reaching wot of 4000 rpm

[larryeddington]

Well I still cannot determine how to get my f28 twin 318s to advertised WOT. Best I can get is 3000 rpms, new engines just installed along with clean re cupped props from my f28 that is being scrapped. It was suggested to check the distributer, I checked initial advance and it was 5 degree. Rev the engines and the timing advances as it should. I have gone through the carbs and verified the secondaries are opening. Also the bottom is clean and trim tabs are up.

It was pretty much exactly the same with the only engines in 3k rpm and 20 mph.

It was suggested that the fuel filter could cause this, it seems to me if the filters are starving the engines the engines would be demonstrate some rough running or acts attributable to running lean. The run as smooth as silk but will not turn Trojans suggested speed, 30 mph and 4000 rpm.

I am down to thinking it just may be the carbs, after all 30 year old carbies may need to be tossed.

Your thoughts please I am out of ideas other than above.

[mikeandanne]

two things jump out from your post----are you saying that the boat is behaving the same now as with the old engines? If so maybe those props are net letting the engines spin up
---restricting the fuel on both engines would be very hard to do with bad filters and have both engines the same imho,even if you did the carbs wouldn't go lean ,as there would not be enough fuel to get the secondary air valves open with afb's and engines would not accelerate under load
----are both engines fed from the same fuel tank?----thats it from me ---Mike

[ready123]

Does the linkage allow for carbs to be fully open at full throttle? The fact at WOT you see no poor running situation suggests you may not be getting carbs fully open.... Have someone else at the helm and check throttle linkage position on the carb while at full throttle.

[captainmaniac]

There are also the stupid silly bugger questions... are you reading 3000 on the tachs on the console, or a separate handheld tach connected directly to the engine (there is a switch on the tach for #cylinders, and if it is set to 6 instead of 8 it will scale incorrectly). How are you measuring the 20mph - speedo connected to a thru hull (that may be fouled or not spinning freely), or separate GPS?

Don't get me wrong - I am not trying to insult your intelligence, but sometimes people get messed up by blindly following instruments and don't realize that marine instrumentation may not be as accurate as what your car has, for various reasons....

GPS may even has its issues .. yes, mine is a bit 'old school', but if my altitude was really -27 feet last week (on Lake Ontario), I would have been in serious trouble!

[k9th]

I had the same issue on my port side engine last year and found out that the choke was not opening completely and therefore, since it is a mechanical linkage, would not allow the 4bb to open. I wire tied the choke to the complete open position and voila! - she went to rated RPM at WOT.

Just a thought to check.

[larryeddington]

GPS and depth/speed (mechanical) agree with my phone gps speed ap. max speed is 18 to 20 should be close to 30 so yes I am reading the tachs all read the same for old engines and new engines. I will check on back but doubt it as indicated speed is comparable to tach reading. Will check rpms against tack with a strobe rpm meter just in case. The boat has separate fuel tanks and each engine seems to consume about the same amount of fuel on a run.

I have static checked the carbies and the secondaries do open and air flappers are free. Next will look down their throats while under way at WOT and see what I see. Possible that fuel is not going out secondary ventura nozzle. I have a second set of carbs I guess will have to try but I do not believe 4 of them would do the same thing. Unless somehow when I put in kits the wrong gasket under the secondary nozzle was the wrong gasket, I suspect this might be possible. I suspect problem is carb related but having the devil of a time chasing it down. Gonna try blocking the choke open as well. Though visually does not seem to be problem, but honestly have not visually looked while under full throttle.

The props are off of my parts boat same performance as ones I took off, have not had the originals for this boat re-cupped, cleaned and set up.

Anybody jump in.

[canuckkb]

My 26' searay reacted very similar when I replace the engine. I had installed a fully rebuilt engine, which was supposed to give me a substantial horsepower improvement. After the break-in hours, the engine could only reach WOT using the original prop. Using the predicted new pitch and diameter, the engine would barely break 3400 rpm. Turned out the break-in did not loosen the tight engine, and probably did not fully seat rings and valves. I don't really know as I am not a mechanic. Anyways, within the next 20 hours or so of operation, the WOT slowly crept up to the mid 4000 range. I say this because you said that you had new engines. Are they new to the boat or rebuilt / crate engines.

[larryeddington]

thanks, but the engines are jasper rebuilds with about 50 hours on them and should be loose. Prop is what I believe to be original they are 14/11 cupped. I checked with prop shop and they can add or subtract up to 2 inches of pitch, ergo 14/14 or 14/9 cupped or not. First I am going to try my second set of carbies which I rebuilt and see what I get.

[captainmaniac]

I am starting to lean in the same direction as Ready... you are just not getting enough throw in your throttle cable. Maybe try opening the throttle wide from the helm, then disconnect the linkage at the carb, and see if you really are wide open.. Maybe a detent in the throttle itself is stopping you from givin' 'er.

[larryeddington]

Captain, I did check that but only static not underway, looked like wide open to me. But could get underway with a helmsman and disconnect the cables and manually go to full throttle, that will be another check I will do.

[captainmaniac]

Captain, I did check that but only static not underway, looked like wide open to me. But could get underway with a helmsman and disconnect the cables and manually go to full throttle, that will be another check I will do.

I am not saying to do it under way - a little two dangerous in my mind! What I meant was to check it at the dock - without the engine running - and just see if the throttle at the carb has any more range after the helm throttle hits the stops.

[larryeddington]

Cappy,

That is what I referred to as static check, which it was fine, linkage going full open. Underway would not be too dangerous with a helmsman, at the end of the day he could just turn off the engines if emergency occurred. The wheels on it are 14/11 cupped. I may have to have my second set of props re pitched to 14/10. Any other F28 owners know what props you are using and do you get 4000 rpm and about 30 mph?

[Paul - SW Ontario]

thanks, but the engines are jasper rebuilds with about 50 hours on them and should be loose. Prop is what I believe to be original they are 14/11 cupped. I checked with prop shop and they can add or subtract up to 2 inches of pitch, ergo 14/14 or 14/9 cupped or not. First I am going to try my second set of carbies which I rebuilt and see what I get.

Did you end up trying your second set of carbs? Were the results any different?

[larryeddington]

will try them this thurs or friday, next trip to boat. still stuck.