At my wit's end....need carb help - Wrist Twisters
 
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post #1 of 21 Old 10-06-2012, 10:22 AM Thread Starter
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Unhappy At my wit's end....need carb help

Okay, I need help with our SV650S. A few years ago it had sat long enough that the gas went bad and gummed up the carbs (among other things ) I got it back up and running at that time, but it just wasn't quite right. Over time, I've taken everything apart, soaked the carbs in cleaner, installed rebuild kits, re-jetted, and followed recommendations I found through lots of internet searching for the needle and fuel screw settings. The bike runs great at anything above idle....and there's the problem. It idles like shit.

Okay, I'm exaggerating a little, but the idle is enough of a problem that it detracts from the enjoyment of riding. At a stop, you have to occasionally give it gas or it will sometimes die.

Here's a description of its behavior. When you first let off the throttle when coming to a stop, it idles fine. After a short time, it will start to occasionally cough and stumble, the revs will surge a little, it'll idle okay for a second, then cough again, etc, while the overall idle speed drops.

I've checked the passageways, and shot both carb cleaner and compressed air through all that I could find, so I think (hope!) that's not the problem. I've also done my best to sync the carbs, to no avail. I'm about to give up and just take it someplace

If anyone has advice, please let me know. If you need any more information, or a video, just say so. I'm hoping this sounds familiar to someone, and you can tell me what I'm overlooking.

Thanks for any help, guys.

'96 DR650, '01 SV650, '10 Aprilia Tuono 1000R
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post #2 of 21 Old 10-06-2012, 01:37 PM
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Look into reseating your throttle bodies and/or air intake between the air filter housing and the throttle bodies. Spray carb cleaner around air intake hose joints, vacuum lines, etc. If the idle picks up, you have a leak somewhere.

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post #3 of 21 Old 10-06-2012, 02:17 PM
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I would pull the carbs, clean the pilot/idle jets and then sync them after re-install. Also check your air box for leaks/cracks around the boots. None of this is SV specific, just general carb stuff.

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post #4 of 21 Old 10-06-2012, 04:56 PM Thread Starter
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Thanks for the suggestions; will give them a shot. This must be carb-related, right? Since it runs well otherwise, it can't be valve/timing issues, can it?

'96 DR650, '01 SV650, '10 Aprilia Tuono 1000R
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post #5 of 21 Old 10-06-2012, 05:09 PM
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Quote:
Originally Posted by Superdog View Post
Thanks for the suggestions; will give them a shot. This must be carb-related, right? Since it runs well otherwise, it can't be valve/timing issues, can it?
Correct. You most likely have an air leak somewhere. Either that or your float bowls/fuel diaphragm is sticking. If its the diaphragm, you can use some automatic transmission fluid to lube it up.

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post #6 of 21 Old 10-06-2012, 06:22 PM
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Had a similar problem on my KLR. Don't know if a single cylinder counts, but it had a petcok and fuel filter issue. Replaced both, so I'm not sure which was the problem.

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post #7 of 21 Old 10-07-2012, 06:28 AM Thread Starter
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Hmm...it has screens in the carbs. Will check those today when I take the carbs out......again.

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post #8 of 21 Old 10-07-2012, 08:44 AM
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Quote:
Originally Posted by Superdog View Post
Hmm...it has screens in the carbs. Will check those today when I take the carbs out......again.
It sounds to be low speed fuel circuit delivery rate and/or fuel feed to the float bowl.
Check EVERYTHING that relates to that.
Both cylinders affected same ?
If so, a common problem affecting both carbs.
But both carbs could have the same problem so it could carbs and not pre carb.
Air screw should not be problem, as long as the end shape that controls is still real good.
Low speed (aka pilot aka idle) jet could be involved, in particular the weenie air emulsion holes.
How good is the float needle and seat ?

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post #9 of 21 Old 10-07-2012, 12:05 PM Thread Starter
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Quote:
Originally Posted by mcromo44 View Post
It sounds to be low speed fuel circuit delivery rate and/or fuel feed to the float bowl.
Check EVERYTHING that relates to that.
Both cylinders affected same ?
If so, a common problem affecting both carbs.
But both carbs could have the same problem so it could carbs and not pre carb.
Air screw should not be problem, as long as the end shape that controls is still real good.
Low speed (aka pilot aka idle) jet could be involved, in particular the weenie air emulsion holes.
How good is the float needle and seat ?
Hard for me to tell if it's both carbs...I'm thinking one has the problem. Replaced the needle/seat (was part of the rebuild kit). Jets have been replaced, so they're clean. Checked the emulsion tubes this morning, and they look/behave good (shot carb cleaner through in reverse).

The front cylinder seems to have more carbon build-up on the valves than the rear, so this morning I took a carb that I originally bought to scavenge the parts from, put all of the new stuff on it, and stuck it in the bike (I had previously soaked it in cleaner, and cleaned the passageways). I think it's a little better, but still can't hold a consistent idle like I want.

FWIW, I tried the WD-40 test and couldn't find any leaks. One thing I didn't do, and now I'm thinking might be the issue, is re-check the float height (doh!). I remember having a tough time getting them set right to begin with, and I wonder if one is off just enough to allow the same amount of vacuum to pull too much fuel during idle? Have I been stupid to overlook that as a possibility?

Thanks for the troubleshooting help!

Stu

'96 DR650, '01 SV650, '10 Aprilia Tuono 1000R
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post #10 of 21 Old 10-07-2012, 02:20 PM
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Quote:
Originally Posted by Superdog View Post
Hard for me to tell if it's both carbs...I'm thinking one has the problem. Replaced the needle/seat (was part of the rebuild kit). Jets have been replaced, so they're clean. Checked the emulsion tubes this morning, and they look/behave good (shot carb cleaner through in reverse).

The front cylinder seems to have more carbon build-up on the valves than the rear, so this morning I took a carb that I originally bought to scavenge the parts from, put all of the new stuff on it, and stuck it in the bike (I had previously soaked it in cleaner, and cleaned the passageways). I think it's a little better, but still can't hold a consistent idle like I want.

FWIW, I tried the WD-40 test and couldn't find any leaks. One thing I didn't do, and now I'm thinking might be the issue, is re-check the float height (doh!). I remember having a tough time getting them set right to begin with, and I wonder if one is off just enough to allow the same amount of vacuum to pull too much fuel during idle? Have I been stupid to overlook that as a possibility?

Thanks for the troubleshooting help!

Stu
Float level can be causal.
An old trick to tailor the low speed circuit is to raise level to slightly enrich, as the increased liquid level adds a wee bit more pressure from liquid column height as is helping get flow in the low speed circuit - it's NOT all from vacuum, despite most thinking so.
This is also a half haired thick tactic for correcting ancient carbs built for older higher specific gravity fuels, that need correcting for modern day lower SG gasolines.

A bent float arm tab or both floats not being aligned could be part of it.
Keep in mind that a lean idle misfire can fool one into thinking that richness is the problem.

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post #11 of 21 Old 10-08-2012, 08:59 AM Thread Starter
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Re-set float heights, and the idle seems to have improved, but still not consistent. The occasional 'cough' is gone now and it seems less likely to die when idling. What's left sounds like a vacuum issue...but I haven't been able to find a leak. Will try again with the WD-40 today. Going to replace the plugs again too, just in case.

'96 DR650, '01 SV650, '10 Aprilia Tuono 1000R
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post #12 of 21 Old 10-08-2012, 09:05 AM
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Quote:
Originally Posted by Superdog View Post
Re-set float heights, and the idle seems to have improved, but still not consistent. The occasional 'cough' is gone now and it seems less likely to die when idling. What's left sounds like a vacuum issue...but I haven't been able to find a leak. Will try again with the WD-40 today. Going to replace the plugs again too, just in case.
Also make sure that the float bowl vent hoses are not pinched.
There's no dyndjet kit in is there ?
The one that takes a vacuum tap off the airbox?
Something like that.

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post #13 of 21 Old 10-08-2012, 09:21 AM Thread Starter
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No kit installed; I bought the specific jets I wanted to install. This thing does have a vacuum operated fuel pump of sorts, though. Hmmm....

'96 DR650, '01 SV650, '10 Aprilia Tuono 1000R
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post #14 of 21 Old 10-08-2012, 09:30 AM Thread Starter
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Umm....pulled the vacuum line from the 'pump' and it was full of fuel.

Crap! How did I miss that?!

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post #15 of 21 Old 10-08-2012, 09:56 AM Thread Starter
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I think this is the culprit. Now to see if they sell just the diaphragm, or if I need to buy a whole new unit.



I really think this is it. Rear cylinder was getting a little extra fuel from the pump. The wet spots are where it was weeping through to the vacuum side.

'96 DR650, '01 SV650, '10 Aprilia Tuono 1000R
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post #16 of 21 Old 10-08-2012, 11:49 AM
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I think this is the culprit. Now to see if they sell just the diaphragm, or if I need to buy a whole new unit.



I really think this is it. Rear cylinder was getting a little extra fuel from the pump. The wet spots are where it was weeping through to the vacuum side.
Very likely.
And if one is duff from aging and not mishandling, then the other one is likely on its way also.

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post #17 of 21 Old 10-08-2012, 12:28 PM Thread Starter
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Confirmed. Put a temporary fix in place until I can source the right material, started it up, and it's so much better. Held an idle speed very well now.

It's a single pump that feeds both carbs; was just driven off of the rear intake.

Evidently the vacuum petcock is failing now too. The rear cylinder was full of fuel when I went to start it. Should be okay for now with the fix in place; I'm 95% sure that it went through the fuel pump and into the intake, not through the carbs.

'96 DR650, '01 SV650, '10 Aprilia Tuono 1000R
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post #18 of 21 Old 10-08-2012, 07:02 PM
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Isn't ethanol laced gas great?

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post #19 of 21 Old 10-08-2012, 07:41 PM Thread Starter
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Yeah, I'm loving it right now

Since the cylinder was full of gas earlier, I've already drained the oil. Fortunately, I didn't detect any gas smell in the oil. Guess the rings must still be pretty good

What's the proper procedure to get gas out of a cylinder? Probably not what I did; I pulled the plug and spun the starter. Gas everywhere! Whee!

'96 DR650, '01 SV650, '10 Aprilia Tuono 1000R
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post #20 of 21 Old 10-09-2012, 01:18 PM
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Quote:
Originally Posted by Superdog
Yeah, I'm loving it right now

Since the cylinder was full of gas earlier, I've already drained the oil. Fortunately, I didn't detect any gas smell in the oil. Guess the rings must still be pretty good

What's the proper procedure to get gas out of a cylinder? Probably not what I did; I pulled the plug and spun the starter. Gas everywhere! Whee!
Same procedure on a dirt bike dumped in a river and sucked water in the intake. Only you HAVE to change the oil after, lol...

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post #21 of 21 Old 10-09-2012, 07:52 PM Thread Starter
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Vid...for the heck of it!

Since I said I would post one, here 'tis. I just realized I suck at video :P I realized after doing this with my camera that it would have probably been easier with my phone...and probably wouldn't have had to convert the format to make it manageable. Oh well. Ignore the 'trial version' text


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