Hip001 Posted May 28, 2007 Posted May 28, 2007 Thank you for taking the time to reading my problem. I have 2 Yamaha bikes right now both with the same problem. When I first start them they only run on 3 cylinders. Once it warms up or if I rev it high the 4th cylinder kicks in. And once hot it runs on all 4. I've went through both carbs with carb cleaner, carb wires(for making sure jets are not clogged) and compressed air for testing the jet passage ways. Both bikes had been sitting and the carbs were gunked up. Even replaced with new gas and some sea foam in it also. The Seca II has Mikuni carbs, not sure of the brand of the Maxim. The left cyl on the Seca is the one and the right cyl on the Maxim are the ones that start off cold. I've swapped the plugs, tested compression(with my thumb), and tested spark. Not sure what to try next. I've went through carbs before with good sucess but found it odd that I have two Yamaha's doing almost the same thing. I do not have a carb sync tool but would like to get one, any recomendations on this would be great too! Thank you for any advise you can give me here! Hip
aunty Posted May 28, 2007 Posted May 28, 2007 Thank you for taking the time to reading my problem. I have 2 Yamaha bikes right now both with the same problem. When I first start them they only run on 3 cylinders. Once it warms up or if I rev it high the 4th cylinder kicks in. And once hot it runs on all 4. I've went through both carbs with carb cleaner, carb wires(for making sure jets are not clogged) and compressed air for testing the jet passage ways. Both bikes had been sitting and the carbs were gunked up. Even replaced with new gas and some sea foam in it also. The Seca II has Mikuni carbs, not sure of the brand of the Maxim. The left cyl on the Seca is the one and the right cyl on the Maxim are the ones that start off cold. I've swapped the plugs, tested compression(with my thumb), and tested spark. Not sure what to try next. I've went through carbs before with good sucess but found it odd that I have two Yamaha's doing almost the same thing. I do not have a carb sync tool but would like to get one, any recomendations on this would be great too! Thank you for any advise you can give me here! Hip Just an opinion here but, get the carbs balanced.. get a shop to do it.. its a lot cheaper than you think! also make sure theres not an air leak into the defective cylinder.. that would explain why its there when cold but not so noticable when its warm, this could simpley be a splt rubber inlet manifold or one of the clamps that hold it being loose. if your woried it may be the leads or something like that.. Wait till its dark, take the tank off (there will be enough petrol in the carbs to start it for a while) start it then look for sparks or arcs lighting up. let us know how you get on, Dave.
Hip001 Posted May 28, 2007 Author Posted May 28, 2007 Just an opinion here but, get the carbs balanced.. get a shop to do it.. its a lot cheaper than you think! also make sure theres not an air leak into the defective cylinder.. that would explain why its there when cold but not so noticable when its warm, this could simpley be a splt rubber inlet manifold or one of the clamps that hold it being loose. if your woried it may be the leads or something like that.. Wait till its dark, take the tank off (there will be enough petrol in the carbs to start it for a while) start it then look for sparks or arcs lighting up. let us know how you get on, Dave. Aunty, Thanks. I may have to do that even though I like to do most of the work myself. Thanks! Hip
Paul Mc Posted May 29, 2007 Posted May 29, 2007 Hi. If you're satisfied that the carbs are clean and not blocked (have you checked that the vacuum pistons move freely in the 'affected' carbs?) and the mixture is correct (no leaks on the manifolds etc) then there's either a problem with compression or spark. As you've checked spark, then compression is last - a possible issue with 1) rings or 2) valves. Rings are easy to check - you've done a compression test with your finger/thumb - I'm assuming that you've gotten all the cylinders roughly the same? In the affected cylinder, test the compression and then pour a small amount of engine oil into the cylinder, give it a few moments and repeat the test: if compression increases (she may spit out a little of the oil) then the rings are an issue (the oil bridges the gap, increasing compression). A proper compression tester would be a good idea here instead of the 'digital' test... If there is no increase in pressure, go to valves - check the clearances on all cylinders, with particular attention to the exhaust valves on the affected cylinders. The timing can be confirmed as being okay at the same time (as you need to set TDC when checking the valves). If the rings are okay, valves okay but compression is down, could be head gasket - if that's the case, get back to us. IF the compression is fine and the timing correct then it's spark (coils, HT leads etc) or fuel (or CDi, but that would normally affect all/half the cylinders). Paul
Hip001 Posted May 29, 2007 Author Posted May 29, 2007 Hi. If you're satisfied that the carbs are clean and not blocked (have you checked that the vacuum pistons move freely in the 'affected' carbs?) and the mixture is correct (no leaks on the manifolds etc) then there's either a problem with compression or spark. As you've checked spark, then compression is last - a possible issue with 1) rings or 2) valves. Rings are easy to check - you've done a compression test with your finger/thumb - I'm assuming that you've gotten all the cylinders roughly the same? In the affected cylinder, test the compression and then pour a small amount of engine oil into the cylinder, give it a few moments and repeat the test: if compression increases (she may spit out a little of the oil) then the rings are an issue (the oil bridges the gap, increasing compression). A proper compression tester would be a good idea here instead of the 'digital' test... If there is no increase in pressure, go to valves - check the clearances on all cylinders, with particular attention to the exhaust valves on the affected cylinders. The timing can be confirmed as being okay at the same time (as you need to set TDC when checking the valves). If the rings are okay, valves okay but compression is down, could be head gasket - if that's the case, get back to us. IF the compression is fine and the timing correct then it's spark (coils, HT leads etc) or fuel (or CDi, but that would normally affect all/half the cylinders). Paul Paul, Thank you for your reply! Looks like I got some work to do. Will look at these areas later this week. I did notice that both bikes had dry manifolds. Could this be the problem? Thanks! Hip
Paul Mc Posted May 29, 2007 Posted May 29, 2007 "dry manifolds" - do you mean that the rubbers (between carb and engine, or between air filter housing and carb) are old/dry and cracked? If they are still seated correctly, that shouldn't be an issue - they should still seat/seal correctly. One 'test' for leaking manifolds is to spray a can of WD40 (do you have similar material in the states - or plusgas/easystart instead?) around the area - if air leask in, then the engine should run a little higher revs as the material is drawn in through the cracked manifolds... Another thing to look at is the actual colour of the plugs in the affected cylinders, determine if they are running lean, determine if fuel is reaching the cylinder when the cylinder refuses to kick in (should be damp/smell of fuel etc) and such like - definately do all the non-invasive checks that you can before deciding that it's a head gasket or similar (before you start to pull the engine apart!). Paul
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