New Boom Vader - Need help converting to Mikuni carb

[veezx20]

Your air idle has nothing to do with higher throttle, like i said anything after 3/4 is your main jet. You cant effectively diagnose from the plug unless your doing a plug chop, to do that you need to run it where the main jet takes over and kill the engine amd pull over and pull the plug.

[ QUOTE=prismways;253198]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.[/QUOTE]

[veezx20]

Go bigger on the jet!

Originally Posted by 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]

Yeah, I'm starting to think it something to do with range from 1/8 to 3/4, which points to the Needle Jet and Jet Needle. I know I can adjust the clip to move the needle up or down to increase or decrease amount of fuel.

When I looked at the current setting, it is on one rung above the lowest rung on the needle so that tells me it was set to run a little richer (probably due to the carb being sold as a kit with cone filter)

Originally Posted by veezx20

Your air idle has nothing to do with higher throttle, like i said anything after 3/4 is your main jet. You cant effectively diagnose from the plug unless your doing a plug chop, to do that you need to run it where the main jet takes over and kill the engine amd pull over and pull the plug.

[ QUOTE=prismways;253198]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.

[/QUOTE]

[prismways]

Are you suggesting to increase the main jet size from 100?

But I am thinking it's in the mid range where the Needle Jet and Jet Needle are the main drivers.

What is interesting is that it had ran fine for a few miles before it started exhibiting stalling symptoms. And if I let it "rest", it would allow me to ride further, but at a diminished throttle level.

Originally Posted by veezx20

Go bigger on the jet!

[prismways]

I will also look into this:
=========================

Phantom out of gas issue

http://www.vn750.com/forum/22-carbs-...revention.html

[veezx20]

Dude pod filters increase the air a shit ton, go up on the jet and see how it is, if it was the needle it would sputter but 3/4 to full would be fine as your not running on the needle circuit that much at that point. Throw a bigger jet in and see, trial and error my friend. I have kz650 with 4 carbs i put bigger cams in and a 4in1 exhaust amd modded my airbox, not once was my needle my big culprit it was always the jets and yes at that point you fine tune by moving the clip on the needle, your deff running way lean to cause it to die out.

Originally Posted by prismways

Are you suggesting to increase the main jet size from 100?

But I am thinking it's in the mid range where the Needle Jet and Jet Needle are the main drivers.

What is interesting is that it had ran fine for a few miles before it started exhibiting stalling symptoms. And if I let it "rest", it would allow me to ride further, but at a diminished throttle level.

[prismways]

I hear you. The jet was at 120 previously and still had hesitation issues.

will make sure I try all possible options. I honestly think there is a fuel delivery issue.

thanks

Originally Posted by veezx20

Dude pod filters increase the air a shit ton, go up on the jet and see how it is, if it was the needle it would sputter but 3/4 to full would be fine as your not running on the needle circuit that much at that point. Throw a bigger jet in and see, trial and error my friend. I have kz650 with 4 carbs i put bigger cams in and a 4in1 exhaust amd modded my airbox, not once was my needle my big culprit it was always the jets and yes at that point you fine tune by moving the clip on the needle, your deff running way lean to cause it to die out.

[jacaquarie]

As I read your symptoms of starting to bog down at open throttle for any length of time am inclined to think fuel supply. Almost as if the tank is not venting and holding the vacuum or negative pressure on the fuel. Try a ride with fuel cap off or loose. If that works look for clog in fuel cap air vent.


Good luck.

[veezx20]

My bike was experiencing vacuum lock, but it didnt matter how much throttle i gave it, when it locked it was dead, i found the egr was installed laying on its side as they dont mpunt it correctly and the check valve was closing not letting and pressure by, i removed all emission items and still have a junk carb that came with the bike. Waiting for my replacement......

Originally Posted by jacaquarie

As I read your symptoms of starting to bog down at open throttle for any length of time am inclined to think fuel supply. Almost as if the tank is not venting and holding the vacuum or negative pressure on the fuel. Try a ride with fuel cap off or loose. If that works look for clog in fuel cap air vent.


Good luck.

[prismways]

I am almost 90% sure the stalling is due to a gas tank vent issue. (Not sure it is a vapor lock issue, although it is similar results)

Yesterday, after tinkering with the carb, I took it out for short spin and almost immediately, it stalled on me and I couldn't get it started again. It would crank and crank and even with the enricher lifted, it wouldn't start. I had to push it back to the garage. I gave up for the night. I did some more research and came across the gas vent issue.

In the morning, I came out and popped the gas cap and it started immediately. I came home from work and it started fine too.

So I took the plastic around the gas cap off and I saw the vent tube. I noticed that it was underneath the plastic instead of being thread through the opening of the plastic piece and it was not routed through a guide that was intended to hold the vent tube. I believe this caused the vent tube to be pinched by the plastic, resulting in the vapor lock. So I rerouted it and am keeping my fingers crossed.

It's raining here today, but am looking forward to going out for a ride when it stops so I can verify if I had resolved the issue.

I also took Veezx20's advice and increased the main jet to 125 and moved the clip my jet needle down to the lowest rung so that it will run richer.

It sounds a lot better and doesn't seem to hesitate when I give it gas, although this is in neutral and no load.

I will let you guys know how everything goes when I take it out for a spin.

thanks for all your help! I have quite a bit buying this cheap chinese bike instead of the Honda Grom. It's been a great learning experience.

Originally Posted by jacaquarie

As I read your symptoms of starting to bog down at open throttle for any length of time am inclined to think fuel supply. Almost as if the tank is not venting and holding the vacuum or negative pressure on the fuel. Try a ride with fuel cap off or loose. If that works look for clog in fuel cap air vent.


Good luck.

[Skin Mechanic]

Sorry for being late to the party. Ditto veezx20's suggestion to up jet, especially after you've installed the new exhaust. Sounded like you were running outta gas. In addition to the gas cap check everything else, fuel lines, filter, petcock, and inspect the inside of the tank with a flashlight for rust or trash. You may have gotten some bad gas, it happened to me twice with my old bike, it bogged down and stalled. I had to limp back home 40+miles in 3rd gear. I pulled the petcock and the filter screen was clogged with trash. Anywho, I had to go with a lager jet because I did an exhaust wrap and chopped 5 1/2" of the stock muffler and cored it out. Your exhaust choice looks good, kinda like the titanium cans on my aprilia. You'll have to post some pix of the install, and a video of how it sounds.

[prismways]

Yeah, it definitely felt like it was running out of gas, but I had a full tank. It would bog down when I tried to accelerate. The petcock and filter was brand new. The gas could be a problem but less likely.

On a different note, I looked at my exhaust and realized it's one continuous piece so not really sure how I'm going to install the new muffler. Most likely I will need to chop it up but still determining what is the best course of action.

I might try changing the front sprocket first.

Thanks for your input!

[veezx20]

I jist installed the ar low mount exhaust, you can get the old one out without cutting, you have turn the exhaust and work it out between the shock and swing arm. I ended up cutting tye head pipe of the stock exhaust and having it welded to the new one.

Originally Posted by prismways

Yeah, it definitely felt like it was running out of gas, but I had a full tank. It would bog down when I tried to accelerate. The petcock and filter was brand new. The gas could be a problem but less likely.

On a different note, I looked at my exhaust and realized it's one continuous piece so not really sure how I'm going to install the new muffler. Most likely I will need to chop it up but still determining what is the best course of action.

I might try changing the front sprocket first.

Thanks for your input!

[prismways]

Thanks for the tip. That looks great!

I would like to try and keep the exhaust up top, but if it's easier to cut and weld, I can take to a shop.

Originally Posted by veezx20

I jist installed the ar low mount exhaust, you can get the old one out without cutting, you have turn the exhaust and work it out between the shock and swing arm. I ended up cutting tye head pipe of the stock exhaust and having it welded to the new one.

[PhildoScaggins]

Originally Posted by prismways

I believe this caused the vent tube to be pinched by the plastic, resulting in the vapor lock. So I rerouted it and am keeping my fingers crossed.

I was having this problem yesterday. I could hear the tank squealing like a pig after even the quickest of rides. When I pulled the tank cover off the breather hose was pinched pretty bad. Took it on a 10 mi ride after and it had stopped/ running smoothly.