Bogs at takeoff when fully warm, valves maybe?

Hello,

Recently I got my XJ 550 Seca running very nicely, carbs are balanced and floats are wet set. Inside of carbs are super clean and I went up sizes of the jets as recommended by chacall (I have a 4-1 exhaust with aftermarket muffler).

However, when the bike is fully warm and no choke is on, the bike stumbles when first taking off, and I can feel (and hear) that the bike is lower on power.

The reason I mention valves, is I have not adjusted them (the bike has 17k on them, not sure last time they were checked). Do valve clearances change from heat? I.E. are the clearances so close to being out of spec that when they warm up they ARE out of spec and this causes a loss of power?

Thanks for your time.

 

Yes, clearances do change when valves are hot, this is the reason why the manual says to check them on a cold engine.

 

Definitely check your valve clearances.

However, I too had somewhat of an over-rich condition when hot on my bike. The thought was to richen the mixture to compensate for the 4 into 1 exhaust I had put on, but had to lean it back out to get rid of the off idle stumble.

What were the stock jet sizes for the pilot and main jets, and what sizes did you change them to?

Did you raise the needle heights as well?

 

Valve clearance should be checked every 5k

 

Although Valves do need to be in specs; bogging-out upon take-off usually points to a Mixture issue.

Bogging generally happens when the Mixture is too Rich.

There are a number of reasons why the Mix may be too Rich.
To get it sorted all-out; you need to go-over all the steps of Cleaning, Adjustments and Fine Tuning.

The process begins with verifying those Valve Tolerances.

Welcome to the world of "Wrenching"

 

the one thing that chacal's recommendations state is that those calculations are only a starting point. One thing I've just recently found out is how the pilot and main air jets react with the fuel jets. I had an off-idle stumble on my 650. I started messing with my pilot air jets and found a setup that seems to work well. I will be purchasing more sizes in the future to see if I can fine tune the setup even better.

Just my 2 cents,

 

DANGER, WILL ROBINSON! DANGER! Valves not maybe, more like probably.

If the bike has 17K miles on it and the valves have been ignored (likely) then you're about to burn one if you haven't already.

That should have been the first step in the carb-sync process. I strongly suggest you check them immediately lest you damage the motor. Maybe you'll get lucky and somebody before you knew what they were doing.

You really need to check them right away.