Knocking at tick over.

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  • #6012
    tony54
    Participant

    Hi, im new to the 750 twin, i have a 1983 ltd with 11000 kms, it had been stored since 1986, i fitted a new battery, cleaned the main and pilot jets, the bike is now running but not realy smooth, is the knocking sound normal at tick over, my bike is fitted with Mikuni carbs, and there doesnt seem to be a fast idle on choke, if i start the bike and leave it idle it just stalls, any advice would be handy ,regards Tony.

    #13399
    Mikeonabike
    Participant

    Hi Tony, I would check points/timing, balance carbs and maybe turn up tickover up a little.

    Mike J

    #13392
    Kaptainkwak
    Keymaster

    Hi Tony54

    I would initially look at timing but your on electronic ignition so that shouldn’t be an issue.

    If the engine revs drop to low (below 1000rpm) the engine does struggle and can make a knocking noise as it slow fights to turn.

    That leaves me to carbs. I am guessing that if the bike has been stood for a long period then they could well be gunged up inside. I would suggest taking them off and doing a thorough strip down and clean. Check for any wear and tear and replace parts that look dodgey. There are refurb kits on ebay.

    Once cleaned refit, prime and balance them. Also check the rubbers holding the carbs on are in good order. I would also recommend fitting new plugs too.

    #13402
    tony54
    Participant

    Hi captain kwak, i took the cabs of today, and dismantled everthing, i did notice that they wernt sync, i cleaned all jets and jet holders, also one float is higher than the other, what is the correct setting?
    Should the bike fast idle on choke, ther is no fast idle cam like on the kehin carb, i assume the vacuum created by the open choke mechanism is enough to keep it on fast idle when cold. Do you suggest ultrasoon or would carb cleaner and compressed air be enough. intake rubbers and diaghrams are good. thanks so far for your help, cheers Tony.

    #13393
    Kaptainkwak
    Keymaster

    Hi Tony54

    In most cases I have found carb cleaner and compressed air to be good enough for cleaning.

    Good spot with the syncing of the carbs. That will really cause havoc with starting and running. You should be able to balance them good enough to run quite well then use vacuum gauges when you start her up again.

    I am unaware of a dimensional setting for the carb floats. I always start with the tang horizontal then use the clear tube to set the levels in the bowls as described in the manual.

    When set up properly the bikes revs will increase on choke as the engine initially warms up. that is the sign to reduce the choke.

    #13394
    Kaptainkwak
    Keymaster

    Hi Tony54

    In most cases I have found carb cleaner and compressed air to be good enough for cleaning.

    Good spot with the syncing of the carbs. That will really cause havoc with starting and running. You should be able to balance them good enough to run quite well then use vacuum gauges when you start her up again.

    I am unaware of a dimensional setting for the carb floats. I always start with the tang horizontal then use the clear tube to set the levels in the bowls as described in the manual.

    When set up properly the bikes revs will increase on choke as the engine initially warms up. that is the sign to reduce/cut the choke.

    #13403
    tony54
    Participant

    Hi captain kwak, thanks for the info, tomorrow at work i will give every thing a good blow through with compressed air and carb cleaner, i noticrd that the left hand carb had much more gunge, reason being my bike is not fitted with a centre stand, and it was stored on side stand. Are you using synthetic oil in your bike? we use it in all the Mercedes models.i will post some pics of the ltd as soon as i get the hang of it. cheers for now Tony.

    #13395
    Kaptainkwak
    Keymaster

    Do NOT use synthetic or even semi synthetic oils. The clutch plates will slip.

    I believe some use semi synthetic oil but I suggest you should only use mineral oil. I would recommend either 10/40’s or 20/50’s

    #13404
    tony54
    Participant

    Hi captain kwak, put the carbs back on the bike, after having cleaned, and flushed with carb cleaner plus blowing every thing through with compressed air. when i started the bike i pulled the choke out to first notch, bike starts no problem with a slight increase in revs, but as bike warms i have to keep turning the idle down [ of choke } untill its at operating temp, i cant ride the bike any distance because it doesnt have reg plates. If i let the engine cool of then start again then i have to turn the idle back up other wise it will just stall. Ive adjusted the idle mixture screws to 2.5 turns. i replaced idle jets with nr 45 thats the same size as what was in there, would that be .45mm?. I have contact with a Kawasaki dealer here, he is pretty up to date with the older bikes, he suggested i ultraaoon the carbs and start all over again. well thats the update untill now. monday im of to Portugal for three weeks hols, cheers for now Tony.

    #13397
    Michael
    Participant

    Hi Tony,
    welcome !

    I was on holidays for more than four weeks and a total of about 7.300km to and in Norway. My spouse on a Y1 (LTD, 1982) and me on a K1 (LTD, 1983). My uncle was with us on a Y2 (LTD, 1983).
    http://www.z750twin.de/twin_modelle.htm

    All three LTDs are very close to stock setup and had the same issues.

    With the fully warmed engine the idle speed (Leerlaufdrehzahl) where at around 1.800 rpm. All of them started without any issue when they were cold.

    Have a lot of experience with Z750Twins, but no real idea how to cure that.
    Just live with that, it was the most reliable setup that we could gain 😉

    Cheers, Michael

    #13400
    Mikeonabike
    Participant

    Jets are measured by there flow rates not the hole size.
    I seem to have been lucky with mine, standing for ten years, quick clean and off it went.
    Altered the pilot screws at a later date to stop the exhausts popping on the overrun but tickover is still fine.

    #13405
    tony54
    Participant

    Hello Michael, are you the german guy from the 750 twin site? if so i liked your posts on the Mikuni carb and head gasket repair. Thanks for the info, im going to have my carbs ultrasooned, and then start again. You say your bike idles at 1800rpm, that is high, am i right in assuming that if you adjusted the tick over lower, that it would stall when cold? I work for Mercedes as a mechanic, i also had my own work shop selling and repairing classic cars, Ive had alot of expierence working on English twins and triples, and American twins. I know you can have two identical factory supplied engines, and one will run beautiful, and the other wil run crap, maybe ive got an engine that runs crap, what do you think, cheers Tony. PS ich spreche auch Deutsch.

    #13401
    Mikeonabike
    Participant

    Just a little thought! Have you had the compression checked? low compression on one or more cylinders would cause low rpm problems.
    I think the carbs you have will have a “Starter Jet” which is not a choke as such, just a enrichment system which is much better than the old “Choke flap” It may or may not increase the RPM.
    Many people used fully synthetic car oil in the early days (also branded as bike oil) which caused problems, this is because cars do not have wet clutches so manufactures add PTFE (Polytetrafluoroethylene) as a friction improver,(Google it) It is this which caused problems with bike clutches which if worn or only just up to the job in the first place causes slip.
    Fully synthetic oil designed for motorcycles is far superior to that sludge that comes out of the ground, oil change intervals can be doubled and the biggest advantage to our big twins is when we get stuck in traffic and the temp rockets quickly synth oils do not burn and clog the rings so easily as it can take an extra 25oC or so before it brakes down.
    Would you put crossply tyres on your bike if you could fit radials!!
    However I just put the cheapest #OOPS# I can find in my bikes, My Moto Guzzi I have had for 35 years and over 125,000 miles with no problems on mineral oil 😉

    #13398
    Michael
    Participant

    Thank you Mike and Tony,

    yes, I am the german Michael and in constant contact with KK.
    Good to hear that my photostories were helpful 😉

    The choke system of the LTDs just enriches the mixture and has no impact to the butterfly valves (Drosselklappen).

    In normal cases it is a kind of a ritual to turn the idle screw to adjust the idle speed when the engine warms up. On our tour through Norway we had a lot of baggage with us, which doesn’t make it easier to reach out for that screw 😉
    Tony, you are right. If we set the idle speed to e.g. 1100 rpm when the engine is hot, it will start ok when cold with choke engaged, but it doesn’t have a stable idle speed in that time when choke is disengaged and engine is fully warmed/hot.

    On the other hand we had several stops, enjoying the scenery. Engines cooled down and the restart worked best when the idle screw wasn’t touched.

    Simply it caused less stress with the higher idle speed setting. Not that cool, but easier 😉

    Ok, I may investigate that situation.
    Have done a compression test with my Twin and it has exactly 10 bar on both cylinders (cold engine). Very good value and both are absolutely identical.
    Can check with a “Colortune” glass spark plug if the hot engine idles to lean or to rich.

    We have used 20W-50 mineral engine oil.

    @Tony: Wo hast du deutsch gelernt ?

    Cheers and Prost, Michael

    #13406
    tony54
    Participant

    Hello Micheal, ich bin in deuchland geboren, ich habe sechs jaren dar gewohnt, ich habe der kawa in Braunsweig gekauft, ich vinde es nicht einfach in deutsch zu schreiben. Any way back to the Mikunis, they are thoroughly clean and ready to go. im also rebuilding front calipers and master cyilinder. cheers Tony.

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