XJ750 Dies When Hot - Won't Start

Hey guys

My '82 XJ750 was running like a champ about 2 weeks ago, and then I ordered and installed the Mac 4-1 exhaust, and it's all gone to hell since.

Before the exhaust install the bike ran like a top. It had a perfect idle speed and pulled hard through every gear.

It now stutters coming from a stop, which I know is probably because of the exhaust and needs a new set of main jets, even though Mac says no rejetting is required for the full system on a stock air box, which is what I'm running.

When the bike is warming up it will idle and run fine, but after about 15 minutes of riding, it will start to hesitate, even under full throttle, and eventually won't stay running, die, then won't start again until it's cooled down.

Where should I begin here? Just remove the carbs, install bigger jets and hope that resolves it?

 

Might be a jet thing, might be a coincidence. Glad you are running an air box, sure makes it easier to trouble shoot. I believe there are others here who have the same exhaust and can confirm or deny the re-jetting thing.

Meanwhile:
Was anything else changed/ adjusted when the new exhaust was put on?
How old/ what condition is the air filter and of what type? (paper/ foam/ etc)
Last time valve clearances were checked?
Last time carbs were rebuilt?
The second part sounds like a fuel starvation thingy... and may or may not be associated. You have gas? Petcock is functioning proper/ vacuum line to petcock is not collapsing? In-line fuel filter condition/ type?

 

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