Yet Another Throttle Body Sync Question

[FiveSpeedSquirrel]

Hi there, new oilhead owner, a 2000 BMW R1100R with 51k miles. I've got some mild surging, but otherwise I love the bike. The bike was very well maintained by the previous owner. The bike has the correct model Autolite spark plugs (known to be less surge-prone, from what I have read). I also completed a valve adjustment. The surge is around 2500-3200 RPM. No surging at highway speeds. I've attempted the sync the throttle bodies both before and after the valve adjustment, using the following write-up. I built my own "manometer" for the job.

 

http://www.ibmwr.org/r-tech/oilheads/tb-synch.shtml

 

The issue I am having is the interaction between the Big Brass Screws (BBS) and the right side throttle cable. I loosen the right side throttle body cable, then synchronize the low RPM as instructed, using the BBS on both sides. Then I slowly tighten the throttle cable on the right side until the vacuum is even between the cylinders around 2000-4000 RPM. However, once I get this High RPM Sync dialed in, the cylinders are no longer balanced at idle. Whenever I tighten the right side throttle cable for the High RPM Sync (allowing more air into the engine), the idle vacuum at 1200 RPM is unbalanced because too much is coming from the right side cylinder. I can adjust the right side BBS to fix the idle vacuum, but then the high RPM sync is out of balance again. I can't ever seem to get both low RPM and High RPM in balance at the same time.

 

What is going on here? Is my right side throttle cable not closing all the way at idle by the time I get the High RPM Synced?

[roger 04 rt]

That's just what is happening. Although usually you can get l/r balance by adjusting only the right hand tb cable, sometimes you have to adjust the left side.

 

On my 1150, I want just a little slack in each side. That means adjusting off-idle TB balance with the adjuster turns inward, so that I'm never adding tension to an already tight cable.

 

Your cable setup may be different but that's the idea.

 

If your fuel injectors are out of balance, you may never be able to remove the surging, no matter how well you balance the air. It may make sense to have them cleaned and flow tested. There is also a kit of R1200 matched injectors and adapters you can buy.

Edited March 5, 2017 by roger 04 rt

[Selden]

Have your removed the BBS, cleaned them, and cleaned out the air passage?

 

Some R1100/R1150 engines are more prone to surge than others; mine doesn't surge at all, but others have reported bikes that are nearly unrideable. Roger's theory of injectors out of balance sounds pretty good.

[FiveSpeedSquirrel]

I haven't cleaned out the BBS yet, but I may try that next.

 

I hadn't heard of the R1200 injector swap, thanks for pointing that out! Reviewers of this swap are reporting more power, smoother vibes, and less surging. That mod might be in my future!

[Michaelr11]

For around $50 - less if you find someplace local - you can send your injectors to a place that will clean them and provide a report showing before and after injector flow performance. That would be a good baseline for balancing the throttle bodies. Remove the BBS and clean them off and clean out the passage. The BBS is only used to set the balance at idle. Once idle is set, balance above idle using the throttle cable. Recheck idle, it should not have changed unless you tightened a cable so there is no longer any free play. I used to balance cables at 1500 RPM, but now I find that I get a better ride by balancing at my typical ride RPM 4-5K RPM.

 

At your mileage it is unlikely that your throttle bodies need a rebuild. But keep in mind that when you get closer to 90-100K miles the TB shaft will be worn enough to leak air and make it difficult to balance because you'll have extra air coming in.

[roger 04 rt]

Cleaning the BBS is always a good idea but it's not leading to the problem described in the first post. That is due over tightening the RH adjusted.

[Lowndes]

Hey, FiveSpeed,

 

Keith Gibbons at Injector Rehab (Injector Rehab) has a pair of matched injectors with adapters for the TB's. These are cleaned and flow tested throughout the entire range, not just one setting. Test report provided. Mine looked brand spanking new. If they are refurb, I couldn't tell it. New ones are $30 more.

 

Interesting videos of the flow testing, too. Super nice guy, funny stories about boat racers. I thought BMW drivers were anal.

 

I got a set of his EV14's to replace the EV3's on my '99 R1100S (very similar and shares some parts with the 1150). $149 with postage. FAST service from NJ.

 

I added the AF-Xied (Nightrider.com) at the same time so I can't tell you which made the most difference. I can tell you that it runs SO much better now, especially startup, from a standing start, roll-on, etc. SO MUCH smoother, too. It was VERY cold natured before. That's gone. Runs cooler, too, but that is most likely the AF-Xied, which is supposed to help surging also.

 

 

[avu3]

For around $50 - less if you find someplace local - you can send your injectors to a place that will clean them and provide a report showing before and after injector flow performance.

 

For around $50 - less if you find someplace local - you can send your injectors to a place that will clean them and provide a report showing before and after injector flow performance.

 

I have personally shipped to

RC Engineering

https://www.rceng.com/Fuel-Injector-Cleaning-P43C0.aspx

 

and Witch Hunter

http://witchhunter.com/process2.php

 

I now use Dr Injector locally, but they also do shipping

http://www.doctorinjector.net/7301.html

 

Scott

[Jim Moore]

As you roll the throttle shut you should hear a loud "snap" as the stop screw hits the plate. If you're not hearing the snap your throttle cable is holding the butterfly slightly open. If so, put a half turn of slack in the left cable, then re-synch with the right cable.

 

Lots of folks think I'm a heretic, but I like to do my "high speed" synch just off idle, at 1800-2000 rpms. You're trying to measure the difference in throttle openings. The difference is greatest as the butterflies just start to open.

 

You may still have some surging after it's synched. You can also try removing the cat code plug. It's in the fuse box under the seat.

[dirtrider]

As you roll the throttle shut you should hear a loud "snap" as the stop screw hits the plate. If you're not hearing the snap your throttle cable is holding the butterfly slightly open. If so, put a half turn of slack in the left cable, then re-synch with the right cable.

 

Lots of folks think I'm a heretic, but I like to do my "high speed" synch just off idle, at 1800-2000 rpms. You're trying to measure the difference in throttle openings. The difference is greatest as the butterflies just start to open.

You may still have some surging after it's synched. You can also try removing the cat code plug. It's in the fuse box under the seat.

 

Morning Jim

 

That is the most accurate RPM range to do a TB sync. Ideally a person wants to do the cross side TB throttle plate sync (or balance) with the throttle plates closed as far as possible but ABOVE the major closed-throttle-plate idle BBS influence.

 

The more closed the throttle plates are then the higher the intake vacuum per degree of plate opening. That equates to a lot more vacuum delta per degree of plate opening.

 

That (almost) closed throttle plate operating range is also the most critical to light throttle engine surging.

 

Or put another way-- the farther the throttle plates are open during the sync then the more air flow through them at a lower vacuum delta so the balance loses a lot of precision.

 

It sure doesn't hurt to set them at 1800-2000 rpms then re-check as the throttle is slowly opened from there then closed back to 1800-2000 rpm range. But if the cross side vacuum is set right-on at 1800-2000 rpms but isn't close at 3, 4, & 5 K then there is a serious engine problem or intake restriction on one side.

 

The important thing to check for when doing a TB sync (balance) on the BMW boxer is that both side throttle cams lift off the idle stops at the very same time & hit the WOT stops at the VERY SAME TIME. If they don't then something is seriously wrong with the throttle system (like base idle screw settings, or worn TB parts, or ?????)

 

The small outlier here is on the very early 1100 engines with the single cable systems as those are very difficult to get to lift off the idle stop screws at the very same time under all engine temperature ranges. BUT they should hit WOT at the same time. On the single cable systems it usually takes a compromise so the best place to put that compromise is on the curb idle side as no-one rides the bike with the throttle plates closed all the way on the idle screws.

 

 

 

[FiveSpeedSquirrel]

Thanks to all of you for the detailed responses. This is super helpful. I will work on the bike again this week and see what I find.

[FiveSpeedSquirrel]

So I worked on the throttle bodies again, and loosening the left throttle cable did the trick! Throttle bodies are now balanced

[MarkAZ]

Thanks for the explanation, DR. That all makes sense. I synced mine at about 4000 rpm because it seems like that's where I spend most of my cruising time and I'd like it as smooth as possible then. I'll give it a try at 1500-1800 and see how that works out.

[dirtrider]

Thanks for the explanation, DR. That all makes sense. I synced mine at about 4000 rpm because it seems like that's where I spend most of my cruising time and I'd like it as smooth as possible then. I'll give it a try at 1500-1800 and see how that works out.

 

Morning Mark

 

One thing that you (& all tuners) need to keep in mind is: if you balance the throttles at 4000 rpm's sitting still that (unloaded) RPM isn't the same throttle plate opening as going down the road in high gear with a decent road load on the engine.

 

Next time that you have some time on your hands put some masking tape on the twist grip at the switch housing

then use a pen & mark the throttle position at 4k sitting still. Then re-mark with a different color pen at 4k running down the road in high gear.

 

Also keep in mind that a perfect throttle sync (balance) is a great place to start but that doesn't always equate to a better running engine. A perfect cross side air flow balance ONLY balances the air flow. By itself air doesn't make any engine power it's a fine balancing line of PROPER air flow vs ideal fuel flow.

 

If you have perfectly matched air flow to each side at xxx RPM's but one side fuel injector is spraying in more fuel then the other side then you want more air flow to that higher fuel delivery side for best runability.

 

A richer overall fuel mixture (within reason) can do a good job of covering up slight discrepancies in injector fuel flow vs balanced air flow.

 

Back in the old 1100/1150 days (before decent fuel modifiers that can richen the fueling) we would purposely set the cross side sync (TB balance) to be perfectly equal side to side at 1500-1800 rpms then ride the bike for a day or two. Then would purposely skew the balance a few inches of H2o on the L/H side then ride the bike a few days again. Then reverse it & skew the H2o a couple of inches on the R/H side. (it didn't take long to find a happy medium of less surge & slightly better engine smoothness with one side throttle plate slightly ahead of the other side (we never went very far past the obvious cross side skew but my guess is it was due to unequal fuel delivery by both side injectors).

 

The new trend seems to be in using the 1200 fuel injectors in the older boxer bikes as those seem to give more even fueling.

 

 

Bottom line here: matched air flow doesn't mean much without matching fuel flow from each side injector. BUT, an overall richer fuel air mixture (richer combustion mixture) can sure go a l-o-o-o-o-n-g way towards cover up a side to side fueling discrepancy.

 

The 1200 bikes addressed this by having a separate o2 sensor on each side so the fueling computer could keep the side to side fueling somewhat even & balanced.

 

 

 

 

[MarkAZ]

Good points. Thanks!