gemini Posted October 15, 2007 Report Share Posted October 15, 2007 i've got a 4 mil cub on alky, just got the motor back two weeks ago from an override repair. took it to LS and it ran real strong for 10 passes or so then it quit pulling on top end. took it back to camp and pulled the plugs out and the tip of them were gone. put a colder plug and put larger mains in b/c i was told it was running lean. took it out again the next day and it ran like a bat outta hell again. ran good the following day, but it only made a handful of passes. took it home thinking all was well, went to ride this wknd and made 4 passes or so and it quit running again. pulled the plugs out and the tips were melted off again. let it sit for majority of the day and put some b8es plugs in it at the end of the day and ran it for like 2 runs and it would never clean up and after the second run it died and wouldnt start again. any ideas why it keeps melting plugs off? Quote Link to comment Share on other sites More sharing options...
theshee Posted October 15, 2007 Report Share Posted October 15, 2007 You said it died and wont start now? If thats the case you prolly burned it down. Plugs melting is usually a sign of a lean condition, hope you didnt burn a piston. Were you checking your plugs after every run? Did you check them at all when you were running? Quote Link to comment Share on other sites More sharing options...
gemini Posted October 15, 2007 Author Report Share Posted October 15, 2007 i was pretty sure the lean issue was resolved b/c it was blowing raw methanol out the pipes and still melted a plug. pulled the head off last night and come to find out it the right piston is missing a piece and part of the top ring is also gone. left piston looks fine other than the fact that it looks like it got a little too warm. both o-rings on the head that are supposed to seal off the domes are blown out at the rear of the cylinder (same place that the piston is gone) and it was blowing all the engine compression into the water jackets and forcing the water ouf of the radiator which is probably the biggest reason it got hot. the cylinders are still in pretty good shape. i'm still not sure why it melted the second set of plugs even when raw fuel was coming out the exhaust. any ideas? Quote Link to comment Share on other sites More sharing options...
FASTOYS Posted October 15, 2007 Report Share Posted October 15, 2007 The only reason for this to happen is: LEAN, either by air leak, lack of octane, or lack of enough fuel ! Your running Alky so i doubt its lack of octane....soooooo its gotta be one of the others. Surely your not blowing raw fuel out at the end of a 500 ft run when your wide open are you??? Quote Link to comment Share on other sites More sharing options...
2strokespirit Posted October 15, 2007 Report Share Posted October 15, 2007 (edited) You probably have a air leak on that cylinder, check out around your reed cages for a blown reed gasket and check the base gasket. Are there a hole in the centre of the piston or is the piston burned away on the exhaust side? Edited October 15, 2007 by 2strokespirit Quote Link to comment Share on other sites More sharing options...
bansheeseat$$ Posted October 15, 2007 Report Share Posted October 15, 2007 Sounds like to me that you had an intake leak from the start and it got progresavly worse untill it started to melt the piston too.The raw fuel coming out the exhaust was more then likely because it didn't have enough compression to properly combust the alky that was in the cylinder. Another thing to check also is your water pump,Make sure it is turning and the propeler has blades on it. Quote Link to comment Share on other sites More sharing options...
badassbanshee479 Posted October 15, 2007 Report Share Posted October 15, 2007 who set the carbs up?? do they have power jets in them?? are you running bigger bowels? fuel pump? how far are you racing?? Quote Link to comment Share on other sites More sharing options...
gemini Posted October 15, 2007 Author Report Share Posted October 15, 2007 The only reason for this to happen is: LEAN, either by air leak, lack of octane, or lack of enough fuel !Your running Alky so i doubt its lack of octane....soooooo its gotta be one of the others. Surely your not blowing raw fuel out at the end of a 500 ft run when your wide open are you??? not at the end of a run, but if its sitting there and you rev it up it'll blow raw fuel out Quote Link to comment Share on other sites More sharing options...
gemini Posted October 15, 2007 Author Report Share Posted October 15, 2007 You probably have a air leak on that cylinder, check out around your reed cages for a blown reed gasket and check the base gasket. Are there a hole in the centre of the piston or is the piston burned away on the exhaust side? its burned away on the intake side Quote Link to comment Share on other sites More sharing options...
gemini Posted October 15, 2007 Author Report Share Posted October 15, 2007 who set the carbs up?? do they have power jets in them?? are you running bigger bowels? fuel pump? how far are you racing?? yes they have power jets, stock bowls 39mm pwks, yes it has a vacuum fed fuel pump, not racing more than 300' Quote Link to comment Share on other sites More sharing options...
FASTOYS Posted October 15, 2007 Report Share Posted October 15, 2007 not at the end of a run, but if its sitting there and you rev it up it'll blow raw fuel out Not to be jerk but you cant always tell what the main jetting is like sitting in camp revving it up. Its like people trying to read a plug chop after driving all the way back to the truck and idling for a bit. Yours may very well be rich on bottom but lean on top. Better start with a pressure test first! Quote Link to comment Share on other sites More sharing options...
2strokespirit Posted October 15, 2007 Report Share Posted October 15, 2007 Not to be jerk but you cant always tell what the main jetting is like sitting in camp revving it up. Its like people trying to read a plug chop after driving all the way back to the truck and idling for a bit. Yours may very well be rich on bottom but lean on top. Better start with a pressure test first! agree, no way to check a plug if the motor does not work, the motor must do some work and not run freely. Quote Link to comment Share on other sites More sharing options...
badassbanshee479 Posted October 15, 2007 Report Share Posted October 15, 2007 do you happen to know what the mains and dump tubes are drilled to?? also, how many turns out did ya have the power jets? Quote Link to comment Share on other sites More sharing options...
gemini Posted October 15, 2007 Author Report Share Posted October 15, 2007 Not to be jerk but you cant always tell what the main jetting is like sitting in camp revving it up. Its like people trying to read a plug chop after driving all the way back to the truck and idling for a bit. Yours may very well be rich on bottom but lean on top. Better start with a pressure test first! valid argument there. i'm leaning towards there might be an air leak on the right cylinder (where the hose barb taps into the intake side to feed the fuel pump) but just to make sure, how do i go about doing a pressure test? Quote Link to comment Share on other sites More sharing options...
okbeast Posted October 15, 2007 Report Share Posted October 15, 2007 valid argument there. i'm leaning towards there might be an air leak on the right cylinder (where the hose barb taps into the intake side to feed the fuel pump) but just to make sure, how do i go about doing a pressure test? Dude on here named RNBrad has a walk-through of how to do it. As for how big the mains were, not sure. We drilled some out bigger after he melted the plugs the 1st time and he had the powerjets all the way open. Quote Link to comment Share on other sites More sharing options...
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