about dyno tuning - the dyno guy will help advise what to do with the jetting, but some are not as knowledgable as others. I got bit by one of these guys recently, when they convinced me to raise my needle rather than extend the pumper squirt. But much trial/error, dyno time, and conversations with THEBOM have landed me where I am now. Based on recent conversations, it seems most DS's THEBOM tunes on his dyno, and my bike now as well, at sea level, use the #97 needle (standard) on the 2nd groove from top, 30 pilot, idle mixture screw 3/4 turns from seated, and accel pump set to squirt from just off idle until 3/4 throttle. The main jet is really the main thing to spend the dyno time on, and you tune for peak power with the sniffer helping to guide you the right direction.

when I dyno tuned, the midrange was really lean, and they kept telling me to raise the needle. I did, and got it ironed out for best overall power on the dyno. but then trail riding it sucked. it was a product of the dyno guy's method of making pulls - they gently bring the bike up to about 3 or 4K on the tach, activate the chart recording, then slam the throttle to wide open. There was never really a time period where they spent enough time at mid-throttle to really know exactly what the needle was doing at all. The dip in midrange on the chart ultimately proved to be from not enough squirt from the pumper to fill the lag from the stab - raising the needle achieved what they were looking for, but in the wrong manner. This made stabbing the throttle more responsive, but too rich while maintaining partial throttle. So rich that the bike would stumble on trails at the transition where the needle and pilot overlap. This led to a path of pilot swapping, but still masking the real issue. The needle needs set where it meters the mixture correctly while maintaining that throttle position, and the pumper must be used to fill the flat lag caused by stabbing to wide open.

It was once thought the pumper is only used to fill the lag coming off idle. Turns out its a key component throughtout the throttle travel. I used to have it set to stop squirting at 1/2 throttle, but after all the dyno tuning and talks with THEBOM, it is now clear that she needs to squirt thru 3/4 throttle. Had I understood this to begin with, I would have saved close to $100 worth of wasted dyno time. hence the purpose of this post - I hope it may be able to help you!

 

I RAN IN TO THE SAME THING. I HAD MY TM45 DYNOED LOCALY. THE NUMBERS AND AIR FUEL CURVE LOOKED GOOD BUT AFTER TRAVELING 250 MILES TO GO RIDING THE QUAD RODE TERRIBLE. I WAS FOULING PLUGS IN 20 MINS, ANY TECHNICAL SECTION THE BIKE WAS LOADING UP MAKING IT VERY DIFFICULT TO MANUEVER. I RETURNED TO THE DYNO AFTER GETTING BACK IN TO TOWN AND SPOKE TO THE GUYS THAT DYNOED MY BIKE AND THEY SAID IT WAS DUE TO TEMPEATURE CHANGES. EVEN THOUGH IT WAS ONLY A 25 DEGREE DIFFERENCE FROM MY HOME TO WHERE WE WENT RIDING. THEY DID NOT WANT TO REMEDEY THE PROBLEM AND WANTED TO CHARGE ME FOR MORE DYNO TIME. THATS WHEN I SAID FORRGET IT. NOW MY KMS EFI SHOULD BE HERE NEXT WEEK!!!! BETWEEN TRYING DIFFERENT CARBS, DYNO TIME, HAVE TO REJET FOR DIFFERENT TEMPS AND ALLTITUDES, THE EFI WILL BE MONEY WELL SPENT FOR ME. NOW ONLY IF I COULD GET IT IN MY HANDS!!!! [img]i/expressions/face-icon-small-happy.gif[/img]

 

Spend a couple hundred bucks and install an EGT meter (exhaust gas temp.) on the quad and tune the carb. in 1/4, 1/2, 3/4, and wide open specs. according to egt temps. on your own time costing nothing compared to multiple dyno runs going on 4K rpm and up pulls, the dyno is good for comparing one mod to another on internal mods from time to time, but dial your carb in with an EGT, and it will be an overall ridable quad with no carb issues.
Just my 2 cents.

 

the problem with my dyno guy was that he was only experienced with tuning vacuum slide carbs on street bikes, and had no real flat slide or accel pump experience. knowing what I know now, the tuning experience should be minimal with minimal pulls and under $100 when all done. its chasing the wrong notion that ends up racking the cost.

The EGT gauge is a good idea, and certainly a great option, especially for guys with no dyno close at hand. But they may or may not get you too peek power on the main jet dialing as well as a dyno can. I changed main jets many times just to experiment and find out what being a jet too rich or lean would cause, and while a couple main jet sizes caused a HP change, the EGT reading was not changing much, just a few tenths.

Also FYI for EGT guys, I made best power around 13.2:1 a/f ratio.


As for EFI - it is on my list and I will have it eventually. I travel too much to too many altitudes and climates every year, and EFI would be a dream. While rejetting for altitude is not a very difficult task, it would be nice to elliminate the need, and always know I am dead nuts on wherever I am, whenever.

 

what does 13.2:1 air fuel compute to in e.g. temps. ? I'll guess around 1400 degrees for gas, 1250 alky?

 

hey in the last sentence of the second paragrah above, where I said the EGT only changed a few tenths, I meant A/F ratio, its been a long night here being a slave to the grind.

But I am wondering what the a/f ratios compute to in egt's. You hear a lot to shoot for 14.7 a/f ratio, which is where fuel economy is, but it has been found that more power is found being richer as mentioned, closer to 13:1.
Is the 1400 degree egt for economy, or power? If I had an egt, and knew an approximate conversion, then knowing that my best power is at 13:2:1 it would be easy to dial in to the power on trips with big elevation changes, like going from here at sea level to 5K in Utah or something, as I travel lots every year to dune. You got me thinkin now...

 

Best power air to fuel ratio is 12.7:1, but 13:1 is real close. I cannot help you to give you the temperature range for this mix, but when you tune try and get as close as possible to 12.7 for best power under acceleration.

 

Cool, thanks Freez. I did not go rich enough on the main to get below 13:1, as the dyno tech was telling me I was getting "too rich" even though I was making more power than I was at 14:1. Sounds like I may have had a little bit more to gain.

Another interesting thing I noticed on the charts comparing hp to a/f ratio, was that as I over-reved beyond my peek hp producing rpm, the a/f ratio really started getting richer. With my peek power being made around 7K, I tuned for the a/f ratio to be around 13:1 there, and as the rpm rose beyond 8K the a/f ratio started taking a little dive and was down to 11.5:1 by 9K. That's fine, as I should be shifting by then anyway, but still interesting how the increased air velocity seems to effect fuel flow.

 

I like the ratio of around 13:1 for two reasons. 1st it makes more power, 2nd, keeps the combustion temperatures down compared to running at say 14.7:1. Both great advantages.

Drawback, it creates a bit more carbon deposits compared to running the bike at 14.7:1, but if you change your pistons once every year or two it should not matter much. With cars that last thousands of miles this might become a problem when the motor starts getting old. On, ATV's you might just have to change your plug a bit more often, but that’s that.

One other thing I have noticed with the air fuel ratio thing on the dyno. Getting 12.7:1 is very critical for rpm, from 1500 to around 6000 RPM. Getting it right adds very noticeable improvements in the torque output and a little bit on HP, but after about 6000 RPM, getting between 11.5:1 and 14:1 A/F ratio, hardly makes any big changes in power output. The effect is marginal and hardly worth breaking your head over.

Like you mentioned, I would not be too worried about that rich condition at high RPM and besides, if the motor still runs well, that extra fuel is just keeping things cooler. Just make sure it is not running lean, the rest is fine.

 

So then I guess if you don't have a Dyno available or have a EGT gauge you're screwed?