Odd carb behavior?

[jp9094]

I recently (April) had a Siebnrock 860 kit and NEW Bing carbs fitted to my 1983 r 65 LS. After 620 miles (1000 Km) I changed the oil and filter and retorqued the heads and reset the valves (finished this 2 days ago). When I took the bike for a ride today it started to idle at almost 2000 rpm indicated on the tachometer! When I received the bike from the technicians the idle was at 500 rpm indicated  on the tach, but sounded a lot quicker to my ear. I attempted to reduce the idle on the road, which was successful, but I lost the balance of the carbs. Returning to my garage I attempted to balance the carbs with the home made balancer I have used in the past without success. The left carb seems to suck much more than the right no matter how I turn the adjusters. Now the fuel just pours out of the right side carb??

So, how could adjusting the valves affect the idle?  Any help will be appreciated!

TIA

[dogshome]

My 860 is happiest idling around 1000 to 1100 rpm.

I would say you simply have a carb problem and nothing to do with the valve adjustment.

[Barry]

So, how could adjusting the valves affect the idle?

It can't very much except for a small amount due to the fact that changing valve clearances also makes a small change to valve timing. If you open up valve clearances the idle speed may rise due to the reduction in valve overlap improving efficiency because less fresh mixture goes straight out of the exhaust.  The effect is more pronounced when the mixture is set relatively weak. To put it another way the engine will idle on a slightly weaker mixture setting when clearances are opened up. But these are relatively small effects and wouldn't account for the big change you experienced. 

I think you have issues with the tach not reading accurately and with carbs both idle settings and issues with the right carb flooding. The flooding will have to be resolved before any further attempts at tuning.  Odd that new carbs should flood but it might just be some debris causing the float needle to leak. Once the flooding is fixed I'd go back to base settings on the carbs and work from there.

To do a rough check on the accuracy of the tachometer I'd ride at a fixed rpm in 5th and compare that with the indicated speed or better still a radar or GPS indicated speed. I know for example that mine should be doing approx 39mph at 3000 rpm.  Yours should be a higher speed because of your higher final drive ratio. I have all the gear ratios on a spread sheet so if you tell me your final drive ratio I can give you a more accurate figure.

[jp9094]

Barry,

Many thanks for the reply. I do not place any faith in the tach. However, I believe I can tell the difference between 500 rpm indicated and 2000 indicated by the sound alone,

Given this fact I am at a loss for the change absent any external force. I will be cleaning the carb tomorrow and will go from there.

Another stupid question. Why were there no covers on the vacuum ports on the carbs? I always thought there were plastic covers (or screws on the older models) on these.

[dogshome]

There should be screws. M3.5 I think. Surprisingly they don't make a huge difference if left out, but obviously not ideal.

[Barry]

Yes definitively M3.5 x 0.6

If you happen to be in the UK it's the same thread as electrical screws used for securing light switches and power sockets. I've used these in the past as a temporary measure when I lost an original screw. Otherwise M3.5 is not a common screw size.

[Bob_Roller]

You can find vacuum system rubber caps at auto parts stores usually in a blister package  .

[jp9094]

Just an update. Have gotten the bike to idle at a reasonable RPM : 750 indicated on the tachometer. However when I try to balance the carbs with my home made manometer ( which I have used successfully in the past ) the left carburetor seems to suck all the fluid from the other side no matter what I do to the idle settings. How can this be?? Any advice appreciated.

[Bob_Roller]

Have you tried going back the beginning of the carb sync ?
Get the engine up to operating temp before synching the carbs .
Loosen the throttle cables at the carbs, back off the idle adjustment screws, place the feeler gauge in there and tighten the adjustment screw until it just grabs the feeler gauge, then adjust one half turn in on those screws .
I use the thinnest feeler gauge I have, .003 in.
At least you know that both are set the same at the beginning .
I use long regular screwdrivers for adjusting, I put a stripe on the end on the handle, so I know how much I've adjusted .
It can be a tedious process at times .

[Barry]

Just an update. Have gotten the bike to idle at a reasonable RPM : 750 indicated on the tachometer. However when I try to balance the carbs with my home made manometer ( which I have used successfully in the past ) the left carburetor seems to suck all the fluid from the other side no matter what I do to the idle settings. How can this be?? Any advice appreciated.

It might be that one of the vacuum take offs is blocked. I confess I've never tried to poke a wire through but it is quite a small opening in the venturi so a blockage is possible.

[jp9094]

Barry, that was one of the first things I tried! Thay are not that small, in fact a regular sized paper clip passed quite easily!

Many thanks for the replies.