Backfired now won’t run right??

[azsxr]

I was just finishing up the break in and doing a plug chop on my 96xp with proks. 75 low and 145 highs. The plugs looked a little dark I turned the low and hi adjuster in a 1/4 turn each started it up and got a backfire. I thought it must of loaded up. Tried to restart it
and it didn’t want to so I pulled the choke and it started right up but died when I tried to give it gas. I can get it to run if I pull the choke for a sec and feather the throttle. I get it to run and than when I left off the gas the idle goes down to 1600-1700 and back up to 2300-2400 and than drops to 1450. When I give it gas again it bogs like it’s rich and either clears up and takes off or dies.
The thing is it ran awesome before the backfire and now it acts like it’s lean and than rich?
Could I have popped a seal?

Thanks

 

[mikidymac]

Typically a backfire is from a leaky needle and seat flooding the engine.

I would check the carbs before thinking you blew a seal.

 

[azsxr]

It’s brand new 6 hrs on it

 

[azsxr]

Now the mag plug is white And it was coffee and cream this morning.
I’m ready to torch this fucking thing
Thanks for the help

 

[kenfyoozed]

why not reset the carbs to where they were before the backfire and try again.

 

[azsxr]

Already did and the mag cylinders is lean now

 

[kenfyoozed]

Sounds like a carb issue. I would go back through them with an OEM Mikuni kit, following the FSM and or the carb sticky.

 

[azsxr]

I’ll pull the carbs and keep my fingers crossed

 

[azsxr]

So I got the carbs pulled and the arm for the N/S is over bent and I can see at least a 16th of an inch maybe more gap on the Mag carb. I don’t think the diaphragm is making enough contact with the arm to open the N/S all the way.
How could this happen? It was good and I stoped checked the plugs it backfired on restart and never ran right after?
WTF?

 

[azsxr]

Well that helped but not the problem the idle is unstable and kinda wants to runaway.
FML

 

[kenfyoozed]

Runaway signals a lean condition I believe. When you did the carbs did you test the popoff pressures and the perform the leak down test?

 

[azsxr]

Yes I did recheck the pop off and the carb held 10psi for 10min

 

[Sportster-2001-951C-Stock]

Did the RV timing look okay? Compression okay?

 

[azsxr]

Rev timing was good I’ll check the compression this evening .

 

[JeremyD615]

I’m sure you’ve already done it, but have you swapped those plugs for new ones? Also, have you checked the fuel lines/filter/selector for air leaks? It doesn’t sound like an air leak is your issue, but it’s easy enough to go through and rule out...

 

[azsxr]

Yep changes the plugs and have the fuel line coming from the reserve nip to the filter to the carbs.
I have a bad feeling about doing the compression test.

 

[azsxr]

150-150
Idk I’m going to drain the fuel and fog it till winter. I have 3 other skis to ride
another 96 xp , 96 blaster and 92 xp so I’ll be alright.
This thing kicked my ass and I know when to say when.

 

[azsxr]

So the lake I had a room at for the 4th has been closed for weeks due to fire.
I got bored and pulled the head today and found something

 

[Sportster-2001-951C-Stock]

To me it looks like the ring has been wiped of oil film as it passes the edge of the incorrectly chamfered port?

 

[azsxr]

Yeah
Do you think I can get away with chamfering,
hone and new rings?
Would this cause it to run all jacked up?
Thanks and Happy 4th

 

[Sportster-2001-951C-Stock]

May have a broken ring due to ring sticking to cylinder wall? The compression could be low as a result, low compression runs jacked up. So would a blown crank seal.

If piston ring land isn't damaged, I think chamfer, light hone and new rings you're back in business but make sure piston clearance is measured by a machinist who knows how and owns the micrometer set,, confirm ring-end clearance with piston locating pin diameter as well.

Something caused the ring or piston to stick looks like, no chamfering of port wipes oil off the ring perimeter face, lack of clearance, lack of oil, too much heat (lean).

It would be good to know what the compression was, but whatever's going on there needs to be addressed.

 

[azsxr]

150 psi

 

[Sportster-2001-951C-Stock]

150 psi will run fine. Ugly wear pattern but not THE problem

 

[azsxr]

Before I pull the engine I’m going to swap carbs from my running 96xp and see if there the problem.

 

[Sportster-2001-951C-Stock]

That would definitely rule out a carb issue, worth a try IMO.