Carbureted LSX Forum - old school tuning (no wideband)




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sandeggo
05-25-2011, 11:19 AM
I cant run an O2 sensor on my boat due to running wet exhaust.
Here's what my setup is doing
Think of the setup as a car with a ton of stall and a single speed tranny.

Tip in from idle is fine.
Punch from idle it will bog or die.
It idles fine (approx 8-900 RPM's) and fires up with one push of the gas peddle before cranking.
Running WOT isn't possible. MAX is 5300 rpm's and it will bog with peddle left.
What I am thinking is the WOT bog is a lean condition.
I haven't messed with the carb at all except for float adjustment.
5.3L stock with a 750 DP holley. #2 pill. (map disconnected)
fuel pressure is 7lbs
I can reach the intake behind me while running WOT and have thought about giving it a little spray of carb cleaner or something to see if its rich. Any comments on this??

I am planning to mess with the timing and jetting this weekend so any help would be appreciated as the boat is 250 miles away from home and I can only tune it on the weekends.


Ravenous T\A
05-25-2011, 11:34 AM
I am doing what alot of people who have that Bog are doing by upgrading to a 50cc accelerator pump. There are some guys who have rejetted, switch bleeds and etc...but this seems like a quicker fix

Ravenous T\A
05-25-2011, 11:37 AM
Here is a thread that may help u too
http://www.ls1tech.com/forums/carbureted-lsx-forum/1340946-carb-stumble.html


sandeggo
05-25-2011, 11:42 AM
Yeah I have read that thread and plan on doing the conversion. My issue with my setup is the top end

jimmyblue
05-25-2011, 11:51 AM
"Wet exhaust", how wet? Back in the day I welded O2
bungs into the manifolds and used narrowband sensors
for idle screw / cruise jet selection. Is there a dry spot?

Is the fuel pump up to the load at WOT? Is pressure
hanging tough?

sandeggo
05-25-2011, 12:07 PM
"Wet exhaust", how wet? Back in the day I welded O2
bungs into the manifolds and used narrowband sensors
for idle screw / cruise jet selection. Is there a dry spot?

Is the fuel pump up to the load at WOT? Is pressure
hanging tough?

its water injected right near the head ports. Its done to cool the exhaust. The fuel pump is staying right around 6-6.5 WOT. The total fuel travel from the tanks to the pump to the motor is only 3 feet of hose.

Pop N Wood
05-25-2011, 03:31 PM
Man, if it is that far off try two jet sizes larger and see what difference it makes.

I would get the jetting right at cruise then worry about accelerator pumps later.

I know you can use propane to check for vac leaks at idle, and even to check the idle mixture. Not sure if it works at WOT.

By the way, I assume this is the first time you have run the motor and that it didn't run right then suddenly go bad?

Also don't forget the basics, like good ignition, no leaky carb gaskets, blown power valve, fouled plugs.

sandeggo
05-25-2011, 04:34 PM
Correct I have ran it twice and its acting like it always has. It runs perfect in the mid range and has gobs of power. I have the assorted jet kit so I will try fattening it up a bit. I bought the 50cc kit today so I can try that as well. The carb is brand new with no leaks and I sure hope the power valve is working.

tennerv8
05-27-2011, 03:03 PM
Okay everybody hold on a second. If he's using the ignition pills, they have a 5500 rpm rev limiter built into them. It sounds like his rpm issue is that, not the carb. Pull the pill out and tune it on your laptop.

speedtigger
05-27-2011, 09:27 PM
Okay everybody hold on a second. If he's using the ignition pills, they have a 5500 rpm rev limiter built into them. It sounds like his rpm issue is that, not the carb. Pull the pill out and tune it on your laptop.

Wow. I guess we missed the obvious.

sandeggo
05-28-2011, 09:56 AM
It wasn't hitting the rev limiter. I have hit the rev limit a couple times when I catch air.
I did a basic timing curve, fattened up the secondaries to 82's, and put the 50cc on. It's running better but I gotta throw a little more timing to it. The top end bog is almost completely gone and the off idle stumble is almost 100% gone. I didn't change the squirter yet and I'm running the brown pump cam.
0-800 rpm 20*
800-4500 31*
4500-5500 29*
5500 on up 31*
I'm also now hitting 78.1 mph on gps.
Before I hit 72.4

3pedals
05-28-2011, 03:18 PM
have you adjusted all the free-play out of the accelerator pump linkage?
there are 2 positions the pump cam can be set at as well, set it to provide the most pump linkage movement at beginning of throttle movement - to get the greatest shot of fuel at tip in. this will improve the off idle stumble.
for the top end bog, I would make a hard run in the range that boggs, and quickly shut the engine down and check the plugs. if they have any white on them it is LEAN, if they are wet and/or black, its rich. I would guess its lean, as the engine will bog if its too lean, but it will start to missfire and sputter if its too rich.
Barrett

gjestico
05-29-2011, 02:23 AM
Okay everybody hold on a second. If he's using the ignition pills, they have a 5500 rpm rev limiter built into them. It sounds like his rpm issue is that, not the carb. Pull the pill out and tune it on your laptop.

I think thats only partially true. You can change the rev limit with the interface and still use the curve 'pills'. I am doing it. For now.

tennerv8
05-29-2011, 05:42 PM
I think thats only partially true. You can change the rev limit with the interface and still use the curve 'pills'. I am doing it. For now.

Yes but the second you plug the pill in it erases any saved programing. Doesnt it? I may be wrong.

S10xGN
05-29-2011, 07:45 PM
Yes but the second you plug the pill in it erases any saved programing. Doesnt it? I may be wrong.

I don't know that it "erases" it, but it definitely overrides any user programming.

tennerv8
05-30-2011, 08:16 AM
I don't know that it "erases" it, but it definitely overrides any user programming.

Yes thats what i meant.

sandeggo
06-04-2011, 10:46 AM
ok so now I'm a little more confused. I jetted up the secondaries and made my own timing curve. well now the motor will only spin 5100 but the boat goes faster.
Is my above timing curve too conservative?

3pedals
06-04-2011, 02:22 PM
how is this engine built, what cam, compression etc? maybe it just doesnt have enough power to go any faster than 78mph on water. I assume it direct connected to the drive?, or does it have some kind of fluid coupling between the engine and drive? I dont understand how the boat can go faster with less rpms?

sandeggo
06-04-2011, 02:32 PM
It's a bone stock 5.3. It can go faster with less rpms if the power is more efficient. The rpms and top end speed are not directly connected. The motor is connected with a spicer driveline, like a little driveshaft. For example my old motor turned 6300 rpms but only went 64.

3pedals
06-04-2011, 02:45 PM
I would try changing your timing curve from 800 - top rpm up to 33* strait, and see how it responds, I wouldnt bother with a timing dip at torque peak. what do your plugs look like after a full load run? if you can post a picture of what you find, it might help.
you need to kill the engine immediately after top speed of the run to avoid coloring the plugs with anything other than WFO throttle.

EDIT: I just checked out your build thread, NICE setup, I like!!

sandeggo
06-04-2011, 03:00 PM
I've never pulled the plugs yet. They're still stock. Next trip out I'll throw more time at it and see how it responds. I was told you really can't read the plugs on the newer motors.

3pedals
06-04-2011, 04:09 PM
I've never pulled the plugs yet. They're still stock. Next trip out I'll throw more time at it and see how it responds. I was told you really can't read the plugs on the newer motors.
well, its the unleaded gas that makes reading the plugs hard.
As long as there are some deposits on the plugs, you can make a hard pass, and then you will be able to see a change in color of the deposits. Cardboard brown is close.
You wont get it perfect by reading plugs on unleaded gas, but you will be able to get it close.

S10xGN
06-04-2011, 06:59 PM
...For example my old motor turned 6300 rpms but only went 64.

With the same prop? That's just not possible without something (other than the prop) slipping somewhere. Maybe the tach readings are off, can you check that?

sandeggo
06-05-2011, 09:03 AM
Well it's sort of confusing as the boat doesn't have a prop, it's basically a ditch pump. It's possible because the more torque and power this new motor has, makes the boat set back and rides higher out of the water, creating less drag. The more power it has, the faster it will go. The pump is only gonna move so much water at any rpm range. On the back of the boat there's a piece of aluminum called a ride plate, you want the boat to rock back and set on it. Last year the old sbc didn't have enough power to keep it there so it would porpoise even though it was spinning faster.
Oh and the tach is a brand new auto meter that matches the rpms on the laptop.

S10xGN
06-05-2011, 07:59 PM
Well it's sort of confusing as the boat doesn't have a prop, it's basically a ditch pump. It's possible because the more torque and power this new motor has, makes the boat set back and rides higher out of the water, creating less drag. The more power it has, the faster it will go. The pump is only gonna move so much water at any rpm range. On the back of the boat there's a piece of aluminum called a ride plate, you want the boat to rock back and set on it. Last year the old sbc didn't have enough power to keep it there so it would porpoise even though it was spinning faster.
Oh and the tach is a brand new auto meter that matches the rpms on the laptop.

Sorry, forgot that it was a jet. Either way, never heard of a motor not wanting to go WOT w/o bogging. Sounds like it's going dead-lean. Have you had the carb apart to inspect the fuel & air passages, especially the secondary side? How good are the valve springs?

allblowdup
06-06-2011, 04:34 PM
It's a bone stock 5.3. It can go faster with less rpms if the power is more efficient. The rpms and top end speed are not directly connected. The motor is connected with a spicer driveline, like a little driveshaft. For example my old motor turned 6300 rpms but only went 64.

The only way you can turn less rpm's and go faster in the saem boat is to change impellers or have the intake plugged up. What pump and what impeller? With your timing at 21 or so at start it ahouldn't even start worth a crap. Something is real fishy there. Can you verify your timing?

sandeggo
06-07-2011, 09:29 AM
Sorry, forgot that it was a jet. Either way, never heard of a motor not wanting to go WOT w/o bogging. Sounds like it's going dead-lean. Have you had the carb apart to inspect the fuel & air passages, especially the secondary side? How good are the valve springs?

It's a brand new carb, I pulled the bowl off to jet it up and everything looked great. Even had the blue nonstick gaskets. Jetting it up helped alot. This weekend I will double check the fuel pressure at WOT and turn the timing up.