MG-Cars.info

Welcome to our Site for MG, Triumph and Austin-Healey Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB Technical - HIF carb float adjustment

Partly disassembled my HIF4 carbs today, after some sudden rough running and fuel overflowing from the rear carb. This was caused by some small bits of rubber from new fuel hoses I've just fitted. I've cleaned all that out of the carbs, but noticed something odd about the float position:

Referring to the SU booklet, and the Haynes SU manual, the float should be 0.02" to 0.06" below the level of the float chamber face (when carbs are inverted). Before I undid any of the internals, I measured my carbs, and found they were both between 0.06 and 0.07 ABOVE the float chamber face. This is the first time the carb has been opened up since leaving the factory (in 1980) and I can only assume this was how it was originally set up (if not, what could have caused the float positions to have changed?). I'm just wondering how critical this float setting is, since the carbs have never given any trouble in the last 30 years.
Brian Shaw

Brian if indeed the carbs have never been opened up and altered, then it certainly demonstrates that some variation is tolerable. After all you are only 0.01" off the upper limit! You may even find some workshop manuals quote different figures.Or could this variation be some seat wear? Apart from your most recent problem if all runs well don't loose too much sleep over it? Mike
J.M. Doust

Mike - I think you misunderstood me. The manual specifies -0.04" (+/- 0.02") and my carb float is +0.06", = 0.10" off spec.
Brian Shaw

Brian, hope this doesn't com across badly ;o)
Are you sure you are measuring the at the correct point on the float? The measurement is taken across the centre of the float in the dip near to where valve pin is located. The outer edges of the float are well above the point where the readings are taken.

MGmike
M McAndrew

Sorry Brian, I have read wrong, but as MGmike says, be sure you are reading at the right point.Float level errors have an effect on fuel delivery, seat problems will cause leakage and erratic function. Mike
J.M. Doust

Thanks MGmike/Mike - I was measuring at the wrong point (should have read the manual properly). Just had a quick look at the carb and the float level loooks about right - I'll measure it properly later but it looks like it's ok.
thanks guys
Brian Shaw

This thread was discussed between 30/01/2012 and 31/01/2012

MG MGB Technical index

This thread is from the archives. Join the live MG MGB Technical BBS now