Trojan Boat Forum

Hi fellows:

For the last year I have chased the ellusive 4000 factory rated RPM on my 1976 F30 with twin Chysler 318's.
After replacing everything except the engines we finally solved the mystery of the low RPM problem.
FLAME ARRESTORS no GOOD!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Flame arrestors plugged up, (Air filters). Metal flame arrestors corrode with salt air and stop up choking off air flow to the engines. This results in an excessively rich fuel air mixture at higher throttle postions resulting in engine RPM "Bogging Down".
Correct timing is a must and NEW FLAME ARRESTORS are essential.

Another tid bit of info: Do not over prop your engines or you will be replacing them soon!!!!!!!!
The factory called for 14 inch dia. 11 pitch super cupped props when the boat was new and light weight. (14/11 props). I now use 13 inch 8 pitch and thats it. (13/8 with medium cup). The boat go's on step quick and the engines are not overloaded.

Good Luck
Tom Scott

Recently purchased a 72 31 flybridge express and ran it 250 miles home. I chased down every possible cause (I thought) for the low RPM issue, about 1,800 was all I could squeeze out of her, so It was a very slow, fuel expensive trip home; setting the timing did help a bit... about 300 extra RPM , but that was after I returned home and had the proper tools, had them tuned "by ear", close, but not quite...
After I read your post, I got into the SCUBA gear and looked at the props, sure enough, found a pair of 14/11 props. A set of banged up 14/8 "spares" was found in the bilge, so I sent them to the prop shop for restoration and tuning. It will be very interesting to see the results when I make the switch! The flame arrestors are not an issue here on the Great Lakes, they look like new and have been cleaned with carb cleaner then blown out with compressed air.
Thank's for the tip and I will post the results when I get the props back and make the switch!

I spent most of this summer tweaking and tuning trying to get more performance out of a remanufactured lm318 I installed in my 1975 Trojan F-26 this spring. The carb was rebuilt by http://www.carburetorUSA.com in NJ, which solved my problem. Previously I was only able to get 3500 rpm and a disappointing top speed of 14-15 knots. Priot to the carb rebuild, she seemed to be straining at all speeds.

I was able to hit 4000 rpm with the rebuilt carb with a top speed of 18.2 knots [two runs in opposite directions ranged from 18.0 to 18.4]. I can cruise economically before the secondaries kick in at about 13 knots, which is where the boat feels comfortable. She is up on a plane at that speed with the wake flattened out. That may not sound like a speed demon, but I'm satisfied with it. This boat isn't really built for speed. I extended the keel and replaced the rudder with a larger one to improve tracking stability and maneuverability. I had expected increased drag from these changes to have some impact, but was convinced that the engine wasn't running up to snuff.

I ended up with a bit of a flat spot in the throttle at about 3200 rpm, just before the secondaries kick in, but I'll deal with that another day. When the secondaries kick in, the rpm jumps from 3200/3300 to 3500/3600, and up from there.

My biggest mistake was transferring the carb, intake manifold & distributor from the old engine to the replacement without doing anything to check them out or fix issues that I was not aware of.

If you are interested in the history, look at Chrysler threads in the forum on http://www.marineengine.com/discus/mess ... 1124648871 beginning in July to see how I learned about replacing the advance springs in the distributor, which I was able to get done locally for a very reasonable price. Fixing the distributor got me from about 2800 RPM to 3500, and solved a back firing issue. It took the carb rebuild to get the rest.

CarburetorUSA told me that the carb had been rebuilt previously and the choke linkage was not assembled correctly. Straightened that out, cleaning out the carb and adjusting things did the trick.

I'm still running my 14 dia. x 10 pitch prop with no cup. (reconditioned this spring) I had gotten input from another Trojan F26 owner, indicating that performance on the F-26 is very sensitive to putting a slight cup in the prop. I didn't find this to be necessary.

summarizing for future reference:
1975 Trojan F-26, factory remanufactured LM318, FWC, 14 dia x 10 pitch prop no cup, velvet drive 1:1 straight drive. Rudder increased in size from 12" h x 5" deep with 1" dia shaft to 17" h x 12" deep woth 1.25" dia shaft. Keel extended ~6 inches from original lines.

Here is what I measured. This is the average of two runs in opposite directions.
rpm knots
2,600 10.9
2,800 12.3
3,000 13.4
3,200 14.5
3,600 16.1
4,000 18.2

This Speed and power data is not a precise science. These measurements are very sensitive to loading the boat. One person on board and half a tank of fuel yields better performance than full tanks and the whole family on board.
Regards,
Chuck