LM318 Low RPM

Agitator · Post by **Agitator** » Thu Jul 12, 2007 10:49 pm

OK guys, I'm baffled. 1971 Trojan 26'. 318 that runs smooth as silk. Starts easy, idles great. When under a load will only turn 2500rpm. Rebuilt carb, new springs in distributor, timing dead on, new fuel filters, new fuel pump, new plugs, points, condenser. No change at all. The trim tabs don't work yet and at 2500 I don't get on plane. At WOT it still runs great. No misses, skips or stalls. It just don't turn but 2500. I disabled the linkage and manually opened the throttle all the way. 2500rpm..no more. Next is to clean the fuel intakes and get the tabs working. Any other ideas? I am lost.

jordan · Post by **jordan** » Fri Jul 13, 2007 12:02 am

I just started having the same problem with my port engine, would run 4200 rpm then quit running ( no spark ) after playing with the ballast resistor it started idling and running great up to 2400 rpm. I'm headed up to the boat this week end to install a new resistor and control module. I will keep you posted.

Jim

prowlersfish · Post by **prowlersfish** » Fri Jul 13, 2007 6:38 am

is the bottom clean ?

randyp · Post by **randyp** » Fri Jul 13, 2007 9:28 am

WOT spec is 4000 rpm. Check those filters for accumulated crud. Gas tank vent plugged? Carb gummed up? Gas tank the old galv steel version? If so you may have rust in the bottom. I had this problem and could only get to 2800 rpm, then slowly kept on losing power. Ideas a-plenty. Welcome to the world of old boats. Whatever it is, it's fixable. Happy hunting!

obeejr · Post by **obeejr** » Fri Jul 13, 2007 1:52 pm

Distributor advance rusts up and stops working on a lot of the non-electronic ignition systems. That will keep you from hitting the proper wot.

JuiceClark · Post by **JuiceClark** » Sat Jul 14, 2007 8:18 pm

Sounds like it has to be fuel related. I would imagine if the distributer cap was getting rusty it wouldn't idle as nicely. Moreover, if the other engine is starting to act similarly, it would just have to be skanky gas clogging up the gas uptake or filter.

Whenever something blows my mind I assume it's the carb and have the mechanic come...and it usually is. But in that case it's usually the opposite of your deal - it idles and starts rough but runs nicely at high rpm. Gotta be fuel.

Tony in Ft Myers, FL
1982 F-36

jordan · Post by **jordan** » Tue Jul 17, 2007 1:30 am

I just got back from the boat, put the $ 6.00 ballast resistor in and mine now runs 4200 rpm again. Before it sounded like yours but now runs great. Good luck, Jim

chucka · Post by **chucka** » Tue Jul 17, 2007 11:27 am

I had a similar issue with a 318 a couple of seasons ago. I tried replacing the distributor springs and looked for intake manifold leaks, but that didn't find or fix the issue. Eventually I sent the carb out for a rebuild which solved my problem. If you put a timing light on and can see the spark advance as you increase the throttle, (You should have full advance by 2500 RPM) and have good manifold vaccuum readings then a carb re-build might be the next logical step. The carbs are subject to gumming up and the ethanol added to the fuel in the last couple of years just makes the situation worse. The rebuilder also adjusted the throttle plate / choke linkage, which is kind of delicate on the Carter AFB. Before I sent it out, the secondaries would not open at all. Afterward, they kicked in at about 3200 RPM and she took off reaching 4000 RPM.

I used the guys at http://www.CarburetorUSA.com . They did a good job, but took a little longer than their website indicated. Overall I would recommend them.

Good Luck
Chuck

Agitator · Post by **Agitator** » Fri Jul 20, 2007 6:05 am

hanks guys. Installed the trim tab motor yesterday. Now it gets on plane and I gained 300RPM's. But I'm still turning only 2800. I'm thinking I'm not getting enough fuel volume. Today I'll run it from a gas can instead of the tank to see if that makes a difference. I'll change the ballast resistor at the suggestion of someone, check the vacuum and may change a fuel line. The one between the pump and carb is kinked - maybe not enough to make a difference but I'm grasping for any little thing now.

Agitator · Post by **Agitator** » Fri Jul 20, 2007 9:40 pm

Here we go again. Seems to be getting plenty of gas. I hooked a hand pump up to the fuel line and can pump plenty through the line. Replaced the coil and resistor. I do have the galvanized tanks and I get some rust in the filter. But it doesn't seem excessive. In line filters are clear enough to blow thru. I still may have fuel problems,though. 2800 is all it will turn. IT does sound a little bogged but really runs pretty smoothly through out. Today as I was coming in it gradually fell from 2800 to 2400 and stayed there. I get steam out of one of the exhaust at high RPM's. Is that normal? Temp runs about 160-170.
I am also losing trans fluid. Its not leaking in the bilge. Could the cooler be cracked internally letting the fluid escape into the cooling water? Could that be the "steam " I see?

I should have taken up flying!

Agitator · Post by **Agitator** » Sat Jul 21, 2007 7:17 pm

Compression checked at 115 - 120 cold all cylinders.
Ran the gas from a clean can to the fuel pump bypassing the tanks. 2800 RPM's.... I did get it to 2950 at one time but I think the increase was due to a very good trim tab setting.Then after a few minutes it slowed to 2800 again. Of course it was about then I busted a trim hose. Engine runs smooth through out, 4 barrels open... I'm missing something. Any idea why the I'd lose rpm's? That twice that's happen. Seems the engine just wanted to slow down. The first time from 2500 to 2200, then today from 2800 to 2500...still runs smooth though........

Agitator · Post by **Agitator** » Sun Jul 22, 2007 6:39 pm

Prop Question.
Still can't increase the RPM's. Marina guy questions the prop size.
This is a Trojan F26 with a LM318 and a paragon V-drive.
I can not find the prop recommendation. Any body have a similar setup and know what prop size I should have?
I do not know what it currently has on it.

randyp · Post by **randyp** » Tue Jul 24, 2007 2:50 pm

I have the original prop on my 77 F-26 - Federal Equipoise Super Cup, NiBral Bronze - 14x9. Still made by Michigan Wheel, and they are on the internet. The steam you are getting from the exhaust ( you only have one exhaust, unless somehow they squeezed another engine in there...) should be coming from the raw water exhausting at about 140F. If you are getting a lot of steam it could be an indication of a bad head gasket, but I doubt this. You may need to clean the carb or have it rebuilt, but I still think you are getting rust and gunk from the galvanized tank into your carb. It's easily dissolved and suspended in the gas in the tank so some of it may have passed throught the in-line filter. Your gas line pick up is on the bottom of the tank and that's where the rust is. I'm just going from my personal experience. Replaced the old galvanized tank with poly tank, had it tuned up, including new spark plug wires, plugs, etc, and it runs like a charm. That was in 2000. I just had it retuned this spring and it jumps up to 4200 rpm+ which is over the 4000 rpm spec. WOT should be 4000 rpm and top speed (GPS) with light load and clean bottom is 24-25 mph. It will cruise all day at 3000 rpm - about 18 mph.
You're losing tranny oil so it's leaking somewhere. If the tranny's the culprit you should have gotten some signals by now (noise, slippage, etc).
Keep looking to the fuel system as the culprit.

Agitator · Post by **Agitator** » Tue Jul 24, 2007 3:17 pm

Randy, Thanks...
I am sure the leak is a seal so we are gettnig ready to pull the tranny.
I've rebuit the carb but I'm like you, I think its gas related. I did bypass the tank and ran a hose from a gas can but blew a trim tab hose as we started off (That's always fun!) But even without the trim tabs working, I couldn't tell a difference. It never got on plane. I'm beginning to wonder if the cam lobe that moves the pump is worn. I have not done a fuel pressure test yet but it sucked gas through a clear 3/4 hose from the can pretty easily.

Would you think something in the transmission is causing the low RPM ?
It shifts fine and pulls good.

Anything else in the drive train that may cause this?
Something siezed, tight or ???

Thanks to everyone for their input.

randyp · Post by **randyp** » Tue Jul 24, 2007 4:06 pm

I looked at your earlier posts and those from others. Here are some things that were mentioned by you and others, and then not mentioned again.

1. Kinked fuel line. Did you replace it? Just looking at the fuel passing through a hose may not mean there's not enough volume going through if the hose does have a kink.
2. Carb - you rebuilt it or was it rebuilt by a pro? No offense, by maybe the pro's can do a better job.
3. Not mentioned, but suspicious - fuel pump working to spec?
4. Not mentioned, but suspicious - plugs and wires new or still moldy oldies?
5. Thermostat? 170 F seems a bit high for raw water cooled engine, and I doubt you have fresh water cooling on a 1971 318.
6. Tranny slipping? The paragon drive is just about the same as the Warner Velvet Drive at a 1:1 ratio. If there's slippage you wouldn't notice it since it does not shift gears in forward like an auto tranny in a car.
7. Throttle linkage set to specs? They can stretch over time and can be readjusted at the throttle control. Remove the cover and take a look. You'll see what I'm talking about. You may not be getting full throttle at the carb, even though the arm is all the way forward. It can also get loose and start to slip back under power. Is there play in the throttle control, or can you easily move it back and forth with very little effort?
8. And finally - that rusting galvanized gas tank. You won't see the rust on the outside until it's too late and it's corroded through from the inside. Then you have your own Exxon Valdez deal!!

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LM318 Low RPM

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