Volvo Penta 5.0 GL-H loss of rpm

[LongRifle]

Hello,
Im a long time follower and reader just decided to run this by the experts. I have a 2007 chaparral sunesta 214, Volvo penta 5.0 gl-h that we bought last year with no problems.
Last winter I dropped it off to winterize, tune up and replace gimbal bearing. When I picked it up they put new spark plugs, wires, cap, rotor, oil change, impeller and bottom paint.
Due to my profession I’ve been busy this summer with dealing with riots and things so I haven’t had a chance to use not that much this summer.
I noticed not would not get to WOT (4400-4800) rpm and was only getting about 3600 and maybe 28 mph. Last year no problem getting to wot at 42 mph. Same prop used as last year, 14.5x19 aluminum four blade. First thing was replace prop using g prop finder and it came up with 15x15 stainless 4 blade. Change out prop and got up to 4200 rpm at same speed 28 ish.
Started troubleshooting tank and bypassed with portable outboard, no difference.
checked temperatures at idle with infrared thermometer and it looked good
Checked ignition coil and showed it was out of specs in multimeter and had weak spark. Replaced it and was able to get up to 35-36 mph still only at 4200 rpm.
Checked vacuum pressure and it held steady at 17 in/Hg.
checked with timing light and it’s at 12 BTDC, should be at 10 BTDC. Rpm’s match tachometer with engine light.
Checked fuel pressure and it’s at 8 psi from idle to 2500. Last night took it on test run and noticed alarm buzzing from under helm and water temp gauge was past 175 maybe about 190ish. Back it down from full throttle and and alarm goes away. I’ve since drained manifold and impeller hoses, a little sandy but nothing crazy.
I am at a loss, don’t think carbureted engine has a knock sensor that would cause “limp mode” or anything.
Just for giggles I’ll replace thermostat sensors to make sure it’s not “overheating”.
Thank you in advance! Rick

 

[alldodge]

Howdy
Original prop would reach 44-4800 rpm

After tune up now it doesn't. Start with verifying firing order 1-8-4-3-6-5-7
Next do a compression test

 

[LongRifle]

Alldodge,
Thanks for the information. I will check spark plug wires and cap for proper firing order again. I’m going to order a compression tester but won’t be able to check anything until I get back to the boat this Saturday. I guess I’ll see how the plugs look during compression test.

If the firing order was messed up wouldn’t the boat run like crap, misfire, smoke, etc? The boat runs fine up to WOT

 

[muc]

Alldodge,
If the firing order was messed up wouldn’t the boat run like crap, misfire, smoke, etc? The boat runs fine up to WOT

Not necessarily, it depends on what cylinders got swapped.
Are you using the timing shunt properly when checking timing?

 

[LongRifle]

Yes, I am using the timing shunt properly, followed Don’s directions.
I’ve ordered new plugs, wires, cap, rotor, impeller, thermostat and all new sensors (oil, water temperature, etc) along with a compression tester.
I will check compression as well as trace wires back to cap this weekend first before replacing things.
Last year I was using the 14.5x19 4 blade and reached my wot rpm range around 4600. Shouldn’t the 15x15 wot rpm be much higher if everything was working correctly? Should I put the old prop back on just to see if the coil changed anything or do you think I still have an issue? I know the 15x15 will lose a little top end speed 35/36 mph current at 4200 rpm, versus last year getting 40-42 depending on water and load conditions.
My cousin thinks all is fine with the boat and that after bottom painting it this year (first time) and changing prop that this is all the boat will do now. He reminds me constantly that it’s not a speed boat! lol

 

[muc]

Yes, I would try the old prop.
Yes you should have gained RPMs with the 15X15
Bottom paint should slow you a little, not that much.
Have you added weight to the boat?
Might be good to check total ignition advance. Should be 28° all in by 2400 RPMs
I wouldn't worry about the 10° vs 12° couple of degrees won't hurt on this engine.

 

[LongRifle]

Ok so it’s been a busy spring and summer of trouble shooting this damn thing with no success. I have done the following since spring and still can’t get above 4,000 rpm at 30 mph less then 1/2 tank of gas, trim makes no change to rpm. This is worse then last years performance. I replaced coil last year with one from Napa so I don’t know if it has to be marine or not, it said it was compatible with SBC. Something is wrong and can’t figure it out. I have replaced or checked the following:
-checked and verified correct firing order on cap
-engine timing is 12btdc and 30 at 2500 rpm, I can’t adjust distributor due to how tight they put security hex head screw in.
-New AC Delco spark plugs and wires
-Changes oil 10w40 full synthetic and filter
-New cap and rotor
-All new sensors (thermostat, manifolds and oil pressure)
-new water pump and impeller (expensive mistake)
-new thermostat and pulled out housing to inspect
-2 new AGM batteries 24 cranking and 31 for deep cycle
-compression test results: #1=172, 2=172, 3=172, 4=192, 5=175, 6=178, 7=179, 8=185
-cleaned and rebuilt carburetor
-vacuum gauge showed steady 17hg last year and still does, can’t get it any better adjusting air mixture screws. Stays steady at constant throttle up to 3000. Will drop to 5 and then goes back to 17 with a throttle blip
-fuel pressure still shows 8psi drops to 7 at 3500 in neutral no load, didn’t try it under load adjust at dock.
The boat runs fine and sounds fine just not getting wot, like i ran out of throttle. Engine temps primarily stay around 175 maybe slightly warmer then drop once thermostat opens. Exhaust risers stay at about 90-100 at idle and 105-110 after running it for awhile. Even my dad who has worked on engines says it’s not lugging or misfiring. I checked throttle and it opens all the way up on carburetor. The only thing I need to check is the riser elbows and y pipe to check for exhaust obstruction, doesn’t make sense because shop had drive off to replace bellows and gimbal bearing. All the problems happened after they did that and a tune up. I am going crazy on this. Is there anything electrical to check?
I’m going to check engine harness and all connectors that I can and clean with electrical contact cleaner. Also just for giggles going to check all spark plugs with tester to make sure I’m getting spark.
Also I’m getting a strange squealing noise on front port side, couldn’t isolate it the other day without my stethoscope and rain was coming. Hopefully just an idler or tensioner bearing. Also has a weak and very faint alarm from under helm while running at 3200-3400 rpm, If I move throttle it stops. I had the same thing last year so I thought I had a bad sensor. Is this an actual alarm or bad ground or connection?Please help!!! Thanks!

 

[Senior B]

What's you're oil level at? I ask as my neighbors boat had a very similar issue after routine maintenance and lost a lot of top end. Wound up being that the shop overfilled the oil by a lot like they never drained it and just pumped in 5 more quarts. It wasn't milky just grossly overfilled. Removed the excess and WOT RPM went from 3600 to 4800. No Fooling. Good luck.

 

[Lou C]

Changing prop to a 15x15 should have put you at or over 5,000 rpm based on your previous results.
I’m wondering how you’re measuring speed & rpm. Boat speedometers (if not GPS) and tachs are not all that accurate. After all you’ve done I’d want to verify those #s with a digital tach hooked up to the coil and a GPS measure of speed. At idle speed my dash tach is off by 100-150 rpm at high speeds I have not checked it but it’s probably more. I use the GPS function on my fish finder/gps for speed. Does the boat feel slower than last year?
One thing not mentioned, is this a 2 or 4 bbl carb and if a 4 bbl have you verified that the secondary throttle valves are opening at higher rpm. There is a Holley trick with a paper clip on the secondary diaphragm rod that can show if in fact the secondaries opened.

 

[LongRifle]

Changing prop to a 15x15 should have put you at or over 5,000 rpm based on your previous results.
I’m wondering how you’re measuring speed & rpm. Boat speedometers (if not GPS) and tachs are not all that accurate. After all you’ve done I’d want to verify those #s with a digital tach hooked up to the coil and a GPS measure of speed. At idle speed my dash tach is off by 100-150 rpm at high speeds I have not checked it but it’s probably more. I use the GPS function on my fish finder/gps for speed. Does the boat feel slower than last year?
One thing not mentioned, is this a 2 or 4 bbl carb and if a 4 bbl have you verified that the secondary throttle valves are opening at higher rpm. There is a Holley trick with a paper clip on the secondary diaphragm rod that can show if in fact the secondaries opened.

I verified tach with engine timing light, show’s rpm’s and speed has always been with gps. The analog tach is pretty damn close to what the timing light is showing. This is a Holley 2 barrel. I agree the 15x15 should be over 5k rpm compared to previous 14.5x19. I wouldn’t say the boat seems slower, I was just was going off my previous posts to compare. I’m on Lake Erie so it all depends if there is chop or not, very seldom is this lake completely smooth like glass.

 

[Lou C]

Holley 2bbl. Was the power valve replaced & is it the correct rating for vacuum readings on your engine? Power valve on these functions as an enrichment device. What do the center insulator porcelain look like on your spark plugs? Blistered white (too lean) or black/brown (too rich) should be light tan/grey.

 

[LongRifle]

Holley 2bbl. Was the power valve replaced & is it the correct rating for vacuum readings on your engine? Power valve on these functions as an enrichment device. What do the center insulator porcelain look like on your spark plugs? Blistered white (too lean) or black/brown (too rich) should be light tan/grey.

Yes power valve was replaced, it was a Volvo penta direct rebuild for Holley 2 barrel so I hope power valve is correct. I contacted Holley before purchasing to just buy a 2300 kit and they said the only that makes it Volvo Penta is the power valve and he didn’t know if a general kit would be the correct one so I spent twice as much for a Volvo Penta rebuild. Spark plugs are all tan. Even last years looked good minus the fogging oil which I cleaned off but still replaced.
I can’t find the documented vacuum readings on VP 5.0gl. Some articles say SBC should be 18-22 others say some engines are 17-21. One article said some engines like 15 to 17. It’s right at 17 and steady which is right on the border of late ignition timing. So that’s why I thought timing might be retarded but it’s actually advanced more then spec. Initial base timing is currently at 12 btdc, spec says 10 btdc for 89 AKI fuel. Yes, I am using the timing shunt correctly. Also should be 28 for total advance at 2400, mine is currently at 30 so it’s not retarded.

 

[LongRifle]

What's you're oil level at? I ask as my neighbors boat had a very similar issue after routine maintenance and lost a lot of top end. Wound up being that the shop overfilled the oil by a lot like they never drained it and just pumped in 5 more quarts. It wasn't milky just grossly overfilled. Removed the excess and WOT RPM went from 3600 to 4800. No Fooling. Good luck.

Funny, I pulled about a quart out last year after shop winterized it. I did the same thing in the driveway on the trailer when I winterized last year. I put in the recommended 6 qts without thinking about left over in the drain pan. I took out at least a quart a couple of weeks ago and that at least got rid of the oil pressure alarm that was going off when I gave it throttle to get on plane. Dipstick shows halfway in the “safe” area now, no change to rpm though. Did I damage something. Should I take more oil out?

 

[Senior B]

I would not take more oil out if it's with in the parameter on the stick. Correct power valve for your carb & engine is 4.5 I believe.

 

[LongRifle]

I would not take more oil out if it's with in the parameter on the stick. Correct power valve for your carb & engine is 4.5 I believe.

I'm using the "stock' power valve that came with the volvo penta rebuild kit. Found information showing it's an 8.5 for 5.0GL D/E 500 cfm 2300 2 barrel. Which going off Holley's information and the fact I idle at 17hg vacuum, 8.5 should be correct.
I replaced spark plugs this year with MR43LTS pre gapped @ 0.044". The manual calls for 0.060". Should I gap them or should they be fine? Reading conflicting information on this. Keep the AC delco's or try NGK?

 

[Lou C]

I would gap them to spec the ACs are fine