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Discussion Starter · #1 ·
Seeing John's post about the carb on his R80 reminds me of a question I have. When I got the bike it would only run on one pot when cold so I stripped the carbs and cleaned everything out paying special attention to the choke circuits and now the bike starts on both cylinders from the off.
The problem I have is these doesn't seem to be any fast idle so in order to keep things going I have to apply a little throttle. If I adjust the throttle stops to keep it ticking over when cold on choke, the revs rise to about 1500 when warmed up.

Am I missing something or is that just the way of these old Beemers?
 

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The Sultan of Bling
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Seeing John's post about the carb on his R80 reminds me of a question I have. When I got the bike it would only run on one pot when cold so I stripped the carbs and cleaned everything out paying special attention to the choke circuits and now the bike starts on both cylinders from the off.
The problem I have is these doesn't seem to be any fast idle so in order to keep things going I have to apply a little throttle. If I adjust the throttle stops to keep it ticking over when cold on choke, the revs rise to about 1500 when warmed up.

Am I missing something or is that just the way of these old Beemers?
Have you balanced the carbs?
 

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The Sultan of Bling
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Well I use a carb balancer myself. :D

Also just struck me Boris did you set the tickover with the engine up to heat and removing a plug from alternate sides?

LF, heading to my pit after a day fettling in the garage but if you want details of balancing the carbs I'll post them tomorrow night. :thumbup:
 

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Deer Dodger
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Well I use a carb balancer myself. :D

Also just struck me Boris did you set the tickover with the engine up to heat and removing a plug from alternate sides?

LF, heading to my pit after a day fettling in the garage but if you want details of balancing the carbs I'll post them tomorrow night. :thumbup:

:withstupid: :D:D:D:D Cheers :thumbup:
 

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Discussion Starter · #6 ·
Eh ???
How do you do that then ??:confused:
Yes I have. Well had... I balanced them cold after the carb rebuild and it started and ran beautifully on choke but when I was out it was ticking over at 1500 so I knocked both screws back an equal amount. and since then it ticks over lovely when hot but not on choke.

I suspect you have hit the nail on the head though. I really should go through everything again from setting the valve clearances then getting the bike hot and setting the balance at idle. That may well do the trick but it will have to wait till I get the brake callipers back on.

Out of interest do yours tick over when cold on the choke without throttle and how soon can you get the choke off?
 

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The Sultan of Bling
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Yes I have. Well had... I balanced them cold after the carb rebuild and it started and ran beautifully on choke but when I was out it was ticking over at 1500 so I knocked both screws back an equal amount. and since then it ticks over lovely when hot but not on choke.

I suspect you have hit the nail on the head though. I really should go through everything again from setting the valve clearances then getting the bike hot and setting the balance at idle. That may well do the trick but it will have to wait till I get the brake callipers back on.

Out of interest do yours tick over when cold on the choke without throttle and how soon can you get the choke off?
All of mine tick over sweetly throttle free, weather dependent it's full choke, wait about 30 secs then down to half choke, minute later choke off.

Just to reiterate, set tick over with the bike hot and set each pot separately as low as they will go before stalling, when both are running the tick over will rise but should be around 1k if not lower. My PD ticked over at slightly under 800 rpm would you believe.

Another thought. Have you checked the air mixture setting?
 

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Discussion Starter · #9 ·
All of mine tick over sweetly throttle free, weather dependent it's full choke, wait about 30 secs then down to half choke, minute later choke off.

Just to reiterate, set tick over with the bike hot and set each pot separately as low as they will go before stalling, when both are running the tick over will rise but should be around 1k if not lower. My PD ticked over at slightly under 800 rpm would you believe.

Another thought. Have you checked the air mixture setting?
I've read about this business of balancing by shorting out plugs but I just used my vacuum gauges. Is there a reason why this is bad?

As for the mixture screws I put them back where I found them before cleaning and left alone. Should I be checking these and I assume, instead of the usual method, there is a special BMW way using a bratwurst.
 

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Bloody furriner
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I usually get the chokes off ASAP (I have separate choke pulls on the carbs themselves. Less drama than the Y cable setup.) and that means I have to keep a bit of throttle on for the first mile or so. After that it's warm enough to keep itself going.

There isn't a handy idle speed knob like I had on the dommie, and I miss that sometimes but it's never really a problem.
 

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Bloody furriner
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Mixture, I usually pull a spark plug out so you basically have a single, then adjust idle mixture for highest rpm. Then again for the other side.
 

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The Sultan of Bling
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Just a very quick one from me pit, removing a plug on alternate cylinders is not for balancing, it's to set the idle speed. Important bit here just for clarification, remove the plug and earth it to the cylinder head to prevent damage to the electrics, don't just take the plug cap off.

I use a Morgan Carb Tune for balancing but only after sorting tick over and air screw.

Just wanted to clarify the plug bit in case anyone runs out to give it a go :)
 

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The Sultan of Bling
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As for the mixture screws I put them back where I found them before cleaning and left alone. Should I be checking these and I assume, instead of the usual method, there is a special BMW way using a bratwurst.
Define usual method :)
 

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Discussion Starter · #14 ·
Just a very quick one from me pit, removing a plug on alternate cylinders is not for balancing, it's to set the idle speed. Important bit here just for clarification, remove the plug and earth it to the cylinder head to prevent damage to the electrics, don't just take the plug cap off.

I use a Morgan Carb Tune for balancing but only after sorting tick over and air screw.

Just wanted to clarify the plug bit in case anyone runs out to give it a go :)
But don't you set idle speed using the throttle stops which are the self same throttle stops you use for idle balance?

I set the tick-over to 1000 revs and balanced the carbs either turning up or down either carbs throttle stop as necessary to keep the tickover to 1000 and get the vacuum the same.

Once I did that I raised the revs using the twistgrip and set the cable adjusters for an even vacuum at about 2000-2500 revs. Then I checked there was still slack in the cables at tickover and the balance was still OK.

So once you have set the tickover for each side by shorting out plugs what do you then adjust for idle vacuum?

My bike has points. If I was to go this route do I still need to ground the plug as there is no electronic ignition to blow?
 

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The Sultan of Bling
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But don't you set idle speed using the throttle stops which are the self same throttle stops you use for idle balance?

I set the tick-over to 1000 revs and balanced the carbs either turning up or down either carbs throttle stop as necessary to keep the tickover to 1000 and get the vacuum the same.

Once I did that I raised the revs using the twistgrip and set the cable adjusters for an even vacuum at about 2000-2500 revs. Then I checked there was still slack in the cables at tickover and the balance was still OK.

So once you have set the tickover for each side by shorting out plugs what do you then adjust for idle vacuum?

My bike has points. If I was to go this route do I still need to ground the plug as there is no electronic ignition to blow?

I think I see what may be causing the fast tick over.

The method I use was shown to me by a friend when I bought my first one years back, who's not only a mechanic but has been riding Airheads for years and still rides the 100 PD he bought new in 1992 and has now nearly 200K on the clock but runs like a Swiss watch.

Forget about using the vacuum gauge to set an idle balance, set idle as mentioned on each side with the plug out and hot using the rev counter and turning it to the lowest it will tick over or around 800 rpm, once done you should find the combined cylinder tick over will be higher say about 1000 rpm, thats all that's needed for the tick over, it does not need gauges.

From there use your gauge and the cable adjusters to set a balance with the throttle cable adjusters on the carbs, (don't touch the throttle stops) but look for the balance about 4000 rpm.

As for grounding the plug none of mine have electronic ignition, I do it as I was told to by someone I trust totally when it comes to these things. :D

Try it and see how it goes. :thumbup:
 

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Discussion Starter · #16 ·
I think I see what may be causing the fast tick over.

The method I use was shown to me by a friend when I bought my first one years back, who's not only a mechanic but has been riding Airheads for years and still rides the 100 PD he bought new in 1992 and has now nearly 200K on the clock but runs like a Swiss watch.

Forget about using the vacuum gauge to set an idle balance, set idle as mentioned on each side with the plug out and hot using the rev counter and turning it to the lowest it will tick over or around 800 rpm, once done you should find the combined cylinder tick over will be higher say about 1000 rpm, thats all that's needed for the tick over, it does not need gauges.

From there use your gauge and the cable adjusters to set a balance with the throttle cable adjusters on the carbs, (don't touch the throttle stops) but look for the balance about 4000 rpm.

As for grounding the plug none of mine have electronic ignition, I do it as I was told to by someone I trust totally when it comes to these things. :D

Try it and see how it goes. :thumbup:
Cheers. I'll give it a go. What's the best method you can offer for grounding the unused plug lead? Preferably one that doesn't involve me getting a shock.
 

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The Sultan of Bling
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Cheers. I'll give it a go. What's the best method you can offer for grounding the unused plug lead? Preferably one that doesn't involve me getting a shock.
Duct tape to hold it against the fins, it won't be on long so minimum residue. :thumbup:
 

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Discussion Starter · #18 ·
Duct tape to hold it against the fins, it won't be on long so minimum residue. :thumbup:
Using a spare plug and duct taping that or shoving something like a screwdriver up the suppressor cap and taping that to the fin?

I think I need a picture.
 

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The Sultan of Bling
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Use any plug as long as you take the one out of the cylinder, makes a lovely popping sound when the engines running:)

Just place the plug into the cap, place it into the recess on the casing where the plug mounts and use the tape to make sure it stays in contact. After a while you'll not even need the tape.

If you want a picture I can get one when I get home.
 

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Discussion Starter · #20 ·
Use any plug as long as you take the one out of the cylinder, makes a lovely popping sound when the engines running:)

Just place the plug into the cap, place it into the recess on the casing where the plug mounts and use the tape to make sure it stays in contact. After a while you'll not even need the tape.

If you want a picture I can get one when I get home.
Ahh so you remove the plug. That's at odds with the other threads I've read that say they attach something (whatever that is) to the leads and short each sides out for a few seconds at a time without stopping the engine. Clearly you can't do that if you have to unscrew the plug each time.
 
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