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Discussion Starter #1
Hello, group. Long time without posting.
I was reading about the k75 in http://en.wikipedia.org/wiki/BMW_K75

I see: "They are powered by a 740 cc liquid-cooled inline three-cylinder engine with Bosch fuel injection. The US EPA specific engine produce 68 hp (51 kW) while all others produce 75 hp (56 kW)"

I dont know why and how US models lost 7 HP.

I've a US model but i live in Uruguay, where europe model are allowed. Do you know how can i modify my bike to a european model and have a gain of 7 HP?

It sounds as a good idea for me.

Any coments are really apretiated.

Thanks all,

Fabian
K75C 1986
Uruguay
 

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Don't know about the K75, but had an early Canadian 85 K100RS, Eurospecs camshaft sure gave them extra HPs. :teeth
 

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PsyKotic Waterfowl
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Internet Rule #1: Don't believe everything you read on Wiki.

They'd most likely change the fuel mapping in the L-Jetronic and/or the intake/exhaust cams. but I've looked at the part numbers for those in other countries like Germany and the UK and they're the same as the US part numbers. There's also no indication in the parts listings anywhere that there are different cams for different countries like there usually is..

Heck, even BMW NA doesn't have their sh*t together. If you look at the 1990 sales literature it says the K75 puts out 70 hp but the 1995 stuff says it puts out 75 hp. Weird, huh?

Is Wiki right or wrong? Got me. :dunno:

I'd be inclined to just not worry about it and go riding.
 

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Discussion Starter #5
Hi flyingduck!

i agree with you about internet, because that i've looking at the haynes manual in Chapter 2 :Engine.

it seems to have a difference in compression ratio in late US models (10,5:1) and uk ones (11:1), so they talk about 70 and 15 HP respectively.


And in chapter 7 ignition:

Advance rage:
US: 26 degrees
UK: 24 degrees

Static ignition timing:

US: 4 degrees BTDC (cranckshaft angle), 0.10 mm BTDC piston position
UK: 6 degrees BTDC (cranckshaft angle), 024 mm BTDC piston position

These are the only differences i can find.

As you say, i just need to ride!.

And as i've read, my bike is from january 86, and the gap between US and IK started " somewere between february and july", so maybe i've this 7h working.

Thanks!

Fabian
 

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PsyKotic Waterfowl
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Good info. Since you mentioned the compression ratio I went to take a look at the pistons. I can't tell what the details are from the parts catalog but it does show that some sort of change over that occured to USA pistons in 6/88.

FYI: The heads appear to be the same.

I think that was also when they changed to the newer rings that let less oil seep by when parked on the side stand.

Did the change in the pistons change the compression? Got me.

Here's a post where Don Eilenberger ran dynos of an 87 vs. a 92 and got identical results:

http://www.bmwmoa.org/forum/showthread.php?2853-K75S-HP-amp-Compression


I have the 88 and 93 Haynes manual which both show the difference between the US and UK models. I'd assume they were working with an 86 or 87 when putting the 88 manual together.

One thing I did that seems (according to my not-so-reliable butt dyno) to have improved performance on my K75 was to install some Gen 2 Bosch fuel injectors that some guy was selling on Fleabay. The Gen 2s have a four hole pintel cap that atomizes the fuel better compared to the Gen 1 that shoot a single stream of fuel. The theory is that it improves combustion.

It's a popular mod among the Jeep crowd:
http://www.youtube.com/watch?v=bHf-6ohkgbA

The guy isn't selling those injectors on Fleabay anymore but if you want his email then drop me a PM.

Then there's the advancing the timing 3 degrees trick. I've neveer played with that but was thinking about trying it on my K75 later this month,
 

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FlyingDuck said:
One thing I did that seems (according to my not-so-reliable butt dyno) to have improved performance on my K75 was to install some Gen 2 Bosch fuel injectors that some guy was selling on Fleabay. The Gen 2s have a four hole pintel cap that atomizes the fuel better compared to the Gen 1 that shoot a single stream of fuel. The theory is that it improves combustion.

It's a popular mod among the Jeep crowd:
http://www.youtube.com/watch?v=bHf-6ohkgbA

The guy isn't selling those injectors on Fleabay anymore but if you want his email then drop me a PM.
Neat video, thanks for sharing.
Do you know the part number for the Bosch Gen 2 injectors that will work with a K75? I've considered getting mine cleaned but it may be better to get "new and improved".

Thanks.
 

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PsyKotic Waterfowl
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stokester said:
Neat video, thanks for sharing.
Do you know the part number for the Bosch Gen 2 injectors that will work with a K75? I've considered getting mine cleaned but it may be better to get "new and improved".

Thanks.
Don't know the part number for them but Fleabay seller Osidetiger (not affiliated) was selling them for $25 each which is only a little bit more than getting them reconditioned. I'd guess that if you drop him an eBay message that he can hook you up.
 

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Discussion Starter #9
Txs flying duck.

Nice video, and article.
I;m interested in the inyectors too.

As i supose now after reading, my january 86 bike has full power.

Whay i;m going to do im the future, after adjusting the valves, replace filters and may be new inyestord is to put it on a dyno for test.
If i do taht for shure i;ll post results.
:)
 

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More interest in Gen 3 for K75

Same interest from me....K75RT 1995 that I thought I would send the FI's out for cleaning but would consider replacing with Gen 3 injectors. If someone identifies the actual p/n for Gen 3 for K75, please post here.
 

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I know the Bosch Motronic ECU for the K12 has statement references in its code to the lower power version of the KRS. With an Efi system modding the ECU software is the easiest way to reduce power.

What puzzles me on the K12 is the same ECU code is used across all horsepower options. I do not have a detuned bike/wiring diagram to compare, but it may be something so simple as a link in the wiring loom that tells the ECU to use reduced power maps.



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