'84 R80RT Idle Drop

[05hexhead]

New to me '84 R80RT.

I am having a slight issue with the idle speed that momentarily drops about 250 RPM's, after driving under load, before returning to the set idle speed. The bike runs up to red line very smooth and strong and she does not miss a beat. She will idle at 900 no problem until she returns off higher RPM's. So I have to set the idle at around 1100, as it can stall when it drops too low while shifting.

I have checked for sticking advance with a timing light and everything looks smooth. 32mm Bings have been cleaned and sync'd, slack throttle and choke cables and 3/4 setting for idle screws (no difference set at 1 turn either), valves set, new plugs that look perfect after 600 miles.

Any suggestions?

Thanks

[Ray from Indiana]

Your idle mixture setting is probably a little lean. Suggest fattening it up a tad.

[SteveD]

Your idle mixture setting is probably a little lean. Suggest fattening it up a tad.

I was going to suggest a little rich. Doesn't lean make it idle a tad high
Idle should be set at 1100. The lower setting at 900 is ok for earlier bikes, but too low for the post 1980 models.

The interesting statement for me was ...

.. 3/4 setting for idle screws (no difference set at 1 turn either

Maybe the idle screws need new o-rings or the little holes need a clean out?

[Jeff in W.C.]

I would definately start with the mixture. You indicated 3/4 setting on the mixture screws. Those are only starting points. The carbs should be adjusted to represent ideal mixture at operating temp. Also, as Steve D mentioned, something seems a miss if you're getting no change in adjusting the mixture screws.

[George Ryals]

This is the interesting statement to me........ " as it can stall when it drops too low while shifting."

[05hexhead]

This is the interesting statement to me........ " as it can stall when it drops too low while shifting."

If I set the idle at 900 and was riding up to a stop sign and had the clutch in the engine would quite often stall when the idle did a dip before returning to the 900 setting. That is why I am having to keep the RPM's set higher so the engine does not stall.

The statement that the mixture screw setting of 1 turn did not make a difference was in reference to the dip in the RPM's still continued.

I will try new mixture O-rings and a richer setting and see if that helps.

Thanks,
Nick

[Jean]

+1 or +2. If the idle mixture screw adjustment to ONE turn out made no difference it indicates something is wrong (clogged) in the flow path. Also agree that 900rpm is too low for the '84 bike with (assumed) lean set-up on the carbs.

You did not say WHICH carbs were fitted. Only that they are "32"....can you supply the rest of the numbers and that might help us a tiny bit more. It's not unusual to swap carbs...
I put a pair of 64/32/9 & 10 on my /5 and they are soooooooooooo nice compared to the "correct" ones. Also have them on the '78 R80/2 conversion. (REALLY!)

[Deleted User 72]

+1 or +2. If the idle mixture screw adjustment to ONE turn out made no difference it indicates something is wrong (clogged) in the flow path. Also agree that 900rpm is too low for the '84 bike with (assumed) lean set-up on the carbs.

You did not say WHICH carbs were fitted. Only that they are "32"....can you supply the rest of the numbers and that might help us a tiny bit more. It's not unusual to swap carbs...
I put a pair of 64/32/9 & 10 on my /5 and they are soooooooooooo nice compared to the "correct" ones. Also have them on the '78 R80/2 conversion. (REALLY!)

I believe that 64/32/9 & 10 ARE the correct carbs for a /5. That might be part of the unproblem.

[Deleted User 72]

This is the interesting statement to me........ " as it can stall when it drops too low while shifting."

If I set the idle at 900 and was riding up to a stop sign and had the clutch in the engine would quite often stall when the idle did a dip before returning to the 900 setting. That is why I am having to keep the RPM's set higher so the engine does not stall.

The statement that the mixture screw setting of 1 turn did not make a difference was in reference to the dip in the RPM's still continued.

I will try new mixture O-rings and a richer setting and see if that helps.

Thanks,
Nick

My '77 R100 was stalling coming off high rpms to idle. I found the valves to be too tight and loosened them to spec. Idles fine now. FWIW

[SteveD]

Good point Native...valves first, then carbs.