Help!!

Davidm90 · L Plate Warrior Joined: 09 Apr 2012 Karma :

Hi guys. Looking for a bit of help. I've recently bought an off road bike. I've been told its a Yamaha DT 125 1992. I'm not 100% I have been given a load of spares with the bike but I have found that the carb on my engine is onto the bottom end but the carb on the other engine is onto the top end/bore. The bike does not run. But if you pour petrol into the plug hole then kick it it starts then dies. I feel it's not sucking fuel into the cylinder as its drawing air. I have looked to buy gaskets kits and possibly a full engine but all the engines I see for sale have the carb going into the top end. Could anyone tell me what bike I really have and or what engine? And if anyone has any pointers on why it doesn't run? Its sparking and I've cleaned the carb any ideas? I could post up pics if they would help?

Davidm90 · L Plate Warrior Joined: 09 Apr 2012 Karma :

I have noticed a lot of views on my post but not one reply. Does this mean nobody knows the answer to my questions?

G · The Voice of Reason Joined: 02 Feb 2002 Karma :

Davidm90 · L Plate Warrior Joined: 09 Apr 2012 Karma :

It's def a 2 stroke. I've tried the choke up and cleaned the carb I'm getting fuel to the carb but the engine is not inducing fuel into the cylinder. Any ideas? The spare engines carb is on the bore and the engine in the bike the carb is on the crankcase. Can't upload pics at the moment will try again later.
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Help

wildmark13 · Derestricted Danger Joined: 24 Apr 2012 Karma :

Is it an Air-cooled DT engine? Some two stroke engines have the carb attached to the barrel, usually earlier models - my trials bike (yam ty80) was the same. These engines work due porting in the cylinder block that allows the fuel to flow in where it is needed. Engines with the reed block on the crank work the same but there is no need for a port to take the intake charge down into the casing as it is already there. I very much doubt the two barrels are interchangeable, although there is a possibility they are both made by yamaha for different year models. Look for stamped markings or part numbers you can use to identify them, and post some pictures!

Here are a few possibilities in case you still haven't got it running. Something is messing with the flow dynamic of your engine, this could be anything between the airbox and the exhaust outlet. If you know there is a spark, and the compression is adequate (you need to check this too, try to roll the bike backwards in first gear, or feel the kickstart lever, there should be a fair amount of resistance). Other things to check for is that reed valves are fitted into the reed cage, that they are not frayed, spit or gummed up. Take the exhaust off too and have a look in the barrel, what is the condition of the piston, is it scraped up? IS the exhaust port blocked up with soot? You may need to clean out the exhaust silencer or expansion chamber if there is a blockage, try to blow compressed air through and see what happens.

If you get the bike started up and it begins to run like crazy and revs out instead of idling, it may be that a crank seal has gone in your engine. If it's bad enough it might prevent the machine from running, you can remove and replace these using self tapping screws if you don't want to split the engine cases.

Finally, make absolutely certain that the carb is set up, if you have an owners manual check the position of the adjustment screws, needle circlip, and that the needle and slide fitted are the ones recommended.

Good luck starting your bike!
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