Bike dies when opening throttle

[whwar9739]

Ok so brief synopsis of what is going on and what I have tried.

Currently the engine starts up and idles great, however, when I get to 1/4 to 1/2 throttle the engine starts cutting out and eventually dying. So far I have tried cleaning the carb twice the second time letting the 'hard' parts soak for 18 hours. I have tried adjusting the pilot screw, removing the air filter, cheap man's check for a short. And all with nothing. I have checked that the petcock is clean and all hoses to and from, gas flows freely when put in pri position. I plan on trying g to check the amount of fuel in the float bowl after both idling and killing the engine by opening the throttle. Any other suggestions?

Also I have check the spark plug, and even changed it out.

New battery and currently kept on the tender when not working on it.

Checked the vacuum passage on the petcock as well as the vacuum line all is clear there.

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[jonathan180iq]

It has to be an air fuel deliver issue. Even though you say you've checked the obvious things, that's what it sounds like to me.

1/4 - 1/2 throttle indicates something to do with the needle jet. Check all the connections there. Make sure it's sliding properly and that the little spring that operates it isn't binding or something.

[mhoneycutt84]

It has to be an air fuel deliver issue. Even though you say you've checked the obvious things, that's what it sounds like to me.

1/4 - 1/2 throttle indicates something to do with the needle jet. Check all the connections there. Make sure it's sliding properly and that the little spring that operates it isn't binding or something.

First off Hello everyone, both WHWAR9739 and I are new to the forum here. Him and I have been trying to get this bike running smooth for a bit now so any help is appreciated. So far I've read a lot of great info on this bike.

jonathan180iq, am I correct in assuming you are referring to the diaphragm slider needle? When we had the carb apart last time I didn't notice anything out of the ordinary with it. This is however the one thing we really haven't played around with in the carb yet.

Have any suggestions on what to look for exactly? The diaphragm looks to be in pretty decent condition, and the slider does move up and down freely, just with the normal slight drag you would expect from the diaphragm.

The one part that I am not 100% confident on is the orientation of the needle jet itself...it slides in under the main jet and main jet holder but is it possible we could have put it in upside down? IDK I'm just running through the options but ANY suggestions on what to look for would be extremely helpful.

Thanks!

[jonathan180iq]

I haven't had one of these things open in a long time so I'm usually just going by memory.

Check out Quimrider's thread about how to adjust the needle jet. It had some pretty good photos. From what I recall, there is a way to get things easily turned around when reinstalling and thus not allowing it to function properly.

Also, the seat of the diaphragm itself can get knocked out of the ringed groove fairly easily when you are reinstalling the black top cover. If it's even offset the least bit, it will pinch between the cover the carb and cause a slight air leak. You have to make sure that's all cleaned and sealed in order to go forward.

I say that 1/4-1/2 throttle is most affected by the mid range controller (the needle jet) because of general carb theory and I'll stand by that. It doesn't tell you exactly what the issue is, but it will at least tell you where to look.


-How does it respond when you put it in neutral and rev it into the 1/2 throttle range? Does it do the same? Have you guys tried the good old fashioned WD-40 leak test trick to see if the idle or throttle behaves differently when you spray different parts of the intake with it? - Also, check the "S" tube that connects the crank case to the bottom of the air box. And check that the drain tube coming form the bottom of the airbox is sealed off at the bottom.

[whwar9739]

Does the same thing in neutral. I will definitely check out that other thread.

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[jonathan180iq]

It's good that it happens in Neutral. That just verifies that it's definitely a mixture problem.

[raul10141964]

check the main jet and the flout level an needle

[whwar9739]

One little tidbit if I start opening the choke, I can get it to rev a little higher

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[raul10141964]

main jet is clog

[whwar9739]

All 3 jets have been checked several times. All 3 have been soaked in a carb cleaner, all of them have been run through with spray carb cleaner. And for S&G I tried brand new gas, still same thing. Checked the diaphragm, all looks good. The needle appears to function fine, goes up and down freely in the needle holder. Even checked the nozzle(?) inside the main jet to ensure correct orientation.

[raul10141964]

check if part #13 is not missing or damage part # 38
http://s11.postimg.org/b0gcs78b3/gz_parts_manual_11.jpg (http://postimg.org/image/b0gcs78b3/)

[whwar9739]

13 is the nozzle I was talking about, I even verified correct orientation of it. I have not yet double checked 38

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[whwar9739]

Also wanted to add that I checked the fuel amount in the float bowl both after killing the engine by opening the throttle and by voluntarily shutting the engine off. Level was the same each time.

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[raul10141964]

check the number of the main jet (120 or more )

[whwar9739]

Just to make sure I'm checking the right 'main' jet. We are talking about part #16 correct, and not 28 or 29.

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[raul10141964]

yes part #16

[whwar9739]

Well folks, finally decided to hang up my mechanic's belt and let a pro at it. Thanks for all the help and I will definitely post the results.

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[whwar9739]

Well folks turns out it was 2 issues, two jets were switched around, and the o-ring on the pilot screw was cracked and in the hole. The bike is all up and running g great now. Thanks for everyone's help.

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[2011Suzukidude]

My GZ only has 2,600 miles on the clock.
i can only do around 35mphand at full throttle
in 5th gear. I'm not a mechanic. What could it be?

[OldNTired]

My GZ only has 2,600 miles on the clock.
i can only do around 35mphand at full throttle
in 5th gear. I'm not a mechanic. What could it be?

Well, for one thing start a new thrsd so people notice you and your question!
And when you do, give us some information about your bike,
and as detailed a description of the problem as you can.
Mention any maintenence you have done lately, as well as
the age of the bike and any mods you may have done to it.