New Boom Vader - Need help converting to Mikuni carb

[Skin Mechanic]

Originally Posted by prismways

so does this pretty much mess me up if I need to get it inspected in MA?

They do require an inspection and I assume some type of EPA regulation.

If so, You'll have to return it to stock for the vehicle inspection. and switch it back out afterward. Or move to a state that doesn't require inspections

[prismways]

Yeah, I made sure there was clearance in the front and no chance of the fender hitting the air filter. This was the orientation of the original carb.

Originally Posted by Skin Mechanic

Orienting the new carb in the same direction as the old one will put the cone filter a coupla inches away from the scorching hot crankcase, and the slipstream will be hitting the base of the air filter, causing more turbulence in the intake. That being said, it looks like prismways' cone filter is really close to the fender. It could get knocked off going over rough pavement. The intake that came with my carb kit was shorter so it had to be installed facing forward.

[Skin Mechanic]

My stock carb was aimed at the clutch cable, I flipped it forward before getting the Mikuni. It ran poorly in either direction. If my new carb would fit on the taller stock intake I would swap it out just to get it further away from the engine. Hmmmmmm, maybe I can cut the mounting flange off the stock intake and use it as a spacer.

[prismways]

What size jet did you end up going with? Do you think 120 is too big for this size engine? Would I need to adjust any of the smaller jets if I went with this one? thanks

Originally Posted by Skin Mechanic

My stock carb was aimed at the clutch cable, I flipped it forward before getting the Mikuni. It ran poorly in either direction. If my new carb would fit on the taller stock intake I would swap it out just to get it further away from the engine. Hmmmmmm, maybe I can cut the mounting flange off the stock intake and use it as a spacer.

[prismways]

So I changed the main jet from 120 to 100. The air/fuel mixture screw is turned two full rotations from the closed setting, which I believe is close to factory.

So I was able to get my bike to start and run but I am noticing that it only starts with the enricher plunger lifted up (which means it is adding extra fuel). It starts easy but it's revving super high at around 3,000 rpm.

I try to lower the idle by turning the idle screw counter clockwise and it does not lower the idle. But if I turn it clockwise to tighten, I can eventually increase the idle further but that's not what I want.

I lower the enricher plunger to about halfway and the idle slows to between 1500 to 2000.

If I lower the plunger all the way, the bike dies. I know that ideally, the plunger should be closed after the bike warms up and this should be the normal operation state.

At half way, when I apply the throttle, it feels like it is struggling to generate power. It's sluggish and this is without a load on the engine.

I am thinking it might be one of the following causes:
- stuck throttle
- air leak somewhere
- air/fuel mixture screw
- pilot screw (but I haven't messed with this)

[Skin Mechanic]

If the carb is adjusted properly, you shouldn't need to use the choke to start it, except in cold weather. Sounds like it's too lean. Run the bike for about 30 seconds and pull the spark plug, reading the plug will give you an indication of your air/fuel mixture.

http://www.onallcylinders.com/2012/1...r-spark-plugs/

[veezx20]

You need yo get the bike warmed up without the choke when your trying to adjust the idle, i believe you should be 2.5 turns out on the air/fuel screw, the main jet you changed wont come into play until your 3/4 throttle and higher, your pilot jet is what controls everything from idle to a 1/4, the needle is what controls it inbetween. Make sure you have no vacuum leaks as this can wreak havoc on you trying to get the bike running properly. You can spray starting fluid around your intake manifold to see if you sucking air, if the motor races when your spraying it you have a leak

Originally Posted by prismways

So I changed the main jet from 120 to 100. The air/fuel mixture screw is turned two full rotations from the closed setting, which I believe is close to factory.

So I was able to get my bike to start and run but I am noticing that it only starts with the enricher plunger lifted up (which means it is adding extra fuel). It starts easy but it's revving super high at around 3,000 rpm.

I try to lower the idle by turning the idle screw counter clockwise and it does not lower the idle. But if I turn it clockwise to tighten, I can eventually increase the idle further but that's not what I want.

I lower the enricher plunger to about halfway and the idle slows to between 1500 to 2000.

If I lower the plunger all the way, the bike dies. I know that ideally, the plunger should be closed after the bike warms up and this should be the normal operation state.

At half way, when I apply the throttle, it feels like it is struggling to generate power. It's sluggish and this is without a load on the engine.

I am thinking it might be one of the following causes:
- stuck throttle
- air leak somewhere
- air/fuel mixture screw
- pilot screw (but I haven't messed with this)

[prismways]

Thanks Skin!

Originally Posted by Skin Mechanic

If the carb is adjusted properly, you shouldn't need to use the choke to start it, except in cold weather. Sounds like it's too lean. Run the bike for about 30 seconds and pull the spark plug, reading the plug will give you an indication of your air/fuel mixture.

http://www.onallcylinders.com/2012/1...r-spark-plugs/

[prismways]

Thanks for the tips Veezx20! I haven't really tested the full throttle yet, but I will see how things go. I will have to adjust my air/fuel again. I plugged up my EGR per Skin's recommendation and it definitely helped.



So I figured out what my problem was. I had way too much slack on my throttle. When Skin mentioned that it could be a too lean situation, I focused on that.

I closed the enricher plunger and applied some throttle and I was able to start the bike. I also increased the idle screw a bit to make the idle more stable. From there, I adjusted the throttle so that the idle is stable and I'm able to start it in a second or two.

I took it out for a spin and holy cow, this is a new motorcycle. It accelerates so smoothly and is such a joy to ride now. There is a very slight sluggishness in fourth gear and I'm not sure what is attributing to that. For now, I cannot complain. The bike is super fun to ride now. I definitely recommend the carb kit that I got from Amazon.

I plan on upgrading the sparkplug and possibly doing the muffler next. I ordered the 16T sprocket but not sure I want to take that on.

Originally Posted by veezx20

You need yo get the bike warmed up without the choke when your trying to adjust the idle, i believe you should be 2.5 turns out on the air/fuel screw, the main jet you changed wont come into play until your 3/4 throttle and higher, your pilot jet is what controls everything from idle to a 1/4, the needle is what controls it in between. Make sure you have no vacuum leaks as this can wreak havoc on you trying to get the bike running properly. You can spray starting fluid around your intake manifold to see if you sucking air, if the motor races when your spraying it you have a leak

[prismways]

So this is what the final install of the carb kit looks like. There is plenty clearance for the air filter. There is no way I could have turned it around as there is not enough room due to the location of the starter.

So glad it's running smoothly now. I will monitor the top end acceleration to see if the problem goes away over time.

[Skin Mechanic]

Glad to hear things are almost back to normal. I ordered a 16T sprocket for mine but there wasn't enough slack in the chain to install it. The chain should stretch out enough to swap the sprocket after a 1000 miles, I only needed about 1/8" slack. Anywho, I pulled my spark plug a coupla days ago and it was carbon fouled (too rich). The carb was shipped with a 195 main jet installed and came with smaller jets. I down jetted it to a 155 and checked the plug again. It's a little lean, so 'll up jet to a 165 after work tomorrow and take it for a spin around the hood. Riding the little monster reminds me of why I fell in love with motorcycles. Which exhaust are you looking at?

[prismways]

Thanks for all your help Skin. Much appreciated. Wow, those jets seem really large in size. Mine is only 100 now.

I ended up buying this muffler from Wish.com:

https://www.wish.com/c/5848d337090bf14ca02d5943

Not sure what to expect, but it looks great and the ratings are solid.
The budget price was attractive. I will let you know how it goes.

I will hold off on the sprocket upgrade for now too.

thanks again.

Originally Posted by Skin Mechanic

Glad to hear things are almost back to normal. I ordered a 16T sprocket for mine but there wasn't enough slack in the chain to install it. The chain should stretch out enough to swap the sprocket after a 1000 miles, I only needed about 1/8" slack. Anywho, I pulled my spark plug a coupla days ago and it was carbon fouled (too rich). The carb was shipped with a 195 main jet installed and came with smaller jets. I down jetted it to a 155 and checked the plug again. It's a little lean, so 'll up jet to a 165 after work tomorrow and take it for a spin around the hood. Riding the little monster reminds me of why I fell in love with motorcycles. Which exhaust are you looking at?

[prismways]

So there is definitely something wrong with my carb. I took it out today and was able to make it about 3 miles and then things went south. I am seeing that if I open the full throttle (or more than 1/2) for an extended period of time, it will begin to bog down.

It gets so bad that it will start to stall and have trouble accelerating. Even if I just give it a little bit of gas, it will start to stall. I had to pull over at a nearby gas station. After being at the station for about 10 minutes running, I notice it will idle perfectly fine at 1500 RPM. So I waited and talked to some folks at the gas station. I used some carb cleaner and tested to see if there were any leaks and the engine did not race or bog when I sprayed it around the intake pipe or manifold, but I did not see anything like that.

I see that if I turn it off and let it "rest" for a moment or two, it starts up fine. After determining that it seemed to be stable, I try to make it home. I can ride it through all four gears if I give it minimal gas, nothing more than a 1/8th of a turn on the throttle. I can't make it over 35mph or it starts to bog down and hesitate.

If I start to give it more gas (more than 1/3 throttle), it starts to bog down even more and I'm reduced to a crawl. Eventually, I can't even give it a little gas before it stalls. It seems like I'm flooding the carb or something, but that is just a guess.

So I approach a hill and I need to apply more throttle to try and make it up the hill and I am seeing the hesitation and bogging coming on and I'm not even going very fast. I'm literally inching my way up the hill on first gear, trying to make it to the top. I have to pull over a few times as it stalls when I try to give it gas and I'm only barely moving.

So I'm stuck on the side of the rode trying to make it up the moderate hill, feeling like a chump. I end up turning off the bike for maybe 2 minutes tops. And when I crank it up, it starts fine and I'm able to ride at minimum throttle through all four gears and it is not hesitating (!). But as soon as I try to get over 30 - 35 mph (by applying more throttle) I can feel the hesitation start so I have to back off because I don't want to stall out again.

So by riding on minimal throttle and not going over ~ 30mph, I'm able to get home fine and it's running good with no hesitation.

I am thinking there is an issue with the main jet or the air fuel mixture.

So do you think I'm flooding it when I apply the throttle over 1/4 turn of the wrist?

[prismways]

So as I am reading up on this symptom, I see people say it's more of a running lean situation. But why would it get so bad that I'm reduced to literally having to push my bike along after it bogs to a crawl and I'm trying to accelerate from a stop.

So if I'm lean at the high end, should I increase the jet? or increase the air / fuel mixture?

My idle is perfect and consistent at 1500rpm. I do notice that when it bogs down and I am stuck on the side of road, my idle is higher at 2K but it is very consistent and no sputtering.

[prismways]

Here's an image of my spark plug. It doesn't look too out of the ordinary compared to the chart below: