Building a SP125C / 101B Kart Saw

[burl1984]

I'm having trouble getting my NOS 125/101b started. I have basically sourced all my parts NOS from ebay and some other sources. There are only a few parts that are not NOS but I did re-furbish the used parts as best I could. The saw was running a few weeks ago until the supposed NOS crank decided to strip and blow out at the keyway instead of the keystock itself on the flywheel. I have recently installed another crank and re-assembled the saw. Now all I can get the thing to do is POP every once in a while. It seems to want to flood super easy and after clearing the flooding issue it seems starved for fuel. If I choke it, it instantly floods. The carburetor is a 1972 BDC14. Any thoughts?

Thanks,

Burl

 

[54stude]

Was the carb nos? Could it have been modified for alcohol? If so, it might be hard to regulate it down enough for gas.

 

[2dogs]

I have a friend with a 101b NOS motor and he is looking for a chassis to put it in.

 

[burl1984]

The carburetor was used, how would I identify if it was modified for alky? I re-tested today for pressure and vacuum and it's still good on both. It's got super high compression as well, way more than my 3120xp.
I may order another BDC14 carburetor and re-build it as well to trouble shoot.

 

[Jacob J.]

The BDC14 wasn't even really a great carb when they were brand new. You might have much better luck with a large bore Tillotson or Mikuni.

 

[54stude]

If you screw the high jet all the way in to close it off, can you get it to start and idle good using the choke to start it?

 

[burl1984]

The engine is in disassembly mode right now from the pressure/vacuum tests. I'll try the screw in the high method tomorrow. What's the ball park I should be in for turns out on the low for initial settings?

 

[54stude]

Try 1/2 or 1. And you should need some choke to start the saw cold. Once it starts and idles on the low. Turn out the h jet to tune it to be rich. But clean up when loaded in a cut. There are some good carb tuning threads here or on as if you need tips.

 

[burl1984]

Ok thanks for the info, I'll try that tomorrow upon re-assembly.

 

[54stude]

The BDC14 wasn't even really a great carb when they were brand new. You might have much better luck with a large bore Tillotson or Mikuni.

Is there a snowmobile, watercraft, chainsaw, or bike carb that would be preferred in this application? Something with a 32 or 34mm Venturi maybe?

 

[Jacob J.]

Is there a snowmobile, watercraft, chainsaw, or bike carb that would be preferred in this application? Something with a 32 or 34mm Venturi maybe?

There is, I'd have to do some research on it. All of the long time kart guys I've worked with say that the large bore, single pumper early BDCs are poor performers. I tried a 14 once and it was just garbage.

 

[burl1984]

I re-assembled the saw this evening and tried the all the way in on the high and .5-1.0 turns out on the low. The saw pops a little longer than before the pressure/vacuum tests but still doesn't want to idle. It seems way rich still. If i turn the low in any further it won't pop at all. I'm thinking the carburetor may have been modified for alky as mentioned in an earlier post. I have a NOS carburetor coming. I would be interested in a jetski carburetor if it was easily adaptable.

 

[ozflea]

The BDC14 wasn't even really a great carb when they were brand new. You might have much better luck with a large bore Tillotson or Mikuni.

What a load of chodswhople there fine if you know how to set them up

 

[burl1984]

I have a used BDC16 and a rebuild kit as well. I was kinda not wanting to run alky to start with.

 

[cpr]

Stick with it. The single-pumper BDCs are finicky around lever hight. If it's flooding, set it at even with carb housing and adjust from there. There's no BDC voodoo, just patience.

 

[heimannm]

I would like a bowl of that chodswhople to go with my soba noodles please.

My 101 did not run very long before ingesting the needles from the pin bearings but the BDC seemed to work just fine.

As Sir Charles says, patience is a virtue.

Mark

 

[burl1984]

The carburetor was used, how would I identify if it was modified for alky? I re-tested today for pressure and vacuum and it's still good on both. It's got super high compression as well, way more than my 3120xp.
I may order another BDC14 carburetor and re-build it as well to trouble shoot.

Compression is 150~ psi on the MC and the OEM 3120 is 125~ psi. So I guess my use of the term super high compression could be interpreted many ways.

cpr, I'm a super noob when it comes to setting lever height. I'm not sure what you mean by level with the housing. Is there a thread that specifically goes into detail about this procedure?

Thanks,

Burl

 

[burl1984]

http://www.arboristsite.com/community/threads/mcculloch-carburetors.122113/

Is post #11 what is meant by setting the lever at the height of the housing?

 

[cpr]

Yes

 

[burl1984]

I got the NOS BDC14 in the mail and checked it out. The only thing that looked like it needed to be replaced was the duckbill valve. The lever height on the NOS carburetor was a ways above the height of the housing. I did not adjust it because I figured the supposed factory setting was adequate. The result are the same when trying to start the saw it still only pops a few times and either floods easily or doesn't seem to be getting the proper amount of fuel.

I'm wondering if I should use a different head. The one I have on the saw currently was labeled as NOS High Compression option. Terry Ives a Kart specialist recommended using a non-high compression head in the chainsaw application to get higher RPM's. I'm wondering if the High Compression head would work better with Race Fuel or an alky blend with the BDC16 carburetor.

I have the standard compression head but it's not a NOS product. I did mill out an tap it for a compression release valve so it should be just a matter of dis-assembling the saw to swap out the head and re-torque the head bolts to try this new configuration.