Topic: Cylinder 4 fouling plugs

[SamP]

Continued working on my 77 550k today.  Stock air box, foam filter, MAC 4into1 exhaust.

Quick recap, I ran a chop at WOT and determined I needed 100 mains - nice chocolate brown on the tip. Running tests at 3/4, and when I synced after dropping the clip to the lowest position on the needle I noticed cylinders 1 and 4 were drawing more vacuum. Asked the forum if that would have affected my previous chop reading at WOT and the consensus was not to worry about it.

Fast forward to the bottom of the mountain to run a chop at 3/4, and I remove my plug on 4 and it's carbon fouled to hell, which made no sense at all - cylinders have been running lean, so a fouled plug doesn't fit into that equation. I had checked float levels previously and all were lined well.

So I put the fresh plugs in and gun it uphill at 3/4. Bike is pulling nicely and I'm going uphill at about 75 on the way. Get to my stop, kill the engine, pull the clutch,  coast to a stop. Plug 1 is lean, barely registering any deposits, and plug 4 is leaner still, with virtually none (reminder, this plug was fouled to hell on the ride to the mountain).

So I rode home with the new plug in 4, got home and checked the plug  - fouled again. Did a vacuum leak test with some carb cleaner. Sprayed the carbs on the air box side and the manifold side, no increase in RPM.

I've always had issues with number 4 so I'm wondering if the carb is just cursed or what. I've noticed when I'm syncing that if I nudge the slide or the linkage between carb bodies, it messes with the vacuum, more so on 4 than any other body. Sometimes just blipping the throttle will make the vacuum weaker or stronger on that cylinder.

What's more is I realize that I can't enrich the mixture at 3/4 any further since the clip on the needle is at the lowest notch. To enrich I'll need to bump up mains to 102s (ran 105s and fouled the plugs, again, unless my sync was bad), which would theoretically make my fouling issue on 4 worse.

I'm at a loss here and don't know where to go with this. I'm probably going to double check my sync, purchase some 102s, and start looking for more pd46s online just in case...

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[BomberMann650]

This is curious.

Are you using the a/f mix screw to fine tune anything?

How is the compression on that cylinder?  Valves in spec?

And which carbs?

[SamP]

I'm not using the mixture screw until I've got mains, 3/4, half and quarter all dialed in. They are set to spec 1.5 turns out.

Compression was good last I checked, but I'll check again. I think it was 120.

Lapped the valves myself and checked tappets as well. Carbs are PD46A.

The fouling started happening after I lowered the clip on the needle. Before lowering, the fouling was mostly resolved.

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[calj737]

The fouling started happening after I lowered the clip on the needle. Before lowering, the fouling was mostly resolved.

Please confirm exactly which slot you are in. 1 is the bottom, nearest the tip, 5 is top farthest from the bowl.

If you are in position 1, then you will be pulling massive amounts of fuel, and you need to raise the position to reduce the fuel. Then set about adjusting the A/F mixture in combination with the proper jet sizes.

You talk about "up and down the mountain". What elevations are we talking about?

[SamP]

I'm in position 1, so the needle is drawing lots of fuel. But if that were the issue, my plug chop should have demonstrated that which it did not - it was very lean. I've run chops for WOT with 110s and 105s and they both were black and sooty. 100s had a chocolate color, so I stayed there, but think my sync could have been off. But running the same test for 3/4 on the same mountain showed ridiculously lean plugs.

My current elevation is about ~600-700 feet, and the mountain is about 1800 by the time I hit the kill switch.

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[calj737]

With those settings, I question your fuel level. Using the Clear Tube method, be 100% certain they are within 3mm of the bowl surface. With the swaps and changes of jets, its very likely you're either too low on the fuel, or, you're getting a fuel flow obstruction.

[SamP]

Well, I ran some tests. Compression was lower than I thought. 70-60-65-78. Oil didn't seem to bump those numbers substantially, so I checked my valves and made some minor adjustments. Afterwards they were 70-70-70-78. Oil did not do anything afterwards, but I think I may need to ride for a while to burn the oil from the pre-adjustment tests first before it would make a difference.

Checked the fuel level with the clear tube method. I think they were all too high, so I lowered them. I'd had issues with this method before - if the petcock was on when I opened the drain plug on the float bowls, the gas would surge and go way higher, as it seemed to create space for the fuel to go and would then overflow. If it was off, I could get a decent reading of the fuel level, I just had to account for her gas that was in the line. Not a great workaround, but I couldn't get why this would happen so I just dealt with it. Today that wasn't happening except for in carb #1, and I got the fuel level to about a quarter inch below the the top of the bowl with the petcock on 2, 3, and 4.

Carb 1 was different. As soon as I opened the petcock, gas rushed into the tube, and rose way over the line. I cut the petcock off, I closed the drain screw, and checked the bowl level only to find it about a half inch from the top - much lower than the tube indicated, which was quickly climbing over the bowl top by about a half inch.

So I screwed on the bowl and just let it fill with the drain plug closed for about a minute. Turned off the petcock, opened the drain screw and the gas slowly crept into the line.... And kept climbing. Over the top of the bowl. I closed the drain screw, removed the bowl and easily determined the gas was no where near that height, even accounting for the drained off gas.

My float needles are good, and keep the inlet closed, I've tested this. But for whatever reason, the tube draws gasoline out of the bowl and if the petcock is on, causes the bowl to overflow. I eventually capitulated and set the gas height to about where he others are, since the clear tube method wasn't cutting it.

Put her all back together and started her. She ran a little rough, and cracking the throttle cold caused it to bog down, but I might try and do another sync and see what my WOT chop looks like again. I'm thinking I still may need 102s since my 3/4 chop was so lean (picture of plug from cylinder 1 included)



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[calj737]

I'm sorry to harp on you, but, if your float valves aren't working properly and cutting off the fuel during the Clear Tube method, you will NEVER solve your tuning issue. This is a critical aspect and the measurements need to be very accurate.

[SamP]

Even if the gas cuts off when the drain screw is closed? I'm not having any flooding issues or overflowing carb bowls otherwise. I do have some extra float needles I can plug in and see how they run.

Also, I realized I ran my compression test cold. Will warm up and test again

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[harisuluv]

You should post some general pics of your setup.  The one picture we have is of a spark plug.

Pictures that would help you include well lighted, framed, focused pictures of:

-Your whole bike (we can see the exhaust setup, air intake setup, general bike state and modifications if any
-pictures of your carburetors from multiple angles inside and out(super duper closeups of specific parts don't really do much)

Your entire thread so far is a little too disorganized and random to really follow.  I think you could get the information you need but it's just all over the place.

[SamP]

It sounds more complicated than it is after all I've gone over, from plugs, valves, to fuel level, to syncs, so I understand. I'll post pics when I can if the forum would find that helpful, but the basic specs are 1977 550k, stock air box with freshly oiled foam filter, 4to1 exhaust. Pd46a carbs, 100 mains, 42 idles, mixture at 1.5 turns out. New manifold o rings, fresh manifold gaskets, new air box boots. Clamps are in good condition, number 4 looks a little loose but it's not - sprayed carb cleaner across it with the engine running, as well as the rest of the connections, and no RPM increase. Confirmed good contact, and that's pre fuel metering as well, so no vac leaks.

I think Cal is onto something with the fuel level. Lowering it made idling rougher, so I think it's too low now, but I'll play with that and report back. I still find the whole jostling of the slide tube or linkage bar messing with the vacuum on 4 troublesome. Hopefully fuel level will help with that? We'll see...

The main problem remains #4 fouling despite a lean plug chop at 3/4 and the clip on the needle on the lowest (richest) setting.

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[harisuluv]

I still find the whole jostling of the slide tube or linkage bar messing with the vacuum on 4 troublesome. Hopefully fuel level will help with that? We'll see...

Well that linkage is the choke mechanism.  Messing with it would move the flaps--wouldn't we expect jostling the choke to affect the rpm?  If not the other explanation would be some kind of air leak, which you yourself said you ruled out with liberal carb cleaner test. 

It is really hard to follow how you are checking/adjusting your fuel level with the clear tube test because when you start talking about the fuel level you also talk about doing x to the drain screw which then changes the fuel level, but you'd have to have the tube inserted where the drain screw is to read it..

Also, you keep talking about the fuel level being much higher than the bowl, but if that were the case, it should be draining out the overflow, which you say it isn't.  Sounds like you also need to check that your overflow has no blockage. 

YES PICS WOULD HELP.  THEY ALWAYS HELP.