Vortec 350/Volvo Penta - wont go past 3300 RPM. UG!!!

[Jersey13]

Hey all. First off, thanks for any help in advance. Great board. Been a member for about 11 years and have gained a lot of knowledge. Thanks.

I've been troubleshooting an issue on my uncles boat and cant seem to figure this issue out. It will not get past 32-3300rpm. I've worked on motors since about the age of 10 (44 now) so i know enough to be dangerous I'll list his boat specs and what we've done to try resolving his issue, without success... so far!

SPECS

1985 25ft Cat Limbo
Marine Power Vortec 350
Delco Voyager HEI Marine EST Ignition
Edelbrock Performer intake
Holley 4160 600cfm carb
Volvo Penta 190 Dual Prop

WORK DONE TO RESOLVE ISSUE

Rebuilt Vortec heads - compression on all cylinders right about 200psi
Rebuilt Holley carb
New HEI Ignition coil, module & pickup
New plugs, wires, cap & rotor
New exhaust manifolds & risers

This motor starts up immediately and sounds perfect. It will go beyond 3300rpm in neutral no problem. When we first dug into this issue, we checked timing - used the shunt, set it @ 10deg, removed shunt, increased RPM's and watched it advance to around 30-32deg - good, but didn't help. Then checked compression and found out there were a few cylinders low with one that was @ 70psi. Had the heads rebuilt, now all @ ~200psi - good, but didn't help. Checked fuel pressure @ carb while running WOT, 7psi. Checked throttle linkage for full range of motion - good. Checked manifold vacuum - good. Swapped out the Holley w/vacuum secondaries with known good Edelbrock 600cfm w/manual secondaries - no help. NOTE: The Holley secondaries aren't opening under full throttle for some reason which i'm thinking it needs to be rebuilt (possible bad secondaries diaphram) but i held the secondaries wide open while @ WOT and all it does is dump more fuel and growl a little deeper. When we swapped it out with the Edelbrock w/manual secondaries, it did the same thing so i've ruled out the carb being the cause of the issue. Maybe the vacuum secondaries on the Holley would open up if the RPM's went a little higher? Not sure but not concerned much about that right now since more fuel doesn't help our situation! lol. Also, it does get to 3300rpms without the secondaries opening but again, with them wide open and more fuel dumping, hardly any increase in power. Feels like we're dragging the trailer. Yes, i've checked, there is no trailer attached under boat

So figuring that now we know it's getting fuel, has good compression, the only thing left is spark. Replaced the plugs (gapped @ .40)cap, rotor & wires, all HEI. No help. Made sure the coil was getting a good 12v. Decided to replace the ignition coil, module and the pickup last night just in case they were acting up under load. Took it for a run in the bay, still... only 32-3300rpm @ about 30mph (GPS). Unfortunetly, i don't have the prop size/pitch but my uncle has assured me that this boat ran up to 46-4800rpm with the prop that's currently on it. It has never been re-pitched and there are no visible signs of damage.

So... the only thing left we can come up with is that possibly the outdrive is causing the problem. It does vibrate a bit when under load and a bit more when WOT. We're thinking maybe the gimble bearing, ujoints or maybe even gear bind? Not even sure if any of these would hold it back from reaching proper RPM? Anyone experience this as a cause of limited RPM?

Any advice, info, suggestions would be greatly appreciated. I'm at a loss at this point and fully frustrated but will not give up!

THANKS! - Jersey

 

[Don S]

Re: Vortec 350/Volvo Penta - wont go past 3300 RPM. UG!!!

Is the drive trimmed up enough when running? If too low, the bow will plow through the water not plane on top of it, and it will kill your RPM.

 

[Jersey13]

Re: Vortec 350/Volvo Penta - wont go past 3300 RPM. UG!!!

Hey Don. Yes, trimmed up perfect and gets on plane without a problem.

 

[Don S]

Re: Vortec 350/Volvo Penta - wont go past 3300 RPM. UG!!!

Hook a vacuum gauge up to the intake manifold and see what it tells you.

 

[Jersey13]

Re: Vortec 350/Volvo Penta - wont go past 3300 RPM. UG!!!

@ idle w/plates closed, it was at a steady 20in.

 

[bruceb58]

Re: Vortec 350/Volvo Penta - wont go past 3300 RPM. UG!!!

What is the past history of the boat?
Has it ever gone faster since your uncle owned it?
Is the boat in the water? Does it have growth on the hull?
You absolutely sure the firing order is correct?
How old is the fuel? Ever try to run it on a seperate portable tank?

 

[Jersey13]

Re: Vortec 350/Volvo Penta - wont go past 3300 RPM. UG!!!

Thanks for the replies guys.

Past history - owned and chartered in Florida by Wild Willies Charters. Sold to someone in NJ that had Jerry's Marine repower it with the MarinePower Vortec 350. Uncle bought the boat about 5 years ago.

Uncle never pushed the boat until one day when his buddy popped the hatch and manually opened secondaries and the boat almost jumped out of the water from 30mph. After that, he had the Holley rebuilt but it never ran like that again. When i started digging into the issue back in June, found full manifold vacuum was all over the place. Did a leak down on the cylinder that had 70psi and failed. Pulled heads and found that cylinder sucked up an intake valve. Figured, no wonder why vacuum secondaries weren't opening. Once both heads were rebuilt, compression good. vacuum good, still no secondaries and it didnt help opening them manully. Swapped carbs, still no difference - 32-3300rpm max.

Boat is still in water and hull is clean, trim tabs all the way up, outdrive clean.

Checked the firing order 1-8-4-3-6-5-7-2 multible times. Was hoping we had a wire crossed - no such luck.

After checking fuel pressure @ carb @ WOT (7psi) we ran it off a 3 gallon gas can just because. Same result, same psi.

The answer's got to be here somewhere, just got me baffled. Does anyone think or have had an outdrive actually load a motor down from vibration caused by bad bearings, u-joints, alignment...etc? Not sure if that's even possible. Knock sensor came to mind today but damn, there is no knock sensor. Lol.

Any and all ideas are greatly appreciated.

 

[Don S]

Re: Vortec 350/Volvo Penta - wont go past 3300 RPM. UG!!!

when his buddy popped the hatch and manually opened secondaries and the boat almost jumped out of the water from 30mph. After that, he had the Holley rebuilt but it never ran like that again.

Just because a carb gets rebuilt, doesn't mean it works. Maybe it's time for a new carb, because that one has never worked right.

 

[Jersey13]

Re: Vortec 350/Volvo Penta - wont go past 3300 RPM. UG!!!

Swapped it out with a known good, manual secondary Edelbrock 1409 600cfm and runs exactly the same. Can watch the extra fuel dumping past the secondary plates while they're wide open.

What else you got Don? Lol. Thanks.

 

[Tail_Gunner]

Re: Vortec 350/Volvo Penta - wont go past 3300 RPM. UG!!!

Uncle never pushed the boat until one day when his buddy popped the hatch and manually opened secondaries and the boat almost jumped out of the water from 30mph. After that, he had the Holley rebuilt but it never ran like that again. When i started digging into the issue back in June, found full manifold vacuum was all over the place. Did a leak down on the cylinder that had 70psi and failed. Pulled heads and found that cylinder sucked up an intake valve. Figured, no wonder why vacuum secondaries weren't opening. Once both heads were rebuilt, compression good. vacuum good, still no secondaries and it didnt help opening them manully. Swapped carbs, still no difference - 32-3300rpm max.

That is a oxymoron... Manually opend the secondary's ran strong...and a bad valve????? Rebuilt the heads and still nothing????? new carb and the same thing. What effects a engine solid engine...timing...induction.... Dont assume your carb's are right they have never been on or off fix... during the hey day of carburation it was a black art....or do you have a hiddnen monkey in the bilge... Bilge monkey syndrom

 

[dypcdiver]

Re: Vortec 350/Volvo Penta - wont go past 3300 RPM. UG!!!

When you did the heads, did you have cause to remove the camshaft? Valve timing could be out by a tooth or so.
However I would be leaning towards the carb being the cause.

 

[Pesimist]

Re: Vortec 350/Volvo Penta - wont go past 3300 RPM. UG!!!

Years ago I battled a similar problem on a Master Craft, same troubleshooting steps you've taken - very frustrating. Turned out to be a parially collapsed exhaust duct.

 

[Jersey13]

Re: Vortec 350/Volvo Penta - wont go past 3300 RPM. UG!!!

Gunner - I haven't come across a bilge monkey. It was last season his friend did that with the secondaries. Over the winter, he had the Holley rebuilt. Tried it when this season started and it didn't help. I got involved around June when we found the head issues. No idea if the valve, low compression was present last season or just started this season. I didn't assume the holley was built right. This is why i rebuilt the Edelbrock before we tried it. I've rebuilt a few carbs in my day so i'm pretty certain it's spot on. Thanks for your input.

Diver - Cam wasn't touched when the heads were rebuilt. I guess it could have skipped a tooth but i would be very surprised considering how perfect that motor runs up to 3300rpm. Once it gets pulled from the water this winter for outdrive maintenance, maybe we'll pull the front cover to check the cam/crank alignment if the problem hasnt been resolved by then. Thanks.

Pes - When we replaced the exhaust manifolds & risers, we made sure both exhaust ducts were clear. Thanks.

I'm assuming that you guys never heard of or dont think it's possible that an outdrive could reduce RPM from vibration caused by bad bearings, u-joints, alignment...etc? Like i said, i'm not super versed on outdrives so i don't know if this is even possible. Please let me know your opinions on this.

Thanks for all the ideas, suggestions & effort.

 

[bruceb58]

Re: Vortec 350/Volvo Penta - wont go past 3300 RPM. UG!!!

If you were losing that much power in the outdrive, you would be working on your outdrive right now.

Personally, I would be getting the numbers off the props just to make sure they are what you think they are. I know your uncle said they were original but it would be nice to know. Who knows, maybe they aren't a a matched pitch set.

 

[Jersey13]

Re: Vortec 350/Volvo Penta - wont go past 3300 RPM. UG!!!

Thank you Bruce. I was thinking the same, if it were that much binding/bearing play to restrict that much RPM, wouldnt the heat eventually grenade something? And again, i just dont have enough outdrive experience to make that call. Appreciate the knowledge. That will be the first thing done when it's pulled out of the water - check the prop size/pitch. He did have a chip repaired on one of the props (not sure how long ago - before the issue or after?) Maybe they swapped out props on him or like you said, mixed up the matched pair. I read yesterday that it could cause a major issue running a mixed set of props on that duoprop system. My Wellcraft only had a single prop so no experience with the dual setup. Again, thanks.

 

[Tail_Gunner]

Re: Vortec 350/Volvo Penta - wont go past 3300 RPM. UG!!!

Ok here on the water at 3200 or the stall point give the carb a shot of gas externally..shot glass works well..this is dangerous though be careful..if it builds up you have a metering issue

Timing this should work on that dsit..Loosen the dist again start the engine set the timing light to 30. Run it to 3200 and roatate the dist until you reach 0 and lock it. At idle you you should be at 8...this is done in regular mode and should be dead on.

That timing is based off 30 degree's of advacne at 3200...I see some module's are set up for 2600 did i read that right?

 

[Jersey13]

Re: Vortec 350/Volvo Penta - wont go past 3300 RPM. UG!!!

Thanks Gunner. I will try the "gas shot" idea if i can get back down there this year before it gets too cold. Stripers are coming so i hope i do get the chance!

I'm pretty darn sure it's getting plenty of fuel because (1) i can see it flowing like crazy once the secondaries are opened, on both carbs & (2) because when we ran it off of a 2 1/2 gallon gas can, it ate about 2 gallons of it in less than 2 minutes of WOT with secondaries wide open! That actually seemes a bit excessive to me for fuel consumptiom, and that's why we started attacking spark. I was also surprised it wasnt backfiring rich if it wasnt burning all that fuel.

We've timed it both ways - with the "shunt" (that puts it in base timing mode) not connected, brought the RPMs up to where she stops advancing (about 2500rpm) and set it to about 30-32. Once it was brought back to idle, she reads around 25. Connect the timimg shunt, it reads 8-10.

Then we did it reverse - timing shunt connected, into base timimg mode, set @ 10, locked down, disconnected shunt, brought RPM's up until advancing stops and it read 30-32.

I've done this with 2 different timing lights to be sure one wasn't faulty.

I think i'm stuck at this point until it's pulled out and we can get a good look at that duoprop. I'm not even sure what letters/numbers would be right for this size boat but from the Volvo Penta charts, i'm guessing around a B5.

Thanks again for your suggestions/info.