Confused about jetting and my spark plug reading

So yesterday I finally got my xr500 (dual-carb) running and driving after a month long top-end rebuild. I dropped in a weisco 10.25-1 piston (1mm overbore) also has a non snorkel airbox mod

I went up 2 sizes on the pilot and and I believe 3 on the main jet circuit. I've been experimenting and the stock pilot jet seems to work the best but it has really hard starting.

I'm just wondering if possibly main jets are small or to big causing the pilot to be off. Also the plug seems too rich but after I've been cranking on it for a while I see no fuel on the tip of the plug. ImageUploadedByThumper Talk1391829976.311954.jpg

Pilot is too big

Are you adjusting your fuel screw?

Have you adjusted your valves?

Pilot is too big

Are you adjusting your fuel screw?

Have you adjusted your valves?

I haven't adjusted the fuel screw yet because I've forgotten about it when the bike is running. I have adjusted the valves they are in spec.

I thought since I have bigger piston I would also need more fuel in addition to the airbox.

Also I know I'm going to get crap for not running high octane fuel but I'm running regular gas currently with the weisco.

I haven't adjusted the fuel screw yet because I've forgotten about it when the bike is running. I have adjusted the valves they are in spec.

I thought since I have bigger piston I would also need more fuel in addition to the airbox.

Also I know I'm going to get crap for not running high octane fuel but I'm running regular gas currently with the weisco.

 

A larger piston does not need 'more fuel'. 

Airbox / Exhaust / changes dictate changes in jetting.

A larger piston does not need 'more fuel'.

Airbox / Exhaust / changes dictate changes in jetting.

So do you think my main jets are causing the hard starting?

Does it start easier hot?

Was it snorkel mod'd before the new piston?

Warm it up good, get a new plug in it, restart and idle a few mins, cut and check the color.

Extreme rich or lean can mock the opposite condition! Above test and the ability to adjust idle mix screw are the way to know which way its off. I doubt its caused by the main jet, unless its wildly off.

It's the pilot/needle/fuel screw that dicatate hard staring, unless your main is 5 sizes too big...

 

Difficluty in starting cold is often leaking intake valves.

 

You should bump start it, get it hot, adjust the fuel screw, and then kill it, and see if it starts any different cold or hot.

Edited by TheKoolAidMadeMeSick

It's the pilot/needle/fuel screw that dicatate hard staring, unless your pilot is 5 sizes too big...

Difficluty in starting cold is often leaking intake valves.

You should bump start it, get it hot, adjust the fuel screw, and then kill it, and see if it starts any different cold or hot.

I went back to stock jets on the main carb and left 2 sizes up on the secondary main jet.

Replaced the plug and she started 2nd kick. Maybe the old plug was fouled, maybe the carb likes the old jets better... I just don't want losing power because it's running to rich.

I do believe my issues are gone.

The go to jetting on those carbs was to go up two sizes on both mains, shim the needle .5mm and go up on the pilot two sizes, dictated by fuel screw adjustment....assuming you are fully uncorked.

The go to jetting on those carbs was to go up two sizes on both mains, shim the needle .5mm and go up on the pilot two sizes, dictated by fuel screw adjustment....assuming you are fully uncorked.

Thats what I had originally planed but some how I ended up with 2 sizes up on the main carb which I didn't want to send in the jets for exchange because that takes for ever to ship.

She's running pretty good so far. It warmed up 20degrees today so I'm sure that has made a diffrence. It is starting in fewer kicks than before the rebuild so I'm really happy about that!

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