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Running lean on 650GD...new main jets needed?

MisterCinders said:
To raise the needle, you don't shim the bottom, you thin out the spacer on top, so the spring pushes it higher. Unless your needles don't have a spring?
Click to expand...
Good catch, MisterCinders.

I would have had to think about that for awhile.

You see, this is why this forum is great. Good dialogue happening right here.
 
7981GS said:
Right. :o
He would have to drop the clip and place the shim on top of it to do a half-clip type of improvement. Duh!
doh.gif


Eric
Click to expand...

You can drop the clip a slot and thicken the top spacer to double back, or you can stay in the current slot and replace the thick top spacer out with a stack of washers that is thinner than the original spacer.
 
update on the jetting

update on the jetting

tkent02 said:
I haven't jetted a 650 for a pipe yet, but usually the air box makes a bigger difference than a pipe. 110 is stock, 115 might be enough with the pipe and stock air box, maybe it will take more. Careful testing and doing plug chops will tell you. Just a guess, I might buy 120s, 117.5s and 115s to start with, and try the biggest ones first.

Please post your results, I need to do this with my 650 soon as I get the pipe on there.

Z1 sells them the cheapest.
Click to expand...
Tom,

I didn't start off with the 120s as my gut told me it would be too much. I upped the mains to 115s, and retained my setup (highest idle, vacuum synch). The result was a very slight, just off idle hesitation, and a slight rise in hot-idle rpm, from ~1100 to ~1400 rpm (read off the tachometer gauge).

Last night I redid the highest idle. I thought I'd have to lean out the mixture, but I actually ended up at 2.5-3 turns for all of the screws, which was out 1/2 turn from where I had them with the 4 into 1 with the stock jets and airbox. Took it out for a spin last night and had absolutely brilliant acceleration all the way to 3/4 throttle with no hesitation.

It was too late to do plug chops, and I'm still looking for a good place to do them, but I'll keep updating as I go along.

My problem now is: the bike is running really well :dancing:

What do I work on that doesn't take the bike off the road :confused: ?
 
Last edited:
tkent02 said:
I would wait to see. With CV carbs, a bigger main jet will enrich the midrange as well, so there might not be any needle raising required.
Also a 4-1 pipe doesn't really flow more than the stock system until the engine is wide open and wound out, again it might not need any needle raising. It's easy enough to do later if needed, you don't have to remove the carbs to raise the needles or to replace main jets.
Click to expand...

How do you replace the main jets without removing the carbs?
 
Caferacernoc said:
How do you replace the main jets without removing the carbs?
Click to expand...
On some bikes it is easier to get at the main jets than others.

I had a close look at the clearance under the carbs on my 650, and it is POSSIBLE but I did not try it. Allen head cap screws on the bowls help, and a very thin ratchet would be of tremendous assistance. You are not going to get a stubby screwdriver under the float bowls and get enough torque to turn out the float bowl screws. On the other hand, once you do get the float bowls off, accessing the main jet would be pretty straight forward.

AZR (?) says he's done it, but on bigger bikes, if I remember correctly. I'm still waiting to see pictures from people who have done it successfully.
 
I've been following this thread in great anticipation, as I also have a 650G (82) with a 4-1 and stock airbox with vacuum sync and highest idle methods performed. I'm not sure exactly what pipe is on there, as I did not install it, the PO did.

With that said, BigD, would you say the 115's are the right main jet? Have you given the bigger sizes a shot for comparison?

I'm currently running 115's with my set up as well. My dilemma is that as a new rider I'm unsure about what kind of power to expect out of the various rpm ranges. Up to about 4.5K rpm, I get great power, but find that above this the power/throttle response starts to diminish. Seeing as how the bike red-lines at 9.5K rpm, it seems a bit early to be losing power. Are you experiencing this as well?

Again, I am still learning to ride, so plug chops are probably out of the question for another little while for me. I'm tempted to to try going up 2 sizes to the 120's just to get a feel for the difference.

-Daniel
 
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