Gannz

So I came here looking for prop advise and ended up with a new carb. LOL

Went to tune the carb and the vacuum gauge was jumping between 10-15 Hg. Tracked down a rocker that was too tight. I backed it off and got about 15-16 Hg. The gauge said the timing was late so I advanced it, adjusted the mixture screws and idle and got about 18.5-19.5. Idle is 800 RPM.

Did some checking and most people with the LT4 are only pulling 14-17 Hg. Should I back off the timing to original settings and the 15-16 Hg? Sounds better IMO at the 15-16. It's more of a mellow tone and has a lope but now I'm second guessing because the gauge says it's late. I set the timing 2 years ago and don't remember what I set it at but I can dust off the timing light and check it if it would help. I know I set it at what the general consensus recommended and I'd guess that was 30-32.

The idle mixture screws seem really lean... only about 3/8 of a turn past seated. I fiddled with them for a long time and have all 4 corners set evenly and that's the setting that gave the most vacuum and best idle.

Also, what's up with the gauge fluctuating 1 Hg? Cheap Chinese gauge? Normal for the cam? Worn valve guides? Check plug gaps? Nothing to worry about?

Didn't get a video at 15-16 Hg but here's the current setting. Valve covers are off so it's a little noisy...

https://youtu.be/ltsudjnmL50

Jonesyfxr

iTrader: (1)

First off, I'll start by saying I'm not a boat carb tuning pro by any means......but carb tuning in a boat is totally different than in a car. A car you want the highest vacuum possible but in a boat it's a tad different. When you drop a boat in gear, there's a sudden load placed onto the engine and if it's too lean the boat will most likely die. I'd set your idle mixture screws a tad rich and start from there. Splash the boat at the dock and with the boat still on the trailer dial it in.

I'm sure others will chime in. I hope this helps.

Best of luck!

SB

iTrader: (1)

If you have a Tbolt IV, set total timing and let the initial end up where it ends up..

If you have an adjustable timing curve distributor, your engine will like between 14*-16* degrees initial. It will idle smoother and less lope, oh crap, that's right, people have to have their lope...lol.

You vacuum gauge's writing ' timing too low' is a generic staement based off of many factory car engines as most have 20"hg+ vacuum.

A healthy and timed correctly race motor may have only 2"Hg or so vacuum at idle.

Mr Maine

I have that cam in a vortec 350. Total timing is 32, initial about 16. It idles at around 14 to 15 inches of vacuum.

Gannz

How's this look/sound? 32*, 15 +/- Hg, 750 RPM

Front side: https://www.youtube.com/watch?v=WO7MB69aGso Back side next post...

Gannz

Back side: https://www.youtube.com/watch?v=xjyG-zRL1tg

Jonesyfxr

iTrader: (1)

Doesn't sound bad, just don't forget to trim the engine down when running the engine to avoid stress on those pesky U joints.

SB

iTrader: (1)

Holy crap you are right - suprised ujoints aren't smackin scit.

Gannz

Doh! I know better but forgot to lower it. Thanks for the reminder.

She's running good. Gained another 150-200 RPM but I'm guessing that's because of the valve that wasn't closing all the way.

getrdunn

iTrader: (7)

[QUOTE=SB;4468754]If you have a Tbolt IV, set total timing and let the initial end up where it ends up..

If you have an adjustable timing curve distributor, your engine will like between 14*-16* degrees initial. It will idle smoother and less lope, oh crap, that's right, people have to have their lope...lol.






I go for the Honda Accord idle. NOT......