rpm on gray 4-90 with 11-11 p

what type of rpm should i be turning with with the 11-11 on a 17' boat, i'm not reaching anywhere near the 4000 the motor should be reaching. I was noticing the motor ddi seem to be working out some cobwebs, most likely gum/varnish in the carbs. I hope to post some pics on the boat next week.

I finanally got the boat in the water this last week after installing a both a new gas tank and fuel pump on the 4- 90, all for $65. I was able to cross reference the pump a t a my local auto value store under continental 4 cyl tractor motors, the auto value location in brooklyn mich is very helpfull with such things, its one of the best auto stores i've come across.

GT - Did you put a non-marine fuel pump in?
That's a no-no!

William, Just a couple extra thoughts here!! Have you checked the timing? Have you synchronized the carbs? If anything, to me you are under propped! I'm swinging a 11 X 12 on my 60 HP 4cyl. The boat is however smaller.

William, The dual carbs can be trickly to synchronize. You will need 2 manometers to hook up to check the vacuum on each. The throttle linkage is then adjusted so the vacuum matches. It's not the biggest problem but a lot of playing around. It seems you get one adjusted and then a adjustment on the other throws off the first. If you do not have or have access to manometers, you can get about 10' of 1/4" ID clear plastic flex tubing. On a piece of plywood, mark horizontal lines with 1 inch spacing about 18" height. (19 lines) Cut the tubing into 2 pieces, form it into two "U"'s about 2" apart and staple them on the plywood. One end of the tubing stops at the top of the ply and the other gets connected to the carbs. Fill the "U" tubes half way with water and a couple drops of red food dye. As vacuum is applied to the ends connected to the carbs, it will draw the water column up on the suction side. The combined total of height difference will be vacuum in inches of H2O.

Here's a commercial manometer.

William, You mentioned that the carbs may be gummed and varnished. They are nothing like modern ones and are pretty basic, You may want to open them up and just do a cleaning.

William, Very interesting! With my little 4, I had rebuilt it and then stored it for 8 years while I was working on the boat. Got it all done started it up and had a bad miss/rough run problem. I screwed with lots - timing (thats when I found out I had bolted the flywheel on 180 off and had to hook up the timing light to the #4 instead of the #1!!). carb , plugs, points, etc. The only thing left was a stuck valve. I had always been a firm believer in Marvel Mystery Oil so I added it to the oil and gas. 30 seconds after restarting it came to life!! Haven't had a problem since. I did run a compression test on it last summer and it was at the top of the spec. The Marvel Mystery is now part of my oil changes. I also use it mixed 50% with engine oil for winter storage fogging.

Gary, I too have seen the abandoned projects! I have a friend with a late 30's pickup. That thing has sat for 30 years!

In my case on rebuilding the engine, I had all the machine work done and then I did the rest. When done, I did run it on the stand and it was fine. Then the 8 years of storage stuck the valve. It's pretty common on flat heads because of the vertical position of the valves and lubrication coming up from the bottom. They aren't easy to keep lubed when stored.

William, It sounds like that parts store that got you the pump are well tuned to older engines. They should be able to help. If not, try graymarine.com - they bought out all the gray parts stock. The head gasket however isn't marine specific so the standard Continental will work.

79nautique wrote: you just might as well just have head redone if one valve is bad your going to have more and it's all ready off anyway

Chris, Mill the head?

William, Clean it up and put it back together! I wouldn't even change the valve guide. (unless way out of clearance spec) I called a friend who rebuilds lots of the Hercules (Chris Craft) and the Continentals (Gray). He confirmed exactly what I described in my post about my stuck valve. He sees it a lot from storage. Wait until the day when you do the whole engine.

While I had him on the phone, I asked him to confirm the max rated HP RPM. I stand corrected that the 4000 you had, is the figure in the book! There is only one other Gray of that time that has the 4000. It's a 6 rated at 175 HP. He cautioned me to warn you that just because they are rated at the 4000 it's not the best idea to prop it up to that. Just as I said, the 3800 would be good.

BYW, The book says you need to run premium gas! Very important as they knock very easily. You may get by with retarding the timing 1 or 2 and then use mid grade but probably not worth it.

Time for a update, haven't had the time to get on here lately. I was able to clean up the stuck valve, I think pete was right about it from long term storage. A phosphor bronze gun cleaning brush did the trick quite well.

I did run into a bit of a problem when I went to torque the head with its new gasket. I started by torquing the head in 10 pound incremets up from 30 pounds in the proper sequence, at the 140 pound setting on the wrench one of studs cracked, so the head is off again. I called around to some of the tractor repair shops, it seems they reguarly replace all the studs on the continetal engines. Luckily the stud snapped at the top, so theres something to get ahold of.

So its off the the machine shop to get the studs pulled and replaced

Will