R1100RT single cable idle synchonisation

[dmsantam]

Good evening all, I've put my 1100RT back together after a throttle body rebuild, and I am stuck on one issue - synching at idle with the BBS's. 

 

I have the early 1100RT with the single cable that goes to the left side, then the right side. New throttle cables installed, Dan Cata TB rebuild kit installed. Plates centred in the TBs. No slack on the right side cable, and it appears that the two TB cams move at exactly the same time. I can easily get the off-idle (1500+ rpm) synched perfectly (i use a morgan carbtune). 

 

The BBS are spotless, and new orings installed. Starting with 1.5 turns out on each side, the vacuum is uneven. To get them the same, the right side needs to be closed completely, and the left side open about 3 turns. When I turn the left side in completely, I can notice the engine not happy, but not so for the right side. I believe the base idle screw on the right side has been messed with by the previous owner. 

 

I have currently just left them both 1.5 turns out, and synched the TBs at higher than idle RPM only, and the bike is running well, but with about 1250-1300 hot rpm idle. I'd like to get it sorted correctly, and would appreciate advice on how to set the right base idle screw (if my theory is correct), or any other ideas. 

 

cheers,

[dirtrider]

8 hours ago, dmsantam said:

Good evening all, I've put my 1100RT back together after a throttle body rebuild, and I am stuck on one issue - synching at idle with the BBS's. 

 

I have the early 1100RT with the single cable that goes to the left side, then the right side. New throttle cables installed, Dan Cata TB rebuild kit installed. Plates centred in the TBs. No slack on the right side cable, and it appears that the two TB cams move at exactly the same time. I can easily get the off-idle (1500+ rpm) synched perfectly (i use a morgan carbtune). 

 

The BBS are spotless, and new orings installed. Starting with 1.5 turns out on each side, the vacuum is uneven. To get them the same, the right side needs to be closed completely, and the left side open about 3 turns. When I turn the left side in completely, I can notice the engine not happy, but not so for the right side. I believe the base idle screw on the right side has been messed with by the previous owner. 

 

I have currently just left them both 1.5 turns out, and synched the TBs at higher than idle RPM only, and the bike is running well, but with about 1250-1300 hot rpm idle. I'd like to get it sorted correctly, and would appreciate advice on how to set the right base idle screw (if my theory is correct), or any other ideas. 

 

cheers,

Morning  dmsantam

 

With that much discrepancy between sides (IF) the throttle cable on the L/H side has some slack at curb idle (choke off), and the R/H crossover cable has JUST enough slack to allow the throttle plate arm to FIRMLY rest on the base idle screw (you positively need to verify this).  

 

Then,

 

What's left then is that one side (or both sides) throttle plates are not centered correctly. Did you back the base idle screws out so no throttle lever contact BEFORE & DURING the throttle plate centering?????????????????

 

The other big mistake most make on the single cable systems is: Using the choke to start the engine before TB balancing. If the choke is used before balancing then that works the L/H main cable in the wrong direction on the throttle pulley. So you end up with cross side inaccuracy after the cable works it's way back to normal position on the TB pulley.

 

When balancing the old single cable systems ---ALWAYS--- do not use the choke to start the engine (if it won't easily start then just use the twist grip to hold the throttle open a little during engine starting. Plus, before starting FULLY open & close the throttle a few times to work the cable back in correct position on the L/H throttle pulley. If the main cable is out of position (out of proper clocking) that effects the crossover cable's length going to the R/H TB pulley.      

[dmsantam]

Hi DirtRider, 

 

Thanks for your reply. I can confirm that the cables are as you describe, and I did not use the choke at all. Before starting the bike, i twisted the throttle to WOT and released it 3 times to be sure. 

 

Quote

 Did you back the base idle screws out so no throttle lever contact BEFORE & DURING the throttle plate centering?????????????????

 

No I did not. I think this is where I messed up. What i did was mark the throttle plates before i removed them by drawing along the shaft top and bottom, then when reinstalling I tried to follow those marks, and with a strong light behind the throttle body, get as much equal light all around the plate. 

 

I just read a post you made a while back about backing out the base idle screws exactly two turns, which allows the plates to be tight in the TB bore, and tightening up the plates, and then turning the base idle screws back two turns so they are where they started. Is that the best way to proceed? If you have any other advice on throttle plate centering, please advise. 

 

cheers,

[dirtrider]

1 hour ago, dmsantam said:

Hi DirtRider, 

 

Thanks for your reply. I can confirm that the cables are as you describe, and I did not use the choke at all. Before starting the bike, i twisted the throttle to WOT and released it 3 times to be sure. 

 

 

No I did not. I think this is where I messed up. What i did was mark the throttle plates before i removed them by drawing along the shaft top and bottom, then when reinstalling I tried to follow those marks, and with a strong light behind the throttle body, get as much equal light all around the plate. 

 

I just read a post you made a while back about backing out the base idle screws exactly two turns, which allows the plates to be tight in the TB bore, and tightening up the plates, and then turning the base idle screws back two turns so they are where they started. Is that the best way to proceed? If you have any other advice on throttle plate centering, please advise. 

 

cheers,

Morning  dmsantam

 

You might need to re-address the throttle plate centering. Also making sure the throttle shaft is properly centered latterly so no air gets around the ends of the throttle plate.  

 

The strong light behind the throttle plate is a good way to sort of verify plate centering but that doesn't work very good if you can't completely close the throttle plates tight to the throttle bore. 

 

The other thing to look for is worn throttle plates, if the motorcycle was ridden a long time with worn throttle shafts then sometimes that can wear the throttle plate edges if the worn shaft allowed the plate to contact the throttle bore. Or, I have seen a few that were ridden with worn throttle shafts where the throttle plate kept bumping the throttle bore long enough to move the plate on the shaft. So marking & then reinstalling to marks might not equal best plate centering. 

 

The throttle plates are not round, they are somewhat oblong so the plate clocking is also very important to allow the plate to close properly all the way around. 

 

Also, make sure that your intake boots (between throttle body & engine are not leaking).

 

Also, make sure the engine valves are adjusted properly & the engine has somewhat equal compression as you won't be able to get the balance equal side to side (with matching throttle body settings) if the vacuum on one side is not the same as the other side. 

 

The single cable system is kind of a pain to work with if you are perfectionist, as there can be a lot of give & take on getting the single cable system balanced at both idle, above idle & at higher throttle openings.  

 

You need to sort of set your priorities on the single cable system, I always set my priorities to get the best balance in the light throttle RIDING range.  You don't ride it at curb idle so that can be a (give) place, the just off idle (light throttle) is where the surging is the worst (this is a take place), at mid to full open throttle  there is so much air flow & lower engine vacuum that a little off here will never be felt or noticed. 

 

The two places I always tried to get the best was light throttle cross side balance & trying to make sure that both side throttle plates STARTED opening together. Once open a ways not such a big deal but you want them to start opening together if possible. You never want the R/H side to start opening first, the L/H side has the TPS sensor so that side controls adding fuel at throttle plate opening. 

 

If the L/H side opens a little earlier then both sides get more fuel so not much noticed in throttle up. If the R/H side opens first then there is short time that the R/H side gets more air but no added fuel to go with that air. 

 

On the single cable system (when set up correctly with even throttle plate air flow at low openings ) you should be able to completely remove the R/H side BBS screw & not see any changes as the crossover cable is usually tight enough to hold the R/H side at idle position (on a hot engine) as  the crossover cable changes length slightly as it heats  cools.

 

There is BIG reason that BMW went to the added cost, added complexity, & added assembly time going to a bowden box split cable system. Most dealer tecs couldn't get them right, and some of the better tecs that understood the system & could get them close either didn't  have the time or didn't take the time it takes to get the them close in the areas that count.  

[dmsantam]

Great info, thanks dirtrider.

 

The shafts on my bike were not very worn, and I can see no evidence of wear on the throttle plates. The little wear on the shaft was enough to cause some clacking at idle though and sounds like that annoy me. 

 

How do you ensure the shafts are centred laterally? From memory it had circlip on one side, and pulley had a nut holding it on. I don't recall any lateral play. 

 

I will remove the throttle bodies, recenter the plates and have another go.

[dmsantam]

I removed the throttle bodies, loosened the plate locknuts and the plate screws, turned the base idle screws out exactly 2 turns, and tightened up the plates. Then I turned the base idle screws back to where they were originally Checking with a strong light before and after, there was some difference, but it didn't look like i was that far off. 

 

Unfortunately symptoms were still much the same after a synch. The BBS on the right side was still way off from the left side, and when screwing it all the way in, the engine didn't labour like it did when i screwed the left side in. I noticed that the blue paint on the right side base idle screw was absent, so i think the previous owner has messed with the base idle screw on that side. The left side still had the blue paint intact. 

 

So, I decided to try resetting the base idle screws, taking note of their original position in case I had to revert them back. I followed some advice I found in a different thread: 

 

Quote

Simplified Zero=250 mV Procedure
--Loosen all throttle and fast idle cables
--TBs and BBSs must be clean
--Set TB BBSs to 2.5 turns (just a starting point) and make them equal.
--Center and fully close both TB butterfly valves
--Set TPS to 250 mV and lock TPS screws (no further adjustment of TPS required)
--Open left TB and count stop screw turns after contact until TPS reads 340 mV. Lock left stop screw (no further adjustment).
--Set right TB stop screw open same number turns as left.

--Start engine, warm up to at least 3 bars.
--Balance at idle using only right TB stop screw, do not touch BBS. RPM does not matter
--Lock right TB stop screw
--Continue with a normal TB sync.

 

This worked a charm. Ended up with a nice 1100rpm hot idle, BBS were within 1/2 a turn of each other. I did have to get the idle slightly off balance to get the off idle to be more in balance, as noted in other threads about single cable systems. 

 

I went for a 200km ride yesterday with a good friend who has a near new R1250RT, and the bike was performing marvellously. No surging, no strange vibrations. 

 

cheers,