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Just my words. I just talked to my dad, who is an old car mechanic. He said the same thing, if it runs fine without then skip the pump - one more less thing that car break :)
I am just curious why Honda have spent money on developing this pump, if the bike can run fine without.
What is the purpose of the pump?
I've been working on a small project using Ian's comments and guidance on this subject (Thank you, Ian).

This led me to investigate replacing the Original fuel tap/petcock with a later model fuel tap, including the revised fuel system layout.

Just for reference, the attached shows the 2 layouts from the parts catalogue side-by-side.

Just to confirm Okyo, which fuel tap do you have?

If you have the OE RR-N/P fuel tap, a strong recommendation is that you replace it with a later model tap (with the intake depression diaphragm unit on/off valve).
 

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Just my words. I just talked to my dad, who is an old car mechanic. He said the same thing, if it runs fine without then skip the pump - one more less thing that car break :)
I am just curious why Honda have spent money on developing this pump, if the bike can run fine without.
What is the purpose of the pump?
So, I made an eBay purchase of a later (used) fuel tap. Ian had warned that they can be quite pricey, not eye watering, but once I'd priced in a refresh kit it wasn't "cheap". Much cheaper than the near £200 for a new one. :eek:

During my various searches I'd seen some UK-supplied very low cost fuel taps - allegedly for a CBR900RR, although there was a feature missing - and, after all 1/ it was only £11/$13.50, and, 2/ It might be cheaper than a Reman kit, so I bought one. Please see attached. Apart from the missing feature, they are very, very similar. Not Keihin, but, by appearance/external dimensions, a good pattern part. :smile
 

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I deleted the pump completely from my 93. It doesn’t have one, and doesn’t need one.

There should be a fuel filter in there as well, but can be run in line from petcock to carbs if you remove the pump. Just disconnect the connector and call it a day.
But ...... it was the insides that were most interesting.

The fuel tap/ball bearing arrangement parts are interchangeable. Note: I did not remove the internal plate & seals, a bit tricky to replace due to the "rivets".

The vacuum diaphragm is a different simpler/fewer parts design.
 

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There should be a fuel filter in there as well, but can be run in line from petcock to carbs if you remove the pump. Just disconnect the connector and call it a day.
Ian, I cannot see an in-line fuel filter in the later (RR-V>) parts diagrams. Is there one? Or, is the in-tank screen filter a finer filtration than the RR-P filter, it is definitely a different part number (and then the tap outlet goes straight to the carbs)?


The "Reserve" tube on the Cheap/New fuel tap is quite a bit shorter than the OE tap. Which means that, unless I do something about it, I will have a bigger fuel tank :grin, but will be panicking as soon as I hit reserve with the lower reserve capacity! :crying
 

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Discussion Starter #126
Thanks for the tip.

What are the upside swapping to a new model fueltap?
When I disassembled the tank and the tap, it’s like the fuel filter is stuck inside the tank – is it supposed to do that?
 

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Thanks for the tip. What are the upside swapping to a new model fueltap?
The Standard RR-P tap, it is just a manual tap. If, when you turn the engine off, you forget, and leave the tap in the On/Reserve positions (and/or the Off position has a leak), then fuel flows to the carbs and "floods the cylinders", draining the tank. In the std RR-P fuel system, the fuel pump prevents this.

With a later RR-V style tap, it is a manual tap PLUS an automatic additional "valve". When the engine is running, low pressure from intake port #1 acts on the diaphragm opening the second valve allowing fuel to flow. If the engine isn't running, no low pressure and the second valve is closed. The position of the Manual tap (or any leaks) will not matter, the second valve prevents flow.

So, this is a strong recommendation. :grin
 

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Thanks for the tip. When I disassembled the tank and the tap, it’s like the fuel filter is stuck inside the tank — is it supposed to do that?
Hah! In my experience, the in-tank filters structural plastic seems to swell and so, "they are all like that, Sir". :wink

I have had to (very carefully) brutalise them out of the tank with thin nose pliers before now, trying to make sure that I didn't leave any loose parts behind. Patience is key. No swearing :devil
 

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Ian, I cannot see an in-line fuel filter in the later (RR-V>) parts diagrams. Is there one? Or, is the in-tank screen filter a finer filtration than the RR-P filter, it is definitely a different part number (and then the tap outlet goes straight to the carbs)?


The "Reserve" tube on the Cheap/New fuel tap is quite a bit shorter than the OE tap. Which means that, unless I do something about it, I will have a bigger fuel tank :grin, but will be panicking as soon as I hit reserve with the lower reserve capacity! :crying
Hi Duncan, no, the SC33's did not use an in line filter. However, in addition to the plastic mesh on the fuel pipe, Honda added the same style filters on the inside of the float needle valve seats to aid in filtering. That was yet another change from SC28 to SC33. The float needles were enlarged (larger OD) and thus allowed more fuel into the bowl. That in of itself could be another factor in the fuel pump removal for those years.



Needle seat screen.jpg
 

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Hi Duncan, no, the SC33's did not use an in line filter. However, in addition to the plastic mesh on the fuel pipe, Honda added the same style filters on the inside of the float needle valve seats to aid in filtering. That was yet another change from SC28 to SC33. The float needles were enlarged (larger OD) and thus allowed more fuel into the bowl. That in of itself could be another factor in the fuel pump removal for those years.
Very interesting, Ian. So the SC33's have a removable/serviceable float valve seat with integral filter! Huh. I didn't know that. Logical since, with no in-line filter, it is likely to actually filter stuff and need to be cleaned/replaced.

I'm going to take a look at my spare RR-P carbs, I remember that the float seat wasn't removable/serviceable, but I thought that there was a (permanent) filter above the float valve. Unlikely to do much in normal use, since the system has an in-line filter ......... but, maybe for contamination after a re-assembly or debris from a failed fuel pump, it would act as the last line of defence ......
 

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Very interesting, Ian. So the SC33's have a removable/serviceable float valve seat with integral filter! Huh. I didn't know that. Logical since, with no in-line filter, it is likely to actually filter stuff and need to be cleaned/replaced.

I'm going to take a look at my spare RR-P carbs, I remember that the float seat wasn't removable/serviceable, but I thought that there was a (permanent) filter above the float valve. Unlikely to do much in normal use, since the system has an in-line filter ......... but, maybe for contamination after a re-assembly or debris from a failed fuel pump, it would act as the last line of defence ......

I should have clarified: the picture was for reference only. I have to check my SC33’s and see if they are removable. Not entirely sure.

I know I’ve never been able to see any filter on the 28’s (maybe because the hole is smaller), but it was noticeable in the 33.

I’ll find out in the spring when they come off again 👍🏻
 

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You will need 1/a new fuel hose from the tap outlet to the carbs, plus 2/ the small diameter hose from the brass nipple on port #1 to the diaphragm nipple.

Then you are good to go. :wink :grin

P.S. The original RR-P fuel tap handle should fit your new tap. Or, I prefer the Sc33 fuel tap handle, it is 7mm longer but looks like it will not protrude beyond the frame. Regardless, note to self: I just need to remember to remove the tap handle before I try to remove the tank and scratch the handle! :devil
 

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I should have clarified: the picture was for reference only. I have to check my SC33’s and see if they are removable. Not entirely sure.

I know I’ve never been able to see any filter on the 28’s (maybe because the hole is smaller), but it was noticeable in the 33.

I’ll find out in the spring when they come off again 👍🏻
Just checked my spare carbs, Ian, and this is the filter element above the float needle.

These carbs are VP80B's UK RR-N to RR-S Part Numbers, just like the OE ones on my RR-P.

Float needle seat isn't removable, and I only saw the filter when I split the carbs and was blowing out all of the channels with an air line.
 

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Just checked my spare carbs, Ian, and this is the filter element above the float needle.

These carbs are VP80B's UK RR-N to RR-S Part Numbers, just like the OE ones on my RR-P.

Float needle seat isn't removable, and I only saw the filter when I split the carbs and was blowing out all of the channels with an air line.
I had what I thought were a set of sore SC33 carbs from eBay, but now I’m not sure if they are. I can’t compare to my 99’s because they’re still on the bike, but I did dig one out of the bin and noticed that the screen goes almost the entire width of the fuel tunnel, which seems even more than your SC28. It would appear that nothing is at it seems lol.

I love that you are into this as much as I am, Duncan. I need more friends like you :wink :grin

E48EEB61-62DD-4FAB-84EA-DA038CA7E5E6.png
 

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I had what I thought were a set of sore SC33 carbs from eBay, but now I’m not sure if they are. I can’t compare to my 99’s because they’re still on the bike, but I did dig one out of the bin and noticed that the screen goes almost the entire width of the fuel tunnel, which seems even more than your SC28. It would appear that nothing is at it seems lol.
Definitely a more pronounced filter, Ian. What is the VP part number stamped on the carb body?

I love that you are into this as much as I am, Duncan. I need more friends like you :wink :grin
:plus1: Agreed, Ian. I like (need) to know how things work and 'standing on the shoulders of giants', sharing knowledge accelerates the learning ..... hopefully to do something useful with that knowledge! :grin:thumb:
 

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Discussion Starter #139
Happy New Year

No it is all stalled a bit because of sick kids, wife and my self. Then birthdays, christmas and New Year.
So I have to get up in gear soon :)

Allan
 

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Happy New Year

No it is all stalled a bit because of sick kids, wife and my self. . .

Allan
Gee, a man ought to get his priorities in order!:grin:wink

Happy New Year to you Allan. Obviously I hope all are well, and all is back on track soon.
 
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