Why am I overheating so often?

Have an 82 seca 750. I bought about 2 months ago. It ran great, changed the exhaust to a 4-1 straight pipe with a baffle then it overheated.

I took it out 2 weeks ago down the highway and it significantly overheated. Took an hour and a half before I could start it again. Since then one cylinder overheats pretty fast at idle.

I am wondering if I need to overhaul the engine or if I just need to change the fuel/air mix or rejet.

 

Carbs will need to be retuned for 4-1 pipe.
First thing have a look at the plugs . That will give you an idea of what's wrong. Post a pic of the plugs please

Next do you have original air box? I hope you do!

 

you need to set the valve clearance and check for vacuum leaks.
read the spark plugs for jetting changes
how can you tell one cylinder is over heating ?

 

+1 what they ^ said.

How do you know for certain? Did you synch and colortune with the stock configuration?

Not if the compression numbers are good. Imo return to stock (the stock pipes are designed to allow the necessary flow and back pressure) to make it run great, swap the pipes, make it run great.

Gary H.

 

The bike does have the box air filter. The two plugs on the left are from the left side of the engine and vis-a-versa.

I'm getting a spark from all the plugs but I think it's only the left side that's firing in the cylinder. As the engine is running I can feel the heat coming from the left 2 header pipes but nothing from the right. Also the engine sounds a lot weaker at idle and when I feather the throttle.

 

Dude, it's an air cooled bike. When you feel the heat coming off of it it's because the wind is blowing it onto you. If you were truly overheating you'd notice a sudden and significant power loss at speed. Getting an XJ to overheat takes work. You do need to rejet though. You have 3 lean plugs ( two look like they may not be burning fuel at all) and one that's burning oil ( maybe due to a bad valve guide seal). The weakness at idle is likely due to the idle circuits on the two cold pipes being plugged. Once you rev the engine and transition to the mains they begin getting fuel and firing.

You need to go to church.
http://www.xjbikes.com/forums/threads/in-the-church-of-clean.14692/

 

Yeah, I open up the throttle and the biked wasn't going any faster, like I lost power.

I was testing the bike parked and idling.

When I was riding 2 weeks ago I lost power on the highway and pulled over to let it cool.

The block was driven hot. Usually after a ride I can pretty much touch the motor. This time I couldn't get close to it.

 

Well in that case I'd start with a compression and leakdown test to see if it's worth looking at further.

Is the clutch the original, or is it new? You may have felt clutch slip. And I don't know about how thick your skin is, but mine gets burnt if I try to touch the engine after a ride.

 

Curious if an IR thermometer would be of use in case like his to check cool and hot cylinders and pipes. What would a typical temp range of heat fins be after a hard ride on a hot day?

 

Lean fire caused by faulty carbs and 4-1 exhaust combined with light weight oil.
Sounds like a recipe for a hot engine!

Is it time to go to Church yet?

~Ghost

 

Once he finds out if it's worth the effort or not.

IN THE CHURCH OF CLEAN

 

Check that the vent in the gas cap is letting air in.