Registered: 1389189685 Posts: 2
Reply with quote #1
I am on year 2 of my briggs 206 racing in a Polaris 120 Snowmobile for Ice Ovals and I cannot get more than 5750 out of the engine on the track regardless what gears I use. On the Stand I can slowly increase the throttle to about 3/4 and get it to 6100 but if I open the throttle the entire way from the start and hold it 5750 is all I can get. It spits and sputters and not like its hitting the rev limiter. If I have it at 6000 plus with the throttle at 3/4 and then open it all the way I get the same result.
I have opened the spark plug gap to .040
I reset the float level per your video
The valve lash is set at zero cold
I cleaned the carb and jets
Am I missing something here? We ran this last year with no problems but this year I have had this haunt me. One other thing to mention is I do not run a fuel pump as the gravity feed of the tank is very good, I never had a problem last season but I thought I would bring it up.
Any Help would be greatly appreciated!
Registered: 1382354195 Posts: 7
Reply with quote #2
If it spits and sputters I believe the valves might be floating. Maybe the springs are worn out. My two pennies. Good luck
Registered: 1381194547 Posts: 10
Reply with quote #3
The valve springs should not be wore out yet... Have you tried the adjustable main jet from 4 cycle central?
Registered: 1389626188 Posts: 1
Reply with quote #4
Are you running a fuel pump?
Registered: 1308750586 Posts: 189
Reply with quote #5
Are you seeing your times similar to last year or to others in your class? The reason I ask that is you might have nothing wrong but let me explain. Whatever tach you are using works by AVERAGING the time between sparks. Our rev limiter works by eliminating a spark in a defined algorithm. Most tachs, due to cost, are accurate to +/- 100 rpm. They read only so many times a millisecond where as a high dollar system might read twice as many times or more. My first point is depending on where in the cycle your tach reads your rpm results WILL vary beyond what is actually happening. Slowly creeping to the rev limiter verses full or 3/4 throttle under no load really isn't an accurate way to 'test the rev limiter' the spark sequence that we developed was created with a defined load. Under less load you will get a 'bouncing' effect. If you creep it mimics what the engine would see under load. When you try no load, your RPM will not exceed the max rpm BUT might read lower than on the track. So you are getting to the max rpm when you slowly approach it on the stand. That, to me, says all is well on the engine side of things (with a couple of caveats I will mention below that also mimic everything working.) IF your sled has a bind in the track under load that might be why you are having a low reading. My other suggestion would be to take your tach lead and rewrap it. The number of windings sometimes impacts the repeatability/accuracy of the system. Pull the batteries out (download whatever data you want first) and reinstall them. My caveats: Is your carburetor drain hose pinched or do you have your valve cover breather or carburetor drain restricted? If it is pressure could be building in the carburetor or in the engine itself creating systematic drag. Do you have an air leak in the intake or exhaust? Sometimes, even a small air leak can be more or less impacted by the vibration of the engine. Is anything in a bind? Your sled track? Again, if the engine gets to the RPM under no load but doesn't under load is something in the drive train stopping it? Is your fuel new? Is there feedback in your system causing interference or a short? You can test this by removing the ground (kill switch wire). Obviously you need to do this SAFELY and on the stand. It's incredibly unlikely but why not rule it out? Could the choke cover (where the level on the carburetor is) have become loose? That might bleed some air into the system making it run erratic at times. As far as jetting I wouldn't believe that this is an issue. We have tested the engine jetting and even in the teens the air fuel ratio is still where I would tell someone that jetting adjustments won't show up on the track. Have you done ANYTHING different? If it worked last year and doesn't this year, from changing the cap on the fuel tank to a zip tie to removing the carburetor, I would think about making a list of things and see if one of those changes made the difference. I'm sorry to throw a lot at you but whatever it is I know it’s small but it’s hard to problem shoot without being hands on. You might also ask for help from others running the 206. Maybe they can take a look and just 'spot' something.
Registered: 1308169248 Posts: 115
Reply with quote #6
make sure the valves are adjusted properly.
Set to zero clearance. Just so you can rotate the push rods with your fingers. __________________ Jimbo