M-88 Carb floods on 42-WLAMy friend

[Hack]

My friend swapped out a Mikuni for a pro rebuilt Linkert M-54 that did not work then a 20230623_104429.jpg20230627_133527.jpg M-88, from the same supplier that is currently on his stock motor WLA bob job.
Problem is the machine runs consistently rich, real rich to where it won't run in traffic or idle down.
As soon as he shuts off the gas at the petcock in a few seconds it runs great as it always did until it starves and stops.
He/we have swapped out floats (both Duckies) needles and seats, levers and lowered the float a bit to increase pressure on the needle. He also installed and checked the intake seals, peek, although it never had a previous problem with the brass seals.
Still runs like crap. Is consistently running rich even with the low speed needle turned all the way in.

I have an assortment of old OEM used seats and valves, some have smaller internal diameter and have round valves and some are bigger with square shaft. Since they all have the same part number I wonder what is the difference?

I'm basically a Panhead guy and have very little knowledge of the 3 bolt and other flathead carb business so any help sorting this out will be most appreciated.

[T. Cotten]

My friend swapped out a Mikuni for a pro rebuilt Linkert M-54 that did not work then a M-88, from the same supplier that is currently on his stock motor WLA bob job.
Problem is the machine runs consistently rich, real rich to where it won't run in traffic or idle down.
As soon as he shuts off the gas at the petcock in a few seconds it runs great as it always did until it starves and stops.
He/we have swapped out floats (both Duckies) needles and seats, levers and lowered the float a bit to increase pressure on the needle. He also installed and checked the intake seals, peek, although it never had a previous problem with the brass seals.
Still runs like crap. Is consistently running rich even with the low speed needle turned all the way in.

I have an assortment of old OEM used seats and valves, some have smaller internal diameter and have round valves and some are bigger with square shaft. Since they all have the same part number I wonder what is the difference?

I'm basically a Panhead guy and have very little knowledge ofthe 3 bolt and other flathead carb business so any help sorting this out will be most appreciated.

They run rich, Hack,..

When they cannot run any other way. This is usually because of a vacuum leak.

Please review Diagnostic #1:
http://virtualindian.org/11techleaktest.html

Unless the manifold is absolute, any fiddling with the carb is futile. Beware you must use a constant, regulated air supply. Many get false negatives with tire pumps, etc. (And please beware that mass-produced PEEK seals have ruined the "brand"!)

...Cotten
PS: The round needle design was '50 or so and later OHV.
PPS: The "pro rebuilt" Linkert is unfinished.
PPPS: Unless the Duckies have swollen from fuel, they really should remain at a quarter inch.

[Rubone]

My friend swapped out a Mikuni for a pro rebuilt Linkert M-54 that did not work then a 20230623_104429.jpg20230627_133527.jpg M-88, from the same supplier that is currently on his stock motor WLA bob job.
Problem is the machine runs consistently rich, real rich to where it won't run in traffic or idle down.
As soon as he shuts off the gas at the petcock in a few seconds it runs great as it always did until it starves and stops.
He/we have swapped out floats (both Duckies) needles and seats, levers and lowered the float a bit to increase pressure on the needle. He also installed and checked the intake seals, peek, although it never had a previous problem with the brass seals.
Still runs like crap. Is consistently running rich even with the low speed needle turned all the way in.

I have an assortment of old OEM used seats and valves, some have smaller internal diameter and have round valves and some are bigger with square shaft. Since they all have the same part number I wonder what is the difference?

I'm basically a Panhead guy and have very little knowledge of the 3 bolt and other flathead carb business so any help sorting this out will be most appreciated.

Panhead or flathead makes no difference on how the carb works. The pictured carb has an adjustable high speed needle in it, M88s did not come that way and it may be a clue. Does it still have the fixed jet in it? Has it been converted to external vent? Was the venturi changed? Is the float offset correctly?

[T. Cotten]

One more scenario, Hack...

The common WLA fuel lines compell the bowl to be indexed with the floatvalve of the bowl to be inboard of the HS needle, almost square to the body, when sidebowl Linkerts were designed for it to be directly beneath the HS needle assembly.

The float can be properly offset for this, but the entire carb, with indexed bowl, must be inverted so that you can suck upon the valve to be certain it closes completely, as the float easily hangs up upon the bowlstem.

(A rubbing float allows the level in the bowl to rise above spec, enrichening both idle and power circuits beyond their design. The bowl assembly is considered to be its own metering circuit.)

....Cotten
PS:"Indexed" just means its clocked for a trial. Hope that makes it more clear.... .. . . .

[dukekleman]

With the carburetor fully assembled and held upside down,
test the needle and seat function with a vacuum tool. If things are all correctly assembled it should hold 25 inhg.
As mentioned earlier by Rubone, is there a fixed jet being used along with the high speed needle?

[T. Cotten]

...Still runs like crap. Is consistently running rich even with the low speed needle turned all the way in...

These things are diabolical, Hack.

At speeds over thirty or so, the idle circuit reverses to supply air to the highspeed circuit. Thus a completely closed lowspeed needle would starve the highspeed for air!

Since the lowspeed knob bottoms out on the lift lever, and has a safety spring in case it really does hit the seat, it is hard to observe. Inking both needle points will give an indication of contact; Dry-erase markers are great for that, as well as for finding float-to-bowlstem interference:

DRYERASE.jpg


Often they hang up on the gallery quite high:

stemgall.jpg

A buoyant float set at a quarter-inch gives a fuel level in the bowl of five-eighths, and the rest of the carb depends upon that.

Hope this helps,

....Cotten

[Hack]

Thanks for the information to all, I'll pass it on. Diabolical seems to be the operative adjective at this point. How can something so simple be so troublesome? Do too many cooks spoil the stew? Also there is a fixed jet screwed into the bottom of the body stem. Will need to research the whole internal/external vent thing.

[T. Cotten]

... Diabolical seems to be the operative adjective at this point. How can something so simple be so troublesome?....

Imagine doing carbs for a living, Hack.

Do too many cooks spoil the stew?

Even my repops ain't perfect. (But at least Folks know where to find me....)

...Also there is a fixed jet screwed into the bottom of the body stem. Will need to research the whole internal/external vent thing.

88s came with a #1 fixed jet, but should be replaced with a gallery plug, like the other plugs, when used with an adjustable needle.

The M88, and a couple of other HD Linkerts, had their air correction vent cut into the bottom of the venturi like the majority of Indian Linkerts, and dubbed 'internally vented':
741-1VNT.jpg


The majority of HD Linkerts were vented with a hole through the side of the body, but it would be a booger on an M88.

....Cotten

[Hack]

So if he has a fixed jet on the bottom of the body stem AND what appears to be an adjustable needle, especially the high speed needle, would that be enough to cause the carb to run too rich?? We have gone over all the rest of the setup multiple times and and the bike runs great 5-8 seconds after we shut off the fuel, until it starves out and stops. If we turn the fuel back on before it quits it will run great until it floods and sputters. That is the crux of the situation.
Confirmed internal vented venturi.

[dukekleman]

For what it's worth, I'll share a story with you relative to your issue at hand. Back in 17' I was riding out to Sturgis and ran across a guy having the same issues you describe in your post. He was in a parking lot and I asked if I could help. The bike was a 1961 Panhead, fully restored 2nd owner he told me. I tried adjusting his carburetor and it would not respond to adjustment. I took it apart in the parking lot, checked the float, looked for debris and any obvious oddities, nothing. Knowing how people clean jets over the years on this freshly rebuilt M74 Linkert I had only one thought left. Being know one in the area we were had Linkert jets, I came up with this idea. Tried it and this paper clip worked wonders for his panhead, gas mileage and spark plugs. We exchanged numbers and he rode 2,800 miles with this paper clip in there with no problems. When he got home he wanted to leave it alone, I convinced him to take it apart and put in a new replacement correct jet I sent him for free. Friends still today. 20260.jpeg20261.png

[T. Cotten]

So if he has a fixed jet on the bottom of the body stem AND what appears to be an adjustable needle, especially the high speed needle, would that be enough to cause the carb to run too rich?? We have gone over all the rest of the setup multiple times and and the bike runs great 5-8 seconds after we shut off the fuel, until it starves out and stops. If we turn the fuel back on before it quits it will run great until it floods and sputters. That is the crux of the situation.
Confirmed internal vented venturi.

Yes, Hack,

The #1 jet was enough for a stock motor on 1940s fuel, and although the needle might add more for an overbore, or ethanol fuels that require more volume, the needle would probably meter better without it.

Your symptoms still suggest a vacuum leak has you pouring fuel into it.

....Cotten

[BigLakeBob]

For what it's worth, I'll share a story with you relative to your issue at hand. Back in 17' I was riding out to Sturgis and ran across a guy having the same issues you describe in your post. He was in a parking lot and I asked if I could help. The bike was a 1961 Panhead, fully restored 2nd owner he told me. I tried adjusting his carburetor and it would not respond to adjustment. I took it apart in the parking lot, checked the float, looked for debris and any obvious oddities, nothing. Knowing how people clean jets over the years on this freshly rebuilt M74 Linkert I had only one thought left. Being know one in the area we were had Linkert jets, I came up with this idea. Tried it and this paper clip worked wonders for his panhead, gas mileage and spark plugs. We exchanged numbers and he rode 2,800 miles with this paper clip in there with no problems. When he got home he wanted to leave it alone, I convinced him to take it apart and put in a new replacement correct jet I sent him for free. Friends still today. 20260.jpeg20261.png

Hard to see the picture, so you made the ID of the jet smaller using the clip?
Thanks, your insight on topics has been most helpful.

[dukekleman]

Yes, that is correct. I got a paperclip from the hotel lobby, bent the paper clip into the form in the photo. The High speed needle went through the looped end and the straight end was inserted into the jet which had been oversized by someone throughout the years I'll assume. This allowed the high speed needle to actually have influence when adjusted and he said he then was getting about 34 mpg on average. Either way, it was a good road side fix, he learned of the cause of his problem and we had good laughs about it.

[T. Cotten]

... Either way, it was a good road side fix....

It begs the question, Duke,...

How did it get so far out on the road in the first place?

....Cotten

[BigLakeBob]

It begs the question, Duke,...

How did it get so far out on the road in the first place?

....Cotten

Maybe his manifold leak equaled things out.