So I have search the site high and low and could not find the answer to my dilemma. I recently purchased a 97 cbr 600 f3 for my wife and the previous owner said the fuel pump went out and he just took it out and gravity fed the old girl (got a fuel pump on order just incase that's the problem), but upon getting her home I took her for a ride and noticed once she hit about 45 mph she started spitting and sputtering and would pretty much lose all power. So I got to looking the bike over and noticed a few thing, first was the fact the bike was missing every bit of the ram air so I figured maybe that was the problem so I purchased the ram air and all the hoses back to the air solenoid and cleaned the carbs while I was doing all this work (noticed all the jets were factory 135 and 138). Took her for a ride and still spitting, so then I noticed he had some aftermarket exhaust (mid pipe and can) and he gutted the can (yes, gutted an aftermarket) so here's my question.

Would having an aftermarket exhaust with gutted can affect the air/fuel ratio this much or does not having a fuel pump hurt that much? Sitting still the bike has excellent throttle response and off the line she's like a rocket but once the air starts moving thru her she gets all choked up.

Sorry for the long read but im losing faith in getting her running and my wife is getting impatient as she is ready to ride.

Thanks for any advise,

Chris

 

Have you pulled the plugs to see what its doing. The plugs will give you insight to the mixture. Perhaps they could need replacing....

 

+1 demon....also, when the PO convert it to grav. feed, did he took off the gas filter? Can the filter be very dirty which disturb the gas flow when feeding at higher pressure? Just throwing in the possibilities...

 

the exhaust should not effect it the way you describe. minus the spitting and sputtering i had a similar problem. my f4 ran fine at idle and would pull ok up to about 5-6k rpm, it felt like the clutch was slipping or it was loosing power. i had a bad connection to the fuel pump and a bad/clogged fuel filter. i rewired the fuel pump and got a new filter. it runs good again

one thing that i noticed with my fuel system. (before i replaced the filter) while diagnosing the problem, to test to see if it was a bad fuel filter i test rode the bike and had to ride without the filter for a day til i got a new one. soon as i rode it without the filter i knew that was the problem, it pulled really strong again like normall. however, when i put the new filter back on it ran even stronger and with a lot better, smoother throttle response. in other words the fuel filter did make a very noticable difference in the function of the whole system. i know what it feels like when its functioning with a new fuel filter, when its clogged and when there is no filter at all. there is a difference in all three ways. just not any sputtering or spitting like you said yours is doing. give it some time, you'll get it. we will help

o, check the vent breather hose or hoses coming off the fuel tank to make sure they are not kinked or blocked. check all fuel hoses for kinks, and check all the vaccum hoses going around and to the carbs. did you check the vaccum pistons, needle and spring in the carbs? sticking floats? maybe the little air induction tubes have a filter thats clogged, check it and it might have a little breather hose coming off it check that to...if its anything like the f4.

im sure there is a manual on here somewhere for the f3. there are some real f3 experts on here..they will chime in soon

 

The previous owner when taking off the fuel pump deleted the filter as well, but I will pull the plugs and see what I can find out. But if a plug were fouled wouldn't you notice it during trying to start up and during idle and throttle response? When I first got the bike I figured for sure the carbs were jets were clogged due to him running it straight with no filter, but everything in the carbs looked pretty clean. The PO claimed he just replaced the plugs prior to me buying the bike but I know ppl will say anything to sell you something.

 

Is it just my phone not letting me download any of the manuals, or are all the manuals blocked so people can't access them free?

If anybody has the manual downloaded and wouldn't mind sharing it would you send me a copy to my email? Its: shaggy08xr@gmail.com

 

all i have is the f4 one. you should be able to down load it from a laptop or desk top computer

 

Thanks for the help bro, I figured out that it was just my phone being ****. It downloaded just fine to my desktop.

So now to fill everybody in a little more on my dilemma. I pulled the carbs of once again just to make sure I didn't miss anything and I noticed that the first and fourth main jets were not 135. They were 136, so my question is this. The 1,4 jets being 136 and the 2,3 jets being 138 would this cause my mid and high range spitting and sputtering? Otherwise, everything looked good.

Help me, please.

 

try this.... On the right hand side you have a tube going from the air box into solenoid and then there is a tube from the selenoid into the carbs. Remove the selenoid and connect those two tubes together. Remove all tubes from the other side of the bike which are coming from the front of the bike.. . All the small tubes and solenoid are only working when u are riding under 12kph.

 

To answer your question directly... and assuming you have checked all the fuel related problems (including fouled plugs)...
Yes. Open exhaust does affect the fuel air at the engine. It's complicated and relates to backpressure keeping expelled and unburned fuel in the chamber a hair longer for more complete combustion. Yamaha's are well know for this very problem. It is very common to have to rejet the carbs (or change injectors) when an open exhaust is installed on a stock bike. One of the cures (on certain bikes) is changing the crancase ventalation as well, but this gets complicated and probably does not apply to your situation.
Bottom line is severe reduction of backpressure affects fuel combustion, and the smaller the cc's, the greater the affect. Also reduces low end torque by a small amount. If you are going to run open pipes, rejet and run hotter plugs. The unburnt fuel will foul the standard plugs quickly. And do not open the gap on the plugs to compensate... you run the risk of contact with valves or pistons if your tolerences are very small.
I would replace the baffle or install an aftermarket exhaust, and than readdress the problem after that. All of this is assuming, as I said earlier, that you have already ruled out the other problems suggested in this forum.