Backfire Flame + Bogging + High RPM By motley (Read 1,319 times)

[motley]

Tittle says it all other than I'm not really getting anywhere with speed.


The engine was sold to me from Parts For Scooters as a engine that was ready to go other than gear oil and engine oil. 
I have done what I can, anything in depth "Taking apart the engine" would require me to pay movers to ship the scooter to get it worked on "45 mile trip there and 45 miles back ". 

I don't really know as to what the problem would be other than air and fuel at the carb. As well the air filter, as well my exhaust is not stock. Everything is technically the exact same setup. Other than I played with the air fuel mixture idle whatever screw...

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Any help with this at all would be highly appreciated!

[motley]

I was capable of getting my hands on some main jets. I swaped the stock one out for a 90, and that was seemed to remove a clucking like sound. There's still a backfire.

I also ran some test on the variator. The variator is not engaging to the belt unless the rpm's get close to 6,000, then it attempts to move. I tested some sliders that where 6 gram, They moved the variator outward at 4,500 rpm's, but that's not good enough. So I found a cheap set of rollers that are 8.5 gram. This will give me a little safety on rpm's. As well should give me some speed instead. Hopefully my problem will be fixed when that part comes in.

I'm still playing with the carb kinda. My stock air box would not fit and I just started using this version today:

Seems to be working fine now. I'm just trying to find the right setting for the throttle body, pin, or whatever you call it, I have it set to dead center at the moment 

[lostforawhile]

is this a 50? you need 4.5 or 5 gram rollers your rollers are way to heavy,you have flames because you are too rich

[lostforawhile]

you have the weights backward, these engines are supposed to run at high rpm, heavier rollers will keep  it from going into the highest ratio, and it will basically stay in low gear, the variator doesn't "engage the belt" the belt is always engaged, the clutch engages at a certain RPM. Also your main jet is too big, why won't the air box fit? they run best with the stock airbox, heavier rollers will work with an engine that has more torque, such as a BBK, but not  stock 

[motley]

Thank you Lostforawhile for responding, It was sold to me as a 50cc... So far it's proving to me to be something else otherwise.

I changed the jet to a lower jet to retest it, and it honestly ran worse, the clucking like sound increased in density, even with the stock airbox rigged on. Number #90 on upjetting seems to do the trick, I reset the pin to dead center, part of the throttle body I think is what it's called? sorry :/.

Well with the rollers, it came with 5 gram. And the rpm's instantly hit 4k before you even start moving. It's also time to start inspecting those little springs on that stock clutch. At 4,000 rpm's I am only going 5 mph.. That's so wrong.. I then told myself it's time to inspect the cvt area while the bike is running. And sure enough, the variator does not engage unless it get's close to 5,000 rpm's. And it sounds terrible. It slightly reminds me of a weed eater running with no string on the head..

I ordered a simple cheap set of 8.5 gram rollers, not really name brand, but it will really be good for testing. I don't live in the city so low rpm's and higher top speed on these long country roads will work out. Let alone Low rpm's on a break in would be much better D:.

The stock airbox issue.. The engine I ordered was hardly half an inch longer than mine and the bolts don't meet up.
Even if I created a custom mount to bracket to the cvt area, then that mount to the airbox, the rear spring has a slight angle that pushes into the airbox in the rear now. I would have to slightly heat it up with a heat gun in attempts to reshape it just a little. Seems like a hassle so I intend to just order a new stock one latter on "Trying to cut all of this spending atm"

Also the flames are gone after up jetting. It was kinda cool to see for a second, but i feared it D:

*Please keep in mind I am not a mechanic, I just happen to be mechanically inclined D:

[lostforawhile]

it sounds like you are trying to put a long case engine on a short case frame, there are two styles of 139 QMB, the engine is supposed to hit high rpm before the clutch engages, that's perfectly normal, they run around 10,000 rpm normally. the engine will rev up, then the belt will gradually shift from low gear to high gear, and accelerate, but the engines rpms are supposed to stay up, it's a CVT transmission, not a motorcycle with gears. Forget everything mechanical you might know about engines, these are not cars, and they aren't motorcycles, so most of what applies doesn't transfer over. the 5 gram rollers are fine, the normal range on a 139 QMB is around 4.5 to 6 grams depending on rider weight and when you want the variator to move, the weights you have are too heavy and will bog the engine. On acceleration the engine will rev way up, then will stay high while the belt shifts between pulleys to accelerate the scooter then levels off , I don't know whats going on with the jetting but the 90 is dumping even more fuel then the 88 and should make the flame issue worse, I have a 63cc version of the 139QMB,  with a non restricted exhaust, and I can't even run a 90.  As far as your clutch, it's centrifugal it's not supposed to engage until the rpms go up, did you change your contra spring on the clutch? or the clutch engagement springs?   it sounds like it has racing springs installed, is this scooter new? or used? it's possible someone swapped them, if they did, you need stock engagement springs and maybe a blue contra spring 

[motley]

Yep that's what accidentally happened I installed a longcase when I had a shortcase. My scooter has the 10 inch wheel which required me to use a pry bar to pry into the tire to be able to remove|install the wheel and tire. And I sadly did not know much of what I was doing when I ordered the complete engine. I have to get my swing arm modified as I can not find a replacement for it.

I do promise you that these rpm's the bike hit's are not normal on take off D: . My last engine I finally stopped worrying about red lining the rpm's. 4 months latter blown motor. the entire insides sounded like everything flew apart and broke. my weight jumps between 150 - 180 a lot. Also.. It looks like someone did that thing to the variator where they put it on a device and it starts spinning and the remove a layer of the face. The variator itself is extremely light. I'm sorry but something tells me to use heavier rollers.

As for #90. non stock exhaust, and I have that non stock air filter. Probably has something to do with it.

I did nothing to the engine modification wise, But what you said told me the name of what I meant, "clutch engagement springs". I plan to take the clutch off today to inspect to see what range of rpm's they are set for. I failed to look at the contra spring. but I never seen any interesting color other than black. so it might be stock, no clue yet haven't looked.

The scooter is old, it's a 2008. I intend to possibly sell it once I get it where I want it. Then just buy a new one.

This is the motor I installed www.partsforscooters.com/Engine_longcase_4-stroke_qmb139?sc=31&category=133210

[lostforawhile]

The spring colors usually designate the strength of the contra spring,blue is just above stock, the three clutch engagement springs should be stock springs for most uses, the race ones require you to rev the engine to engage the clutch. If it came with the engine assembly they are stock. Don't worry about the engine rpms, you had a mechanical failure,it happens, but they need to rev up to be in their designed power band, they are like big weed eater engines. It's nerve racking but it's what they are designed for,and sometimes chinese engines blow up,it's just what hapens,break the engine in right,then run good synthetic oil,and keep it changed

[motley]

I was capable of looking at the contra spring color, it has that standard charcoal black color so it is probably just standard. I failed to look at the engagement springs as that was a vital inspection. I have blue ones stored away that I got with a kit. I think they said they were 1,500. Could be wrong.

I happened to install the 8.5 rollers, they have a real nice takeoff speed, The rpm gauge hit somewhere around 3,500 rpm's once the variator started moving forward. If they are stock engagement springs this is about accurate now where as before the variator would start engaging at 5,000 rpm's. and it would peak out in a scream and never made it to the flywheel like thing at all, it hardly moved. sorry I don't know the name :/.

So I could use possibly 6.5 grams. That would probably work out great. but once this break in is over I would really like to put the stock rollers back in for one last test. I just prefer to keep things low during the break in.

I think after my break in oil change I am going to run Castro gtx in the engine. Every engine rebuilder I know only uses this brand. I kinda want to do a secondary break in where I drive it normal, but I want to get a little hard on the engine more often. After this I might consider the synthetic. My only focus is a proper break in, I might finnaly drive the scooter however after the fourth oil change honestly.

Besides, Once I start running synthetic in the engine, It's going to be another break in all over again technically. I just personally don't think it's wise with how I drive.. I drive really hard on these engines typically 7 miles without even stopping. It's going to take some time, but I honestly sadly fear synthetic from past experiences. I'm getting anxiety from thinking about it D:

[lostforawhile]

the reason you run synthetic in an air cooled engine, is it can handle much higher heat then standard oils, you only have one break in period , this allows the parts to wear together, such as the rings to the bore, the cam shaft, valves to their seats etc, there is no second break in, once the parts are worn together, they are worn together, even briggs and stratton is going synthetic, you run regular oil for the first 1000 miles and vary your speed, no extended runs etc, the regular oil allows enough friction, for the parts to wear together, you change it at 500 miles, then again at 500 miles, then change to synthetic, the synthetic is so slippery you can't break in parts on it, this is good once the engine is past break in. Also the 139qmb chinese engines, call for 15-40 which is heavy duty diesel oil. the typical powerband you want these engines to run in, is about 8,500 rpm, they have no torque, so you have to keep the rpms up to get it to move properly

[lostforawhile]

see if this helps understand your CVT 

[czmdiver]

This thread is some hilarious comedy. keep it going please
Something like the blind leading the blind and dumb and dumber put together the only thing is i can't figure out who is who.
The plethora of misinformation and total bunk is deep and a indication of the pathetic state of our Youth...

[motley]

Okay, I want you to take the time out and quote everything that's wrong.

If a synthetic break in sounds wrong to you then that's bad. Once you convert to synthetic your not supposed to change back to conventional oil. The engine has to create a build up or whatever, I can bring out my documentation if need be, I prefer not to as I just got off from work. This goes far in depth.

I hope your not on of those guys on those forms that make people feel dump D:. If so kick me and ban me from here

[lostforawhile]

That's a myth from the early days of synthetic oil,and no one said go back to conventional oil,you break in an engine on conventional,to allow enough friction for the break in process. Then switch to synthetic and stay with it,

[lostforawhile]

Jan 25, 2018 12:15:15 GMT -6 czmdiver said:

This thread is some hilarious comedy. keep it going please
Something like the blind leading the blind and dumb and dumber put together the only thing is i can't figure out who is who.
The plethora of misinformation and total bunk is deep and a indication of the pathetic state of our Youth...

what the screw is your problem?