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Discussion Starter #1
Hello,

I just bought my first AT, '96 RD07a with 67k on the clock, all original with full service history. Only mod is that the fuel pump has been changed to mikuni. And there's heated grips and a power outlet for the GPS.

Engine sounds healthy, fires right up when cold and the bike goes really well.

But after 30-40 kms of riding the bike suddenly loses power. It doesnt pull, will barely do 80 km/h in 5th and feels like it only fires on one cylinder.

First time it happened I pulled over and tried to see if anything was cooked. No signs. A couple of minutes later I start it and it sounds fine. However, after this it'll act up with shorter intervals.

When I went back in the night (after 5 hrs) the weather was colder - and as I suspected - it took a little longer before it happened, but again, suddenly there's no power.

I had a full tank of fresh gas and I tried to turn the inline fuel filter to see if it was blocked on one side, but no success.


To me, it seems like something is getting affected by heat. But what? I've searched on forums but couldnt find anything I could apply to my situation. Oh, and the temp. meter stays in the bottom 1/4 so it doesnt over heat.

I would really appreciate some hints to where to look before I start wrenching...

Thanks!
 

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Electrical? Coils? Maybe - can you test them? Or get a local mechanic to?
 

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Discussion Starter #3
Update: I took the bike out for a little spin (half hour) just now. I runs like a champ, idles starts. No problem.

There was a guy over at another forum that suggested that after riding for a while a vacuum built up in the gas tank. Which would explain why it could run after being off for some minutes (where it could suck in air) and then building up vacuum again, so i'm going to check the breather hose for the fuel tank.

@futter: I was thinking that too. But it just doesnt make sense when I can ride for 1/2 hour with no indications of coil failure?
 

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Have you read my post Fuel Starvation (some of the replys could be useful to you) its is a very similar problem when i 1st go out it runs for quite a while but once it cuts out its more often after that and i dont have a clue, Ive tried the breathers as thats what i thought but they are clear :confused:
 

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I'm no electrical wizz, but I remember reading that coils may produce a spark when cold and not under load but, if they are on the way out, will struggle to produce one when the bike is running.

Could you swap the coils with someone elseand take the bike for another spin?
 

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Discussion Starter #6
@mikethebike: Read your thread and yes it sounds very similar. Problem is that in order to test it you have to go quite far and when the problem then occurs it a pain in the *** to get home :(

@Warthog: I'll take the bike out for a longer ride today to see if I can replicate and then try and see if it is vacuum in the tank (lift the tank lid off). If not... I will see if I can find some friendly AT owners in the area with a set of coils.
 

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I had the same problem a few years ago, turned out it was the Mikuni fuel pump http://www.xrv.org.uk/forums/africa-twin/10073-mikuni-fuel-pump-mounting.html. I did the mod mentioned on the fifth post of this thread, but changed to a facet pump as i felt i couldn't rely on the Mikuni.

You could by pass the pump and see if it cures the problem, with a full tank you should be able to run for 80/90 miles.

Eamonn.
 

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I had the same problem a few years ago, turned out it was the Mikuni fuel pump http://www.xrv.org.uk/forums/africa-twin/10073-mikuni-fuel-pump-mounting.html. I did the mod mentioned on the fifth post of this thread, but changed to a facet pump as i felt i couldn't rely on the Mikuni.

You could by pass the pump and see if it cures the problem, with a full tank you should be able to run for 80/90 miles.

Eamonn.
+1 also fuel filter getting hot and vapour locking.. relocate fuel filter and replace with a facet pump :thumbup:
 

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Discussion Starter #9
Hi all,

I'm back again from today's test ride. As expected, after approx. 40 kms of, the engines gets jerky and wont rev. This was after a period on a long straight doing 90 km/h. Pulled in and lifted the gas tank lid. No hissing sound. Started it up and same thing happened after about 2 km.
Pulles in again and let it stand for a little while. Then I rode to the nearest gas station, being careful not to rev beyond 3000 rpm (i'm thinking if fuel flow is slow, it's best not to rev it).

I then filled it up to the brim (6,5 liters).

I think the whole stay at the gas tank was 5 minutes so the motor didnt cool down substatially. Although, I was able to ride 35 km again before it acted up. This time doing 100 km/h on the highway. I backed up on the trottle and let it coast for a little while and then slowly applied more trottle and then it started responding again. Then the highway ended and I rode the last 7 km in city traffic without any problems.

Here are my observations so far:

1. It typically happens around 4500 rpm on a straight at a speed of 80-110 km/h
2. When the bike loses power, I stop for a few minutes and I can then putter along with low rpm. But if I go into high rpm it happens after a few 100 meters.
3. Filling it up to the brim seemed to help for a while.

So it seems more like fuel than electronics. I will try bypassing the pump as eammonj and raymo suggest. After reading the Mikuni thread I am also inclined to buy a facet pump just to be safe ... anyone know a good online shop in EU that has them?
 

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Hi all,

I'm back again from today's test ride. As expected, after approx. 40 kms of, the engines gets jerky and wont rev. This was after a period on a long straight doing 90 km/h. Pulled in and lifted the gas tank lid. No hissing sound. Started it up and same thing happened after about 2 km.
Pulles in again and let it stand for a little while. Then I rode to the nearest gas station, being careful not to rev beyond 3000 rpm (i'm thinking if fuel flow is slow, it's best not to rev it).

I then filled it up to the brim (6,5 liters).

I think the whole stay at the gas tank was 5 minutes so the motor didnt cool down substatially. Although, I was able to ride 35 km again before it acted up. This time doing 100 km/h on the highway. I backed up on the trottle and let it coast for a little while and then slowly applied more trottle and then it started responding again. Then the highway ended and I rode the last 7 km in city traffic without any problems.

Here are my observations so far:

1. It typically happens around 4500 rpm on a straight at a speed of 80-110 km/h
2. When the bike loses power, I stop for a few minutes and I can then putter along with low rpm. But if I go into high rpm it happens after a few 100 meters.
3. Filling it up to the brim seemed to help for a while.

So it seems more like fuel than electronics. I will try bypassing the pump as eammonj and raymo suggest. After reading the Mikuni thread I am also inclined to buy a facet pump just to be safe ... anyone know a good online shop in EU that has them?
From what you're saying here I would be looking really hard at the fuel pump. It's sounding like it's not providing a sufficent supply of fuel to the carb. As suggested before check the routing of your fuel lines and the fuel filter to rule out the possibility of the fuel vapour locking. If this looks OK then bypass the fuel pump and with a full tank test again. Remember it'll only give you about 100km range using gravity feed. The problem appears to be in your fuel system so you can rule out the coils etc for now.
 

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Discussion Starter #11
@ukTiffy: I think you're right. I just checked the service book and the mikuni was installed almost 40.000 km ago.

I'll go check my fuel/breather lines and filter. And if it isnt all bad I think I'll go for a 40105 Facet pump. For 32 punds on ebay UK it would be a relatively inexpensive solution ;)
 

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Latest news: I have checked the carb overflow lines (the ones coming out from the bottom bowl, right?) and they go straight down from the carb to a "Y" section and end behind the engine. Looks ok to me.

Lots of flow through the fuel line and inline filter. I have now bypassed the fuel pump by connecting the fuel inlet tube (green) to the fat tube that was connected to the outlet tube (pink) and goes to the carbs. Took it for a short ride and it ran just fine.

As soon as possible I will fill it up and see if I can pass the 50km mark :thumbup:

A have also ordered a new 40105 Facet pump and fittings on ebay...
 

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Hi all,

I'm back again from today's test ride. As expected, after approx. 40 kms of, the engines gets jerky and wont rev. This was after a period on a long straight doing 90 km/h. Pulled in and lifted the gas tank lid. No hissing sound. Started it up and same thing happened after about 2 km.
Pulles in again and let it stand for a little while. Then I rode to the nearest gas station, being careful not to rev beyond 3000 rpm (i'm thinking if fuel flow is slow, it's best not to rev it).

I then filled it up to the brim (6,5 liters).

I think the whole stay at the gas tank was 5 minutes so the motor didnt cool down substatially. Although, I was able to ride 35 km again before it acted up. This time doing 100 km/h on the highway. I backed up on the trottle and let it coast for a little while and then slowly applied more trottle and then it started responding again. Then the highway ended and I rode the last 7 km in city traffic without any problems.

Here are my observations so far:

1. It typically happens around 4500 rpm on a straight at a speed of 80-110 km/h
2. When the bike loses power, I stop for a few minutes and I can then putter along with low rpm. But if I go into high rpm it happens after a few 100 meters.
3. Filling it up to the brim seemed to help for a while.

So it seems more like fuel than electronics. I will try bypassing the pump as eammonj and raymo suggest. After reading the Mikuni thread I am also inclined to buy a facet pump just to be safe ... anyone know a good online shop in EU that has them?
That sounds very much like a fuel pump failure to me
 

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Latest news: I have checked the carb overflow lines (the ones coming out from the bottom bowl, right?) and they go straight down from the carb to a "Y" section and end behind the engine. Looks ok to me.

Lots of flow through the fuel line and inline filter. I have now bypassed the fuel pump by connecting the fuel inlet tube (green) to the fat tube that was connected to the outlet tube (pink) and goes to the carbs. Took it for a short ride and it ran just fine.

As soon as possible I will fill it up and see if I can pass the 50km mark :thumbup:

A have also ordered a new 40105 Facet pump and fittings on ebay...

the pump is mounted to the engine casing.. the one with the hot generator :confused:.... and with a nice metal conductor to get heat into it!!


you could try to remount it ina less hot location with insulators... or.. just fit the facit pump and save all the hard work :thumbup:
 

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Latest news: I have checked the carb overflow lines (the ones coming out from the bottom bowl, right?) and they go straight down from the carb to a "Y" section and end behind the engine. Looks ok to me.

Lots of flow through the fuel line and inline filter. I have now bypassed the fuel pump by connecting the fuel inlet tube (green) to the fat tube that was connected to the outlet tube (pink) and goes to the carbs. Took it for a short ride and it ran just fine.

As soon as possible I will fill it up and see if I can pass the 50km mark :thumbup:

A have also ordered a new 40105 Facet pump and fittings on ebay...
I had the same problem with my Mikuni. Some how fuel gets introduced in the vacum line giving you those fuel starvation symptoms....and your troubleshooting proved it when you bypassed the Mikuni. The Y fitting fix for this that African Queens suggested never worked either...see pic. It's a dangerous pump in fast flowing traffic. :eek:
Problem solved when facet installed.

 

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Discussion Starter #16
Re: AT completely loses power. Mystery?

Hi all,

Thanks for all the help so far, it's really appreciated as I am a total novice (less than a week with the bike).

So today I headed out with a full tank and a bypassed Mikuni pump. And guess what. After 25 km it did the same thing again! Again it was on the highway and I was doing around 100 km/h.

Pulled over, checked gas tank. Almost full. took off side cover and checked rectifier and CDI with my hand to see if they were hot or in other way affected. Nothing.

Managed to get home.. It would barely do 80 km/h in 5th gear.

Took off tank and air box to get a look. Bike looked relatively clean and tidy.

1. Choke cable doesnt stick. Pulled it gently out of the little black plastic housing and watched it move. Looked fine.

2. Carb overflow tubes: took them off and checked for any blocks. I could blow air through all three.

3. Inline fuel filter: not blocked.

4. Spark plugs: I couldnt check them as I didnt have the right size socket. Maybe I'll change them just to make sure. (but why would they fail after 25km and then work again after a little while?)

5. Only thing I could find was that the rubber tube going from the cylinder (just after the rear carb manifold) to the back of the mikuni pump was rotten. But the pump was bypassed so how could it affect anything?

here's the end that was connected to the back of the mikuni pump


and the other end was connected to the cylinder here. They were both connected to the "Y" piece that GSPD750 mentioned, also with an oil trap.



and then there was this hose under the tank. Looks like a overflow hose but wasnt connected to anything?




So, to sum it up: Bypassed pump, lots of gas, gas is flowing through filter, bike runs fine for 25 kms, then bogs down... any ideas?

Thanks,
 

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Electrical? Coils? Maybe - can you test them? Or get a local mechanic to?

I'm no electrical whizz, but I remember reading that coils may produce a spark when cold and not under load but, if they are on the way out, will struggle to produce one when the bike is running.
I agree, though it could just be an earthing problem rather than requiring replacements. Look at your electrical loom and make sure it is all in good order and the earthing points are free of corrosion. It may seem unlikely, but it is possible and will cost you absolutely nothing to try.

Good luck! :thumbup:
 

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Re: AT completely loses power. Mystery?

Hi all,



, to sum it up: Bypassed pump, lots of gas, gas is flowing through filter, bike runs fine for 25 kms, then bogs down... any ideas?

Thanks,
I still think it's fuel related. That vacum line did not look healthy and I suppose you could hook up the mikuni one more time to confirm now that you know the vacum source is 100% good. I don't think it's that unusual to get a fuel starvation symptom even with a full tank (with pump bypassed)...sooo try the mikuni again or buy a facet.
 

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Is it worth going back to basics?

What affects a bikes running?
Fuel supply (tank, pump, carbs, filter and piping),
air supply (filter), exhausts,
Sparks (coil, leads, plugs),
ignition timing,
valves and compression,
Cooling system.
Others...?

What might change as a bike gets hotter?
Fuel supply (tank, pump, carbs, filter and piping),
Sparks (coil, leads, plugs),
valves and compression,
cooling.
Others...?

What is likely to be affected by revs?
Fuel supply (carbs),
air supply (filter),
Sparks (coil, leads, plugs),
ignition timing,
valves and compression,
Cooling system.
Others...?


See which parts fit the bill in all three and then try and eliminate them...
Not trying to teach grandma to suck eggs, mind...

Good luck
 

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Discussion Starter #20
Good news: I think I fixed it!

Bought some new rubber hose today and hooked the mikuni pump up with the new hose insted of the crumbling old ones.

went thorugh all the electrical connectors I could find, cleaned the surfaces and gave them contact spray.. It actually seemd like there was a bit of moist inside the big connector for the CDI.

checked the chokes again and massaged them a little to se that they were moving freely.

made sure that all overflow and breather hoses were properly routed and weren't pinched by anything before i put the tank back on.

started it up and almost instantly I could hear that the engine sounded differently. not much but enough to notice.

after letting it warm up I took it out on some fast roads, and boy does it go now! it feels completely different, has better throttle response and marches along with 120 km/h without skipping a beat.

What a relief! This has occupied most of my awake hours for some days now.. to celebrate, here's a photo. I found a grass field with some tracks from a 4X4 that I thought could be fun to explore.


I'm really looking forward to some long tours now. Thanks to all for the great help and support!
 
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