81 srx help

[cotterpin]

Took my 81 out today for first ride since new top end. Got it with melted pistons, (ehaust side). Its been setting since 99 so I put new pistons and rings in and cleaned carbs. ran it up on a jack stand and it sounded ok after a few adjustments. loaded it onto truck and took it to friends farm to test and further adjustments. Unloaded and fired it up and had a bad bog. I fethered the choke it picked up took off strong and boged again. I took it around the field doing that hoping it would clear up. It started running worse brought it home tore it down and found I melted the piston on the PTO side along with the paint on the exhaust side pannel, which I just had repainted and decaled. YEA! I'm thinking pluged mains on the pto sie carb. When I loaded it fuel poured out from somewhere. I looked around thought it was probably the tank vent. Any Ideas? Thanks, Tracy

[Vmax540]

Tracy, what a bummer....What size was the piston wash(clean area) ? The wash at the transfers should be no bigger than ~ the size of your thumb nail. Gutted air box, porting, head shaved, fuel and of course jetting are key factors. http://www.vintagevmax.com/reliablitity.htm I have to wonder if you might of had a leak in the cylinder to carb boot, base gasket or even the PTO crank case seal ? B.T.W. get some reflective and even better is the insulated type silver heat tape for the inside of the panel.

[cotterpin]

To my knowledge it is all stock. The pistons are or were brand new as well as the rings so there was no wash area. I sprayed break cleaner around the heads, carb mounts, base of cylinders, PTO crank seal and around pump side of the motor while the sled was running. It didnt change in rpm at all. Like I said when I bought the sled it had two burnt pistons. Both on the exhaust side. I think he was running it to lean. He was doing alot of drag and lake racing. He also had the oil injection unhooked and was running premix gass. I checked the oil pump and hooked it back up it seemed to be working fine. I know alot of people dont trust the oil injection but I wanted to keep it as origonal as I can. I have to tear the carbs down and check the jetting for size and clogging. Could the carbs be out of sinc and would that cause it? It would start and idle fine but when I throtled it up over 5000 rpm it would idle down around 3000 rpm and stay there. I turned the throtle stops out till it seemed to idle at 1800 rpm and stay there. When I took it out for a test it Idled at 3000 rpm again. I thought the carbs were out of sinc so I adjusted the throtle stops all the way out and turned them in till they touched the stop and then turned them in the same amount of turns. It only burnt the PTO side this time and only slightly not as bad as when I got it. I checked both plugs and the pto side melted the electrode but the mag side seemed to be burning nicely and the piston looks ok. When I got it both pistons were burnt down to the rings on the exhaust side. Thats usualy from running lean right? I have a real nice set of ported cylinders and pistons I can put on it along with a nice head. I just want to make sure I have the problem fixed. before I run it again. Thanks. Tracy

[Bob Vehring]

I'd start at the fuel tank and work forward. I'd also check to make sure all parts are stock or if they have been modified. If the sled was used for racing theres a good chance someone has done some work to it

[Vmax540]

First thing we do when buying a sled is tear into the carbs. to clean and Write down/check jetting sizes. Certainly check the sync but, I do not believe this is the issue. Lean.....Air leak, lean jetting, water in the gas and also, check your pulse lines to F.P.

http://www.smellofdeath.com/lloydy/pist ... _guide.htm

[cotterpin]

I picked up some carb cleaner and Yamaha bond tonight after work. I'm going to tear the carbs down and check the jetting this comming weekend. I believe they are stock, at least according to the last owner. He claimes he didnt change anything except the clutch to a Comet 108. He said the sled ran good except for the clutching, the old YPZ, so he went to the Comet. The cylinders wernt ported and I used to race with him back in the late 70's up until about 85, so I know he's not liying. I think it might be the pto side carb has a blocked passage or jet causing that side to run lean. I might try to go a little fatter on the mains. It appears to be pumping plenty of fuel. There were no air bubbles and the lines are solid with fuel. I checked for air leaks and there's no water in the fuel. Other than cloged passages or lean jetting I dont know what else to think. If I cant fix it I'll go back to running my 78 SRX's I understand them. Thanks, Tracy

[Vmax540]

The pulse lines can have a crack and still pump enough fuel. Keep us updated on what you find.