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Euro-style dual TM38 flatslide carb installation

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Re: Euro-style dual TM38 flatslide carb installation

PostAuthor: faffi » Tue Dec 04, 2018 1:54 pm

Hellgate wrote:On inline 4 motors I would typically sync at 4,000. Smoother at cruise speeds.


In my experience, you need virtually no trottle to rev the engine to 4k rpm in neutral, significantly less than what you need to maintain 4000 rpm in top gear on a level road. So while you set sync to that rpm range, the throttle settings will differ. Or am I wrong on this?
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Re: Euro-style dual TM38 flatslide carb installation

PostAuthor: nanno » Tue Dec 04, 2018 3:22 pm

On directly operated carbs you actually have to operate the throttle quite a bit...
http://viragotechforum.com/viewtopic.php?f=12&t=43227 - Nanno's accumulated findings (and blatant show-off) - infos on my TR1's, my performance and reliability mods and a bit of show-casing of the stainless steel exhausts I build

http://greasygreg.blogspot.co.at (My blog - Greasygreg.blogspot.co.at)
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Re: Euro-style dual TM38 flatslide carb installation

PostAuthor: faffi » Tue Dec 04, 2018 5:25 pm

Don't think I've ever observed a carb with direct piston operation in action, but this video of a CV carb during a run is pretty interesting. To me, at least...

https://www.youtube.com/watch?v=zfIPz6ypN4o
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Re: Euro-style dual TM38 flatslide carb installation

PostAuthor: nanno » Sun Dec 16, 2018 3:47 am

The last bit of fine-tuning comes in the shape of having to get a different needle. Specifically one that is a bit richer than the one that is currently in, especially in the first 1/4 of the needle operation.

After quite a bit of research, I found the data for the following table containing the recommended needles for a Mikuni TM38:
Image

As a result I ordered a set of 6FJ40ies, as the bike is running an oversized pilot jet at the moment. (Causes it to run really rich, when hot and give me sub-par gas-mileage.) Which I hope to cure with the richer needle. That being said, I also (sort of) created my magnum opus on how to jet carbs, determine the right needle and various other lesser issues. If that's the sort of thing you're into (and lots of reading), then please go ahead and have a look. Generally, if you guys want to have more info on how I go about tuning carbs poured into articles, let me know and I'll give it a shot - I've got some ideas on best practices, fault finding and others. Mainly because I've been chasing a few on the TR1 and my XS-Triple sidecar (which is also running on flatslides and gives me plenty of headache).

Blog-Post: https://greasygreg.blogspot.com/2018/12 ... ed-to.html
http://viragotechforum.com/viewtopic.php?f=12&t=43227 - Nanno's accumulated findings (and blatant show-off) - infos on my TR1's, my performance and reliability mods and a bit of show-casing of the stainless steel exhausts I build

http://greasygreg.blogspot.co.at (My blog - Greasygreg.blogspot.co.at)
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Re: Euro-style dual TM38 flatslide carb installation

PostAuthor: faffi » Sun Dec 16, 2018 12:34 pm

Will be interesting to see if theory meets real world performance - fingers crossed it will go your way :cl:
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Re: Euro-style dual TM38 flatslide carb installation

PostAuthor: nanno » Sun Dec 16, 2018 2:32 pm

faffi wrote:Will be interesting to see if theory meets real world performance - fingers crossed it will go your way :cl:


Well if it does, you would benefit as well, as there's always some room for improvement on your VM38s :cl:
http://viragotechforum.com/viewtopic.php?f=12&t=43227 - Nanno's accumulated findings (and blatant show-off) - infos on my TR1's, my performance and reliability mods and a bit of show-casing of the stainless steel exhausts I build

http://greasygreg.blogspot.co.at (My blog - Greasygreg.blogspot.co.at)
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Sex: Male

Re: Euro-style dual TM38 flatslide carb installation

PostAuthor: faffi » Mon Dec 17, 2018 3:27 am

Well if it does, you would benefit as well, as there's always some room for improvement on your VM38s


Now you tell me :ops:















:bg:
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Re: Euro-style dual TM38 flatslide carb installation

PostAuthor: Hellgate » Fri Dec 21, 2018 11:04 pm

faffi wrote:
Hellgate wrote:On inline 4 motors I would typically sync at 4,000. Smoother at cruise speeds.


In my experience, you need virtually no trottle to rev the engine to 4k rpm in neutral, significantly less than what you need to maintain 4000 rpm in top gear on a level road. So while you set sync to that rpm range, the throttle settings will differ. Or am I wrong on this?
Yes, the throttle setting is different as you have to open it to get to 4k.
Pete
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Re: Euro-style dual TM38 flatslide carb installation

PostAuthor: nanno » Sun Dec 23, 2018 3:31 am

I gotta edit all the pictures etc. for the blog post in about 10.5hrs, but the visual difference between a 6FJ40 and 6FJ41(stock) is staggering. I do particularly like the fact, that the 6FJ40 looks a lot more like the 6DP01, that I ran with great success in my old VM38-roundslides, which were VERY NICE on the midrange.
http://viragotechforum.com/viewtopic.php?f=12&t=43227 - Nanno's accumulated findings (and blatant show-off) - infos on my TR1's, my performance and reliability mods and a bit of show-casing of the stainless steel exhausts I build

http://greasygreg.blogspot.co.at (My blog - Greasygreg.blogspot.co.at)
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1979 RD250/R5/DS7-hodgepodge (in bits)
Sex: Male

Re: Euro-style dual TM38 flatslide carb installation

PostAuthor: nanno » Wed Dec 26, 2018 4:06 am

Just a quickie: This is the picture to go with the post above:

CCNXo_NGhI/AAAAAAAAD9w/HMBECfJz2gYJG-ydXfJZ7nWp_29QXS3PQCLcBGAs/s1600/P1210001.JPG" alt="Image" class="resize_me" />

As you can see, thee 6FJ40 is a lot slimmer. It looks rather dry overhere, if I can get rid of the inlaws quickly enough, I might give the old girl a quick shakedown and see if this goes in the right direction.

Full blog-post here: https://greasygreg.blogspot.com/2018/12 ... riple.html
http://viragotechforum.com/viewtopic.php?f=12&t=43227 - Nanno's accumulated findings (and blatant show-off) - infos on my TR1's, my performance and reliability mods and a bit of show-casing of the stainless steel exhausts I build

http://greasygreg.blogspot.co.at (My blog - Greasygreg.blogspot.co.at)
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1979 RD250/R5/DS7-hodgepodge (in bits)
Sex: Male

Re: Euro-style dual TM38 flatslide carb installation

PostAuthor: nanno » Sun Jan 13, 2019 3:19 pm

The re-jetting story has come to a (fruitful) end. 6FJ40 is the answer, as are 17.5 pilots and 175 mains.

Starts up straight away, more midrange and a smaller pilot for better fuel economy. I am loving it already. Air-screw needs a bit of tweaking, but I could only ride round the yard as all the roads are salted to buggery.

https://www.youtube.com/watch?v=skjFfFrvof8
http://viragotechforum.com/viewtopic.php?f=12&t=43227 - Nanno's accumulated findings (and blatant show-off) - infos on my TR1's, my performance and reliability mods and a bit of show-casing of the stainless steel exhausts I build

http://greasygreg.blogspot.co.at (My blog - Greasygreg.blogspot.co.at)
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1979 RD250/R5/DS7-hodgepodge (in bits)
Sex: Male

Re: Euro-style dual TM38 flatslide carb installation

PostAuthor: faffi » Sun Jan 13, 2019 3:51 pm

At first I thought "that engine sounds impossibly relaxed to be turning 4k rpm". Then I understood it didn't :bg:

Cool of you to share your findings :GJ:
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Re: Euro-style dual TM38 flatslide carb installation

PostAuthor: nanno » Sun Jan 13, 2019 5:06 pm

Yup that tach is on the task-list for this Winter. *sigh* No such thing as quality anymore, only lasted 116.000km and 37 years and got hammered by multiple instances of the onboard voltage going through the roof... :cl:
http://viragotechforum.com/viewtopic.php?f=12&t=43227 - Nanno's accumulated findings (and blatant show-off) - infos on my TR1's, my performance and reliability mods and a bit of show-casing of the stainless steel exhausts I build

http://greasygreg.blogspot.co.at (My blog - Greasygreg.blogspot.co.at)
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1979 RD250/R5/DS7-hodgepodge (in bits)
Sex: Male

Re: Euro-style dual TM38 flatslide carb installation

PostAuthor: faffi » Mon Jan 14, 2019 2:11 am

Yeah, they don't make them like they used to... :bg:
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Re: Euro-style dual TM38 flatslide carb installation

PostAuthor: dazthebiker » Tue Feb 19, 2019 11:27 am

I've just ordered the same carbs, looking forwards to getting them on. Even if they dont work any better they look so much faster than the hitachis!

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Re: Euro-style dual TM38 flatslide carb installation

PostAuthor: nanno » Wed Feb 20, 2019 6:13 am

You're in for a bit of a surprise then... :cl:
http://viragotechforum.com/viewtopic.php?f=12&t=43227 - Nanno's accumulated findings (and blatant show-off) - infos on my TR1's, my performance and reliability mods and a bit of show-casing of the stainless steel exhausts I build

http://greasygreg.blogspot.co.at (My blog - Greasygreg.blogspot.co.at)
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Sex: Male

Re: Euro-style dual TM38 flatslide carb installation

PostAuthor: dazthebiker » Fri Feb 22, 2019 10:25 am

nanno wrote:You're in for a bit of a surprise then... :cl:


Hopefully!

Do you have any thoughts on intake length? The carb kit i have bought comes with aluminium collars that bolt to the head and then rubber connectors to go between them and the head. So i could either use that option or the standard intake mounting rubber. There's probably 20mm difference in the length of intake between the carbs and the valves using the different mountings. Im not using the standard airbox (having cut all the holes out of the frame and smoothed them over) so carb position doesnt affect anything else for me.

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Re: Euro-style dual TM38 flatslide carb installation

PostAuthor: nanno » Sun Feb 24, 2019 2:15 am

Errm, if they come with collars... they are most likely TM34s, which are too small for this engine and also not the carb I am using...
http://viragotechforum.com/viewtopic.php?f=12&t=43227 - Nanno's accumulated findings (and blatant show-off) - infos on my TR1's, my performance and reliability mods and a bit of show-casing of the stainless steel exhausts I build

http://greasygreg.blogspot.co.at (My blog - Greasygreg.blogspot.co.at)
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1979 RD250/R5/DS7-hodgepodge (in bits)
Sex: Male

Re: Euro-style dual TM38 flatslide carb installation

PostAuthor: dazthebiker » Mon Feb 25, 2019 3:40 am

Definitely 38's as they are here and fitted! bought from Mikuni Oz, they supply new collars to move the carbs back slightly so that the stock air intakes line up apparently. Ive no idea on whether that would work or not since i dont have the intake elbows or the frame ports anymore

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Re: Euro-style dual TM38 flatslide carb installation

PostAuthor: nanno » Mon Feb 25, 2019 4:35 am

Would you care to take a picture - sounds highly interesting what they are doing...

Personally I am led to believe, that with directly operated carbs, you're after some crispy throttle response, which is best achieved by putting the carbs as close to the head as possible. If you bought the TM38s with 43mm throats, the VM38-200 inlet rubbers will be a perfect fit.

Cheers,
Greg
http://viragotechforum.com/viewtopic.php?f=12&t=43227 - Nanno's accumulated findings (and blatant show-off) - infos on my TR1's, my performance and reliability mods and a bit of show-casing of the stainless steel exhausts I build

http://greasygreg.blogspot.co.at (My blog - Greasygreg.blogspot.co.at)
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1979 RD250/R5/DS7-hodgepodge (in bits)
Sex: Male


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