Topic: Plug read opinions?

[fxef79]

Opinions are like #$%*s, right?  But what’s your opinion of these plugs? They were new when put in, then I ran her good for 30 miles. Some stop and go, but mostly it was 3rd and 4th gear at between 50-70 mph. I have the dual mikuni carbs and manifolds, which absolutely explains why the #2 and 3 plugs are way rich - the carbs point right at the intake runners for the inner cylinders. But what’s your take on the outer two?  Too lean?  When I got this bike all four plugs were just absolutely jet black all the time - way rich. I’ve leaned the pilot jets, main jets, and dropped the needle one slot. Did I go too far? Oh… and I already know everyone’s opinions of the mikuni dual setup.. haha. I have a rack of carbs to rebuild but will also need to source a decent set of 78k/PD carb boots. For now, the mikuni duals is what I have to work with.


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[seanbarney41]

What gas do you have in the tank?  How was performance?  I would say, obviously, 1 and 4 are on the lean side of good, but 2 and 3 ain't gonna keep running good for long that rich.  Maybe try one heat range cooler plugs in 1 and 4 and 1 (or more) hotter in 2 and 3?  I have yet to hear of that Mikuni 2 carb set up working for anybody, either in person or hearsay.

[fxef79]

What gas do you have in the tank?  How was performance?

89. Ran like a scalded dog up to 70mph. Had it up to 8000 rpm a couple times. I really couldn’t get over that on the roads I was on, and this is a hardtail trike, so at that speed I’ve already got a winky brown eye going over every little bump. I think it would do 90 no problem. I think 100 would be really pushing it. I honestly don’t want to take it that fast on this old Harley rear differential.


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[seanbarney41]

In that case, I wouldn't mess with 1 and 4...just try to get 2 and 3 less sooty

[newday777]

There is a proper way to do plug reading to know how your bike is running. Riding around at various speeds and returning back to the shop to pull the plugs to read the color is not getting the accurate reading.
All tuneup procedures must be done before you take it out on a test run. New plugs for each change to get accurate readings.

A description on getting a good reading.....

What is a plug chop?
A plug chop is referred to taking a motorcycle out on the road at certain speed and RPM for a few minutes, without changing the throttle position. Once the few minutes are up, the rider quickly pulls in the clutch, shuts the engine off, and coasts to a stop. Once pulled over, all plugs are removed and the spark plug color is inspected.

 

What should I do before a plug chop?
Simply put, the motorcycle should be in great running condition.

The electrical system should be putting out over 13V to the battery.
Valve lash must be within specification for even compression.
Proper point gap and ignition timing if applicable.
No vacuum leaks.
Carburetors must be synchronized.
Install brand new spark plugs.

I've not dealt with makuni carb conversions, though have seen them, so I can't comment on them. You said 1&4 are manifolded together and 2&3 together??? Do you have special intake manifolds??? The usual set up is 1&2 and 3&4 together.

[fxef79]

I've not dealt with makuni carb conversions, though have seen them, so I can't comment on them. You said 1&4 are manifolded together and 2&3 together??? Do you have special intake manifolds??? The usual set up is 1&2 and 3&4 together.

I never said 1&4 are manifolded together and 2&3 together. That really would be odd. And if that really were the case, then given the color of the plugs i showed it would be obvious that one carb is way off. No, the carbs are one on 1&2, and one on 3&4.

[fxef79]

There is a proper way to do plug reading to know how your bike is running. Riding around at various speeds and returning back to the shop to pull the plugs to read the color is not getting the accurate reading.

Absolutely understood. I wasn’t trying to run a formal plug chop for each circuit on the carbs (idle/pilot, needle/needle jet, main). I was just doing a “shakedown” run. With this much difference between 2 plugs on the same carb I wanted to solicit some opinions, as well as ask some opinions on the actual color of the outer plugs. Reading the color of plugs is an arcane art, and my very limited experience means I might be interpreting “a tan color” differently than others do.

[TwoTired]

I can’t imagine those manifolds are ever going to provide equal mixtures to both ports.  At velocity the inners being more of a straight shot before the split will get more mixture due to inertia of the mix, and starve the outers.  Air and fuel do have mass.  And inertia tends to keep a mass going in the same direction until an applied force changes it.

I suspect you will have to add some internal curved vanes inside to even out the proportion of air being split.  But, then obstructions in the intake path provide problems at high velocities.  Honda kept that path between carb and head port short and straight for a good reasons.  The bike was then shaped around what made the engine work well.

Hard to believe making inner cylinders run hotter for more efficient burning is going to be enough to correct a mixture inequality.  But, I am just doing this from the armchair.

Have you seen any other set ups like this work well?

Best of luck!

[pjlogue]

I've not dealt with makuni carb conversions, though have seen them, so I can't comment on them. You said 1&4 are manifolded together and 2&3 together??? Do you have special intake manifolds??? The usual set up is 1&2 and 3&4 together.

I never said 1&4 are manifolded together and 2&3 together. That really would be odd. And if that really were the case, then given the color of the plugs i showed it would be obvious that one carb is way off. No, the carbs are one on 1&2, and one on 3&4.

Well, after seeing that pic, it explains a lot.  These are pulse feed carbs and with the two very different flow paths between cyls 1&4, 2&3 it explains your very different plug readings.  Do yourself a favor and forget trying to "tune" the carbs so you will have equal plug readings.  It will never happen.  It would work if the flow paths were equal like the 1-2 splitter upthread. 

Your best bet is to get the stock carbs/rack back on the bike.  If you have to run the bike like that I would be very careful about burning a piston or valve with your out board cyls running so lean.

-P.

[newday777]

I never said 1&4 are manifolded together and 2&3 together. That really would be odd. And if that really were the case, then given the color of the plugs i showed it would be obvious that one carb is way off. No, the carbs are one on 1&2, and one on 3&4.

Well, after seeing that pic, it explains a lot.  These are pulse feed carbs and with the two very different flow paths between cyls 1&4, 2&3 it explains your very different plug readings.  Do yourself a favor and forget trying to "tune" the carbs so you will have equal plug readings.  It will never happen.  It would work if the flow paths were equal like the 1-2 splitter upthread. 

Your best bet is to get the stock carbs/rack back on the bike.  If you have to run the bike like that I would be very careful about burning a piston or valve with your out board cyls running so lean.

-P.

Good to finally see a picture and more likely cause of the richness of 2&3

[fxef79]

Good to finally see a picture and more likely cause of the richness of 2&3

Yes. Although my original question wasn’t about why 2&3 are rich. I already know why they are rich. Because of the poor alignment of the dual carb manifolds (although it’s been pointed out that it could also be due to points or coil problems).




My original question was about opinions on the color of plugs 1&4.

[newday777]

Good to finally see a picture and more likely cause of the richness of 2&3

Yes. Although my original question wasn’t about why 2&3 are rich. I already know why they are rich. Because of the poor alignment of the dual carb manifolds (although it’s been pointed out that it could also be due to points or coil problems).




My original question was about opinions on the color of plugs 1&4.

1&4 look good to lean for new plugs with the brown on the ground leg.

Lots on the web on reading spark plug colors.
https://www.motorcyclezombies.com/rebuild-tune-motorcycle/carbs-fuel-air/spark-plugs/