Author Topic: Bis revving high  (Read 3228 times)

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Bri W

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Bis revving high
« on: November 28, 2017, 08:24:45 PM »
Hi.  I am currently having a problem with my Bis. It starts fine and seems to run ok. Then when it reaches temperature it suddenly begins to rev really high on idle. I have worked out that it is something to do with the Throttle kicker (vacuum)solenoid. This must get a 12v signal from when the engine reaches temperature. I have proved it is to do with the solenoid as when I disconnect it, the engine runs fine. I also sucked on the pipe going from the carb to the inlet on the solenoid and the engine rev'd high whilst creating a vacuum. Any ideas what the problem may be? What is the effect of me not having the solenoid connected?

Thank you for reading my post.

Xylaquin

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Re: Bis revving high
« Reply #1 on: November 28, 2017, 11:17:24 PM »
Hi Bri,

It's meant to do that. Basically when the engine gets to a certain temperature the radiator fan starts to spin, for whatever reason the fan draws a lot of power to the extent it noticeably lowers the revs. To compensate, the solenoid increases the revs so that it balances out.

You could bypass the solenoid... it would just mean your engine would have lower revs when the fan is on. I don't have a solenoid on mine, it's yet to cause me problems, but I don't have a solenoid only because the previous owner of my BIS wired it up so that the fan is manually controlled. If you have a normal BIS, I'd keep the solenoid and run the car as it's supposed to.

So, is your radiator fan not spinning when you notice the revs going up?
« Last Edit: November 28, 2017, 11:19:43 PM by Xylaquin »

Bri W

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Re: Bis revving high
« Reply #2 on: November 29, 2017, 12:29:41 PM »
Thank you for the reply.
To be honest I didn't notice the fan running. It was revving that high I just turned the engine off and let it cool down. At the minute I have left the solenoid disconnected. Do you know if there is a way of adjusting the amount of revs when the vacuum solenoid kicks in? The car idles fine in normal operation. 

Xylaquin

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Re: Bis revving high
« Reply #3 on: November 29, 2017, 07:13:38 PM »
Get a flat-head screwdriver and turn this to adjust the revs:


However I'd make sure your radiator fan is turning when the revs suddenly go up and the temperature gauge is about half way. It sounds as if it's not... and that's going to be a problem.

Bri W

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Re: Bis revving high
« Reply #4 on: November 30, 2017, 05:21:01 PM »
I will take it out and get it up to temperature and let you know what happens with the fan. If the fan is running I will adjust the screw. I am sure I have heard the fan kick in but don't know if it was on when It was revving high. Thank you for the response.

Bri W

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Re: Bis revving high
« Reply #5 on: December 01, 2017, 05:01:07 PM »
Hi Xylaquin,

My last post must not have loaded. I had the Bis out today. I got the engine up to temperature and the fan was not running. When I looked at the fan I noticed that there were some wires disconnected from bi-metallic coil (I believe that's what it is). I checked with a fluke that there was a 12v signal present at the 2 disconnected connections. I shorted across the connections and the fan came on. Which I suppose is a bonus as it isn't seized. However, I think that the coil/connections may be at fault. I will have to look at it further. Looking at the 2 connections mounted on the fan they seem to be a bit iffy. It also looks like there should be a 3rd connection (which may have snapped off). Do you have a picture of how this should be connected? Or any pdf . How does the coil interact with the temp sensor and solenoid?
I am trying to get a picture of the fan connection for you but I can't get its size below 82KB
Cheers Bri

Bri W

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Re: Bis revving high
« Reply #6 on: December 01, 2017, 05:12:07 PM »
Hopefully these pics work.

Bri W

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Re: Bis revving high
« Reply #7 on: December 01, 2017, 05:19:32 PM »
The coil

Xylaquin

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Re: Bis revving high
« Reply #8 on: December 01, 2017, 06:29:18 PM »
My BIS is wired up differently to standard, however I can confirm that there should only be two connections on the fan... everyone's fan looks like it's got a snapped-off third connection but here is picture of a new one:



Try see if you can clean up the connectors, you can get electrical contact cleaner from good motor factors if need be. Then simply connect the wires back in.

Alternatively, the cheapest place I could find a new resistor for sale was here:
http://www.ricambinuovi.com/store/_uk/prodotto.asp?IDp=14015

zebec63

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Re: Bis revving high
« Reply #9 on: February 28, 2018, 05:35:34 PM »
Hi,
  Does anybody know what the coil actually does.
Is it some kind of speed control for the fan ?
Cheers
Shaun

Gadge

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Re: Bis revving high
« Reply #10 on: February 28, 2018, 06:15:31 PM »
Yes basically. The cooling system on a BIS is two stage. When the engine temp reaches a certain point the current to the fan is diverted through this coil so a reduced output goes to the fan so it runs at a slower speed. As the engine temp rises again to near boiling point (2nd stage) the current is diverted away from the coil so the output to the fan is direct so it can run at full speed.
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