pressure in the intake

[Quadruplecccc]

I have a two part problem here. First my motor runs hotter than normal. ( replaced h2o pump , thermo. and checked to make sure there are no water restrictions,{good flow}), and 2nd I have found that there is presure in the intake instead of vacuum. Does anybody have any Idea what may be causing these symtoms? HELP!!! Thank you!

 

[jtybt]

Re: pressure in the intake

Of course that's not supposed to happen but this question cries out for more history of previous problems and work done to remedy those problems.

Also, type engine would help.

 

[Quadruplecccc]

Re: pressure in the intake

History: 1976 351 windsor, 233hp with standard cooling.Picked up this boat for parts as my motor has h2o in oil. This new motor came with papers being a re-man . Previous ownner did not have enough money to complete project,so, what seemed a resonable price I took it off his hands since I needed many parts that this boat had to offer to make my project better. Previos owner had builder install a higher duration cam to give a little bit more hp. So now I estimate it will push about 250 hp. Back on track: I did a motor swap and then realized he had the cooling hoses rerouted. I put them where they are supposed to be and checked around for anything else obvious. All looked good. Started her up and ran so so, Checked timing and found that he had the distributer 180* off and at about 12* before tdc. noticed it was running to warm. Put #1 at tdc and put dist. and wires where they need to be. Set timing as close to zero as it would allow at idle @ 700rpms. Still runs hot. Changed water pump, checked circ. pump, checked to make sure water is comming through each hose, All good but still runs hot. Upon restarting at on of the checks I saw a litle puff of smoke come from carb. I investigated to find a hole in the carb to intake gasket an exhaust coming out of it. At first I thought the higher duration cam was adding extra heat to the motor but this shouldn't be the case. Took new thermostat out and tried again , still heats up past 150* , rerouted hoses the way previous owner had them goes up to 150* with 140* thermo in but then gives spikes up to 175*. No water in oil but did notice what looked likr exhaust steam coming from on of the hoses when removed. Sorry it got so long!

 

[jtybt]

Re: pressure in the intake

Heck, could be an extreme cam with too much overlap. Could be the engine was built for a hotrod.

Do a comp and leak-down test. Not knowing what cam is in there, I wonder what a vacuum test would show...but do one.

 

[Quadruplecccc]

Re: pressure in the intake

Oh, I forgot to say I did a comp. test. Had about 130 psi on all cylinders but one. That one showed just shy of 140psi. I never did a leakdown test before . Can you describe it? Also , a vac test? how would I do this if i have press. in the intake?

 

[Silvertip]

Re: pressure in the intake

If you don't know how to do a vacuum test, how did you determine the intake had pressure instead of vaccum? A simple puff of smoke when an engine shuts off is not a sign of intake pressure. An open intake valve can let vapor/smoke out the carb. If the engine indeed had positive pressure in the intake the engine wouldn't run because the carburetor requires vaccum in order to draw fuel and the cylinders are filled with the mixture as it DRAWN into the cylinders. It can't run with positive pressure. Nor can the engine run with the distributor 180 degrees out and the timing set to 12 degrees. Your info simply does not correspond to what really happens in an engine.

 

[Quadruplecccc]

Re: pressure in the intake

Last posts read that I saw a puff of smoke. I traced it to the carb to intake gasket that has a hole in it. As the motor runs there is constant exhaust coming out of this hole. Sprayed wd-40 at this spot while running and the wd blew back at me . Sprayed all around intake finding no other spots with draw or pressure. Can't explain why , this is why I'm here. This will be a learning experience. Hopefully we can figure this out!

 

[cr2k]

Re: pressure in the intake

Shy of cracked heads, the only place you will get exhaust from the intake is the small runners right next to the carb, on both sides. This is the heat riser which routes exhaust to the intake to heat up the carb. So you probably have bad or incorrect intake gaskets, or they were installed wrong.

 

[Quadruplecccc]

Re: pressure in the intake

Let's take it one at a time. Supposing the intake gaskets were installed wrong. Would that create a hot motor condition because the exhaust gasses are not going where they should? Motor was purchaced as a long block so, the last place the last owner would have had the chance to make a mistake was here.

 

[jtybt]

Re: pressure in the intake

Older intake manifolds had a direct exhaust riser connection from the exhaust port in the head to the intake manifold. You're probably getting that coming out from the intake. Probably rusted thru manifold.

Engines can run with dist 180* off.

 

[Quadruplecccc]

Re: pressure in the intake

would that cause the engine to run hot or could there be a crack in the head causing the same symtom?

 

[dan t.]

Re: pressure in the intake

some fords had a egr port in the intake manifold, these used a egr plate with a egr valve between the carb and intake. pull off the carb and look for an extra hole,find a way to plug it, some can be tapped for a pipe plug ,others need a plate of some type between the carb and intake

 

[gbeltran]

Re: pressure in the intake

I'd try more timing and see if that helps cool it down. Aftermarket cams don't work very well with stock timing curves. What's the total timing when it's running at speed?

 

[Quadruplecccc]

Re: pressure in the intake

tried several different setting for timing but none seemed to help. Total timing at speed looks to be about 30*btdc. I suspect the cam and the crank were off by a tooth or two when installed. I've been told this would create a hot motor and would also open the exhaust valves too early causing pressure in the intake. Has anyone heard of or seen this happen ?

 

[mkast]

Re: pressure in the intake

Even if the exhaust valve opened early, how would that get into the intake manifold?
The intake valve is still closed.

 

[Quadruplecccc]

Re: pressure in the intake

I know it doesn't sound logical or even possible but something has to be causing this to happen. Are you asuming that the cam shaft and the crank are in time? If so what do you think would happen if the two are off by a little?

 

[Bifflefan]

Re: pressure in the intake

Last posts read that I saw a puff of smoke. I traced it to the carb to intake gasket that has a hole in it.

replace the intake gasket. probably has the wrong one in it.

Set timing as close to zero as it would allow at idle @ 700rpms. Still runs hot.

Timing problem... AINT GOT NONE....
you timing is to far retarded. the fire is going out the exhaust instead of burning in the cylinder. you need about 6 to 8 deg at idle.
when its to far retarded the fuel doesnt fully burn before the exhaust valve opens and the fire goes out into the manifolds, also burns valves and runs hot. this may also explain the hole in the intake gasket at the crossover.

 

[Quadruplecccc]

Re: pressure in the intake

Yep! Last time I set it , it was at about 8*. Ran ok there, still hot, still pushing exhaust out from under carb. This is crazy

 

[Bifflefan]

Re: pressure in the intake

Yep! Last time I set it , it was at about 8*. Ran ok there, still hot, still pushing exhaust out from under carb. This is crazy

the only thing i can think of is they used to have a passage in some intakes that ran from the exhaust crossover to the top of the intake where the carb sits. this was to help in warming the carb to run better (not). pull the carb and see if there is a small hole under it on that side. if so you will need to tap and plug it, or put in an intake gasket that has the exhaust holes blocked off.
as for the running hot, it may have something to do with the exhaust manifolds. i read something about the flappers or passages or some thing in there. I have an outboard so i do know alot about the I/O's. but i do know Ford engines.

 

[Quadruplecccc]

Re: pressure in the intake

I'll check for that passage under carb and see if it's there. As far as the exhaust shutters,I just replaced them. Manifolds and elbows are a couple years old and haven't been used that hard in the salt. i did check them and they are not blocked.