hei timing question

[dyingdeadman]

I got my hei installed, but the motor seems to run kinda rough. when its in gear (at a stand still/stopped) it seems to surge a little. my carb isnt in very good shape but will be fixing that hopefully next weekend.also the engine seems to be pinging or rattleing a little during acceleration. sry rambling. anyway the engine is a stock 402 b.b. have 2 questions

1. what degrees should I set the timing at?

2. could the bad carb be causing the problem or could it be a vacuum leak some where.

[mrein3]

Originally Posted by dyingdeadman

I got my hei installed, but the motor seems to run kinda rough. when its in gear (at a stand still/stopped) it seems to surge a little. my carb isnt in very good shape but will be fixing that hopefully next weekend.also the engine seems to be pinging or rattleing a little during acceleration. sry rambling. anyway the engine is a stock 402 b.b. have 2 questions

1. what degrees should I set the timing at?

2. could the bad carb be causing the problem or could it be a vacuum leak some where.

If it is pinging on acceleration you need to back the timing off until that goes away.

I have a HEI in my new 383. I started at 8 degrees before. It pinged pretty good when I got on it. Right now it is at 4 degrees before and works good.

The rough running could be the carb. To check for vacuum leaks spray carb cleaner around all the usual places - base of carb, intake, etc. If the idle picks up because of the carb cleaner you know where you have your leak - if any.

[PICKMUP]

A lot of these HEIs have way too much advance built in. Some up to 45. You need to get this down near our original specs. A timing light with adjustable advance helps check these.
When they have too much internal advance, you can't get them to run well. If you set them at the crank for good low end power (8-12) they will ping like crazy. If you set them so they don't ping, the motor will be dead at lower rpms.

[Huck]

Another key point on upgrade to HEI is the plug gap. Where the stock gap recommendation is .035, on an HEI the plug gap is recommended to be in the .045-.060 range. Also make sure the ignition lead that goes from your fuse box or ignition switch is a heavier gauge then the stock wire as the HEI pulls more juice. You can also play around trying to run off full manifold vacuum or ported vacuum as I've seen trucks run on one or the other---.
Good Luck--Huck

[mr402]

I run about 10 degrees on my 71 402. It has a little more cam than stock so it can take more advance. I also installed a curve kit with light springs and have an adjustable vacuum advance. No ping problems on regular gas.

[dyingdeadman]

thank you, i am going to go out and play with it and see if i cant get it dialed in. dont think my timing light has the ajustable advance.

[GMC AMI]

A lot depends on the compression ratio of the engine and octane grade of fuel you are using on the spark knocking. The lower the compression, the more timing advance you will be able to run without the pinging on a lower octane fuel. You should be able to run at 8 degrees with no problems.

[dyingdeadman]

ok well, for some reason i cant find the timing marks on the balancer, but i pluged the vacuum advance and kinda timed it by ear and it runs quite a bit better. still a little pinging under high acceleration but at least it runs smoother.think i might have to get the curve kit so i can get it fixed right.