Difficult tuning. Hey dan!!

[Angus67]

Grrrrr. I have a 200 cc witha vm26, 22.5 pilot, 110 main. Needle fourth notch. I cannot for the life of me get this tuned in! Compression is 180, valves set correctly. Nice blue spark. I start out one turn on the idle mix, and it just snaps and farts out the exhaust. No “snicking “back thru the carb. When i pull the choke, the idle steadies, but is way high.
In my experience when the choke is pulled on a warm engine, it should stumble because it has tto much fuel, too little air.
Im 5 turns out on the mix, and shouldn’t be that far out. Nothing changes except easier starting.
I have not history on this bike, nor does the previous owner. Could it have been kitted to a 250cc? I have a 25 and a 27 pilot, but all info points to 22.5 or 25.
When i try the 25, same issues.
Really frustrating
Im guessing i have the idle in the middle.
And it still wont start with a air filter..
Its so difficult to adj the mix while its running. I had to modify a extended mix screw so it wouldnt hit the starter. I cut a groove in it for a screwdriver, and have to use a flexible screwdriver to get at it.
Ive tunned many bike carbs, mostly cv’s so im no newb
What am I missing?

[Ariel Red Hunter]

Originally Posted by Angus67

Grrrrr. I have a 200 cc witha vm26, 22.5 pilot, 110 main. Needle fourth notch. I cannot for the life of me get this tuned in! Compression is 180, valves set correctly. Nice blue spark. I start out one turn on the idle mix, and it just snaps and farts out the exhaust. No “snicking “back thru the carb. When i pull the choke, the idle steadies, but is way high.
In my experience when the choke is pulled on a warm engine, it should stumble because it has tto much fuel, too little air.
Im 5 turns out on the mix, and shouldn’t be that far out. Nothing changes except easier starting.
I have not history on this bike, nor does the previous owner. Could it have been kitted to a 250cc? I have a 25 and a 27 pilot, but all info points to 22.5 or 25.
When i try the 25, same issues.
Really frustrating
Im guessing i have the idle in the middle.
And it still wont start with a air filter..
Its so difficult to adj the mix while its running. I had to modify a extended mix screw so it wouldnt hit the starter. I cut a groove in it for a screwdriver, and have to use a flexible screwdriver to get at it.
Ive tunned many bike carbs, mostly cv’s so im no newb
What am I missing?

I would recommend a thorough carb cleaning job, making certain that NO jets or passages are blocked, and that the float level is correct. Another cause of this problem is a vacuum leak in the intake pipe....ARH

[Angus67]

There are no vacuum leaks.

[Cravin01]

When you pull the choke and it idles too high that means it's starving for fuel, at full choke it gets just enough to run. More than likely it's original jetting is close enough to run with room to see change from some adjustment. So it leads me to believe it may be a restricted jet or gummed up carb, possibly a vacuum leak.

[Megadan]

Originally Posted by Angus67

I start out one turn on the idle mix, and it just snaps and farts out the exhaust. No “snicking “back thru the carb. When i pull the choke, the idle steadies, but is way high.
In my experience when the choke is pulled on a warm engine, it should stumble because it has tto much fuel, too little air.
Im 5 turns out on the mix, and shouldn’t be that far out. Nothing changes except easier starting.

Everything you mentioned sounds like a lean condition, If the idle improves on a warm engine with the choke engaged, then that also confirms a lean condition. Another way to know would be to block off the air filter to reduce arflow - same concept. The reason your idle increases is because the air fuel ratio is closer to optimal. This same idle increase is part of idle drop mixture tuning, aka adjusting the idle mixture screw to find the highest and most stable idle. Once you find said highest stable idle, you then would adjust the idle back down.

If you are confident that you have no vacuum leaks, then I would suggest jumping up to that 27.5 pilot just to see how it behaves. It seems like a drastic change, but considering it takes you past 3 turns out to even get a somewhat decent idle, a full step up might be what you need.

One thing you weren't clear on is the throttle position at which these running issues happen. Idle? Just barely opening the throttle - like a light steady throttle while going at low speed?

I am fairly sure you mentioned going through and cleaning the carb really well a couple of times, but if not then ARH's suggestions are definitely worth a look. The smallest piece of debris in the pilot circuit or idle mixture passage can cause all sorts of hell.

Dialing in a carb can be a long tinkering process when you have no direct analog or other setup to start from. The CG250 should be close, but it may take a few changes. You might find that the pilot jet size and mixture settings are almost the same as the 250, Even though the 250 is larger, the extra 30cc's will also mean that there could be a slightly weaker intake signal through the same size carb on the 200 engine, thus needing a larger jet size to compensate for the lower "Draw" on the jets during an intake stroke.

Also keep in mind that cooler weather will also mean the jets may need to be a tad richer as well than many of the setups you are looking at with the CG250 bikes - which are likely all figures from the warmer parts of the year.

Just keep in mind these throttle ranges to help diagnose running issues with the setup.
Idle mixture and up to 1/4 throttle is mainly affected by the pilot size
1/4 to 3/4 throttle is mainly affected by the needle position
3/4 to wide open is main jet size.

[Angus67]

Found vacuum leak. This is one of thew ones. Ill get another on the way.

[Azhule]

Wow... big gash

[timcosby]

Originally Posted by Angus67

Found vacuum leak. This is one of thew ones. Ill get another on the way.

duct tape it for now and ride the piss out of it

[Ariel Red Hunter]

Originally Posted by timcosby

duct tape it for now and ride the piss out of it

That's a good suggestion. That will let you get the carb more dialed in before the new intake gets here. I know that you already know not to overtighten the two mounting bolts for the carbs, and the two nuts used where the intake attaches to the head...ARH

[Angus67]

Yep. Just snug with some smear of greaes on the orings

[Ariel Red Hunter]

Originally Posted by Angus67

Yep. Just snug with some smear of greaes on the orings

Good man, good man...ARH

[Angus67]

I was able to salvage the first new one, the one with the stripped hole. Running much better, but 3&1/2 turns out and on the fifth notch. Cant find my 27.5.

[Ariel Red Hunter]

Originally Posted by Angus67

I was able to salvage the first new one, the one with the stripped hole. Running much better, but 3&1/2 turns out and on the fifth notch. Cant find my 27.5.

I used to change pilot jets up until the idle mixture was at 1 and 1/2 turns out, and the bike ran good (but not "perfect") with the needle in the middle slot. then I went on to the main jet, then back to the needle to 'tweek' the 1/2 to 3/4 throttle response....ARH

[Angus67]

Huh. I will try that when i find my 27.5 pilot.

[Weldangrind]

A general rule of thumb is that if you need to back out the pilot mixture screw more than 2.5 turns, the slow jet is too small.