idle hangs with lighter slide return spring.

[stainlesscycle]

i've not figured out why this is happening. i ran the heavier spring and it worked fine for last 3 months, but i was sick of the right arm pump i was getting from having the draggy throttle. i've had this lighter spring on in the past and it did the same thing i am describing here.

i switched to the light spring, and throttle opens so smooth and easy, and i can get into the meat of the power without gripping tighter. it's 1000* better, and i can ride faster with less fatigue.

BUT idle wants to hang, and it kinda drags me along a bit. i've lubed and slackened the cable, played with idle and air screw (even adjusted the idle screw way out, so it was definitely closing), even tried another light spring, that i stretched. nothing works. is the lighter spring just not slamming the slide down with enough force to 'keep it shut'? i can hear it hitting the idle screw. i'm assuming that when i'm coming from wot, that the velocity of the mixture is burbling the slide up off the stop?????? or the velocity of the air is stopping it from settling down? the slide is smooth, with no nicks or burrs, as is the slide bore. or am i just imperceptibly leaning on the throttle enough to barely lift the slide??? i thought that was the case, and added a bunch of slack in the cable, but that did not fix it.

it's just a goofy thing, but it drives me nuts. i'd like it idle down asap, just like the heavier spring does.. i can fan the clutch a tiny bit to drag the motor back down to idle faster, but that takes concentration on something i'd rather not focus on. any solution??

 

[pscook]

You can stretch the spring and then cut a couple of windings off to change the rate, maybe get it in between the current rate and the "too stiff" rate. Find a spring rate calculator and make some changes. If you have another light spring as a "just in case," then you can experiment at will.

I'll look for a link to a good calculator. I spent some time researching spring rates for an old YZ80 so that I wouldn't bottom it out while loading it into the van.

 

[stainlesscycle]

i'm gonna try machining a preload bushing, gotta look and see if i can figure out a way to preload spring without losing the ability to pull slide all the way up.

 

[pscook]

Here's a decent calculator. I used it for reference rates, fairly successfully:

http://www.pontiacracing.net/js_coil_spring_rate.htm

I have used this one before, it does require some assumptions. But it will give you a solid reference when you lop off a couple of extra coils:

http://www.engineersedge.com/spring_comp_calc_k.htm

You should be able to determine a decent "middle ground" spring rate from these links.

 

[gasgasman]

I went to a Motion Pro cable and the drag is a lot lower than the OEM cable.

 

[stainlesscycle]

I went to a Motion Pro cable and the drag is a lot lower than the OEM cable.

i checked cable, it's not dragging. it's entirely the spring rate that is effecting mine.

 

[GMP]

My throttle is super easy, as was the case on my previous two GGs, and I never had this problem. Try getting a new spring.

 

[blitz11]

Could it be some sort of slide / slide guide wear issue? Things are worn, slide gets cocked, and won't return all of the way? Aerodynamic loads forcing the slide against the wall, keeping it from returning?

Just thoughts.

 

[Neil E.]

I had trouble with my stop screw once I removed it. The factory sealer came off and the screw would rock around in the bore. This meant the slide would not come to rest in the same place and I would get a different idle speed. I made up a new brass slide stop screw with an oversize M5 pitch diameter and it works perfectly now.

Even though your slide strikes the screw, the screw could be moving around based on the different spring pressures. The stock hole is fairly sloppy if you test the fit with a standard M5 screw.

 

[blitz11]

Good one. Hadn't thought of that.

 

[stainlesscycle]

I had trouble with my stop screw once I removed it. The factory sealer came off and the screw would rock around in the bore. This meant the slide would not come to rest in the same place and I would get a different idle speed. I made up a new brass slide stop screw with an oversize M5 pitch diameter and it works perfectly now.

Even though your slide strikes the screw, the screw could be moving around based on the different spring pressures. The stock hole is fairly sloppy if you test the fit with a standard M5 screw.

never thought of that. that could be it - not near the bike now, is the stock idle screw m5x.8?

 

[Neil E.]

Yes M5 x .8 (11 250 with a 36 ASII). I machined it oversize on the lathe then finished the last bit with a dia that was adjusted oversize. I cleaned it up a bit at a time until it was nice snug fit. I had to make up a new die holder to allow for the extra expansion. The threads in the carb felt tapered; probably the hole was cast with a taper.