k75 throttle body sync mess Help!

[jimmyenglish]

Hello. I'm submitting this post for contention for ******** of the year award. I'll be volunteering in the cyber cafe in Wyoming so you can congratulate me there.

So I successfully adjusted the valves on my 93' k75 with 60k on it. THe idle was higher and like a genius I turned the middle throttle body screw to adjust it. Of course, nothing happened. THen I realized I turned the wrong damn screw! Now it backfires like hell. I mean like a .357. The TPS clicks just fine

I saw Paul Glaves post on another bmw site about discombobulated throttle valve screws. I cranked all screws (brass) out 1/4 turn and hooked up my homemade POS manometer to bodies 2 and 3. I had the tee fitting installed on the last one. Well it instantlly sucked all the tranny fluid I used into the 3rd throttle body. I said the hell with this as now I have to wait an hour for all the bubbles to settle. I'm going to invest in a dial type gauge setup. This was too messy. Anyway...

I tried to put the middle throttle body back to about what I remember and turned all brass screws out 1 full turn. It's a mess. THe bike runs really well actually but back fires like a cannon. It even idles good. Yet, I know it's a synchronous disaster. The valve adjustment went a long way! Where should I start in putting this back in order? THanks so much everyone! You guys rule!

Sincerely,

******** of the Year

 

[mrich12000]

Ask don B he has a website tha should show what to do. Also Paul may wade into this goodluck..

 

[breyfogle]

SHOTY: It might be easier/faster to check with Beemer-Boneyard about an "unadjusted" replacement.

 

[deilenberger]

IF I had to guess - the Throttle-Position-Switch (TPS) isn't closing when it should. That's the black box on the rear end of the throttle-bodies. When it doesn't close correctly - you end up not turning off the injection on de-acceleration, so you get a rich mixture into the cylinders, which ends up in the exhaust where it basically explodes.

K75's are known for this - but it usually can be controlled.

First - please tell me exactly what screw you adjusted that you shouldn't have? The base idle adjustment screw IS in the center (more or less) of the throttle bodies.

http://www.realoem.com/bmw/showparts.do?model=0572&mospid=47908&btnr=13_0519&hg=13&fg=15

PN-3 - is the TPS, PN-17 is the idle adjustment screw.

It will do no harm to adjust the idle adjustment screw. IF this is what you adjusted, chances are good that you have it screwed in too far (idle too fast) and it's keeping the TPS (PN-3) from closing.

To fix this:

Loosen the two screws holding the TPS to the rear end of the throttle bodies. You want it so it can turn fairly freely. Unplug the connector from it.

Now start the bike - and adjust:

- Brass screws to 1 or 1.5 turns out from gently bottomed out
- Idle adjustment screw to get engine idling at 1,000-1,100 RPM

Shut off engine.

Leave the throttle alone, and get your ear down next to the TPS. Turn it counterclockwise (looking from the rear) until you JUST hear it click. Now turn the throttle ALL the way open, and listen - you should hear it click again. Snug up the screws at this position, and check the setting hasn't changed. You should hear a click JUST as the throttle fully closes - and when it is fully opened.

Reconnect the TPS wire.

Go for a ride - see if it stopped backfiring.

When you get your manometer setup - balance out the brass screws so the vacuum at idle is equal. You should be able to do this without changing the idle and TPS adjustments. If the valves are adjusted correctly, and there are no intake leaks - and you didn't twiddle the inter-throttle-body-screws (hidden by "protective cap" - PN-2) - the brass screws should end up very close in adjustment.

Good luck!

EDIT - one other guess.. IF you adjusted the actual idle screw and nothing happened, that's 'cause the TPS or the choke-light-switch are holding the throttles open. Adjusting the TPS as described above will eliminate that. If you have the choke light switch (rearmost TB) - make sure the small aluminum spacer hasn't been lost that keeps it from screwing in too far.

 

[BUDDINGGEEZER]

I am assuming that since the bike runs and idles OK, that the backfiring is occurring on deceleration. If that's the case you have closed that throttle plate too tight and that cylinder is running lean, which makes for hotter exhaust temp.

I know the recommendation is to get a new throttle body if those screws are ever messed with, but I don't believe that. I did the same thing as you on #4 1/4 turn before I realized what I had done and put it back 1/4 turn and have no problems.

These are originally set on a flow bench. If you know were a flow bench is, you can get them dead on. Probably cost a lot and evolves removing the throttle bodies, but cheaper than buying new or used and you still have to remove them.

Since they are screwed up, what harm can you do to try and fix?

You can get the engine up to temp and open #3 in small increments till the bike quites backfiring. Might take a little while, but costs nothing.

You could buy (if you don't have one) an infrared thermometer. Get a friend to hold the throttle at say 3K rpm and take a temp reading of the exhaust headers. #3 should be hotter than the other 3, which should be pretty close to each other. Open #3 throttle plate until the header temperature is the same as the other 3. You should be pretty close.

Then do the throttle sync and your ridding smooth.

Since I did the same thing, I guess I have **** for brains too. I went to the doctor with a head ache and he gave me Preparation H.

Let us know how you come out.

Ralph Sims

 

[DcnDog]

Thread jack!

Don,

Would the TPS being out of adjustment also cause hesitation? My sons K75 definitely has excessive backfiring on decel, so I will perform the adjustments as you describe irregardless (p.s. idle is excellent).

Thanks,
Dan

 

[deilenberger]

Thread jack!

Don,

Would the TPS being out of adjustment also cause hesitation? My sons K75 definitely has excessive backfiring on decel, so I will perform the adjustments as you describe irregardless (p.s. idle is excellent).

Thanks,
Dan

If the TPS was way out of adjustment it might.. maybe..

What the TPS does on the K75 is tell the L-Jetronic the throttle is closed and it can turn the injectors off. The L-Jet turns them off until the engine speed reaches about 1,500 RPM, then it turns them back on to prevent stalling.

If the TPS is closing late - the injection will continue even with the throttle closed. That leads to a rich condition.

If the TPS is closing early - the injectors might turn off too soon, which possibly could cause a hesitation. I've never seen this - so it's a WAG. If the hesitation is on acceleration, I'd first be looking at the air-flow-meter (in the filter box) to make sure the "door" on it swings easily..

EDIT - in thinking it through, IF the injectors never turn off - on decel you would end up with a very rich mixture, and the rich mixture could cause hesitation as you start to accelerate.. so..

Yes - check the TPS setting.

 

[deilenberger]

I am assuming that since the bike runs and idles OK, that the backfiring is occurring on deceleration. If that's the case you have closed that throttle plate too tight and that cylinder is running lean, which makes for hotter exhaust temp.

Problem here... on fully close throttle - all the throttle plates are fully or near-fully closed. The idle air is provided by the brass adjusting screws. I can't see this causing a cylinder to run hot.

I know the recommendation is to get a new throttle body if those screws are ever messed with, but I don't believe that. I did the same thing as you on #4 1/4 turn before I realized what I had done and put it back 1/4 turn and have no problems.

You were lucky. You only did one, and you knew how far you turned it. Not everyone is that lucky.

These are originally set on a flow bench. If you know were a flow bench is, you can get them dead on. Probably cost a lot and evolves removing the throttle bodies, but cheaper than buying new or used and you still have to remove them.

Since they are screwed up, what harm can you do to try and fix?

No harm.. but it can probably be really frustrating.

You can get the engine up to temp and open #3 in small increments till the bike quites backfiring. Might take a little while, but costs nothing.

You could buy (if you don't have one) an infrared thermometer. Get a friend to hold the throttle at say 3K rpm and take a temp reading of the exhaust headers. #3 should be hotter than the other 3, which should be pretty close to each other. Open #3 throttle plate until the header temperature is the same as the other 3. You should be pretty close.

Then do the throttle sync and your ridding smooth.

Since I did the same thing, I guess I have **** for brains too. I went to the doctor with a head ache and he gave me Preparation H.

Let us know how you come out.

Ralph Sims

 

[BUDDINGGEEZER]

Don,
You could very be right that the TPS could be open and dumping to much fuel and causing the engine to backfire.

However, if you will read the post, the gentleman says the TPS clicks like it is suppose to. Maybe you missed that. I must assume that an individual that can adjust their valves , and says the TPS is working, knows what he is talking about. That would rule out you TPS not closing, rich running condition.

Lean running internal combustion engines will pop, and backfire on declaration. It is a problem motorcycle manufactures have with EPA regulations.

If he has the throttle plate tighter than the other 2 that cylinder will run leaner and hotter.

You don't know if I'm lucky or not. It may be that once in a while I know what I'm doing. Yes I did one and according to his post, he only mess with one.

It may be frustrating to straighten out the throttle bodies, but i'm guessing that $627.50 for new ones is too.

If it turns out that the TPS is not the problem, I've missed your solution on syncing the throttle plates or is it throw those away and buy new?

I hope you are right and the TPS adjustment fixes his problem. As, a matter of fact, I had not read your solution to the problem, when I gave him mine, so this was not a challenge to you. I guess we typed at the same time and I don't type fast. Mine was an opinion based on his post. However you did challenge me.

Ralph Sims

 

[jimmyenglish]

Thanks for all the good info fellas! You guys are awesome and I really appreciate this forum.

First - please tell me exactly what screw you adjusted that you shouldn't have? The base idle adjustment screw IS in the center (more or less) of the throttle bodies.

http://www.realoem.com/bmw/showparts...19&hg=13&fg=15

Don I wish I could say I turned item #17 but I didn't. I know that that is the idle adjustment screw,between bodies 1 and 2 and it is backed out all the way. Part #2 are those rubber caps covering the manometer connector. No, I turned the middle screw (between bodies 2 and 3) with the anti tamper paint on it. I was going through my Clymers and I don't know how I misinterpreted the two.

I am assuming that since the bike runs and idles OK, that the backfiring is occurring on deceleration. If that's the case you have closed that throttle plate too tight and that cylinder is running lean, which makes for hotter exhaust temp

Yeah Ralph the backfiring is on deceleration. It's always done the light burble thing like I guess they all do but now it's this occasional, scare the hell out of you, "I'm being shot at!" type. It would be nice to take the unit to a flow bench but I don't have that kind of dough and this is a main source of transportation for me.

So the screw I turned is the adjustment for body #3? Only reason I ask is because when I was turning it (screw#2) the valve on (body) #2 was moving and I put it back by eyeing up 1 and 2. Another peculararity was when I was attempting to do the sync the brass screws where turned way out. I mean like 4-5 turns each. now they are about 1.

Anyway, I'm going to try again tonight; rearmed with all this great info. I'm going to see if i can score some vacuum gauges. Bike still runs real good. Honestly, I can hardly tell a difference. Yet, I know it's messy and the backfiring is unacceptable. Still riding to Commerce GA with the girlfriend for the Elmer Trett Nationals this weekend. If any of you are going let me know. I'll buy you a brew!

Thanks for all the great info everyone!

John

PS. Here's the link with the Paul Glaves fix.

 

[deilenberger]

Don,
You could very be right that the TPS could be open and dumping to much fuel and causing the engine to backfire.

However, if you will read the post, the gentleman says the TPS clicks like it is suppose to. Maybe you missed that. I must assume that an individual that can adjust their valves , and says the TPS is working, knows what he is talking about. That would rule out you TPS not closing, rich running condition.

Bad assumption IMHO. Think what happens if the TPS is rotated too far anti-clockwise (holding the TB's open) - it still clicks. It still holds the throttle open. I did miss his mention of the "clicking" - but that still doesn't mean the TPS is adjusted right.

Lean running internal combustion engines will pop, and backfire on declaration. It is a problem motorcycle manufactures have with EPA regulations.

But that's not the case with K75's - the K75 is an afterburn condition caused by (1) too much fuel - getting in the exhaust pipe (2) excess oxygen in the pipe, usually caused by a missing mica gasket between the header and the pipe. And it does it on de-cel only, when fuel should be cut off - but isn't if the TBs aren't fully closed or - as is more often the case, the rider isn't fully closing the throttle (especially on downhill runs in the mountains where the bike runs rich due to elevation, and the rider is using engine braking..)

Result of the two conditions - BANG.

If he has the throttle plate tighter than the other 2 that cylinder will run leaner and hotter.

You don't know if I'm lucky or not. It may be that once in a while I know what I'm doing. Yes I did one and according to his post, he only mess with one.

In this case - IMHO you were lucky. You caught your mistake and had noted how far you'd turned the screw. The OP apparently wasn't that lucky. From my read - he doesn't really know where the screw was when he started.

It may be frustrating to straighten out the throttle bodies, but i'm guessing that $627.50 for new ones is too.

If it turns out that the TPS is not the problem, I've missed your solution on syncing the throttle plates or is it throw those away and buy new?

Not yet - but eventually a number of people have done exactly that (especially on the K100 - where 4 are almost impossible to fix once screwed with. One chap did build a flow-bench to re-adjust his.. I'll address this when I know more.

I hope you are right and the TPS adjustment fixes his problem. As, a matter of fact, I had not read your solution to the problem, when I gave him mine, so this was not a challenge to you. I guess we typed at the same time and I don't type fast. Mine was an opinion based on his post. However you did challenge me.

Ralph Sims

Sorry if you consider it a challenge to state facts as I see them... it wasn't intended as one. Your statement "I've missed your solution on syncing the throttle plates or is it throw those away and buy new?" might be considered by some to be a "challenge" - but I know that it's hard to pass along body language and emotion in text based mediums, so I'll assume it wasn't.

 

[deilenberger]

Thanks for all the good info fellas! You guys are awesome and I really appreciate this forum.

Don I wish I could say I turned item #17 but I didn't. I know that that is the idle adjustment screw,between bodies 1 and 2 and it is backed out all the way. Part #2 are those rubber caps covering the manometer connector. No, I turned the middle screw (between bodies 2 and 3) with the anti tamper paint on it. I was going through my Clymers and I don't know how I misinterpreted the two.

Bummer.. And interesting that the idle adjustment screw is backed all the way out..

Yeah Ralph the backfiring is on deceleration. It's always done the light burble thing like I guess they all do but now it's this occasional, scare the hell out of you, "I'm being shot at!" type. It would be nice to take the unit to a flow bench but I don't have that kind of dough and this is a main source of transportation for me.

So the screw I turned is the adjustment for body #3? Only reason I ask is because when I was turning it (screw#2) the valve on (body) #2 was moving and I put it back by eyeing up 1 and 2. Another peculararity was when I was attempting to do the sync the brass screws where turned way out. I mean like 4-5 turns each. now they are about 1.

Think what's happening here. This is almost for sure a sign the TPS *is* holding the throttle open. IF the TPS is holding the throttle open - the last TB is the one the TPS is attached to. If it isn't closed, but IS being held open by the TPS, then adjusting that screw will change the position of the butterfly on TB2. Think about it for a bit.. (the other clue is the backed out idle adjustment screw..) and for some reason, most mechanics always back out the brass screws. They never seem to try turning them in. Dunno why - just is.

Anyway, I'm going to try again tonight; rearmed with all this great info. I'm going to see if i can score some vacuum gauges. Bike still runs real good. Honestly, I can hardly tell a difference. Yet, I know it's messy and the backfiring is unacceptable. Still riding to Commerce GA with the girlfriend for the Elmer Trett Nationals this weekend. If any of you are going let me know. I'll buy you a brew!

Thanks for all the great info everyone!

John

PS. Here's the link with the Paul Glaves fix.

Great link. What Paul doesn't cover is:

- Make SURE the TPS isn't keeping things open or interfering with other adjustments. The bike will run just fine with it disconnected or even removed. Only thing is - the injection won't be shut off on de-cel and the extra rich mixture won't be available on full throttle - but for purposes of tuning, you're almost better simply removing it.

- Make SURE there are no vacuum leaks. This means the crankcase vent hose (Z hose behind TB3), all the O rings (brass screws and injectors) and the throttle-body mounts to the head. Quick test for this is with carb-cleaner (flammable kind) very carefully spritz'd (TINY spritz) around the TB assembly and injectors while the bike is idling. ANY change in idle indicates a leak. Leaks have to be fixed before even thinking about making these adjustments.. And I trust you to be careful and not torch the bike or yourself doing this (outside, fire-extinguisher, etc.)

- Make SURE the valves are adjusted as perfectly as possible..

Since you're basically using the engine as a flow bench - all the above have to be true to get the TB back into reasonable balance..

I prefer a set of mercury (GASP!) tubes for this particular job. Switching a Twin-Max around is a PITA, and the mercury tubes are nicely damped, making the adjusting easier. Having a visual indication of balance, easily seen at idle and above makes it easy. Do not drink or inhale the mercury - it is a heavy/toxic metal.

 

[DcnDog]

Don,

Post #7, thanks! The plugs show very rich.

Again, thanks,