Couple issues noticed after BBK

[coal]

After a tough fight learning and figuring out how to install a BBK I did it. Tuned it how I could with what was available to me. Bike runs much better and I feel much safer riding it on the street. There is however a couple of issues I am running into that my lack of experience can't help me. Here is what I have installed so far.

This is a ATM-50-A1

82-85 BBK

Kei-Hin Tunable Carburetor

Some Jettings

Replacement Ring for Exhaust

Tachometer

Rocker Assembly

Head Assembly

So far all of this runs rather well I believe, but two issues arise. One during 1/2 to 3/4 throttle especially after trying to accelerate from low speed the engine feels like its kicking a little. Like it loses power for a split second before returning to power. I notice the engine adopts a lower tone for a moment when I feel that kick. WOT and idle feel just fine with no issues. I have tried adjusting the diaphragm which it was set at the center. Move it up one position leaner and the engine adopts a hollow like sound and rpms shoot up with no moving of the bike. One position richer and it I don't know maybe just my mind but I feel that it performs a little worse but it still functions. Wondering if anyone knows what is going on so I can work on it.

The other issue is the high fuel consumption. I do understand that by definition of a BBK that it will use more fuel than it would before, but at the rate it is consuming it now I feel like that is an issue in itself. Anyone know what I should do to figure out if it is an issue or just what my engine now consumes.

I believe I am still in the break in period so not sure if that will have any noticeable effects on the aforementioned.

[gsx600racer]

I would suggest lowering the clip(raising the needle(richer)) vs moving the clip to a higher slot(lowering the needle(leaner)).

Doing what you did made it leaner. Better to error on the rich side vs lean side.

2nd, you might want to play with the pilot and main jets. Seeing this is a "fresh" build. I would run it some and keep an eye on the spark plug(color). Give the engine a chance to break in, then play with the tuning.

[coal]

Sept 20, 2018 13:57:49 GMT -5 gsx600racer said:

I would suggest lowering the clip(raising the needle(richer)) vs moving the clip to a higher slot(lowering the needle(leaner)).

Doing what you did made it leaner. Better to error on the rich side vs lean side.

2nd, you might want to play with the pilot and main jets. Seeing this is a "fresh" build. I would run it some and keep an eye on the spark plug(color). Give the engine a chance to break in, then play with the tuning.

I can try the jets a bit more but I am running an 83. The next one I have is an 85 and that floods the cylinder.

[ratdog]

OK, I know your all waiting for this... run your bike at WOT as much as possible and as little idle as possible for a few miles, the pull the plug and post a pic of the tip. We are interested in the “white part” of the pit of the plug. This will give us an indication of where your mixture is. Are you using premium gas? A BBK needs at least 91 octane, and I prefer 93 octane. If you have 5 or more hours on the engine, oil is very cheap. Change your oil and veryclosly examine your drain oil. Best to look in the sun. We are looking for little silver flakes. If you don’t see any, things are good

[coal]

Sept 20, 2018 22:47:22 GMT -5 ratdog said:

OK, I know your all waiting for this... run your bike at WOT as much as possible and as little idle as possible for a few miles, the pull the plug and post a pic of the tip. We are interested in the “white part” of the pit of the plug. This will give us an indication of where your mixture is. Are you using premium gas? A BBK needs at least 91 octane, and I prefer 93 octane. If you have 5 or more hours on the engine, oil is very cheap. Change your oil and veryclosly examine your drain oil. Best to look in the sun. We are looking for little silver flakes. If you don’t see any, things are good

Thanks I do believe I am running a rich setup Plug is covered in black carbon like substance but is easily wiped away. It is also not wet at all. I have to change the oil because it appears my fuel is leaking into it making it thinner and less viscous. I don't know if this is an issue that will resolve itself or if there is something wrong with the rings. Otherwise after running it for awhile I do not see very much if any silver particles after the first oil change. I will check again today after changing the oil since ive been running it off and on for a week totaling 3 hours. If there is anything else you need to know please tell me. I do want to make this bike run right and last for quite awhile.

[coal]

One other note I replaced the airbox with a cone filter and ran it with a 85 jet. I did not notice any of those stuttering issues I felt. So I am wondering what is going on with my previous setup. Do I need more air for those middle ranges. If so why does adjusting the needle toward slightly leaner take away my power. Still working on the oil change as of now.

[micscience]

I run my main jet a lot higher than 83. 83 seems more like a 50cc scooter size setup that is what I find in most 50cc scooters. I think my main jet is at 90. I haven't fully tuned my carb but it has ran fine. I got the carb with a 93 so I lowered it a bit.

[coal]

Sept 21, 2018 18:53:05 GMT -5 micscience said:

I run my main jet a lot higher than 83. 83 seems more like a 50cc scooter size setup that is what I find in most 50cc scooters. I think my main jet is at 90. I haven't fully tuned my carb but it has ran fine. I got the carb with a 93 so I lowered it a bit.

I'm running 85 now. Feels okay. I do have a 90 but I'm not sure if I need it. I'll keep messing with it and see what runs better for me.

[kavandershadow]

I have a 50mm BBK installed on my scoot, and had running issues at first too; although mine issues were at idle to mid throttle. I had an 83jet, the original 50cc carburetor and stock air box. Stuck a pumper carb w/auto choke, cone filter and a 90 jet. Runs mint now.

[ratdog]

You plug is your view into the bike. That’s why I keep asking posters to take a pic of their plug so we can see it. Messing with the jetting is of little value if you don’t know where you are. The pod filter will lean the bike out a good deal. If you were running rich, and put a cone fileron it, it would run a good deal leaner.

The biggest indicator of running rich it your engine RPM. With correct jetting your engine might run an easy 8500 rpm. Put in too rich a jet, and suddenly the engine might fall on its face when it hits 8000 rpm.

A too lean engine will often back fire when you close the throttle, will run much hotter, and often will have a “lean surge” when opening the throttle suddenly ( the engine will bog then catch)

I think you mentioned you ran a compression check, what was that compression? I’m sure you know, but when you run the compression check, you should hold your throttle wide open.

Your needle position only effects lower/ mid RPMs. Once your engine is above about 4500 rpm it no longer will have a measurable effect on the engine preformance. Your mixture screw only effects idle speed mixture. While this will effect starting ( most of these bikes start best with the throttle closed) it has no effect on your high speed preformance.

Do you have a stock ignition in the bike? I have found that most aftermarket CDIs make the bikes much harder to start.

also what octane gas are you running?  A correctly installed BBK will greatly increase the compression of you bike.  Run no lower then 91 octane and frankly, I would run 93 octane

[coal]

Sept 23, 2018 8:01:47 GMT -5 ratdog said:

You plug is your view into the bike. That’s why I keep asking posters to take a pic of their plug so we can see it. Messing with the jetting is of little value if you don’t know where you are. The pod filter will lean the bike out a good deal. If you were running rich, and put a cone fileron it, it would run a good deal leaner.

The biggest indicator of running rich it your engine RPM. With correct jetting your engine might run an easy 8500 rpm. Put in too rich a jet, and suddenly the engine might fall on its face when it hits 8000 rpm.

A too lean engine will often back fire when you close the throttle, will run much hotter, and often will have a “lean surge” when opening the throttle suddenly ( the engine will bog then catch)

I think you mentioned you ran a compression check, what was that compression? I’m sure you know, but when you run the compression check, you should hold your throttle wide open.

Your needle position only effects lower/ mid RPMs. Once your engine is above about 4500 rpm it no longer will have a measurable effect on the engine preformance. Your mixture screw only effects idle speed mixture. While this will effect starting ( most of these bikes start best with the throttle closed) it has no effect on your high speed preformance.

Do you have a stock ignition in the bike? I have found that most aftermarket CDIs make the bikes much harder to start.

also what octane gas are you running?  A correctly installed BBK will greatly increase the compression of you bike.  Run no lower then 91 octane and frankly, I would run 93 octane

Sorry for taking so long to get back to you. I changed the oil and adjusted some things then took a picture of the sparkplug as it is now. It is no longer black with that carbon like buildup. Now it's this dull Grey color. I removed the baffle from my airbox so it's letting more air in. Idle jet is 33 and main is an 85 I'm at 7000ft altitude. It feels like it runs well and that bogging or kicking issue no longer appears. No I didn't do a compression test I just checked it it compresses at all using my hand to check for pressure. I'm not sure what the pressure it gets to. Diaphragm is a notch into a more rich setting. Hope that's everything you asked for.

[ratdog]

Ok, your looking at the wrong thing. You need to look at the insulator “white part” not the electrode. It should be tan in color.it maybe that you just don’t have enough miles on it, but right now it looks very lean. I would go to your next bigger jet size and get some time on it. Try to get a bunch of WOT on it with little idleing and pull it again. Just a personal thing, but I would not use a resistor plug next time.

I will be honest, at 7,000 ft, that seems very rich, but the plug tells the tale

[coal]

Sept 23, 2018 20:29:42 GMT -5 ratdog said:

Ok, your looking at the wrong thing. You need to look at the insulator “white part” not the electrode. It should be tan in color.it maybe that you just don’t have enough miles on it, but right now it looks very lean. I would go to your next bigger jet size and get some time on it. Try to get a bunch of WOT on it with little idleing and pull it again. Just a personal thing, but I would not use a resistor plug next time.

I will be honest, at 7,000 ft, that seems very rich, but the plug tells the tale

Okay I see thank you. I'll ride it as it is now before switching just to make sure. My next bigger jet is a 90 so that is a really big jump.

[ratdog]

Well that big of a jump, if your bike was jetted right, would chop a good deal off your max RPM. Let’s say you pull 8500 rpm now, if you were currently jetted right, the move to the 90 would chop you max RPM to 7500-8000. I. Would do the 90, and see if it hurts your top end any.

The very best preformance comes from a slightly lean mixture. But we are not dealing with drag bikes here. Better to go richer and let your engine run cooler, and maybe last a little longer

[coal]

Okay I suppose I can try the 90 tomorrow morning and see what happens. Will return with results.