Petrol smell in boot and speedo misreading fixes
Discussion
For info / future reference. Have sorted two probs that have been bugging me with my Griff 500 (yr 2000).
1. No liquid fuel leak, just a strong petrol smell in boot after car left a few hours. There was no obvious sign that anything was wrong other than the sender flange bolts appeared to have been overtightened. The gasket appeared to be serviceable. However cup washers had only been fitted to two of the five bolts. Apparently they were a TVR recall item and prevent fumes leaking from the bolt holes in the sender top plate. Removing two of the old bolts was a PITA - threads seized. Trimmed/hacked heads down until I could pull sender plate over them. Then stilsons to wind out the bits. Care taken to keep swarf out of tank. Resolved by replacing fuel sender gasket, bolts and nylon cup washers.
2. Speedo (Caerbont electric) was reading 15mph low at 70mph (and 7mph low at 30mph) - not helpful when approaching Gatsos! Also way off the 10% legal tolerance. Speedo has a bank of 10 dip switches to calibrate the pulses per mile setting (ppm). Found from my calculations that the 'ideal' setting based on wheel size / rotations per mile computed against the speed sender pulses would also not give me the correct speedo reading. Instead, I calculated a ppm correction factor to the current setting (based on 15mph under reading at 70mph). Result - speedo now reads accurately at 70mph and above, with 2-3 mph over indication at 30mph. Calibration info (ppm to dip switch settings) from CAI's website. This info may not be of use for cars with earlier/different speedometers.
1. No liquid fuel leak, just a strong petrol smell in boot after car left a few hours. There was no obvious sign that anything was wrong other than the sender flange bolts appeared to have been overtightened. The gasket appeared to be serviceable. However cup washers had only been fitted to two of the five bolts. Apparently they were a TVR recall item and prevent fumes leaking from the bolt holes in the sender top plate. Removing two of the old bolts was a PITA - threads seized. Trimmed/hacked heads down until I could pull sender plate over them. Then stilsons to wind out the bits. Care taken to keep swarf out of tank. Resolved by replacing fuel sender gasket, bolts and nylon cup washers.
2. Speedo (Caerbont electric) was reading 15mph low at 70mph (and 7mph low at 30mph) - not helpful when approaching Gatsos! Also way off the 10% legal tolerance. Speedo has a bank of 10 dip switches to calibrate the pulses per mile setting (ppm). Found from my calculations that the 'ideal' setting based on wheel size / rotations per mile computed against the speed sender pulses would also not give me the correct speedo reading. Instead, I calculated a ppm correction factor to the current setting (based on 15mph under reading at 70mph). Result - speedo now reads accurately at 70mph and above, with 2-3 mph over indication at 30mph. Calibration info (ppm to dip switch settings) from CAI's website. This info may not be of use for cars with earlier/different speedometers.
Edited by Tavan on Wednesday 17th June 10:23
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