Engine Tuning Issues

[Night Rider]

My engine has been running badly for quite some time now: stumbling and stalling at idle, misfiring through the airbox at steady RPMs, occasionally knocking when I twist the trottle. Only to get worse on hot days. Last year I've brought my bike to the dealer for a tune up, but that didn't really solve the stumbling at traffic lights and the coughing through the airbox.

 

I've expected it was running too lean for a while. After reading all the TPS and throttle balance topics on this forum - and last week I had a few days off - I decided to try doing it myself with a little help from a friend. I first tried following a MG workshop manual, but it was so badly translated I ditched it quickly and switched to the forum method instead :-)

 

First I've set the TPS to 150mV with the rod disconnected, idle screws and "choke" cam backed off. Then I adjusted the idle screws for a TPS reading of 520mV. What I discovered is that, even with the air bypass fully closed it was impossible the get an acceptible low idle: 2-3000 RPM when hot, if correctly set to 150mV. So i went for "Micha's method" instead and set the TPS from idle.

I tried to get the idle as low as possible: 1300 RPM on the tacho, with bypass opened 1/4 of a turn and barely an offset from the bypass screws. Then I've adjusted the TPS to 550 mV (just a guess for that RPM, should be maybe set higher) and rebalanced the throttle bodies.

 

However, the idle is a bit high, my motorbike is running a lot smoother now at slow speeds through traffic and mpg has gone way up.

No sneezing at all. It does knock sometimes when I open up the throlle between 3-4000 RPM, so it isn't perfect but I managed to get it a lot better in tune then my dealer (well respected here) managed to get it.

 

Still, there is the problem of the high idle, it's impossible to get it lower without closing the bypass screws entirely. I suspect two things: airleaks? or aren't the throttle valves fully closing anymore?

I don't suspect the rubbers: they only seems superficial cracked and I've replaced them two years ago. And I measured the TPS and the voltage is increasing smoothly from 150mV to 4.85mV, so I think it's ok as well. But I did notice the springs underneath the throttle bodies are very dirty and seems to be dripping fuel a little bit on my garage floor. Do they breath air? (I've been reading the "Throttle Body Seal Replacement" topic with great interest.) I mananged to balance my throttle bodies very well, I don't expect to get the throttle bodies balanced with air leaks. What I do notice is that I had to twist the TPS a lot to get it to 150mV, could it be the throttle bodies aren't fully closing anymore after all? Or maybe I'm overlooking something?

 

Does anyone know what the correct TPS reading should be around 1200-1300 RPM?

 

A lot of questionmarks, I know :-)

 

(I hope my English grammar is understandable, I'm not used writing this technical. ;-))

[Kiwi_Roy]

Have you tried adjusting the idle stops with the little allen grub screws in the throttle bodies?

 

They show clearly in this topic

Frequently Asked Questions - TPS Setup and Throttle Balance Tuning

 

You start with the screws backed right out

 

Is it possible the fast idle cam is holding the throttle open?

[Night Rider]

Have you tried adjusting the idle stops with the little allen grub screws in the throttle bodies?

 

Is it possible the fast idle cam is holding the throttle open?

 

I double checked everything when I set the TPS to 150mV, right idle screw was completely backed off as well the fast idle cam (and connection rod disconnected). I'm thinking either something inside is holding the throttle open or it's breathing air through an airleak (but vacuum balance is fine).

[Kiwi_Roy]

I have never tried it myself but one way of checking for an air leak is to pass an unlit propane torch around the intake. Any leak will suck in propane and make the engine speed up. Do this outdoors of course.

How many miles(km) on your bike, I would expect the throttle bodies to last at least 80,000 kM before wear is an issue.

Hopefully someone with a lot more experience than I will speak up.

[Night Rider]

I have never tried it myself but one way of checking for an air leak is to pass an unlit propane torch around the intake. Any leak will suck in propane and make the engine speed up. Do this outdoors of course.

How many miles(km) on your bike, I would expect the throttle bodies to last at least 80,000 kM before wear is an issue.

Hopefully someone with a lot more experience than I will speak up.

 

Hmm, not really fond of using propane but I thinking of buying some start pilot to spray on the throttle bodies to check for air leaks.

 

My motorcycle has 40,000 KM at the moment. It had 13,000 Km when I bought it a few years ago but already had the clutch, front and rear axle bearings replaced as well as the rear monoshock. So I'm not sure if the 40,000 KM are correct.

[gstallons]

I have never tried it myself but one way of checking for an air leak is to pass an unlit propane torch around the intake. Any leak will suck in propane and make the engine speed up. Do this outdoors of course.

How many miles(km) on your bike, I would expect the throttle bodies to last at least 80,000 kM before wear is an issue.

Hopefully someone with a lot more experience than I will speak up.

 

 

You should be sure to remind people to use the propane torch not lit.........

[v11cafe]

TPS 0 position is 150mv +-15mv, maybe you could play a little with that?

When rod is disconnected what is your idle?(unless you use one screw method where the rod keeps open the right butterfly)

If so decrease left screw to the desired idle and rebalance.

 

Last idea- have you cleaned the injectors?

Fast idle could be the result of less fuel-more air.

 

Sorry if I am no help.

[Tom M]

I use the Micha method because I couldn't get my TPS to 150mV with everything disconnected. The solution is don't bother with the 150mv setting. Getting the TPS reading to 525/530mV at 1100/1150rpm is what you need to concentrate on.

 

Did you back the right side throttle stop off then use the left side stop screw to adjust the idle? I didn't see that in your writeup. If not then here's what you might want to try:

 

- Connect the link between throttle bodies

 

- Back all the way off on the right side idle stop

 

- Set the air screws to 1 full turn open

 

- Start the bike and warm it up to operating temp

 

- Make sure the fast idle cam isn't hitting the right side throttle

 

- Use the left TB throttle stop screw to adjust the idle to 1100-1150 rpm

 

- Now set the TPS to 530mV

 

Hope this helps...

[Night Rider]

TPS 0 position is 150mv +-15mv, maybe you could play a little with that?

When rod is disconnected what is your idle?(unless you use one screw method where the rod keeps open the right butterfly)

If so decrease left screw to the desired idle and rebalance.

 

I used the one screw method, setting the idle by using the screw on the left throttle body (and backed off the right screw). After balancing I closed the right idle screw until it barely touched to eliminate slack if any. I can't see any drawbacks using this method. But even with both idle screws backed off, the idle is pretty high.

 

Last idea- have you cleaned the injectors?

Fast idle could be the result of less fuel-more air.

 

Never thought about the injectors, I'll buy some fuel injector cleaner to add to my fuel and see if that helps. Never can hurt.

 

Sorry if I am no help.

 

You're very welcome

 

 

I use the Micha method because I couldn't get my TPS to 150mV with everything disconnected. The solution is don't bother with the 150mv setting. Getting the TPS reading to 525/530mV at 1100/1150rpm is what you need to concentrate on.

 

That's how I finally managed to get everything tuned. I think my TPS at zero must be something like 250mV now, I nevered bothered checking it yet. The problem is that I can't get my RPM lower then 1200-1300rpm (on my tacho) without closing the bypass screws entirely and with the idle screws both backed off (as good as) all the way. So I set the TPS to 550mv for the higher idle (which is just an estimation, could be too low).

 

Did you back the right side throttle stop off then use the left side stop screw to adjust the idle? I didn't see that in your writeup. If not then here's what you might want to try:

 

That's how I did it, only I've openend the bypass screws only 1/4th of a turn to lower the RPMs as much as I can and set the TPS to 550mV to compensate for an idle RPM of 1300.

[fotoguzzi]

Have you tried adjusting the idle stops with the little allen grub screws in the throttle bodies?

 

Is it possible the fast idle cam is holding the throttle open?

 

I double checked everything when I set the TPS to 150mV, right idle screw was completely backed off as well the fast idle cam (and connection rod disconnected). I'm thinking either something inside is holding the throttle open or it's breathing air through an airleak (but vacuum balance is fine).

 

you did back out the other (left) stop screw? there is a stop screw on both TB's and they both need to be backed out or the tie rod will keep tb open from the left stop screw.

[Night Rider]

you did back out the other (left) stop screw? there is a stop screw on both TB's and they both need to be backed out or the tie rod will keep tb open from the left stop screw.

 

Yes, rather, I disconnected the tie rod to be sure.

[gstallons]

My engine has been running badly for quite some time now: stumbling and stalling at idle, misfiring through the airbox at steady RPMs, occasionally knocking when I twist the trottle. Only to get worse on hot days. Last year I've brought my bike to the dealer for a tune up, but that didn't really solve the stumbling at traffic lights and the coughing through the airbox.

 

I've expected it was running too lean for a while. After reading all the TPS and throttle balance topics on this forum - and last week I had a few days off - I decided to try doing it myself with a little help from a friend. I first tried following a MG workshop manual, but it was so badly translated I ditched it quickly and switched to the forum method instead :-)

 

First I've set the TPS to 150mV with the rod disconnected, idle screws and "choke" cam backed off. Then I adjusted the idle screws for a TPS reading of 520mV. What I discovered is that, even with the air bypass fully closed it was impossible the get an acceptible low idle: 2-3000 RPM when hot, if correctly set to 150mV. So i went for "Micha's method" instead and set the TPS from idle.

I tried to get the idle as low as possible: 1300 RPM on the tacho, with bypass opened 1/4 of a turn and barely an offset from the bypass screws. Then I've adjusted the TPS to 550 mV (just a guess for that RPM, should be maybe set higher) and rebalanced the throttle bodies.

 

However, the idle is a bit high, my motorbike is running a lot smoother now at slow speeds through traffic and mpg has gone way up.

No sneezing at all. It does knock sometimes when I open up the throlle between 3-4000 RPM, so it isn't perfect but I managed to get it a lot better in tune then my dealer (well respected here) managed to get it.

 

Still, there is the problem of the high idle, it's impossible to get it lower without closing the bypass screws entirely. I suspect two things: airleaks? or aren't the throttle valves fully closing anymore?

I don't suspect the rubbers: they only seems superficial cracked and I've replaced them two years ago. And I measured the TPS and the voltage is increasing smoothly from 150mV to 4.85mV, so I think it's ok as well. But I did notice the springs underneath the throttle bodies are very dirty and seems to be dripping fuel a little bit on my garage floor. Do they breath air? (I've been reading the "Throttle Body Seal Replacement" topic with great interest.) I mananged to balance my throttle bodies very well, I don't expect to get the throttle bodies balanced with air leaks. What I do notice is that I had to twist the TPS a lot to get it to 150mV, could it be the throttle bodies aren't fully closing anymore after all? Or maybe I'm overlooking something?

 

Does anyone know what the correct TPS reading should be around 1200-1300 RPM?

 

A lot of questionmarks, I know :-)

 

(I hope my English grammar is understandable, I'm not used writing this technical. ;-))

 

I sync the throttle bodies by; (1) disconnect the linkage connecting the 2 throttle bodies. (2) make sure throttle kicker is backed off to not affect anything. (3) back throttle plate screws out completely. (4) put a .002" feeler gauge between adj. screw & contact point on lever. Turn screw in til it touches and has good tension on the feeler gauge. (5) remove feeler gauge and turn screw in one turn. (6) repeat process to other throttle body. (7)put a .010" feeler gauge between the adj screw and the stop on the l.h.side throttle body and a .008" feeler gauge on the r.h. side throttle body. (8) connect the linkage to the two throttle bodies. (9) tighten (you may have to lengthen the rod before doing this)the plastic knob until the r.h. side feeler gauge falls out of position. This operation will require plenty of hands. Think about what is going on to understand what you are doing. This will have the throttle plates synchronised. (10) your warm idle speed is adjusted with the idle screw of the l.h.side screw.

The airflow screw on each throttle body is a trim or balance adjustment. You want them to be turned in or out an equal amount before you start balancing them. I think my TPS is around 0.450v at idle speed ?

[fotoguzzi]

 

 

I sync the throttle bodies by; (1) disconnect the linkage connecting the 2 throttle bodies. (2) make sure throttle kicker is backed off to not affect anything. (3) back throttle plate screws out completely. (4) put a .002" feeler gauge between adj. screw & contact point on lever. Turn screw in til it touches and has good tension on the feeler gauge. (5) remove feeler gauge and turn screw in one turn. (6) repeat process to other throttle body. (7)put a .010" feeler gauge between the adj screw and the stop on the l.h.side throttle body and a .008" feeler gauge on the r.h. side throttle body. (8) connect the linkage to the two throttle bodies. (9) tighten (you may have to lengthen the rod before doing this)the plastic knob until the r.h. side feeler gauge falls out of position. This operation will require plenty of hands. Think about what is going on to understand what you are doing. This will have the throttle plates synchronised. (10) your warm idle speed is adjusted with the idle screw of the l.h.side screw.

The airflow screw on each throttle body is a trim or balance adjustment. You want them to be turned in or out an equal amount before you start balancing them. I think my TPS is around 0.450v at idle speed ?

Nice and concise! I'm copying this just so I'm sure to do it by the book, GS, do you do rally's? have we met?

[Tom M]

 

I use the Micha method because I couldn't get my TPS to 150mV with everything disconnected. The solution is don't bother with the 150mv setting. Getting the TPS reading to 525/530mV at 1100/1150rpm is what you need to concentrate on.

 

That's how I finally managed to get everything tuned. I think my TPS at zero must be something like 250mV now, I nevered bothered checking it yet. The problem is that I can't get my RPM lower then 1200-1300rpm (on my tacho) without closing the bypass screws entirely and with the idle screws both backed off (as good as) all the way. So I set the TPS to 550mv for the higher idle (which is just an estimation, could be too low).

 

Did you back the right side throttle stop off then use the left side stop screw to adjust the idle? I didn't see that in your writeup. If not then here's what you might want to try:

 

That's how I did it, only I've opened the bypass screws only 1/4th of a turn to lower the RPMs as much as I can and set the TPS to 550mV to compensate for an idle RPM of 1300.

 

Have you tried to pull the right side throttle closed with your hand while the bike is idling and the stops are backed off? It could be that your throttle cable has a kink or no slack at all and that's not letting the return spring pull the throttle all the way closed.

 

There's one other factor that could be contributing to your problem: The idle trim setting in your ECU. It can only be checked and adjusted by someone with a diagnostic tool (dealer) or with aftermarket software and an interface cable (VDST or equivalent). There was a member here a few years back that had a hell of a time trying to tune his bike until he checked his idle trim and found that someone had set it to +25. Once he had it reset to zero he did the Micha tune and his bike finally ran right.

[mznyc]

I haven't seen it mentioned if you checked all exhaust joints yet.Headers,fore and aft of the X-over.