McCulloch 640 carburetor swap

[jason6586]

ok, so I’m not really swapping carbs, my saw doesn’t have a carb but it had the old crappy flatback carb and I would love to install a tillotson HL in its place, has anyone done this on a similar saw? I went and grabbed an HL and my initial thoughts are I need to find something with a throttle shaft that’s compatible and then figure out how to use the choke since the original came with a primer pump. Any helpful tips or ideas would be great.

 

[CausticUC]

Likely you will need to make custom throttle and choke levers (which is not usually too hard), the important part, in my mind, are not those two items.

The important parts are the bore size and the bypass design. You will need to investigate how your original carb functioned to determine if the HL series even has a match, and what jet sizes you might need as they will probably be incorrect.

 

[PerkAdan]

I used a Tillotson HL63B carburetor. I took the stud out of the top of the carburetor and installed a bolt. The factory throttle shaft worked with no modifications. The choke I used a 10-10S choke rod with a little bending. The fuel line I had to grind down the tit to get the fuel line to fit on. But all worked out great.

 

[jason6586]

View attachment 726290 View attachment 726291 I used a Tillotson HL63B carburetor. I took the stud out of the top of the carburetor and installed a bolt. The factory throttle shaft worked with no modifications. The choke I used a 10-10S choke rod with a little bending. The fuel line I had to grind down the tit to get the fuel line to fit on. But all worked out great.

Thanks for the info, that looks like a simple and painless swap from a work, modification and cost perspective at the least. Did you have to do any modifications to the intake manifold or did the bore of the carb & impulse port line up correctly where it needed to be? Also are you able to fit the air cleaner mount over the top of the carb without issue? When you say you ground down the nipple do you mean the fuel inlet on the carb itself?

What model Mac did the HL63B that you used come off of, it looks like it has yellow overspray so I just assumed it came from a donor Mac. Do the factory carb settings work or did you have to adjust it outside of the spec. parameters to get it to run correctly? I haven’t dealt with a lot of the flatback Mac carbs but I would assume the performance of a HL is comparable or even better than the old flatback Walbro. I have no clue for the life of me what the engineers at Mac were thinking when they had Walbro design that gem of a wasted piece of aluminum vs utilizing something that was already proven throughout the industry and readily available from Tilley in the HL. I have no doubt that the HL will be leaps & bounds better when it comes to rebuild and servicing especially from the pocketbook perspective plus it’s something that I already have on the shelf when we are talking about rebuild kits.

Thanks again

 

[PerkAdan]

No modification. It drops right in with no modification. The intake and impulse line match up perfectly. The air cleaner works fine too.
The carb came out of a 1-52 donor saw. I put the motor out of the 1-52 into my Mac 15.
With the carburetor adjustment, I always start out one full turn on both High and Low.
Yes the fuel inlet on the carburetor I had to make it smaller to fit the fuel line on.

 

[jason6586]

No modification. It drops right in with no modification. The intake and impulse line match up perfectly. The air cleaner works fine too.
The carb came out of a 1-52 donor saw. I put the motor out of the 1-52 into my Mac 15.
With the carburetor adjustment, I always start out one full turn on both High and Low.
Yes the fuel inlet on the carburetor I had to make it smaller to fit the fuel line on.View attachment 726316

Thanks for the reply, that’s a nice looking saw with a little upgrade, those projects usually are the most enjoyable for me anyways. I have to dig around to see what I all have laying around for HL’s or donor saws to find one with the most compatible throttle shaft, the one I grabbed just for mock up will not work unless I swap throttle shafts. I was even going to look around on amazon since there are a few aftermarket options out there in the HL size, the main issue with that is quality since I haven’t had the best luck with some of those China aftermarket carbs. I had ordered one to replace the one on my neighbors ice auger last month and finally after they sent me the 4th replacement I got one that actually worked properly without leaking gas like a sieve but you can’t expect a whole lot when you pay $11.99 for a whole carb, fuel filter, fuel line, gasket and clamp kit.

 

[2broke2ride]

I put one in a 440, cant remember the model now and I'm putting an HL19 in my 1-86 now. Like was said, throttle linkage works, I just bend the original pressure im mor linkage to work the choke.