hightower, did u notice a difference with this longer active pump stroke and leaner clip position??

 

No Scoundrel, you're not screwed. Part of my point here was that the Dyno can trick a guy on the other circuits besides the main jet. Me and it sounds like Saint both got screwed up by an inexperienced dyno guy on our needle settings and pumper squirt. But I do believe that most guys on a stock bore bike will be best off with the 2nd groove from the top and pumper squirting to 3/4 throttle - based on my own experiences and THEBOM's. Guys with no pumper, or a pumper not squirting long enough, may think they need to raise the needle based on throttle response, but all that causes is beign too rich while maintaning mid throttle while cruising. The dyno can be used to tune the needle and pumper, but only by a guy with more experience in these carbs using the right methods.

As far as the main jet goes, we all know the dyno is, was, and will be the best tuner for knowing you are set at max peek power, and EGT's can help a guy get there too, as well as a/f ratio monitors, but knowing you are trying to tune for peek power makes red-neck dynoing and seat of the pants a tool that can be used to. Not the best tool of course, and always room for a little error, but basically the main jet that gets you up the Sand Mt. climb that fastest is the jet that belongs. Or if all you have is flat land, you can run your buddy making jet changes and the one that gives you the best results is close to where you belong. I really have gotten to the point of being able to feel the difference in power from betweem a 5 increment jet change, feeling the difference moving just 2.5 I cannot, but I can get a bike within wearing a flat slide carb within 2 or 3 sizes of correct with seat of the pants and feel. While 2 or 3 jet sizes on the dyno can equate to a couple ponies on the DS, it is still close enough for us weekend warriors who aren't putting our pink slips on the line. But some guys have a hard time feeling the jet differences, and inconsistencies in racing ability make it hard that way too, and for these guys the dyno is almost a must for main jet tuning.


eRo being set up like I am now, which is how THEBOM told me to do it prior to getting thrown for a loop by the dyno guy - 2nd groove from top, squiritn thru 3/4 throttle - yes there is a difference. The needle is now where it belongs for maitaning mid throttle cruising speeds with no sputters or flat spots, and the pumper is squirting long enough to fill any lags that would otherwise be caused when slamming throttle from mid to wide open. While having the needle higher felt stronger in the midrange, the low end was sooooooo rich is sputtered hard trying to come off 3,000rpm after crusing at it for a few seconds. With the needle set too high, you could be in 2nd gear, or even 1st, holding about 1/8 throttle maintaning about 3K on the tach, and then as I gently give it more gas the bike would fall on its face. This was because it was too rich at that point where the needle taper starts to rise, and it needed lowered.

 

hightower, i had my air snorkle off today watching the pump squirt. i noticed if u put a long squirt duration, the pump remains active alot. even if i just slowly apply throttle, not stab it hard, the pump trickles out a little bit of fuel all the time i'm applying throttle. anybody else notice this with their tm?? wouldn't this extra fuel introduced during a slow applying of throttle cause a rich condition? if the throttle is stab anytime between idle and 3/4, the pump is active to provide the needed extra fuel but the slow application of throttle does not need that extra fuel from the pump? the way to combat this over rich condition would be to make the needle slightly leaner but that would make the mixture lean while maintaining a throttle position because the pump does not add extra fuel while maintaining a constant throttle position. just some thought here ... also, why don't u put the pump active for the entire throttle range. as of now, if u stab the throttle from 3/4 to full, there might be some lag.

 

Yes you are right eRo, as I have noticed that too about the pumper. This is what makes using the #50 more important, as the #70 the carb comes with is dumping too much during those times. The #50 nozzle is the leanest they have for this carb, and at some times the fuel it adds may be a bit much, but not for long enouch a time to cause me any issues. I've not had any performance issues from it.

You can let it sqirt to full throttle, but I have noticed that not all carbs will pump that long, for some reason, some of the carbs I have worked on seem to stop around 3/4 or barely after, maybe because the angle between the white lever and the pump rod increases so much. The white levers on these carbs are a tiny bit different form one year to the next I've noticed, mine is older and will not pump to full, but newer modesl seems to be a touch different and can. If it will pump all the way, it may be of further aid, but its not as necesary as the pumping at lower throttle openings because at 3/4 throttle the rpm is normally high enough that jamming on to full has no hesitation. The higher rpms have more vacuum acting on the main jet, and thus pull more fuel easier.

 

What main jet did you end up with. I am at sea level and would like to get it pretty close. so far I have;
#97 needle
#30 pilot
#50 nozzle
idle screw 3/4 turns out
acc pump just off idle to 3/4

 

Good post HT [img]i/expressions/face-icon-small-wink.gif[/img]

I'm running the following:

150 main
97 needle in the middle grove
30 pilot
1 full turn at the idle mix screw.

I like mike a scratch rich as I'm on the button. Seems to work better with the above setup.

I think my bike runs better with a 145 jet though (not on the button).

This set up is for 750ft above sea level.

Check in with your specs guys. It will help everyone.

 

Hightower,
Thanks for the info. Good stuff ....I changed mine to these specs and felt my bike ran the best it ever has while at DS Days at Sand Mtn., far cry from the NO2 guys but I was outrunning stockish 450's pretty good. I was able to put the 15T front back on that we switch out at St. Ann's this spring and pick up some more speed up the hill.
Getting the little white spacer in the right place helped a little 2[img]i/expressions/face-icon-small-blush.gif[/img] highly recommended.