bogging @ 1/2 to full thottle By oldbikerarlo (Read 3,000 times)

[oldbikerarlo]

 Ok my gy6 150, I did aBBK 170cc, 30mm carb with 125 main jet and uni filter. big valve head, I had a 4mm stroker crank installed but have gone back to the stock crank. (Didn't like the vibration). I have an A9 cam. and a high flow exhaust. It excellerates great to 1/2 throttle, then falls on its face, till I back off, I can get to full throttle but real slowly, a little at a time. So am I needing more jet? less jet?

[alleyoop]

Go down on the main jet, try a 120 if still to much try a 117.5 etc.. When you open the throttle the 30mm is letting a lot of air in. That is why if you back off and slowly throttle up it settles down some.

Just to give you a good reference my motor is bored out I have a 62bbk and a 60mm stroker 2+ 182ccs from 149.6. I have a 24mm carb with a K&N filter and a 122.5 main jet and a #38 pilot jet. I tried a 125 to start and it was to much it would start popping at around 50mph.
Alleyoop

[oldbikerarlo]

Thanks Alley, I had to drop down to a #115 jet and its running just a touch fat. But I'm going to leave it at that, I live in Tucson Az. So the engine gets a lot of heat off the road. Thanks again

[alleyoop]

Great! probably the right jet is a 112 for that puppy but at least the 115 you are sure it is not running lean.
Good job ride safe.
Alleyoop

[geh3333]

Aug 27, 2014 20:56:43 GMT -6 oldbikerarlo said:

 Ok my gy6 150, I did aBBK 170cc, 30mm carb with 125 main jet and uni filter. big valve head, I had a 4mm stroker crank installed but have gone back to the stock crank. (Didn't like the vibration). I have an A9 cam. and a high flow exhaust. It excellerates great to 1/2 throttle, then falls on its face, till I back off, I can get to full throttle but real slowly, a little at a time. So am I needing more jet? less jet?

what type exhaust is on your scoot ? And how r u oiling the uni ? A 115 is light for your setup . Also what type of 30mm carb do you have . I been working with another with a 170cc setup with a 30mm carb and he is also having a problem running rich , but his is bogging with a 115 . I'm starting to thing some of these 30mm carbs are not a true 30mm cast . For example I have a 32 mm carb on my 58.5 setup and I'm running a 125 main and it's running perfect , just slightly rich . I'd like to take a look at these 30mm carbs that r being sold . Also 115 mains are used a lot on setups without a bbk or a bigger head . They are often used when upgrading to a uni and a high flow exhaust . I wouldn't be concerned however with a bigger carb and your setup you should be able to pull more air and fuel " that would give u an increase in horse power"

[alleyoop]

The huge difference is the weather and Arizona is hot hot hot and in those temps you have to cut down quite a bit on the fuel that is why someone with the same or similar setup may have a different jetting due to where they live. Motors to run right need more fuel in cooler climates and less in hot climates.
In places where temp swings are around 20-30 degrees and your carb is set for cooler weather you will find that if the temps rises the motor looses power to much fuel or may even struggle and may be necessary to tweak the Fuel Ratio Mixture for the temp change. If your carb is set for hot weather 70+ and if the temps drops down 60s and below, it will run lean.

So a carb jetting setup depends a lot on the type of climate you live in as well as elevation type of air in your area, a Hot Climate Less Fuel, Cool Climate more fuel. Now a 30mm carb feeds more air and fuel than a smaller carb. So a 115 main jet in a 30mm carb feeds more fuel than it would in a 24mm carb, bigger carbs have bigger passages . A 150 stock with just a free flow exhaust and filter and a 24mm carb will work good with a 115 main jet and normally a #35 pilot jet.
Alleyoop

[geh3333]

Here in many US states " including pa" it also reaches 90+ degrees so that desent explain the reason the carb is running better with a 115 . This is happening to other members in other states then Arizona . Something is going on with these carbs . I've always said that a bigger carb will pull more fuel and air , but it only pulls more air at top end " closer to wot" If you have a 24mm with a 115 main and a 30 mm with a 115 main , many think the 24 mm will pull less fuel at bottom end but that's not true . The 24 mm will pull about the same as the 30mm at bottom end " this is with the correct pilot in both "38-39 for a 30mm and a 35 for a 24mm" now as the carbs reach mid throttle the 24 mm will still tend to pull the same amount of full then the 30 mm , it's not until you reach near wot that the bigger carb begins to pull more fuel through the main 115 then what a 24mm carb will . This has to do with the amount of suction that each carb pulls at bottom end and top end . The 24mm has more suction power at bottom end then the 30mm but as you reach top end the 30mm makes surpasses the 24mm suction buy bein able to pull more air at and fuel at a higher rate then the 24mm . My 32mm " even in over 100 degree weather still run very good " . There is something going on with some of these 30mm carbs or it could be that my exhaust is more " free flow " then most . There can also be a problem with some of the heads not being ported as good as my ncy racing head . There can be many reasons why it's not taking a bigger jet , even to much oil on a uni can cause this problem . A 115 being to rich on a 30mm carb " like the one it mentioned in my last post " is def not right and he is in cooler weather then Arizona . Also many of the bigger carbs have the accel pump at takeoff that helps the bigger carb near bottom end . So his carb is running right with the extra fuel at takeoff but at half throttle it Boggs ? " atleast I'm assuming it's was running ok at takeoff since he didn't mention it "

[alleyoop]

Nothing wrong with the carbs it is just to much of a carb for the motor is all. I will always disagree on having a 250 carb on a 150 it is overkill and creates nothing but problems. A 150 motor with a BBK would be more reliable and run better and make more power if the 24 or even a 26mm carb was on there and just up jet it. The ccs are not there to be able to take such big gulps of air and fuel, the motor is lacking about 100ccs for such a big carb so you will have problems trying to get the motor to produce. Sure you can get the motors to run with a big carb but it will be sluggish on takeoffs and getting up to speed. They have bigger defusers, different tapered needles and all this creates problems for a motor not capable of taking that much, so now you have a de-tune problem to much fuel and to much air.
Alleyoop

[JR]

I'll agree with this also by one simple principal and it's this. Same scenario as a water line. You take a 3" water line at a certain pressure and then measure the flow/output of the water then reduce the line to 2" and then take the same measurements and it's simple, the output is now what a 2" line will allow.

Use a 30mm and in some cases I read when people even put a 32mm carb on and then reduce the output with a head that is machined to 24mm. It's simple I don't care if you jet it to allow a 5 gallon bucket of fuel and if you even can get enough air flow and exhaust to handle the extra, you still can only put it through a 24mm entrance like trying to put a 500lb man through a 18" door, it's not happening.

So why not put the same amount of fuel and air through a carb with a matched outlet size? I mean even then one can put so much fuel through a OEM carb that they choke the engine down. Now you want to match it with a ported, machined and in a lot of cases four valve head open the exhaust and a nearly to nothing exhaust and free flow filter then yea you can do that but those people are racers and have short lived engines, do that to a normal everyday scooter, run it wide open and expect to be on the side of the road with a burned up engine at 2k in miles, doesn't make sense? Want more speed get a 250, want a scooter that will run 10k+ mildly tune it, PM it and ride it in a way it'll last.

These engines are no more than a simple lawn mower engine, not a complicated thing and they have just like a lawn mower limitations, hell you can even hot rod a mower and burn it up, people do it! Myself I have a old 1988 V-twin 14hp Craftsman mower that I still run every week with two work cart wagons behind it for my yard tools/work and it uses a little oil but it'll start any time of the year and my other two mowers and even maybe it will outlast me but they've been run accordingly to their limitations and took care of.

Got 4 scooters in all from 50cc to my wife and I's 250's, my 250B has over 15k in miles, still runs like a top wouldn't be afraid right now to get on it and head to California but it's been taken care of and at times I've run the piss out of it in brutal heat and for long stretches of 400+ miles a day but other than raising the needle in the carb and a little cooling mod help along with good PM it's been left alone.

If I decide I want a scooter that can run 80+ MPH all day long I'll get a Silverwing.

JR

[geh3333]

You have to first have experience when fitting a bigger carb to understand it's possibilities , these scoots have way more potential then you two think . This is the first time I've seen others have problems with a 115 being to rich with that type of setup . A 120 -122 main jet should be no problem on their setup . Pulling more fuel and air through a head is one way to up horsepower " this is common sense for any mechanic" . It's been proven that even a 32mm carb can be used with great success on a 150cc based scoot . " been done more than once" many have also used the 30mm with great success " and that's with main jets bigger then 115. If it's not a carb problem then it is more then likely a head problem . 2 of the recent engines came from scrappy with the gy6200 head , and bothe have had problems with running too rich on either a 115 or a112. Whoever is doing the work on these heads are probably not doing a good job . And then our buddy here with a big valve head " which I'm guessing might be the cheap one off of eBay who many have said was not worth buying" and it's only taking a 115 with a 30 mm carb ? It's obviously a problem other then " over carb" . Then again if it comes down to the heads not being able to handle the bigger carb then it is an over carb problem , but that's due to bad quality head work.

[geh3333]

The problem with your theory jr is that you have never measured the amount of air and fuel that any 150 scoot" stock or with mods" can pull through the head " wether it's a stock head or an ncy racing head with bigger intake and exhaust ports" so you can't say what carb is to big or not . You have to go out and prove it like I did. After my variator issue was fixed my scoot just about pulls the front wheel up at takeoff " just like with my old Koso on there" my 24 mm carb wouldnt even take a122 main because it was too restrictive " not pulling enough air" but he 32mm took a125 and runs like no other with a58.5 bbk . . You don't see many running at 67mph although I have seen some with a 32mm efi with a 58.5 bbk run over 70mph . And this is all on straight runs .

[JR]

Sept 14, 2014 16:30:21 GMT -6 geh3333 said:

The problem with your theory jr is that you have never measured the amount of air and fuel that any 150 scoot" stock or with mods" can pull through the head " wether it's a stock head or an ncy racing head with bigger intake and exhaust ports" so you can't say what carb is to big or not . You have to go out and prove it like I did. After my variator issue was fixed my scoot just about pulls the front wheel up at takeoff " just like with my old Koso on there" my 24 mm carb wouldnt even take a122 main because it was too restrictive " not pulling enough air" but he 32mm took a125 and runs like no other with a58.5 bbk . . You don't see many running at 67mph although I have seen some with a 32mm efi with a 58.5 bbk run over 70mph . And this is all on straight runs .

One you do not know what I have or have not done as far as any set up on any engine. I was working with anything from trip deuces to double 4 barrel holleys on engines in the 60's so lets stay away from assumptions and stay with facts.

My theory as you stated was based upon a stock scooter and not a BBK which is not what this poster has and I should have stated that, my bad. But in theory it still holds that once a person reaches a certain threshold as far as fuel/air/exhaust is concerned then bigger can actually be worse. BBK isn't this giant leap like some assume? Standard piston is at 125cc = 52.4mm and only a touch more at 150cc and 58.5mm isn't even noticeable with the human eye so again you can only put so much fuel/air to it and that's a mathematical equation that holds true and you don't have to be a certified mechanic to know this.

Now if you're making it work for you with your set up than that's fine and dandy, good deal but it doesn't say it's works the same for everyone on every engine in every place, not rocket science and having a discussion on what, how, when and why is all great but lets keep it to "this is what works for me and you might give it a try"

Also temps along with altitude and humidity do influence any engine. Today it was in the low 50's here at my house this morning and I took my 250 fro a spin and with cooler temps and lower humidity she really ran sweet, couldn't say the same thing a couple of weeks ago when I rode 30 miles to Conway at 94F. It does make a difference with these factors in the equation just as much as how these engines are set up. You say there is a quality difference in things made such as carbs, won't disagree with you one bit on this possibility. I've got two of the 250's both exactly to the same except what they are called, exact same engines and set up to the last bolt and yet my 250B will out run my wife's 250A plain and simple. Why? Don't have a clue?  

JR

[minesweeper]

Sept 14, 2014 16:30:21 GMT -6 geh3333 said:

The problem with your theory jr is that you have never measured the amount of air and fuel that any 150 scoot" stock or with mods" can pull through the head "

OK, I can't keep my mouth shut. I guess you have a dyno with intake monitors? You know, the several million dollar kind? I know engineers that did testing at the Harley facility in Talladega Alabama and I have been to the testing facility several times. You do not have the kind of equipment to intimate you measured the volume of air flowing through a head. And to suggest guys like JR and Alley just haven't experienced enough to know what's going on is unfathomable. They were at the track in the 60's son....the six-tees. They've both been inside engines up to their eyeballs, all kinds of engines, countless times. They know how they work, all of them, including the GY6. Show respect where respect is due, these guys earned their creds.

[JR]

Sept 14, 2014 16:30:21 GMT -6 geh3333 said:

The problem with your theory jr is that you have never measured the amount of air and fuel that any 150 scoot" stock or with mods" can pull through the head " wether it's a stock head or an ncy racing head with bigger intake and exhaust ports" so you can't say what carb is to big or not . You have to go out and prove it like I did. After my variator issue was fixed my scoot just about pulls the front wheel up at takeoff " just like with my old Koso on there" my 24 mm carb wouldnt even take a122 main because it was too restrictive " not pulling enough air" but he 32mm took a125 and runs like no other with a58.5 bbk . . You don't see many running at 67mph although I have seen some with a 32mm efi with a 58.5 bbk run over 70mph . And this is all on straight runs .

Yes I did see your straight run:

Watched it 3 times to make sure I was seeing it right, ya kind of have to pay closer attention at my age. :-/This was indeed a nice downhill run George and at almost 1000ft above sea level in Masontown and the temps down on that cloudy day you could for sure get a good run.

You know I live in the hills (Ozarks) and I can even get my old stock Bali to haul butt down Petit Jean Mt. which is in my front yard.   Air was good that day and it helped your scooter some. But bring it out here on a good old hot 95F with 80+ humidity day here in Arkieland and get on it and give it a go, I'll even find you a "perfectly" flat spot to give it a run and then you can for yourself see how other conditions effect a engine, hell at 95F plus with that kind of humidity it'll even effect you.

JR

[minesweeper]

FLAT! Is that what he said?! George.....come on man, we didn't just fall off of the turnip truck. The road is going down into a small valley, it's called negative incline :

Bravo for getting a 150 up to 67 going down a ski slope.....I mean downhill.....I mean a flat surface. It takes quite a bit of something to go 67 on a scooter.....especially in a 30MPH zone. Well thanks for an enjoyable video. Is your next one about how you invented the internal combustion engine? I can't wait to see it.