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MT-11 Blowing Air instead of exhaust.


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#1 hormehouse

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Posted 15 March 2015 - 01:16 PM

I recently bought a MT-11 and had it shipped over to Hawaii. It is only running on the right side and blows cold air out of the left pipe. I rebuilt the carb with no change so I swapped both complete carbs to see if the problem followed. No change. I swapped plug wires and the right still runs good but no change on the left. Verified spark from the left plug and installed new plug just in case. I pulled off left valve cover and intake valve had about 1/4" gap so I closed the gap and now get occasional "Pop" but still won't run. Pulled carb and verified the intake valve is opening but it still doesn't fire. Verified gas to carb too. I am out of ideas and the closest motorcycle shop is a 90 minute drive away, way too far for a 1 cylinder ride. Any ideas or suggestions to try, being new I don't know a lot about these bikes but am learning really quickly!

#2 shoetou

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Posted 15 March 2015 - 04:02 PM

the carbs may need the needle changed use a Kohler needle one if you do a search on here you can  find the part # . the Russian needles the o ring at the end go south and the carbs don't work . then start from the beginning and set your valve lash timing and then set carbs and then balance them  out . you can find valve specs on here too. I did have a coil go  bad on my  16 one side quit working used a Ural one . some people use Harley coils
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#3 dneprlover

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Posted 15 March 2015 - 05:16 PM

If you have found a 1/4" valve gap, you have probably lost the valve stem cap off that valve. Check it is still in position and if not, search for it . Set the valve gaps per the book and do a compression test. I can't post links using this tablet but someone will point you to Charlie Harvin's site for the online manuals. Which ignition system is fitted under the front cover?

Best to start at the beginning and work logically

Valve clearances
Ignition timing
Fuel supply

How familiar are you with Dnepr's and what are your mechanical skills. How we pitch the advice depends on your answers.

#4 Russ Noe

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Posted 15 March 2015 - 11:28 PM

Valves first, as recommended by dneprlover!
~RN

#5 hormehouse

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Posted 15 March 2015 - 11:57 PM

When I pulled off the valve cover there was a small metal disk which, looking at my manual, appears to be a valve cup but my manual doesn't show where it goes exactly. I'm thinking a compression test is a really good idea (Thank you Dneprlover) as a next step I believe that will tell me if the valves are not doing what they are supposed to be doing. Do you know what the compression range is on the 650cc motor? I can't wait to be able to go riding! Thank you all for your help!!!

#6 lobofuego

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Posted 04 April 2015 - 08:11 AM

In the perfect world... with atmospheric pressure at 14.7 psi...and a compression ratio of 10.1...10x14.7 would be 147 psi as the maximum pressure available....so with a ural at about  8.1 that would be about 120 psi...

#7 hormehouse

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Posted 04 April 2015 - 11:43 AM

I have tried everything I can think of and all of your most helpful suggestions and still nothing, I'm hoping to take it to a BMW mechanic early next week. I have not been able to check compression but have checked and oiled the rings, replaced head gasket, adjusted the valves, verified spark and replaced the plug and still nothing. At higher than idle RPM's it feels like it's starting to fire both cylinders but as soon as the RPM's get lower the left cylinder still blows weak we cold air.

#8 lobofuego

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Posted 05 April 2015 - 09:17 AM

If only air is coming out ...then fuel isn't going in....???, I would run it and chuck a bit of fuel into the carb, and see what happens!

#9 hormehouse

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Posted 05 April 2015 - 11:18 AM

I swapped carbs knowing the right cylinder is running fine and thinking if the left one is a problem them the problem should follow the carbs. The right one worked fine with the left carb and the left cylinder still doesn't run… I've not tried putting gas into the intake port, wasn't sure how much to try. Thank you for your suggestion!!

#10 lobofuego

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Posted 10 April 2015 - 08:58 AM

Oh a little capful  should cause her to fire...if not and its not the carb...can only be an air leak!!....what we used to do, ! is braze a hollowed out plug to an air line adaptor, and pressurise cylinder, this showed up as a hiss of air, and is called a cylinder leakage test....but I do feel that this has a simpler explanation!!

#11 Muravey

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Posted 12 April 2015 - 05:41 AM

Sounds indeed like an air leak. I've had it happen for a number of reasons, like worn-out valve seats, an overly tightened valve, a bad / loose / blown head gasket, a carb adaptor flange (if applicable - some older heads have vertical carb mounting holes that need adaptors for the "newer" K-6x carbs) that discretely nudged itself into the cylinder's cooling fins and led to a crooked head installation etc.

First two photos below show what such a flange (third picture) can do to the sealing surface of the cylinder and gasket if it doesn't clear the fins properly and forces the head to be tightened at an angle relative to the cylinder. Note the wide spiral-like dent in both surfaces. That caused a loss of compression. Fourth picture is the piston working in such an environment. Loss of compression and running below optimal temps result in impressive carbon build-ups. Still ran though, I had no idea about the issue until I took the cylinder apart to replace the gasket underneath it. :)

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Or it may have a simpler cause. One nice summer night I was merrily ploughing down the motorway at an incredible 100 km/h when I noticed that the right-hand cylinder would cut off if I let the revs drop below WFO. I stopped to inspect the issue after I decided that enough was enough. It turned out that I hadn't properly fastened the carburetor to its head on that side and it had almost fallen off. :) One heck of an air leak!

Do pardon if the following suggestions are old news or if they come off as pretentious.

Valves - check for leaks

Are you sure your valves don't leak at the seats? A simple leakdown check you can perform with the head out involves pouring some gasoline through the intake and exhaust ports. One at a time, to avoid drenching yourself in petroleum products. Hold the head at an angle so that the gasoline goes towards the valve seat through the port. If the gasoline doesn't immediately begin to seep between the valve head and seat (should take a few seconds until it does), you're good. If it seeps / pours right through, a valve job is in order.

But don't stress yourself too much. Remember that these are simple machines built to run even if they hurt a lot. Before properly repairing the heads on my bike, they had worn valve guides, two of them had been press-fitted in the heads from the wrong direction, the valves were leaking and so on. Still started on the first kick, idled and ran.

Valves - setting the clearance

Easiest way to set the valves is to bring the engine to TDC (there is usually a "///" or "B" mark for TDC on the flywheel just after the "P" mark, as explained below) two times. First for a piston, then for the other. If there's no mark for TDC on the flywheel, just take out the spark plugs and use a screwdriver or any other sort of relatively rigid feeler through the spark plug hole to tell when the piston is at its furthest out. At that point, one of the pistons will be between compression and combustion, meaning that its corresponding valves should be completely shut and there should be a gap between the rockers and valve stems. Check the gaps on that side now.

The manual wants a fancy, pretentious, BMW-airhead-like 0,07 mm gap between rocker and valve (with or without that valve cap, forget about it if you don't have it). I found that a loosey 0,1 mm gap allows for all manner of Dnepr-like expansions and will harm naught. If the rocker has a lot of axial play on its shaft between the aluminium mounting pegs, this is a great time to shim that play out. Leave just a wee bit for expansion. Double-check your work and then rotate the crankshaft another 360 degrees to bring the other piston between compression and combustion. Check it, set it.

Ignition - timing

In Dneprs, I noticed that the left cylinder also tends to act funny (particularly at idle) when the timing is too advanced (spark occurs too early). Might also have to do with the lobe placement on the camshaft, apparently there aren't two identical ones out there.

Anyway, one way to set the timing is to pull out the rubber plug out of the crankcase on the left side to reveal the flywheel inspection hole. Gently hand-crank the kickstarter until a P mark appears on the flywheel (keep eyeballing it through the inspection hole). Take off the unbelievably thick aluminium timing cover off the engine (the one behind the front wheel, it's fastened by a single 14 mm nut to its stud) and, after that, the small tin cover off the timing advance mechanism. Now turn the ignition on and (I assume that you've got the mixing-bowl-of-doom-type centifugal advance ignition on your MT-11, see second picture below) use a relatively small flathead screwdriver to pry the timing cam's counterweights apart. The spark should occur when the counterweights are completely open. If not, adjust the stator by means of loosening its bolts and rotating it either way. If you've got the newer Russian / Ukrainian electronic contactless ignition, forget about checking the counterweights - there are none. Just get it started (advance it if you have trouble firing it up) and then jiggle it around. Or viceversa. :)

Regardless of the ignition system, I strongly recommend you proceed to manhandle this setup after you get the engine running. It'll often be the case that a better timing advance will be achieved on-the-fly. Slowly retard or advance it while it's running until you get the highest stable idle rpms. Keep in mind that carb tuning does influence this. Too much advance will cause detonation - you'll know you've advanced it too much when the idle goes rough and the bike starts potato-potato-ing like a Harley. Retard it too much and you'll get a rock-solid idle, but you'll also make it the slowest thing on the planet.

Ignition - coil

As others have pointed out, I wouldn't rule out coil woes. The original hand-wrapped coils are nigh crap, and so are their seemingly more evolved successors that have traded textile wrapping for shrink-tubing. Went through a handful of either of them until I gave them up. Would they spark? Yes. But would they work properly? Nope. Difficult starting, colossal stuttering at low revs, intermittent cut-offs on acceleration (opening up the throttle would let in lots of gas that the weak spark would be unable to ignite).

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Having just replaced a sexy Nippon-Denso twin coil yesterday due to it shorting out from overheating, I can say that you should not believe a spark when you see it. Bike went dead all of the sudden - always happens in a convenient place, this time right in front of my home after three hours of unbelievably thick traffic on a warm spring day. Checked everything, leaving the coil for last - would you suspect a coil right off the bat if it was sparking? I didn't, thought it was the contactless ignition to blame. Hell, it even fired on one cylinder after I changed the plug with the rustiest spare I could find (always the best plugs!), though the idle was clearly rough and would die off after a few seconds of sputtering. The spark was visibly weak, a thin white asthmatic spark. Blame it on the sunny weather at first. An ohm-meter then revealed that the bad coil had a resistivity of 2,4Ω instead of the 3,7Ω shown by a good one. To my simple mind, this means there's a short in it somewhere and that it can no longer produce that high a voltage to generate a strong spark.

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A year ago, when I installed this coil as a fix-all solution to my ignition woes, I didn't give its placement a good thought. At the time I was just too happy about having found a Japanese coil that fit in place of the original without modifications. It did indeed run great while it lasted. But these engines run HOT and them engineers picked a bad place to mount all this sensitive electrical equipment. It was probably less of an issue when they came up with the idea sixty years ago, with all that three-cars-a-day-traffic and cooler Ukrainian climate. Not to mention the occasional water-cooled (read: snow- / river- / bog-cooled) adventures.

So if you can pick up a higher-quality twin coil like this one (off a '90s Suzuki GSXF and quite a few other models, I think), do so. Just try your best to install it someplace cool, maybe externally, if space is abundant and clean looks are not your main concern. Or put some serious holes in that aluminium cover to help cool stuff down.

Over here, due to a soon-to-be-history abundance of old cars and motorcycles, we sometimes have an easy time locating 6-volt coils. You can use an alternate coil setup (BMW airhead style) with two 6-volt single-lead coils. One HT lead for each cylinder. Connect the coils in series: to do that, identify the positive and negative connectors on both of them, they've got one of each; run a kill-switched +12V to the positive terminal of one of them, then run a wire to connect that coil's negative to the other's positive; the negative of the 2nd coil connects to the ignition contact breaker (classic points or whatever replaces them now). They're going to work as a single 12-volt coil, but each will have its HT lead connected to a separate spark plug. Got a friend whose '69 M63 Ural works like a charm using this setup.

Carb tuning

You said you already tried swapping carburetors to no avail, so they're probably not the main culprit here. When they do step forward as the next thing that has to be set, pick one side and screw in the carb's mixture screw (they be vertical, on the side, just above the float chamber) until the rpms drop, then slooowly unscrew it until you get the highest stable rpm on that cylinder. After that, reduce the idling speed (if it's considerably higher now) by screwing in the top bolt (K-63 / K-65) or unscrewing the small side screw (K-68 / Karteh VDC-03). Repeat until you needn't adjust it anymore, then move on to the other side. Keep your cylinders ventilated if you're going to do it for long, a simple fan or two will do the trick. And take off that timing cover while you do it!

Water in the float chambers is a reality for these carbs and they don't really like it in huge amounts. Good luck! Let us know what you find. ;)

#12 racepres

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Posted 12 April 2015 - 08:52 AM

Pretty Long Winded...I don't type that good!!! But, very well done, and a good tutorial for the Uninitiated....
Good for you Muravey :cheers:

#13 hormehouse

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Posted 12 April 2015 - 03:51 PM

A HUGE thank you Muravey for your most excellent and helpful post! at this point it seems the float valve needle isn't shutting off when the float goes up effectively drowning the cylinder in gasoline. The mechanic says it runs great above 1/4 throttle but still doesn't idle properly. He is adjusting the carbs then will sync them and I am hoping I will have my bike on the road this week! I will let you all know what the final diagnosis is. Thanks again to all, what a great group of Russian Iron lovers!

#14 Muravey

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Posted 12 April 2015 - 05:42 PM

If only my problems could be solved by changing the float needle! :P Glad you're on the right track! Sorry for overdoing it, but thank you @Racepres and @Hormehouse! :)

As @Shoetou pointed out, these float needles rely on an o-ring to shut off gas. Kind of makes you wonder why they bothered to make them resemble actual working float needles in the first place. As a quick roadside fix, we would buy a cheapo refillable gas lighter, break it apart and salvage the valve o-ring. It fits on the carb float needle, but some of them are made of low-grade rubber and expand somewhat after prolonged exposure to gasoline. Get rid of them if they do and buy another lighter. :)

Can't wait to see some pictures and vids of your bike.

#15 racepres

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Posted 13 April 2015 - 08:18 AM

Forget the Lighter!!!!
If the think has those o-ring float needles...It is Crying for Walboro needles...Made an Unbelievable difference in my MT-11

BTW When switching to Walbore Needles, make sure that one of the o-rings does Not get left behind in the Seat!
Ask me why I know that!




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