hi guys ive just rebuilt my l28 and i have put a performance camshaft in it my qestion is how much will this change my timing i cant seem to get it to start and its seem to be a timing issue .all timing gear has been set to factory settings

You would need to change timing to get max power out of your new cam but it shouldn't allow you to start the engine.

I would advice to check again.

First, do you have sparks? are you sure gas is going through carbs?

Then, I would check firing order to make sure it is ok, check also dizzy orientation at TDC.

Check timing while cranking also if you can.

TDC on the compression stroke....

You need to give us waaayyy more info then that.

What's it doing?

Spitting?

Hitting but not starting ?

Turn over easy?

Like said above - sure its nothing else?

Verified spark?

Degree the cam?

Like Steve said, we need way more info. The common mistake is to have the distributor 180° off, but it could be a lot of different things. Have you built a Z motor before> Did you start with a new chain and gears? Give us the build details and we'll help you.

its on tdc its not 180 out ive got spark and fuel all timing gear is new yes ive built l series engine,s in the past but not with a bigger cam.the car was just turning over when it did fire it back fired thou the exhaust and flamage out the carb

Your going to have to do better with your post. I am struggling to read your run on sentences. I would love to help you, but I need to understand you.

Have you degreed a cam before ?

Did you have the timing cover off when you installed the new cam so you could count the sprocket teeth.