Hey Weber guys

[ahdoman]

Thanks to the info on the board here I've got my Weber running pretty good. Now my only problem is trying to get it to start when hot. Anybody else ever experienced a problem getting the bike to start when it's hot? If so, how did you fix it or how do you start it?

On another interesting note: I was talking with a guy who is pretty proficient with tweaking air cooled engines with dual carbs. He was saying that he will sometimes run different jets on the same carb because of the way the engines cool. It made me think, I know our cylinders run at different temps and the manifolds have different angles. Has anybody ever set up different jetting for the horizontal vs vertical cylinders?

[jayh]

Sometimes when mine is really hot,it will idle really slowly on initial startup for a second or two,then return to normal running. If it doesn't fire straight up or if it stalls, I use a fraction of throttle on my second attempt of starting.Not a fistfull of throttle though or you'll flood it. J

[higgy]

Thanks to the info on the board here I've got my Weber running pretty good. Now my only problem is trying to get it to start when hot. Anybody else ever experienced a problem getting the bike to start when it's hot? If so, how did you fix it or how do you start it?

On another interesting note: I was talking with a guy who is pretty proficient with tweaking air cooled engines with dual carbs. He was saying that he will sometimes run different jets on the same carb because of the way the engines cool. It made me think, I know our cylinders run at different temps and the manifolds have different angles. Has anybody ever set up different jetting for the horizontal vs vertical cylinders?

Hi Jay

Perhaps you are having an ignition issue ? Mine,at least the last time it was running just required a quick squirt from the pump and maybe slight crack in the throttle to get her going. I have changed out the stock coils on both the 906 and the 907 and have opened up the plug gaps a bit. Dyna 3ohm on both and NGK iridiums dr8eix


Would be interesting to know exactly what the difference in cylinder temp really is. See know reason why slightly different jetting from side to side wouldn't help.

[jayh]

G'day Higgy

It's common practice to run different jetting on the rear cylinder with dellortos on the 500 and 600 pantahs,because of reduced airflow and hotter running temperatures.I'm not sure if this is an Australian thing because of our climate or if it is common place world wide ? Fatter on the rear mains I think from memory,but I'd have to check my invoices to see what they sent me last time to be sure. J

[ahdoman]

The guy I talked to says he's got a special rig he uses to monitor the engine temps on the aircooled's; he puts a temp sensor ring on each plug and has each one attached to a temp guage. That way he can monitor the temp of each. Then he messes with jetting and mixture according to what his data shows him. That's a lot of work with probably minimal differences but he's got a pretty impressive history of building some truely fire breathing engines. Some race classes only allow minimum mods so getting an engine to run at it's top is critical.

Anyway - back to the hot start issue... any ideas? I've got the bottom of my tank insulated and I've even taken the time to sleeve my fuel line with heat reflective tubing. So it's either got to be in the carb or the manifold. Maybe I'll try to put a heat shield between the airbox and the engine?

[Mc tool]

K100 Go cart racers use that temp thingy ( its called a thermocouple ) under the plug and actually fiddle with the main jet whilst on the hop according to what it tells them. There carbs are usually Tillotsen with screw adjustable jets ..... sorta like a chainsaw carb I have not been able to logic out the difference between left and right carb idle screw settings on my Guzzi
Hamish

[ducbertus]

having different jetting for different cylinders is not uncommon.
Bevelheads like the 900 SuperSport ran 152 main jet in the front and 155 main jet rear, due to the location of the inlet and exhaust port of the rear cylinder.
Measuring the temp. is a good thing to get them "balanced" in heat dissipation.

Bertus

[ducapaso]

It sounds like oil vapour from gearbox. Try removing the pipe from the air breather close to the battery and have a long ride to clean the engine fron oil fog. Afterward you might need to have a leaner CO carb tuning.

[ducinthebay]

I have always run the rear cylinder one jet richer on the mains, and kept everything else the same. Of course you make some adjustment in the cables and throttle stops when you balance the carbs. Some older british cars actually ran different/cooler plugs in the center cylinders because they had only one carb and couldn't cool the center cylinders as well as the outside ones.

As far as hot start, the old addage is that a lean engine always starts easier than a rich engine. Try adjusting the idle circuit a bit more lean and see if that helps you.

Cheers, Phil