backfiring after jet install, jetting fuel mixture?

[dayzeedawg]

I installed a Yoshimura pipe, and a Ivan's jet kit. It starts easier now. The problem is when I accelerate it to @ 5k then let off the throttle it lets out a light back fire. It has stock air filter, and the fuel mix screws are set to four complete turns out as per instructions. I have not synced the carbs but I plan to, just need to get a manometer,or vacuum gages. I have one of those hand held brake bleeders that has a vacuum gage, could I use that.

[jetmerritt]

You need to disable the PAIR system to fix that.

Mine does it too and as far as I have read, you need to totally remove the secondary air system. Install block off plates on the block and remove the valves and hoses.

It's an emissions thing and I don't think it robs any horses, it just adds clean air to the exhaust which provides an opportunity for any unburned fuel to reignite in the exhaust system and for some reason in it's stock form it will not do that.

I kinda like the pop's, but to each their own.

hopefully someone will chime in with a link or some pics.

[GregS]

Just a vacuum gauge will not work to sync the carbs. The vacuum pulses will make the gauge unreadable.
Even with the PAIR system disabled or removed you will get light puttering on decel. Lean mixtures can also add to this, but it sounds like that shouldn't be the case with your settings / jet kit.

[dayzeedawg]

So I should not worry about this. I just wanted to make sure before I put the ignition advance on. Where is a good place to get a manometer or vacuum gage set?