High RPM sputter/miss...? (7200) By mapbike (Read 12,030 times)

[mapbike]

Hello, problem solvers.....!


Rode my scoot to town this morning and when I settled in at about 7200-7300 RPM's @ about 50-52MPH everything was fine for maybe 3-4 miles and then it kinda sputtered and cut out, I backed off the throttle just a tad and it was fine, then I brought the RPM's back up to 7200 or so again and after a few hundred yards it sputtered again, it's the kind of miss that would make you think it is starving for fuel......shrug!

It has done this once before lately but it had never done it before until I changed my main jet up to a #115 from whatever the stock jet was, other than the jolting type miss it has started at those RPM's it's running fine, just a high speed high RPM intermitant miss that comes and goes not constant, but I know something isn't right somewhere.

This engine has approx. 2040 miles on it now and the valves have not been touched yet and I've never changed the fuel filter yet either, so could either of these be a possible area that I may need to address?

Thanks in advance for any & all input.

Peace, Shan

[JR]

Yes Mapbike both need to be done valves and filter even if this is not the problem they still need to be done with that many miles.

Another quick thing to check is the wiring connections on the CDI and coil? Sometimes a miss like this can be a bad connection at higher RPM's? Keep us informed.

JR

[mapbike]

Ok JR I will do asap, thanks for the quick reply....

[cruiser]

You may also be running a little rich. Would especially show up as the weather gets hotter. Here's an explanation of rejetting:

thescooterprofessor.proboards.com/index.cgi?board=carb&action=display&thread=183

[alleyoop]

Yes, he is running on the rich side, actually a 112 will fix the problem the 115 is to fat.
Alleyoop

[mapbike]

If that is the csae and I am running rich right now, matbe that will be taken care of when I get the Uni filter and the new free flowing shorty exhaust put on next week.

That should lean me out a bit and may fix this issue for me, as to the heat it has been 100+ degrees for the last 44 days here in central Texas, just broke a record set in 1952 yesterday if I remember right, hasn't been this hot this long since then.

So what do you fella's think?

Hold off on rejetting for now and see if the Uni filter and the Shorty Exhaust leans me up enough to correct the rich condition?

I will go ahead and change the fuel filter and I will also check the valve lash as well, I'm sure the valves are a bit tight after 2069 miles.

Shan

[alleyoop]

Yea, wait and see with the UNI that should lean you out some and be just right.
Alleyoop

[mapbike]

Thanks Alleyoop,

Thats what I'll do, it has never stumbled like that until I put the #115 jet in and then thats when it started, so I do believe you are right on with the rich condition diagnosis....

Thanks again all, Peace
Shan

[alleyoop]

You can verify it very easly, which it is, it is an old trick and very accurate and It works at all speeds.

When it starts to act up on you Just BACK OF THE THROTTLE a little maybe a 1/4 inch on the grip and HOLD it there.
A. If it Speeds up on you your LEAN
B. If it Hesitates, Sputters or Settles down your RICH.
Alleyoop

[mapbike]

Alley...,

When I just slightly back off the throttle when it sputters it settles right down and runs without a hitch, it only sputters/cuts out a WOT at above 7200RPM's and doesn't do it immediately it will run at that RPM for a short spell and then the jolting cutting out will happen, at that point like I said I can just back off the throttle a bit and it runs smooth as silk.

I believe you and cruiser both hit the nail right on the head when you told me it sounds like a rich condition, your description of what that will cause is exactly what my engine is doing.....

I'm gonna pull my spark plug and check it's color also, if it's fairly dark, this will be another indication of it being to rich also, I ordered the #115 jet from scrappydogscooters actually wanting a smaller one but his sizes take a big jump from what he calls "standard " to #115 then #125 & #135, I knew the 125 & 135 would be way big for a stock engine so I just went with the 115 hoping it wouldn't also be to big, I also have a #120 that I ordered from Steve @ monsterGY6 but I'm not gonna mess with it at first when I put the Uni Filter and the New Shorty Exhaust on, it could be that the #115 will work just fine with my near future set up and if it is just slightly small I will likey try to drill the jet to a size between the 115 & 120 and work with it until I get that nice light chocolate brown plug color and good throttle response.

I'm really hoping to get back the lost top end speed I have lost by creating enough power to get me back to the 60MPH flat out cruise speed, so far most of what I've done to my scoot has hurt my top end, when I got this scoot it would cruise easy at 60-62mph on the flat with no head wind or incline, now I have the orange CDI, the orange Coil, 12g equivilent roller weight, a gates 842 belt and the "performance" variator the scrappy dog sells, all of this has increase my lower end slightly and for sure helped keep the Rpm's and power up on the hills but I have lost around 8-10mph cruise speed, I weigh 198lbs so I'm not a heavy weight but not a light weight either and my weight is the same as it was when my scoot would run me 60-62mph on the flat.

I'm loooking to move my variator roller weight up to the 12.5g - 13g area and stiill have hill pulling power and maybe also get my cruising speed back to at least 58-60mph without having to turn 7500+RPM's to do it.

I know increase air flow through an engine with good compression and correct timing will add HP and torque so I'm hoping the UNI and the better exhaust will make at least a slight improvemnet that will help recover some of the top end I lost, my scoot came with 16 or 17g rollers and had a sluggish bottom end, I changed to sliders @15g and and lost top end and gain almost nothing at the bottom, still was sluggish IMO, I went with three10g rollers and three 14g rollers and my bottom end really came alive but at 12g equivilent weight I took a pretty big hit on my top end speed, I'm trying to find that happy medium where I will still have good bottom end without as big of a top end sacrifice.

Sorry for the long post hear, just wanted to explain what I've done to this point, what my results have been and what I'm hoping to achieve.

Thanks Alley.....

Peace, Shan

Jul 24, 2011 9:12:20 GMT -6 alleyoop said:

You can verify it very easly, which it is, it is an old trick and very accurate and It works at all speeds.

When it starts to act up on you Just BACK OF THE THROTTLE a little maybe a 1/4 inch on the grip and HOLD it there.
A. If it Speeds up on you your LEAN
B. If it Hesitates, Sputters or Settles down your RICH.
Alleyoop

Attachments:

[sprocket]

mapbike.. oil that UNI.. I keep seeing people running them dry and they wonder why they need a ring job every 1500-2000 miles...

The rule of thumb I have used for years is... go up 2 jet sizes for a free flow filter and 2 jet sizes for a free flow exhaust.

BUT

Thing have changed. If your stock filter is foam, you likely don't need to go up in size for the UNI

My experience is it is trial and error. If you get the carb dialled in you may gain about 3-5 MPH at WOT, but often I have found that the WOT will in fact be less than stock...

You will probably have better results tuning the CVT and shifting the power curve of the engine. These engines all seem to have a 'sweat spot' usually at about 85% WOT and you can shift this somewhat until you hit the CDI rev limiter...

But unfortunately anything you do to the CVT will impact either the top end or the take-off... the trick is to find a happy medium you like...

But your gains will not be great... there is no replacement for displacement...

[mapbike]

Yep, I have some very high quality Foam Filter oil that I use on my Nitro R/C trucks and buggy, and yes you are right about it be very important that the UNI or any foam filter be oiled with the correct oil..... this excludes K&N Filter oil because it isn't designed for foam filters and isnt tacky enough to be good in a very dusty environment.

My stock jet wasn't marked so I have no idea what size it is/was, I just ordered the 115 because other than "standard" that was the smallest scrappydog offered.

My stock filter is the round paper type for the under seat filter box(Hunter Style)...

If I can get the engine breathing a bit better I may work my way back up in roller weight a bit, I tried the 15g sliders with the performance variator and didn't like it much gained a bit of low end but lost a few MPH on the top, I put my stock variator back in and put some cheapy black rollers in and still had the same top end and made nice gains on the bottom end over the sliders and "performance variator".
I haven't tried every combination yet so I may still end up with sliders and the perf. var. in the end if I can find a combination that works with them but so far both of them decreased performance, still have some more experimenting to do though so those parts may work out if set up different.

I did try a 1500RPM main spring and hated the way the clutch performed with it, I waisted $15 + shipping on that thing, didn't help bottom end at all and cost me about 12-15 MPH on the top.....that was a big joke on my scoot for sure.

I'm leaning toward getting as much extra Torque from my engine as possible and finding my happy spot with variator tuning and possibly an 846 drive belt to help just a tad on the top end if I can stand heavy enough weights to see a benefit from the longer belt.

You're spot on......" no replacement for displacement "

I've built some pretty salty small block Chevy's back in the day and I never once got a 283 or 327 to pull like one of the 406cid small blk. Chevy's I built, more cubes = more torque and the torque is what gets you moving.......

Everything is determined by getting that sweet spot at the right place and then we just have to be content with knowing they are doing all they can do.

You're very right on every point you made here, thanks for the info. I'm all ears on these GY6 engines, I dont claim to know much about them yet, still a bit of a noob to them, I've been building and working on small engines for 30+years but each type has there own personality and I can see already that these are pretty good but also very limited in their stock form.

Thanks again sprocket.....

Peace, Shan

Jul 24, 2011 13:32:09 GMT -6 sprocket said:

mapbike.. oil that UNI.. I keep seeing people running them dry and they wonder why they need a ring job every 1500-2000 miles...

The rule of thumb I have used for years is... go up 2 jet sizes for a free flow filter and 2 jet sizes for a free flow exhaust.

BUT

Thing have changed. If your stock filter is foam, you likely don't need to go up in size for the UNI

My experience is it is trial and error. If you get the carb dialled in you may gain about 3-5 MPH at WOT, but often I have found that the WOT will in fact be less than stock...

You will probably have better results tuning the CVT and shifting the power curve of the engine. These engines all seem to have a 'sweat spot' usually at about 85% WOT and you can shift this somewhat until you hit the CDI rev limiter...

But unfortunately anything you do to the CVT will impact either the top end or the take-off... the trick is to find a happy medium you like...

But your gains will not be great... there is no replacement for displacement...

[sprocket]

I think one of the best things you can do to these engines is put on a 4 valve head and piston. I rode a scooter the other day that was stock except for a Ruima type head and free flow exhaust and I could not believe the increase in power...

My guess was maybe 15%... very noticeable...

.provoscooter.com/scooters/gy6/ruima-4-valve-racing-cylinder-head-gy6.html" rel="nofollow" target="_blank">.provoscooter.com/scooters/gy6/ruima-4-valve-racing-cylinder-head-gy6.html

Throttle body EFI and a free flow exhaust.. are impressive as well.

[mapbike]

Yeah Man, sprocket

I've looked seriously at that head at scrappydogscooters.com he sells that same set up for $199.00, he also sells a Big Valve custom ported head that kinda caught my eye as well, I was thinking either of these with the 59mm BBK & maybe the 30mm carb and alum. intake might offer a nice performance increase, might be a good set up for the 846 belt and some 14-16g sliders or rollers.

might end up being a good winter time project.......!

Peace, Shan

Jul 25, 2011 10:43:57 GMT -6 sprocket said:

I think one of the best things you can do to these engines is put on a 4 valve head and piston. I rode a scooter the other day that was stock except for a Ruima type head and free flow exhaust and I could not believe the increase in power...

My guess was maybe 15%... very noticeable...

.provoscooter.com/scooters/gy6/ruima-4-valve-racing-cylinder-head-gy6.html" rel="nofollow" target="_blank">.provoscooter.com/scooters/gy6/ruima-4-valve-racing-cylinder-head-gy6.html

Throttle body EFI and a free flow exhaust.. are impressive as well.

[mapbike]

Maybe save my pennies and just spring for that 200cc GY6 scrappydog is selling and put the 4 valve head and a couple other things on it........ I bet that would get my little scoot scooting right along......!