Hope all is well, 01 GTS 720, pump throttle

[CRei]

So decided to mess with the GTS, new rebuild engine few seasons back from bottom up. Runs great. So taking off at idle you need to pump the throttle then it takes off runs fine. Compression is good, carb was gone through at engine rebuild, replaced fuel lines and filter also fuel selector. Any idea where to look now? Thanks

 

[noviceskier]

Pump the throttle as in trying to prevent it from dying on you? Or pump the throttle as its revving up on you, and then slowly taking off?

 

[mikidymac]

I think yours has the accelerator pump carb. So either the accelerator pump isn’t squirting or your pilot circuit isn’t perfectly free and clean.

 

[JeremyD615]

Either way, it’s time to pull those carbs and go through them with genuine Mikuni kits. If it’s been a few seasons, it’s not worth leaning the motor out wondering whether the carbs need rebuilt or not.

 

[CRei]

It idles ok, just coming out of the hole it bogs have to pump it to get it going, not sure if its fuel or an air leak.

 

[mikidymac]

Sounds like accelerator pump or pilot circuit.

 

[matempl]

My 97 gti has the same issue. I purchased it last season. Went completely through the fuel system. Hoses, filters, carb kit, runs great except that out of the hole if you punch it it will bog a bit. If you slowly accelerate or feather or (pump) the throttle it is fine. I used it last season as it was but plan to address the issue this season. It’s a 717 single carb. I played with the adjustments but no difference. Was thinking pop off but don’t remember what it was other than it was in spec but there is normally a wide range. Can’t remember how pop off effects acceleration.

 

[Gritzlor]

My '97 GS 720 behaves like that while still cold, I need to use the choke just a slight bit to get it to start, then feather it for the first 30 seconds maybe while it's warming up. After that everything's OK.
Same setup..single carb 720, bone stock with less than 80hrs since new. Brand Mikuni kit in the carb and all fuel lines new.

 

[CRei]

Ok if I pull this thing off and rebuild with genuine kit , where can I find the correct needle and seat? And what gram spring do I use? Pop off around 35? Thanks

 

[mikidymac]

2.0 needle and seat.
Reuse your spring, don’t use the ones in the carb kit.
Only genuine Mikuni parts.

 

[CRei]

Thanks, thinking about going new carb from Bay Area, says 1.5 needle seat and 95g spring , you think this is a ok set up?

 

[mikidymac]

Nope, run the correct jetting and parts for your model.

 

[CRei]

Ok I def agree, I’ll get a rebuild kit OEM and a 2.0 N/S. The spring P/N is 270500428 but does not tell me what color it is. Pop off 36-40 and low 1 high 0

 

[mikidymac]

Pretty sure it is the 95 gram spring. But pop-off will be more like 32 psi.

 

[mikidymac]

2.0 needle and seat.
Reuse your spring, don’t use the ones in the carb kit.
Only genuine Mikuni parts.

 

[CRei]

Sounds like accelerator pump or pilot circuit.

Is there a way to rebuild the accel pump, is there a check ball in there that gets stuck? Thanks

 

[mikidymac]

Yes and yes. Take it apart and clean it out but don't get carb cleaner on the rubber parts.

 

[CRei]

Yes and yes. Take it apart and clean it out but don't get carb cleaner on the rubber parts.

Ok cool do accel pump parts come in the kit or is it a separate purchase? Thanks

 

[mikidymac]

No not in the kits.

 

[CRei]

Ok carb complete apart also took apart accell pump diaphragm looks ok, hoses I hook a vacuum pump to they held vacuum no leaks. Removed the jets sprayed the crap out of them and looks have some very fine debris come out. Went over carb with a fine tooth comb don’t see any check ball, where it’s location?? Ordered new Mikuni kit with 2.0 N/S. From Bay Area power sports. Thanks for your help hope you are safe