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Old 10-04-2012, 02:22 PM   #1
bushyb OP
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Location: Rotorua, New Zealand
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Shoud I replace my diode board?

I am sure this has been asked before; I just couldn't find the answer that fits my situation. After setting up a 1982 R100RS that had been is storage for 8 or 9 years the job is complete and looks good and I am happy at the outcome. I have also asked some of this before. I have fitted a new battery, had the started serviced and new solenoid fitted, replace the relay, checked the float level etc. All is good. In the mornings I struggle to start the bike it is almost as if there is too much compression yet if I crank it a couple of times it as if the battery gets flat. I then put it on charge and go to work. When I am back from work its warmer ever so slightly then it starts. Once it starts its fine and will start again and again that afternoon and evening with prolonged brakes in-between. Once it starts it runs great so there are no issues with the float level or the fuel settings and tuning.
The generator light comes on when the ignition is turned on and once started goes out as it should and shows no sign that it is not charging. I do believe there is no short anywhere that will cause the battery to lose charge.
I am not to clued-up with electrical things but I did read somewhere that there might be a damaged diode that when the ignition is turned off the battery leaks back through the diode board creating a loss of battery power or charge. That is what I understand from the reading.
My thoughts are that this could be the situation, that the bike struggles to start and that the diode board needs replacing. There must be some simple tests to check the diodes but I think I will struggle with understanding the process and measurements.
This is the million dollar question: Will a bad or defective diode board create a situation that makes the bike difficult to start and having to top up the battery constantly?
I have just managed to start the bike and checked the volt metre its showing about 13 volts at about 2000 rpm, if I rev it a bit it goes a bit over that.
One other thing it sometimes starts with the choke 1/2 on and other time with the choke off. When I use the choke it is as if it struggles even more. I have made sure the choke start valve is in the right way round.
Any thought welcome.
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Old 10-04-2012, 06:08 PM   #2
Biebs
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Starting

1/2 choke works to start then use 1/2 choke. My 74 r75/6 starts at 1/2 choke.

Also test battery / for leak down by disconnecting battery at night reconnect in the morning see if it starts.

How old is the battery?? There is a way to test diode board.



Don't throw money at it fix it!!!
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Old 10-04-2012, 06:56 PM   #3
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I'd second that suggestion - disconnect the negative battery lead (at the negative terminal) once it's parked at night. See how it does in the morning.

There are basically two sides to this equation - the battery and the starter - although the wiring and connections add a third. It's gotta be one of those three.

When the engine is cold it presents the heaviest load to the starter and battery. If connections and cables are good, then it's one of the two. Since the battery has been replaced, I'd check out the starter or the main battery positive lead. The starter grounds through its base and mounting bolts, so if it's loose and oily, there won't be much electricity flowing.

At this point I'd say it's either the starter or the connections. Especially if it still has the hard start symptoms tomorrow morning after disconnecting the negative lead tonight.
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Old 10-04-2012, 07:06 PM   #4
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Just because the battery s new does not mean that it is good. I've seen new batteries that didn't work. Have it load-tested to verify its condition. Have you considered trying to jump the battery from that of a car?
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Old 10-04-2012, 07:21 PM   #5
bushyb OP
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Quote:
Originally Posted by Biebs View Post
1/2 choke works to start then use 1/2 choke. My 74 r75/6 starts at 1/2 choke.

Also test battery / for leak down by disconnecting battery at night reconnect in the morning see if it starts.

How old is the battery?? There is a way to test diode board.



Don't throw money at it fix it!!!
Thanks. Great ideaI will start it this evening and run it for a while with the charger connnected so it is as full as possible. Then disconnect the battery and charger and then reconnect it tomorrow morning and try it and will let you know.
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Old 10-04-2012, 07:31 PM   #6
bushyb OP
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Quote:
Originally Posted by Biebs View Post
1/2 choke works to start then use 1/2 choke. My 74 r75/6 starts at 1/2 choke.

Also test battery / for leak down by disconnecting battery at night reconnect in the morning see if it starts.

How old is the battery?? There is a way to test diode board.



Don't throw money at it fix it!!!
Thanks, I have got 2 new batteries because at first I thought it was the battery. Thanks. It's a great idea! I will start the bike tonight with the charger connected and run it for a while so that the battery is as full as possible, And then diconnect it and try it tomorrow morning.
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Old 10-04-2012, 07:37 PM   #7
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Quote:
Originally Posted by manic mechanic View Post
Just because the battery s new does not mean that it is good. I've seen new batteries that didn't work. Have it load-tested to verify its condition. Have you considered trying to jump the battery from that of a car?

Yes in the begining there was no difference! I have not tried that lately. Must say that when I have run the battery down a bit and I charge it, the charge picks up quickly back to fully charged.
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Old 10-04-2012, 07:46 PM   #8
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Quote:
Originally Posted by Wirespokes View Post
I'd second that suggestion - disconnect the negative battery lead (at the negative terminal) once it's parked at night. See how it does in the morning.

There are basically two sides to this equation - the battery and the starter - although the wiring and connections add a third. It's gotta be one of those three.

When the engine is cold it presents the heaviest load to the starter and battery. If connections and cables are good, then it's one of the two. Since the battery has been replaced, I'd check out the starter or the main battery positive lead. The starter grounds through its base and mounting bolts, so if it's loose and oily, there won't be much electricity flowing.

At this point I'd say it's either the starter or the connections. Especially if it still has the hard start symptoms tomorrow morning after disconnecting the negative lead tonight.
Thanks I have checked all the connections and believe them to be good, The battery is new (2 off) and the starter has been checked and is good. I am sure there must be an answer to it and its going to be something small maybe a connection that I have missed or something like that. I have also added a extra earth wire from the battery.
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Old 10-05-2012, 12:14 AM   #9
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Are the float bowl gaskets in good condition? If the holes are very compressed, damaged or too rounded then they can let too much air into the "choke" aux starter system, making it too lean and difficult to start.

If you get lucky, you may avoid lots of time and money via a quick inspection or change 'em if they're old anyhow.


Quote:
Originally Posted by Motobins tips and tricks
Found at Motobins home page.....Cold Starting Problems can often be cured by replacing your old float chamber gaskets unless they provide a really air-tight seal around the choke fuel pick-up tube, the fuel level in the auxiliary chamber will not be raised, and the cold start mixture will not be further enriched during initial operation. The Auxiliary Carburettor itself can often become loose, so being by-passed and ineffective; the resultant air leak will also promote 'surging' at about 40 mph on a small throttle opening change the gasket every few years, and make sure the screws are really tight.
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Old 10-05-2012, 03:36 AM   #10
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Cool2 warning.

Do NOT run the bike for more than a couple of minutes WITHOUT a LARGE BOX FAN blowing on the engine.

Do NOT remove the front engine cover WITHOUT FIRST DISCONNECTING THE GROUND CABLE.

Do NOT STRIP OUT THE SPECIAL HOLLOW BOLT AT THE TRANSMISSION, GROUNDING THE BATTERY!

Good Luck!
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Old 10-05-2012, 03:49 AM   #11
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What did 'starter serviced' consist of?

Were the bushes replaced? The bushes are the bearings that the stater shaft runs in, if they are worn then the starter will run very slowly under load, especially when the bike is cold.

The easy solution is a new Valeo starter from euromotoelectrics, and if you are really cheap then the generic Valeo copy from the same source.

I don't think that your stater problems have anything to do with your diode board

Also make sure that you choke cables are properly adjusted so the choke works properly.
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Old 10-05-2012, 04:21 AM   #12
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What you describe might be an electrical problem but could easily be mechanical - cold start problems can often be traced back to mechanical and carb set-up. It's always a good idea to eliminate the obvious things before going for the more difficult. May I suggest doing a thorough service before replacing the diode board.

Start by changing the oil

Then check in roughly this order:
  • valve clearances
  • spark plugs and spark plug gaps
  • cables (throttle and choke)
  • points gap (as Spo123 says, disconnect the battery before you remove the front engine cover)
  • timing (better to do it with a strobe light with the engine running rather than just doing static timing)
  • carbs - tuning and balancing. Do this last
  • Did I miss anything there?
When you got the bike back on the road did you overhaul the carbs? New gaskets and o-rings, check all the needles, jets and seats? etc? The Bing carbs have separate main, idle and choke circuits - the idle circuit runs through the float bowl and has a tendency to collect crap. A 30 year old bike can collect a lot of crap in the carbs. Might be worth cleaning out the carbs and replacing the float bowl and choke gaskets (as boxerboy81 suggests) at the least.

All that is good maintenance anyway and won't be wasted effort even if it doesn't fix your problem.

If none of that works then several others have suggested electrical and other things to check. Don't forget that you can check the diodes with just a multimeter (if you search youtube you'll find plenty of videos showing how to do it). Replacing a faulty diode on the board can be done for about $2-$5 (again search youtube for how to do it). That's a lot cheaper than buying a new diode board. Diodes that are fried will often look fried, have you inspected the diode board?

Good luck and have fun.
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Old 10-05-2012, 11:58 AM   #13
bushyb OP
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Quote:
Originally Posted by boxerboy81 View Post
Are the float bowl gaskets in good condition? If the holes are very compressed, damaged or too rounded then they can let too much air into the "choke" aux starter system, making it too lean and difficult to start.

If you get lucky, you may avoid lots of time and money via a quick inspection or change 'em if they're old anyhow.
Thanks I ordered and replace the float bowl gaskits with silicone real gaskits.
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Old 10-05-2012, 12:07 PM   #14
bushyb OP
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Quote:
Originally Posted by chasbmw View Post
What did 'starter serviced' consist of?

Were the bushes replaced? The bushes are the bearings that the stater shaft runs in, if they are worn then the starter will run very slowly under load, especially when the bike is cold.

The easy solution is a new Valeo starter from euromotoelectrics, and if you are really cheap then the generic Valeo copy from the same source.

I don't think that your stater problems have anything to do with your diode board

Also make sure that you choke cables are properly adjusted so the choke works properly.
Charles
Thanks Charles, the auto electric guys could not find a fault and I also checked it, Brushes were good as new at about 14mm long if I remember, front bush was a bit worn and was replaced, replaced solinoid. It was tested with load and was good.
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Old 10-05-2012, 12:34 PM   #15
bushyb OP
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Quote:
Originally Posted by motog View Post
What you describe might be an electrical problem but could easily be mechanical - cold start problems can often be traced back to mechanical and carb set-up. It's always a good idea to eliminate the obvious things before going for the more difficult. May I suggest doing a thorough service before replacing the diode board.

Start by changing the oil

Then check in roughly this order:
  • valve clearances
  • spark plugs and spark plug gaps
  • cables (throttle and choke)
  • points gap (as Spo123 says, disconnect the battery before you remove the front engine cover)
  • timing (better to do it with a strobe light with the engine running rather than just doing static timing)
  • carbs - tuning and balancing. Do this last
  • Did I miss anything there?
When you got the bike back on the road did you overhaul the carbs? New gaskets and o-rings, check all the needles, jets and seats? etc? The Bing carbs have separate main, idle and choke circuits - the idle circuit runs through the float bowl and has a tendency to collect crap. A 30 year old bike can collect a lot of crap in the carbs. Might be worth cleaning out the carbs and replacing the float bowl and choke gaskets (as boxerboy81 suggests) at the least.

All that is good maintenance anyway and won't be wasted effort even if it doesn't fix your problem.

If none of that works then several others have suggested electrical and other things to check. Don't forget that you can check the diodes with just a multimeter (if you search youtube you'll find plenty of videos showing how to do it). Replacing a faulty diode on the board can be done for about $2-$5 (again search youtube for how to do it). That's a lot cheaper than buying a new diode board. Diodes that are fried will often look fried, have you inspected the diode board?

Good luck and have fun.
Thanks I have just about done all that you mention here, especially the cards and new gaskits. I have not re-set or checked the valves or timing. The bike was in good running condition when it went in storage. Once started the bike goes very well, so I could be wrong but I believe the settings are correct. See my new comment. Thanks
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