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dfwilson

4Rt How Often Does The Fan Run

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Just got a 2005 4RT and compared to either my 03 Scorpa SY250R or my 04 Beta Rev3 the fan seems to run a lot more of the time. Is this normal? Are there any problems with the water pump impeller wearing out?

The air temperature while riding was about 60 F or 15 C

Thanks

DFW

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Yeah they run pretty much constanty when they're upto temp. If there's any problems the fan won't cut in and coolant will trickle from the pump cover.

It may be worth checking the water pump gear/shaft as they get very scored if its done alot of work. Change shaft, seal and I think 2 bearings.

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All Honda 4 strokes seem to run hot. That was a really good looking bike you picked up. I doubt you have any issues. Too bad you couldn`t ride with us!

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If the older Monts run at around 1800 rpm idle ,like the new 4rt ,that will be why the fans cut in all the time . they're running at twice the speed of other bikes therefor probably half as hot again . If they don't well i'm just speaking pish !

Edited by shyted
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I've never seen a 4RT with a idle speed at 1800 rpm, I have mine set at 1200 rpm. I think with the idle at 1800 rpm, you're always riding with a slipping clutch at very low speeds

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I've never seen a 4RT with a idle speed at 1800 rpm.

Just gone and checked my manual for you. Montesa 4RT manual quotes set idle speed to '1800 rpm. Plus or minus 100 rpm'.

Its obvious when standing around 4RTs how they run at a higher idle than other 4 strokes. And Great fun listening to a Honda TLR twinshock while following it down a hill ticking over at 800 - 900 rpm. Whereas my 4RT is running at twice that, fan going, and clutch in to get slow enough and not go up its rear. Of course the 30 year leap in tech means the brakes actually stop me rather than just retard the downhill journey and fuel injection gives it a no-lag throttle response. I tried turning down my idle but found that the bike stalled too easily, especially when opening the throttle after a period of very low revs ( eg after getting to the bottom of a steep hill and then opening the throttle to climb up the otherside).

As to the fan, when starting the day, my routine is to let the bike idle until the fan kicks in; a lengthy period of about 3 minutes during which time the 4RT comes up to operating temp. Jumping on and riding away before this rewards with clutch slip.

In a forest, with little airflow and riding slowly I'm conscious the fan can be running continuously. Never had a problem with that. It is doing its job. Just one owners experience.

Also have a look at an Ossa 280. The fan is not out in front as the petrol tank sits there. Fan sits out of the airflow compared to traditional thinking on its placement. Fan runs, bike stays cool; doing good honest work.

Edited by ross brown
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I know the manual advises an idle speed of 1800 rpm but have you checked it with a rev counter?

I've got a Stihl EDT 8 rev counter that's pretty accurate and believe me, anything over 1200 rpm already sounds high let alone 1800 rpm.

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I run my '05 4RT at about 1900 RPM idle. Yes, I have a tachometer / hour meter on it. Like Ross Brown said, I found that running less than that I would stall the bike creeping around a corner or just cracking the throttle from idle. I do have a 9 tooth front sprocket so can creep pretty well just on the throttle.

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After I got back from a little trip to the local training spots I did some testing on my 4RT.

My fan runs for about a minute and cuts back in after about 20 - 25 seconds.

For those who don't know what 1800 rpm sounds like:

In the video you can hear my 4RT idling at about 1100 rpm, I then raise the revs to about 1800 rpm and hold it there for a while with the throttle.

https://www.youtube.com/watch?v=uWk73kxHRcM&feature=youtu.be

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I run my '05 4RT at about 1900 RPM idle. Yes, I have a tachometer / hour meter on it. Like Ross Brown said, I found that running less than that I would stall the bike creeping around a corner or just cracking the throttle from idle. I do have a 9 tooth front sprocket so can creep pretty well just on the throttle.

Are you sure there's nothing wrong with your bike? I never had that problem with the idle at 1100 rpm, even with a 10 tooth front sprocket.

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.... In the video you can hear my 4RT idling at about 1100 rpm, I then raise the revs to about 1800 rpm and hold it there for a while with the throttle.

Are you sure you have the rpm counter set for a single-cylinder 4-stroke? Your 1100 rpm sounds like it's over 2000 rpm, and sounds faster than my bike at idle. Mine is at the manual specified 1800 rpm, done using a Pulse PET-1100 set for a 4-stroke thumper.

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After I got back from a little trip to the local training spots I did some testing on my 4RT.

My fan runs for about a minute and cuts back in after about 20 - 25 seconds.

For those who don't know what 1800 rpm sounds like:

In the video you can hear my 4RT idling at about 1100 rpm, I then raise the revs to about 1800 rpm and hold it there for a while with the throttle.

https://www.youtube.com/watch?v=uWk73kxHRcM&feature=youtu.be

That sounds more like 1800 rpm and more like 2500 rpm when you open the throttle. I have tried 1200 rpm before and that sounds way slower than that.

Are you sure you have the rpm counter set for a single-cylinder 4-stroke? Your 1100 rpm sounds like it's over 2000 rpm, and sounds faster than my bike at idle. Mine is at the manual specified 1800 rpm, done using a Pulse PET-1100 set for a 4-stroke thumper.

I have the same Pulse PET -1100 and run 1800, stops stalling and easier to start.

Did try 1500 rpm, but it was harder to start. If you don't like the 1800 idle, because it's too fast in turns, lower the standard gearing to either a 10/43 or 9/42 to slow it down.

Edited by jj65
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Guys, I have to agree with others, your video sounds like your idle is way higher than 1200rpm. I have a OPPAMA Pulse Engine Tachometer PET-1100, which is very accurate, as used by Josep Banyeres. I have my idle set at 1850rpm and it sounds about what your idle speed is (1200).

The PET-1100 has various settings for 2 stroke, 4 stroke and multiple cylinder choice.

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My ridding buddy has a 4RT and his fan runs a lot, but not really any more than the fan on my 315R. I let the 315 warm up until the fan comes on, that is my indicator that it is warm enough to ride.

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