Hey Vinney - Reversition?

[coupedeville]

Re: Hey Vinney - Reversition?

Jl; Have a look here <br /><br />www.centuryperformance.com/vacuum<br /><br />It's a very nice explanation of how to use a vacuum gauge, and what the results mean.

 

[jlshields]

Re: Hey Vinney - Reversition?

MrBill, Re: vacuum gauge vibration. Heads have been rebuilt, valve guides, 3 angle valve grind, spring height measured and shimmed .030. Did this before the teardown also. I still wonder if the overlap in the cam or maybe the dual plane intake. I took the vacuum reading at the port between the carb and #8 cyl. John

 

[MrBill]

Re: Hey Vinney - Reversition?

jlshields: At idle, your vacuum reading should be steady, the intake-exhaust overlap (assuming stock cam) should not have any bearing on the problem. When depressing the accelerator quickly the vac should drop to 2 or 3, jump up to the 18-20 range and level about 15. Continue to check the easy stuff, like timing, fuel/air mix, spark plug gap or other ignition difficulty. One other issue may cause a fluctuation in the vac reading - leaky head gasket...could it have been damaged or pinched during replacement? A one page vacuum guide showing vacuum guage activity and probable cause will help you. They're in most shop manuals. You are also consistant in using the termninology "vibration". Does the gauge move very rapidly (over 10 times per second) or rather slowly or intermittently? Viewing one of the charts will probably best allow you to match your symptoms with possible causes. Good luck.

 

[jlshields]

Re: Hey Vinney - Reversition?

MrBill, It's stock. The needle isn't a fluctuation, it's a vibration, maybe 10 times a second. Slows as engine speed increases. The heads were milled .010. It did the same before the rebuild. It's got to be something in the way of engine design. I have the manual that came with the gauge(SnapOn). It says bad plugs, but they're new, improper gap, but they're .040, ignition points, it's electronic(ThunderboltV), high tension cable leaks, ran my bare hand along all plug wires and coil wire, nothing. Distributor cap, or weak ignition coil. All check out OK and coil resistance is within spec. Tried backing initial timing to 8*. Book calls for 10*. Adjusted idle mix using vac gauge,and plugs set to the book, .040. Would like to take reading from another location but between carb and #8 cylinder is only port The engine runs good and starts better than new. I'm stumped!!! John

 

[flashback]

Re: Hey Vinney - Reversition?

mr. shields, if all you say is in order, then most likely, you have a leak in the manifold or carb......check any and everything for an intake leak..just a thought.......good luck.........

 

[jlshields]

Re: Hey Vinney - Reversition?

flashback, did that too. Sprayed starter fluid around intake to head gasket and carb base with engine running, no change. While intake was off even removed exhaust crossover splash guard looking for cracks. I still feel that if there is enough overlap in the cam to suck water from the exhaust riser into the exhaust manifold or cylinder there would certainly be enough to affect vacuum readings. John

 

[P.V.]

Re: Hey Vinney - Reversition?

Mr. Shields, how about running the motor with the OD off?? And a water hose connected to the incoming water inlet??? Perhaps a mechanical "glitch" with the gears/bearings, u-joints,gimbal bearing, etc.... is part of the "problem"????

 

[jlshields]

Re: Hey Vinney - Reversition?

 

[Billpayne]

Re: Hey Vinney - Reversition?

Asking Venny from Wilmington to Contact me RE: Reversation on 5.7 Marine Power, roller cam, (Vortex???) Repower on Cobra drive. Engine runs great when it runs. I have spent too many week ends with a spark plug wrench and hydrolock. I am from Wilmington and e-mail bpayne@ec.rr.com. Looking for solution. Thanks, Bill

 

[flashback]

Re: Hey Vinney - Reversition?

hey team effort, I don't know if vinny is around any more. but give us a new posting with all the info on your boat, engine,drive, year, make, etc and maybe we can help you. in general, if the cam lobes overlap, in other words, if the exhaust is open at the same time the intake is open, then you risk drawing water into the cylinder for the compression stroke. water does not compress very easily, so the engine locks up. the static line which is basicly the water line in relationship to your engine should be lower than the risers by 8 to 10 inches, more if your cam is radical. so to make a long story short, the more cam you have, the more riser you need......there are folks on this site that can tell you exactly the part numbers, and specs. but i think i have explained the idea rather clearly......good luck.......

 

[MikeK2B]

Re: Hey Vinney - Reversition?

Is this vacuum through the exhaust a problem with just prop exhausts or can this happen to thru-hulls too? I was considering changing to a thru-hull system, and since the engine sits low in the boat, its looking more worth while to convert.

 

[akriverrat]

Re: Hey Vinney - Reversition?

through hull may be better but with enough cam it WILL happen if you have WET exhaust. especially at low rpm.