the question is carb or timming ok here goes i have a mild built 468 it is 12.5 to 1 comp has a 629 629 lift cam 306 duration 106 lobe sep the heads are stock oval ports with porting and larger valves and has 1.7 roller rockers solid lifters and holley strip dominator intake with a 1050 cfm holley carb also it has msd distributor and 6al box. the question is the car runs and idles great when you stop and go to launch the car it will backfire threw the carb and die. but if you stop and let the car get up to like to 2 mph and then give it full throttle it will spin threw all 3 gears runs great so is the problem with the carb or in the timing advance/timing Thanks for any help

 

With that large of a cam, you may have to play with timing a little to get a better take-off. Are you running a stall converter? If you have an auto that will help out a lot. As for tuning the carb.... hopefully someone who knows it better will chime in. I've never been the greatest at that.

 

it has a 3800 stall with a th400 behind it

 

It's hard to give an accurate assessment as to a problem. It's not a "BBC" issue. It's a mechanical or tuning issue.

"stock oval port heads" with .629 lift. Are the valves hitting the pistons which could have bent a valve? Are the bottom of the spring retainers hitting the top of the valve guides?

What's your current base and total timing? When does it reach full advance? My timing is locked out at full advance and I have no timing issues at low rpm.

 

kinda sounds like you are going lean out of the hole. Have you tried larger squirters yet?

 

nothing is hitting i had the valve guide cut down for positive seals and also i have 190psi in all cylinders my timing at idle was anything from 8 to 15 and mt total timing kicks in at about 3000 rpm which i i have had everything from 25 to 35 right now as the car sits it is at 9 at idle and 28 total. i have not changed out the squirter yet they are right now.025 should i try and go up on the squirters

 

squirters sound to small, really Id want full advanced to come in around 2000.maybe lock out the dist. sounds like the engine is going lean between idle and full throttle. how do plugs look? locking out is really the way to go unless your driving it on the street alot.

 

might sound like a dumb question but how do I lock out the timing when I have weights and springs also what size squiter should I go to and thanks again for everyones help

 

you have an msd right, dist. go to their website and get inst. I would think 10 more on the squirters.

 

I limited the advance on my old dist. There are extra holes in one of the moving parts in the dist. I just put bolts in there, and they stop the full motion of the mechanical advanced. This way timing at idle can be around 20-25 degrees with full timing still 35-38.

 

ok now i know how to lock out the timing i will do it tomorrow what should timing be then is idle and total timing going to be the same then hows that work ? I am a dumb a$$ when it comes to anything timing

 

Locking out the timing means there's no mechanical or vacuum advance. The timing is fixed in one position and will never change throughout the rpm range. Set your timing to full advance and lock down the distributor. If there's too much advance, the engine may want to kick back when cranking over. An ignition with a start retard will prevent that. Below 500 rpm, the ignition retards the ignition enough to start the engine. When rpm goes above 500 rpm, it goes back to full advance.

If your timing marks are jumping around too much, your timing chain is too sloppy and should be replaced. If the block has been line honed a few times, you need a shorter chain. Set the timing to 32* and start from there. I currently have my timing locked out at 37*.

Your stall speed is also a little low for that camshaft. With a 306 advertised duration, a stall speed closer to 4500 should be used.

What's the list number on that 1050 dominator?

 

28 total is way too little timing, that setup wants much more.

 

The problem is the carb, you need bigger accelerator pumps, or larger squirters, and maybe a richer idle. I big bog on acceleration or backfire but good power on slow application of throttle is almost always a lean fuel condition.

 

i got new squirters today i was told by an engine shop to go with a 35 first then a 40 so i got both i am going to try it when it stops raining

 

ok here goes I put the 35 in and it ran a lot better but still had a little backfire then I put the 40 in and helped a lot so then I just started to go up in timming then I got up to 38 degrees and it ran great no backfire at all

 

you are learning young jedi

 

You probably picked up 20-30 HP from just advancing the timing that much.

 

thanks for all the help but now i have one more question what is a good plug to put in the engine