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Discussion Starter #1
Hey guys,

I acquired this bike from my Dad about 1 1/2 years ago. It is all factory as far as I can tell and has 4,000 miles. It had been sitting for a couple years when I got it so I drained the fuel, disassembled and cleaned the carb, replaced the fuel lines, replaced the spark plug, replaced the battery and changed the oil (Maxim motorsport oil). After this it starts and idles perfectly but has a significant bog on acceleration and backfires through the exhaust. I got sidetracked on other projects and just got back to it last month.

Since then I've recleaned the carb, removed and flushed the gas tank, checked the air filter, adjusted the valves and ran a compression test (175 psi). With the air intake duct removed from the carb I can see the slide is moving freely and there is a heavy mist of fuel coming from the needle off idle. If I hold my hand in front of (not covering) the air inlet it gets fuel on it. There is air pulsing out of the carb inlet and also the crankcase vent hose. With my temp gun the exhaust pipe near the head reads about 850 degrees revved up in the shop. The bog is worse under load and the new plug is already getting black.

I've been a diesel truck and equipment mechanic for 20 years but this single cylinder unit is new territory for me. Are the air intake pulses normal for a single cylinder? I've searched this forum and Googled a lot looking for a fix.

The auto choke moves freely, is spring loaded out and measures 5 ohms across the coil. The needle on it is perfect and I can't see issues with the seat although its tough to see into the carb.

I removed the spark arrestor to see if maybe the exhaust was restricted and had no change.

I thought maybe timing so I tried to follow the procedure in the manual to check timing with a timing light through the inspection hole but it was splashing too much oil to see the marks. I read about the flywheel magnet issues so I thought maybe the magnets had come loose and damaged/bent the ignition pick up so I removed the magneto cover and found that it has the updated flywheel (looks like it could be an RM Stator FW) and no damage to the stator or pick up.

The carb has all the factory jets and the only thing I haven't verified is that the needle is factory. I'm near sea level, maybe 200 feet.

I'm stuck on troubleshooting until I get the mag cover gasket and reassemble that but I'm nearing my wits end. I was studying up on the CVK carb last night and have a better understanding of the Pilot screw and that it effects A/F ratio over the entire range not just idle. Am I over thinking this? Is it simply a pilot screw adjustment? I'm at 1 3/4 turns out per the manual base setting.

Sorry this got so long but any input would be greatly appreciated.

Thank you!

Keith
 

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Discussion Starter #2
Nobody? I know I got long winded but I'll take anything at this point, information, opinions, guesses.......

I haven't ridden in years but rode with a friend a couple weekends ago and got the bug again. Help me get back out there. :smile

Keith
 

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Discussion Starter #4
Thanks for the reply Door.

The collar is in place and the diaphragm is seated correctly. The slide moves freely by hand and under vacuum while running the engine.

I did read that jetting thread and will refer back to it once I get the cover gasket and get the engine back together. Parts are supposed to be here tomorrow.

I did check my valve timing last night by referencing the timing mark to piston TDC and valve overlap. I didn't pull the rocker cover to verify the cam timing marks. That may be my next step if adjusting the pilot screw doesn't lean it out. I also checked the resistance of the ignition pick up and it's in spec.

I have a video that shows how much fuel is coming out the needle/main jet and shows fuel mist blowing out the carb inlet but it doesn't look like I can post it here.

Keith
 

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This is an interesting one as you have checked everything. The "choke" is really an enricher on these carbs correct? Sounds like it's rich but it might just be the wrong jet for sea level. The air intake is clear of obstructions? No mice taking up residence while it was stored.
 

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I’m sure you know this, but make sure you are on compression TDC as the marks line up on exhaust as well. Valves should be loose at TDC compression.
 

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Discussion Starter #7
Firecat,

I agree that the "choke" is an enricher and it is the one thing that I'm still trying to completely understand. Most of the information I've found on those is not specific to the AC unit and seems to talk about the plunger extending when the wax pellet is heated. Mine is spring loaded out which seems backwards. I've checked the resistance across the unit and it's not open. I've been leery of jumpering battery power to it without knowing if that's the proper procedure for this specific unit. I will turn the key switch on tonight and see if it generates heat over time.

Jets are the stock sizes listed in the manual and I would think our thick air at sea level would cause it to go lean vs rich. The intake is clear and it still runs rich without any of the intake ducting connected (open carb).

Door,

Yep, both valves closed at TDC Compression and Valve Overlap occurs at TDC Exhaust. thumbguy

Thanks!
 

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Discussion Starter #14
Door, I had previously looked at all those links and videos but thank you. The video on the "choke" is the one that has me questioning if it's correct for the AC unit. Has anyone tested their AC unit with that process? That one is considerably different than the AC part and I haven't found any info that seems to pertain directly to the AC part.

The fact that mine is spring loaded to extend makes me think it probably retracts when heated but that is only speculation. I've got a few minutes before my fire board meeting tonight so I'm going to go check it out.

Thanks, Keith
 

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Discussion Starter #15
The service manual and wiring diagram both call the unit an electric choke so I'm sticking with choke. :)

I tested mine following the procedure in the video above and it tests good. I did press in the tab and remove one pin from the connector to make it easier to connect jumper wires without shorting them together.

It was 55 degrees and 0.720" from the body shoulder to the cylinder shoulder to start. After 4 minutes it was 81 degrees and 0.855". It does indeed extend when warm.

I checked to see if I was getting voltage to the plug on the bike side and with the key on I was not. The wiring diagram shows that the yel/red wire goes to the instrument cluster connector so I'm thinking it may only be powered with the engine running. I'll retest after I get the side cover back on and can start it.

Keith
 

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Discussion Starter #16
I've got the magneto cover back on and the bike running again.

I checked the voltage going to the choke with the bike running and it isn't 12 volts. It's either A/C voltage or pulse width modulated DC and my meter bounces around and won't get a consistent reading. Using the Min?Max function it captured -1.5V to 2.5V.

Regardless of voltage the choke is heating and when removed after running the bike it was at .910" warm. That's longer than I found while testing so I'm fairly certain it is working and turning off the choke.

I verified that my needle is the factory size "NAZG".

I found this video
and confirmed that the main jet collar is installed correctly.

So I started adjusting the pilot screw and the bike will idle normally with the screw all the way in. It's obviously getting fuel around the idle/pilot circuit from somewhere. It appears there may be a small amount of fuel coming around the needle at idle and there's a heavy mist of fuel coming around the needle at anything off idle.

Any thoughts??
 

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Tear in the diaphragm ? Diaphragm spring broken or not installed correctly. Mid range is usually diaphragm related.
The choke runs off low voltage.
 

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Discussion Starter #18
Would a defective diaphragm cause overfueling? In my mind if the diaphragm is torn the slide and needle will not move as they should causing the needle to stay lower in the main jet restricting fuel and the slide to stay low in the carb bore restricting air. The slide begins to move as soon as throttle is applied and goes to a fully retracted position. That is what I would expect it to do but again I've not looked at one working normally.

As for the spring it is over the tabs on the cap and over the plastic cage that sits over the needle. It's not bent or damaged in any way that I can see and has tension on the cap when I put it on. The cage is installed correctly so that it sits inside the spring.

I have the air box off to access the carb and when I run the engine the crankcase vent hose puffs air enough that I can feel it when I lean over the engine. Is that normal?
 

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Yes that’s normal.
Is the vent line connected going up to the pod?
Any chance you mixed he jets up? They will fit in either hole. Grasping at straws here.
 

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Discussion Starter #20
I have the carb off and disassembled again. I verified the jets are in the correct location.

I'm not sure exactly what you mean when you say is the vent line connected going up to the pod but I assume you mean is the crankcase vent connected to the air filter housing. It is not. I've had the air filter box out while troubleshooting this and the hose is connected to the crankcase side but not the other end.

I removed the valve cover and verified the cam timing marks tonight. I also removed and visually inspected the exhaust header pipe and muffler even though they seemed to have good flow. Everything is clear, albeit sooty. I did notice that the vacuum line to my fuel pump had some cracks in it. None of them seemed to go all the way through but I replaced the line anyhow.

I'm going to let the valve cover sealer dry over night, readjust my valves in the morning and then reassembly the exhaust and the complete air intake system and see how it does.

I hate to throw parts at things but I've read on here that guys have cured problems by replacing diaphragms that had no visible defects so that may be my next step................
 
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