Yamaha TRX850 Enthusiasts Forum

Sucki sucki

negative pressure in the crankcase! I suppose the only disadvantage might be more regular cleaning of the filters hmm thinking about it a bit more... wont the negative pressure make it harder for the piston to go up the barrel or the action of the piston going up might reduce the flow of air going to the carb....

Well I suppose you will let us know!, like the thinking though!

shows that you are thinking too...nice attention to detail.
be interesting to analize the oxygen content in the extractor tube and it would be..hot..gass yes?
and does your home watering system still work..?
nice one

You might want to consider some form of PCV. I've used one of these in my Norton:
http://www.mikesxs.net/product/15-0677.html
but vent into the oil tank rather than the carbs.
This is sufficient to produce a partial vacuum (i.e. a lower pressure than ambient) in the crankcase. This is said to be worth a couple of HP, to which I am rather skeptical, but it certainly makes the engine more oil-tight.

Great job, nice plumbing

Got to make clear that i think this is a spanish TRX (found on the TRX project webpage) not mine, not that good on plumbing!

Not a good idea. Will provide almost no vacuum unless the filter is blocked. The sucking/blowing action of the breather can play havoc with the normal wave action in the inlet tract, which is why manufacturers plug the breather into the airbox outside the filter even though this can foul the filter with oil mist. Using a fast acting one way valve in the breather line will produce much more vacuum and cut pumping losses. I use a brake booster valve. The valve must be capable of following the pumping of the crankcase which rules out normal car pcv valves.

lenny wrote:Not a good idea. Will provide almost no vacuum unless the filter is blocked. The sucking/blowing action of the breather can play havoc with the normal wave action in the inlet tract, which is why manufacturers plug the breather into the airbox outside the filter even though this can foul the filter with oil mist. Using a fast acting one way valve in the breather line will produce much more vacuum and cut pumping losses. I use a brake booster valve. The valve must be capable of following the pumping of the crankcase which rules out normal car pcv valves.

Cheers for that input!

lenny wrote:Not a good idea. Will provide almost no vacuum unless the filter is blocked. The sucking/blowing action of the breather can play havoc with the normal wave action in the inlet tract, which is why manufacturers plug the breather into the airbox outside the filter even though this can foul the filter with oil mist. Using a fast acting one way valve in the breather line will produce much more vacuum and cut pumping losses. I use a brake booster valve. The valve must be capable of following the pumping of the crankcase which rules out normal car pcv valves.

Yep, it`ll also play havoc with fuelling being that direct too. Think hot oil mist laden air when the motor`s being worked hard in perhaps high summer air temperatures, especially those regularly found in Spain.
Weak mixtures are in many ways worse for an engine than slightly rich ones!

But as standard dosent the crank cases vent into the airbox? And they run OK.

Lenny`s post explains this.

I always believe that 4 strokes need good Crankcase ventilation. Plumbing into a vacuum space is not always ideal.

Killerwhale wrote:Got to make clear that i think this is a spanish TRX (found on the TRX project webpage) not mine, not that good on plumbing!

I really think it is your bike Killer, and you are now coming out of the PCV closet.