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Hi,

 

I have been through my Honda VFR 750 Service Manual (1997) as well as Clymer - can't finde any information about flow rate for the fuel pump. Do I need glasses or is it just not there? In any case, the actual number (or reference) would be very much appreciated.

 

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I looked into the common service manual...nothing there either.  My guess is since the pump operates in a pulse-mode.....that a flow rate is not spec'ed.  As long as there is flow from it, not a trickle, but a flow...then it is probably adequate enough to keep the float bowls full.  Since these years will work by gravity flow....at lower speeds....again, it seems like almost any amount of flow out of the pump is good.

 

I have tested others by putting the fuel line into a container and then apply power directly to the fuel pump and watched the flow.

 

Do you have one that is not working at all?

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The pump does work - tested with a short and empty bowls; clicks steadily until bowls are full. I just realise one flaw with my test - I did not test the relay.

 

I should have put my reasons 🙂 A few times (maybe 2-3 during last 12 months, I experienced abrupt power loss (it still accelleration - but its like you switch off x procent power at once) during hard acceleration at about 7-8000 RPM. I'm not able to duplicate it, so I'm somewhat in the dark. I assume it also could be a rarely sticking float too...

 

Earlier this year I cleaned the carbs - jets (boiled in mild vinegar), o-rings changed, new float valves, checked the air-cut-off valves (changed two with cracked o-ring), checked vacuum pistons+needle, cleaned SE (that really helped). Float heights checked (I used one carb to test all floats; now thinking about that approach I realise it assumes all carbs to be totally alike, but as floats are NOT adjustable, I guess that might be ok). Even though everything looked pretty clean before idle is now sooo smooth at 1000 RPM (after a sync and adjusting pilots; pilots NOT adjusted lean of peak - I adjust to about peak).

All jets and needles are stock.

 

As the power loss have accrued again my carbs clean is either a bad job or not the problem. So that is why I though next step would be fuel delivery. Flow rate would have been nice - that could clear tank strainer, fuel filter (about 1 year) and pump. 

 

 

 

 

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Do inspect the "contact points" inside/top of the fuel pump. A replacement kit is available when these are eol/starting to "weld" together. 

 

I will dig out some pictures tomorrow. Close to midnight here...

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the fsm specifies the flow rate.  bypass the often-defective pump relay with a wire.

 

FLOW RATE:  800cc/27 US oz/ minute

 

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open.jpg

 

 

 

IMAG2442.jpg

 

 

 

New set:

apoint.jpg

 

apoint2.jpg

 

 

I filed the old contact point somewhat, but you can see the effects of sparking

 

after1.jpg

 

 

By design, there will always be a spark. This can be diminished by adding a diode in the path.

These pictures were lost when Photobucket ransomed the stored pictuers..... but if you google you will find similar how-to's

 

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Dutchy - thank you; great pictures. I assume this is part of the pressure switch. I have never taken this fuel pump apart and my mind does not quite grasp how pressure is "transferred" to this switch... I guess it make sense once I take it apart.

 

Squirrelman - great. I went reading again - this time with stern focus on details. I'm a little embarrassed - service manual page 19-23 (61MZ700). In my book it reads 900 cc/min or 30.4 US oz/min. My rough estimate is this engine can't consume more than 395 cc/min, so 800 or 900 cc/min does not make any difference at all.

I'm not too thrilled about permanently bypassing the fuel relay... but I do see how this would rule out 1) pickup, 2) CDI, 3) fuel relay and 4) bad connections. Well, more correctly, a problem with one those 4 issues would not escalate into a fuel delivery problem.


Checklist for now is:

1. Flow rate, fuel pump

2. Contact point, fuel pump; check and fix

3. Float levels as they sit in each carb

4. Electrical connectors from fuel pump all the way to the pickup; check and clean

 

Btw - the drawing on page 19-23 is wrong - filter is upstream of pump 🙂 Or do I need a new brain?

 

 

IMG_9287.JPG

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It is part of the pump assembly (on top; in the drawing above to the right).

 

AFAIK, the way it works is that as the plunger rises if will eventually push the contacts towards each other. This causes a "short"(hence a spark) which will cause the plunger to fall back. And repeat.

I once posted a small video of this in action but it is lost forever...

 

Your bike WILL run OK w/o the fuel pump, just re-route the hoses.  I'd make sure (jist guueessing) that I'd not let the fuel level in the tank drop below 1/4.

 

The fuel relay ensures that if the engine stalls, so will the pump. To avoid that (in case of a crash for instance) the engine is off but ignition still on, fule will continue to be pumped.

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1. Flow rate, fuel pump:

Must have messed up time or something - I got 2216 cc/min.

I will run that test again as that number appears quite high compared to the 900 cc. I think the number may also high because my tank is full.

 

2. Contact point, fuel pump; check and fix:

They looked fine (much cleaner and almost no dust compared to above pictures - I did not have my macro, so no picture).

Filed, cleaned and tested.

 

3. Float levels as they sit in each carb

I found that one carb must have a manufacturing error. The height from axle to bottom of brass seat is about 1 mm less compared to the other carbs (see picture of a good one). The brass seat is slightly raised on the "bad" seat. That gave that float a wrong height of about 1.5-2 mm (less fuel).

 

I wonder if 2 mm less fuel is enough to get the main jet dry??

If that is the case, then the slow-jet should also have been "lean" - I don't recall any problems adjusting the pilot-screw back in the spring.

 

What would you do - get another carb or give the float som heat to make it fit correctly??

 

4. Electrical connectors from fuel pump all the way to the pickup; check and clean

Cleaned (no visible corrosion found)

 

 

Skærmbillede 2019-08-19 kl. 21.10.23.png

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I tested flow rate of that fuel pump again - and I still get 2000-2200 cc/min!

Usually a broken/bad pump is low flow or no flow - so this situation is new to me with too much flow.

Is it a potential problem just waiting to happen with this pump?

 

About that one carbs that  appears to lower the fuel level due to wrong position of float - could that explain sudden loss of most of the acceleration that have happened a few time.

Talking about fuel level in the bowls - how much tolerance is realistic up and down of the 13.7 mm specified in the service manual?

Would it be best be to source another carb or a complete carb assembly - or dont worry about it?

 

 

 

 

 

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float setting tolerance is about + or - 0.5mm.  i wouldn't worry about as you can compensate by resetting float height.  not likely a cause of any sudden problems.

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Problem and solution continues on this thread

 

 

 

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