vacuum and overheat

[fireman57]

Same '83 50hp 'rude. How much vacuum should the main hose under the carb pull. Right now I have none and can neither blow through it or suck any air out of it. Have an overheat problem that comes and goes too. New impeller and pumps water fine. had water in the bottom cylinder due to a black plastic cap (no idea where it came from) in the reeds. Ran fine afer that with no overheat. Had exhaust leak and pulled the powerhead and replaced ran fine and did not overheat. After having the head on it's side for the gasket replacement got junk in the carb so took them back off and cleaned. Now running good but overheating again. Stuck, any suggestions?

 

[Silvertip]

Re: vacuum and overheat

Are you sure its really overheating. If the head is too hot to touch, its overheating. Check for stuck thermostat.

 

[fireman57]

Re: vacuum and overheat

Thermostat works fine dropped into a pan of hot water. Have a new one on the work bench but the old reacts immediately. Engine even drops rpm a little when it opens up. Still curious about the vacuum.

 

[R.Johnson]

Re: vacuum and overheat

On the overboard water indicator, or pee hose, route the the hose up, and over the back side of the power head, and see what you get.You would not have a vacuam on the lower carb hose, you would have 2-4 lbs. pressure from the fuel pump. Disconnect the hose on both end's, and see if it is clear. You would have a vacuam on the intake side of the fuel pump. That would be about 2-4 in.lbs. on your vacuam guage. If you make a check with a vacuam guage, prime the carb first before hooking up the guage. Primer pressure against the guage will damage it.

 

[fireman57]

Re: vacuum and overheat

That sucker pees about four feet. I'm going to pull the head again and make sure that something didn't break loose and clog the passage. If I have to I will take the exhaust cover off too. Don't have another exhaust cover gasket handy but I do have another head gasket if I need one. Just put this one on so I'm hoping I can reuse it. I guess I wasn't very clear about the hose. I'm talking about the one under the bottom carb that comes out of the block and fits onto a stud from the airbox.

 

[R.Johnson]

Re: vacuum and overheat

The hose to the airbox is nothing but a drain hose for unburned fuel, or condensation. Before taking things apart, route the indicator hose as I suggested. That will break up a air, or steam pocket. It makes little difference in this case how far it will through a stream. How is it routed at this time. Looping it up, and over the block should not take more than a minute.

 

[fireman57]

Re: vacuum and overheat

Will do. I just assumed (I know, I know)that hose would be the main vacuum for the engine. Just for my curiosity how does running the hose up and over the engine break up an air pocket? Does it make the pump work harder to move the water through the jackets?

 

[fireman57]

Re: vacuum and overheat

Well that didn't work. I even held the hose more skyward over the head. It did sputter at first and then resumed full stream. I can lengthen the hose if you think that will help. Any other suggestions? Thanks for the replies.

 

[R.Johnson]

Re: vacuum and overheat

Did the engine cool down after the sputter? How are you taking tempature on this enine? Is it going beyond 160 degree's? Are you chasing an unknown by the "seat of the pants"? Such as A HAND ON THE HEAD? Over the block routeing can break up a steam, or dead air pocket pocket if this is what you have. Think siphon here. Does the engine cool down if you increase the speed, and force open the poppet valve's? Is the cooling water getting in, but can't get out? Take the cover off the thermostat housing, and see how much flow you have, if full flow, you have a blockage down stream.

 

[fireman57]

Re: vacuum and overheat

Didn't cool down after the sputter and yes I'm using the old hold your fingers on the head for a three count. Could do it before but definitely not now. I understand how the over the head would work but it hasn't yet. It does not cool down if I increase the rpms. I can't put it in gear as I am running in a 55 gallon drum and no room for the prop to spin. Will pull thermostat cover and check flow. Thanks for hanging in here with me.

 

[fireman57]

Re: vacuum and overheat

R.J. I pulled the thermostat again and after several runnings got a plug of "snot" out from that passage. Guess it would leave enough water going through to open the stat but not enough water to cool the head. Thanks for everything.