89 Mercury 150 XR4 Black max

[Princechuck]

I have a 89 Mercury 150 XR4 Black max, it was running bad, cutting out and hard to start, I have rebuilt the carbs several times, new float seats and jets installed with all new gaskets, it ran like a champ for about a week and started running bad again and hard to start, after talking to local mechanic I found only firing on 2 cylinders on 1 side, but would start and idle correctly, that is key words ( would Idle correctly) I purchased new switch boxes and installed them, them was harder to start than ever and back fires badly. I then bought a new stator and installed, now it will start easier but wants to Idle at 4000rpm, I found some air leaking around the carb gaskets and fixed that issue, but still idles around 2000-3000rpm I can't get to Idle down. Sorry long winded. Does anyone know why now it will not idle down and Idle was fine before switch blocks and stator replaced, I have put old parts back on and it pops and cracks won't start. Appreciate all help I can get on this. Thanks

 

[Dukedog]

I purchased new switch boxes and installed them, them was harder to start than ever and back fires badly. I then bought a new stator and installed, now it will start easier but wants to Idle at 4000rpm, I have put old parts back on and it pops and cracks won't start. Appreciate all help I can get on this. Thanks

any of that type (above) of problem "usually" relates to wiring to coils/switchboxes or timing etc?.. wrong somewhere.. double check ya work jus 'cause!.. it happens..

high idle rpm is "usually" linc n sync/idle timin', to big idle jet, air leak/broken, bent reeds... are you setting idle speed/rpm with idle timing only?.. in tha water, in gear???

do you have an oem manual?.. should be a water cooled 40 amp system???

 

[Princechuck]

Could the Reed valves cause idle high? Would bent or stuck open Reed cause motor not to idle down?

 

[Dukedog]

any of that type (above) of problem "usually" relates to wiring to coils/switchboxes or timing etc?.. wrong somewhere.. double check ya work jus 'cause!.. it happens..

high idle rpm is "usually" linc n sync/idle timin', to big idle jet, air leak/broken, bent reeds... are you setting idle speed/rpm with idle timing only?.. in tha water, in gear???

do you have an oem manual?.. should be a water cooled 40 amp system???

see above...….

 

[racerone]

I need to know !-------How can a bent / broken reed valve cause fast idling speed ?

 

[Dukedog]

wrong air/fuel mixture goin' ta that cylinder.. fuel that usually "puddles" and is sucked into tha block in a different hole goes straight in that hole.....

 

[racerone]

Say again -----Post # 6 means nothing to me.----I do not understand that lingo.

 

[Dukedog]

ona carb v6 each hole has a "bleed" line that goes to a different block cylinder (hole).. when that cylinder is ona down stroke and not firin' it sucks excess fuel air from tha puddling that has accumulated in tha original hole in front of tha reeds to be fired on its next stroke.. this keeps tha balance of fuel/air to all cylinders even.. that's why "lapped" reed blocks with good sealing reeds idle so much better/smoother than reeds that are gapped open like a "P" coat sleeve...……….

 

[Dukedog]

but.. a bad reed, bent, broken or gap has gotten to big, can go either way.. it can show as a slightly higher idle and/or can cause it to load up at idle.. best ta check 'em either way

 

[racerone]

A broken reed would mean low or no crankcase compression.----That cylinder would not produce any power so how could the motor run faster ?

 

[Dukedog]

agree on "what" it should do but experience with 'em has shown me it can and will do either with idle...… had 'em do both as said above...……. jmo.