How large a fuel line is needed for 85cc

Modifiedmark · Dec 11, 2010

I am getting ready to replace the damaged lines in my 5200's and 4200's.

They have been using 3/16IDx5/16"OD lines but I never really liked that big of line in the tank as its not real flexable to let the fliter follow the fuel in the tank.

I'm wondering where everyone else thinks the cutoff would be for how much a 1/8"ID line could supply a 85cc engine. I'm thinking it might be right at the edge of delivering enough fuel.

MS460WOODCHUCK · Dec 11, 2010

What is the inside diameter of the fuel filter outlet? This is usually what I go by.

Modifiedmark · Dec 11, 2010

John, thats a good point, seems like they were big though. I'll look today and see if any have there OEM style filters on them.

I just threw this out this morning and have not even looked at them and we all know how my memory works now a days. :hmm3grin2orange:

MS460WOODCHUCK · Dec 11, 2010

Modifiedmark said:
we all know how my memory works now a days. :hmm3grin2orange:

I'm sure it's better than mine!:hmm3grin2orange:

lawnmowertech37 · Dec 11, 2010

Modifiedmark said:
I am getting ready to replace the damaged lines in my 5200's and 4200's.

They have been using 3/16IDx5/16"OD lines but I never really liked that big of line in the tank as its not real flexable to let the fliter follow the fuel in the tank.

I'm wondering where everyone else thinks the cutoff would be for how much a 1/8"ID line could supply a 85cc engine. I'm thinking it might be right at the edge of delivering enough fuel.

Mark if it is the line im thinking of its brittle line the one that come from poulan themselves i have about 3 of them on hand but i have seen that line get brittle thru the years

Bob Wright · Dec 11, 2010

My 100cc 1001 has a 1/8" line in the tank. I made the carb fittings from brass and they were smaller than that...Bob

Saw Dr. · Dec 11, 2010

Hey Mark,

If you can estimate how long she'll run on a full tank of gas, and then measure the capacity of the fuel tank, the math is pretty simple. I have some aviation charts for fuel line flow rates, but I bet they're too big. Probably not too hard to find something out there though. If you go with the same fuel filter that the modern 100+cc Stihl and Husky saws use, I can't see how you'd go wrong.

Modifiedmark · Dec 11, 2010

I get to thinking some more and I'm thinking my 99cc Husqvarna 1100's fuel line is probably not any bigger then 1/8"ID.

Modifiedmark · Dec 12, 2010

Saw Dr. said:
Hey Mark,

If you can estimate how long she'll run on a full tank of gas, and then measure the capacity of the fuel tank, the math is pretty simple. I have some aviation charts for fuel line flow rates, but I bet they're too big. Probably not too hard to find something out there though. If you go with the same fuel filter that the modern 100+cc Stihl and Husky saws use, I can't see how you'd go wrong.

Tim, what filters are you talking about?

I have been thinking of useing the original Poulan/Tillotson type filters. The large dia ones with the felts on them.

They have a fairly large hole in the stud on them. Do the felt type not flow as good as some others?

Like I said I want to use a heavy filter, seems if I don't use the felt type, the Husky style seem pretty good.

I did do my 4200 like this yesterday, used a 3/16" ID line going through the carb area with a 3 1/16 barb under it with a 1/8" ID line hooked onto it inside the tank.

I really don't like that setup too well. I'm looking to see if I can find a metal adapter to screw into the tank with a 1/8 barb on one side and a 3/16 on the other.

Anyone got a idea what used a fitting like that I could use to adapt to these saws?

Bob Wright · Dec 12, 2010

Modifiedmark said:
I really don't like that setup too well. I'm looking to see if I can find a metal adapter to screw into the tank with a 1/8 barb on one side and a 3/16 on the other.

Anyone got a idea what used a fitting like that I could use to adapt to these saws?

I know a guy with a machine shop that can make anything with a picture or a drawing. I made some straight fittings for my Echo's from alum with 3 /16x1/8 barbs. Let me know...Bob

pioneerguy600 · Dec 12, 2010

I am a little late to the party but to answer the original question, I usually check the ID of the inlet nipple on the carb, that tells me the amount of fuel the engineers figured the engine would need. On a Pioneer 600 for example a 1/8" ID line would cause it to fuel starve, on a modern 85 cc engine a 1/8" ID line would flow all the fuel that can get through the carb nipple.
Pioneerguy600

Modifiedmark · Dec 12, 2010

Bob Wright said:
I know a guy with a machine shop that can make anything with a picture or a drawing. I made some straight fittings for my Echo's from alum with 3 /16x1/8 barbs. Let me know...Bob

Bob, I was already thinking that, I'm checking a couple things today and I might be in touch.

pioneerguy600 said:
I am a little late to the party but to answer the original question, I usually check the ID of the inlet nipple on the carb, that tells me the amount of fuel the engineers figured the engine would need. On a Pioneer 600 for example a 1/8" ID line would cause it to fuel starve, on a modern 85 cc engine a 1/8" ID line would flow all the fuel that can get through the carb nipple.
Pioneerguy600

Jerry I'm with you on your thoughts but alot of these older Poulans what used a 3/16" inlet on the carbs still had 2 piece fuel lines with a 1/8 line in the tank. The 74cc 245 is a good example of this.

These dang 3/16 x 5/16" lines are just too big and stiff to move around inside the tank.

I will look today but I'm sure my Husky 1100cd only has a 1/8" fitting on the carb and the line is probably 1/8 ID as well.

pioneerguy600 · Dec 12, 2010

Jerry I'm with you on your thoughts but alot of these older Poulans what used a 3/16" inlet on the carbs still had 2 piece fuel lines with a 1/8 line in the tank. The 74cc 245 is a good example of this.

These dang 3/16 x 5/16" lines are just too big and stiff to move around inside the tank.

I will look today but I'm sure my Husky 1100cd only has a 1/8" fitting on the carb and the line is probably 1/8 ID as well.[/QUOTE]

Yes and that is a different set of parameters, the line needs to fit over the fittingings and carb nipples so either the smaller dia line needs to be a moulded line with the ends enlarged to accomodate the fittings or the line diameter needs to be increased entirely. The smaller diameter line would flow enough fuel but the fittings determine the ID size of the line. With this newer fuel line like Tygon it is increasingly difficult to get good in tank lines that will be flexible enough to allow the filter/pickup to stay on the bottom of the tank and also be able to move side to side when the saw is tipped.
A lot of the mid sized Pioneers used a screw in fitting at the tank where the smaller line in the tank increased on the outside to accomodate the carb fitting. I have been able to get the Tygon to streatch a little to go over the fittings by soaking the end in some hot water but if the line needs to be streatched a lot it will do it but seems to crack later on.

Pioneerguy600

Modifiedmark · Dec 12, 2010

pioneerguy600 said:
Jerry I'm with you on your thoughts but alot of these older Poulans what used a 3/16" inlet on the carbs still had 2 piece fuel lines with a 1/8 line in the tank. The 74cc 245 is a good example of this.

These dang 3/16 x 5/16" lines are just too big and stiff to move around inside the tank.

I will look today but I'm sure my Husky 1100cd only has a 1/8" fitting on the carb and the line is probably 1/8 ID as well.

Yes and that is a different set of parameters, the line needs to fit over the fittingings and carb nipples so either the smaller dia line needs to be a moulded line with the ends enlarged to accomodate the fittings or the line diameter needs to be increased entirely. The smaller diameter line would flow enough fuel but the fittings determine the ID size of the line. With this newer fuel line like Tygon it is increasingly difficult to get good in tank lines that will be flexible enough to allow the filter/pickup to stay on the bottom of the tank and also be able to move side to side when the saw is tipped.
A lot of the mid sized Pioneers used a screw in fitting at the tank where the smaller line in the tank increased on the outside to accomodate the carb fitting. I have been able to get the Tygon to streatch a little to go over the fittings by soaking the end in some hot water but if the line needs to be streatched a lot it will do it but seems to crack later on.

Pioneerguy600[/QUOTE]

Yes I know what you mean with the fitting ID size. Seems the ones on the poulans are very close to 1/8" inside the fittings and you do indeed have to streatch the lines over them.

I never had a problem with them splitting though.

So I take it that you also feel that a full 1/8' of flow is pleanty?

pioneerguy600 · Dec 12, 2010

Modifiedmark said:
Yes and that is a different set of parameters, the line needs to fit over the fittingings and carb nipples so either the smaller dia line needs to be a moulded line with the ends enlarged to accomodate the fittings or the line diameter needs to be increased entirely. The smaller diameter line would flow enough fuel but the fittings determine the ID size of the line. With this newer fuel line like Tygon it is increasingly difficult to get good in tank lines that will be flexible enough to allow the filter/pickup to stay on the bottom of the tank and also be able to move side to side when the saw is tipped.
A lot of the mid sized Pioneers used a screw in fitting at the tank where the smaller line in the tank increased on the outside to accomodate the carb fitting. I have been able to get the Tygon to streatch a little to go over the fittings by soaking the end in some hot water but if the line needs to be streatched a lot it will do it but seems to crack later on.

Pioneerguy600

Yes I know what you mean with the fitting ID size. Seems the ones on the poulans are very close to 1/8" inside the fittings and you do indeed have to streatch the lines over them.

I never had a problem with them splitting though.

So I take it that you also feel that a full 1/8' of flow is pleanty?[/QUOTE]

I think you would be fine with a 1/8" ID line

Eccentric · Dec 12, 2010

On many of the molded lines used in saws, the fitting ends may be 3/16"....but there's often at least one section that necks down to 1/8". The fuel line on the McCulloch 77 I used to have was 1/8" ID. 1/8" Tygon fit perfectly on the nipples. While that saw was certainly not a high-revver, it was still 120cc...

Wildman1024 · Dec 12, 2010

Eccentric said:
On many of the molded lines used in saws, the fitting ends may be 3/16"....but there's often at least one section that necks down to 1/8". The fuel line on the McCulloch 77 I used to have was 1/8" ID. 1/8" Tygon fit perfectly on the nipples. While that saw was certainly not a high-revver, it was still 120cc...

Word is born playa! :agree2:

All my homelites use pretty small fuel line and they are 80cc to 114cc. The biggest line I need to use is a 3/16 id just cause the nipples are big on the carb and tank. The line on the inside of the tank is actually a 3/16 od feeding the bigger line and 112cc never runs out.

I would use the smallest line you can get to work so it stays pliable and air tight.

Stihl-Pioneer · Dec 12, 2010

I don't know if this will help at all:
http://www.tygon.com/peristaltic-pump-tubing-formulations.aspx

Modifiedmark · Dec 12, 2010

I'm now convinced the 1/8" ID line will be fine. I got to working on my craftsman 4.2 and 5.2 and they still have there OEM fuel filters in them.

The filters have 3/16" nipples on them but the hole inside is less the 1/8".

I bought a bunch of Poulan NOS parts a while back and there were some tank fittings in there. They fit just right but there press fit and it will be almost impossible to replace the line that way without removing the fitting.

There were also two tank fittings for a Poulan 361 and they will be just perfect. There 5/16" fine threaded to thread into the tank! I will use the 2 for now and I have a parts saw that has one, maybe I'll send it to Bob for a pattern and have him make up a few more of them.

This is going to work out very well this way. The 1/8IDx3/16OD line will move around in the tank great this way.

I'm out in the shop now but will post up some pictures later.

Modifiedmark · Dec 12, 2010

Here is what I came up with.

Here is the press in fitting as used on a Poulan 306/245, I went ahead and used it on my Craftman 4.2 for now but I know it will need replaced when ever the fuel line needs replaced again. Fits perfect though just press it in.

Here it is seated in the tank.

Here is the threaded fitting as used on a Poulan 316 or such. I only had two of these and will need at least a few more. Too bad there NLA from Poulan!

These work very nicely, just drill the hole in the tank out just a bit and run a 5/16" fine thread tap in it. This will allow the fitting to come out when you need to put a new line on it.

Here it is with the tank line put on it, used a 1/8IDx3/16OD line on it and it works in the tank well that way.

Here it is threaded into the tank.

How large a fuel line is needed for 85cc

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