I went to have the Prairie dyno tuned today and left worse off than when I started. I just had the cams,heads,jetkit,and modified exhaust done so I figured to make the most of the mods I would have it tested on the dyno to make sure I had the jetting close.

When I first got there I explained what I wanted done and they put it on the dynojet dyno. They peg the throttle and brought it to 65mph @ 7900rpms and shut it down. The air/fuel ratio read 18.5 to 1. 35.3 RWHP, 37.1 RWtq. He comes out and tells me it running way RICH. That was an indication of how it was going to go. He went up one size in the front and down one in the rear on the main jets only. Then pegged the throttle again and shuts it off at 65mph now the air/fuel ratio was 12 to 1, 26.6 RWHP and 28.1 RWtq and he says ok its done!!

Im no expert but first of all isnt 18to1 lean not rich? Also If the throttle is pegged from start to finish can you really tell about the pilots or needles or is it just main jets? Next with the air/fuel guage shoved in the middle of the pipe (he drilled a whole through the middle) will that acurately tell what both cylinders are doing or just the one that the pipe in the middle leads to? He never touched the needles or air screws and they were the main ones I was unsure of.

Its aggrevating to pay someone over $100 to take HP away from your quad and say its better now. Then on top of that he tried to change the numbers and say the first run was actually the second (like I wasnt there watching) and I shouldnt pay attention to those #s because the clutch kit throws it off. I Also hate the fact that after all the money spent on this Im not getting any better #s than stockers. Even though it will go over 70mph and wheelie at will. I just dont understand. Opinions welcome. Sorry for the long post.

 

I don't know where in MO your from, but if your close enough to justify the trip, Richards Recreation in Kevil Kentucky has a dyno and knows how to use it.

 

That's too bad Rivermud. I hate to hear stories like this. Unfortunately you don't have to have a high IQ to buy a dyno.
Yep, your right.
Nope, your right again.
Your right again.

Sounds like the A/F guage was not even working? There is no way in hell you are going to make 9 more ponies with an 18 to 1 motor than a 12 to 1 motor.
Don't let them near your quad or any of your friends quads for that matter. Sorry again for the bad experiance.

 

Thanks daren, I went to quincy IL to do this one I might have to try kentuky or Kansas next.

When I went there I figured my jets were off because it was 130f-138r Dynojets (thats what felt best) that was 18-1 af he changed them to 132f-136r and that went to 12-1 af

looking at that it would tell me he went up in the front and down in the rear and richend it up that much it seems like the front was the only thing being measured. Since I lost power do you guys think I might be better off at 132/138? Or leave it and lean the needle one clip?

 

Doctorturbo, I didnt even think it was possible to loose 9 hp from changing one jet size on both carbs. It had a window and monitor outside of the bay and I watched every move he made along with the computer. I couldnt believe the results but I was shocked when he said "ok its done". I thought he just did something wrong and had to make another adjustment.

 

Rivermud did you supply the jets? Did you take him for his word on the jets he put in? You might take a peek and see what is really in there. And don't believe the #'s on the side. I've seen more than one drilled out. Your right again, there is no way a one jet size would make that much difference in power.
I don't even think it's possible for and engine to run on 18 to 1? I just have never ran a motor that lean so I just don't know? Maybe someone else can chime in. Somewhere around 15 and change to 1 the thing starts popping big time. Something sounds really goofy there? Did you get the printout? I know a non-heated O2 sensor takes awhile to read correctly.

 

Doctorturbo, I did supply the jetkit, but it probably wouldnt hurt to double check to make sure hes not far sighted. He gave me a partial printout. He kept the big number on one page and gave the better air/fuel ratio on another page. so basicly I have half of 2 runs.[img]i/expressions/face-icon-small-disgusted.gif[/img] It was an hour drive there in 30 degree temps and it was basicly taken straight off the truck into the dyno room straped down and ran. So the only warm up it got was from the truck into the shop. About 50ft. As far as the o2 sensor it was stuck in, turned on, The quad started went imediately to full throttle and turned off for rejet. Needless to say I am very unhappy with the work of TNT Action sports In quincy IL and would discourage getting service there.

 

14.7 to 1 is a perfect fuel mix. You get a little more performance being a little on the rich side.

 

12.5 to 13.0 is very good a/f ratio for power. if he used an o2sensor in your exhaust (wideband only) then it doesn't take long for jetting but where the sensor goes in he should of put in a bung. did he? was where he put in the sensor sealed good as not to let any air seep in? i.ve only seen dyno with sniffers thats not to say anything bad about 02 sensors as i have one also but not a dyno.

 

jet up one in the front, one down in the rear? WTF? That don't sound right IMO. Do you know what sizes they are? Sounds like he's not aware of the proper jetting scheme between front and rear cylinders. They should only be one to two sizes offset not four.