main jet inquiry - help needed By godfeast (Read 2,044 times)

[godfeast]

Ive had a few issues with my 150cc longbo/sunl adventure over the past few years, but it mostly boils down to me frying my top end via running lean.

I've replaced the top end/engine 5 times in 2 years, and I'd really like to figure this out before I end up doing it again.

The situation:

Scooter is my only ride to and from work.

Work is 20 minutes away down I4 - scooter has to run at wot the whole way and back 8-10 hours later x5 a week.

I cant afford another ride - wish I'd bought a 250cc or a motorcycle way back when I had cash, but at this point, i'm barely getting by.

I just replaced the top end a couple months ago and I had been begging rides (not happening anymore), so the scooter just got out of breaking in at about 250 miles, but had been blowing oil and showing all the signs of running lean again despite adjusting valves, checking exhaust mounting, checking intake mount, and playing with the idle adjust on the side of the carb.

I decided to buy another top end (knowing what to expect) and put it together yesterday. The second ring had frozen up in the piston as expected, but no other real damage done.

I removed the valves, de-carboned the head, lapped valves, and replaced all gaskets with new ones.

The carb in place had been upgraded from 107 main jet to 114 right after the last head blew on me. I also adjusted the needle as far as it would go for richness.

The bike has a uni filter setup and a "free flowing exhaust" I bought off a guy back a while ago ( he had opened it up and broken off the pipe just inside the muffler itself then riveted it back together).

I live in orlando florida, so its run at seas level, no real hills, and temps are typically in the 80's on nearly every day of the year (some nights falling into 60's but not often).

In this scenario, what size main jet would you think I should run?

[alleyoop]

You say you run that thing at WOT all the time WHAT ARE THE RPMS that your running at. High RPMS kills motors faster than anything else(beside running LEAN). I would bet that motor is screaming.

Since you say you HAVE to run at WOT all the way means you need speed to keep up with traffic.
What speeds do you have to run to keep up with traffic on that road?

On one of your runs when you come home Take the plug out and see what it looks like and put up a picture of it. Depending on what the plug looks like you could get a 117 Main jet.

BUT for your situation I Recommend putting in taller gears in there so you can get more top end speed with LESS RPMS and you won't be running it at WOT all the time. That will cost you a lot less than a top end and all the work that goes with it. Gears are cheap and you will be able to keep up with traffic and the motor will just purring.

Just so you know, my Trike is heavy 350lbs and I am 180lbs. Once i get up to speed, at 50mph my rpms are 5100, at 60mph my rpms are 6100, 65mph rpms are 6500, my rpms NEVER get to 7000rpms.
Alleyoop

[godfeast]

This scoot doesnt have a tach, so I have no way of knowing exactly ( but I've been a commercial driver for years and I can tell that its probably pushing itself to the limit just from listening).

I4 is a disaster for everyone ( worst highway in the state with the worst drivers in the nation - speeds set at 65 but 80+ is the usual. I ride as close as I can get to 65, which is why I tweaked to a uni and open exhaust, with high rollers in the first place.)

It's a worse case scenario in any situation, and if I had a financial choice, I'd never even consider taking a scooter on that highway - pretty much risking my life every day, but we do what we have to in order to get by.

I had consider gearing, but from what I had read, if I am not using a big bore then I wont have power to make use of the gearing and I'd just end up losing my top end and becoming an ornament on a semi's front grill.

Is this wrong? If so, then I may start looking around for a gear set.

[godfeast]

While I am waiting on a reply to the above (and please dont hijack the thread btw), I realized that the last time I played with the carb, I had help from a friend who adjusted the float.

I have no idea how to do this myself, and the friend is no longer around, but having googled a bit, I can see that a poorly adjusted float would cause issues too - problem is, I dont really understand the various posts and pages that try to describe how to adjust these.

Anyone familiar with it? I'm trying to get as many variables out of the way as possible.

[alleyoop]

Oct 18, 2012 12:09:51 GMT -6 godfeast said:

This scoot doesnt have a tach, so I have no way of knowing exactly ( but I've been a commercial driver for years and I can tell that its probably pushing itself to the limit just from listening).

I4 is a disaster for everyone ( worst highway in the state with the worst drivers in the nation - speeds set at 65 but 80+ is the usual. I ride as close as I can get to 65, which is why I tweaked to a uni and open exhaust, with high rollers in the first place.)

It's a worse case scenario in any situation, and if I had a financial choice, I'd never even consider taking a scooter on that highway - pretty much risking my life every day, but we do what we have to in order to get by.

I had consider gearing, but from what I had read, if I am not using a big bore then I wont have power to make use of the gearing and I'd just end up losing my top end and becoming an ornament on a semi's front grill.

Is this wrong? If so, then I may start looking around for a gear set.

The POST by the other fellow has been moved from this thread.


A lot of guys always say things that they themselves have no experience they heard it from someone else and they repeat and pass on the bad info. I see a lot of that on posts giveing out bad info to someone with a problem.

You should invest on a Tach they are pretty cheap, I believe all scoots should have one for tuneing as well as knowing if the motor is running good or when the motor or cvt needs some attention.

But if you go with 2up and 2down on the gearing you will hardly notice any difference in your low end and mid-range. From the way you describe how it is running at WOT it appears you have enough RPMS and the motor is strong.

Here is a nice Tach that has no delay registering and can be installed in 5 minutes. Just mount it where you can see it and wrap part of the wire on the coil and that is it. I have a built in tach on mine but I have one of this tachs as well just wanted to see how it works and it works great.
Alleyoop

Scroll down and they show the installation:
trailtech.net/tto.html

[godfeast]

Thanks for the input on that.

I tried to adjust the carb myself yesterday and failed to where it wont run at all - seeing a lot of what looks like sand or something in there anyways, so I'm stuck at either cleaning the carb and trying to readjust correctly or just buying a new one if I can find one cheap enough.

Still waiting on ideas for a proper main jet size too while I deal with these other problems because in the end, I will still need to tackle that.

[alleyoop]

I mention a jet size up a couple of responeses. You say you have a 114 main jet BUT you have not looked at the PLUG after a WOT run with what you have. Seeing as you have blown your top end it is running LEAN on those long runs at WOT. So get a Main Jet 2 sizes greater than what is in there.
BUT you need to see how the plug looks like after a run that is very important to know just how LEAN it is running.

What is killing your motor is HEAT, and the only things that keep them cooler is enough FUEL, AIR and OIL. Running LEAN really gets them HOT quickly. Also the way your running I would change the OIL every 500 miles that is a cheap investment to help the motor get good lubrication and cooler.
Alleyoop

[godfeast]

Thanks alley. I didnt see the size comment up above. I just pulled apart and cleaned the carb today and found a vacuum line that had been torn - so fixing that and tomorrow I should be running at least and able to do a plug chop to see where I am at.

Hoping main jets arent too hard to find locally as well, so I dont have to order and wait on one.

BTW: whats a good accurate resource for changing gears? I've only been into the final gears once before and it looked like they were pressed on, so thinking I may need some insight into how to do this job without a machine shop if possible.

[wheezy]

Oct 18, 2012 12:09:51 GMT -6 godfeast said:

I4 is a disaster for everyone ( worst highway in the state with the worst drivers in the nation - speeds set at 65 but 80+ is the usual. I ride as close as I can get to 65, which is why I tweaked to a uni and open exhaust, with high rollers in the first place.)

It's a worse case scenario in any situation, and if I had a financial choice, I'd never even consider taking a scooter on that highway - pretty much risking my life every day, but we do what we have to in order to get by.

Wow! I totally understand your reasoning, but I've got a 250, and I only take I-4 when I have absolutely no other choice. I've had it up to 75 on I-4, and just don't like not having any speed left in reserve to get out of an idiots way. I take 17/92 instead of the interstate, even then I have some surface neighborhood streets I take when things get too idiotic. Are you taking I-4 just to save time, or is there any way surface streets would be possible? It would take longer, but you wouldn't be burning out your top end every few weeks.

While I think you'd be on the right track going up a couple sizes to try to cure the lean, at this point it still seems a guess that you are lean. As Alley said, it may be that you're running at WOT on an air-cooled motor for extended periods of time. I have done that in my 50cc, and after a while the heat would seem to predetonate the fuel. I'd have to reduce throttle to get it back.

Without knowing your total situation, and it's just a suggestion, but I would look into financing a 250 or greater for a short period of time. My view is you are very lucky the top end has not failed while you were screaming down the interstate.

[alleyoop]

Pieces going straight up through the SEAT!!..
Alleyoop

[godfeast]

OK, got a couple jets in and found out I had to do another repair.

It seems my old problem was 2 part - not only was my main jet too small, but I had a torn air cut valve (damn thing was split almost all the way around the base).

Im still trying to find my sweet spot on the jets, but after adjusting a bunch and using a 120 main jet atm, this is what the plug looks like:





Im not even going to say I have any experience with plug chops, this being my first try, but from what I am reading, this should be about the right look - yes?

The bike idles fine and runs through its range good; the only issue still left is a slight chugging/sputtering when I completely release throttle and go to an idle. Its not severe, but its there.

Can I get a comment on what that might be and if I am correct in having found my ideal jet size according to the plug pics?

Thanks again guys - and once I have this gremlin down Im going to need to bug ya again for changing gears, lol.

[alleyoop]

WOW! thats with a 120 main jet? To me that is running on the lean side at WOT. I would get 2 more jets a 125 and a 122.5 and first put in the 125 if to much then the 122.5. You always want to run just a little richer on the top end you do not want to be on the edge. Because if any little thing happens it will run Lean before you know it.
Alleyoop

[godfeast]

I kind of suspected this. I ran it out around the area a bit and after a few i was noticing that the gargling on letting loose of the throttle turns into a series of 2-3 crackle/pops.

I have a 125, but when I had that in I was bogging about 1/3 of the way through throttle - around 35mph, and it would go away and run fine afterwards, but I figured the bogging ment it was too rich...

This scooter is driving me nuts.

Im going back to the 125 (i dont have anything between 121-124) and I'll just have to figure out the bogging situation or ignore it I suppose; anythings better than doing another top end.

[alleyoop]

Yep little Lean, You can put in the 124 and that will help the 1/3 bog and that should be good for the top end. If it still bogs in the lower end DROP the NEEDLE move the CLIP up one slot to get rid of the bog on the lower end if still try moving the clip one more slot up. The lower end is running a little rich.
Alleyoop

[godfeast]

I put the 125 back in and to started off trying to fix the bogging by adj the needle to lean it up.

That didnt work so well,as the bike bogged still and now still backfire on deceleration.

I put the needle back and its doing the same thing.

Ive adjusted the float and the needle several times and nothing I do can fix the backfiring.

Im beginning to think this issue isnt related to the carb - checked the intake manifold and shows no cracks or suggestions of failure.

I looked at the exhaust studs ( too hot to check by hand) but they dont look backed out, all though they could be I suppose.

Any ideas?

Im lost on this one and Ive already missed a weeks worth of work spending days at a time trying to fix this.