Backfire

[adam79]

My bike, which I bought a month ago, bogs down in the high RPM range when riding, and backfires. Steadily over time the backfire has got worse and louder. The other night I had the brilliant idea to re seat all of the pilot(?..I think that's what they are called, the single screw on top of each carb) screws on the carbs, and then turn them out 2 1/2 turns. Now the bike just backfires when I try to start it. I'm taking the carbs off to clean/rebuild them, so my question is: Is the back fire I'm experiencing all due to carburetor trouble or is their another suspect? Will a proper cleaning/rebuild fix my backfire problems?

[randy]

It's a good bet that you need to do a valve adjustment. on these bikes, the valve clearances tighten up over time, sounds to me like you have severly tight valve clearances, may even have some so tight that they're hanging open.

[prometheus578]

Randy's advice is sound. And even if that's not the main problems, it's good to know just where your clearances are at, as they do change.
Could be carb/fuel related. What do your spark plugs look like?

[adam79]

I havn't looked yet at the spark plugs, but I will. I looked in the maintenance section and could not find the procedure or tools needed for a valve adjustment. Does anyone know where I could find that?

[randy]

Get yourself a service manual, preferably a genuine yamaha manual, the clymer's is know to have gross misprints. Both are available on ebay.

[dbeardslee]

Out of synch carbs can make 'em backfire to, as well as frontfire and sideways fire too. Have you had them synched?

[adam79]

I could not find the service manual for the 79 special . I did download the service manual for the 1978 XS1100E, but I do not know if the the valve clearances it gives are the same for my bike (79 XS1100SF)

[bikerphil]

valve clearances

The 78 + 79 heads are the same, so the clearances should be the same too. 80 +81 uses a different head. Here's a link for a manual that covers 78-81. Just type in make and model..


http://web.ebscohost.com/serrc/searc...0sessionmgr103

[redbone]

try wires too

sounds like a problem i had once....start with the easy stuff and check your plug wires and caps. find the tech link on this site, use a multimeter to find [or not] the correct resistances. i too started to mess with the carbs only to find it was just bad wires and caps. hope this helps.