Speed issues?

[Tom Jerome]

Wanted to run this by the forum, I have a 1999 Pursuit express 3000 with Cummins 4bta 250hp in it. The possible issue I am having is getting the speeds that others get with this vessel. Props were redone to 19-22 or 19-23 cant recall, aftercoolers serviced (they looked decent), new injectors and valves adjust last season. New cutlass bearings and shaft seals. No smoke out the exhaust and fuel burn seems to be on par with factory test. I cruise at around 2400 rpms and only get around 20-21knots fully loaded and WOT is 3100rpms at 26-27knots (was on a day with 3ft seas at 7 sec). I am not sure what else to check and/or if there is an issue. It’s been like this ever since I got the vessel so I am not sure if its even an issue but seems like it could be. Nothing with how the engines run is apparent that could be the issue and the running gear has all been redone. 

Factory specs: 

RPM	MPH	KNOTS	GPH	MPG	NMPG	STAT. MILE	NM	DBA
600	7.7	6.7	1.8	4.28	3.72	839	730	79
1000	9.8	8.5	2.6	3.77	3.28	740	643	80
1250	10.6	9.2	7.4	1.43	1.24	280	243	85
1500	15.3	13.3	8.2	1.87	1.62	366	318	85
1750	19.4	16.8	11.2	1.73	1.5	339	295	86
2000	24.8	21.6	14.2	1.75	1.52	343	298	87
2250	29.2	25.4	18.4	1.59	1.38	311	271	88
2500	32.3	28.1	22.2	1.45	1.27	285	248	89
2750	34.8	30.3	22.8	1.53	1.33	299	260	92
3000	37.2	32.3	23.6	1.57	1.37	309	269	92

 

Topic

[Clark Leighs]

Just a suggestion.   Get the props checked as they are now.    They may be off, one compared to the other, but you won’t be able to see the difference.    Otherwise you are chasing a phantom.  The load may be slightly higher on the lagging engine.

If they are off then get that corrected.           Then test for prop corrections to get the revs up.

[Tom Jerome]

next step

that is my next step as I have done everything else in the article you said to check. do you happen to know the thread side for the fitting on the side of the fuel filter housing for the 4bta? Find articles on where to check and how but not the fitting size needed. 

[Tony Athens]

The 100% sure way to eliminate whether or not you have a “not getting fuel issue” is simple.

Install a liquid filled 0-50 PSI -ish gauge on the on-engine fuel filter– Compare engines pressure– if you maintain over 15PSI at all times on the outlet side of the fuel filter, then getting fuel is not the issue.  Use a long fuel hose to the gauge to eliminate pulsations…. 

IMO, I think you are expecting more than the engines have to offer  considering their age and forget the +/- 5% tolerance in these engine as to overall performance 

[Tom Jerome]

issue

hey Tony,

 

I am not so much worried about hitting factory specs. Main concern is being able to hit the proper RPM’s and to have the proper load on the engines. I am just making sure everything is mechanically right before I adjust the props.  Also secondary issue is the port engine lagging behind the starboard when getting on plane. At around 1500rpms the ports lags back a good minute and the starboard spools right up and gets on plane. That engine eventually pulls the port side up. There is also a fuel leak back on the port when it sits for 24hrs have to reprime it. After reading your article on troubleshooting low power and the 2 symptoms leads me to believe I have a fuel issue.

[Mike Uliasz]

Tom, This a a little off subject regarding the engines, but the Pursuit express 3000 and 3400 are balsa core boats above the water line.  I have the 3400.   And the sale brochure numbers are bare bones boats without options like a hardtop, enclosure, tower (do you have an upper station?). Waxed bottom vs bottom paint …. etc.  The balsa core has the potential to hold moisture/water which = weight, another factor to look at.  Mine had issues with the hard top & fish box hatch. Search the hull truth:

• ‘1999 Pursuit express 3000 balsa core’, might have some moisture/weight issues
• ‘1999 Pursuit express 3000 4bta’ and you might find someone’s sea trial results which would be a much better bench mark than the sales brochure

Good luck Mike

[Tony Athens]

Maybe I am missing something but where is the issue?

Comparing your performance today to a factory seatrial/test and or  sales hype brochure  from 25+ yrs ago is not even close to applicable..

Help me out here and tell me where the issue is..

 

Tony

 

 

[Tom Jerome]

turbo

turbo is fine, no play at all. Leaning towards fuel issue and several mechanics have said the same. Neutral WOT I am hitting 3200rpms is that the correct high speed stop? Fuel solenoid is opening all the way, I thought about switch the lift pump and/or return check valve to see if the issue follows. 

[Tom Jerome]

will do

I will be down at the boat tomorrow. I was sort of leaning towards a turbo issue, but its only about 5yrs old and I would think I would be getting black smoke. I do have fuel leak back issue on that engine (port) when it sits more than 24hrs I have to use the priming pump. I also just came across this article to read look into. https://www.sbmar.com/featured-article/understanding-low-power-troubleshooting/

Might could be a fuel starvation issue. Also do you know what the high speed stop should be set to and the procedure? I assume in neutral WOT I should hit 3400??, Part of my thought on the WOT rpms might be a mechanical stop and just want to ensure that is all good before I redo the props.

[Steve Lewis]

Kinda sounds like the turbo is sticking.  Please post some pictures of the Port Engine and focus on the exhaust setup. 

[Tom Jerome]

lag

Its not the levers those i adjusted to match, When trying to get on plane, i throttle up slowly from to about 1500rpms or so and then you hit that dead spot til the engines push the vessel through the water. The starboard engine will push up through rather quickly and hit 1800/2000rpms while the port is still lagging behind at 1600ish then eventually catches up. This is a fairly new issue within the last 6 months. if its on the calmer side I can play with the throttles and keep them fairly close and they come up to planning speed about the same time but if it s rough i get the lag. I hope im explaining it properly. I will take a video next time im out.  

[Steve Lewis]

Can you quantify the difference between the engines?  For example, my engines are not an exact match on throttle response.  When I advance the throttles with my right hand I have to twist my wrist counter clock a bit to get the right lever out ahead of the left a bit to keep the strbd engine close to the port engine.  I do not use the engine sync I use “Steve Sync” and I adjust the levers manually so that when cruising both engines are at 2220 +/- 10rpm as reported by smartcraft.  The levers are not even with each other but I am ok with that.  This falls into the 5% tolerance category in my mind.

Are we talking this kind of lag/difference or something more substantial?

 

[Tom Jerome]

ok

I will double check the mechanical linkage. I am fairly certain the throttles are hitting the high idle stop… Does that need to be adjusted? I think its set to 3100rpms in neutral. I vaguely recall reading somewhere it should be set to 3300rpms?? There is no sync unit on this vessel, any suggestions on the uneven planning? Sort of at a loss there

[Steve Lewis]

TJ,

You can look at the mechanical linkage that moves the throttle lever on the engine.  When your Throttle at the helm is at full forward deflection are you getting the corresponding full deflection with the lever on the engine?  That can be tested with the engine off and see if there is any play left on the engine side.  Adjustments can be made in the cable.  The other thing that can be limiting is any kind of engine sync unit.  Make sure that is off when you are doing your WOT tests.

If you rule all of that out then Prop Pitch is most likely your next avenue and you are looking at 2 inches or more.

 

[Tom Jerome]

results

ok so the results are in, I calibrated the tachs both digital and analog with laser and everything is set right. At WOT I am only getting to 2800RPMS so I am about 300 rpms off. Which seems like alot, no other performance issues noted other than my starboard engine gets up on plane quicker and the port is lagging behind. Once it catches up no issues, no smoke or oil from either engine. Not sure what is causing this as the running gear looks ok and is fairly clean, no different than the starboard side. My first though is something is wrong with the wheel but it looks ok. Any suggestions on what else to check would be appreciated. As far as WOT at 2800RPms could there be something stopping me from going about the 2800 mechanically? High idle stop? I just want to make sure everything on the engine is set right before I get the props redone. I have heard of some engines having a stop that limits you to your cruise speed. Factory prop is 4 blade 19-23, current prop is 4 blade 19-22.5. 

Second note, attached photo is the top one the sender and the bottom the alarm switch for oil pressure? Also the metal screw is that a good port to check oil pressure at? The one above the filter is a bit tight to get a fitting into. Thanks 

[Tom Jerome]

prop size

prop shop just called me back and they are 19-22.5 4 blades, I will be getting measurements this weekend. If i recall on a spec sheet for the 4bta EGT are in the mid 900’s

[Steve Lewis]

Not sure if there is a formula.  I have seen people ask the forum what they find to be a normal range.  Tony and/or Rob might know what temp range to look for on your engine.

[Tom Jerome]

thanks steve

I will look into the EGT, is there a formula that translates for fuel burn to EGT? found this also https://www.sbmar.com/articles/boost-egt-and-horsepower/

[Steve Lewis]

TJ,

Yes that is a good assessment of your situation.  1 inch of pitch removal is a great place to start.  Make that pitch modification and then run for a season and see how it feels.  And yes to the idea that propping to achieve ~105% of rated RPM will reduce load at all RPM’s  Most importantly the cruise rpm range where you probably do most of your running.  Since you have mechanical engines you might consider installing EGT gauges as a way of watching your engine performance.  Fuel burn @RPM translates into Exhaust Gas Temp @RPM.

The inch that we took out this year reduced my full load fuel burn at 2140 from ~29gph to 26gph.  I did not decrease my speed very much at 2140.  I moved the 29gph burn rate up the rpm range about 100 rpm.  So I have reduced the load on the engine in my cruise range and I can run at 2220 in the 28-29gph area at “My Full Load” and I get a reasonable rate of speed.  It will get better as we burn through the fuel.  I have also noticed how well the engines advance in rpm as I throttle up from hull speed to planing speed.

I will be putting this all to a real world test as we take our trip this summer.  It’s a 3 day/leg run from our home port over to Buffalo NY(visiting my family).  I will carry only the fuel(plus a reserve) I need on that leg of the run and take on fuel as we pull into port each day.  That allows us to run with 1/2 to 3/5 in the fuel tanks which will give us a healthy reserve in case our plans change on any one of those days.  

That is a medium load for us and should translate into better fuel burn numbers.  I keep a detailed log on trips so that I can document things and see any positive or negative changes.

[Tom Jerome]

steve

Hey Steve,

 

So I read over that document you made and the various articles contained in it. I want to ensure I understand it all correctly. Since I am running mechanical 4BTA’s my main focus should be to achieve 3100 RPMS while running and loaded down and roughly 3200 RPMS  in neutral since I can’t accurately measure fuel burn? If I am only running at 3000 RPMS which is the rated speed then I need to adjust my pitch down by 1 correct? Being able to run at 3100 RPMS at WOT reduces the load placed on the engines at the other various rpms? Thanks everyone for the help.

[Tom Jerome]

high speed stop

What is the best way to check if my high speed stop is set correctly? Is this done while in gear and running or in neutral?

[Author]

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