Fuel pump relay question

This is for my '84 VF750F, but I'm sure could also apply to other models.

When I was getting this bike running again - the fuel pump wouldn't run unless I bypassed the fuel pump relay.

So that's what I did - stripping the ends of both wires and splicing them together with a wire nut. I know some use a toggle switch - but for now I just wanted to get the bike to operate....period.

The bike starts up and runs very nicely but after a short period of time (maybe 5 minutes or so) it sounds like it's bogging down.

This is while on it's center stand in neutral. But when I take it out - it also doesn't sound right - seems fuel related to me.

When I turn on the key before starting the engine....I hear the fuel pump come on......and it continues to run even after the engine has run for a while. In other words.....I don't think it's shutting off at all. Isn't it supposed to only run when the fuel pressure drops below a certain point? And isn't that a function of the carb floats shutting off the fuel when the bowls are full?

Lastly....could this be why the engine is bogging after a short period of time?

I rebuilt these carbs and the floats all seemed to be working fine and I also replaced the parts that usually come in the kits.

TIA for any input and help!

 

I have had pumps on VF/VFRs that never seem to get up to pressure and I think the diaphragms were going bad. While I didn't experience any possible starvation issues, I didn't keep them on the hike long enough to want to find out.... like not in my driveway.

I would swap with a known good unit and see if you experience an improvement. Then work on sourcing a replacement. That pump is unique to that bike (well maybe a Magna), but not any other Interceptors. I adapted the newer style straight spigot pump to all of my 1000Rs and F.

 

Interesting.

So you're saying the carbs are getting fuel starved.

Wow...that makes much more sense than what I thought was happening....that the carbs were getting too much fuel.

What you said makes total sense!

Pretty sure I have two used working fp's in my spares for that bike and will dig them out tomorrow.

Would also love at some point to see your "newer style" adaptation.

Thanks, Capt!

 

test the pump by blocking the outlet hole w your thumb to see if clicking stops. if it doesnt, suspect internal valve damage or a clogged tank pickup or filter delivering slow fuel to pump maybe cause of constant clicking, which might wear it out quickly or even cause a fire. check that tank has full flow out, not slow.

check pump valves by blowing air through each way.

 

Good idea...thanks SM!

 

ive been there, ya know anybody with these bikes has been bitten by bad fuel pumps or relays or r/r's often more than once.

 

If your oil is not over filled and smells like gas, you are probably not pushing fuel past your float valves.

And sm's test is a logical step to verify pressure shut off.

 

OK thanks again guys.

I dug out my RC15 fuel pump spares.

Two are brand new aftermarket and one is a used OEM (Mitso) with some splices in it's wiring.

I'd rather use the OEM because the inlet and outlet fuel line barbs are aligned properly.

Will post when I know more......

 

Good afternoon my brothers.....

Quick update - finally got around to working on the bike again and confirmed the fuel pump is not pumping as it should.

I always thought if I heard the clicking sound it was working. Shows how much I know!

I have one of those clear glass fuel filters and the fuel wasn't even being pushed through the filter.

Amazing the bike ran at all!

I just ordered a used working one from eBay but while I await it's arrival I may try to get one to work I already have on hand.

The weather here right now is so oppressive it's challenging to find the motivation for a lot of stuff!

 

Good evening fellow viffers!

Restless mind & body so decided to take another look at the aftermarket pumps I had on hand and decided even though the inlet/outlets didn't align as OEM, I could probably make it work, so did the swap and son of a gun......now I'm not getting anything - no whirling-pumping at all. And I know I had bench tested all 3 of these pumps before stowing them away. So tomorrow I will go at it again and this time use the other working aftermarket pump - this time testing it before install.

As an aside....it's amazing how long these engines will run just off the fuel in the bowls......


With OEM MITSU pump:



With aftermarket pump:

 

With how buried the fuel pump is on a VF750F and some work to adapt, there is no way in hell I would install some generic pump that is gonna crap out and strand you somewhere. But it sounds like the weather is perfect for pushing a bike, so there's that.

Take the time and figure out how to adapt a straight spigot style Mitsu pump that is readily available, new and low-mile used. You will likely not have to worry about it again, but if you do in 20 years or so, the mods are done and you can install the same style.

I have installed used units on my VF1000F/Rs and it is sweet piece of mind. I just look for the newest, lowest mile example I can find that has a return policy. The last 2 I got had about 14K miles on them (and looked brand new) and were between $30-40 shipped. Plus I got a bunch of pre-formed fuel line and clamps to help with the adaptation.

Do as you will and good luck.

 

I have one from eBay on the way - should be here by Monday. It's a working used unit from a low mileage '86 VF1100 V65 Magna and ran me $30.45 delivered. Supposed to be compatible with the VF750 V45 Interceptor.

But I would love to know more about the "straight spigot style" you mentioned, if you have time to provide any details.

Always interested in upgrades but am still relatively new to these machines.

Thanks!

 

Chinese pumps suck and have left most of us stranded more than once. You can get Japanese made pumps which are MUCH better.

 

This was just the first one I ran across, but this style. Used on a bunch of bikes. Genuine Japanese Mitsubishi pump.

https://www.ebay.com/itm/126603493259?itmmeta=01J579HQN24VZB4114RJ74TA7K&hash=item1d7a27ff8b:g:JkYAAOSwoTBmquHZ&itmprp=enc:AQAJAAAA0HoV3kP08IDx+KZ9MfhVJKnDIuH1+3LGj+CNs2sblruZlJBgPoHKHFL1GE7bQ6aYrcobeW0tQZM+vCIF0ZtneBB5RKZbFJRQVR6lzKRrLYB3umQ1jxLORK+ndMgmyfwJbtD7r9yk3wULqOeWa0dhqGw5oDBf4ravkPmJ+2YlmaeHVwbJMVqFE0GnAAb+pWrZMApXJT6gL6VKZFXZEtopJaTP/X5KGSs+XAfh4oT9girxpBwzSL0RYKJmuW22jFP42VTYb4jGkcRDJoLwaJ7SD+4=|tkp:Bk9SR9D6xumpZA&LH_ItemCondition=4

Available with a nipple style vent (shown), or the channel style.

You can go to the K&L Application Guide.

https://dealer.klsupply.com//images/replacement-fuel-pumps_App.pdf

Find the style of pump you want and then look what models take that one. Now find the newest, lowest mile used example that has a return policy. Make it fit and if you like it and want some more piece of mind, you can buy a brand new one from K&L or TourMax. They are not cheap new. That's why I have gone the used route on like 6 now. I even have a couple that have been tested and ready for a replacement. I can buy a half dozen or so before I get close to one new one.

The one dud I got they just instantly refunded me without having to return. On that one I got a bunch of still very good formed fuel line for free.

The problem with buying a used one from a VF-F or VF-S is that they are the same age as the one that just went bad. You can at least gain 20 years and fewer miles with these. And then like I said, buy a NEW one if you want. Can't do that with the OEM style.

 

Agree which is why I ordered one this morning - but wanted to use what I had on hand while waiting for it to arrive. Was curious about the issue I was having and wanted to confirm it was a bad fuel pump causing the problem - that's all.

The irony is the replacement didn't work.....even though I had bench tested it way back before putting it away in my spares room.

No biggie.......will get back on it tomorrow.

Have to say though it felt GREAT to be back wrenching on one of my bikes again....just had to keep a sweat towel handy!

 

OK thanks, Capt......good info! I never thought of a retro-fit job, but like you said.....whatever effort it'd take to ensure more reliability....sure beats getting stranded...that's for sure!

I may reach out again after I have some time to work on this.

Cheers!

 

Right now - and for the forseable future - I'm on a tight budget - so used for $30-40 sounds more like the way I'd go.

But FWIW....I found a brand new K&L for $120 delivered.....from eBay seller Sirius.....from whom I've bought carb kits from.

Seems like a good price for a new one!

eBay

 

I definitely won't post about/from my climate controlled shop right now then. You're welcome. As you were.

Hah! Cheers dude.

 

Also.......doesn't seem like a retrofit would be all that difficult. The pump would just lie on it's side and I'd have to fasten it down. Looks very do-able.

 

Yeah yeah.....I'll get there one day....trust me!

But the winters here.......I mean - who needs climate control!