1450 Carb Adjustment

[Berwil]

My 1450 has started surging and missing when I turn the blades on for the first time. Historically the revs bounce 2-3 times when you flip the switch, but lately it keeps going and will snort and miss. I can smooth it out with the choke which tells me its lean. Once its warmed up (5 min) symptoms disappear, can turn the blades off and on all day without issue. Since you can only adjust the walbro carb with the air cleaner off, what is the trick to setting the air/fuel mixture?

Bill

[J-Mech]

I'm assuming you have the adjustable jet Walbro carb. I would take the carb off and clean it up. If the trouble started all at once, it probably has dirt in it. Unless you changed something, like did a tune up, or the engine has been sitting an long time, it shouldn't need adjusted very often. I'd say it's getting dirty.

If you want to just adjust it, turn the high idle adjusting screw out just a little, maybe 1/2 turn, and see how that affects it. Also, you can download the engine service manual in the tech section, it tells you how to adjust the carb. It is important that you correct the lean condition, as it causes excessive heat, and that can score a piston, melt a head, or ruin a valve pretty quick.

[Berwil]

I remember lean is bad from my dirtbiking days...been there. It probably does have junk in it, last month I putt MMO in the fuel to help with a sticky exhaust valve and more than likely it rearranged the junk in the carb. I was trying to postpone a cleaning and buy some time. With a 4 week old at home now, "me time" is scarce. I'll check out the engine manual and see if a slight adjustment will work till I get a chance to clean it.

On the topic of excessive heat; how much does the muffler shroud affect cooling? I ask because mine is missing. It heats up the hood too hot to touch, and obviously being lean isn't helping. Is it a must have item?
Thanks
Bill

[Mike McKown]

I second richening the main jet.

I always set the main jet by opening the throttle wide open with the mower engaged and then adjust the carb by best sound. Rich/lean/rich. Find where it runs best then richen about a quarter turn.

May not be the right way but it's worked for me for years and I've never melted a piston.

This may not fix your problem but if you're really short on time, it just might get you by. Or you can run with the choke partially on. Not a good idea but that works too.

[J-Mech]

Originally Posted by Berwil

I remember lean is bad from my dirtbiking days...been there. It probably does have junk in it, last month I putt MMO in the fuel to help with a sticky exhaust valve and more than likely it rearranged the junk in the carb. I was trying to postpone a cleaning and buy some time. With a 4 week old at home now, "me time" is scarce. I'll check out the engine manual and see if a slight adjustment will work till I get a chance to clean it.

On the topic of excessive heat; how much does the muffler shroud affect cooling? I ask because mine is missing. It heats up the hood too hot to touch, and obviously being lean isn't helping. Is it a must have item?
Thanks
Bill

It doesn't take long to pull the bowl off and at least dump the junk out. I wouldn't put it off.

The shroud directs the air flow out the front of the engine compartment. Without it, the air has less "direction" and can feed back around to the fan. It's not something that is a huge deal, but it will affect cooling. Running lean is the biggest reason you are getting too much heat. However, I'd find a shroud. Rweaver would be your best bet. I'm sure he has one and can fix you up!

[Roy Najecki]

Bill, the cause might be air is getting into the carb via a worn throttle shaft bushing? That will cause the surging and a lean condition. I suspected this on my 149, so while the engine was running I sprayed some carb cleaner at the throttle shaft just above the carb. Sure enough the engine sputtered, which told me the carb cleaner got sucked into the carb via a worn bushing.