Carb vs Fuel injection

[nick.ct]

One carb and fuel injected throttle body.

I'm 10000% sure it'd be impossible to match the fuelling between the two throughout the rev range.

Now that's more like it .....................

I just thought that by considering the carb'd cylinder as being on its own, the fuelling for that cylinder would look after itself once the carb is jetted correctly.

The idea being that you'd get the smooth idling and low speed running from a carb with an idle jet.

Obviously the ignition timing would still be derived from the Motronic and its sensors.

 

[nick.ct]

Best tips based on my own experience of a '96 1100 which was all over the place in traffic:

Rebuild throttle bodies - Scriminger engineering did a great job.

Replace single cable with splitter box and three cable set up as per later bike.

You won't quite do both for £200 but the difference is incredible. Ask if you need any further help.

90,000 miles on the clock btw.

Dick

Been there, done that, although not with Mr Scrimminger and indeed the improvements are remarkable. This with a '94 1100R with 115K miles.

I'm interested in dropping in a 40mm BING or 40mm DelOrto to replace the throttle body on the RHS. There are many peeps on here who are likely to have some knowledge or experience of the likely consequences of trying this and I'm interested to hear their input.

Steppers has pointed out that balancing them could be interesting, its not just balancing them at any given revs but also at different engine loads that would be a challenge.

 

[Teamin]

http://www.ukgser.com/forums/showthread.php?t=236298

Have you had a look at this

 

[nick.ct]

http://www.ukgser.com/forums/showthread.php?t=236298

Have you had a look at this

Indeed I have........................ From my original post, this is what I am trying to avoid doing

 

[ahutcheon]

Steppers has pointed out that balancing them could be interesting, its not just balancing them at any given revs but also at different engine loads that would be a challenge.

As did I. And you, implicitly, given you believe the carb'ed cylinder will perform better at low engine speeds, so left and right will be behaving differently at least in that part of the operating range.

 

[MattW]

Now that's more like it .....................

I just thought that by considering the carb'd cylinder as being on its own, the fuelling for that cylinder would look after itself once the carb is jetted correctly.

The idea being that you'd get the smooth idling and low speed running from a carb with an idle jet.

Obviously the ignition timing would still be derived from the Motronic and its sensors.

This is so completely ridiculous it's laughable (assuming I understand what you're going on about - ie one carbed cylinder and one fuel injected cylinder on the same engine)...

Even if you got the fuelling for each cylinder individually perfect, they'd inevitably make different power / torque at a given rpm and the engine would shake itself to bits. It'd be like bolting the crankshafts of two different single cylinder engines together and expecting the resultant abortion to somehow behave itself.

Many, many people have got fuel injected oil head BMW engines to work very nicely by taking the time to understand how they work and spending some time setting them up properly. Others have done reasonably intelligent carb conversions successfully but they nearly always involve compromises that depending on your viewpoint are acceptable (worse fuel consumption, custom ignition units, non-working fuel gauge etc).

If you can't get a standard fuel injected oil head engine to work properly, then you haven't got a cat in hell's chance of getting a DIY carb conversion to work properly. And a hybrid fuel injected / carbed engine? You're having a laugh...

 

[Teamin]

I am enjoying this thread for a couple of reasons.

1 because I have a carbed 1100 and

2 which I think is the best bit, is that the question is being asked " what if"

To some it may be obvious and others less less obvious, but the thought process is healthy to work through.

Remember, there are no stupid questions, just stupid answers

 

[nick.ct]

This is so completely ridiculous it's laughable (assuming I understand what you're going on about - ie one carbed cylinder and one fuel injected cylinder on the same engine)...

That's exactly what I'm thinking ....................... and I have yet to hear a convincing argument that its laughable.

Your say

Even if you got the fuelling for each cylinder individually perfect, they'd inevitably make different power / torque at a given rpm and the engine would shake itself to bits. It'd be like bolting the crankshafts of two different single cylinder engines together and expecting the resultant abortion to somehow behave itself.

You've got that already in a flat twin as the firing cycles are out of phase. Two single cylinder engines bolted together on the same cranshaft running out of phase.

 

[MattW]

You've got that already in a flat twin as the firing cycles are out of phase. Two single cylinder engines bolted together on the same cranshaft running out of phase.

This is true of (almost) any engine - one cylinder fires at a time...

However every multicylinder engine ever made tries to ensure that each cylinder is fuelled identically. If the fuelling is different the rotational forces become uneven and the engine runs like a dog. This exactly what is being done when you adjust the brass airscrews to achieve a smooth tickover. Try winding out one of the air screws on your bike and see what happens... You have changed the fuelling one one of the cylinders and it starts to vibrate and run poorly.

There is no way on earth that you'll ever get one fuel injected cylinder and one carbureted cylinder to achieve identical performance through the rev range (or most probably at any single point in the rev range). It would run like a dog.

And to cap it all, you've handily combined all the disadvantages of fuel injection and carburettors in one package. You've still got a box of electronics and FI hardware but you've chucked in the added bonus of a carburettor to look after too.

There's a really good reason that no one has ever tried this before. It's because it is a completely mad idea

 

[nick.ct]

This is true of (almost) any engine - one cylinder fires at a time...

However every multicylinder engine ever made tries to ensure that each cylinder is fuelled identically.

I agree, but is the poor performance ot the FI system when it is used to produce a small amount of power at low revs for example trickling through traffic due to:

1 The imbalance between the FI for each cylinder?

2 The FI system is not very good at delivering variable, small amounts of fuel at low revs?

(ignore for the moment the differences in the wear of each cylinder, compression, cam wear, valve clearance etc which all conspire to make the boxer motor, 2 single cylinder engines bolted to the same crankshaft)

We try our best to get #1 right during servicing but it could be #2 that is the real problem, and the reason why everyone who has had a professional carb conversion done seems to rave about it.

There is no way on earth that you'll ever get one fuel injected cylinder and one carbureted cylinder to achieve identical performance through the rev range (or most probably at any single point in the rev range).

Maybe, but if reason #2 is the cause of the poor running, (which is my supposition) then despite a possible imbalance between carb and FI, at least the one, carbed cylinder is being fuelled correctly during those awkward moments for FI when you are trying to trickle through traffic.

And to cap it all, you've handily combined all the disadvantages of fuel injection and carburettors in one package. You've still got a box of electronics and FI hardware but you've chucked in the added bonus of a carburettor to look after too.

As I stated in my original post, the ECU associated with these engines has, I think, proved very reliable, as have the other bits too. I have no way of absolutely knowing for sure but I suspect the original ECU is more reliable than the circuit boards used when someone does a conversion to carbs. The fact that all the other bits and bobs continue to work whilst continuing to use the original ECU is a bonus. As is the spares situation should the need arise.

I suppose the crux of the question is

Is supposition #2 the real reason for people wanting to change from FI to carbs?

And if so would changing 1 FI to 1 carb (cheap option) be capable of realising an improvement in the bike's ability to effortlessly trickle through traffic without all the snatching we know about?

 

[MattW]

This is so ridiculous that it has to be a joke / trolling but I'll stick with it.

I agree, but is the poor performance ot the FI system when it is used to produce a small amount of power at low revs for example trickling through traffic due to:

1 The imbalance between the FI for each cylinder?

2 The FI system is not very good at delivering variable, small amounts of fuel at low revs?

What poor performance?!

My '94 1100 runs faultlessly at low revs and in traffic without any trace of snatching and surging. Why do people persist in looking for increasingly ridiculous solutions to this 'problem' rather than spending the time setting up their bike properly? If you spent a fraction of the time (and no doubt money) sorting out the actual problem instead of trying out crazy solutions involving carbs and Fi on the same engine then I'm sure yours would run fine too. In the end, if you aren't capable of doing this yourself then perhaps it would be worth paying someone who is capable (like Neil or one of the other BMW specialists).

(ignore for the moment the differences in the wear of each cylinder, compression, cam wear, valve clearance etc which all conspire to make the boxer motor, 2 single cylinder engines bolted to the same crankshaft)

I really don't understand what you're getting at here (do you?). Any multicylinder engine, whatever its configuration, could be thought of fundamentally as a collection of single cylinder engines on the same crankshaft. Just because a boxer engine's cam gear is physically separate, doesn't change this . You can pull a plug lead (or more than one) off most engines and it'll probably still run. Some big marine diesels are actually designed such that you can take a cylinder off line due to mechanical problems but they run at 300 rpm and have massive flywheels and rotational inertia which smooth out the resulting uneven firing impulses.

We try our best to get #1 right during servicing but it could be #2 that is the real problem, and the reason why everyone who has had a professional carb conversion done seems to rave about it.

No, as above, its people who either aren't capable of DIY servicing / fault finding or who are unwilling to pay someone else to do it. I'd wager that most people who have carb conversions done do it 'because they can' or for other reasons such as perceived simplicity or durability, or just because it appeals to them.

Maybe, but if reason #2 is the cause of the poor running, (which is my supposition) then despite a possible imbalance between carb and FI, at least the one, carbed cylinder is being fuelled correctly during those awkward moments for FI when you are trying to trickle through traffic.

You honestly think that a bastard hybrid involving one carb and one FI cylinder could be made to run better at slow speed than even a poorly set up FI motor? Words fail me.

And if so would changing 1 FI to 1 carb (cheap option) be capable of realising an improvement in the bike's ability to effortlessly trickle through traffic without all the snatching we know about?

You honestly think that your proposed 'solution' would be cheap?! By the time you'd invested countless hours of dyno time trying to get it to run (assuming you could find a dyno operator who didn't die of laughter when you showed him your masterpiece), you could probably have bought a new bike.

And for one last time "we don't all know about all the snatching". Get your bike sorted out by someone who 'has a clue' and I'd imagine that in nearly every case you'll find the problem goes away.

 

[richierex]

He He. Wot an example of internet malarky.

Mine runs perfectly from low revs with no problems at all.

R1100RS with GS intake tubes and set up to the finest end of a fart. New plugs, valve clearances adjusted, TPS set up, throttles balanced, perfect.

 

[nick.ct]

And for one last time "we don't all know about all the snatching". Get your bike sorted out by someone who 'has a clue' and I'd imagine that in nearly every case you'll find the problem goes away.

Matt, I have 3 1100 bikes, 1100RS, 1100R, 1100GS, combined mileage of about 250,000 miles and they all run fine. I hold my hand up to needing help to achieve this, but one was a combination of quite a few things being out of adjustment (1100R with 115000 miles)

This thread, as Teamin has realised is about a 'what if' scenario, an effort to find stuff out, bat a few ideas around, get people thinking slightly outside the box. I would like to get one of my 1100 bikes onto carbs but dont wish to spend £1k doing so. Hence the genuine , I hoped thought provoking, question of 'what if' only one carb was fitted.

Steppers has given his 2p worth and I thanked him for that. It's not about 'getting my bike sorted' but trying to think differently and not be shouted down

 

[MattW]

Fair enough, I've said (or perhaps shouted) my piece on this. Go for it if you fancy a challenge

However I still say that there's 'different' and mad as a box of frogs

 

[MATKAT]

My ten pennorth

Imo it is all about who sets the bike up.
GaryH went through my foul running bike (fitted power commander , which he was going to remove) front to back and at 85k miles it is now running like a swiss watch. Bearing in mind that GaryH has brilliantly converted an 1100 to carburettors, even he is impressed with how well my bike is running.

What am I trying to say....... leave it alone and get it set up properly, the difference is amazing. he might even do it for you (at a price ) if you contact him

 

[ahebron]

What about a single carb with equal length pipes to each pot. Be great for torque. Or single point efi and link up the spark bits to that.
What ifs .... are great questions. Maybe we need a subsection called 'What if....'

Adrian