LT4 hot cam manifold vacuum question
 

Trying to get ready for some plug checks and I was messing with carb today trying to set the idle mixture screws. Put a vacuum gauge on it and turned the screws in 1/8 turn increments until the motor died and best I could get was 8-10 on the gauge and is very erratic. I'm running a performer rpm intake and had the idle set at 700-800 rpm. Is this normal for this cam or do I have a problem. Before I drag it into town and put it on an evap smoke machine I was hoping for some input here. Any help would be great.

fixx
 

i should bounce with the idle of the cam.. also if the lifters are to tight it will give you less vaccume..timing will effect vaccume also..

Base timing is 8-9 degrees.

You should get a V6 module, a little more initial will give you a stronger idle. Back the screws out until it stops gaining rpm, then go in slowly until it just starts to affect the idle then go back out 1/8 of turn and do the other side. Once both sides are done wind them in and count the turns then wind them back to where they were set. They should be the same, if not try tweaking a bit more.

A v6 module would give me 18* base. Would it not be hard to start with that much advance? Would a v8-22 make enuff difference to worry about? I guess a v8-20r would be ideal but hard to come by. I'm gonna smoke this ***** tomorrow and find out what's really going on. If 8-10 is all it will pull I'm ok with that but I want to make sure it's not a leak causing it. However at 700-800 rpm this cam has a decent amount of lope. Hoping I don't have to take the top end apart. When does the v8-24 start advancing? Just curious so I can check base and full advance.

Have I mentioned this thing is a ***** to get started and warmed up?

18-20 initial would be great and you won't have any issues cranking. The higher initial timing will allow you to close up the throttle blades a bit which will make your mixture screws more active and give you better control. It will give you a stronger idle and smooth it out some too. I would definitely look for a v6 module.

Sounds good to me, I've found a few for decent prices but I may pull one from our boat graveyard if I can find one there and it give it a go. Can I do a trailer test with my 24* module? I know I can't run it with 18+24 but maybe see how it acts at idle with 18* at base with my current module before I buy a v6 module?

that vacume reading not right should be in the mid teens..you have a issue somewhere...

I just fired it up and soaked the base of the carb and the intake with carb cleaner and it didn't change anything. Looking like no leak

Peanut Butter Man (HAxby) is right on !

Put more base timing in it !

Done a few of these and you'd crap your pants what an extra few degrees of timing at idle will do. Just watch your total.

Forgot to add: I use RPm Airgap's and Holley's with no chokes. Factory 8 base timing make these a *****. Just by going up 4 degrees let's turn into a near stocker.

Foreworn: you'll mellow out the idle....which I like....stealthy.

Should I maybe find a v8-20 module so I can set the base at 12*. For some reason I have it in my head that 18* at base (v6-14 module) is going to fight the starter. My compression is also 10:1 and I don't want it to detonate at low rpm. Just seems that 12* base would be better than 18*. But I may be wrong.

You are. :lolhit:

I promise you won't have any problems cranking. Get the V6 module! Lots of guys are running 30+ degrees locked out. Don't worry about it. You want at least 18-20 degrees initial.

Another thing that someone more familiar with the TB-IV's might be able to confirm is whether or not it has a set timing for cranking. Other modules only have 10 or 15 degrees while cranking and then ramp in the rest once it gets past 400rpm when it knows the engine is running. Anyone know if the TB has this feature? Either way you'll be fine, just thought I'd throw that out there.

Found a v6 module, hoping the guy will get back to me with a price tomorrow so I can get it shipped and on the way. Hopefully this will help the hard start issue. I also like the fact I will only have to rev to 2500 rpm to check full advance. I keep hearing 32* max on vortec heads. How do they run at 30* and how do they run at 34* versus 32*?

I would say 30 is max with vortec heads...on a heavy boat without a lot of H/P I would run 28, those things will KILL the exhaust valves in a hurry if starts det.

Got a v6-14 module that works. Damn thing starts with ease. Never in my life would I have imagined it to make that big of a difference. Only question now is the fact that when the total advance is at 32* the base is at like 21-22. Does this seem normal for this module? Other than that I have no complaints thus far, I'm gonna run it at the lake tomorrow and start prop testing. Do i need to worry about detonation while cruising now since the timing comes all in at 2500 rpm? Should I run 30 or 32 total advance?

The V6-14 is 14 degrees on a V6 engine but is only about 10 degrees on a V8.
I would start at 30* as ezstriper said.

Sounds good, i will set it again tomorrow