6k sputtering but not the carbs?

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mvk24
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6k sputtering but not the carbs?

Post by mvk24 » Wed Jun 21, 2017 7:48 am

Hey guys update from my last post
I got a brand new petcock as suggested by Radare, also got a new set of carbs from someone in PA. rebuilt and installed them. set floats heights to 10mm off the surface, put the 20 pilots in them.
I synced (using the bb trick) and was able to tune each carb to anywhere from 490-515 degrees at idle with a fan blowing on the motor.

Before I did all of this we had an issue with sputtering and lose of power as soon as I hit 6k rpms, however you don't feel or lose any rpms when in neutral its only when moving... I thought this was a carb issue but now with an entirely new set of carbs it must be something else. I noticed the crankcase breather looks cracked but that is not a vacuum line correct?

all of the boots are new with no cracks

the fuel is no longer gurgling in my vac line with the new petcock but I do notice air bubbles in the fuel line (I use clear hoses).

does anyone have any idea where to start? i'm starting to think its something in my engine which I don't have the time or space to open right now so it may be time to take it to a shop if we cant figure it out on here. I think the only last ditch stupid things to do would be new spark plugs, new vac line just in case.

Problems - Sputtering and lose of power at 6k but only when moving. Not in neutral or when clutch revving.
Air bubbles in fuel line
Also it looks like there should be clasps on the air box boots that go on top of the carbs that I don't have.. are there normally and I should track them down on ebay?
the idle is very rough all of a sudden and drops on it own or hangs at 2k after I hold it steady for a moment but its tuned to near perfection so I'm not sure where its coming from.
Bike only has 9k miles on it and sat for 14 years before I picked it up 5 years ago. was running great until 2 weeks ago when all this started

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Vulcano39
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Re: 6k sputtering but not the carbs?

Post by Vulcano39 » Wed Jun 21, 2017 9:07 am

have you checked if there is any crack in the fuel lines and the fuel pump seal, check the fuel filter for cracks. Bubbles in the fuel system is not normal...
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Re: 6k sputtering but not the carbs?

Post by mvk24 » Thu Jun 22, 2017 8:00 am

Vulcano39 wrote:
Wed Jun 21, 2017 9:07 am
have you checked if there is any crack in the fuel lines and the fuel pump seal, check the fuel filter for cracks. Bubbles in the fuel system is not normal...
I didn't check the fuel line thoroughly but that's a good idea I will do that today, just ordered new spark plugs to cross that off the list as well.

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Re: 6k sputtering but not the carbs?

Post by sixtyeight » Fri Jun 23, 2017 5:25 pm

It's tough to troubleshoot from so far away, but if you can rev to redline in neutral,
but not under load, then I would suspect something in the airbox area. Did you get
the carb clamps so it's not pulling air from that space, but only through the airbox?
Then take a look inside, and inspect the air filter itself. Sometimes they get soaked
with gas and/or oil, then dry so they look okay, but won't let enough air pass by to rev freely.

Since the idle went erratic, I would also check each vacuum line, and suspect the fuel petcock, or the fuel pump, leaking vacuum.
Or eliminate fuel delivery problems completely by using a small test tank hooked directly to carbs, eliminate all the vacuum stuff.

If none of that, return to fundamentals: compression test and leakdown.
Spark test by test drive with timing light attached; watch for cut out of spark under load.

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Re: 6k sputtering but not the carbs?

Post by mvk24 » Sat Jun 24, 2017 1:24 am

sixtyeight wrote:
Fri Jun 23, 2017 5:25 pm
It's tough to troubleshoot from so far away, but if you can rev to redline in neutral,
but not under load, then I would suspect something in the airbox area. Did you get
the carb clamps so it's not pulling air from that space, but only through the airbox?
Then take a look inside, and inspect the air filter itself. Sometimes they get soaked
with gas and/or oil, then dry so they look okay, but won't let enough air pass by to rev freely.

Since the idle went erratic, I would also check each vacuum line, and suspect the fuel petcock, or the fuel pump, leaking vacuum.
Or eliminate fuel delivery problems completely by using a small test tank hooked directly to carbs, eliminate all the vacuum stuff.

If none of that, return to fundamentals: compression test and leakdown.
Spark test by test drive with timing light attached; watch for cut out of spark under load.
Sounds like a good list of things to start with, ordered Tygon lines and spark plugs. Will look up how to check the sparks

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Re: 6k sputtering but not the carbs?

Post by radare » Sun Jun 25, 2017 9:52 am

Two things can happen that may affect a bike at a certain speed:

1. Carbs: The mixture can be wrong, either rich or lean, at a transition point (like, say, transition between slides or going to WOT). Are you absolutely certain its not a mixture problem? Just to check, add some tape masking tape to your throttle grip with marks at 1/8, 1/4, 1/2 and WOT so you can see where you are when the problem occurs. Then see if it occurs consistently at that same throttle position. It'll help us understand the problem. The carbs can be perfectly clean but mis-set, either in jetting, in diaphragm spring tension, sticking slides or even a pinhole in a diaphragm.

2. Ignition system: This is less likely, but, a coil which is failing may present itself in this manner. This is more unlikely as it wouldn't be expected at a same RPM consistently.

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Re: 6k sputtering but not the carbs?

Post by mvk24 » Sun Jun 25, 2017 10:17 pm

radare wrote:
Sun Jun 25, 2017 9:52 am
Two things can happen that may affect a bike at a certain speed:

1. Carbs: The mixture can be wrong, either rich or lean, at a transition point (like, say, transition between slides or going to WOT). Are you absolutely certain its not a mixture problem? Just to check, add some tape masking tape to your throttle grip with marks at 1/8, 1/4, 1/2 and WOT so you can see where you are when the problem occurs. Then see if it occurs consistently at that same throttle position. It'll help us understand the problem. The carbs can be perfectly clean but mis-set, either in jetting, in diaphragm spring tension, sticking slides or even a pinhole in a diaphragm.

2. Ignition system: This is less likely, but, a coil which is failing may present itself in this manner. This is more unlikely as it wouldn't be expected at a same RPM consistently.
Ok Will do all this week. The only reason I was thinking maybe ignition is because that 3rd cylinder was sooo rich with the previous set of carbs so maybe I killed that cylinder/spark plug?

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Re: 6k sputtering but not the carbs?

Post by mvk24 » Tue Jun 27, 2017 7:08 pm

radare wrote:
Sun Jun 25, 2017 9:52 am
Two things can happen that may affect a bike at a certain speed:

1. Carbs: The mixture can be wrong, either rich or lean, at a transition point (like, say, transition between slides or going to WOT). Are you absolutely certain its not a mixture problem? Just to check, add some tape masking tape to your throttle grip with marks at 1/8, 1/4, 1/2 and WOT so you can see where you are when the problem occurs. Then see if it occurs consistently at that same throttle position. It'll help us understand the problem. The carbs can be perfectly clean but mis-set, either in jetting, in diaphragm spring tension, sticking slides or even a pinhole in a diaphragm.

2. Ignition system: This is less likely, but, a coil which is failing may present itself in this manner. This is more unlikely as it wouldn't be expected at a same RPM consistently.
Okay so today I did the following

New Tygon Fuel lines and added inline fuel filter since the carbs are all nice and clean.
New Vac line (notived it was pretty brittle and shitty around the manifold port
Changed to Iridium Spark plugs

The idle and warm up are still sporatic. Hangs after a stretch down the road, at a stop it drops to almost nothing and will cut out if I do not rev it.

Also noticed that the lights/headlight dim and get much brighter if I rev it?

did the tape marks on my throttle and no throttle position seemed to matter in the sputtering

I ordered the clamps for my Airbox boots and should be here this week. It was still sputtering a bit at 6k and above. After pushing it a little it seems to do it less now but would hang idle at 3k unless I revved it and then it would drop to normal.... ALSO not sure if this makes sense but when I would shift it almost for a split second sounds like a blowoff valve in a car? not loud or obnoxious but a very fast noise during the shift that sounded like air escaping? any futher ideas gentleman?

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Re: 6k sputtering but not the carbs?

Post by mvk24 » Wed Jul 05, 2017 3:42 pm

Vulcano39 wrote:
Wed Jun 21, 2017 9:07 am
have you checked if there is any crack in the fuel lines and the fuel pump seal, check the fuel filter for cracks. Bubbles in the fuel system is not normal...
So as I stated above, checked/changed all the lines and such. Still idles like shit and sputtering. With a brand new line, fiter, and petcock there still a big bubble in the fuel line.. could the air be coming from the fuel pump?
20170705_170918.jpg
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mvk24
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Re: 6k sputtering but not the carbs?

Post by mvk24 » Wed Jul 05, 2017 3:43 pm

20170705_170951.jpg
I also got the air box clamps but they look exactly the same as the carbs boot clamps?
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