Will someone please help me with set up numbers

jamtinsl3526

jamtinsl3526

Member
As I said in a previous post, I run 425 champ on an epic kart and I weigh 230 myself. We are running a smallish track with tight turns. Running 15-66 if that's an indication of the size of the track. Another bit of evidence to the size and amount of turns is everyone runs 1 1/2 up front and 1 1/8 stagger on rear. I have no problem turning or entering the corner, but from the middle off my rear end starts sliding out from under me. I have to saw on the steering wheel and chase the kart up the track to the outside in order to prevent a complete spinout. There is no banking on this track. My guess is my front is too tight or rear too loose-however you want to look at it. I finally got a set of scales and so now have some numbers. Two things I noticed after the race. I was only running 1 inch stagger on front and back. Would this cause my problem? The other is my cambers are low. Would a change here solve much of my problem. Here are my numbers.

Front 45.9 %
Left 57.3 %
Cross 56.7 %
Total 426.5 LBS
LS Camber +.25
LS Castor - 1
RS Camber -2.40
RS Castor -5.5
Rear Track 40 inches

Any help would be greatly appreciated. At least a set of numbers that I should attempt to duplicate.
 
if it was me and i probably have no real idea never ran a champ but i would start 46.5 nose 59 left 65 cross ...recheck your castor numbers those cant be right camber lf looks good rf id put -2.75 1.5 frt stagger 7\8-1.0 rear
 
I've never raced dirt, let alone champ, but I have this spreadsheet that I use to look at all the corner weights when people post their percentages.

This is only my observation, but I see that you don't have much weight on the LR.

Seems to me the only purpose of stagger is to get both rear wheels turning the proper number of revolutions for the arc they are traveling on in the turns. Seeing as how they are both turning the same number of revolutions, the inside tire has to be a smaller circumference than the outside tire, so that it's not sliding in the turns. I think if you know the diameter of the turn, (the distance across the infield, LR track to LR track) the stagger could be calculated. Coincidentally, I have a spreadsheet that can do that. To make the calculations right, it appears to be better if you measure the rear track center to center of the rear tires.
 
Everyone who is winning is running 1 1/2 inch stagger on front and 1 1/8 on back in order to make the turns. Since the front turns so well but the rear does not follow, will going up in rear stagger help or is going down in rear stagger going to help. Those are my castor numbers. I can change to - 2.75 on RF and + 1.5 on LF to see what happens. Would that cause the problem I'm having? I figured the castor helped the front turn and since it turns fine, I guessed my real problem was somewhere else.
 
jamtinsl3526 said:
Everyone who is winning is running 1 1/2 inch stagger on front and 1 1/8 on back in order to make the turns. Since the front turns so well but the rear does not follow, will going up in rear stagger help or is going down in rear stagger going to help. Those are my castor numbers. I can change to - 2.75 on RF and + 1.5 on LF to see what happens. Would that cause the problem I'm having? I figured the castor helped the front turn and since it turns fine, I guessed my real problem was somewhere else.
Click to expand...

With you current issue adding rear stagger will only make it worse, confused what you saying are your castor numbers but IF numbers you state are correct there way off, get them to stock position, for sure INCREASE RF neg camber and I'd go past 2.75 min of 3, as mentioned I would PM Jamie XXX#40 he knows this chassis VERY well, Tires could very well be as much an issue as numbers.

Good Luck !!
 
jamtinsl3526 said:
Everyone who is winning is running 1 1/2 inch stagger on front and 1 1/8 on back in order to make the turns. Since the front turns so well but the rear does not follow, will going up in rear stagger help or is going down in rear stagger going to help. Those are my castor numbers. I can change to - 2.75 on RF and + 1.5 on LF to see what happens. Would that cause the problem I'm having? I figured the castor helped the front turn and since it turns fine, I guessed my real problem was somewhere else.
Click to expand...

There may be some confusion here, don't get upset with me, but could I asked some questions? Those caster numbers are way different from anything I've ever seen. Those numbers -2.75 and +1.5, what are those numbers? They look like camber numbers more than caster numbers. You said "those are my caster numbers, I can change to
....." but the numbers you give are unlike any caster numbers I've ever seen. Champ karts might be different than flat karts, still, the flat karts I've seen have quite a bit more weight on the left rear wheel. Almost all the flat karts that I've seen have the LF heavier than the RF. Most of the champ karts that I've seen have just the opposite, which is what you have. These are not recommendations, only observations.

　

It is my contention that there is a theoretical "best" rear stagger for every track, and that calculated stagger is based on the turn radius. Sometimes, depending on the track and conditions, that number may need adjusting? Do you know the distance across the straightaway, between the tire tracks the left rear tire would make. Using my spreadsheet, and assuming the track is 80 feet between the straightaways, with 25 feet wide straights, the calculated stagger would be 1 1/8 inches, which is what you have, but is your track 80 feet wide between the straights and 25 feet wide? Many times I see people changing their stagger in the rear to tune the handling. Now if it was wrong to start with, and the change made it right, they might think that changing the stagger is a good way to tune, but in fact they just went from the wrong stagger to the right stagger. Now I'm not saying that my calculated stagger is absolutely right, but it would be a good place to start. If your track is bigger than the one I used for calculation, you might need a little less stagger, and just the opposite if the track is smaller. And then you have to take into consideration the length of the straightaway. If the turn radius calls for a lot of stagger, but the straightaway is really long, (in this case the stagger could slow you down on the straights) you might have to reach a compromise. Only extensive testing will tell you what the best compromise is.

It's called tuning, and tuning is tough! (Al Nunley)
 
jamtinsl3526 said:
Everyone who is winning is running 1 1/2 inch stagger on front and 1 1/8 on back in order to make the turns. Since the front turns so well but the rear does not follow, will going up in rear stagger help or is going down in rear stagger going to help. Those are my castor numbers. I can change to - 2.75 on RF and + 1.5 on LF to see what happens. Would that cause the problem I'm having? I figured the castor helped the front turn and since it turns fine, I guessed my real problem was somewhere else.
Click to expand...

There may be some confusion here, don't get upset with me, but could I asked some questions? Those caster numbers are way different from anything I've ever seen. Those numbers -2.75 and +1.5, what are those numbers? They look like camber numbers more than caster numbers. You said "those are my caster numbers, I can change to ............. " but the numbers you give are unlike any caster numbers I've ever seen. Champ karts might be different than flat karts, still, the flat karts I've seen have quite a bit more weight on the left rear wheel. Almost all the flat karts that I've seen have the LF heavier than the RF. Most of the champ karts that I've seen have just the opposite, which is what you have. These are not recommendations, only observations

It is my contention that there is a theoretical "best" rear stagger for every track, and that calculated stagger is based on the turn radius. Sometimes, depending on the track and conditions, that number may need adjusting? Do you know the distance across the straightaway, between the tire tracks the left rear tire would make. Using my spreadsheet, and assuming the track is 80 feet between the straightaways, with 25 feet wide straights, the calculated stagger would be 1 1/8 inches, which is what you have, but is your track 80 feet wide between the straights and 25 feet wide? Many times I see people changing their stagger in the rear to tune the handling. Now if it was wrong to start with, and the change made it right, they might think that changing the stagger is a good way to tune, but in fact they just went from the wrong stagger to the right stagger. Now I'm not saying that my calculated stagger is absolutely right, but it would be a good place to start. If your track is bigger than the one I used for calculation, you might need a little less stagger, and just the opposite if the track is smaller. And then you have to take into consideration the length of the straightaway. If the turn radius calls for a lot of stagger, but the straightaway is really long, (in this case the stagger could slow you down on the straights) you might have to reach a compromise. Only extensive testing will tell you what the best compromise is.

It's called tuning, and tuning is tough! (Al Nunley)
 
Your numbers don't seem way out of the ball park. Too little RF camber will make you loose middle/off, bump that up. Bring in the RR wheel closer to the frame, narrowing the rear track width. Only go 1/4" at a time. A little does a lot.

Those two things will tighten you up coming off, without hurting you too much on entry
 
Like i said, i weigh 230 myself would it tighten my rear up if i moved my seat towards the motor a little. I can move it about an inch if it would help. Do i have too much weight on my left side? Is that weight not transferring to the right side durring center off due to my seat being too far to the left?
 
jamtinsl3526 said:
Like i said, i weigh 230 myself would it tighten my rear up if i moved my seat towards the motor a little. I can move it about an inch if it would help. Do i have too much weight on my left side? Is that weight not transferring to the right side durring center off due to my seat being too far to the left?
Click to expand...
Hard to help without some feed back.
 
gotcha I always say go to manufacture to get best input drives me crazy when someone gets on here and ask for some help they should contact the person who built there kart first and then if there still struggling then reach out for help jmo
 
Didn't change rf camber but did move my rr in 1/4 inch. seemed to solve the problem. Tried a new set of wheels this time with correct stagger. Was like a new kart. Handling is much better but still having some rear wheel hopping on exit. Getting conflicting input. Some tell me the wheel hop is due to too little air and kart is too tight and I should go up in air pressure. Others tell me it is the opposite. That the kart is loose and trying to grip. Which is it? Secondly, having trouble getting motor to turn. ran 15-66 and only got 6300 rpms. went up on air pressure and to 15-68 and got 6600 rpms. everyone else is turning 15-64, 15-65 and turning 6800. My motor doesn't seem to be able to do that. Thought it was the timing. have cl3 cam and billet flywheel with built in 32 degrees, with a stock key. In my motor however the stock key gives me 34 degrees. I tried retarding the timing with a number 2 key put in backwards, but motor only turned 3800. Everyone told me to advance the timing using a number 7 key. I tried that and with 15-66 motor would only turn 6100. with 15-68 and more air it turned 6600 but I was way off the pace. Any ideas as to where my timing should be?
 
In that ratio range, one tooth on the axle is worth about 100 RPM. Meaning; if you have a 15/66 and go to a 15/67, you have to gain 100 RPM to be going the same speed.

About the hopping, try both, more air and less air, see what works. I'm pretty sure more air will be better.
 
You most likely have too low air pressures if you made those changes then picked up a hop on corner exit..I would try going up on air on all 4 corners at least 1lb, maybe more....you need more air pressure in a champ kart than you do with a flat kart. Your caster settings could also be causing the hop, making weight transfer too quickly and too much, which will overload the RS tires and cause a hop sometimes...i would reset caster to stock position and rescale, then try to find out what air pressures the winners there use and try that before doing anything else. Rear track width also controls weight transfer timing, too wide and weight will transfer too slow or not enough, and too narrow on the rear track then weight will transfer too much/too quickly. You should set the rear track width to around 39 1/2" with the inside of your RR wheel as close to the frame as possible without rubbing the frame then move your left rear hub to set the rear track width.. That is the standard way of setting rear track width. You aren't too far off on setup just need to get it dialed in a little more is all
 
Set your engine timing at 32-34 degrees and leave it alone if using the CL3 cam....dont go by what everyone tells you because each engine can be set up with different timing depending on how their carb is setup and the rest of their build. Get timing to 32-34 degrees and aim for 6700-6800 as your target rpm with the CL3 cam...change valve springs to fresh springs every 5-6 races. That should get your engine really close, you may or may not need to adjust carb jetting after changing the timing...i suggest getting in touch with Jerry at Dover Power and order his Holey Moses carb for your engine once you get the timing set where it should be, Jerry can set it up exactly for your engine for the area you race in if you tell him the altitude where your track is located. Hope this helps.....one thing to keep in mind is that you cannot always trust what people at the track tell you when it comes to information, especially when you are their competition!
 
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