How should I set the left throttle plate screw on my 1150?

[Bill Dennes]

I'm talking about the really hard to reach screw and locknut set on the bottom of the throttle body, kinda toward the inside. It's the screw about which BMW says "The sealed stop screws on the throttles must not be tampered with, or else the basic idle flow setting will have to be reset by the manufacturer."

 

Of course I have tampered with mine, and I think they may be set so the throttle plates are too far closed.

 

This article on the IBMWR board tells how to establish the base position for the left side throttle plate stop screw on the 1100 oilhead. It is a rework of Lentini's zero=zero article.

 

I understand that the 1150 does not need to do (cannot do?) zero=zero due to the self-correcting nature of the Moronic (oops, that's Motronic).

 

So how do I establish the correct amount of opening of the left throttle plate at idle for my 1150? This setting seems to be the cornerstone of synchronizing the idle correctly, etc.

[Rich06FJR1300]

i have never touched those screws and don't plan on it...in balancing my TB's and setting the idle speed its always with the brass adjusting screws for the idle, then balancing the TB's with throttle cables. In all the articles I have read, there never was any mention of adjusting those screws to adjust the butterflies.

[Cali Kid]

Hi Bill, I just finished a long search for a post I made a while back about this. Sorry, can't locate it.

 

However, mine had loosened for whatever reason and fixing it was not the "OH MY GOD" some think it is.

 

Get a hold of a .0025" feeler gauge, a .002" may work also, but I did this originally with the .0025".

 

Have the intake tubes off, then slide the feeler into the left side throttle body. You want it at the very bottom of body where the throttle body valve (TBV) comes into contact with the body.

 

Turn the stop screw in the appropriate direction until you have friction on the feeler. This would be the approximately same amount you feel when doing valves.

 

Once that is attained, tighten the lock nut and check again.

 

The reason for doing this at the bottom, is because the angle of the TBV creates a differential amount of friction. That is, you'll feel the friction when you pull the feeler toward you, because it is dragging on the TBV and pulling it closed. Pushing in on the feeler will reduce friction because it pushes the TBV open ever so slightly.

 

When the stop screw is right, it prevents the TBV from clamping on the feeler as you pull it toward you, and you'll feel the the friction as described above. If the stop screw is closed too much the TBV will clamp down on the feeler and you'll have difficulty pulling on it. Too far open and you have no friction (of course).

If you are doing both stops, just make sure they are as close in "feel" as you can make them.

 

If you haven't messed the right one up confirm the gauge size by inserting the feeler into the right side as described. You should be real close to the .0025" thickness. Don't worry that the feeler is flat and the body round. The feeler is very thin and will match the curve of the body when slid between the valve and body.

 

I determined this from measuring a properly set throttle body. It worked very well on my RT. My brass screws ended up 1/4 turn different when all was said and done. It has run well for more than a year.

 

Once you get the stops set, do the brass screws, then cables as normal.

 

It does work, and it isn't that hard to get right. I'll watch for your results, or PM me if you have questions.

 

Good luck.

[powerman]

Hello

 

I thought about this a little a while back just incase..

I don't think it's magic as BMW has stated.

If the bike runs, I think your halfway home.

All you need to do is a throttle body sync in reverse with the stop screw as last adjustment.

I assume you only played with one of stop screws.

 

1) Adjust stop screw so throttle open slightly like in cali's post above.

2) Slack all throttle cables so they are loose (throttles closed all the way limited by stop screws)

3) Adjust both brass bypass screws to factory specs.

4) Start bike and do throttle body sync by adjusting the throttle stop screw you messed with so vacuum equal on both sides . If rpm to low or to high adjust brass bypass screws equally.

A few comments. I have not done this and I would use a water manometer connected differentially.

 

good luck

[RFW]

I'm talking about the really hard to reach screw and locknut set on the bottom of the throttle body, kinda toward the inside. It's the screw about which BMW says "The sealed stop screws on the throttles must not be tampered with, or else the basic idle flow setting will have to be reset by the manufacturer."

 

The similar set of screws on a K-100 also control the synchronization of the butterflies. Mine had been mucked with at some point by a previous owner.

 

To fix the problem I had to use a high-volume vaccuum vane-pump to suck air through the throttle bodies (one at a time), and record the vaccuum in each at various low throttle openings, then make adjustments to the synch screws to bring all 4 cylinders back into synch as closely as possible.

 

It was extremely tedious, but in the end it worked well. For a boxer, this would be a lot easier, since there are only 2 cylinders. The problem with a 4, is that adjusting one of the 4 butterflies affects the other 3. With only 2 cylinders, adjusting one will only affect one other.

 

Note that this synchronization is only relevant at very low throttle openings. Once the butterflies are open more than a few degrees, slight imbalances that may cause problems at very low throttle openings, are too small to affect the larger amount of intake airflow at around 10° of butterfly opening or more.

 

Bob.

[ShovelStrokeEd]

Or, you could pull both throttle bodies off the bike. Connect a vacuum cleaner to the untouched throttle body and, using a mercury manometer connected to the normal vacuum pickup point, measure the available vacuum at the closed position. Now switch to the disturbed throttle body and do the same, adjusting the stop screw until the vacuum is the same. Essentially you are making your own flow bench.

 

I have never actually done this as I have access to a real flow bench should the need arise. It should work though and would remove all the variables of engine tuning from the equation.

[Haynes]

Bill,

Using the .0025 feeler method described by Cali Kid should do fine. The purpose of the adjustment is mainly to ensure that the throttle plate can never close hard in the intake throat as they have a tendency to jam shut or wear a ridge in the intake.

 

The adjustment must be set somewhere between:

(1) not allowing the throttle to close hard in the intake.

(2) not allowing the airflow through the intake be excessive so the brass bypass screws become ineffective in setting the idle speed.

If the stop-screws are set correctly, your brass by-pass screws should give you the correct range of adjustment on your idle speed.

I've done this procedure a few times for friends on their 1150 bikes. If you are concerned, send me a PM.

[RFW]

Or, you could pull both throttle bodies off the bike. Connect a vacuum cleaner to the untouched throttle body and, using a mercury manometer connected to the normal vacuum pickup point, measure the available vacuum at the closed position. Now switch to the disturbed throttle body and do the same, adjusting the stop screw until the vacuum is the same. Essentially you are making your own flow bench.

 

I have never actually done this as I have access to a real flow bench should the need arise. It should work though and would remove all the variables of engine tuning from the equation.

 

Vaccuum cleaner does not work. I tried this first when synching my K100 throttle bodies, and it was useless. Lots of flow, but nowhere near enough vaccuum at near-throttle-closed position. That's why I dragged out the old vane-type vaccuum pump I mentioned and connected it to a 1/4HP electric motor.

 

Of course you are right: a real flow bench would have been just the ticket.

 

Bob.

[Bill Dennes]

Thanks, Cali Kid! A very useful rule of thumb. This adjustment is the difference between incredibly bad start-off performance (knocking, stalling) and taking off just fine from a stop.

 

My butterflies were way too far closed, due to my following a tuning method that based everything on TPS settings (and did not envision TPS settings changing). Thus, idle speed was done with the "forbidden screws."

 

I am curious about why this has becore more of an issue lately. I imagine that the nature of gasoline that's available in Los Angeles might have something to do with this as we move from MTBE to ethanol additives.

 

I have throttle cables on order and am going to delay a truly serious tune-up until those are installed. Nevertheless, Cali Kid's trick is spot on for rescuing the throttle stop setting default.

[Cali Kid]

Awesome, glad that worked for you Bill.

[Ken H.]

To add to Cali Kid's procedure, after done I would do a quick check of the TPS voltage to unsure it is below 400mv at idle. If not adjust the TPS to 380-390mv or so. If it never falls below 400mv at idle the Motronic will not be able to set the baseline fuel curve when you go through the throttle travel retraining procedure.

[Bill Dennes]

Ken - Thanks for the reminder. Mine was set high, around 575 mv. When I set it down as suggested it ran clanky when starting off until I backed the LBSs out some.

 

Running darn well now, testing interrupted by rain.