Ive just bought a 2002 748s with an 853 conversion and when we went to look at it he told us its done 100 miles in the last three years. Too late then Ive seen and heard it, so obviously HAD to buy it. At first it was really bogging and hesitant everywhere now after 60 miles it feels a bit better but still reluctant to pull off without a handful of revs and slip of the clutch. Ive put a tank of Shell super in as I don't know how old the fuel was and will look for an injector cleaner fuel additive tomorrow. Any other tips?
This might be a silly question but you have had one before haven’t you ? It’s always necessary to give it >3k revs as you slip the clutch home.
As above. OR maybe someone has got the gearing (sprocket sizes) a bit too high, thinking an 848 would pull it! My SPS 1st gear has always seemed a bit high even with the original sprocket sizes. But once it's rolling, its just perfect.
I agree with above. Not much throttle response below 4000rpm. Could be bad fuel? Lowering gearing can help. I never rode an 853 conversion, so could not say.
Personally I wouldn't bother with the 'additive'. Injectors generally either work or they don't. Initially I'd be looking for split fuel hose(s) and replacing the fuel filter, pita job but well documented on here. Chances are it's been neglected and as it's been sat for three years there may well be a load of crap at the bottom of the tank, water ingress E10 retention, yuk. Good clean and inspection first Sir, if I may.
Magneti Marrelli/ Weber IW724 injectors aren't the best , they spit fuel like a cabourettor,rather than spraying it.
Proper carburettors do not "spit fuel" They are accurate metering devices when set up and matched to their design engine.
This may be a silly question but, did the previous owner swap the EPROM chip for one to suit the extra 105cc? You can still buy them if it's still running the old 748 EPROM
I'd start by checking the baseline, TPS, fuelling etc. in short a full service/setup. Otherwise you have no idea what you're chasing.
It has a power commander on and was set up on a rolling road after the conversion. Ive now ridden it the rest of the way home and would describe it as a bit flat on acceleration doesnt really want to go over 100. Also only does 65-67 between fuel lights which is about 15 litres. Im thinking dirty injectors/fuel system. Im going to try and get it booked in with Neil at Cornerspeed for a service and setup, rather than fire a parts cannon at it. I will update in due course (I'm envisaging quite a wailt for Neil lol)
When I had my 916 heads gas flowed by Chris at CJS, he didn't have mapping facilities at that time so it was done elsewhere by Power Commander. Results were great, plenty of power and ran well but, every now and then under certain speed/throttle conditions it would splutter/hesitate a little before picking up. Once Chris got his dyno up & running I took it back for a custom map and it's been perfect since.
I have a 748sps to which I inserted a 916sp motor It didn't suffer from bogging down but it had the same fuel consumption as yours. The very last thing I tested was the air temp sensor. It was knackered. If you need one they can be bought brand new as they were used on several european cars of the same era Mine went very resistive which makes the ecu think it is very cold which then dumps lots of fuel into the engine
