851 A WORK IN PROGRESS 4 – Some Slightly Abstract Tuning

I’ve spent quite a bit of time tuning this thing, but had been becoming increasingly annoyed with a couple of things. One was the extreme variance of the fuel consumption. Anywhere between 12 and 20 km/l. The second was the fact that sometimes it would run really nice on cruise, then other times run rich. I had leaned out the map quite dramatically in the cruise area, but then had some ‘too lean’ issues occasionally.

One of the best ways to actually see what is happening is to ride the bike with the FIM Hand Held Terminal mounted to the top of the fuel tank. On most bikes I use a magnetic tank bag base with a clear pocket. This holds the terminal nicely. The 851, however, being an 89 model, has an aluminium tank. Which doesn’t work too well with the magnets. So the only option is tape. I have become quite apt at this, though I’ve had some pretty good tuition in this area from Duane at FIM. He just loves an excessive tape job.

So, with the terminal taped to the top of the tank, you can ride around and see just how much throttle you are using at a given time, say for cruise or light acceleration, etc. This is extremely useful, particularly with the total adjustability of the memory board. Other info you can get is fuel injection times, coolant temp, air temp, air pressure values and the corresponding trims, spark advance, etc. You can even adjust fueling as you ride along. The only thing you need to be careful of is that you don’t spend too long looking down at the thing on the tank. Looking at where you are going is always a good idea.

Being able to adjust the fueling on the fly is a bonus when you just can’t get something to run right. Sometimes I’ll get frustrated trying to tune out a bad spot, so will make a big change just for the hell of it. In the order of 20 or 30%, rich or lean. It shows you exactly what is happening and, in a few cases, has given me the answer straight up.

With my bike, I wanted to look at the actual fuel times to make sure my changes were having an effect. Duane had emailed me the map in the chip and I had used this to create a spreadsheet with the changes and my new map, so I knew what fuel numbers to expect. I then worked out that at some stage I had reset my new map to the original, so had to start again. The answer to the above-mentioned problems, however, came one cold morning on the ride to work (yes, I do commute on this, it’s great). I was scrolling through the screen displays, moving from screen 1 to 3, when I had a quick glance at screen 2. Screen 2 shows the environmental temps/pressure and the corresponding overall trim they generate.

Although the bike was warmed up, the trim was still over +10%. You can also "turn off" the sensors individually with screen 2, and watch the trim change as the sensor’s influence is ignored. I was expecting the coolant trim to be a problem, but when I turned it off, the trim hardly changed. So next I turned off the air temp. Surprisingly, the trim dropped down to +3% or so, which I next discovered was due to the air pressure. This struck me as somewhat unusual, and I figured would be worth looking into.

When Duane sends me a map, it comes as a single page in a format he set up years ago. It contains the fuel, second cylinder offset (not in the 851’s P7 ECU) and spark maps as well as the environmental trim tables. In this case, these environmental trim tables were what I wanted to see. They lay out the trim, in +/-% that will be factored into the fuel injection time to allow for the atmospheric conditions of the time.

So, what you get is more fuel for a cold engine, more fuel for a cold day, more fuel for high atmospheric air pressures. Although, the amounts have been modified over the years due to problems they generated. From what I’ve been told, very early 851s had a wacky air pressure scale, which led to fuelling issues based on what the sensor was reading. Some of the mid 90s Moto Guzzis had similar problems when used at higher altitudes, as the wacky pressure trim table came into play. This is the sort of stuff Duane will often modify if required in a chip he sells, to make them work better all round. It’s just not the sort of stuff people usually think about when buying a "performance chip" though.

Given the chip he supplied me for my 851 has probably been around for close to 10 years, and based on the original 851 chip, I wasn’t surprised to find that the trims were quite a bit different to the later ones, even the ’93 model 888 trims. I rang Duane and we started talking about this. We both agreed it was a bit odd, and that a revised chip was in order, but then, as usual, we got sidetracked and never decided a course of action. Which turned out to be me changing my mind on the proposed changes about 7 times, and then finally using the "standardized" trims from his new U59 ECU. We did the new chip on a day when I went down for a visit, simply because the only time we actually get anything like this done is when we’re both sitting in his office looking at his computer screen at the same time. Not that any of this was a concern when I first started thinking about it, as I couldn’t walk, let alone ride at the time.

To show what I’m talking about, this is an example from the 851 map, as compared to an 888 map, a 996 map and an air-cooled Cagiva Gran Canyon map. The trims are in %. The air pressure trims have much more to do with altitude corrections than air pressure variations due to atmospheric conditions at a constant elevation, so I have ignored them for this comparison. Temps are degrees Celsius.

851 Overall
851 Revised
Overall Trim
888 Overall
996 Overall
Gran Canyon
Overall Trim
5 5 34.4 41.8 38.6 20.9 20.6
5 65 13.5 4.7 3.1 8.8 4
17 65 4.7 2.4 0 6.4 1
41 89 -6.3 -3.9 -6.2 -3.2 -2

Now 41 degrees might sound like an awful hot day, but we did a big ride one day a while ago on a 38 degree day in Melbourne. The bike was running at 95 or so degrees on the gauge for most of the ride. On this day, I got 20 km/l. Contrast this to my winter commuting fuel economy of around 12 km/l. The approximately 20% trim variation between the very hot and cold days would contribute significantly to a fuel economy change like this, although my inner city riding habits would also not help to some extent. As you can see, the 888 would have a variation of 9.3%, the 996 12% and the Gran Canyon 6% over the same environmental range. All less, but which is the most realistic? Dunno really.

After a little more investigation, however, I came to realise something even more influential - the fact the air temp sensor on the 851 (and 888) is inside the airbox. Even on a cold autumn night, the airbox can get pretty hot when sitting at traffic lights (40 to 50 degrees), with all the heat coming off the engine. Given the large variation in trim for air temperature in the 851 map, in this case, leaning off quite a lot for high air temps, this was provoking everything from backfiring on overrun to a huge stumble on takeoff. This changing trim due to what the air temperature sensor was reading at a given time is where my ‘sometimes rich/sometimes lean’ problems were coming from, but autumn nights in particular, for some reason, really showed them up.

In contrast, the air temp sensor on a 996 or 900SS is under the headlight/dashboard area, and much less effected by engine heat. Which is where the air temp sensor on my 851 has now been relocated. Simply for the sake of consistency.

We also changed the trims for coolant temp when the engine is cold, from -7 degrees coolant temp (not too relevant to me) up to 65 degrees (just below the engine running temp.). This helps the bike start and run when cold on those chilly mornings, so I can now just click the fast idle button on the 916 throttle I have fitted (straight on, std cable even! - although it just sits in the housing), hit the start button and away it goes. The coolant trim at 5 degrees (Celsius) has gone from +20.3% to +37.5%, making the bike idle instead of fire, run poorly and stall 5 seconds later. Repeated 2 or 3 times. You might be wondering how the 996 gets away with the 20.9% overall trim when it’s cold. Dunno. It’s got me wondering too.

There were several months between deciding what I needed to change and it actually happening. So, I ended up turning off the air temperature sensor input – which you can do through the hand held terminal – simply to keep my sanity while commuting on the bike. I was using it for everyday transport pretty much (Minnie Monster was in bits for a while getting some new pistons, head reco and tank repair), and the rich/lean thing had started to get the better of me. Luckily I remembered I could turn off the air temperature sensor’s input - it was infuriating me that much I was about to park the thing and start driving the car.

Before Duane went to the effort of making me a custom chip, I wanted to try some ignition advance testing, just like the 888, to see if there was more power with a little less advance. I had also made slight mods to the ST4 headers, replacing the bit I beat in with a hammer to originally make them fit with a nice rounded bend for swingarm clearance. So I had a few things to test for. The first graph below shows the before / after for the cam dialing job in a nicer graph. Green is before, red after, and 170 km/h is right about 9,000 RPM. Good result. Very loud though, especially the hard snarl coming out of the airbox from under the tank. I had seven months not riding it due to the final leg operation, and was amazed when I got back on just how aggressive the noise from the airbox was. I always wear earplugs when riding it now. It really is quite offensive.

Dynograph courtesy of DYNOBIKE (03) 9553 0018

There was one other change made since the last set of dyno runs, one that I hadn’t considered as significant, but it proved to be not insignificant. There is lots of talk about fuels used and required octane levels, etc, and I’d never really paid that much attention to it all. One school of thought, the one I had pretty much subscribed to, is that the best quality fuel is the best to use (like oils). The other is to run the lowest octane rated fuel you can get away with – ie, without detonation. I recently started running the 851 on std unleaded, which is 91 octane rating out here from memory. The lowest octane you can buy at the servo, and the fuel for the masses pretty much. I hadn’t noticed any changes with the way the bike ran or started or idled (maybe a small idle change, but I had been playing with that), so was pretty happy with the lower cost option.

The after run from the above graph was made using the std unleaded, whereas all previous runs for the 851 (and all the 888 runs) had been made using premium (or high octane) unleaded. The mapping for this run was what I had been running since the last session, and seemed to work very nicely on the road – the air temp sensor influence doesn’t really come into play when the bike’s using large volumes of air or travelling at higher speeds. But I thought I’d try some fuel playing just to see. I started out adding some fuel – the usual 5% steps – and was very surprised when it made more top end power. It made more again with +10%, but dropped away with +15%. This certainly surprised me, as generally more fuel kills the top end without much effect in the middle. And the map I had was based on the previous testing, where an extra 10% at the top end caused a definite power drop. The only thing I can think of is that the lower octane fuel made a little more power, but needed a little more fuel to do it. It’s not much of a power increase, but the first runs had been the best I’d seen for the 851 in this configuration, and it made more power from there! The next graph shows this result. Red is mapping as I had been running from previous testing, green is +5%, blue is +10% and yellow is +15%. Not a huge increase, but noticeable and intriguing all the same. Again, the power peaks at around 9,000 RPM, which pretty much equates to 170km/h wheel speed.

Dynograph courtesy of DYNOBIKE (03) 9553 0018

I emailed Doug Lofgren with the results, and his reply was that he’d seen similar things, saying, "you haven’t said anything yet that surprises me". Also, Duane always tests bikes using std unleaded, unless premium is a specified requirement, as it is for BMW models pretty much. But, please remember that one set of dyno results does not a scientific study make. However, with the new breeds of ‘premium’ unleaded fuels being much more than just high octane, this sort of variation is coming fairly apparent. Many are finding the new, "higher density" premium unleaded varieties are causing plug fouling problems, most likely due to the bike running a bit on the rich side anyway, but it is becoming more common. Given these fuels are designed for modern, closed loop EFI cars, assuming they will work well on older tech bikes may not be such a valid assumption. Something to be aware of. Of course, if your bike is running too lean, they could be the solution to your problems.

So, I then moved on to ignition advance, the main reason I went to the dyno for this test session. The 851 gets even more advance than the 888, with a maximum at the 10,500 RPM map point of 51 degrees. That’s quite a lot. The WOT line (82 degrees throttle opening) from the ignition map is shown below. The fact the advance increases at high RPM I would expect is due to the nature of the bike in original form – std mufflers, std airbox lid, small valves, etc. All these factors would limit the amount of air getting into the engine as the RPM rose. The mods I have made go some way toward reducing the restriction to airflow at higher RPM, so the need for less ignition advance does not surprise me.

x 100
6 8 10 15 20 30 35 40 45 50 55 63 70 80 90 105
3 3 28 30 33 35 38 40 41 42 42 42 45 45 48 51

You can also see the map break points at 600 and 800 RPM. This is something I’ve only seen on 851 maps, none of the later bikes have RPM set points lower than 1,000 RPM (the minimum standard pretty much) and the 851 has different map set points for the fuel and ignition maps. Maybe they were playing with starting issues, but I really can’t see any benefit. Cranking speed is usually around 300 RPM, so the lowest point – 600 RPM – would in reality be a running engine anyway. Odd, but ultimately of mild curiosity value only.

Given the 51 degree maximum ignition advance figure, I ran the tests with +10% fuel, using maximum advance settings of 43, 40, 37 and 34 degrees. Like the 888 testing, setting the maximum advance with the FIM hand held terminal (HHT) limits the maximum only, without changing the minimum. Consulting the above table, running 40 degrees max means the ignition advance is held constant from 4,000RPM onward, running 37 means constant from 3,400 RPM or so. You get the idea.

The graph below shows the result for these tests. A bit too messy to read perhaps, it shows the small, but noticeable changes. Red is std ignition map (up to 51 degrees advance), green is 43 max, blue is 40 max, yellow is 37 max, purple is 34 max. Immediately obvious is that 34 degrees is not enough, and the std ignition map has too much from 8,500ish RPM onward. 40 degrees maximum makes the most power at the top end, so I now added the appropriate ignition map mods to the environmental trim mods on the list of things to change for the custom chip Duane would make me. Having access to Duane is something that it may appear I take for granted sometimes (often?), but this access prompts me to try so many changes, such as these ignition map mods. We also increased the ignition advance in the idle area to a minimum of 10 degrees, which generally helps idle consistency – something the 851 could use. And, to make the engine smoother when rolling the throttle on at low RPM – under 3,500ish, we reduced the ignition advance by up to 20 degrees in places. Check the full map below to see just how quickly the ignition advance is increased with throttle opening at low RPM.

In fact, we just substituted the modified ignition advance map from the 888 custom chip we did for that bike when the testing was complete. Duane had to fiddle a little with the map break points, but it was by far the easiest way of achieving what I had in mind. The 888 map, in comparison to the std 851 map, has much less advance in the 2 to 30 degree throttle range up to 5,000 RPM, making the 888 much smoother down low. Having ridden them back to back some time ago, this was painfully obvious.

Dynograph courtesy of DYNOBIKE (03) 9553 0018

All this adds up to a small, but measurable increase in the 851’s output, and it now is making about 3 more peak hp than it did previously. So I’m quite happy with the results, and even more so with the fact I have learnt something. Well, more than one thing - I also learnt that turning off air temperature sensors via the HHT on a P7 ECU fitted with an FIM additional memory board is map specific, not general. So all these runs were done with the air temp sensor turned on, not off as I thought. I had changed from map 4 – the one I ride on – to map 1 while changing the fueling during the testing, and so caught myself out again.

The other changes made to the non WOT parts of the maps- the trims and ignition advance maps in particular – have made it a much more enjoyable bike to ride all round. It’s this sort of development that I really enjoy, but it’s also the most infuriating when you just can’t figure something out. I have learnt a lot of less obvious stuff with this bike, but it hasn’t been the most pleasant experience at times.

The next graph shows the start of day to end of day result for this trip to the dyno, with the top end improvement fairly clear. Green is where I started, red the days best - +10% fuel, 40 degree maximum ignition advance. Not that I actually use the top end when I’m riding usually – my last ride in the hills saw me lucky to get over 8,000 RPM, so I’m really only using 90 hp at the absolute most. Still riding like a nana.

Dynograph courtesy of DYNOBIKE (03) 9553 0018

The next graph shows my to-date result compared to the first run I did on the bike, way back in early 2001 just after I’d bought it. At the time, it was the first thing I’d ridden for about 5 months, even if it was just on the dyno (and I had to use two crutches to get to that). My surgeon would have had a fit if he’d seen me jump off. The power increases are compounded on the road by the response improvements that have come via the big exhaust, cam timing changes and light flywheel.

Dynograph courtesy of DYNOBIKE (03) 9553 0018

Compared to the 888’s final result though, I still have quite a way to go. Although, the 851 has a climbing torque curve, whereas the 888’s is rather flat, so the 851 feels like it comes on more than the 888, which just goes when you hit it, although the flat torque curve can give the impression not as much is happening. Especially in a straight line. Close in the barriers a bit, however, and the extra speed the 888 builds is apparent once the need for braking enters the picture. First graph is power versus road speed, second is torque versus RPM. The 851 still doesn’t get on too well with the dyno’s RPM pickup, hence the usual patchy at the top end RPM trace. 851 is red, 888 is green.

Dynograph courtesy of DYNOBIKE (03) 9553 0018

Dynograph courtesy of DYNOBIKE (03) 9553 0018

Finally, just to annoy Mike (our webmaster), who has to transfer all the tables I put in the reports into the appropriate format, here is the full std 851 spark map, just to give you all an idea of what it looks like. Sometimes I make changes to areas such as idle or just off idle – like I did to my Guzzi Sport 1100I, to make it a little more responsive to the throttle – as well as full throttle changes. Generally, later model maps don’t have so much maximum advance at the top end, probably due to the fact the 4V engines are much less restricted these days in std trim.

3 3 28 30 33 35 38 40 41 42 42 42 45 45 48 51 82)
3 3 28 30 33 38 40 40 40 41 41 42 42 44 47 46 58)
3 3 28 30 34 38 40 40 41 43 46 46 48 49 50 46 43)
3 3 30 32 34 38 40 41 43 46 47 52 56 58 60 54 33)
3 3 30 32 34 38 40 41 44 46 47 53 60 60 60 58 29)
3 3 30 32 34 39 40 42 46 50 54 58 60 60 60 60 26)
3 3 30 32 34 40 41 46 52 57 60 60 60 60 60 58 22)
3 3 30 32 34 40 43 48 53 55 58 59 60 60 60 58 17)
3 3 30 32 35 41 45 50 53 55 56 60 60 60 58 58 12)
3 3 30 32 36 42 47 52 56 58 59 59 58 58 54 54 9)
3 3 28 30 32 40 46 50 54 56 56 54 52 52 52 52 7)
3 3 23 26 28 32 40 48 50 50 48 48 48 48 48 48 4)
3 3 16 20 24 24 28 42 44 44 44 44 44 44 44 44 3)
3 8 8 14 16 19 24 34 38 36 36 36 36 36 36 36 2)
3 8 6 8 12 16 21 27 34 34 34 34 34 36 36 36 1)
3 8 6 6 8 16 21 26 31 32 32 34 34 36 36 36 0)
6 8 10 15 20 30 35 40 45 50 55 63 70 80 90 105  

The RPM break points are shown across the bottom – RPM X 100 – and the throttle break points are shown up the right hand side – degrees opening. For example, at 5,000 RPM and 9 degrees throttle (a typical cruise situation) the spark advance would be 58 degrees. The zero degree line is throttle closed (no, it’s not that obvious), whereas on the later ECU maps the bottom throttle line is 1 degree usually. This is due to the way the P7 ECU reads the TPS minimum output. The later ECU all read the throttle closed setting as degrees open from throttle butterfly fully closed (ie, idle stop screws wound fully out), which is usually in the region of 1.8 to 2.5 degrees opening for idle. It’s really not important, but I like to explain these things.

Next in the engine area were to be some replacement coils, based on another Brad hopeful (read guess) diagnosis. After I had the injectors cleaned, the idle was much cleaner than before. Since then, however, I have lowered the idle (it was around 1,500 RPM) and the dirtiness has come back with a passion. Lots of hydrocarbons, lots of oxygen, even with the correct CO%. And both cylinders, when checked at the probe points in the header pipes, where the same. I was really wondering about this when I conveniently had a later 851 come in (a ’92) which had a different chip of Duane’s. It idled far better than mine, much the same as the 888 does (which has a good idle just like a later 916, etc), so I now had a measure of sorts. This 851 had the same air bleed-less throttle bodies and P7 ECU as my bike, but the 1mm bigger valves, heavier valve closing springs, later coils and a different chip. I spoke to Duane about it, who said we could have a look at the chip differences, but later came to the conclusion that it probably wasn’t that. Given I can (and have) lean or richen the idle fuel at will, I knew it wasn’t fuel related. Ignition timing can effect idle a little, but I know the 851 and 888 (and most of the other models) maps are very similar in the idle area, so counted that out also. I had been wondering if I’d put the flywheel back on one tooth off, but that’s a offset of at least 60 degrees on this old 6 spline crank, and the results of my above timing test came in as expected, so I counted that out too. I did end up checking this, and was correct.

Which meant it was either software (maybe, but doubtful) or something else. The fact there was lots of unburnt fuel and oxygen coming out the exhaust implied the combustion was bad, so the most obvious place to look was the spark. I had quizzed Duane on these coils quite a long time ago after someone else said they may very well be crap, but he said they always seemed to be a very good coil. My problem was not a general performance one though, but very specific idle/low speed running, so I was curious to see if the coils were an issue. The other thought was ignition (or High Tension) leads.

Lots of people on Internet forums talk about fitting Dyna coils, but this is usually in reference to 2V carburettored models. When one of the members on the Speedzilla forum posted about fitting Dynas to his 900 SSie, I was naturally interested. He listed improved cold starting and idle amongst the benefits, which is something people with 2V bikes usually say. This info came just at the right time for me to be convinced to give it a go, so I rang Serco (the Aust Dyna distributors) and ordered some "Green" single output coils. I was quite surprised by how big in diameter they were, compared to the std ones. I bodged up some leads to test them without actually making brackets, and gave them a go. The result was a non-result – just the same. Oh well, they work well on 2V Monsters I hear.

I then wasted more than one day trying all sorts of other things, even buying some new Bosch injectors to see if mine were just worn out. Again, no cigar. So I now had just over $400 of parts I didn’t need (and couldn’t return). Bugger! I did find the high-tension lead for the horizontal cylinder was open circuit on a resistance test, although replacing it with a good one from another bike made no difference. I did replace both anyway with some leads made up by a local ignition specialist.

So I didn’t resolve my bad idle problem. I have got to thinking it may have to do with the early, softer closing rocker return springs these small valve 851 engines have. Dunno. The more I think about it, the more I am convinced (convincing myself again?) this is the problem. I remember the article on the Ducati.com site a year or so ago about why they use closing springs for a Desmo system, and the reasoning being purely for idle quality. Something I’m not going to persue at this stage.

At this point, I have a few ideas - plus some 748 heads wishing for some bigger valves – that will give me more power. But what I really want is more mid range power. Increasing the power output at or past the 9,000 RPM peak is not really relevant to how I ride this bike. I need more power in the 5,000 to 8,000 RPM range really (900SS perhaps?), so have two options. The first is more compression and big valves, which will give a minor mid range improvement, the second more capacity – 944 or 984 (the most obvious). Well, three options. I can just leave it the way it is and buy something more appropriate. Fourth option? Rev it harder.

Do I hear five?

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