Author Topic: Working through the symptoms  (Read 470 times)

hobo

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Working through the symptoms
« on: June 11, 2017, 11:05:48 PM »
Symba started stalling at high speed (+30mph), and could usually be restarted, until one day a month ago and I had to push it home; hasn't started since.
+verified fuel is entering the bowl
+took carb apart, soaked all parts in carb cleaner, used air compressor to blow passages clean, reassembled
+set float to 10.2mm
+replaced spark plug, verified spark is present by grounding against engine
+compression test: 120psi...low?
+changed oil; old oil smelled like gas

It looks like 120psi is a bit low; to obtain the reading I cranked it with the throttle open and it maxed out at that reading. I was able to get it started briefly, and carefully nudge the throttle up, but it wouldn't stay running on it's own, and eventually would die at high throttle too.
« Last Edit: June 12, 2017, 01:02:31 AM by hobo »

redridinghood

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Re: Working through the symptoms
« Reply #1 on: June 12, 2017, 05:34:20 PM »
Somewhere on this forum is a nice diagram showing this method to take a peek inside the float bowl of the carburetor, but... Here's a short video because I can't find it. https://m.youtube.com/watch?v=PHuB1lyagKM

I know you checked the float height and confirmed that fuel is flowing into the float bowl...but how much fuel? Is there anything impeding the flow of gasoline to the point of fuel starvation, which might be causing the symptoms? 

This is an easy test; just need fish aquarium supplies 🐠(or a trip to a hardware store) for the tubing

Better add this...

The bike in the video is from the olden days before vacuum operated petcocks...if you have a bike with a vacuum operated petcock, you'll need to apply vacuum to it (turn the engine over) to replenish the float bowl with gas as it fills the tube, to achieve accurate results.

Be the first on your block to mount a GoPro cam to monitor the fuel level inside the plastic tube as you ride down the road.

Can't they just make float bowls out of clear plastic? 🙈
« Last Edit: June 12, 2017, 06:28:00 PM by redridinghood »

hobo

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Re: Working through the symptoms
« Reply #2 on: June 13, 2017, 02:10:35 PM »
I forgot to mention, yes, I took clear tubing and hooked it up to the bowl drain and verified that the level in the clear tubing rose to roughly the seam between the bowl and carburetor body. For this reason, I haven't bothered to diagnose the vacuum peacock arrangement.

redridinghood

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Re: Working through the symptoms
« Reply #3 on: June 14, 2017, 05:47:03 PM »
We know your engine is cold...have you checked valve clearance?

hobo

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Re: Working through the symptoms
« Reply #4 on: June 17, 2017, 11:00:15 AM »
Not yet, that's a good idea to check next. I don't get hardly any time to work on it, so it's going slowly.  ::)

petemoss

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Re: Working through the symptoms
« Reply #5 on: June 21, 2017, 02:20:23 PM »
Hobo, after checking your valves for proper tolerances, I would replace the fuel filter. I'm almost guessing that the fuel flow isn't quite enough when you open up the throttle. Also, the fuel petcock works off of the crankcase vacuum. If the line is loose or cracked then it won't allow the petcock to open fully. I had lots of problems with fuelling, when I  first got my Symba.
I eventually had to replace the vacuum petcock with a manually operated petcock and it solved my fueling issues.
2015 Symba 100
2015 Suzuki 650 V-Strom
Some past rides.....
2015 Haley Lowrider
2007 Moto Guzzi California Vintage
2008 Moto Guzzi Norge
2011 Royal Enfield Classic 500
2012 Suzuki DL1000 V-Stom
2012 Harley Switchback converted to Trike
2006 Harley Streetglide
2014 Suzuki DR650 and much more

hobo

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Re: Working through the symptoms
« Reply #6 on: June 25, 2017, 04:57:50 PM »
My .102 feeler gauge slipped in there with a little resistance, while my .127 gauge wouldn't quite slide thru, so that should be within tolerance.

Next step: new fuel filter and to check the vacuum petcock.

petemoss

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Re: Working through the symptoms
« Reply #7 on: June 25, 2017, 10:39:35 PM »
You also mentioned that you could smell gasoline in with the oil when you performed an oil change. This means that the fuel petcock it not fully closing. Thus allowing fuel to continue to flow into the carburetor. If it bypasses the float seat, then the fuel will continue flowing into the cylinder, pass the piston rings and into the crankcase. Installing a manual petcock before the carburetor will solve this problem.
Another thing that I should mention here, is that I was also having an issue where the bike would no longer start. I lost spark. Replacing the spark plug didn't help, so I started troubleshooting the ignition circuit. It almost seemed as if I had a faulty ignition coil or something. I found out that the coil is fed voltage directly from the alternator coil ( not the battery circuit). So I tested the resistance of the alternator coil ( Stator ), and all checked out ok. Then I checked the charging system and all was fine there as well. This was puzzling as everything checked out as it was supposed to. For the heck of it, I tried to start her up, and she fired right up and has been running like that ever since. So the only thing that I could figure was that one of the connections from the alternator, voltage regulator, ECM, or other connectors, must not have been properly connected right from the factory and eventually jiggled itself loose enough to loose my ignition circuit.
( all that after two frustrating days of troubleshooting.)

 I also replaced the vacuum operated petcock from the fuel tank and installed a manually operated petcock. Now she fires up every time, no mater how long she sits for.
 
I had the same fueling issues with an older Yamaha snowmobile. If it sat for a couple of weeks, it would not start for love or money. The only way to get it running, was to squirt a bit of fuel into the carb intake. After a few attempts, it would start, sputter and eventually stay running, after that , it would start even time. It also has the dreaded vacuum operated fuel petcock.

A conversation with a mechanic some time ago, shed some light on these petcocks. He explained that these petcocks need a vacuum from the engine crankcase in order to open up the valve to allow fuel to flow to the carb(s). The problem is, when an engine sits for a long time, the oil from the pistons seeps down into the crankcase ( normal), but now the rings are dry so when you turn the engine over, the lack of oil means that the compression is way low, as oil not only lubricates the piston rings but also helps seal it, thus increasing the compression. Low compression means low crankcase vacuum=vacuum fuel valve not opening fully= low fuel volume.
So in other words, vacuum fuel petcocks= bad idea.

Hope some of this info helps you.

Peter
« Last Edit: June 25, 2017, 10:44:40 PM by petemoss »
2015 Symba 100
2015 Suzuki 650 V-Strom
Some past rides.....
2015 Haley Lowrider
2007 Moto Guzzi California Vintage
2008 Moto Guzzi Norge
2011 Royal Enfield Classic 500
2012 Suzuki DL1000 V-Stom
2012 Harley Switchback converted to Trike
2006 Harley Streetglide
2014 Suzuki DR650 and much more

hobo

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Re: Working through the symptoms
« Reply #8 on: June 25, 2017, 11:19:12 PM »
Yeah, that's all quite helpful, thanks Peter. Especially the bit about an engine that has sat for awhile drying out the rings, resulting in a low compression reading.

Question: what kind of petcock did you replace the vacuum one with? I know you said a manual one, but is there a specific make/model you can recall? Did you pull the vacuum one completely?

petemoss

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Re: Working through the symptoms
« Reply #9 on: June 26, 2017, 06:10:48 AM »
Hobo, I picked a generic online fuel petcock at Napa Auto parts in the small engine parts area. Mainly used on lawnmower engines.
As far as removing the vacuum one from the fuel tank, I removed the tank and then the valve ( it will unthread from the bottom), then I purchased a 1/4" barbed fitting which has a male thread at one end. I ran a thread cutting tap into the hole at the bottom of the tank and screwed in the barb fitting. Then ran the fuel hose back to the carb. I installed the new petcock near the factory fuel filter so that I can access it with the side cover in place. I did post some pictures a while back. Maybe search through my threads to find them. I'm off to work right now so I won't be able to post any pics until tonight
2015 Symba 100
2015 Suzuki 650 V-Strom
Some past rides.....
2015 Haley Lowrider
2007 Moto Guzzi California Vintage
2008 Moto Guzzi Norge
2011 Royal Enfield Classic 500
2012 Suzuki DL1000 V-Stom
2012 Harley Switchback converted to Trike
2006 Harley Streetglide
2014 Suzuki DR650 and much more

hobo

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Re: Working through the symptoms
« Reply #10 on: June 26, 2017, 03:00:03 PM »
That's pretty clear, thanks.

hobo

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Re: Working through the symptoms
« Reply #11 on: July 02, 2017, 09:18:54 PM »
Is there a way to remove the petcock WITHOUT removing the fuel tank? Seems like a lot of stuff that has to come off to remove the tank, like the shocks, which the manual says the rubber bushings will be ruined if I remove...?
« Last Edit: July 05, 2017, 03:11:14 PM by hobo »