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small pressure cookers or carburetors?


sunstroke
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the engine of my K750 is stalled because of an oil leak while driving .... :flame-on!: I bought new cylinders and pistons out of Moldova, however, this was not a success . The Pistons got stuck once the cylinders ran warm, by placing other old Pistons, this problem was solved. After having assembled everything, the Carburetors had changed in to small pressure cookers ...

Does anyone have experience with this?

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Without some fairly sophisticated measuring equipment [$$] you can't measure accurately at Home...I use a Micrometer of the correct size on the pistons, and a Bore guage with the same mic on the cylinders...and my method is imperfect...some can do a better job than I!!!

Vapor lock can only keep gas from entering the carbs...the Typical russian carb has a "tickler" on it that will tell you quickly if you have gas in the bowl or not.

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I do't normally buy new cylinders with pistons, I normally buy new pistons and take the old cilinders with the new pistons to a'n expert.

I was wondering if there was a house method, from what I understand from your story, you're professional but also critical ....

you're right about vapour lock, but this is what happened........ probably the cylinders are running too hot or there is too much heat comming through the carburetor gaskets. On some oldtimers you see a bakelite spacer between the cylinder and the carburetor, but I have not found this for a Dnepr ....

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To those who wish to fit pistons at home a "feeler gauge" will fit them fine. a size of .004 to.005 of inch will give proper clearance, also there must to a end gap on the rings of .013 Minimum, and if you flog it from time to time , a few more thousands, will not hurt a thing. For pressure cooker carbs, go back and make sure that you have at least .004 thousands of valve clearance.......Ken...... Look for a feeler gauge at any auto parts store or machine tool store.

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I am not sure about the K750, but on the Mt 10.36, 11, and 16 you can buy NOS or EU quality pistons and cylinders which are already balanced and have been fitted in the place of manufacture. All you need to do is install them. For example, there is a set of 650 pistons, rings, and barrels (I think NOS) on Ebay UK right now for £65 and £25 postage to the UK probably double to the US. I would imagine this is the same way for the 750 from uralzentrale.com, motoboxer.com, or oldtimergarage.com and would be your easiest "at home" method.

 

As for vapour locking, it is a problem still on the ohv engine if you idle for too long, i.e. taking an hour or more to balance the carbs because your to cheap to buy a twin tune :) The sv K750 will fit a ohv 650 heat shield which can be purchased for cheap but honestly, buy some carbon fibre sheet on ebay and make your own. Seriously helped my problems.

 

Another point to note, is I assume you are in North America or the UK. As such the octane rating you are using is probably around 92-95, that is going to burn a lot hotter and require a lot more compression than what was being used in Russia/Ukraine when the K750 was in production; the 650 until the late 80's early 90's was from the factury to be used on 78-85 octane, so the 750 which I believe ended production around '66 was probably to be used with octane ratings between 65-75. The only really good solution for it is get some, what we call in the UK "EU quality" pistons and cylinders; these are simply manufacture to a higher quality standard and intended to be used with modern fuels. I am sure that there are companies in the US who produce the same kind of quality. They are typically 50-60% more than the price of NOS parts (650 ones usually are around £155).

 

As racepres said, if pressure is coming out of your head into the carb and intake, timing is suspect. If it was an OHV engine I would say check your valve lash first but I don't know if that applies to a SV. Racepres is spot on with their suggestion with the ticklers, that is how I found out mine was vapour locking.

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