OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions On Briggs & Stratton Engines bent flange on vacu-jet

I decided to clean the vacu-jet carby on my 3HP B&S engine because I still wasn't happy that it was running as well as it might. Grumpys great advice in another thread enabled to get the motor running quite well but... a friend has a tiller with the same motor that seems to run better. Anyway, I discovered that the flange that mounts the carby to the engine is quite curved rather than flat and that the gasket was probably not sealing properly as a consequence. This could possibly explain the faster than expected idle (couldn't it?).

How should I go about flattening the flange? I thought of tapping with a hammer but this risks cracking the casting (I really don't know about how malleable the alloy casting might be). another option is to grind or file it flat enough for the new gasket to seal properly.

Any advice from those who have overcome this sort of problem before would be greatly appreciated.
Cheers

The "easy" way involves a couple of extra gaskets between the engine and the flange, I personally would use a flat file but great care has to be taken with that approach

It appears to be a zinc or aluminium casting, so I wouldn't risk trying to bend it back to straight. My method for dealing with such things is just to use my floor-standing 14" disk sander, staying close to the center of the disk to keep the cutting speed low, using light pressure, letting the workpiece cool frequently, and moving it about on the disk so it won't clog the abrasive with soft ground-off particles. (You need a very coarse disk to make this work - I use 36 grit just about all the time, and 80 grit when I need to, I don't even own a disk finer than 80 grit). However before I had the sander I used a file, as Joe said. Because this flange is bent quite a lot, if you have to use a file it will take time and be very tedious unless you use an aluminium rasp, then finish with a file. I do not think you can achieve a satisfactory outcome with gaskets, it is bent quite a lot. Remember that you will get a lot of metallic dust in the carburetor: plug the hole in the center of the flange, and expect to have to clean the carburetor in detail afterward.

With regard to your idle speed, does the throttle butterfly close to the point where its external lever rests against the idle speed adjustment screw, when you set the speed control lever to minimum speed with the engine not running? If not, you have a problem with the curvature of the governor's wire link, or the length of the governor spring.

id put it in a vice and give it a few gentle taps with a hammer, probably only needs a couple of taps, it should take quite a beating before it breaks, just make sure there are no cracks in it to start of with and you should be right, or you could spend 20 minutes grinding and filing and sanding it.

OK, I used the linisher (multi-tool) on my grinder and gently touched it up until flat, taking care to not let it get hot. I then thoroughly cleaned the carby and re mounted it to the engine with new gasket. I am waiting on a new tank gasket to arrive before testing it all out. The governor wire is straight etc.
Cheers

That's good progress Beammeup, but does the throttle close against the idle speed adjusting screw when you set the speed control to minimum, with the engine not running?


The diagram shows the idle screw, with a red oval around it, and the stop it should be against, with a purple circle around it. The throttle is shown wide open, as it should be with the speed control set for maximum. When you move the handlebar lever to minimum, the idle adjust screw must move from where it is shown in the diagram, all the way to press against the stop. If it doesn't press against the stop, please say so and we can talk about how to fix it.

Hi Grumpy,
Thanks for the effort you have gone to to explain things. Yes, the throttle does close against the screw when the speed control is at minimum. It looks like the diagram you have shown when the speed lever is turned around to max. Cheers.

If you consider the idle speed too high, check whether the idle speed screw is touching the stop when you set the speed control to minimum, with the engine running. Remember, the specified idle speed for Briggs engines like yours is normally 1,750 rpm, and the maximum allowable speed is 3,500 rpm for your engine (enforced by the governor, to keep from breaking the aluminium connecting rod). If your idle speed is less than half of your maximum speed, you will arouse the ire of Briggs and Stratton, because there will not be enough cooling air passing through the cylinder head fins. After considering that, if your idle speed is too high, you adjust it by turning the idle speed screw anticlockwise with the speed control set at minimum.