Hello, I new and have a carburetor question.
 

My name is John, Baitkiller was my father and as such is bronzed into all of my forum handles. I have browsed here for years but never registered until now. I am a long time member of THT and a marine surveyor by trade.
My question revolves around my ski boat. I have an old restored Nautique that is bit of a bastard in that she runs a left handed Chevy instead of the Right turning Ford.
I recently replaced the long block from a 1990s 5.7 12 bolt intake engine to a Vortec that by all accounts should make a few more horsepower.
I have the thunderbolt 5 and merc Weber 4bbl.
The old motor ran like raped ape, the new one seems like it runs out of fuel over 4100RPM. It will gain power if I back off the throttle when wide open. i cant even pull one barefooter let alone the three I could with the old motor. Timing is full in at 32* and 3700. I have run on a shop can with no change. Carb has been gone through, new fuel pump installed. new cap and rotor, new wires and coil are ordered. The only thing I have left is jetting.
? Do the vortec heads flow that much more air that I need to drastically re-jet or replace the carbureter?
Advise or suggestions please.
Thank you,

Edit: I tired to correct the poor grammar in the thread title but have been denied. Sorry Mrs. Wilson, (4th grade English) I tried.
John

Curious, what direction are you running the new motor ?

Guessing you don't have a wideband 02 to check the A/f ratios, did you check any plugs for color ?

left handed.
No gas analyzer.
Plugs look a little too clean, light grey, not deep tan.

Everything is the way it was on the old motor which ran bloody great until a valve seat fell out and ended the party. The only changes are that the new engine is vortec. It runs great but has no real power, especially on top but mid range pull is weak too in comparison.

What was the HP on the original motor compared to the Vortec, how close are the cams, I don't think all of the Vortec's were high performance.

Standard 5.7 alpha should have been 280 with the tall GM intake and 4bbl. The new engine I did not build but was t(s)old it should make 340 ish with tall intake and 4bbl. I have no idea what went in it camshaft wise. Both are roller.

Thinking cam specs would be the place to start, if you can get your hands on them. It might just be under cammed and dying at 4100.

Thanks

you need to put a fuel pressure gauge on it to see what its doing from of idle to wide open, also check the timing for full advance

Sounds like it's running out of timing to me.............

Do you know the procedure for the TBV timing adjustment ?
Not the same as a traditional distributor nor the TB IV. I have the procedure from a Merc bulletin if you need it.

fyi: Many people don't know that the Vortec heads take a longer reach plug like the Delco MR43LTS's vs the typical MR43T's.

Yes I do know the timing procedure. key off, jumper in set timing, key off, jumper out. Idle timing is at 9* with jumper and full in at 30* 3700 but my low dollar cheap ass advance light sucks big green donkey d*^%s. I have the correct, longer plugs in it. I have a new fuel pump, manual, installed. It made no difference. I have run it on a 5 gallon can to eliminate the siphon valve and boat plumbing. slight but insignificant difference. I have ordered an advance tape to double check timing.
I am tempted to just run it WOT and turn the distributor up until it pings slightly then back it off. That's the way we did it before advance lights. That should give a few of you a stroke.
I dont know. Its a 600 CFM carb, should be fine. Next step is to check which main jets are actually in it.
I suppose I'm asking if anyone knows if there is s rule of thumb, or standard answer that Yes or No to the need for re jetting with vortec heads over the old truck type all else being equal..
Thanks.

Camshaft and exhaust have more to do more with jetting than cyilnder heads do........unless you put a real good cam and exhaust in beforehand ..and then good heads :)

So I may still have a timing issue? is that the general consensus?

It could be fuel. When the fuel bowl runs dry from not enough supply (be it the pump or fittings or needle and seat or) the engine will usually lay over vs lean popping thru the intake like too small of jets or crap in the jets usually does.

As far as timing, you may need to read more into how the TBV works with mean best timing, rev limiter, and etc. Here is good info from Merc. Start reading .pdf page 16 on. ie; The wholeTBV section.
http://www.boatfix.com/merc/Servmanl/16/16B4R2.PDF

If your older motor died due to a valve seat falling out it was going lean. I had the same thing happen. With the Vortec heads flowing better and the same carb, and the motor falling on it's face at higher rpm you are lacking fuel. Jet up and see what happens. That is the safest thing to do at this point.

The high rise intake will also lean it out some. Personally, I'd swap to a Holley 650

Holley swap is a schlep. Edelbrock is the same thing. Ill go up jets and see what happens.

Research needle and seat sizing also. A few members have run into tuning issues due to the needle and seat not being large enough on the Edelbrocks/Webers.. Yeh, more hp than yours, but not a ton more.

I turned a motor into scrap iron and this was the cause. The boat came from higher altitude, (Lake Powell) and had been tuned accordingly. I exchanged the metering rods using the smallest ones I had in my kit but that wasn't enough.......BOOM

Thanks for the help guys. Im going to run it again Sunday then pull a plug for another look.

You may already know this, the reading is most accurate if you can just turn the key off at the RPM you want to check.

Yeah, i know.
thanks.
ealked into napa thisd morning ans ssw a edebrock 1409 marine for 500. Almost did it lol.

Don't know if you can trust it, https://www.ebay.com/itm/Carburetor-...from=R40&rt=nc

seller has zero feedback on zero history.. shipping is 2 bucks..
Seems legit :)

Thanks for the link, wish it could be trusted!

Best of luck !!

Thought I would post back.
Changed the wires and coil, turned up the timing from 30 to 32* all in. I did see some corrosion in the coil socket and the timing strobe that used to be erratic is now very steady.
Runs much better now. I saw (analog) 5000 RPM with decent pull. I killed the key and pulled #5 plug. Looked nice and tan. I have some pics on my phone I can put up later.
I feel there is still more in the box performance wise but it's close now.
Thanks much.
John

I have done a few vortec set ups, normally they do not like timing over 30 total, they themselves raise compression. last I did I had comp grind a custom roller to make max power @ 5500, using performer RPM intake and a 600 edelbrock runs very well, It is in a light sterndrive setup. I did a twin engine setup a while back, ran ok but never performed like we thought it should...but it was on old shortblocks(killed heads why we went vortec) jump ahead current, one engine got overheated and killed, so bought 2 reman for builder in Fl and now one is down on power after very few hours, just getting into this as we speak..