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red78ta · 10-15-2006, 10:01 AM

Have HEI with vacuum advance, trying to get some more advance for performance buit 400. Problem is my advance canister is hitting the intake & can only get the factory spec setting of 16 degree's. Like to push it to about 20. The engine is a 78' 400 with 6x-4 heads, 30 over, 9.5:1, tomahawk intake, Crane 234/242 duration @ .050 lift & 473/488 lift, Jet perf. Q-jet stage 2, Dynomax ceramic headers with 2.5" Pypes exhaust with the "X" & flowmaster muflers. This combo runs & sounds GREAT but breaks up at full throttle & thinking I need more advance.

cjawood · 10-15-2006, 10:47 AM

You willl have to pull the dist. and rotate it back a couple teeth.
Then you can advance it more. Your advance canister will be back more to start with.

Motor Daddy · 10-15-2006, 11:05 AM

Or you could just advance the wires on the cap one position in a clockwise manner and rotate the distributor counter clockwise.

red78ta · 10-15-2006, 01:02 PM

my engine guy tried both those idea's & couldn't get it to start

Was thinking maybe he did something wrong but he's pretty good so ..........

Motor Daddy · 10-15-2006, 01:20 PM

Find another engine guy!

j69shep · 10-15-2006, 01:56 PM

Before you change engine guys, check and see if your distributor is in right. The vacuum can should be on the drivers side rear. You'll get alot more adjustment if it is on that side. If it is on the passenger side, you'll definitely hit the intake while adjusting. You'll have to re-wire the cap with the rotor pointing to the new #1. Good luck. J69

Motor Daddy · 10-15-2006, 02:10 PM

j69, If he is hitting the manifold while trying to increase spark advance (rotating the distributor clockwise), the can is on the drivers side.

red78ta · 10-15-2006, 05:21 PM

Yes the vacuum canister is on the driver's side. Actually had the same issue before the build with the factory intake. Was considering pulling the distrubitor myself & trying the one tooth advance & see what happens. Was also thinking the break up could be the curve kit, maybe need more total advance, not initial advance. Runs awesome at idle & part throttle. Thanx for all your input.

goatracer · 10-15-2006, 08:38 PM

Are you still using your vacuum advance. If not you can just tweak the canister inlet a little for clearance. Sounds hillbilly, but that's what I did. My motor seem to like 18 initial, 38 total. Just my two cents. Bryan

Billy177 · 10-15-2006, 10:03 PM

your mechanic probrally rotated the plug wires the wrong way cause on a pontiac it rotates counter clockwise

red78ta · 10-19-2006, 07:05 PM

I pulled the dist. myself, advanced a tooth & checked all the wires. Set it about where I thought it shoud be & fired right up! Adjusted the initial timing to 20 BTC. Still breaks up at full throtle, not as bad but still there. Wierd thing is now it also wants to stall when in gear & had to adjust the idle screw in more to get it to igle at 1050 in park & 850 in gear. Usually when advancing the timming the idle goes up & you have to turn it down.

68fbird455 · 10-19-2006, 10:01 PM

Red - Stop, take a breath. your inital shouldnt be at 20 degrees for that combo. I had darn near the same set up and same problem on a 400 that i pulled out of a 77 t/a for my '68. Actually it was exactly the same set up except for the intake. (I had the RPM) What carb are you using? Listen you dont need 20degrees --bring your timming back to like 12-15, borrow a good carb from a friend and use a 1/2" - 1" spacer. Make sure your vacuum line is correct AND you dont have a vacuum leak somewhere! Get a carb from a buddy and put it on there. Give it a try. Also - the spacer - The spacer made all the difference. I know it sounds wacky cause you listen to it and think you need timming. I did the same thing. My carb wasnt doing justice int he vacuum department the base was warped. I had everything out of wack. I put my buddies carb on and started over and it took 15 minutes to get it dialed in. Let me know and good luck.

Billy177 · 10-20-2006, 01:18 AM

be careful 9.5:1 with iron heads and 20degreese inital timing could ask for troubble. and what does it do when it breaks up?

red78ta · 10-20-2006, 05:22 AM

Have a new JET Perf. Q-jet stage II 750. Don't appear to be any vac. leaks. & can't use a spacer because of the shaker. any other ideas? the factory setting on this engine was 16 BTC. 20 sounded kinda high to me also but figured I'd give it a shot. Do I need more gas? richen the carb? - When I floor it the engine starts to like sputter & "break up" from idle or any speed. & yes I am using the vac. adv.

Billy177 · 10-20-2006, 01:08 PM

hows the fuel pressure? and what are your plug gaps set to

red78ta · 10-22-2006, 01:55 PM

billy177 - don't know & don't know. running a 110 gpm mechanical pump & will have to ask my builder what he gapped the plugs at. Everyone can calm down, turned timing back to 13 & still little change. Thinking some carb adjustments are in order, thanx for all your input on this issue.

cerino2000 · 10-23-2006, 07:15 PM

Sounds like it might be starving for fuel. What are the conditions when it is breaking up? By that I mean, when you are going down the road in 1st gear and flooring it and as soon as it gets to XX RPM it starts breaking up? How about if you are standing still in nuetral and rev it to that RPM? Does it break up then? What gears?

red78ta · 10-23-2006, 07:46 PM

cerino - don't really get to it in neutral/park. Not particular rpm either, can floor it from stand still, while rolling in any gear, or even gradualy raise the rpms & speed then floor it. So yes, I agree it is fuel starvation at WOT. Got few other minor issues to tie up, then off to the dyno for tuning.

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