Running rich

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Harijsk
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Running rich

Post by Harijsk » Mon Nov 13, 2017 3:44 am

Looking for advice.
Just rebuilt the MT11 engine - new pistons, electric ignition, K65T carburetors with size 55 main jets(have no ideo what's with the idle jets :( ), needles are set to the most deepest position, air mixture screws are full two turns out, but still running rich (I can see black smoke coming from the exhaust, I can smell the petrol and plugs turn black and die after few hours of running), floats were set according to some K65t pdf found on the internet.

The question is - should I look for smaller main jets or is there something else I should tinker with?

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Re: Running rich

Post by Snakeoil » Mon Nov 13, 2017 11:26 am

First thing you need to do is Google the Amal website and find their tuning guide. You asking if changing the main will help your problem would indicate that you do not understand how carburetors work. I'm not dumping on you here. But you need to learn how they work and then troubleshooting and tuning will be something you can do on you own.

If the idle screws are indeed air screws, and you have them out two turns, that is 1/2 turn more than what is typically where they should be. And you did not mention if that setting provides the best idle. Regardless, having them out means you are adding air which in turn indicates that your pilot jets (aka idle jets) are too big. The engine does not even know what size main jet is in the carb until you get to about 3/4 throttle.

Rather than have you do it, here are two links that will get you better informed. Simple slide carbs are all pretty much the same from an operational POV. So, these links will get you well grounded.

Bushman's tuning tips - http://www.jba.bc.ca/Bushmans%20Carb%20Tuning.html

Amal Tuning Guide - http://amalcarb.co.uk/downloadfiles/ama ... _guide.pdf

Mikuni Round Slide Tuning Manual - http://www.mikuni.com/pdf/vmmanual.pdf
Regards,
Rob
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Re: Running rich

Post by rivers » Mon Nov 13, 2017 1:51 pm

I know nothing of Dnepr specs and even less about the K65 carbs, but as Rob said though carbs all have their specific specs depending on application but they all pretty much work the same so for diagnostics basic "theory" is a good thing to have a firm grip on. I have no idea what size jets you should berunning to get even ballpark but depending on how the K-carb manufactures assign the size number 55 mains sound very lean for a 650 motor. Your idle/pilot jets will be significantly smaller in size and number and that's where your issue likely is. not the mains. Most carb manufactures number their jets by acctual hole size but some assign an arbitrary number to their jets and all it means is bigger part number = bigger jets. So 55 mains are either an arbitrary assigned part number or they're already crazy lean (be the same scenario with the pilots). You'll need to find a real KMZ guy to give you correct jetting specs for your motor and carbs. With your quickly fowling plugs you're definitely not getting a clean/complete burn but is it from a too rich mix or weak spark? If it were me the first thing I would do "before" tweaking the carbs is install brand new fresh plugs, ground them on the cyl and test for quality of spark. No matter what you do good or bad to the carbs is going to fix a limp spark issue. I'm no real mechanic but have learned chasing your tail just results in one really tired dog, with no satisfaction to be had. :(
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Re: Running rich

Post by Wildhorse Cafe » Mon Nov 13, 2017 2:04 pm

Harijsk wrote:Looking for advice.
Just rebuilt the MT11 engine - new pistons, electric ignition, K65T carburetors with size 55 main jets(have no ideo what's with the idle jets :( ), needles are set to the most deepest position, air mixture screws are full two turns out, but still running rich (I can see black smoke coming from the exhaust, I can smell the petrol and plugs turn black and die after few hours of running), floats were set according to some K65t pdf found on the internet.

The question is - should I look for smaller main jets or is there something else I should tinker with?
Make sure your air filter is clean, you'll be surprised. :roll:
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When you set out on your journey to Ithaca
pray the road is long , full of adventure, full of knowledge
not expecting that Ithaca will offer you riches
Ithaca has given you the beautiful voyage

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Harijsk
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Re: Running rich

Post by Harijsk » Mon Nov 13, 2017 2:52 pm

Air filter - new.
Okay, I made a mistake describing my situation. Size 55 is for choke., Main jet is 165. (got them with a repair kit from ArbaletUkraine)
And I do have a fair knowledge on how carburetors work, and if I had jets with which to size down, I wouldn't even post here, would just go down and check what happens.

Do idle jets come in various sizes? I've been googling all over for jets, but have failed to find various sizes for MT's.
But now I'm gonna resort to soldering them shut and redrilling to a smaller size.

btw regarding electronics - it was running perfect with mikuni CV carbs(maybe a bit lean), meaning it's only a carb issue, had to remove them though due to them being too big for this engine.

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Re: Running rich

Post by dneprlover » Tue Nov 14, 2017 6:49 am

You have several problems, the carb jets will not be one of them.. Black smoke is usually burning oil. Compression test results?

First , dismantle the carbs and clean them out, blowing through all orifices with an air line. This should always be done with all East European or Chinese carbs before installation.
Put the carbs back together with the mixture needles in the middle slot and the idle mixture screw about 1 and a half turns out from soft seat. Pay special attention to the seals and seating of the enricheners.

With no float bowl or gasket fitted, turn the carb bodies upside down and set the floats so that the seam on the side is parallel to the carb body joint face when at rest. This distance should be 13mm if correct.
If the float needles are oe soviet with the tiny washer pressed on? Get rid of them and fit Walbro or Kohler needles.

K65 are generally good carbs and unless you have been sold cheap Chinese copies, I can't see any obstacles to setting them up. Your troubles will centre round the floats or enricheners if it is carb related.

PS.It also helps if you introduce yourself, state your location and say ' please' sometimes
Neval BMW/MT11 800cc hybrid, Neval 2wd MT10-36, Neval standard MT10-36, Neval MT16, another MT11, BMW/MB650 hybrid , K750m and an MB750 with locking diff.

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Re: Running rich

Post by Snakeoil » Wed Nov 15, 2017 11:55 am

Black smoke is usually burning oil.
On what planet is black smoke an indication of burning oil? That is 100% incorrect.

Blue smoke is oil. Some may see it as white smoke. Black smoke is fuel and an indication of a rich fuel mixture. Dry black soot on the plugs is another indication of a rich mixture. Black OILY soot on the plugs is an indication of oil burning, but can be both since the oily soot masks the powdery soot of a rich mixture.

If you are planning to drill solder and drill pilot jets, you will need a set of micro drills. If you have done this before, then you already know that.
Regards,
Rob
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Re: Running rich

Post by dneprlover » Wed Nov 15, 2017 12:25 pm

Snakeoil wrote:
Black smoke is usually burning oil.
On what planet is black smoke an indication of burning oil? That is 100% incorrect.

Blue smoke is oil. Some may see it as white smoke. Black smoke is fuel and an indication of a rich fuel mixture. Dry black soot on the plugs is another indication of a rich mixture. Black OILY soot on the plugs is an indication of oil burning, but can be both since the oily soot masks the powdery soot of a rich mixture.

If you are planning to drill solder and drill pilot jets, you will need a set of micro drills. If you have done this before, then you already know that.
Forgive me please. I'm colour blind and anything remotely dark is burning oil to me.
Neval BMW/MT11 800cc hybrid, Neval 2wd MT10-36, Neval standard MT10-36, Neval MT16, another MT11, BMW/MB650 hybrid , K750m and an MB750 with locking diff.

Harijsk
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Re: Running rich

Post by Harijsk » Wed Nov 15, 2017 2:51 pm

Black is for rich, blue is for oil - That's engine 101.

I have the drills, and it was a bit challenging without a proper drill head and doing it with a hand too. And now it's too lean when revving up, gonna redrill it to a larger hole (previously it was ~1+mm, new one is 0.6mm, which was expected to be too smal). btw, drill was sticking in the solder, thus had to use oil when drilling it.

But now I must ask about the principle of the carburetor, as I understand from all the reading and googling, and comments here, the Idle should not be influenced by the main jet, or am I wrong? As in I could completely solder shut the main jet and it should start and idle? :D
Cause now I have a feeling it's idling too rich too (will confirm in upcoming days)(choke valve works correctly), do I really need to look in to the pilot jet, or I have to tinker with the external air mixture screw and that's it?
I'm even considering using O2 sensor for fine tuning, but I'd need to use the wide band probe which is a bit too expensive just to play around.

And those who complained about I not using "thank you", "please" and so on - I'm a practical person, I don't care for small talk. If someone needs help, I help no matter how many "pleases" and "thankyous" are in the question/sentence. And if I need help, I get to the point. I wouldn't want to read 100 pages of BS to help someone with maybe a simple yes or no question.
And regarding all the information being on google - I know, I've read some of it, but I'd like to believe forum is a place for discussion, and conversation and some advice. Thus if I wanted to read google top to bottom or dissect and research russian designed carburetor - I would, but I prefer discussion and opinion from people with at least some experience.

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Re: Running rich

Post by Red Dwarf » Wed Nov 15, 2017 3:31 pm

Harijsk wrote:But now I must ask about the principle of the carburetor, as I understand from all the reading and googling, and comments here, the Idle should not be influenced by the main jet, or am I wrong? As in I could completely solder shut the main jet and it should start and idle?
I can detect a difference in cold start behavior when I change main jets.
It's very small, as in changing the length of time I need to open the enricheners in cold weather.

I believe you can eliminate the main jets and successfully start,idle and make useful power at partial throttle.
I'm not going to try it though.
Those main jets are an important part of our cooling systems. :cheers:
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Re: Running rich

Post by Snakeoil » Wed Nov 15, 2017 9:06 pm

Theoretically, you. Could remove the main and you would not know until you got to 3/4 throttle.

Brit bike riders have reported finding the main in the bottom of the bowl and bike ran okay.
Regards,
Rob
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40 Pilots, 122 Mains
Before you say something stupid, always ask yourself, "What would Harpo say?".

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Re: Running rich

Post by Peter Pan » Thu Nov 16, 2017 12:07 pm

Possibly with a Brittney running at low revs why not. I believe the Norton did it once and was just spitting a bit more then normal. The Japaneese high revers do not like to go with the main jet playing "Maraca" in the bowl. Eventually some when once upon the time I learned to find the right torque spot between loose, fix and broken.
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Re: Running rich

Post by Harijsk » Wed Nov 22, 2017 1:52 pm

Ok, my carbs sometimes are overflowing, mostly always I think, float needles are not doing their job or something there.
Any opinions on PEKAR K-68? as in are the float needles by default better or are they the same crappy $#!+ as previous models?

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Re: Running rich

Post by Peter Pan » Wed Nov 22, 2017 2:02 pm

On Jawa carb the needle used to become sticky. A thorrow bath in a strong solvent like thinner or carb cleaner optimum in a ultrasonic cleaner used to make the small spring loaded tail working smooth again. Needed to do that every half a year.
Sophie Travelair = Patrol 2013
8 weeks 12.000km Oregon-Alaska-Oregon
With a DIY foam air filter the rig runs well even in tropical rain = :moto:
Final drives: 1. at 5000km, 2. at 34.000km(+friction plates) 3. at 42.386km
transmission: 1. 40.000km. 2. installed
Engine: 1. 43.388km crank replacement: Back on the road since 23.Okt.2019 :party:

The Avatar are 2 rice grains stating life's essence:
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=> Attitude makes the difference!

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Re: Running rich

Post by rivers » Wed Nov 22, 2017 2:20 pm

Harijsk wrote:Ok, my carbs sometimes are overflowing, mostly always I think, float needles are not doing their job or something there.
Any opinions on PEKAR K-68? as in are the float needles by default better or are they the same crappy $#!+ as previous models?
Could be a bad needle or seat but could also be a sinking float. If they are solid composite, when old they can act like a sponge. If hollow plastic or brass they can get holed and take on fuel. Those are easy to check. Pull them and submerge them under water and look for air bubbles or shake them for any sloshing/weight movement.
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