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Old 07-22-2012, 05:42 PM   #80 (permalink)
renault_megane_dci
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Quote:
Originally Posted by redyaris View Post
...ferther to the problems of the VT500 V-twin; the rear cylinder is inadequitly cooled because it is shielded by the front cylinder, the solution Honda uses is to put a larger main jet in the rear cylinder carb [Honda VT 500 front #112, rear #122] this reduces the heat generated by the rear cylinder [cheep and effective]. the normal main jet size for a 250cc cylinder is #110 [Honda CB250].
So by improving the cooling of the rear cylinder the main jet can be reduced to #112 the same as the front. This will also improve fuel econonomy. may even be able to go to #110 main jets.
The way I plan to improve the rear cylinder cooling is with a small 1.9 watt fan [solar powered] aimed at the rear cylinder & head, from the side. This may work well because the cylinder and head are fined, just like an air cooled engine! In fact when at the Honda dealer I looked at the new V-twins; they are all fined like an air cooled engine even though they are liquid cooled?! With this set of modifications I may be able to get into the 80 -90 mpg range consistantly, and no poor/marginal cooling isseus...
I don't know a thing about this engine in particular but what if, due to packaging / design issues, Honda prefered the bigger jet solution over a properly designed cooling circuit ?

Is the water from the rear cylinder coming straight from the cold side of the rad ?
If not, I would mess with the water pipes first.

The small fan concept is not ideal because those fan become useless at speed and I believe it is where you have your cooling issue.

How about a bigger rad now that you have room ?
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