Vstar 1300 | Throttle Body Sync

Jroddy13 · Sep 7, 2025

I messed with the sync screws like an idiot trying to lower the idle a tad before I actually learned how these bikes work and what certain things do. Problem is I can't get it back in sync. I have a manometer, which I used. I can get it synced at idle but any amount of throttle and it starts to drift pretty bad. Please please PLEASE DO NOT TELL ME TO REFER TO THE SERVICE MANUAL bc it's not telling me in depth how to do it. Someone told me bc the front (factory set and not suppose to touch)got messed with and now there's no baseline that I have to readjust the butterfly's in the throttle body. Also says your TPS should read 15-17 when in closed position and mines reading 19.. Was told to adjust that down lower as well bc it'll throw everything off.

So what I'm asking is what EXACTLY do I need to do, STEP-BY-STEP DETAILED INSRUCTIONS! PLEASE AND THANK YOU!!

lesblank · Sep 7, 2025

The service manual has pretty detailed instructions.

I know you asked for step by step detailed instructions, but not sure how much detailed I can get.

You are looking for a even reading at idle. Above idle the vacuum pulses are quicker and erratic. You sync at idle.

You base reading for lowest cylinder should be 9.4 to 11.

Jroddy13 · Sep 7, 2025

So, I can't really do this with only a "DIY" manometer I'm assuming?

lesblank · Sep 7, 2025

I would and do use a home made manometer. I only quoted reading for reference. When syncing, you are getting the two throttle bodies to open at the same time. Get them synchronize at idle, and you are good.

dogshome · Sep 7, 2025

Hiya, from what I've learned, yes the air screws are just for idle. The butterflies are closely linked in the same housing and ostensibly non-adjustable. If you have some free play in the cable and have not altered the TPS position, you should be able to get it stable at idle (only).

If the O2 sensor is connected (not linked out with a resistor), then the idle mixture should sort itself out.

Jiggling about above idle can't be adjusted - I don't know if you have any mods to the bike, but if you have a non-standard exhaust and /or inlet, without ECU mods or fuel commander etc, then it's probably due to the weak mixture caused. The O2 sensor doesn't affect this area when the bike is stationary.

How is/was she running at low speed/throttle? Do you have any inlet/exhaust mods?

Vstar 1300 | Throttle Body Sync

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