Max rpm 2800

plansea · Post by **plansea** » Tue Mar 01, 2011 9:27 pm

I remember reading about other guys not being able to reach maximum rpm, so after searching old posts I concluded my problem was fuel. First I cleaned all filters and fuel lines, then looked for the anti-siphon valve, (which does not exist on my boat. probably removed by the previous owner). Next i decided to remove the elbow and dip tube to check for restrictions or clogging. Of course the elbow twisted off at the top of the fuel tank. No real surprise, my trojan is a 1974 F36. Sorry this is so long, my problem is when attempting to remove what is left of the elbow,(with an EASYOUT) I was only able to turn the dip tube. Of course it doesnt want to come all the way out. What do you think about pushing it down into the tank, and then removing the broken piece, making a new dip tube and elbow assembly and reinstallig. It appears that the dip tube is just 3/8 copper. Thanx for any thoughts or better ideas. Larry

Big D · Post by **Big D** » Tue Mar 01, 2011 9:41 pm

I take it you mean you're going to let part of the tube fall to the bottom of the tank? I don't know that I'd be comfortable with that but that's just me. Would always think in rough water that it would toss around and eventually damage the fuel sender.

Do you know what an anti-siphon valve actually looks like? If you don't it could very easily be confused with a regular fitting at the top of the tank where the hose clamps on. Your pick up tube should have a screen on the bottom.

I take it you haven't resolved the RPM issue?
What led you to believe it is fuel related? There are various possibilities.

rossjo · Post by **rossjo** » Tue Mar 01, 2011 10:18 pm

Larry,

Ross down the creek here. Saw your boat when I was out yesterday & Friday. Wondered if you'd had it out in a while. Sounds like you're still battling demons.

Q's:
1) How old is your fuel?
2) Do you have a pic of the top fitting on your tank?
3) What size props do you have? Clean bottom?
4) Has the boat EVER run above 2,800 RPM with the current prop setup?
5) What carbs? Rebuilt recently?
6) Fuel/water separators?
7) 2 tanks? Each engine on its own tank?

Neither engine runs above 2,800RPM?

Let's go fishing! What size shafts you got? I have a couple sets of props we could try, 1-1/4" ID I believe. Yours are probably 1-1/2"

prowlersfish · Post by **prowlersfish** » Tue Mar 01, 2011 10:52 pm

Can you get to the tube through the sender hole ? Is there a extra fitting on the tank where a new tube can be installed and plug off the old one ( on mine there are but the tanks have been replaced .

I had a tube fail on mine it was part of the tank ( remember tanks where replaced) the tube had to be crack near the top as the engine would suck air not fuel , the tube was 5/8 I ended up running a 1/2 tube inside of it , worked like a charm no issues 600 hours latter . I made a extra tube in case the other side failed but never has. No sure if you could do this as your tube maybe to small ( my tanks were set up for diesels )

plansea · Post by **plansea** » Tue Mar 01, 2011 10:53 pm

Thanx Big D, I too am uncomfortable with leaving the pick-up tube in the tank bottom, just dont know how to remove it. I have only a 3/8 flare fitting onto a 90 with a npt bottom screwed into the tank. No anti -syphon valve. I have a mallory electronic distributor, i've changed the resistor, double checked the timing. ( I have an advancing timing light. I get 35 degrees at about 2400 rpm.) Neither engine will turn over 2800. (never have!)
Capt Ross,
I do not believe i have any corn gas. I use fuel from Chas Harbor Marina ,they have only Premium non ethanol
I will take a picture tomorrow
1&3/8 shafts, 20x20
Boat has never run over 2800(even in neutral.)
Carbs are new elderbrock
2 tanks each engine seperate

Lets do go fishing IN YOUR BOAT!
Larry

prowlersfish · Post by **prowlersfish** » Tue Mar 01, 2011 10:55 pm

Not even in neutral ? check you tachs

Hows the speed on the boat ?

what engines do you have ?

plansea · Post by **plansea** » Tue Mar 01, 2011 11:05 pm

Good thoughts Paul, I've pulled the dip tube up about a 1/2 inch, but its really tight. My 125 gal tank is nearly full and i hesitate being too agressive. The tube is only 3/8 dia,so your solution is probably not feasible this time. There is another fitting about 4 inches away but the plug won,t budge. (Even with P B Blaster) But if I can remove it that probably is my best shot. Larry

captainmaniac · Post by **captainmaniac** » Tue Mar 01, 2011 11:50 pm

plansea wrote:Boat has never run over 2800(even in neutral.)

What do you get speed wise under way? If you get over 16 knots, the engines are spinning more than 2800 RPM. If not, you may have a real issue.

If you can't get any reasonable speed out of it, you either have a serious fuel or air obstruction, distributor is seized (and not advancing therefore engine cannot accelerate), timing, or 'tired engine' issue.

If you *do* get past 16, you probably have a simple tach calibration issue... simplest and cheapest test to start : put a separate tach (or multimeter with tach capability) on the engine to confirm if you can trust your tachs first, then look at the more complex stuff.

I know with my new (5 years ago or so) Teleflex tachs, there is a switch on the back that you set to indicate if your engines are 4cyl, 6cyl, or 8cyl... and it calibrates accordingly... but it's not really a 'switch' - its more of an dial that you turn to add in the right calibration factor . Last year one of the tachs suddenly decided to read WAY off (read almost 2000RPM at idle)... turned out to be something sticking internally ... just cranked this calibration 'switch' back and forth a few times and then set it back where it belonged, and suddenly the tach read correctly again.

alexander38 · Post by **alexander38** » Wed Mar 02, 2011 3:38 am

+1 on the tachs. Is check the rpm's out to make sure 2800 is a real number firsf, as for the fitting in the gas i've got nothing for you there sorry.

plansea · Post by **plansea** » Wed Mar 02, 2011 7:00 am

Both tachs(cabin and bridge) read about the same. I have ordered an engine test tach/analizer that should be here fri or sat. I have BB Chrysler 400 cu in, 280 hp. I do have one cylinder at about 85 lbs on the starbord engine, all others about 120. I know the engines are tired, but i can get only about 18 -19 mph. I do have a leak on the port trim tab but even when working properly I have never been able to get on plane. Larry

jimbo36 · Post by **jimbo36** » Wed Mar 02, 2011 11:44 am

plansea, I have a 74 F36 Tri cabin with the same fuel tank fitting/pick up tube issue that you discribe. I posted this a couple of years ago here without any ideas for the solution.

My problem is on my port fuel tank, which services the gennie that I have never used, so I ran a fuel line from the gennie fitting to the fuel line at the tank fitting and plugged the fitting hole with epoxy. I tryed an easyout as well without success. Touchy area to work, not much space and, of course, no heat, etc. What to do??

On your RPM issue, looks like you have covered the bases here except for the one that is going to provide you with the fix.

All I can say is my F36 with the same engines runs at about 24 MPH @ 3500 RPM. I too have an issue with my starboard engine not wanting to go over the 3500 mark. I suspect the advance in the distributor is my problem.

Geoff R · Post by **Geoff R** » Wed Mar 02, 2011 6:12 pm

Double check your firing order sounds like there could be a few wires mixed up with 20x21 props she should do 3800 to 4000 no trim CCW distributer rotation CW eng 18436572

prowlersfish · Post by **prowlersfish** » Wed Mar 02, 2011 9:02 pm

Are sure a 280 hp will turn a 20x21 ? thats the prop often used with a 330 hp I believe

As far as doing 18-19 knots and not be on plane . you would have to be on plane

Big D · Post by **Big D** » Wed Mar 02, 2011 9:11 pm

Geoff, i'm pretty sure CW (RH) rotation engine would be 1-2-7-5-6-3-4-8. Distributors on both engines should rotate CCW.

Big D · Post by **Big D** » Wed Mar 02, 2011 9:23 pm

Plansea, just read your second post again regarding timing. Does anybody have an advance curve for this engine, somehow 35 degrees at 2400 RPM doesn't quite sound right to me. Anybody else have a comment on this?