# briggs & stratton 18hp twin



## 2mcgrath (Oct 10, 2003)

having a problem with my 18hp twin cylinder model 422707 thats about to drive me crazy.it seemed like a coil problem because it would shut off and was hard to get cranked when it got hot,so i changed the coil out no luck still the same problem,so i assumed it had to be a fuel issue,i cleaned the carb and rebuilt the fuel pump,still no luck same thing.ive also tried other carbs and it still does this.i blowed the fuel lines out to make sure they were clear,ive checked for water in the fuel,installed a new airfilter,new sparkplugs.and nothing has seemed to fix it,ive also checked the vacuum line and the fuel line both seem to be ok.sometimes before it shuts off it will act as though you have throttled the motor down and then finally it will shut off.this problem just come about all of a sudden was running fine prior

sometimes you can pour fuel down the carb throat and it will crank and sometimes you can mow a whole yard without a problem,then sometimes it wont.but it has gotten to where it will not crank unless you pour fuel into the carb throat.could the compression be low and be causing this problem?but i mean it doesnt use any oil or smoke.any ideas you guys might have would be great


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## 30yearTech (Sep 14, 2006)

Could be a problem with the valves. These engines are prone to having the valve seats come loose in the block. I would check the valve lash on all the valves to see if they are within specs, and if they are out, then I would pull the heads of and inspect.


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## 2mcgrath (Oct 10, 2003)

thanks what should the lash be set on for this motor?


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## 30yearTech (Sep 14, 2006)

You should be able to locate all the needed specs for your engine at this link:

http://www4.briggsandstratton.com/miscpdfs/RNT/Engine Specifications Chart_ms3992.pdf


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## 2mcgrath (Oct 10, 2003)

cool thanks alot


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## 2mcgrath (Oct 10, 2003)

well tried all that everything was ok,valves look good and appear to be seating good,however it does look like one of the headgaskets has been leaking on one side,because there was some oil and what not on two parts of the gasket and the gasket was pretty blackened in those areas,and there was quiet abit of carbon build up,also the exhaust valve on top was white like it had been running lean on that side.would a leaking head gasket cause this sort of problem?


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## 30yearTech (Sep 14, 2006)

Yes, a leaking head gasket can cause a hard to start problem.


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## 2mcgrath (Oct 10, 2003)

follow up,finally figured it out,i had checked the vacuum line for the fuel pump but i decided i would check it one more time,the outside of the line looked fine,so i looked over the inside really well and saw a small cut in the hose,so i trimmed but ends of the line and put it back on and it fired right up and runs perfect again.so thanks for the help and thankfully its fixed


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