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Bf 150 Rough Idle Skipping a beat

OK. Thanks for the clarification. Still would like to see what Mike says about that.

Have you eliminated to possibility of a vacuum leak?
 
Hmmmm so you bypassed the two filters and the low pressure fuel pump. Interesting. I assume that the portable tank was elevated above the VST in order to dump enough fuel into the VST. Why not also plug the portable tank directly into the low pressure fuel pump via the fuel line coming out of the low pressure fuel filter? That would eliminate the LP fuel pump as the source of the problem.

On my 225, there is a vacuum hose that comes off of the intake air bypass control which goes into a diaphragm that activates a spring-loaded set of bevels in the intake manifold. When changing out the high pressure fuel filter it is necessary to loosen that diaphragm and move it aside. It is real easy to forget to check and re-connect the vacuum hose when you re-install the diaphragm. Also, the diaphragm can fail. So gently push the arm back into the diaphragm, and hold your finger over the opening in the tube that the vacuum hose attaches too. When you let go of the arm, it should come out a little bit and stay there until you remove your finger. If so, then the diaphragm is operating correctly. If not, the diaphragm is leaking air and must be replaced. Unfortunately, it looks like a replacement is not available, since that diaphragm is part of the entire IAB assembly.
 
Thanks for your help
Yep diaphragm isn't in the way for the 150, although I did as you said and the arm does acuate when the hose is removed. so I am guessing that works.
I can attach an (elevated) portable tank straight the the high pressure fuel pump. and manually pump the bulb to eliminate the low pressure pump from being faulty.
The part I cant work out if I remove the hose part 7 from the intake manifold it runs smooth
http://www.boats.net/parts/search/H...F150A4 XA/INTAKE MANIFOLD INJECTOR/parts.html
The intake manifold sucks air from where the hose attaches
 
I'm sort of out of ideas. Hopefully someone else will jump in that knows the 150 intimately.

I don't know the specs, but would certainly check the vacuum pressure. Are you sure that your timing is set correctly?
 
Thanks for the help - Ok so I plugged elevated portable tank into straight into vst to bypass low pressure pump - no change. So it could be high pressure pump - throttle position sensor or maybe something else. Time to book it in to another mechanic
 
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