Greetings to all my rotary firends from Mike Walker

[mike59bike]

Hi. I've just joined the forum on Graham's advice and I am very impressed with the contributions. I have converted my Commander to electronic fuel injection and would like to share some experiences with other members. I use Jenvey throttle bodies and MTech (Megasquirt) ECU on fuel injection only (ie at the moment I am keeping the existing digital ignition unit as set up). The engine responds brilliantly at largish throttle openings, but at low speeds it has an annoying hunting or surging. Graham suggests this might be because I have propped open the existing throttle butterflies and am using the throttle in the Jenvey bodies, giving a long inlet tract. Does anyone have a view as to whether I ought to re-establish the old throttle butterflies (very close to the inlet port) - I could run the two throttle butterflies in parallel. Also, what is the best place for this technical discussion on the forum? Not the greetings page, probably. Mike Walker

[andy588tt]

Hi Mike Congratulations on having a fuel system that works! Brian Crighton would be best to answer your question.We have been on the Ford fleet test program for over twenty three years now and I remember the first ever fuel injection system fitted to a Fiesta we had from Ford -this had the same problem as you have.The cure? Because of a catalytic exhaust system a sensor was fitted onto the exhaust manifold. The set up worked well upon collection from Dunton. The pick up was spot, on great for motorways, but slowing down was hair raising - it wanted to keep going and this got worse in town. Coming to a T-Junction the revs kept at 1800 rpm for about fifteen seconds then died down to tick over at 1000 rpm, but while the engine was revving at 1800 rpm it wanted to pull you into the road. To over come this we pulled the hand brake on and lifted the clutch - the drag on the engine pulled the revs down. The exhaust sensor redirected unburnt fuel back into the engine so the cat was kept clean. BUT another sensor fitted in the intake manifold registered a large amount of air/fuel after the throttle pedal was released. The system was too slow with reaction timings of throttle opening requirements of air/fuel mixture.Ford fitted different injection nozzles but the breakthrough came when a faster chip was fitted in the ECU and on remapping number fifteen came in it was sorted. Now the ECU thinks for itself anticipating what the driver is going to do with gearing and speed and fly by wire - the calculations are mind boggling.I am no expert but with direct injection into the combustion chamber the delivery of fuel is instant, but the further the injector is away from the combustion chamber, the longer the response time in throttle opening and closing times causing over fueling at slow engine speed as we found in our Ford test cars. The biggest problem you have is measuring the correct air/fuel requirement as to base for setting up your fuel mapping in the first place. Brian Crighton is very cleaver but Im sure he too had to make a guess as to the air/fuel mixture to get his bike to work.Ford made a 1000cc three cylinder two stroke fuel injected engine but thats another story? Ride SafeAndy

[mike59bike]

Thanks, Andy. Brilliant reply - I think the MegaSquirt V4 unit (the latest one) I am running has a very fast ECU and the problem with surging feels like over-fuelling (the plugs soot up annoyingly easily). The rotaries have always been problematical on tickover, so I understand - the originals reverted to one-rotor tickover to try to obtain a bit of engine drag at low speeds. Could the timing of the fuel injection be the problem, do you think? The people at MTech (supplers of the MegaSquirt system) say it doesn't matter at all at what part of the intake cycle the squirt occurs, but I am not sure. I can't really test the thing without running it under a load ie on a dyno. Anyone out there got a dyno to play with? Mike

[Richard Negus]

Hi Mike,Long time no speak !Your low speed surging sounds similar to the F1; there, the induction tract between trochoid and butterfly is so large that significant amounts of exhaust gas can accumulate in it during overlap, diluting the mixture and creating a mis-fire. All the smooth running, peripheral-ported rotaries have the butterfly as close to the trochoid as possible.A prototype F1 Sport did have, at one stage, Mikuni carbs and housings with butterflies. We spent some time trying to get the link between carb and housing butterflies working together, but without it being noticeably better than the standard F1.In your installation, I presume you have a throttle position sensor on the new butterfly spindle. Can you put it on the original spindle (in the rotor housing) and use the original throttlesonly ? The injector doesn't have to be near the throttle; during development of injection systems at Mid-West, I ran with the butterfly by the housing and the injector at the end of a 14" ram pipe with no noticeable effect on power or response. Icing of the ram pipe was problem though.With regard to injector timing, if the 'squirt' happens as a tip seal is passing the inlet port, oil will be washed off the seal and increase the wear rate. Ideally, the first of the squirt should arrive at the trochoid just as the apex seal has passed. Also, the speed at which the fuel is squirted is constant, subject to constant fuel pressure, whereas the tip seal speed varies considerably, requiring the injector 'on' point to be variable.R.

[mike59bike]

Thanks, Richard. Good to hear from you and I hope "retirement" is suiting you. I am getting more and more convinced the surging problem is related to the length of the intake ducts. My set up at the moment consists in holding the existing butterflies full open (simply by clamping the operating cable against a nearby mounting bolt) and relying on the Jenvey butterflies which are situated at the throttle body. The throttle position sensor is on one of the throttle bodies, and I have made up a split cable system to operate both together (you can't use a normal throttle link because the frame gets in the way). What I could try, I suppose, is a cable link between the Jenvey throttle and the "old" butterflie, in other words link it so that both sets of butterflies open together. If this works I could then dismantle the Jenvey, but I can't think having two sets of throttles in series would be a serious shortcoming (ie they should both open full bore at the same time). What do you think?I am intrigued by your comments about exhaust gases accumulating in the inlet tract - is this because of the overlap? Why does this overlap occur in the first place? Presumably the effect of the overlap disappears at higher revs because of the inertia of the gases in the inlet tract, but at low speed there is nothing to prevent some gases bypassing the exaust and entering the inlet tract (especially as it is under suction at that point). Anyway, it makes more and more sense that the throttle butterfly position is critical in this set-up. I'll let you know what effect this has, I'm going to expeiment a bit with it. Regards, Mike

[Richard Negus]

What I could try, I suppose, is a cable link between the Jenvey throttle and the "old" butterflie, in other words link it so that both sets of butterflies open together. If this works I could then dismantle the Jenvey, but I can't think having two sets of throttles in series would be a serious shortcoming (ie they should both open full bore at the same time). What do you think?

Before making a link, why not fix the injector body throttle fully open and re-connect the original butterflies to the twistgrip? If you kept the original carburettor outlet, with idle adjuster screws, that would give you a fine adjustment for idle air control.Do your injector bodies have the injectors upstream of the butterflies, or down stream? What bore size are the bodies? Mid-West are 32mm, but that engine isn't expected to idle below 1800rpm. The F1 has 34mm carbs and seems to idle smoothly (with sufficient ignition retard).R.