Fuel pump?

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ted johnson
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Joined: Fri Jun 15, 2007 7:59 am

Re: Fuel pump?

Post by ted johnson » Sat Sep 21, 2019 2:39 pm

Firstly, the gasket surface on top of that cylinder looks as though it's been grooved and filled with something-maybe epoxy? Not a good situation at all. I have yet to see a head gasket survive with that little area to prevent blowout. My Pop once had a big bore saw Mac that Russell Karting cut the head off from for Pop. There was about the same amount of area left as your block exhibits. We couldn't keep a head gasket in it for love nor money. I hope you'll be luckier.
Secondly, I'd still suggest disassembling that engine and installing new crank seals and gaskets. While you're at it, invert the piston and rod in a can filled up well past the wrist pin with solvent, and let the assembly sit in there for a day or two. Empty the solvent out and blow out the wrist pin bearing. Put the rod and piston back in the can and fill it past the wrist pin with thin oil-maybe 3-In-One or 10 weight. Let the bearings soak for a day. Mac wrist pin needle bearings are a weak point, and a good clean and soak won't cost much time or money. Reassemble the engine using NEW rod screws, and follow the torque requirements for all the screws carefully.
Thirdly, if it were my motor, I'd find a Tillotson HR carb, throw away the BDC Mac carb and mod the reed cage to pulse the Tillotson. It requires filling the four pulse holes in the big Mac reed with four No. 8-32 socket head screws, drilling a new pulse hole for the Tilly and using the proper gasket for the Tilly. Somewhere, there's a picture tutorial on the procedure. The cage has to be tapped for the No. 8-32 screws, and they need to NOT protrude thru past the gasket surface on the reed cage. The heads of No. 8 socket heads will clear the flange and gasket on the HR Tilly. The HR is far easier to service and tune, and EC Carbs in Tennessee has all the gaskets and diaphragms to rebuild the HR Tilly. Ted

Matthew denton
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Joined: Thu Sep 12, 2019 6:43 pm
Vintage Karting items owned: Maybe a 1970 margay pro x
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Re: Fuel pump?

Post by Matthew denton » Sat Sep 21, 2019 6:24 pm

Hey ted. Thanks a lot for that very informative reply, I think I this might be a good project for me and my 2 sons. They are very impatient. Lol. And want to ride a GoKart already. I think I’ll throw a stock GX270 (I have laying around) in the kart while this is getting rebuilt “right”.

ted johnson
Posts: 1469
Joined: Fri Jun 15, 2007 7:59 am

Re: Fuel pump?

Post by ted johnson » Sat Sep 21, 2019 7:40 pm

Matthew, there are usually HR Tillotson carbs on eBay. One of those would make your new venture a lot easier. Folks that have experience can make the big McCulloch carbs work fine. The Tillotson is just a lot simpler to tune and to maintain. Just be sure to buy one that is drilled for gasoline, unless you plan to run alcohol.
I'm still concerned about that black line on the head gasket surface of the cylinder. Ted

Rob Voska
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Joined: Fri Jun 15, 2007 9:04 am

Re: Fuel pump?

Post by Rob Voska » Sat Sep 21, 2019 9:53 pm

If you get an HR carb get a HR181 or HR 191.. Stay away from all the others as some have external pulse lines and require modification.

What Ted said on the rod needles!

I don't see anything wrong with the top of the cylinder. Is it flat?

Nice full circle crank ya got there......... :-)

ted johnson
Posts: 1469
Joined: Fri Jun 15, 2007 7:59 am

Re: Fuel pump?

Post by ted johnson » Sun Sep 22, 2019 9:34 am

Hey, Rob. Over on the left side of the gasket surface is a thick black line that goes from the outside edge to maybe 1/16" or 1/8" from the liner. It looked like a groove that someone filled with something like JB Weld. Maybe it's just a bit of stuff laying there. It may just be nothing. Even if it's a groove filled with epoxy it may still be O.K. Anyhow, the crank is cool!
The comment about torqueing the screws is important. No. 10 screws are none too strong to begin with!
Sure wish you were coming to Tucson with Bob K. We'll be glad to see him. Ted

Matthew denton
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Joined: Thu Sep 12, 2019 6:43 pm
Vintage Karting items owned: Maybe a 1970 margay pro x
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Re: Fuel pump?

Post by Matthew denton » Mon Sep 23, 2019 5:58 pm

Yea the top of the cylinder has a piece of something on it. Lol. Idk i think it a paint chip or something. Fell right off.

ted johnson
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Joined: Fri Jun 15, 2007 7:59 am

Re: Fuel pump?

Post by ted johnson » Mon Sep 23, 2019 6:46 pm

Great! Ted

Mark Loraine
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Vintage Karting items owned: ProX 77,McC R1,Bug Stinger Dual.
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Location: SWNY14755

Re: Fuel pump?

Post by Mark Loraine » Sat Nov 09, 2019 11:39 am

You do not need an external fuel pump.
the residue left behind indicates that it was run on Methanol and not purged with gas/oil after running it.
you wont be able to run this carb on gas if it has been convert to alcohol.
The full circle crank is a nice addition to this engine. (as seen in other posts.)
MC91 series IPL..... http://www.smallenginediscount.com/MC91IPL.pdf
regards,
Mark L./SWNY

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