Rich plugs, lean symptoms

[MisterCinders]

Running plug tests on the idle circuit. Just putting around town at low throttle settings.

3 of the plugs are black and sooty. Rich.

But I am getting loads of popping on deceleration which I thought was a lean signal.

Idle is pretty solid at 1000. No hanging idles either.
Of the line there may a very slight hesitation, but it's too close to call. Exhaust is clean, but smells a little gassy.


New orings. Clean carbs. Valves are right. Etc.

Jetting is

17.5 pilot
Needle at second lowest spot.
Fuel screws at 3/4 turns.
Air screws at 2.5 turns.

I don't have much room in the screws to shed the richness.

[rustybronco]

Running plug tests on the idle circuit. Just putting around town at low throttle settings.

3 of the plugs are black and sooty. Rich.


Jetting is

17.5 pilot
Needle at second lowest spot.
Fuel screws at 3/4 turns.
Air screws at 2.5 turns.

I don't have much room in the screws to shed the richness.

Put the 15 pilots back in it, or turn in the fuel screws to 5/8 and reset the air screws.

what main jets are in it?

[chuck hahn]

When mine had the Vand H 4 into ones i was running 105 mains, 17.5 pilots mixture screws out 1 turn and air screws out 1 1/2. clip in the center groove... If that helps get a baseline for you.

[MisterCinders]

When mine had the Vand H 4 into ones i was running 105 mains, 17.5 pilots mixture screws out 1 turn and air screws out 1 1/2. clip in the center groove... If that helps get a baseline for you.

Did you also have pods?

Mains are 122.5. Was going to go to 125, after many suggestions here.

[Big T]

If you've only been creeping around town, you haven't gotten on the mains as yet. So don't change those out yet

Plugs chops are required at this point, plus some higher RPMs

[MisterCinders]

If you've only been creeping around town, you haven't gotten on the mains as yet. So don't change those out yet

Plugs chops are required at this point, plus some higher RPMs

Yeah, I was trying to do the pilot circuit chop. Putt around town at low throttle, kill engine, coast to stop, check plugs.

With that sorted, I can try the higher throttle chops.

Reset the fuel screws to about 5/8, air screws to 1.5. Trying to find highest idle, but cannot hear it.

We'll see.

[KEITH KRAUSE]

17.5 pilots are usually the best for your mods. Decel' popping can be difficult to mimimize without causing other (worse) problems. Your motor is in it's leanest condition with the rev's still up but the slides closed. The PJ circuit can supply enough fuel at the more normal rpm's associated with closed/smaller throttle openings but not higher rpm's. Going to a 20 PJ can help but then the bike generally runs too rich at closed/mimimal throttle openings and poor mileage and dark plugs are the result. So I've always found a 2.5 increase works best if you can't get the PJ circuit to run well by richening the pilot fuel screws underneath up to their max' effect range of maybe 4 turns out.
Of course, the carbs need to be carefully synched and the side air screws adjusted for highest rpm first. The side air screws usually end up 1 1/2 to 2 turns out. A starting point for the pilot fuel screws underneath is harder to guess as they're originally set at the factory and because of differences per cylinder, they can be set differently from each other. Typically, they come from the factory at 1/2 to as much as 1 full turn out. I generally start with the screws out an additional 1/2 turn from factory.
The jet needles need richening and 1 position richer (e-clip in 4th groove from the top) is the minimum needed. More often the needles will need to be richer. Position "4 1/2" may be better. That requires a jetting spacer of close to .022" thick. Place the spacer directly on top the e-clip and the e-clip in the 5th (bottom) groove. Test again. Some have found the jetting needs to be at it's richest, position 5. Position 4 may work but be sure to check.
Main jet preference seems to be from 125 to 130 for a good running 750. A few owners claim to run even larger mains but a typical choice is 127.5.
Also, I suggest removing the two floatbowl vent lines when running pods. Leave the ports open. This helps eliminate fuel/venting issues in some comditions, especially windy conditions.

[MisterCinders]

17.5 pilots are usually the best for your mods. Decel' popping can be difficult to mimimize without causing other (worse) problems. Your motor is in it's leanest condition with the rev's still up but the slides closed. The PJ circuit can supply enough fuel at the more normal rpm's associated with closed/smaller throttle openings but not higher rpm's. Going to a 20 PJ can help but then the bike generally runs too rich at closed/mimimal throttle openings and poor mileage and dark plugs are the result. So I've always found a 2.5 increase works best if you can't get the PJ circuit to run well by richening the pilot fuel screws underneath up to their max' effect range of maybe 4 turns out.
Of course, the carbs need to be carefully synched and the side air screws adjusted for highest rpm first. The side air screws usually end up 1 1/2 to 2 turns out. A starting point for the pilot fuel screws underneath is harder to guess as they're originally set at the factory and because of differences per cylinder, they can be set differently from each other. Typically, they come from the factory at 1/2 to as much as 1 full turn out. I generally start with the screws out an additional 1/2 turn from factory.
The jet needles need richening and 1 position richer (e-clip in 4th groove from the top) is the minimum needed. More often the needles will need to be richer. Position "4 1/2" may be better. That requires a jetting spacer of close to .022" thick. Place the spacer directly on top the e-clip and the e-clip in the 5th (bottom) groove. Test again. Some have found the jetting needs to be at it's richest, position 5. Position 4 may work but be sure to check.
Main jet preference seems to be from 125 to 130 for a good running 750. A few owners claim to run even larger mains but a typical choice is 127.5.
Also, I suggest removing the two floatbowl vent lines when running pods. Leave the ports open. This helps eliminate fuel/venting issues in some comditions, especially windy conditions.

Hi Kieth. It was your advice that got me to my current jetting. Problem I am running into is very rich at pilot circuit -- i.e. black sooty plugs.

What baffles me is the popping on deceleration -- which I understood to be a lean symptom. Tried the fuel screws at about 5/8. Still could not find highest idle (I just suck at that I guess), but I tried the air screws at about 1.75 - 2 turns out. Again the bike performed well, except for decel where it popped like mad. Plug chop showed rich sooty plugs.

I wonder if this is a timing issue?

[KEITH KRAUSE]

Before checking jetting, the timing must be spot on and the valve clearances set correctly. Carbs must be vacuum synched. That's just basic tuning.
Also, you said 3 plugs looked rich, but I assume 1 looked OK? Any idea why?
The pilot circuit is by far the most difficult to get an accurate plug read on. Ever watch an older bike idle with a vacuum tool attached and you'll see why. Varying/pulsing vacuum levels, along with many other reasons, make it difficult for the carbs to draw the same amount of fuel at closed/ lower throttle settings. Only careful cleaning/adjusting and tuning can minimize this. And the fine tuning for the pilot circuit, the pilot fuel screws for EACH cylinder, are originally set by the factory with high tech equipment.
If the carbs are cleaned properly and all parts in good condition and the motor has uniform/good compression, then you can tune and expect good results.
The stock 15 pilot jet sometimes works if you richen the pilot fuel screws underneath. The screws have a richer effect as you turn them out up to about 4 turns. After that they are beyond their effective range and if lean conditions are still there then you go with a larger pilot jet. Decel' popiing can also be caused by leaking at the header. Check for leaking before blaming all popping on the pilot circuit.
If you did the plug tests at mimimal throttle and they are dark, then it's rich. Yes, you can still have decel pop with dark plugs. In your case the decel pop should be related to closed throttle and the darkening of the plugs at anything other than closed throttle.
Once the bike is fully tuned you can try again. If you still have the 15's, install them and try 1 1/4 turns at the pilot fuel screws to start. Test when fully warmed up, and if still dark then try leaner pilot fuel screw adjustments. I generally suggest trying the stock pilots first with richer screw adjustments and if you cannot get them rich enough then go to 17.5.
Decel pop is hard to eliminate and usually a certain amount is OK. Trying to completely eliminate it causes worse problems. That's what happens when you change the flow of air through a motor tuned/designed to pass less air.