Weird running 1979 R65

[Mender]

Hi, I recently bought an R65 which ran really rough and leaked oil from the base gaskets and pushrod tube seals. I replaced the gaskets and seals and cleaned the carbs with compressed air and carb cleaner, replaced the diaphragms, and spark plugs and set up the carbs. It now starts and runs lovely. However! when running at about 6000rpm in fifth it is fine when on the power but if I roll off the throttle a tiny bit it feels really rough back on the power is fine. Secondly after a bit of a thrash today I returned home and it would only tick over on one cylinder, as I got off to investigate it slowly chimed back in on both. I reckon a jet is clogged or a passageway in one of the carbs, but where? Any ideas would be thankfully received.  

[nhmaf]

Could be partly clogged jet or sediment from the tank obstructing things, but another thing to consider - are you still running the original coil and plug wires?   How about the condensor & points?

When these bikes seem to run out of steam, it is sometimes an airleak  around the diaphragm, or maybe between the carb and the head.

[Mender]

Cheers, will take the carbs apart first.
 I visited your neck of the woods courtesy of the Royal Navy HMS Minerva back in 1971, I remember a pretty lady in a Mk1 white Mustang took me for a ride to the White Mountains.

[JBwell]

I had a similar problem on my 80 r65.  It was the float level in one of the carbs.  After cooling down, I turned on the fuel valve for a couple minutes, then carefully removed float bowls.  One has gas about 1/4 inch from top, the other was over a half inch from top.   Adjusted the "tang" under the needle, checked again and both were about 1/4 inch from top.  Problem went away.

[montmil]

Check the Idle Air screws and jets first. That air/fuel circuit is in play when the bike is, well, idling. A stoppage of fire on one cylinder might be traced to that side's circuit. Carefully count the turns required to remove the needle screw. You'll want to return it to its last position to check for proper idle on both cylinders.

[Barry]

Mender,

Your symptoms at 6000 RPM sound like the classic roll off test for selection of the correct main jet. When the throttle is rolled off a touch at 6000 RPM it momentarily richens the mixture. If the engine runs rough when you do this that usually indicates the carb is set up too rich. If the engine pulls better when you roll off then it's set up too weak.


On the float levels it is important that they both be the same but it's not normal to set float levels to have a removed bowl full to 1/4" from the top as the level will rise substantially when fuel is displaced by the floats and carb body castings.  1/4" from the top is very close to flooding and will cause a rich mixture particularly at idle.   1/2" is closer to correct.

[JBwell]

Respectfully Barry if I set mine at 1/2'' below the rim I don't think it would run at all. After I made the adjustment everything improved.  Starting , idle, higher speed, everything.  Not saying where I set my carbs is right for all carbs but works for me.  I had read on this forum that someone had a stumbling problem at higher speeds and that the float height was very critical.  My carbs have the floats that just sit in the bowl over a rod that sticks up.  Are all the Bings like that?

[JBwell]

Barry I re read your post and I see just what you are saying.  When I said 1/4'' from top of rim, that was with the floats still in the bowl.  And certainly if not in the bowl then that level would be much too high.

[montmil]

...My carbs have the floats that just sit in the bowl over a rod that sticks up.  Are all the Bings like that?

You may have the Bing accessory Alcohol Resistant Independent Float & Bowl Kit. This item has been a bit problematic for owners. Expensive to purchase as the kit requires entirely different float bowls. "...over a rod that sticks up" is what caught my attention.

Some owners have eventually bitten the bullet and converted back to OEM bowls n' floats to cure their fueling problems. I have the OEM Bing floats in all three of my Airheads and have never had an alcohol-related issue.

http://bingcarburetor.com/bmw/cvaccessories.html

[Barry]

JBwell,

1/4" from the top makes much more sense now. The Bing independent float kit is relatively rare due to it's very high cost. With stock floats when the bowl is removed the floats stay connected to the carb via the hinge.

If you haven't already seen this, Snowbum has some very specific advice for setting up the Bing independent floats. http://bmwmotorcycletech.info/bingindependent.htm

[montmil]

...Snowbum has some very specific advice for setting up the Bing independent floats...

on top of the trash can.
 [smiley=whistling.gif]

[nhmaf]

I've got them on my R100, and I still haven't got the thing running right yet.   The R65 (knock wood) has the old originals and still runs like a top up to redline

[Kookaburra]

Whilst we are on Bings, I need pointing in the right direction to fix a running problem.

I have recently replaced the needles and seats on the 1985 R65 so readjusted the relatively new  float bowls as per the parallel eyeball method and cross checked with the Snowbum 24mm depth method. The bike exhausts now pop during deceleration when the throttle is closed.  What is this an indication of- mixture too rich?, too lean? Float bowl levels too high? too low?  :-/

[montmil]

The bike exhausts now pop during deceleration when the throttle is closed.  What is this an indication of- mixture too rich?...

Yes. A bit too rich.

Usually, when a new problem pops up, it's best to readdress your last change. Are the needles the same taper size as previous and are they in the same needle grooves? Plus the float level alteration.

[Barry]

he bike exhausts now pop during deceleration when the throttle is closed.What is this an indication of- mixture too rich?, too lean? Float bowl levels too high? too low?Undecided

It depends because it can be caused by air leaks but I would normally say it's usually caused by a weak idle mixture.  How does the engine behave with regards to it's need for cold start enrichment ? Is it very cold blooded indicating weak or starts and runs with little or no choke indicating rich.