[DannyChaos]

1991 CBR 600 F2.
Bike stutters and surges under excel,back fires and pops under decel.
Carbs and all jets are clean. Has all the fuel it could ever need. Plugs are in great shape no lean burns or black. All hoses in good shape no leaks of any kind.
I dumped alot of money into her last season and she ran like a cat with a hot pepper up its ass. Winterized through the snow,fired right up and has been through about 6 tanks of fuel so far this season. About two days ago on a long trip home from upstate ny I felt a bog when pulling away from s light.Thats when all this crap started. Bike still screams under full excel but when crusing along or pulling away from a stand still it decides to have fits. Valves were all checked at the end of last season and were all right where they should be.Carbs were synced last season when they were jetted.Im lost at this point and could really use some help.
This bike was gonna begin its transformation into a fighter this season but with the shit luck I have been having so far Im not sure it will ever happen.

 

[black93lx]

bad gas? kinda sounds it. Seafoam and see what you get.

 

[DannyChaos]

Funny you should say that.I ran sea foam already with no luck.
And it has been going on now through about 3 or four tanks of gas from dif stations.
I also cleaned the hell out of the carbs today and than took it for a spin,still poop.
It almost feels like a miss fire or like its running lean,but the plugs say other wise.
Thank you very much for the reply though.

 

[fire104]

check your coils make sure they are not loose.

 

[rpp1100]

torn diaphragm?

 

[fslflint]

carb boot leak?

 

[DannyChaos]

Good call on the coils,I will give that a look.
As for the petcock,I flipped the spring to the other side of the diaphragm. So there is no vacuum only on and off.
The carb boots may also be something to take a closer look at.I had them apart today and everything looked fine but I wasn't looking directly at the boots.
Thank you all for the ideas and I will look over all of them.
~DC~

 

[up2L8]

Good call on the coils,I will give that a look.
As for the petcock,I flipped the spring to the other side of the diaphragm. So there is no vacuum only on and off.
The carb boots may also be something to take a closer look at.I had them apart today and everything looked fine but I wasn't looking directly at the boots.
Thank you all for the ideas and I will look over all of them.
~DC~

We have a communication error here somewhere.

Are the carb diaphragms ok? that was my first suspect. Is that what you and flint are calling carb boots? My carbs dont wear boots.

and what did you do to the petcock?

air leak anywhere else?

 

[DannyChaos]

Nope no air leaks..as for the carb boots,lol I was talking about the rubber couplers that connect the carbs to the motor. As for the petcock that honda can not get right,I took it apart and moved the spring to the opposite side of the diaphragm.It is a old track trick for the F2s due to the fact that the petcocks always fail.It eliminates the vacuum and turns it to a on ,off and reserve. The carb diaphragms look to be in good shape but I dont know of any way to test them other than by sight.
~DC~

 

[swiftnet]

Does it idle?
What throttle opening does it suck and work right at (grease pen your throttle openings, 0/25/50/100)

 

[Dusaki]

I see that you have a set of nology wires on your bike. Are these the wires with the extra capacitor attached to them? If so I believe there is a ground wire for each wire. Make sure to check these grounds. I've heard some horror stories about these. The wires cut out at low rpms. I would throw a set of dyna wires on and see if that changes anything. Also, make sure you ignition pickup is tight.

 

[DannyChaos]

Yes it will idle,but it chugs a bit.
Half throttle is where it starts to clean up anything under that has a gurgle to it.
But again,that is only when you twist her open slow.If you just grab a hand full fast she opens right up with no problems.
The wires and grounds seem to be working fine,I checked the spark across all 4cyl and it was nice ,bright and even. But for the hell of it I will try my dyna's and see if there is any change.
When I cup my hand over the exhaust and bring the rpms up slow I can almost feel a suction that pulls my hand up against the pipe.But thats only in the rough section of the rpms.
I know that sounds retarded but I want to give you guys anything I can to help get this damn thing fixed.
Again,thank you all for the pointers and I will go over each and every one of them.
~DC~

Ps. (grease pen your throttle openings, 0/25/50/100) Ya lost me there..

 

[Dusaki]

Yes it will idle,but it chugs a bit.

When I cup my hand over the exhaust and bring the rpms up slow I can almost feel a suction that pulls my hand up against the pipe.But thats only in the rough section of the rpms.
I know that sounds retarded but I want to give you guys anything I can to help get this damn thing fixed.


Do a compression check.

 

[DannyChaos]

Man I hope that's not the problem,but good call.
Just got a D tool to adjust the pilot jets,now I just have to find out how many turns out they are supposed to be.
Can I get away with using a comp tester for cars?
Thanks
~DC~

 

[DannyChaos]

I have searched all over the "inter web" and can not find the factory cylinder compression of my bike.Im gonna test it tonight but would like to know what it should be before I do so.
One guy is saying anything over 100,but that is a little to vague for me.
Any help would be appreciated.
Pilots are all set to dyno's chart and carbs are spotless.Im going to dig through the main harness and see if I can find any crispy wires or bad grounds.



"I love you CBR" click click "but this is for your own good" BANG!
~DC~

 

[Dusaki]

Man I hope that's not the problem,but good call.
Just got a D tool to adjust the pilot jets,now I just have to find out how many turns out they are supposed to be.
Can I get away with using a comp tester for cars?
Thanks
~DC~

As long as the thread matches up you should be fine. I wouldn't worry about what they are supposed to read as much as checking for a burnt or bent valve. I would say 110-150psi should be ok.

 

[DannyChaos]

Cool man,thanks alot.

 

[DannyChaos]

First off,thank you all for the help,ideas and pointers.
The problem is solved and she runs better than ever.
I broke the carbs down till they were nothing more than a table covered in nuts,bolts,screws and doodads. Rebuilt um and when I got to the Pilot jets I figured,why not let the ol girl drink a bit.
Rather than the 2 and a quarter turns out that they were at since last summer,I said F it and went almost 3.Slapped them back on the bike and crossed my fingers.
lol Lets just say she has never pulled like this in the whole time I have owned her.
Idle is great,throttle response is dead on.Low end power feels amazing and I think I feel a bit more pull up top as well.
Again ,thank you guys and I will see ya on the road.
~DC~

 

[spondonste]

You can figure out the compression value the bike should give based on the compression ratio. Atmospheric is 14.7 psi so a compression ration of 10:1 is 132.3psi gauge (147psi total). CBR600 F2 is apparently 11.6:1 so you're looking at 156psi gauge for a pristine example with no losses.

 

[vernk]

why would this problem come up suddenly though, afer working just fine for some time? that part eludes me.