Bckfires through carb after muffler install

[junkshow]

Still knocks like the pistons are gonna punch thru the head. I'm at a loss, valves are gapped to spec, no play in the crank, oil is getting to the top end. I spoke with my buddy I got the engine from and he said there was no knocking when he had it (he is a trusted source).

I might just tear it apart again to check the alignment of everything.

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[junkshow]

So I've been a little busy with my 4 month old and the new house so not much progress other than the installation of mikesxs valve adjuster screws.

To me it kinda sounded like the exhaust valves were clacking so I set them to spec, double checked and then triple checked. Still knocked.

I went 1 feeler gauge tighter and just a tiny bit better. Maybe. Tuff to tell.

Kinda at a loss here.

Is there something that I may have missed when I reassembled the top end? What can I check for?

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[junkshow]

Well, it's official. I'm an idiot.

It was a loose cam chain. I checked it before but I was afraid to go too tight with it when running. But after doing everything I've mentioned before with no luck, I finally had enough. I decided, the hell with it, maybe this will break the chain or maybe it won't.

And halleluiah, as I was tightening the adjuster nut, the shit got quieter. Afterwards I ran through the rest of the tune up steps and she now fires on the 1st or 2nd kick and sounds great.

Gonna take it for a spin tomorrow to check my work. The weather here in Denver is gonna be around 50.

 

[fancyketchup]

Great man! Im glad you got it figured out! Dont forget to readjust your valves after messing with the tension on the chain... it can alter it slightly.

 

[junkshow]

Yep, I needed to let the engine cool overnight before I readjusted the valves.

As soon as my 4 month old stops screaming I'll be in the garage getting that sorted out.

Thanks for all the help. Now on to getting the hardtail installed and getting it rideable by summer, but that will be a topic for a new forum thread.

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[kerno]

I had backfire problem on 1977 XS650D. Could be contact breakers points not gapped the same. |Because there are two sets they need to be spot on the same gap or ignition can take place slightly out of synch causing backfire.

 

[KentMoney]

it sounds a lot like un-lubed tappets...

 

[jamesgs4]

By the way, here's my girl in all her glory.

I'll be working 11-12 hour days through Saturday so I can't work on the "popping" issue 'till then. I will update my results this weekend.

Been speaking with Rich at G&L about a HT. I know they've been getting bad press lately, but I'm in Denver so I can follow up with him in person if it's tasking too long.

Have you seen ardcore's tail? it is nice.

 

[junkshow]

I have, and I will be ordering mine very soon.

Tapets are getting lube. I've sorted out the knock and am currently working on the back fire issue. I'm trying larger mains since I've installed those crappy silencers.

They will go away when I get my HT.

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[junkshow]

So an update.

Haven't had much time in the past couple of months on account of the baby boy, but heres what I have gotten done. Increased the primary jets from 25 to 27.5, lowered the needle from the middle position to the #2 position and the kept the mains at 122.5. She starts fine and idles smooth but there is a backfire on drceleration from the right exhaust. Does that mean I need to re-sync my carbs?

Other than that, a neighbor of mine has agreed to help install the Visual Impact brat kit I want. I was gonna go HT but I'm 40 and I've spent the past 26 years abusing my back snowboarding and skating. Gotta keep it soft.

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[junkshow]

Update.

Checked the timing, spot on. Checked the sync, seems to be on.

Still getting sputtering from right side muffler. Ugh!

What am I missing?

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[XSLeo]

It could be a bit of air leak where the mufflers clamp to the headpipe. An air leak can let fresh air into the exhaust and let any unburned fuel that gets into the pipe and ignite.
Worth checking.
Leo

 

[junkshow]

It could be a bit of air leak where the mufflers clamp to the headpipe. An air leak can let fresh air into the exhaust and let any unburned fuel that gets into the pipe and ignite.
Worth checking.
Leo

Thanks Leo, I'll look into that tonight.

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[junkshow]

I removed and reattached the mufflers, checked the header bolts, but can't feel any air leaks. I've rechecked the valves, timing, cam chain, etc. but I'm still getting popping on decel from the right side pipe.

I guess I go back to the last known good setup and start over... One size smaller jet and raise the needle back to the center position.

The frustrating thing is that it's only popping on the right muffler. WTF could I be missing?

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[5twins]

You have a problem on that one side only. Changing pilots and needle settings in both carbs isn't the answer. Concentrate your efforts on that right carb or right cylinder settings (timing, valves, etc.). The manifold may have an air leak or maybe the throttle shaft seals are bad. I would also verify that the float level is correct.

 

[junkshow]

Well 5twins, correct as usual. I started her up, sprayed some carb cleaner at various spots around the carb. Wouldn't you know it, hit the shaft With the cleaner and idle dropped. SOB! Time to locate the seals and tear it down again.

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[5twins]

Don't get the seals from Mike's. There have been recent reports that their current batch is bad. Get them right from a Yamaha dealer, they're not much more and you can be assured of a quality part.