748 also running rough?!
 

I have a 748 Bip, which is pretty standard. The only mod is that the baffles have been removed from the standard cans, and it is rumoured that it had a new chip fitted by Baines, but I havent removed the seal to check.

It has run well since I put it on the road in April, except that when trickilng through villages etc, it had a tendency to spit back through the trumpets when picking up, and recently it started doing it on idle when first restarted whilst warm.

I decided to reset the Throttle Position Sensor. As far as I can remember (yes I now know I should have written it down!) it was reading 190mv, and I reset it to the value in my book- 150mv. I made sure the throttle was fully shut, and took care setting the value, and checked it when the TPS was tigtened back up. However it now runs very rough, especially at low speeds. The pickup is poor and it appears to be running very rich. It also used almost a whole tank of fuel to do 40 miles!

My only theory is that somethging else was mal adjusted as well, and the combined effect masked the TPS setting. The obvious candidate is the mixture pot, but before I get embroiled even more I wonder if any of you have any ideas?

I think the mixture pot only allows a very small range of adjustment, certainly not enough to give the mpg you are getting!

Is it running on both cylinders?

Yes it is. It runs reasonably well at higher RPM, but not below 5000!

Douglas,

The 150mv is a 'base' setting with, as you say the butterfly fully closed. Once the TPS is set, then the throttle stop screw should be used to adjust the TPS value to 287mv (748 EU) this is the correct position for the ECU to use the look up values.

The tickover RPM may need adjusting but this should not involve changing the TPS value.

U2U if you need any more assistance

Pete