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Discussion Starter · #1 ·
I have an RD04 that needs some love. I have following symptoms:

- When the bike has been sitting for a few days, it is very hard to start
- When I manage get it started and warmed up, it starts very well, after the first kick of the starter motor
- When the engine is cold like after a couple of hours or overnight it usually starts well, except if the bike has been resting in a drafty or windy location
- When I rev up on idle, it will often cut off and stop running
- Idle is steady but there's a lot of popping and backfire

I suspect there's 3 separate issues at play, the first couple of symptoms might be due to the carbs drying out? Is there a seal that I can replace, I'm unfamiliar with carbs, I need to learn :)
The revving up on idle shutting of the engine may be fueling or jetting? I must add this only started more recently, while the first issue has been going on for a long time, but has been getting worse.
The third issue may be false air on the exhaust pipe connections or the muffler wool being gone, any other ideas?

Much appreciated!
 

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I can't speak to all of your issues but I've an RD04 which, like yours, isn't keen on being left alone for more than a few days. I normally have to churn the motor over a few times on the button, then I wait a few second, rinse/repeat 3 times and bingo - this with full choke. My understanding is that this is merely an undocumented feature of the RD04 :p.
 

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My rd07 is the same after a few days its like there is no petrol in the carbs but gives 50mpg runs really well and tickover is fine and always starts first on one cylinder then a couple of seconds later they both fire
 

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The lack of fuel thing?
You can short the relay out to avoid this, take the connector apart and use a short piece of wire to connect the black and blue to the black and red wire on the fuel pump cut off relay.
Bottom of page 4/22 in the Haynes manual.
Something to do with the fuel evaporating or draining out of one carb' when the bike has been stood for a while. It will start on one pot reluctantly, then fuel pump kicks in as the float chamber level drops and the other carb gets primed.
I used to do this but stopped bothering when I realised that it is not a problem.
With a flat or tired battery it could be a game saver.
 

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Beer monster.
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The RD07a had a modification done which linked the breathers. This stopped fuel evaporation over time on these.
I fitted a larger tank on mine and it started to drain fuel back when stood overnight, as the fuel tap was now lower than the pump. I've fitted a one way valve just before the pump and this has cured it.
 

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Discussion Starter · #6 ·
It's not starting badly like some of you describe above, I need to crank it for about 5 minutes before it starts, running the pos battery (that I bought in Montenegro after a bad welder killed my good battery) flat... :)

The RD07a had a modification done which linked the breathers. This stopped fuel evaporation over time on these.<...>
Do you have some more information on that? Maybe usefull into doing this on my RD04 as well. Do more recent model years use the same carbs or a different type?

The lack of fuel thing?
You can short the relay out to avoid this, take the connector apart and use a short piece of wire to connect the black and blue to the black and red wire on the fuel pump cut off relay.
Bottom of page 4/22 in the Haynes manual?
<...>
Very useful, going to look into this :thumbright:
 

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Beer monster.
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The carbs did change, later models had a throttle position sensor added, but they were all basically the same type.
 

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Discussion Starter · #10 ·
from what I've been able to find (not much) I assume the carburators are from Honda, not some generic brand like Mikuni or Keihin
 

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Discussion Starter · #11 ·
I bought a can of carb clean, the kind you add to the fuel and then run the engine. I don't have high hopes but I'm going to try it anyway, if that doesn't work I'm going to have to pull the carbs for a proper clean.
Since the issue seems to be around idle RPM's, it's no use trying to run it hard to 'blow out' the crud, right? As the idle jet is separate from the main jet. I guess I should ride it moderately, barely touch the throttle, let it idle, ride calmly?
 

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I can confirm to have the same hard start issue on my RD04. Also found hard way that if you have run out of fuel the bike wont start even when you fill the tank.
I removed fuel pump OUT tube and tried the starter. No fuel was pumped... Tried to push the bike to start. First try failed but I saw that fuel filter was filled fuel more than before. Second try was already success. Motor started and after that starting from starter also worked. Seems like Honda designed some punishing measures to driver - when you where careless not filling tank right time you have to suffer pushing bike to start. :)
Now trying to figure it out what is faulty and how to fix it.
 

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When your carbs are empty does the pump not run when you first turn on the ignition ?

The fuel cut off relay might be at fault ?

On 2nd thoughts it would only be one pump, not enough to help.
 

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Discussion Starter · #15 ·
the add to fuel type carb clean did the trick, I just got back from a 3 week 8500km trip with no issues ;)
 

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I tested today suggestion to connect pump without cut off relay. (Connected blue/black and red/black) When I turned ignition key pump started working. Sound what I have never heard on this bike. (Traveled with it many miles and years) Bike seems to work also without pump.
 

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Coincidentally I've been looking at the fuel pump relay so I'll share what I have found.

The 'relay' is a a bunch of components that have the effect of switching on the pump for one stroke each time the ignition coil is energised by the icu.

The switching bit in the relay is a type of diode which has a connection to make it conduct, called an SCR or Thyristor.

You can think of it as a relay which once switched on stays on until the load, fuel pump in this case, switches off.

The STD Honda pump disconnects from the power at the end of each stroke so the SCR stops conducting and waits for the next coil energisation and it all starts again.

If you want to have a prime switch you can pop a switch between the black wires so you have a priming function and a cutout.

Something else to note is that if you have an electric pump like a facet, I don't think your cutout will work.
 

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I came to the same conclusion that cut-off relay CF304A is not normal 12V relay. It is driven by yellow/black wire from CDI/Tachometer/Ignition Coil that is not normal DC. I tested with multimeter the AC voltage on yellow/black wire and saw it was quite low 100 - 300mV. Also I tested my relay by connecting only yellow/black and red/black wire, started engine - no 12V from output. So my relay is quite probably fried.
Looked Rugged Roads for replacement and saw they are offering CF318 not CF304A. Does anybody know is this going to work or not? I can’t find any spec for those relays.
 

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Andresy you need a load on the relay to take measure ments.

It is normal dc but a short pulse, your meter won't measure it properly.

Test it thusly, 12v to red and black terminal. Load between blue terminal and ground. Touch 12v to yellow and black terminal. Load will switch on and stay on if its a bulb, a small 5w one I'd suggest.

On my rdo7a the part is labeled cf318. It does the same thing as yours. Which terminals are which colour on yours? Start from the plug keyway.
 

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Might wanna check the chokes are operating properly before going into too much wiring/circuit problems. Mine took a few turns to get going but is slightly better since I stripped the chokes out and cleaned/lubricated them a few weeks ago.
 
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