younger son (now 8, but then three) dropping a screwdriver down the exhaust pipe of my old '89 FZR1000. Thankfully it was a D&D slip on, so I could get the thing out . . .

I still think this sounds like a gasflow or carb issue, with the bike only starting with full choke and dying with choke off. Start by synching the carbs. I doubt this is it, but you need to synch them anyway, so start there. If that doesn't do it, go to the carbs. Pull off your gas tank, disconnect the crankcase vent hoses and fuel hoses from the air filter. Check all the fuel and air and vent hoses. Then pull off the air filter (loosening the boots first, of course). As noted before check the condition of the filter itself (although it sounds more like fuel starvation than air starvation). Then loosen the carb boots, disconnect choke cable and throttle cables, and pull your carbs off (having drained the bowls). CAREFULLY (i.e. without stripping the screws) take the bowls off and look at the condition. Clean them with carb cleaner. Pull the pilot jets and main jets. Inspect them with a flash light. SPray carb cleaner. Are they blocked? Shoot some compressed air through them. Clean all the carb passages the same way. Examine the floats. Any cracks? Sound like any fuel got INTO the floats through a crack?

Now -- have you drilled out the air screw plugs? If you have, you may have an air screw adjustment issue. If you haven't, think about trying that modification. There's a tip 'n trick on this. You may have too much air coming in at idle. The air mixture screw may have backed out on one carb. I don't know, but this still sounds mostly like a fuel issue to me.

Ari
 

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Discussion Starter #12
Well, I checked everything but didn't remove the carbs yet. I plan on doing that anyway at some point and drilling out the air screw.
So far I've put one bottle of gumout carb cleaner fuel additive in it ("treats 20 gallons") and one bottle of water remover/fuel injector cleaner ("treats 20 gallons"), then ran it 70 miles. It's improving steadily, so I guess it was probably clogging in the jets after all. I'm surprised the bike ran so well with all of that stuff in the tank since I just dumped it in all at once.

Thanks for all the help and suggestions, I learned quite a lot about the workings of our bikes. I'll update when I pull the carbs and get a good look inside. Right now she starts on a dime, warms up normally, no hestitation or lugging, but still afterfires occasionally at idle and commonly during decel.
 
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andyauger said:
  It sure sounds like misfiring.  Water in the tank would be my second guess.  This usually occurs right away and doesn't get worse.
+1
 

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Good helpful advice above.

Check entire fuel system from tank to carbs again - unscrew fittings on tank and check lines - filters thoroughly - as posted above it sounds as tho it isn't' getting enough fuel - clogged filter? then examine carbs carefully? Synch carbs after all jetting is done, this is not why bike is currently running bad, but will smooth out engine after all is done.
 
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