Electric Fuel Pump Question

[tomk1960]

Does anyone know if the electric fuel pump on the '84 Interceptors runs the entire time the bike is running? The reason I ask has to do with an ongoing starting problem that I (and many others) have with the DOHC 750F, 900F, and 1100F bikes. If any of my DOHC bikes sit for a week or more, it takes a lot of cranking for them to start. If they're started every day then they fire up quickly. Evidently the gas in the bowls evaporates over time creating this problem. There are members in the 1100F.net forum that have owned their F's since new and have said that this was a problem from day one even when they were new.

I'd like to come up with a solution to eliminate all the unnecessary cranking and wonder if an electric fuel pump would help. Perhaps if one was installed inline just before the carbs would fill up the bowls much faster. The only thing is that the pump wouldn't be needed once the bike starts and is running, so I don't know if a fuel pump would cause problems if it ran the whole time the bike runs.

Any ideas or suggestions? Thanks.

Tom

[YoshiHNS]

You could probably try a pump like the 4th gens have. No petcock valve with a prime position?

[gll429]

some of the old hondas needed to be primed up first. i just added a wire from the battery to the + side of the pump and a "press and hold " button to prime the carbs. then turned the bike on. presto! VROOOM!

[schwarzc]

The fuel pump on the ´83 VF750F runs only, when the crankshaft turns. Thats, what I have experienced. I also found a wiring diagram of the VF1000F - same system, see below;

http://binatani.com/wp-content/uploads/2011/10/Honda-VF1000F-internal-electrical-system-Wiring-Diagram.jpg

the fuel cut relay (top, right) is connecetd to the ignition coil for the 2&4 cylinder.

This line is marked with "Bu". It activates the fuel cut relay.
I removed the fuel cut relay on my 83 VF750, because it was broken, and connected the white ("W") and black ("Bl") cables.
Now, the fuel pump powers on, when i turn on the ignition.

other option: put a switch between the black and white line. if "on", it bypasses the relay, serving as a "prime device", as soon as you turn the ignition on, if "off", the bike runs with the fuel cut relay like normally, ....

[tomk1960]

The fuel pump on the ´83 VF750F runs only, when the crankshaft turns. Thats, what I have experienced. I also found a wiring diagram of the VF1000F - same system, see below;

http://binatani.com/wp-content/uploads/2011/10/Honda-VF1000F-internal-electrical-system-Wiring-Diagram.jpg

the fuel pump relay (top, right) is connecetd to the ignition coil for the 2&4 cylinder.

This line is marked with "Bu". It activates the fuel cut relay.

I removed the fuel cut relay on my 83 VF750, because it was broken, and connected the white ("W") and black ("Bl") cables.

Now, the fuel pump powers on, when i turn on the ignition.

other option: put a switch between the black and white line. if "on", it bypasses the relay, serving as a "prime device", as soon as you turn the ignition on, if "off", the bike runs with the fuel cut relay like normally, ....

So I take it that fuel can pass through the pump with no restriction if it isn't running? If that's the casee, it might be worth a try to add one as a primer on one of my F's. If it does the trick, I mod the others the same way.

Thanks!

[airwalk]

when I had those engines they always worked the way you're describing. the carbs have an accelerator pump function & as long as the linkage is adjusted correctly you can twist the throttle repeatedly to squirt raw fuel into the carb throats. takes a decent turn on the grip but will pretty much solve the issue. you may have to "squirt" several times to get the engine firing & then the choke(s) will do the rest. simpler than adding electric pumping.

[schwarzc]

The fuel pump on the ´83 VF750F runs only, when the crankshaft turns. Thats, what I have experienced. I also found a wiring diagram of the VF1000F - same system, see below;

http://binatani.com/wp-content/uploads/2011/10/Honda-VF1000F-internal-electrical-system-Wiring-Diagram.jpg

the fuel pump relay (top, right) is connecetd to the ignition coil for the 2&4 cylinder.

This line is marked with "Bu". It activates the fuel cut relay.

I removed the fuel cut relay on my 83 VF750, because it was broken, and connected the white ("W") and black ("Bl") cables.

Now, the fuel pump powers on, when i turn on the ignition.

other option: put a switch between the black and white line. if "on", it bypasses the relay, serving as a "prime device", as soon as you turn the ignition on, if "off", the bike runs with the fuel cut relay like normally, ....

So I take it that fuel can pass through the pump with no restriction if it isn't running? If that's the casee, it might be worth a try to add one as a primer on one of my F's. If it does the trick, I mod the others the same way.

Thanks!

I am not sure, if i understand you correctly (english is not my mothers tounge), .... as far, as i learned from my '83 VF750F:

Stock condition: fuel can't pass the pump, if the bike isn't running

add switch between black and white cables and switch it to "on", or bypass the fuel relay (connect wihte and black cable): the fuel pump delivers fuel to the carbs, when the ignition is turned on.

btw: sorry, made a mistake in my first post. 5th line: there should be "fuel cut relay" instead of "fuel pump relay".

[tomk1960]

when I had those engines they always worked the way you're describing. the carbs have an accelerator pump function & as long as the linkage is adjusted correctly you can twist the throttle repeatedly to squirt raw fuel into the carb throats. takes a decent turn on the grip but will pretty much solve the issue. you may have to "squirt" several times to get the engine firing & then the choke(s) will do the rest. simpler than adding electric pumping.

I wish it was that easy, but the accelerator pump doesn't squirt enough gas into the empty bowls to start the bike. These bikes have the automatic (vacuum controlled) petcock and that may be part of the problem. Gas doesn't flow freely from the tank to the carbs when you open the tank's petcock. The engine has to be turning to generate the vacuum needed for the automatic petcock to allow fuel to flow through. I may try installing a fuel primer bulb to see if that might help fill up the bowls faster.

[VFRBert]

The problem with these old bikes is the ventilation of the bowls. The lighter fractions in modern gas evaporate to easy, leaving the heavyer fractions behind in the bowls. The fractions left behind, burn not as good as the evaporated fractions of the fuel. For old cb's the trick is easy, close the petcock half a mile before ending a trip. The bowls wil be empty and are filled with fresh fuel after opening the petcock for the next ride. (I have had a cb 750 with this problem) For the VF it is more complicated and i would go for the prime option. Eventually after several weeks, drain the bowls before starting, with fresh fuel starting is much easyer.

[Guest]

Tom, there's no reason you can't fit any small, off the shelf 12VDC fuel pump to an inline four, but there are a couple of caveats.

One, it shouldn't put out more than 3-5 psi.

Second, you should either wire in a relay (which would ultimately defeat its purpose) or put it on a switch to be used only as a prime or after the bike is running. Or both. The reasons that all circuits are switched off while the starter motor is cranking are twofold, to maximize available amps to the starter motor and protect other circuits from surges. A low-psi pump will never defeat a float valve.

Whether it will passively allow flow when off is depending both on the pump and where you locate it--most will allow it and thus if placed fairly level with gas you'll get flow, but if located below it (say, down next to the battery box) and you'll need the pump to run at all.

However, I'm not altogether certain that priming is going to help because the problem appears to be more attributable to fuel issues than low bowl levels, as has been astutely noted. Fuel chemistry has changed such that it bears little resemblance to pump gas from even ten years ago.

Nowadays more than ever it's wisest to cut the gas and run to the stall point, which argues in favor of a full-on pump/relay setup with a dedicated relay bypass switch for priming.

The cool thing about the whole exercise is uniform color-coding across the board, so you can use a V4 wiring diagram to figure out where to insert a relay circuit for the inline 4.

Working out the kinks and producing a kit could be profitable because this very problem rearing its ugly head everywhere and with increasing frequency. I.e., Kawasaki, Yamaha, etc., owners will be interested as well.

Just don't get so busy that you can't powdercoat. LOL!

Jack

[VF1000RS]

My CB1100F with CR33's can still be hard to start. Not as hard as the stock carbs were. If it has sat for any time I roll the throttle probably 5 times then hit the starter button. It will either try to fire or will start. If not then 3 more twists and starter once again and usually will start with a lumpy idle. Full choke of course.

[SEBSPEED]

I noticed this on my 900 and it had me curious.

[tomk1960]

I noticed this on my 900 and it had me curious.

I brought up the same topic over on the 1100F.net forum and many of the guys there have the same issue. If I had the boatload of cash it takes to do it, I'd consider putting on CR carbs (mentioned above) which evidently are a LOT better and start faster. I wish it was as easy as just rolling the throttle a few times, but those darned bowls are virtually empty after sitting for a week. I might try the primer bulb suggestion as it would be a quick and easy experiment.

[Switchblade]

That explains the problems with the 93 I had stagnant fuel. The only thing with a constant running electric pump would be the danger of a accident and a fuel line rupture. That's way there's always a trigger signal to fire a relay ..

[Guest]

Yes, this issue is coming up with increasing frequency. Indeed, there is a "worldwide pandemic" of carburetor failures underway.

So, naturally I researched a little and made some disturbing discoveries.

What we're putting in our tanks is a witches brew of stuff that when it comes out of the refinery merely mimics the behavior of gasoline as we think of it from the old days. By old days I mean as recently as five years ago.

Have a good close look at the MSDS from Tesoro. This is a "recipe" of sorts, with a great deal of variability built into it. A blend from one production run can be vastly different from another owing to whatever they have on hand at the time. Price of sub-components drives this and wouldn't you know it butane costs a fraction of LBP naphtha.

msds.pdf

Congress quietly changed regulations during the Bush years. Well by "changed" I should say "did away with entirely" but I don't want to be a right-wing basher because Obama hasn't exactly been a friend to the consumer either. His appointee to run the EPA demands 20% ethanol, which has riled Sens. Boxer and Feinstein, to name just two--who want the whole matter turned over to the National Science Foundation for rigorous real-life study. Fat chance.

For a little video on this aspect of things see this: http://www.youtube.com/watch?v=TgK7FQFv3lo&feature=youtu.be

Here's the problem at the chemical level: the components don't remain at the same relative concentrations.

Butane, for example, has a much lower vapor pressure than LBP Naphtha (which used to comprise pump gasoline 85% by law.) So they put something else in to suppress its tendency to pre-ignite.

However, in a float bowl (exacerbated by heat but continually nevertheless) the butane evaporates out of the vents but not the suppressor components, which remain behind in increasing concentrations as the process goes on.

And of course if the ethanol in it is saturated with water it only adds its own ignition-suppressing character to the mix.

The end result is, well, precisely what we're seeing. This was predicted by those who were labeled “liberal noise-makers” by the petroleum lobby and their stooges in congress.

Like Nila says, it's not going to get better any time soon. The opposite, in fact.

[VFRBert]

Does anyone know if the electric fuel pump on the '84 Interceptors runs the entire time the bike is running? The reason I ask has to do with an ongoing starting problem that I (and many others) have with the DOHC 750F, 900F, and 1100F bikes. If any of my DOHC bikes sit for a week or more, it takes a lot of cranking for them to start. If they're started every day then they fire up quickly. Evidently the gas in the bowls evaporates over time creating this problem. There are members in the 1100F.net forum that have owned their F's since new and have said that this was a problem from day one even when they were new.

I'd like to come up with a solution to eliminate all the unnecessary cranking and wonder if an electric fuel pump would help. Perhaps if one was installed inline just before the carbs would fill up the bowls much faster. The only thing is that the pump wouldn't be needed once the bike starts and is running, so I don't know if a fuel pump would cause problems if it ran the whole time the bike runs.

Any ideas or suggestions? Thanks.

Tom

Maybe this is the solution:http://www.cmsnl.com/honda-vf750f-84v45-interceptor-usa_model1115/valve-set-starter_16046ma6003/#.UtL_v_seWx0

I read an article about air cutoff valves on the carbs of cb750/900's. These things are air blockers, restrickting air flow, to increase the fuel/air ratio at low rpm. When leaking, starting the bike is difficult. The valve starter set on the vf series, have the same goal. And what many people do not know, even mechanics, is that these valve's wear in time, with increasingly difficult starting.