wont stay running

mobleydrew · 05-25-2015, 05:46 PM

Carb rebuilt, Pilot screw 2.5 turns out, new choke starter (choke) plunger and spring. Starts fine, idles too high, blip throttle idles higher but soon lowers to almost stalling. Turn idle screw up revs up, blip throttle, idles down again and stalls. I keep adjusting idle, keeps stalling after it revs real high.
I have also confirmed that the vacuum actuated petcock is functioning properly, yet, there was a puddle of gasoline in the airbox
Could float need adjusting since it is allowing carb to overfill? maybe a new needle valve?

mobleydrew · 05-25-2015, 08:29 PM

Writing things down sure does help a person self-diagnose. According to the manual, and my particular carb, there is no set "turns-out" for the pilot screw. It just says PRE-SET. P.O. had fooled with it previous to me (cap was already gone), and I can guarantee it was more than 2.5 turns out when I removed it for cleaning. I am thinking now that even 2.5 turns out is still too much. (I was looking at wrong carb spec chart). It is a 13F3 carb.
Whatcha think? Should I try 1.5 turns? 1.75, 2? Even the 13F2 carb is 1.375 turns out.
That may fix the odd idle. Will it fix the overflow of gas into the airbox some how, since the engine will suck in fuel at a slower rate now, at idle?
Thanks for reading.
-Drew

spldart · 05-25-2015, 09:24 PM

I could be totally wrong here but your idle circuit being off isn't capable of throwing an overflow of gas in the airbox.
Your description of the engine running screams big time air leak or as you have already surmised an overflowing bowl... or both.

Well... gas in the airbox... I'd check not only the condition of the needle and seat but the float level.

The fuel needle and seat are probably not worn out. It takes a long time to do that. so...
Clean any debris and make sure float is set properly. Are you super high miles?

My pilot screw was about 3 turns out plus or minus. Pilot fuel circuit didn't seem to overly sensitive to me. This is one of the most f/a ratio stable carbs I've dinked with so with these problems look for an air leak, flooding or other more severe issues.

spldart · 05-25-2015, 09:30 PM

New choke plunger and spring.
Is it fully engaging/disengaging?

mobleydrew · 05-27-2015, 11:29 AM

I have it idling better, at 1.5 turns out, but think 1.5 is starving for air. It eventually stalls. Choke is functioning properly and adjusted float slightly. The gas in the air box, it seems, had been in there for sometime....before I bought it a few weeks ago. Gas was already turning brown, as it does over time....or just discolored as a result of the black plastic air box.
Recommendations on turns out for air screw, since manual just says PRE-SET?
Just trial and error?

blaine · 05-27-2015, 10:28 PM

Start at 2 1/2 turns out.Than with bike idling warm adjust slowly for best smoothest idle.

Water Warrior 2 · 05-28-2015, 01:34 AM

The puddle in the air box is likely from gases and blowby from the crank case breather. This is a common no cost option on GZs and most other engines.

Just kidding about the option part.

You can drain the excess from the air box using the hose that hangs down from the box to below the bottom of the frame. It will have a plug in the end of the hose. Pull out the plug, drain and replace the plug.

mobleydrew · 05-31-2015, 07:04 PM

1.5 turns out, can tell starving for air and stalls, 1.75 turns out, still starving for air but better, still stalling. 2.0 out, revs high then drops down slowly and stalls. 2.5 out, revs higher then drops down slowly and stalls. At the higher turns out, after stalling, difficulty restarting until engine cools. (running so lean that it overheats?)
Only way to maintain idle is at 3,000 RPMs (I have an RPM setting on my meter). I have sprayed engine starting fluid around carb to guarantee no air leaks. Choke plunger not binding.
Do I need to try to be so exact with turns out? Maybe 1.875 turns out?
It is the 13F3 carb, and air screw is not missing the spring, rubber o-ring or washer.
Ideas?

mobleydrew · 06-02-2015, 11:54 AM

Since there is such a big difference in how the bike runs, from 1.75 to 2 turns out, perhaps the small rubber o-ring on the air screw is worn, allowing air to flow through the air screw adjusting orifice. Perhaps a new o-ring and closing off the orifice will correct this. Once I confirm this with a piece of tape, perhaps a dab of gasket sealer will seal it nicely, since the original plug for the hole is long gone.

mobleydrew · 06-09-2015, 02:38 PM

SPLDART- Since 3 turns out worked for you, I think I will try going the other direction, since 2.5 turns and less are not doing it. At low idle, 2.5 turns out will only stay running with high idle speed, thus getting air through the main plunger. Dies if I leave alone at low idle, as thought not enough air getting through.
You have the 13F3 carb?

05-25-2015, 05:46 PM	#1
mobleydrew Member Join Date: May 2015 Location: Lake Forest, Illinois Posts: 36	wont stay running Carb rebuilt, Pilot screw 2.5 turns out, new choke starter (choke) plunger and spring. Starts fine, idles too high, blip throttle idles higher but soon lowers to almost stalling. Turn idle screw up revs up, blip throttle, idles down again and stalls. I keep adjusting idle, keeps stalling after it revs real high. I have also confirmed that the vacuum actuated petcock is functioning properly, yet, there was a puddle of gasoline in the airbox Could float need adjusting since it is allowing carb to overfill? maybe a new needle valve? __________________ Drew in Lake Forest, Illinannoying Multiple motorcycle owner/restorer Yamaha '86SRX600, '87SRX250, Honda '85VF1000R, Ducati '67 250. Login or Register to Remove Ads Last edited by mobleydrew; 05-25-2015 at 06:26 PM.
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05-25-2015, 08:29 PM	#2
mobleydrew Member Join Date: May 2015 Location: Lake Forest, Illinois Posts: 36	Writing things down sure does help a person self-diagnose. According to the manual, and my particular carb, there is no set "turns-out" for the pilot screw. It just says PRE-SET. P.O. had fooled with it previous to me (cap was already gone), and I can guarantee it was more than 2.5 turns out when I removed it for cleaning. I am thinking now that even 2.5 turns out is still too much. (I was looking at wrong carb spec chart). It is a 13F3 carb. Whatcha think? Should I try 1.5 turns? 1.75, 2? Even the 13F2 carb is 1.375 turns out. That may fix the odd idle. Will it fix the overflow of gas into the airbox some how, since the engine will suck in fuel at a slower rate now, at idle? Thanks for reading. -Drew __________________ Drew in Lake Forest, Illinannoying Multiple motorcycle owner/restorer Yamaha '86SRX600, '87SRX250, Honda '85VF1000R, Ducati '67 250. Last edited by mobleydrew; 05-25-2015 at 08:31 PM.
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05-25-2015, 09:24 PM	#3
spldart Senior Member Join Date: May 2015 Location: Stafford, Texas Posts: 604	I could be totally wrong here but your idle circuit being off isn't capable of throwing an overflow of gas in the airbox. Your description of the engine running screams big time air leak or as you have already surmised an overflowing bowl... or both. Well... gas in the airbox... I'd check not only the condition of the needle and seat but the float level. The fuel needle and seat are probably not worn out. It takes a long time to do that. so... Clean any debris and make sure float is set properly. Are you super high miles? My pilot screw was about 3 turns out plus or minus. Pilot fuel circuit didn't seem to overly sensitive to me. This is one of the most f/a ratio stable carbs I've dinked with so with these problems look for an air leak, flooding or other more severe issues. Login or Register to Remove Ads Last edited by spldart; 05-25-2015 at 09:26 PM. Reason: I'm not a mechanic. But I did stay at a Holiday Inn Express last night.
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05-27-2015, 11:29 AM	#5
mobleydrew Member Join Date: May 2015 Location: Lake Forest, Illinois Posts: 36	I have it idling better, at 1.5 turns out, but think 1.5 is starving for air. It eventually stalls. Choke is functioning properly and adjusted float slightly. The gas in the air box, it seems, had been in there for sometime....before I bought it a few weeks ago. Gas was already turning brown, as it does over time....or just discolored as a result of the black plastic air box. Recommendations on turns out for air screw, since manual just says PRE-SET? Just trial and error? __________________ Drew in Lake Forest, Illinannoying Multiple motorcycle owner/restorer Yamaha '86SRX600, '87SRX250, Honda '85VF1000R, Ducati '67 250. Login or Register to Remove Ads
	0

05-27-2015, 10:28 PM	#6
blaine Senior Member Join Date: Feb 2010 Location: P.E.I. Canada Posts: 3,784	Start at 2 1/2 turns out.Than with bike idling warm adjust slowly for best smoothest idle. __________________ If at first you do succeed, try not to look surprised.
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05-25-2015, 09:30 PM	#4
spldart Senior Member Join Date: May 2015 Location: Stafford, Texas Posts: 604	New choke plunger and spring. Is it fully engaging/disengaging?
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05-28-2015, 01:34 AM	#7
Water Warrior 2 Senior Member Join Date: Dec 2006 Location: Squamish B.C Canada Posts: 11,409	The puddle in the air box is likely from gases and blowby from the crank case breather. This is a common no cost option on GZs and most other engines. Just kidding about the option part. You can drain the excess from the air box using the hose that hangs down from the box to below the bottom of the frame. It will have a plug in the end of the hose. Pull out the plug, drain and replace the plug.
	0

05-31-2015, 07:04 PM	#8
mobleydrew Member Join Date: May 2015 Location: Lake Forest, Illinois Posts: 36	1.5 turns out, can tell starving for air and stalls, 1.75 turns out, still starving for air but better, still stalling. 2.0 out, revs high then drops down slowly and stalls. 2.5 out, revs higher then drops down slowly and stalls. At the higher turns out, after stalling, difficulty restarting until engine cools. (running so lean that it overheats?) Only way to maintain idle is at 3,000 RPMs (I have an RPM setting on my meter). I have sprayed engine starting fluid around carb to guarantee no air leaks. Choke plunger not binding. Do I need to try to be so exact with turns out? Maybe 1.875 turns out? It is the 13F3 carb, and air screw is not missing the spring, rubber o-ring or washer. Ideas? __________________ Drew in Lake Forest, Illinannoying Multiple motorcycle owner/restorer Yamaha '86SRX600, '87SRX250, Honda '85VF1000R, Ducati '67 250. Last edited by mobleydrew; 05-31-2015 at 07:29 PM.
	0

06-02-2015, 11:54 AM	#9
mobleydrew Member Join Date: May 2015 Location: Lake Forest, Illinois Posts: 36	Since there is such a big difference in how the bike runs, from 1.75 to 2 turns out, perhaps the small rubber o-ring on the air screw is worn, allowing air to flow through the air screw adjusting orifice. Perhaps a new o-ring and closing off the orifice will correct this. Once I confirm this with a piece of tape, perhaps a dab of gasket sealer will seal it nicely, since the original plug for the hole is long gone. __________________ Drew in Lake Forest, Illinannoying Multiple motorcycle owner/restorer Yamaha '86SRX600, '87SRX250, Honda '85VF1000R, Ducati '67 250.
	0

06-09-2015, 02:38 PM	#10
mobleydrew Member Join Date: May 2015 Location: Lake Forest, Illinois Posts: 36	SPLDART- Since 3 turns out worked for you, I think I will try going the other direction, since 2.5 turns and less are not doing it. At low idle, 2.5 turns out will only stay running with high idle speed, thus getting air through the main plunger. Dies if I leave alone at low idle, as thought not enough air getting through. You have the 13F3 carb? __________________ Drew in Lake Forest, Illinannoying Multiple motorcycle owner/restorer Yamaha '86SRX600, '87SRX250, Honda '85VF1000R, Ducati '67 250.
	0