Linkert Gas Mileage

Linkert related issues
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thsmith
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Linkert Gas Mileage

#1

Post by thsmith »

What kind of gas mileage should I expect with a M61-B linkert. I get about 60 miles to a tank with 3.5 tanks on my 49EL.

Thanks,

Tracy
FlatHeadSix
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Too much fuel!

#2

Post by FlatHeadSix »

Tracy, I would expect closer to 60 miles per GALLON on that 61 cubic inch EL. How many times do the plugs foul out while it burns up that tank of gas? Do you ever get out of 2nd gear? Lotta black smoke? Try setting the float down a little and give the high-speed knob a couple of clock-wise clicks to lean it up a bit, its burning way too much fuel!
thsmith
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#3

Post by thsmith »

Flatheadsix, no fouled plugs at all and bike runs very good. Ride mostly in 4th gear. No black smoke unless I idle for a minute or so. The idle speed jet is turned out 2.5 turns, high speed jet 2 turns. The oil does not smell like gas.

Seems like low gas milage to me too but nothing appears to be wrong except poor gas milage.

She starts easy hot or cold.
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Carb Settings

#4

Post by FlatHeadSix »

You can't complain about a machine that runs good, still sounds like its using too much fuel. If you have the right service manual there's plenty of info about adjusting the Linkerts. 2 turns out on the high speed needle is the recommended starting place for adjustment. The high speed jet is "fixed" so the needle is really only a "trimmer". Your M-61 should have a 1-1/8" venturi, same as an M-36, so use the specs shown for the M-36, book says about 1-1/8 turns open plus or minus a couple of clicks. I run mine about 1-1/4 turns open, book also says running it slightly rich is easier on the engine, saves your valves, reduces overheating chances, etc.
good luck!
mike
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#5

Post by Cotten »

Tracy!

Sixty mpg might be a bit optimistic, but many Pan riders with Linkerts regularly get 35 to 45 mpg, depending upon riding habits, windshields and bags, etc.

Before any tuning concerns can be addressed, the manifold must be pressuretested to guarantee that there are absolutely no vacuum leaks. The tiniest of leaks, which can occur anywhere from the nipple rivet to casting porosities to even the pancover screw over the port, can rob fuel efficiency.

Within the carb there are two commonly overlooked concerns.
The first is a result of aging potmetal from which the venturi is made. Often they shrink to where they are loose in the bore, allowing air to pass around them erratically. The venturi can either be swaged and re-cut to size, or a modern aluminum reproduction installed.
The other point often dismissed in a rebuild is throttleplate wear into the bore, as illustrated in the attachment to this post. Air mixing becomes radically different at low-speeds as at high, and tuning to overlap the speedranges becomes difficult. Repair is accomplished by honing the bore for an oversized throttleplate and venturi, as shown on the right.

Another common gas-sucking problem is modern triple- and quadruple-weight brass floats. (Didn't I already send you an ultralight?)
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thsmith
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#6

Post by thsmith »

Cotton

I am preasure testing the intake tomorrow. I have installed the ultrafloat, inspected both the throtle plate and bore but all looks good. Replaced intake to carb gasket, cleaned fuel screen and bowl. My heads have been converted to o-ring and I did replace the o-rings as the other ones were over tighten.

Bike still starts, idles and runs best with the low speed jet 2.5 turns out. I will report on the preasure test tomorrow. Ultimately I am looking to increase my fuel mileage.

Tracy
thsmith
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#7

Post by thsmith »

All I can say is, PREASURE TEST your intake. I found my intake was leaking even after replacing the over tightened o rings. Took the intake off and did some measurements and found that when the heads were converted to o rings they had to machine the outer flange on the intake to get it to fit between the heads but they did not machine the inner flange by the same amount. This allowed one o ring to fit but not the other side as it would not drop into the slot and bulged.

Ran over to a friends house with intake in hand and we machined 50 thousands off each side of the inner flange, and now the o rings fit nicely on the intake with no leaks.

I will start it tonight and see if I can get the low speed jet turned in to an acceptable range.

I should have known I had a leak as when I would turn the low speed jet from 3 turn out to 2 the idle increase signifiantly.

Cotton, THANKS gain for the float and preasure test. I think I am well on my way to having a better running bike with much improved gas mileage.
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#8

Post by thsmith »

Stated the 49 last night and fixing the intake leak has made a big improvement, bike idles smoother and has more power. My low speed jet is still out about 2 1/4 turns but maybe that is just the way my linkert is going to be.

I just need to run a tank a fuel to see if I have improved fuel mileage.

Thanks to all who provided feedback.
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#9

Post by Cotten »

Tracy!
Needle valves are most sensitive and tuneable when they are close to their seats; 2+ turns out is a bit wide.

I suspect that the M61B #17 fixed jet may have been replaced with a solid gallery plug. Thus your needle must be wide open to accommodate it.

If not, then you may want to try a #19.

Let us know!
thsmith
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#10

Post by thsmith »

Cotten, is this jet marked such if I remove it I will see it stamped on the bottem of the jet ?

Thanks,

Tracy
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#11

Post by thsmith »

By the way I have noticed I do not have an insolater spacer. What are effects of not running one ?

Thanks,

Tracy
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#12

Post by Cotten »

Tracy!

The jet numbers should be stamped on the visible outside of the jet.

And yes, the phenolic spacer is adviseable, as it allows the carb mount to line up correctly.
thsmith
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#13

Post by thsmith »

Cotten, thanks again for your feedback and sage advice. Finding a forum that is so open and willing to share their knowledge is truely a rare thing these days.

Have ordered the insolator, gaskets and fixed jet. I just thought I was done with the carb, I also ordered the o ring intake clamps I saw that you and others recommed over the aircraft style I currently have. I think one advantage of these clamps are you are less likely to over tighten.
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