'85 K75S ongoing starting issues

[szabgab]

Dear all,

I started a new thread, as the theme is a bit different - I'm having more and more problems cold starting the bike, like the problem would be getting worse (actually, it is getting worse). Now I need long cranks - 3-4 second ones to start the bike, after which it runs fine. I do not have a pressure gauge, so I will not be able to measure output pressure, but reading through various threads on the theme, the pump might not be up to the job at hand, most noticeable at cold start, low pressure scenarios. I dug out the pump from the tank, and it is an aftermarket one, badly botched to the dampener, which is obviously falling to pieces by now. Screen is torn, most likely it was not even sitting on the pump, because since I have put it on, just to filter some of the garbage and blocked of the nipple, that is not attached to anything (and no spare return line in the tank either) bike is starting even harder. Today I filled up the tank, and the bike starts a lot easier. Fuel filter is a Mahle, according to the PO changed a short while ago (but I know, even one crap batch of petrol would render it partially useless). I could just go ahead, and replace everything inside, but it is needless to say, I'm not much in the mood of shelling out hundreds of $ for a thing, that might be the fix (or not). (although something like this might be just the ticket - https://www.aliexpress.com/store/product/Free-shipping-16121461576-16121460452-0580463999-52mm-motorcycle-fuel-pump-case-for-BMW-K75-K100-K1100-K1/714961_32808506394.html?spm=2114.search0104.3.36.673a4bc0bX4kzm&ws_ab_test=searchweb0_0,searchweb201602_3_10065_10068_10059_10696_100031_5017615_10084_10083_10103_451_452_10618_10304_10307_10820_10821_10302_5017715,searchweb201603_2,ppcSwitch_4&algo_expid=3bbadcdc-76bd-491e-80d8-a3d3e72adf45-5&algo_pvid=3bbadcdc-76bd-491e-80d8-a3d3e72adf45&transAbTest=ae803_1&priceBeautifyAB=0 ) Any methods of checking, if the pump, filter etc is at fault? I know, how to blow test the filter, but what about the pump? It is an aftermarket pump, that is a car pump, so well inside the specs required by BMW.

On a side note, battery is not great, but it might be more of an alternator issue -   as it is getting 12.20-12.50 Volts at normal idle, around 12.9 at 2000RPM and 13.4-13.5 at 3500 and above with headlight on, but nothing else. I charged the battery, so the baseline was good, and the voltage drops to 9.3-9.4 whilst cranking (again I do not have a load tester, but I thought cranking is just as heavy on the battery). How to check the alternator itself for faults? If anything would be amiss there, would the battery idiot light come on? I have cleaned and checked the brushes, they are very well inside specs, checked and cleaned battery and alternator ports, checked and cleaned earth, and the cables do not seem to be corroded (so at least this is out of the equation)

Thanks!

Gabriel

[Laitch]

You should clean the fuel tank thoroughly to remove all debris. You should replace the pump, vibration damper and check the condition of the pump pre-filter screen. You should remove the tank fuel lines and check them for blockage and condition. Fine particles of debris might be clogging the injectors too. The battery doesn't seem in good condition either. You should check the condition of the alternator brushes. Fuel filters either useful or useless. Yours might be clogged to some degree. There might be a date stamp on it; look carefully.

All these tasks will help. You have purchase a neglected, used moto. Now you are restoring it.

[szabgab]

You should clean the fuel tank thoroughly to remove all debris. You should replace the pump, vibration damper and check the condition of the pump pre-filter screen. You should remove the tank fuel lines and check them for blockage and condition. Fine particles of debris might be clogging the injectors too. The battery doesn't seem in good condition either. You should check the condition of the alternator brushes. Fuel filters either useful or useless. Yours might be clogged to some degree. There might be a date stamp on it; look carefully.

All these tasks will help. You have purchase a neglected, used moto. Now you are restoring it.

OK, I did not reply, till I did not sort some of the things, we spoke about. Battery load tested at a garage and it is fine, brushes measured again carefully - at the lowest point have read under 5mm, so I replaced the whole regulator-brush assembly, as it was cheap enough and I could have not been arsed to desolder the brushes (that cost 2/3 of the whole reg). Battery charges 13.2-13.5V at 2000+ RPM with headlights on, so the next culprit could be the rectifier, well I will not deal with that and leave it be. The monkey nuts are fine, as are the alternator bearings, I have cleaned the slip rings for good measure, but that did not achieve much.

Fuel lines removed and are free of sh.t, the fuel filter I have replaced as cheap insurance, the old one was clogged somewhat, as it was hard to blow through it. Screen is torn and apparently the generic replacement pump is not good, as it creating turbulence in the tank (because it is engineered to go inside a plastic thingy), or so a filter - pump shop told me, from where I wanted to buy a dedicated fuel sock. SO I ordered a Chinese knock-of 52mm pump with ridges and a stainless mesh-screen, the reviews were very good. The bike is still hard to start if it is getting low on fuel, on full tank it starts immediately.