BMW K bikes (Bricks)

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1Back to top Go down    Backfire !! on Sun Nov 30, 2014 4:06 pm

CraigNZ

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Was measuring the loudness of the aftermarket exhaust for compliance with the engineer. You run the bike at approx 4000rpm (in the open) to take the reading. The limit is 100 and that is what its reading. The problem is that I have a backfire which I didn't think was that bad until holding at 4000rpm. It is banging back quite badly and this in turn causes the meter reading to go up to 104 which is way over.
He suggested I do a tune up by balancing the carbs using a vacuum. I don't have the proper one but have seen on the net how to make your own.

Any advice on this would be much appreciated

Thanks

Craig


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1991 BMW K100RS
1999 BMW R1100S
    

2Back to top Go down    Re: Backfire !! on Sun Nov 30, 2014 6:08 pm

Dai

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Before you go that far Craig; have you checked the blanking plugs on the injector bodies? They seem to perish quite easily and will cause the engine to run rough, but I'm not sure that's the primary cause of your backfire. Backfiring is caused by unburnt fuel getting into the exhaust system and then being ignited by the next cylinder to open the exhaust valve. On a non-EFI bike I'd go straight for the timing but that doesn't apply to a K. A leak in the exhaust system can also sound like a backfire; on a K that's the first place I'd check. I'd expect the giveaway to be a patch of black carbon where none should be.


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3Back to top Go down    Re: Backfire !! on Sun Nov 30, 2014 6:11 pm

Inge K.

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@CraigNZ wrote:
He suggested I do a tune up by balancing the carbs using a vacuum. I don't have the proper one but have seen on the net how to make your own.

Hereis a inexpensive model, I would guess that it's better to use a mineral
two stroke oil than ATF as it has a bit thicker viscosity and isn't that easily
sucked in to the cylinders.


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Inge K.
K100RS -86. (first owner), K1100LTSE -94.
    

4Back to top Go down    Re: Backfire !! on Sun Nov 30, 2014 6:38 pm

CraigNZ

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Thanks guys,

Will check out.
Have also searched the forum and got quite a bit of good stuff to work with.


Cheers


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1991 BMW K100RS
1999 BMW R1100S
    

5Back to top Go down    Re: Backfire !! on Sun Nov 30, 2014 6:54 pm

Holister

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I've been struggling to find the cause of my backfires and popping ever since I bought my old girl 6 months ago.
I've replaced rubber bits, exhaust gaskets, tightened exhaust/muffler clamps, replaced sparkplugs but found that a leaking fuel injector was the culprit. I cleaned them and replaced the o-rings/filters. Running Smmoooooth now and not a hint of a pop.



Last edited by Kaptain Holister on Sun Nov 30, 2014 7:55 pm; edited 1 time in total


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1988 K100RT VIN No. 0094680
1989 K100RT VIN No. 0097367 (naked)
1996 K1100RS VIN No. 0451808
Fuel: 95 Octane
Engine Oil:Nulon Full Synthetic 15W50
Gear Box Oil: Nulon Synthetic 75W90
    

6Back to top Go down    Re: Backfire !! on Sun Nov 30, 2014 7:08 pm

Two Wheels Better

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Of course, if that is indeed the remedy to the problem to start, you'll only really be adjusting the throttle bodies for balanced idle and not at 'running rpm' due to the air screws only functioning at low rpms like an idle air circuit does on a carburettor. Attempting to fiddle with the throttle body's locktited linkage adjustments will only cause you headaches and more than likely misadjustment without having access to the proper gauges which measure airflow volume. They are not like balancing carbies at all once you raise rpm and attempt to set the TBs at anything above idle. There are very many posts up here on the forum about various people's attempts. But please let us know how you go.


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1987 K100RS, Big Block '93 K11/K12 hybrid, '09 K1300GT, '07 K1200R, '04 R1150RT, '95 R100 Mystic, '77 R75/7.
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7Back to top Go down    Re: Backfire !! on Sun Nov 30, 2014 7:23 pm

japuentes

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Hi there, you can try this way
Best regards
JAP


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1988 K100RS SE/ABS
    

8Back to top Go down    Re: Backfire !! on Mon Dec 01, 2014 4:32 am

CraigNZ

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Thanks again...
Great idea Jap !
Could only manage a quick scratch around the bike before I was dragged off... BUT, had it just off idle and was listening down near the front end, (didn't have any engine start spray) could hear suction noise. I checked the clamps around the rubber hose between the throttle body and block, they were tight. Looking closely at the no1 I could see a lip in the rubber, a gentle prod with a screwdriver revealed what must be a split as the end of the screwdriver went straight through. Going to have to strip down, the hoses from the air box to the top of throttle bodies have the crimped steel bands to secure them, presume I just cut them off and replace with normal jubilee clip?

Craig


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1991 BMW K100RS
1999 BMW R1100S
    

9Back to top Go down    Re: Backfire !! on Mon Dec 01, 2014 6:12 am

rosskko

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Hey Craig,

sorry to be the first to give the bad news, but the Oetiker clips (the crimped ones you have)are a smaller width than the standard jubilee clips.
The rubbers are pre-formed and are to narrow for your run of the mill off the shelf type clip.

Look for originals (good luck), use cable ties, THIS THREAD or THIS THREAD or search for suzuki clamps.

Just a note, dont remove the lower rubbers from the engine unless you suspect they are leaking, unless it is one of the split ones. they will also need to be re-sealed when replaced if you take them off. K100 has no replcement O rings to go in them.
Clamps are $8 each here so make sure you get the correct ones


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1986 K100RT VIN 0093801K100RT with summer fairing for a northern visitor

Basic/2 6308802K100CJ05/1988

K1100RS 0194321
    

10Back to top Go down    Re: Backfire !! on Mon Dec 01, 2014 6:38 am

nino


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I tried everything to eliminate backfire. Finally I turned the ignition in advance a bit and it cured backfire. You can try, could be easy fix.

    

11Back to top Go down    Re: Backfire !! on Mon Dec 01, 2014 7:29 am

Inge K.

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@rosskko wrote:
Just a note, dont remove the lower rubbers from the engine unless you suspect they are leaking, unless it is one of the split ones. they will also need to be re-sealed when replaced if you take them off. K100 has no replcement O rings to go in them.

If I remember correct, the bike in question is a 4V which have o-rings
between the engine and TB's.


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Inge K.
K100RS -86. (first owner), K1100LTSE -94.
    

12Back to top Go down    Re: Backfire !! on Fri Dec 05, 2014 3:48 am

CraigNZ

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url=https://servimg.com/view/19034243/9][/url]

Not sure why but mine seems to have these trunk ducts between the throttle body and air plenum? Tried google but all seem to have the plenum directly above the intakes....

Thanks

Craig


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1991 BMW K100RS
1999 BMW R1100S
    

13Back to top Go down    Re: Backfire !! on Fri Dec 05, 2014 4:05 am

Inge K.

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You're missing the rubber cap on cyl.1, or the rubber hose to the FPR have
losened from this spigot.

Likely the cause to your problem.


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Inge K.
K100RS -86. (first owner), K1100LTSE -94.
    

14Back to top Go down    Re: Backfire !! on Fri Dec 05, 2014 4:15 am

CraigNZ

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Yes, good spot, the pipe there is what I have pulled off. It goes to some sort of vacuum cylinder that is behind it.
Presume that's the FPR? (whatever that is)



Last edited by CraigNZ on Fri Dec 05, 2014 4:17 am; edited 1 time in total


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1991 BMW K100RS
1999 BMW R1100S
    

15Back to top Go down    Re: Backfire !! on Fri Dec 05, 2014 4:16 am

charlie99

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that is a classic picture of what we call 4 valve models

meaning 4 valves per cylinder ...which is different to many of the earlier 2 valve models which many of us have

the tubes rather than plenum which you have noted are known to crack ...(see many posts about this ...and advice from a local bmw dealer ?)

I think that picture tells many things ....to my eyes I see a leakage on the cylinder headrubbers probably from leakage of the bottom rubbers (between the throttle bodies and the head itself ).

whilst the ignition process is happening and on deceleration the butterflys close ...but there is still some fuel mix inside the chamber before the valve and because there is a really long duration of the valve timing ...some slight blowback from the induction process happens ...

if you have leaky rubbers you will notice the wetness at the head connection to the induction - manifold

if air is able to be sucked in equally as well as expelled you will hear backfires ...

seems like a pull down of those bits and a reseal job might help here ????? but test the integrity of the rubbers themselves in any case ..many have found that they are perished

good luck !!!


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16Back to top Go down    Re: Backfire !! on Fri Dec 05, 2014 4:18 am

Inge K.

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@CraigNZ wrote:Presume that's the FPR? (whatever that is)

Fuel pressure regulator.


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Inge K.
K100RS -86. (first owner), K1100LTSE -94.
    

17Back to top Go down    Re: Backfire !! on Fri Dec 05, 2014 4:26 am

CraigNZ

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Thanks for replies. Definitely have a problem on number one... split. Am going to be stripping down this weekend. I guess on the 4v I do not need to remove the plenum? just free off those crimped bands and pull the pipe away?

Where the best place to get online spares?

Thx


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1991 BMW K100RS
1999 BMW R1100S
    

18Back to top Go down    Re: Backfire !! on Fri Dec 05, 2014 4:34 am

Inge K.

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Is it the rubber underneath or above the TB that is split?
Usually it's the ones underneath that is the problem.


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Inge K.
K100RS -86. (first owner), K1100LTSE -94.
    

19Back to top Go down    Re: Backfire !! on Fri Dec 05, 2014 5:18 am

Inge K.

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If it's the rubber bushing underneath the TB, you can order the bushing and
the Oetiker clamp from Motorworks UK.
I think it would be a good idea to change on all four cylinders while you are
pulling things apart down there.

At the same time I would also have changed the o-rings under the intake stubs
and the o-rings at the injectors.

Also check the rubber hoses to the crankcase ventilation and oil separator.

-------------

If the split is above the TB, you better search a used part, as the hoses above
the TB's and the upper half of the airfilter housing is one part.


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Inge K.
K100RS -86. (first owner), K1100LTSE -94.
    

20Back to top Go down    Re: Backfire !! on Fri Dec 05, 2014 5:36 am

CraigNZ

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Thanks Inge,
Bottom one at the moment, haven't had a good look at the top ones yet.

Will check out the web site

Cheers Smile


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1991 BMW K100RS
1999 BMW R1100S
    

21Back to top Go down    Re: Backfire !! on Fri Dec 05, 2014 5:45 am

Inge K.

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@CraigNZ wrote:, haven't had a good look at the top ones yet.

Normally the ones above the TB's isn't any problem, unless you have been
unlucky with the use of sharp tools.


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Inge K.
K100RS -86. (first owner), K1100LTSE -94.
    

22Back to top Go down    Re: Backfire !! on Fri Dec 05, 2014 5:53 am

CraigNZ

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Thanks Inge, I shall be very careful when I try to get those clamps off....


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1991 BMW K100RS
1999 BMW R1100S
    

23Back to top Go down    Re: Backfire !! on Fri Dec 05, 2014 6:10 am

Inge K.

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@CraigNZ wrote:I shall be very careful when I try to get those clamps off....

You don't need tocut off the clamps above the TB's, only one underneath
each TB......the other ones underneath is a screw clamp.


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Inge K.
K100RS -86. (first owner), K1100LTSE -94.
    

24Back to top Go down    Re: Backfire !! on Fri Dec 05, 2014 6:22 am

CraigNZ

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OK, so I should be able to leave the top ones alone (providing they are not split) and I will have enough room to replace the bottom ones by just removing the bottom clamps?


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1991 BMW K100RS
1999 BMW R1100S
    

25Back to top Go down    Re: Backfire !! on Fri Dec 05, 2014 6:30 am

Inge K.

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I think that you maybe have to loosen all four TB's and if you remove the air filter
you get some more movement.


But first you remove the fuel rail together with the injectors to get som working space.



Last edited by Inge K. on Fri Dec 05, 2014 6:35 am; edited 1 time in total


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Inge K.
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26Back to top Go down    Re: Backfire !! on Fri Dec 05, 2014 6:35 am

CraigNZ

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Will do, as suggested, I will probably replace all 4 anyway

Cheers


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1991 BMW K100RS
1999 BMW R1100S
    

27Back to top Go down    Re: Backfire !! on Mon Dec 08, 2014 2:22 pm

CraigNZ

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Just a heads up and probably a known site. Doesn't have everything but what they do have is cheap enough (injector seals)


http://www.euromotoelectrics.com/category-s/555.htm


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1991 BMW K100RS
1999 BMW R1100S
    

28Back to top Go down    Re: Backfire !! on Mon Dec 08, 2014 7:21 pm

RicK G

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I have bought gear from him and he is good to deal with and some of his prices are very good but it still pays to shop around some of the bits he sells are very expensive, mainly because I think he has not sourced them well.
What I do say with confidence is that you don't seem to get any second rate junk from him.


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Bikes 1993 K1100 LT, 1998 K1100 LT, 1993 K75 RT, 1996 K75RT, 1986 K75 GS, 1979 Z1300 Kawasaki X 2 for now
    

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