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TECHNICAL MOTOBRICK WRENCHING In Remembrance of Inge K. => The Motobrick Workshop => Topic started by: Martin on September 17, 2017, 10:31:21 PM
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I've had my 75 Brick for twenty years. When I first got it I was worried about the backfiring on overrun so I consulted numerous sources. And was told mostly they will all do it to some extent some more some less. And that you could reduce it by not having the throttle partially open on overrun, correctly adjusting your TPS, fix and air leaks, fix exhaust leaks, and have your mixture adjusted correctly.
This has generally worked with only the occasional backfire overrun mainly after giving it a bit of stick. However due to a persistent leak between the muffler and the headers the back fire comes back. I was quoted $50.00 Au for the disintegrating fairy dust gasket ( I recently found out that you can get them for $20.00 Au. I tried various solutions all of which worked for a short period then the leak came back, and the backfiring came back. At the moment I am waiting on the hopefully final solution one of Bocutter Eds collet gaskets. Thanks Ed.
In the meantime due to a sooty tailpipe and higher fuel consumption I decided to have a play with my injectors. I built a test rig to observe spray patterns suspecting I had clogged injectors. I had previously had them cleaned professionally twice and recently I have used an Aldi ultrasonic jewelry cleaner every couple of years as well as running Techron once a year. Even then the Brick still occasionally backfired.
After finding dirty injectors I cleaned them by flushing them forwards backwards, and ultrasonic bathing. Finally got two with the correct pattern, and one with an improved but still bad pattern. I ran out of time so I threw the injectors back in and took it for a run and ran it up to temperature. Using a laser temperature gun showed one was significantly hotter than the other two. I decide to run it only occasionally until I sourced stronger cleaner and a sequencer to pulse the injectors. I was also unsure of the correct colour pintle caps, I had tried to get what I believed was the correct yellow but they were not available. I ended up with green, blue and orange, I had green on originally which I replaced with blue.
To try to find out about the correct colour pintle I decided to go over to a mates place and have a look at a totalled engine he had and check it. Before I left I removed the belly pan in order to get a better shot with the temperature gun. I gave it a bit of stick after it had warmed up, and found that it had ceased to backfire. I tried to get it backfire by leaving the throttle partially open on overrun, no matter what I tried it would not backfire. At my mates place I hit the headers with the temperature gun and they were all pretty much even. I have since tried to get it to backfire by leaving the fast idle open and it still won't backfire. and the exhast is still leaking. I pulled the spark plugs on getting home and they are all the correct grey tan.
At the moment I am waiting for correct pintle caps and the sequencer. The mates son who knows a bit about injection is away for another week.
He is building, not sure if it is finished a multi injector tester cleaner with graduated vessels, and is using a much stronger cleaning solution. once I get the parts I'll pull the injectors and see what sort of pattern I get. At the moment I am stunned that maybe when they cleaned them they did not check the patterns. :dunno
Regards Martin.
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The last mica gasket I tried to install disintegrated while I was pushing the exhaust over it -- yes I know there's a way to do it where it won't disintegrate but for some reason it didn't work. I've been riding for 4000 miles without the mica gasket and haven't had any noticeable or regular backfiring at all. So -- I say f**k that gasket. I'm not seeing any exhaust leak to speak of -- probably because I'm not looking for one :2thumbup:
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Arrgh the backfiring returned, after three weeks of not scaring the c#*p out of anybody Kapow. Just had a look, the last fix has totally disintegrated. It consisted of epoxy coated fibreglass muffler repair bandage, on taking off the muffler all that was left was the fibreglass tape.
Very much looking forward to a package from the good old US of A courtesy of Ed. I put back on a previous fix, a piece of .5mm aluminium sliced diagonally this had sort of worked only slightly leaking. It will have to do.
Regards Martin.
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Ed has entrusted me with 7 of his gaskets which I have been tasked with distributing among members in the U.S..
If anyone is interested in getting one, they can contact me by PM. Payment of $30 which includes postage will be via PayPal which I will forward to Johnny for the support of Motobrick.com. Ed and I are not keeping any of the proceeds.
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Anyway I visited him not long ago and he was hard at work getting a batch of gaskets ready. I picked up one while I was there.
I made 21 gaskets this time. Gryph has 7 and 3 are on their way, probably stuck in Customs, to Martin.
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Thanks Ed for the update, you're probably right about Customs. They're probably now being played with by drug sniffing Koalas. Due to the backing out by a mate who wanted a couple I am now the OZ distributor for The Famous Bocutter Collet gasket. Two available, proceeds will go to Motobrick .com. Due to world wide security problems security dogs at airports are being replaced with Drop Bears, a rather vicious relative of the cute and cuddly Koala.
Look up and live.
Regards Martin.
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I am surprised to hear that K75's all back fire! My K11 has never backfired and I can't make it backfire in over 20k! I am curious to know, don't the 75's stop fuel from going to the cylinders, like the 11hunerts, When you shut down the throttle?(I assume the injectors shut down)until the engine rpm comes down to 2000 rpm and then the fuel to the cylinders resumes? :popcorm
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They do shut down, but it was a bit of a weird thing. BMW apparently acknowledged that some K75's would backfire on deceleration on over run. Some did some didn't, some did it a lot, some did it occasionally. The solution was only a partial one, fix air leaks, fix exhaust leaks, adjust the TPS, adjust the mixture, don't ride down hills with a partially opened throttle. I have had mine twenty years and have only just totally eliminated the backfiring when I built a rig to observe the injector spray pattern. I had previously had them cleaned professionally twice, did them at home quite a few times and ran Techron once or twice a year.
Only when I cleaned them to the point where I could observe the correct pattern did it stop. I tried injector cleaner through my ultrasonic cleaner, then carby cleaner it was only when I ran thinners ( recommended by a local specialist ) through them that they finally cleaned up. The backfiring came back when the exhaust gasket blew out. While I'm waiting for the Bocutter Collet Gasket I fitted an old aluminium one that partially cured the leak yesterday and I took it for a ride and the backfiring has stopped. With the slight leak it does rumble more down hill on a closed throttle. It seems to me that you must have all your stars aligned to stop it backfiring. At this stage I don't know whether I have hit on a cure, or it is waiting to ambush me when I least expect it. :dunno
Regards Martin.
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It seems to me that you must have all your stars aligned to stop it backfiring.
Have you tried casting rice into a cat dish and developing a backfiring solution from the message patterns created therein?
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No Laitch but I have tried using the FORCE but that only led to embarrassment. I waved my hand at a cop and said "This is not the bike you are looking for". He said "Yes it is" and promptly gave me a ticket for speeding. :dunno
Regards Martin.