How much flowwww?

Hey all. I just bought an 86 Vfr 750f from an old roommate that has been neglected by him and other former owners. I cleaned out the carbs really well as it essentially didn't run before. Now she starts up right away with no choke and idles without a hiccup. In neutral the throttle responds appropriately in all positions. Brought it out to test ride after fixing a couple other issues and found that the throttle response was no good. It wasn't boggy or anything, just very slow to accelerate. I could get it up to about 80 on some small roads, but I can tell it wasn't getting anywhere near 100 hp, as my 55hp Yamaha Radian 600 could still smoke the thing I'm sure.

Anyways, there is a clear gas line from the tank to the fuel pump and it appears that it's not pumping much fuel. My roomate installed a new in-line fuel valve and I can see the line is full of gas before it and has just a trickle after it and to the pump. I know that might sound like the fuel valve's fault but I have made other observations that would suggest it is not restrictive, and please allow me to continue. From what I can tell that is not the issue (until I purchase more fuel line to test to see how it works without the valve). My curiosity lies with the fuel pump. I am wondering how it is supposed to act on these bikes. My other bikes are all gravity/vacuum fed so I am unfamiliar with fuel pumps. When I turn the key, the pump appears to be "priming" possibly. It runs for no longer than a half a second. No real gas is drawn from that half-second. No real improvement is made when the bike is running.

Before I go into messing around with carb adjustments I want to see if they are getting enough fuel in the first place. So at what times is this fuel pump supposed to be engaged and should the lines be fuller than just a tiny trickle?

Additional info: Yes its possible that the carbs will need tuning. The bike has a custom Supertrapp exhaust so it could be running lean, explaining the lack of throttle response. I cleaned the fuel filter and it flows well. The tank however is rather dirty inside so a clog anywhere down the system is quite possible. Ultimately just curious if I can blame the pump for now running how/when it should.

Cheers.

 

I'm not a carb expert, so I can't really answer your actual question, but I notice that people tend to put a lot of stock in their bike starting with no choke. As long as I understand correctly, if your cold bike is starting right up with no choke that means that even with lots of fuel condensing before it reaches the combustion chamber the engine is still running rich enough that there's a decent fuel/air mixture. When starting a cold carb'd engine you should really need the choke, it shouldn't be hard to start...you'll just need it till the intake warms up.

 

What does the air filter look like? Should be able to see light thru it.

 

You also might pull the plugs after a wot run. Tan good. Black or white bad.

 

If the fuel cut relay is still attached just jump it and don't use it for a test run to see if that is the problem.

 

You'll only have more carb problems unless you clean out the tank really well. Do the relay bypass, then test pump flow into a jar as outlined in the FSM.

If the bike seems weaker than your Radian (i love mine !), i suspect that not all cylinders are firing.

 

Agree with all of the above, especially the tank.When you think you have it clean, clean it again. Use compressed air through the main fuel outlet on the tank, through the removed petcock, and the ports in the tank behind the petcock. When these holes are clear you should see some fumes coming out of the opened cap. Make sure to test your pump with good clean fuel once the tank is clean, jumpering the pump. This will help you analyze your pump, and push out whatever fluid you used to clean the tank before you hook it up to the carbs.
I believe you have the same pump as my 1000f, FSM states the pump should put out 30 oz/minute +/- 10%.

 

How do you go about bypassing the relay exactly? I haven't located the relay thus far so I could use a little guidance finding it. The engine sounds as I believe it should, but yeah I'll pull plugs to see if maybe a cylinder or two aren't firing. Yes I definitely plan on cleaning the tank, my impatience just has forced me to make sure the bike could run well before I dink around with cleaning the tank...

Air filter is orange and relatively thick so I imagine it was never see through, and it is lightly dirty.

Pawnboy, I'm having trouble understanding your point. From my knowledge, starting a bike without choke would be running it leaner than starting it with choke, as the choke prevents some air from getting in, allowing a rich condition. Running lean generally is not a good thing because it means you are running hot, but upon starting, your engine is cold so it doesn't really matter. Plus by the time it warms up, that mixture isn't technically lean because "no choke" is simply how you run a normal operating temp engine. Starting it w/out choke is technically leaner because the fuel doesn't vaporize as it should like when it is hot, however the same amnt of fuel is still reaching the cylinder, which would seem to help in the cooling process anyways.

Thanks for the input so far.

 

When an engine is cold the fuel will have difficulty vaporizing and will also condense out of the air on its way to combustion chamber, when this happens to a normal fuel/air mixture you usually end up with too lean a mixture to combust. So to combat this in a carbureted engine you have a choke, which enriches the mixture and combined with the previously mentioned vapor problems results in a more correct ratio in the combustion chamber, and voila, combustion. So if a cold engine can start sans choke, then it would stand to reason that it's always running as rich as a properly mixed bike with the choke on.

 

PB, you have alot of theories, reasoning based upon incorrect assumptions and somewhat flawed. On a VFR, for example, the "choke" (enrichment circuit) adds fuel but doesn't restrict air.

A well-tuned VFR with clean carbs will usually start and idle (with the aid of the adjustment screw) using no choke if temps are above about 60 degrees F. I prefer using the idle adjust screw for a fast-idle warmup rather than using the choke for several reasons.

 

I don't believe I ever said chokes always restrict airflow.

 

You're right. I was mistaken. It was Radianman. I do apologize.

 

Ya know. . .these posts come up pretty regularly. "I just bought/found/was given a VFR. It hasn't run in (fill in the number of years) but I am itching to ride it. What do I do?" Sound familiar? Having gone down this road, more times than I care to remember, I thought I would give a bit of advice. You have to check everything. I know it is tempting to put some fresh gas in it and see if you get lucky. You might but you will also spend many more days taking short cuts, getting stranded and finding other problems that weren't as glaring at first.

You have to go through it all. You have to check the air cleaner and the air box for nests. You have to clean and check the carbs, tank, pump and lines. You have to check the cable functions, choke and carb sync. You even have to check the exhaust pipes for obstructions. If you are going to ride it you must check the brakes, the condition of the chain and the tires. These are normal wear items and if the bike is suffering from neglect you can bet it is suffering from a serious lack of general maintenance. The tires will be shot, the battery sulfated and the chain crap. Don't forget the corrosion on just about every electrical plug and junction.

Once you work your way through check list then you are left with that one nagging question "why was it put in the garage and forgotten in the first place?" Many of these bikes just stop being used and that fine. Others develop problems that their owners either don't know how to deal with or find too expensive to repair at shop rates. This is were the fun begins. In a way I much prefer a wreck to a pristine example. You have a pretty good idea why they stopped riding the bike with the wreck.

On the current running issue: if the bike has been sitting and neglected might it be prudent to check and see if you have a brake caliper that is frozen? Just spin the wheels and see.

 

Regardless of how a specific choke works, you are still achieving the same thing to the idea that you create a more rich fuel mixture. As much as I like this debate, and I do (I don't even begin to claim that I know it all), I would like to know where the relay is and how you go about bypassing it. Two topics to this thread now; getting my bike running well (starting with the pump relay), and discussing the choke if we still want to as I love to learn.

 

Big Jim, so glad I was your target; your last straw for people with new VFR's. Seems like if you have seen it all, perhaps you no longer should spend your time on this forum. You have no idea what all I have looked over with this bike. In fact I have looked over the whole thing and sure as heck deemed it safe to ride before I saddled up. Had I not looked it over I sure as heck would not have been able to narrow it down to a couple of possibilities. If you don't have anything productive to say, then please do not say anything.

P.s. No stuck brake calipers (I Checked over the brakes too)

 

With the key off, pull the connector apart for the fuel relay, (right next to the regulator/rectifier) take a short jumper wire and jumper it across the white and black wires coming from the loom. Make sure you have a good fuel supply (I used an auxillary tank) and turn the key on. FSM says to run the pump for either 5 or 10 seconds, cant remember right off, read how much it pumped and calculate for a 1 minute run. I think I ran mine for 15 sec, it gave me a more accurate measurement. Do this with the carbs disconnected and the line from the pump running to a measured container. Once you know your pump is good, and you are ready to install your tank, do this same procedure with your fuel supply running from your tank. This will allow you to see if there are any remaining issues with your tank lines, and to see if the tank is indeed clean. You may have to put a pretty good amount of fuel through the tank to make sure.

 

YamahaRadian, You were not my "target" and I apologize if my post sounded like I was picking on you. I was not. I was making a comment on the general nature of pulling old bikes out of sheds and garages. It is something of which I have lots of experience since I can't stand for a good bike to go to waist. I have done this on every kind of bike imaginable except Harleys and they have their own group that love them.

I brought up the stuck brakes not to be shitty or to question your intelligence but as one of those things that can rob a bike of peak performance when all else seems to be running good.

 

Bikerrineb: Thank you very much. If I have time today I will give that a try.

Big Jim: I appreciate the apology and am sorry for misunderstanding you.

Reg71: Good question. I looked into it a bit before making this thread but am not sure one way or another. I prefer simplicity so it would be a cool route to go since I wouldn't have to rely on one more part that eventually fails.

 

Big jim speaks from experience: " You even have to check the exhaust pipes for obstructions."

Here is what i shook out of a VFR muffler that sat in a shed for just 2 years........