Motobecane air leak after warming up

I have already checked all the usual culprits but no luck. Need to do a leakdown test but wanted to see about any other ideas. It runs well until the head hits about 250 and then develops a serious air leak

Re: Motobecane air leak after warming up

tighten yr head-nuts

Re: Motobecane air leak after warming up

Moped Lar (OFMC) /

Probably leaking around the seals when it heats up.

Re: Motobecane air leak after warming up

How are you looking for vacuum leaks? Most use carb cleaner but that vaporizes on contact with anything hot and will get sucked in to the carb or float away, You need to use something heaver then are so that it falls to the ground use a propane or butane torch (unlit) the engine will rise in RPM or die when you hit the spot.

Re: Motobecane air leak after warming up

If you are using any chemical 'trick' to find vacuum leaks you are wasting time and chemical but at least you will gain in frustration.

Do a proper leak down test by checking for VACUUM leaks. Block intake and exhause and draw air out from the spark plug hole with the piston at BDC. If there is any leak you will not be able to obtain a vacuum with just lung power.

(Some folks may need to ask help from someone who does not smoke or vape)

If your Moby is performing poorly only when hot, check the quality of the spark because most times that is the condenser or the antiparasite plug cap slowly dying. Spark should be blue and snappy, bright enough to be seen in just the bikes shadow and not just total darkness.

> Jeff Parr Wrote:

> -------------------------------------------------------

> How are you looking for vacuum leaks? Most use carb cleaner but that

> vaporizes on contact with anything hot and will get sucked in to the

> carb or float away, You need to use something heaver then are so that it

> falls to the ground use a propane or butane torch (unlit) the engine

> will rise in RPM or die when you hit the spot.

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