Engine running HOT!!!

[underground-mpyre]

So we are trying to bring a '78 XS400 back to life and completely cleaned and rebuilt the carbs, new spark plug and battery. We put on cone pods for filters and after 30 seconds it jumps up to 350-400 degree on the headers. I have a laser temp gauge and I am pretty sure it is not supposed to be even remotely close to that at idle. I am thinking it is getting too much air from the pods and adjusted the idle knob and turned the jets in. What can we do to bring down the temp and still use pods?

 

[willem]

your bike is definitely running lean. You'll need to either switch back to stock air filters, or get bigger jets in your carbs. Have a little search on the forum here (google search, top left search bar, works best). Two sizes up on your main jets and one up on your pilot jets should be a good start. After going up some jet sizes, try adjusting the carbs with the mixture screws again. If that doesn't have enough effect, get either bigger or smaller jets again. Repeat until the bike runs nicely.

 

[HoughMade]

What do you mean: "turned the jets in"?

....but yes, more air in requires more fuel.

BS34s do not control the idle mixture with the air. The idle mixture screws control the fuel supply.

Do you have any air leaks? Also, varying the idle speed with the idle air knob will restrict the air, but with less air flow you will be drawing less fuel too. You want to richen the idle mixture by turning the idle mixture screws out to at least 3 turns.

....we are just assuming those temps. are high. These bikes are not meant to sit still and idle. Air cooled engine have to move to get cooled. Richen up the idle mixture and ride to see if there are signs of it being lean.

 

[underground-mpyre]

Yes, I agree. But when the bike is turned on and running after only 30 seconds, no way it should even be in the ball park of 350-400 at the 1st bend of the headers. Range on that running shouldn't be higher than 300 degrees rolling down the street.
I am going to do a jet kit and see where that gets me. Thanks guys!