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Discussion Starter #1
OK, now I got your attention.;)

I am new to motorcycles since last fall and is getting to know my AT more and more. Have ridden it 600km now.

How should the engine response feel. My AT has a Mikuni vaccum pump

It doesn't run smoothly at lower revs. It feels like I want to stay over 4000rpm.

How are your bikes?
 

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it's about an hour......
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My engine responds well through the lower revs but when in top gear doing 80 - 90 mph it feels like it could do with an extra gear. Top speed is almost 110 at 8000 - 8500 revs, almost in the red.
 
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Mine is fine. I'm no pro but could there be something like dirty carbs, air filter or fuel line ? The choke might also be sticking, that's a well known issue. It doesn't actually stall does it ?
 

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Well, air filter is in the mail and would be here tomorrow. The old one doesn´t look that good. But I will have to wait to test ride as I'm going sking in the very expensive Norway this weekend.

Overall the bike looked ok when I got it but it wasn't really taken care of. I have spend long days in the garage this winter just cleaning and changing smaler parts repainting and mounting heated grips... As the is no service history I have no idea if it is time to adjust valves or anything. Probably the whole bike have been neglected. So I have just finished replacing brakefluid and is going to do all the rest of the service when I have some time.

What should I do first? Replacing spark plugs?
 

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Well, air filter is in the mail and would be here tomorrow. The old one doesn´t look that good. But I will have to wait to test ride as I'm going sking in the very expensive Norway this weekend.

Overall the bike looked ok when I got it but it wasn't really taken care of. I have spend long days in the garage this winter just cleaning and changing smaler parts repainting and mounting heated grips... As the is no service history I have no idea if it is time to adjust valves or anything. Probably the whole bike have been neglected. So I have just finished replacing brakefluid and is going to do all the rest of the service when I have some time.

What should I do first? Replacing spark plugs?
If it has no service history strip it down and do the valves, at least then you know where you stand with the bike, change all consumables and then grease what you can in relation to the bearings.
You should then be able to tell the bike is OK for a few more Decades.
 

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Sounds like petrol has gone stagnant in the carbs, was it parked up un-used for a long time?
 

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Discussion Starter #7
Maintanence, reaching for a smoother running engine and catching up with a non existing service history.

Well I have driven about 600km since winter parking.


I checked the valves this weekend, first time lifting the tank for me. The adjusting took a number of hours but I wasn't in a hurry and the work was not that complicated. I put in new spark plugs as well. I don't know how to tell if the old ones are ok or not. Look at the comparison between old and new.

The Old one is NGK DPR9EA-9. The new one is NGK DPR8EA-9. Both are listed in the specification sheet in Haynes manual.

When the bike was put together (on sunday) it started for the first time this year without choke. It also sounded very smooth and balanced at idlling. Checked that the idle was coorectly adjusted. It was. I took it for a ride today and it felt like there is a bit more power avilable during acceleration and the sound was more "precise and powerful". But I needed the choke to get it started today (the bike is always parked in my garage at room temperature)

Noiced during the maintanence:
-There is a a possible chance to leakage in airbox.
-All O-ring on valve covers is a bit flattened, will change them next time. The O-rings on the inlet valve covers were glued to the bottom of the O-ring grove. I have never seen a glued O-ring before. Should it be glued?
-Left carb rubber seems to have a crack on forward side below the hoseclamp. Don't know if it could be leaking. But the area around is dirty.


Why do it always need choke to start?
 

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Discussion Starter #8
Hmmm... I may be completely wrong here.. :rolleyes:

But couldn't it be that a leaking carb rubber lets the petrol evaporate under a few hours. And that is the reason it needs the choke to get started, (as the mixture is to weak as a result of evaporated petrol from carbs)...

Hey, I'm just guessing here.
 

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Space Emperor
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Tjena, Beffo!

Whats the massive tube connected to your vaacum hole??

I can see I need to check the specs on my plugs also ...
 

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Space Emperor
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The original post says there is a Mikuni vacuum fuel pump fitted. I'd guess this is the vacuum take-off for this.
Ah, right! Never heard of them :)
 

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Ah, right! Never heard of them :)
You wouldn't be the first not to have heard of them. Most people haven't. I've only ever owned one bike with a vacuum pump on it - a Yamaha. The vacuum pump was the most reliable part of the bike! They are a good alternative to the original fuel pump and the facet. As they use engine vacuum to run the pump, there's no electrics needed. The downside is they are slightly bulky.
 

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Space Emperor
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You wouldn't be the first not to have heard of them. Most people haven't. I've only ever owned one bike with a vacuum pump on it - a Yamaha. The vacuum pump was the most reliable part of the bike! They are a good alternative to the original fuel pump and the facet. As they use engine vacuum to run the pump, there's no electrics needed. The downside is they are slightly bulky.
Right, makes good sense .. but can't utilizing the vacuum holes change the pressure of the mix going into the cylinders?
 

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No, it doesn't change the inlet pressure like an air leak would. The vacuum pipe goes to a chamber on the pump that is sealed where it pulses a diaphragm. With the aid of a couple of one-way valves, it's the pulses that pump the fuel.
 

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Beffo, the pump on yours looks very close to the rear cylinder head and bolted directly to the engine doesn't seem like a good thing from a heat or vibration point of view. I'm not surprised you ran into problems with it.
 
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