Back Firing and out of ideas

[Lance Weersma]

Problem solved for the most part. Contacted 650central to buy new jets. They recommended backing out my mix screw 2.5 - 3 turn. That solved most of the stumbling around 2500. The backfiring was also fixed by pulling the exhaust and replacing the gaskets and checking the connection at the 2-1 section. Old gasket vs new

 

[peanut]

so in other words they instructed you to do exactly what we suggested .




"Lance those valve lash settings are too tight. I would be very surprised if the valves are seating consistantly .
As 2M says the symptom is often due to unburnt fuel passing into the exhaust due either to retarded ignition or inconsistant ignition.
It can also be due to valves being sticky or not closing properly preventing proper combustion . Unignited fuel passing into the hot exhaust.

The only other thing I can think of is a leak on the exhaust allowing ingress of air to ignite unburnt fuel or Pilot jets that are too rich maybe.

If it were me I would reset my valves looser first. and check your timing of course

 

[5twins]

Having to run the mix screws at 2.5 to 3 turns out is quite a change from the stock spec for your carb set (about 1 turn). That could indicate you need a bigger pilot jet. If you did use a generic rebuild kit, did you compare the kit jet sizes to what should be in there? Often they are wrong. But then again, running a 2-1 you probably need larger than stock jet sizes anyway. Another questionable item contained in some rebuild kits is the needle. It's usually a generic Y-22. It would be best to stick with the original needles, in your case the 4JN19.

 

[Paul Sutton]

A question while we are on the topic: Valve clearances for XS650 SH are stated as 0.0024" (0.06mm) and 0.0059" (0.15mm) in Yamaha's supplementary service manual. Are these also considered too tight for the later model engines?

Thank you.

 

[Lance Weersma]

so in other words they instructed you to do exactly what we suggested .

passive aggressive? I actually changed the exhaust gasket be yal suggested it... and thank you for that. I then contacted 650 to get a lager pilot jet and he suggested backing out the mix screw. I was just wrapping up the solution to my problem. Someone asked to post when I find a solution. Thanks for making me feel welcome....

 

[Paul Sutton]

Lance - I have a cardboard folder where I print off and keep technically interesting comments from others. For example your photo of the exhaust gaskets will reside there and remind me to replace mine next time it is a part. It will also prompt me of a possible solution if I have backfiring not originating from the carburetors.

It is nice that everyone helps each other like this!

 

[peanut]

passive aggressive? I actually changed the exhaust gasket be yal suggested it... and thank you for that. I then contacted 650 to get a lager pilot jet and he suggested backing out the mix screw. I was just wrapping up the solution to my problem. Someone asked to post when I find a solution. Thanks for making me feel welcome....

ok maybe I was being a little grumpy but 6x weeks of Shingles does that to ya.

The point that I was making allbeit bluntly is that you said it was difficult to know whose suggestions to trust yet you were happy enough to accept the advice of some spanner monkey in a garage who you knew nothing about and almost certainly has no knowledge or experience specifically with the XS650

You said that you has cleaned.... reset.... and synched the carbs so I assumed that that would have included setting the idle air mix screw. This is the problem with trying to diagnose over the internet . You are totally reliant on the posters information.

Glad that you have the bike running well again anyway. That is why we all offer our free time help and advice and experience .

 

[MaxPete]

Howdy all:
I have a question about removing exhaust gaskets. One of mine is stuck (seized?) in the exhaust port of the head. I don't want to damage anything - has anyone found a good way of getting one of these darned things out?

 

[TwoManyXS1Bs]

Hey, Pete. Those kinds of gaskets crush and expand diametrically, locking them into the port. Big problem on some Hondas back when. Just have to use (or make) a stout pick tool, get force/wedged behind it, and go neanderthal...

 

[MaxPete]

Okey doke - I can do that. Thx!