So confused, 1996 VFR wont draw in enough fuel into engine

Ok here it goes. A family member gave me his 1996 Honda VFR750F. The bike sat in for about 5 years. Yeah I know that is a long time. To my surprise, inside the fuel tank looked great. I have worked on bikes that sat around for a while so I know the routine. I have cleaned out the fuel tank, and fuel tank filter. Changed fuel filter. I took apart the carbs and cleaned main jets, main jet holder, idle jet, brass enrichment tube, float valve screen. Basically, where ever I could get a wire through a port or a cleaner down a port I cleaned it with carnb cleaner amd compressed air. The pilot air screws was about 2 3/4 turns out from closed. The carburetor diaphram thing operates smoothly. The bike will now run and idles very smooth and no tapping noise from the engine either.
If I light blip the throttle lightly to about 2500 RPM, the engine will rev very nicely. However, past that all goes to hell especially around 4 RPM and up. In fact the bike wont even rev over 5500 RPM. It just bogs really bad. When I'm riding it, it has very little power above 1/4 throttle, and no power after 1/2 throttle, ( Seriously nothing happens over 1/2 throttle) The plugs are all new.

I took the air box off, attached a fuel line and noticed when revving the throttle the jet needle does not move upward far at all to allow the main jet to supply fuel directly into the engine. I know the main jet and needle jet passages are clear because I cleaned them out well. I'm confused because I know that vaccum is what makes the CV carb system on this bike work . The rubber diaphram does not have any tears in it, however for some reason it's hardly moving in at all to allow the fuel to rush in from the main jet. The carb jets are all stock (125 main jet) The float is non adjustable. The float valve looks great, the ends still have all the rubber on it.

So, I'm thinking about getting a jet kit for it. With larger main jets, and the ability to adjust the jet needle position with clips will allow the main jets to supply more fuel.
Or, am I missing something because the rubber diaphram that moves the jet needle up which then supplies fuel into the engine is not functioning right because of some else, like lack of vacuum pressure. One more thing, the bike is definetly running way too lean, the spark plugs are white with like white crystals on it. A typical lean condition.

Any help would be great.


HRCH

 

Are all the cylinders equally lean? Screens on float valves clean? Stock air filter? Does the engine ever die like it's running oot of fuel? Grasping at straw's from this distance. Not so sure the lack of movement from the slides is a cause and not an affect of the the engine not spinning up. Do not toss a jet kit at it until you get this sorted.

 

Yes all the cylinder are equally lean. All four plugs have white particles on it. They are all lean. It has a new stock air filter. It has an old two brothers racing slip on. The bike will would stahl if i kept the throttle wide open. It seems like its really starving for more fuel. The float valve are great all clean and blown through with compressed air. I can even blow through the fuel inlet and if the float was removed the air will come through the screen. I know the jet needle not getting pulled by the vacuum diaphram may the affect of something but at this point im baffled as to why its happening. Im going to check the manifold vacuum of each vacuum port. I wonder if a valve not opening up far enough could be the cause. But then again all four spark plugs indicates a very lean issue.

Thanks
Hrch

 

I think your carbs need a better clean, especially given the long sit between owners... clean and run a tank of seafoam or two

that being said, have you considered the fuel filter may be clogged and/or the fuel pump is not putting out?

 

Believe me the carbs are clean at least where I can reach it to blow it out or run wire through it. So is the tank. The fuel pump is pumping. I ran a tank of seafoam already. I have replaced the fuel filter. Could the float bowls not filling enough, but the floats are non adjustable. I wonder if I can borrow the fuel pump from my ZX11. It looks similar. The fuel pump may not be supplying fuel fast enough to the float bowl. Very confusing.

HRCH

 

I have a VF1000R engine that runs perfect. I did a experiment and installed a plexiglass window in the airbox so I could see the slides move. You would not believe low little they actually move.

If this was my bike I would take the carbs off and take out the idle jet and look through it to see if I could see day light through the idle jet. If it sat for all those years I would bet money that all the carb clean would not clean those out. The gas turns to brown thick goo. I have had to get a special drill bit and turn it by hand to get the junk out of the idle jet. You can only get the right size drill bit from a model makers supply store.
YOU CANNOT USE A PAPER CLIP. It is way too big. It will also ruin the brass jet.

Make sure you install BRAND NEW FLOAT NEEDLES. End of story.

 

I have that spec, thank you though. However, the float on this bike does not have a metal tang to bend. It's all plastic. I have adjusted float height on my ZX11 and the float did have a metal tang to bend, but not this 96 VFR bike.

I wonder if this whole issue is caused by ignition timing and not something fuel related.
I'm checking the valve clearance now. (just to be on the safe side).

HRCH

 

As far as the idle jet, I did get it clean. I can see light through it. I can also see light through the 3 small pin holes on the side of the idle jet. I also blew through the port where it screws into. I used a wire to break the build up in the idle jet.

I'm wondering if this whole issue is ignition timing. Have there been any issues with ignition timing on a VFR?


HRCH

 

As far as i know, the ignition timing never goes bad unless the cdi is messed up.

 

sounds like fuel starvation, try opening the gas cap and running it. You may have a blocked vent.

 

....just reread first post here and believe this is a case of pinched diaphrams, not properly seated or aligned in the groove between top and top cap. Also, a small air passage (brass tube) could be blocked.

If the slides don't go up and down normally, rejetting won't help.

You can test slide operation easily with compressed air on or off the bike.

 

Ok I just checked all the valves for clearance. Specs says Intake should be .16m +- .03mm and exhaust is .25mm +- .03mm. The rear head all falls within. However the front head cyl # 2 and # 4 outer intake valves are at borderline of .13mm. Cyl # 2 inner intake valve is off, it measures .11mm. Cyl # 4 inner valve is within at .14mm

Should I do anything with the intake valves at borderline? I know I have at least one intake valve to shim down to increase the clearance.

I'm not too sure if these numbers have any effect on how this bike is performing.

I'm going to check the fuel tank vents, however the same thing happens with out without the tank on. I use a separate tank to run the bike when the fuel tank is removed.

I wonder if the fuel pump is providing enough flow??

HRCH

 

The manual tells exactly how to test fuel pump flow into a can.

If the valves are within the service limits, just put the covers back on and check again after 5-8000 miles cuz they're absolutely OK now.

 

Well, as you said the pump is flowing. I checked the pump flow per the factory manual. I measured 200cc for 5 seconds. I did it five times and each time the fuel flowed 200cc. I used the bikes fuel tank as a fuel supply and checked the flow out of the pump. The manual says to multiply that measurement by 12. That would give me 2400cc about 2-1/2 times the minimum flow of 900cc per minute. So I could safely rule out a bad fuel pump. If I open the fuel petcock, fuel will just about poor out of petcock. I guess I can safely say the fuel tank vent tubes are ok.

My brother in law did tell me that the bike ran before he parked it.

HRCH

 

I did find one valve out of spec (.11mm, should be .16mm +- .03mm) but I doubt it's enough to cause a problem. I did went ahead and ordered a shim 2 sizes down. The honda dealership parts guy told me they don't stock any valve shims. The service department told me they don't normally sell shims to people and then decided to look for the size I needed, however the service guy later said they ran out of the size I needed.
So, I once I get the engine back together again, I will continue with the diagnosis.

This dealership also offers ultrasonic carb cleaning. Its $25 if you remove the carb from the bike and dissemble the carbs (remove jets, slides, and so forth). So, I will take it in while I wait for the 1.875 valve shim to arrive.

I still can't understand why bike shops never want to stock any parts. I guess they are watching their operating cost.

HRCH