HELP it just wont run right.

mogollonmonster

mogollonmonster

Member
I've fixed the vaccum leak, I rejetted the carb to .0292. When the needle is in the fattest setting it won't idle runs like poop. In the leanest it only smooths out on the climbs at WOT. I'm running 6.4oz STHILL HP ULTRA to one gallon of 87 octane. (20:1) in a stock SD Stinger.

Do I move up or down a jet size? My meagre knowlage says it's starving but it's running best and putting out more power on the leanest needle setting am I too rich? How do I get it to stop four-stroking? Please help it's my only wheels now.
 
You need to go a size leaner on the main jet, and mess with the carb needle and clip after that. Also, my bike was 4 stroking a bit on long flat stretches at WOT, and i fixed it by widening the spark plug gap far beyond the recommended width. My plug is gapped to 0.189in and that fixed the minor 4 stroking. But you definitely need to go a size leaner on the jet. Just thought i'd mention the spark plug gap thing in case a leaner jet doesn't totally fix the 4 stroking issue.
Good luck!
 
Re: HELP it just wont run right...ALMOST THERE! HELP PLEASE!

Ok I worked down to a .024 jet, dropped to 5oz to the gallon, and piddled with the plug gap. I'm at the leanest needle setting and still fourstroking on the flats below WOT. I need to jet down further right? I found a .023 drill, or should I try to peen the edge of the hole in the solder a wee bit to add a little more constriction? The plug is showing signs of leaning, but still a lot of oil/carbon/black. The head is cool enough to touch in about five minutes. It seems to take a little while to warm up properly, in not sure if that means anything? Running a little cooler, now that there's not so much fuel? Either way I think I'm too rich still.

A prompt reply would help, I know fourstroking can't be good for the motor... But I don't want to blow it up.
 
.024 is a very small jet size. My feeling is you're mistaking something else for "four stroking". You said, "I fixed the vacuum leak". What exactly did you fix/do?

You also said "The plug is showing signs of leaning". Could you explain that? What signs?

You should also know that the needle clip position has nothing to do with fuel delivery after about 3/4 throttle. It only controls fuel flow below that, mid-range down to idle. The most common position for the clip is the second from the top. That will put you in a good ball-park position that can be fine tuned later but second from the top groove will be the best starting place.

You also said, "I piddled with the plug gap". Where did you end up? .024 to .028 is another good starting point. Some like a tad wider gap, some a little smaller but the range I suggested will be about right for most applications.

If your engine has less that 250 to 300 miles on it, it isn't going to deliver the performance it will after it gets some miles under its belt. A new or low milage engine will run poorly compared with one that has accrued some miles. They don't break in quickly and need some time and some hard use occasionally. Don't baby it!

A 'little' four stroking at mid range isn't a bad thing. If your engine is breaking into a good 2 stroke when it's under load or partial load, you really don't have a problem. They don't sing well at all octaves :)

Tom
 
For the vacuum leak I milled the mating surfaces and used a good gasket maker to seal both ends. Carb cleaner and smoother running say that's fixed.
Plug gap is some where in that neighborhood, but wouldn't you know it, my tool has a bunch of dings through there. I'll get the Mike out tomorrow.
By the plug I mean that I'm out of fresh ones so no more choppy choppy. But after many cleanings and test runs it's not as badly fouled, I know it's not a plug chop but its what I have to go by for now. The electrode tip is starting to show just a little brown as opposed to cruddy black.

I tried drilling some holes in the air cleaner, hoping to kinda "reverse choke" and maybe lean it out by letting it draw more air. Hindsight is 20/20 it's "sputtering" a little more now...

I've got about 350-400 miles on it now, but maybe I should just run it like it is for awhile and see what happens?
 
My bike sputters a lot when i am just below the beginning of the powerband, and it 4 strokes quite a bit when i am cruising at the wrong speed for the engine. I don't worry about it. It is also running a bit lean right now, but i just use a 30:1 mix with premium 2 stroke oil for motorcycles. The only thing that i do for the lean condition is keep my trips to 20 mins or under to prevent it overheating. The reason i wrote all this is just to say that these engines don't blow up with every tiny imperfection in the way they run. I started out being super worried about every little sputter and bit of 4 stroking, but now i just feed it 97 octane gas and premium oil, and forget about the little problems. But 2door is right, .024 jet size is too small for most applications. What elevation do you live at? That can effect how it runs and what jet size is best.
 
My elevation, depending on where I am is between 5500-7700ft. I worked down the jet size one at a time till the motor has just about smoothed out. While I'm a bit unfamiliar with the term, it seemed to be fourstroking (a definitive miss between strokes, cutting the power significantly) and just would not reach a respectable rpm, based on exhaust note when it did smooth out. I now have significantly more power, throughout the rpm range, and much higher rpms. It honestly seems to want to run faster yet, but I'm afraid to lean it down and burn it up. It seems to still be running quite cool, and can be touched, even leaned against in a few minutes, but it still stutters and seems to miss, unless climbing a hill or at WOT, there is a distinctive change in the exhaust note when it does this, loud and uneven popping and a noticeable drop in power and speed. I've been told that all those symptoms are "fourstroking" and its caused by being to rich, am I misinformed? Should I just run it for a while and see if it stops, as the motor finishes breaking in?
 
Yes, i would just run it for a while, it will get better as it breaks in. Also, if you are running a stock exhaust then remove the end cap. This will free up flow through the engine, causing it to run slightly leaner, and it may also get rid of the sputtering caused by drilling holes in the air cleaner. And for 5500-7700 feet a .024 jet should be close to what you need. And with 400 miles on it it should be very close to done breaking in, so if it doesn't smooth out pretty soon you'll want to go just a tiny bit leaner, or you could get an expansion chamber exhaust, which will lean it out considerably.
 
Oh, that exhaust cap got cut and drilled at about four miles lol. I've put about another hundred miles on it since my last post. I've noticed a flat spot at WOT, I think it's the stock fuel petcock limiting flow, or I'm still one jet size to rich, not quite sure yet. I'll try changing the valve first. Other than that damn thing runs great, I can't wait for my 56t sprocket, I'm fighting this wind hard pulling my trailer. The hills around here are bad enough, add trailer and WIND and life starts sucking, lol.
 
Well, the stock petcocks do not often limit flow that much, but to test it just pull off the fuel line and open the petcock, as long as there is a small steady flow it should be plenty. If there is not a steady flow, then check the little screen inside the tank to make sure it is not clogged, as that is common. If that still doesn't fix it then check that the gas cap is vented properly. Just take the gas cap off and see if flow improves. If the petcock is flowing properly then go down one jet size.
 
Yep tested flow, no it's not the petcock. I guess I might have to rejet. Bike seems hard to start and it takes awhile to warm up, but it's cooling off here quick, so that's understandable. I'll likely wait another 100mi or so, to make sure the rings have finished wearing in. That and I have to chase down a .023 drill
 
With nearly 500 miles on it the rings are definitely worn in. I break in bikes by mixing 1/2 gallon of 12:1 ratio fuel and go out and go WOT until the tank is empty. That has always worked for me, and i have broken in 4 engines now. Usually it will take about 2 hours to empty the tank, and that is usually about 75-80 miles.
 
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