Running Too Rich

bmetras · 12-22-2016, 07:25 PM

Hello all, first post, new member ..forgive me if this has been covered elsewhere on the site.

Just picked up a 2007 Roketa Sicily 150 cheap.. was advertised as "engine runs well", which it did at idle and off idle, before loading it onto a carrier.. once I got it off the streets of San Francisco and home for a test ride, I found that anything approaching 1/2 throttle the engine would bog terribly (30mph maybe max), release the throttle, smooth running and idling up to about 1/2 throttle, then bog to the point of killing the engine..

This morning I removed the air filter (clean enough) same problem.. removed the bodywork to get access to the carb ...removed the snorkel from the mouth of the carb, and the engine ran really well on the center stand.. took it out for a test and it easily ran over 50mph.. hooked the snorkel back up and the same poor running issue came instantly back.. checked for obstruction in the air intake and it was clear.. the engine idles nicely hot or cold.. when cold, there seems to be a high idle circuit that works, and then it drops down to normal idle after it warms up..

So my question is if there is anything from the tank to the carb that could cause a severe, overly rich condition that would be masked by letting the carb breathe freely without the air/snorkel intake system in place..

Thanks for any insights or further things to test..

Bruce

Roscoe · 12-23-2016, 10:13 AM

Could the snorkel from the carb to the air cleaner box be collapsing or kinked? This sounds more like a lean mixture problem but if it runs OK without the air cleaner and snorkel it must be something to do with those or maybe excessive blow by from the PVC system that feeds into the air cleaner? Double check that snorkel for a mouse or chipmunk nest.

bmetras · 12-23-2016, 11:40 AM

Thanks, I had checked the snorkel for obstructions and it's clear.. I also disconnected the PCV tube from the air intake .. with no change ... It doesn't look like the snorkel collapses on the bike stand when I crack the throttle ... on the stand, it will free-rev ok until I go WOT, then it falls on its face to the point of dying .. haven't pulled the carb off and apart yet.. maybe the float isn't sealing or sunk.. night and day when I pull the snorkel off though ( I have it tie-wrapped away from the carb to test.. raining today, so road testing will be delayed for awhile..

DisillusionedPrepper · 12-24-2016, 01:35 AM

Best bet is to pull the carb apart.
These engines will run up to almost 1/2 throttle without a main jet even being installed. Next take a look at the float to verify it is sealing the needle/seat when inverted. The float should be parallel to the carb body, and the needle seated when the carb is inverted, and finally I would take a very close look at the slide diaphragm for cracks or tears. It may also be swollen or wrinkled looking from ethanol fuel. If it is, you can soak it in detergent/water for 10-15 minutes. That will pull the EToH out of the diaphragm, and give it a new lease on life.

Almost forgot... look at the main jet needle in the slide. Some have an "E" clip that will wear out the slots, and the needle will float around giving all sorts of wacky symptoms.
That clip should be in the center slot from the factory, and the main jet should be marked "102" or VERY close to that.

For shits, and giggles, a new spark plug, and fuel filter followed by a valve adjustment.

bmetras · 12-24-2016, 12:49 PM

Thanks for the great tips... I'm going to pull the carb and see what I see.. although it only has 1230 miles, it's over 9+ years old, so no telling who did what to it.. I was told by someone that the vacuum fuel valve at the gas tank could cause an over rich problem if the diaphragm failed, but I checked that today, and it seems to be working well.. no gas coming from it with engine off and no vacuum.. when I pull vacuum on the lower port, then fuel flows freely from the upper port.. so the fuel valve is working .. the fuel evap lines were disconnected ... I re-connected them and it is running better, but I also did not clamp the snorkel tightly to the carb intake and left the clamp off .. ran to the bank between cloud bursts .. it was very rideable .. I'll test more when I have some time... meanwhile, I'll check out the carb jets and needle position as you suggested .. when I had it running on the stand, I checked that the carb diaphragm/slide assembly was working well with a mirror while I ran the engine to WOT .. it looked to be working great.. Thanks again for the response..

DisillusionedPrepper · 12-24-2016, 09:17 PM

Sounds like your narrowing it down.

I had another thought... The previous owner may have installed one of those K&N "open" type air filters at some point.
That would include up jetting so a close look at the main jet could only help.

Try to verify the OEM main jet size. I do believe it is 102 but i'm not 100% on that.

Oh yeah, The auto choke.
It might be working partially. You mentioned that it does idle down but those chokes are notorious for working part way, and not sealing completely.
They are supposed to move a full 5mm when plugged in, and the key is first turned on. This generally takes about 30-45 seconds. Depending on the stator used these can run on AC (20-30 volts) or DC @ 12 volts.
My best advice is to get a new choke from Ebay or similar. They run about 5 bucks shipped. This way there is little doubt, and a spare IF yours was working.

bmetras · 12-29-2016, 05:19 PM

I pulled the carb apart last night.. Sheng Wey 24mm with a 108 main jet.. a little bit of muck in the float bowl, but not bad.. pulled jets and screws and blew through all of the passages.. didn't seem bad.. put it back together and now the high idle at startup is higher, and the idle is lower, to the point of wanting to die sometimes .. mixture screw seems way too far out after adjusting for optimum idle speed (well over 4 turns out)..

Haven't received the new cold start choke yet .. how is that supposed to work? I tested voltage at the plug (around 12 or 13 volts AC ) when I started the bike .. no reading when I just turned the key on .. when the bike started, it went to high idle and a relatively constant voltage reading.. when it dropped off of high idle, the voltage reading was still constant, yet the valve must have closed to drop the idle so much ..

What I haven't done yet is a valve adjustment and a extensive check for vacuum leaks.. what I did see is that the spark plug is now approaching white.. before I did anything, it was actually a light brown.. I need to do some more testing, but am curious how the choke is supposed to work..

Thanks again for the help.

DisillusionedPrepper · 01-04-2017, 12:10 AM

The choke plunger sits in a passage that allows more fuel when the bike is cold so it does sound like it is working.

I think you may have clogged the idle jet or the air bleed circuit.
You have to completely tear the carb down. Remove the idle mix screw, use a can of carb clean, and the tiny straw to blow thru everything.

There are no sewing needles that fit these tiny idle jets so I find that seperated strands of plain copper wire works in most cases.
For larger jets I use torch tip cleaners that you can get anywhere (almost) for about 7 bucks.

Carbs can get goofy, and take a few attempts to get really clean so I would try again.

Also the white spark plug is showing a LEAN condition. so No riding until you sort it out.
The mixture screw should be between 1.5-2.5 turns off seated. Otherwise you have the wrong idle jet or a dirty carb.

12-23-2016, 10:13 AM	#2
Roscoe Join Date: Nov 2016 Location: N. of Texas and S. of Kansas Posts: 252	Could the snorkel from the carb to the air cleaner box be collapsing or kinked? This sounds more like a lean mixture problem but if it runs OK without the air cleaner and snorkel it must be something to do with those or maybe excessive blow by from the PVC system that feeds into the air cleaner? Double check that snorkel for a mouse or chipmunk nest.
	0

12-24-2016, 01:35 AM	#4
DisillusionedPrepper Join Date: Dec 2016 Posts: 109	Best bet is to pull the carb apart. These engines will run up to almost 1/2 throttle without a main jet even being installed. Next take a look at the float to verify it is sealing the needle/seat when inverted. The float should be parallel to the carb body, and the needle seated when the carb is inverted, and finally I would take a very close look at the slide diaphragm for cracks or tears. It may also be swollen or wrinkled looking from ethanol fuel. If it is, you can soak it in detergent/water for 10-15 minutes. That will pull the EToH out of the diaphragm, and give it a new lease on life. Almost forgot... look at the main jet needle in the slide. Some have an "E" clip that will wear out the slots, and the needle will float around giving all sorts of wacky symptoms. That clip should be in the center slot from the factory, and the main jet should be marked "102" or VERY close to that. For shits, and giggles, a new spark plug, and fuel filter followed by a valve adjustment.
	0

12-24-2016, 09:17 PM	#6
DisillusionedPrepper Join Date: Dec 2016 Posts: 109	Sounds like your narrowing it down. I had another thought... The previous owner may have installed one of those K&N "open" type air filters at some point. That would include up jetting so a close look at the main jet could only help. Try to verify the OEM main jet size. I do believe it is 102 but i'm not 100% on that. Oh yeah, The auto choke. It might be working partially. You mentioned that it does idle down but those chokes are notorious for working part way, and not sealing completely. They are supposed to move a full 5mm when plugged in, and the key is first turned on. This generally takes about 30-45 seconds. Depending on the stator used these can run on AC (20-30 volts) or DC @ 12 volts. My best advice is to get a new choke from Ebay or similar. They run about 5 bucks shipped. This way there is little doubt, and a spare IF yours was working.
	0

12-29-2016, 05:19 PM	#7
bmetras Join Date: Dec 2016 Location: San Rafael, CA Posts: 8	I pulled the carb apart last night.. Sheng Wey 24mm with a 108 main jet.. a little bit of muck in the float bowl, but not bad.. pulled jets and screws and blew through all of the passages.. didn't seem bad.. put it back together and now the high idle at startup is higher, and the idle is lower, to the point of wanting to die sometimes .. mixture screw seems way too far out after adjusting for optimum idle speed (well over 4 turns out).. Haven't received the new cold start choke yet .. how is that supposed to work? I tested voltage at the plug (around 12 or 13 volts AC ) when I started the bike .. no reading when I just turned the key on .. when the bike started, it went to high idle and a relatively constant voltage reading.. when it dropped off of high idle, the voltage reading was still constant, yet the valve must have closed to drop the idle so much .. What I haven't done yet is a valve adjustment and a extensive check for vacuum leaks.. what I did see is that the spark plug is now approaching white.. before I did anything, it was actually a light brown.. I need to do some more testing, but am curious how the choke is supposed to work.. Thanks again for the help.
	0

01-04-2017, 12:10 AM	#8
DisillusionedPrepper Join Date: Dec 2016 Posts: 109	The choke plunger sits in a passage that allows more fuel when the bike is cold so it does sound like it is working. I think you may have clogged the idle jet or the air bleed circuit. You have to completely tear the carb down. Remove the idle mix screw, use a can of carb clean, and the tiny straw to blow thru everything. There are no sewing needles that fit these tiny idle jets so I find that seperated strands of plain copper wire works in most cases. For larger jets I use torch tip cleaners that you can get anywhere (almost) for about 7 bucks. Carbs can get goofy, and take a few attempts to get really clean so I would try again. Also the white spark plug is showing a LEAN condition. so No riding until you sort it out. The mixture screw should be between 1.5-2.5 turns off seated. Otherwise you have the wrong idle jet or a dirty carb.
	0