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XVS 650 classic running too rich


moschmi
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Need help!

I have a Vstar 650 classic, all stock.

Here's my problem:

Starts up no problem. It's running too rich. Symptoms: Spark plugs totally black, fouled. Oil very black, backfiring when decelerating, very bad MPG at around 30, was 50 before.

What I did: replaced all jets, cleaned carburetor, checked float level, changed gas, turned pilot air screw 5 times out (normal 2.5 times).

Still backfiring...

What else can I do?

 

 

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Put the air screw back to where it was, that is just working around not fixing the problem. Engines going rich if there is nothing restricting airflow (like af above) is spark strength. If a plug or coil is breaking down or the is an earth conection going bad the wimpy spark will not trigger the burn early enough in the piston stroke so instead of a strong hot burn you get a slow burn at  lower pressure and temp which leaves a lot of soot/rubbish behind.

There is after that the big ugly of a compression test...

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I changed air filter, I changed spark plugs. Could it be the coil?

I disassembled and cleaned carburetor many times. All parts look good. Blew carb-cleaner and air through all possible holes. Still rich. 

If it is electrical wouldn't I have problems starting up?? But it starts up even without pulling the choke... even in the morning (not so cold here in DC at around 50s now). Maybe it is running on choke all the time...

May need to disassemble that. For that I need to separate both carbs and I was trying to avoid that...

But on the other hand bike runs well, revs without hesitation into high rpm/speed. takes me uphill just fine.

 

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  • 2 weeks later...

TPS was out of specifications. Was at 928 Ohm at slosed throttle and full throttle 4280 Ohm, Changed to 650 - 4000 Ohm. Also changed ignition coils although they were within specs. Cheap, only $17 a piece. I didn't disassemble choke.

Took it for a spin. No more backfiring.

Maybe the TPS was the problem. Will report back after a few runs....  Will check spark plugs and MPGs.

 

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  • 2 weeks later...

It's not that. Same thing.... Tested the compression. Front at 170, back at 165 psi. Looks good.
Could it be a vacuum leak? I'll test for that. The intake manifolds looks somewhat cracked. So I checked the carburetor joints with propane torch and with carburetor cleaner spray. Definitely there are cracks! RPM goes down greatly. Ordered new ones from partzilla.

While waiting for the parts I unplugged the air induction system. No more backfiring. But I am sure it just got rid of the symptoms. Bike still starts when cold without choke.

 

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