Hi guys,

Rather than revive my old thread which is now almost a year old, and a bit cluttered, i think starting a new one might be more appropriate, as i have now managed quite a lot more diagnostic than before. The bike has been sat for almost a year while i moved house, etc etc, but now i just want to get it fixed!

The Background:

Bought the bike (1985 K100 RT) off ebay, non-runner, in boxes. Engine turned out to be seized, so full strip and rebuild with new rings.

Bike now runs, smokey on startup, but nothing unusual, and that clears quickly as it warms up. Power seems there, but if you twist the throttle quickly, or try to really load up fast, the bike bogs, and unless you back off, it will die.


Things wot i have tried:(!!)

New Fuel, Pump, Filter, Hoses, Regulator, Injectors pro cleaned and tested, fuel pressure is good.
New Air filter, breather hose, TPS tested and set, vacuum switch removed, throttle bodies balanced.
Replaced MAF, ECU, and Ignition unit with known good spares.
Removed and tested Water temp sensor - good.
New HT leads, Plugs, and spark-tested each coil output - getting healthy sparks off each.

Compression is good, and consistent across all four cylinders, and advancing the timing slightly makes no difference.

The plugs are slightly sooty, which makes me think the fuel mixture is too rich, but i cant think what else is going to be affecting it.


Anyone got any ideas? Open to all sensible suggestions at this point!


I get such a good feeling riding this bike, but this problem is like banging your head against a wall!lol!

ToGGoT

What you describe is often because it's a bit lean or not getting a rich signal at the opening throttle.
check the system between the throttle bodies and air filter for air leaks especially the rubbers directly above the TBs. Use carb cleaner in a pressure can and spray it around each rubber and see if the idle changes.
Have you got the oil filler plug in and tight (that lets air into the system via the crankcase breather).
The Fuel Pressure Regulator needs the rubber tube from it to the #4 TB just in front of the TPS and that it has the spring former on it, it can kink and cut the signal. this makes the mix a bit richer when you open the throttle by a decrease in vacuum.
If you really open the throttle quickly from idle the engine will often bog unless the engine is up to running temperature. There is nothing to give an enrich signal except the drop in Vacuum and that can take a few engine revolutions.

I've given the whole system a good check over for air leaks, using just that method, and as far as i can tell the whole lot is sealed tight.

Oil filler plug is properly screwed in, and i haven't noticed a blockage/kink in the tube to the regulator.

This problem seems to occur both when the engine is cold, or hot, and doesn't just occur from idle - The most noticeable occasion i came to the bottom of a steep hill doing about 40, took a handful to pull up the hill, and it just gave up. Released the throttle, and opened it slowly, in the same gear, and it pulled me, accelerating, to the top of the hill.

ToGGoT

ToGGoT, what sort of mileage have you managed to get on the bike since getting her back on the road? After I rebuilt my K it took a blast from my place (St Judes) up to the Route 38 Cafe to settle her back in.

500 Miles in the year since the rebuild, then garaged for ~1 year. Was sat with the battery, and the tank removed for that year, and have been fiddling with it for about the last fortnight with renewed gusto!


ToGGoT

Try pushing the starter button when you open the throttle this will not let the starter engage but will still send a rich signal to the ECU because thats what it does to start. If the revs are over I think 1200 the starter is prevented from starting because the eth is removed from the starter relay.
Wrench the throttle and when it bogs hit the start button ans see if that overrides the problem. That way you will know if it is a lean problem or it could be a poor spark which I doubt or even a bad ECU.
I seem to recall a thread about this type of problem on the Motobrick forum but as usual I can't find it. My search skills are terrible my wife says I need a GPS to find the front gate.

Lol!

Thanks for your help!

I haven't tried pushing the starter button while revving - i tried pushing it at idle, and all it caused the bike to do was splutter a bit, then stall, but i'm game for a laugh!

Will have a go tonight and keep you posted.

ToGGoT

Hi, if you are able , take a look at the airflow meter, on mine the flap inside, whos position tells the computer how much fuel to give the injectors was hanging up.

Ok, well, have hit a show stopper that i need to sort out before i go any further.

I decided to check the valve clearances before i did anything else - i already have the cooling system off, so before i put everything back together i guessed i may as well.

It would appear that, although i put all of the shims/buckets in separately labelled bags when i disassembled, i must have mixed them up somehow on putting them back in.

I have 0.20mm, 0.10mm, 0.10mm, 0.05mm on the inlets, and 0.20mm, 0.20mm, 0.20mm, 0.10mm on the exhaust valves.

Haynes says 0.15mm - 0.20mm on inlet, and 0.25mm - 0.30mm on exhaust.


Sadly, it poured down with rain at that point, so i'm going to have to wait until the weather is good, disassemble the whole lot again, and see if i can figure out what on earth i have done.


Having always had screw adjust valves on my other bikes, and always having set them up properly, i have no idea what difference this is likely to have made, but i think i can assume its not going to help my performance issues...


Sometimes i wonder!

ToGGoT

Hi there, I would check the MAF, if the flap is stiff then you'll have an slow throttle response.
Best regards
JAP

Lets hope the numbers arn't worn off, did you put them in number side down???? or did you write down the clearances before doing the dismantle job?

Hi, I hope you wrote down the clearances before you removed the shims and then wrote down the shim thickness with it, then its easy to work back.
However, if not you can do that now. Remove all shims, but keep them marked or separated, so you know which one came from which position, then measure the thickness of the shims. This then, together with the measured clearance will give you an overall clearance for that particular valve. You then can mix/match the shims for most appropriate clearance. Have a good look if they are cleanly seated in the carriers, as at the moment you don't seem to have misplaced them, but have massive reduced clearances. This could be the case if not measured for a long time, particularly with an early bike with valve seats for leaded fuel.
Bit surprised that your clearances are exactly in 5/100's.

Well, that's as close as i can get them with the set of feeler gauges i've got to hand! Close enough for government work!

I'll borrow my mates decent ones when i actually come to get some replacement ones/swap them back around.

I remember sorting the shims into appropriate bags when i took the bike to bits - this is 2 and a half years ago now however, and i've checked/adjusted a few bikes since then, and my mind may well be failing me.


Will strip it all tomorrow night when its not raining , and keep you lot posted.

ToGGoT

Maybe should have explained a bit more.

On my bike the shims between the inlet and the outlet valves are different with very slight variations (IIRC inlet 2.35 and outlet 2.45). If you would have mixed any inlet one with an outlet one (or v.v.) I would have expected far bigger clearance differences. But as you know, measuring is knowing.

I'm kicking myself. I've just remembered that i had my local garage clean out the head when i had it in bits, and they reassembled it for me, and the guy said he had lapped the valves in while he was at it.

I really do wonder about my mental state sometimes.

Might explain the reduced clearances though.

ToGGoT

I would have expected them to tell you about the clearances then! Anyway, it is what it is, isn't it?

Too true!

Right, have measured again with a decent set of feelers, and got slightly closer results.

Have also had all of the shims out, and although the numbers have worn off, i've also borrowed a good vernier caliper, and measured them all, so i know what i've got.


So, next question. I need a few new shims, and i've read i want to spec the Exhaust valves to the outside of tolerance (0.30mm), and the Inlets to the tight side if possible (so 0.15mm). Does this sound correct?

Thanks

ToGGoT

Outlet on the (loose) side, inlet on the thight side.
~If a outlet is 0.31, you leave it like that.............
If it`s 0,33 you change it.

Right, finally got around to fitting the new valve shims.

Fingers crossed, she seems a LOT better! Still smokes a fair bit until she has warmed up, and the fuel pump seems to have got very noisy all of a sudden, but i'm happy otherwise!


So the moral of the story is: Check your valve clearances first!lol!

Thanks everyone!

ToGGoT