93 VFR750F RC36 running rich what can i do before sending it to a bike shop

Good day to all you VFR lovers out there i am a proud owner of a VFR750F RC36 93 model and i am loving every second that i ride her but she is very thirsty and she backfires when i close the throttle, that to me means that she is running rich just want to know what i can do before sending her to a bike shop, and what is the standerd size of the jets on this bike? can any one can help me please?

 

Backfiring on closed throttle deceleration is usually a result of running lean not rich. Check your plugs to see if they give any indication of what's going on. The plugs would be black with excessive carbon building if you are running rich or whitish colored if you are running lean. You want your plug colors to be a brownish color somewhere in between. Next chec for air leaks by inspecting your air filter and carb boots which crack easily due to their old age. Is this bike stock?


Rollin

 

AS far as i know it is stock altough the guy i bought it from derestricted the bike other than that it has a streight open pipe at the back but the frount section of the exuast is standerd

 

Did you check the air filter and carb boots for damage? Also keep in mind that high-flow aftermarket air filters can cause a bike to run lean if the bike is not properly tuned / rejetted to accomodate the increased air flow. The easiest way to test the carb boots is to start the bike and then CAREFULLY spray some starter fluid on each of the carb boots. If you have an air leak the engine should rev up as the fluid is drawn in. Be very careful when doing this and have a fire extinguisher handy :biggrin:

Rollin

 

A bike of this age should probably have the boots replaced.

I had a similar problem as you. Turned out to be a K&N Jetkit. They never seem to run right with Jet Kits installed.

Sorry I am too lazy to read the whole thread but I would have a look at your floats and make sure that they are set at the correct height according to the manual, or even an gasket leak, vaccum piston.

You need to pull the carbs off and check the specs against the factory manual. I did, and then I realized that the jet kit needles were of a different length and thickness than stock! It turned out that was the problem. When I pulled them out and put the stock ones in, everything was fine. Bike fired right up, even with wet plugs.

If you give me the number on your needle jets I will compare it with mine when I get home. If your needles are connected with an adjustable circlip I will bet my wife ( not my life, hehehe) that you have an aftermarket jet kit.

 

I'd get a pipe on that bike, having an open header affects the way the bike runs. Rumors say that due to the complete absence of backpressure and the leaner conditions it causes, it can even burn exhaust valves.

 

(other than the above suggestions) backfiring can be caused by air getting into the header/exhaust system from a leak - igniting unburned gasses in the system. Check for leaks

 

Several areas here where the factory manual can be downloaded as a PDF..

Plugs, boots, jets and floats are all good things to check. Synch those carbs too.

 

manual PDF
Download VFR 750F Shop Manual.pdf from Sendspace.com - send big files the easy way

 

Thanks Guys ill start pulling her apart tomorrow night and check and see whats going on