Track Tac

briggs flathead

N

noahsm1th

New member
I am wanting to run methanol in my Briggs 5hp flathead, a raptor. I'm new to methanol/methanol engines, I was wondering what do I need to do to run methanol in my flathead??? do I need to change something??? do I need different parts or what???
fyi my engine has a ARC billet rod, slightly heavier springs, 28mm Mikuni style carb, and a exhaust.
thanks guys​
 
Gravey39 said:
A new jet for the carb. just look up methonal jets for the raptor. You’ll find them.
Click to expand...
oh thanks man! is that all im gonna need to change?? I was talking to a guy and he said something about I need to change the timing or something like that.... just making sure if that's all I need to change. Thanks
 
noahsm1th said:
oh thanks man! is that all im gonna need to change?? I was talking to a guy and he said something about I need to change the timing or something like that.... just making sure if that's all I need to change. Thanks
Click to expand...
Hmmm, not really too sure on that one. I’ve never had an issue just changing the jets out. But I only ever ran my raptor at the track for
 
I know you’d get more performance out of it. I just never ran it in a race so I never cared about switching or fiddling with the timing. I’m not too versed with engines anyways. I just knew about the jets.
 
Methanol burns much slower than gasoline, therefore, the fire must be ignited sooner to gain the power benefit from using it.

Jetting will be somewhat influenced by the timing set.
More timing, more fuel.

Your overall strategy influences this.
 
You really haven't give us enough info to determine a actual jet size...
Theres basically 2 different type of these Chinese Knock off carbs.. The one thats a copy of the actual Mikuni is a decent carb and you can buy replacement jets for them... The other one (Lesser priced ones) are a hit and miss and very little back up parts available (AS I have been able to find)

But you really need a few extra jets to drill and experiment with.. UNLESS someone has the exact mm carb you have and will share their findings.. So you need to give the actual mm size, the hi and low speed jet size that in it stock and a name that might be on it...

As for timing we need to know what flywheel thats on the engine to determine a offset key number that would get you close.. Close is all we need to be in most cases... WE need to get up around 32-36 degree range...

Good Luck in your venture..
 
Dover Power said:
You really haven't give us enough info to determine a actual jet size...
Theres basically 2 different type of these Chinese Knock off carbs.. The one thats a copy of the actual Mikuni is a decent carb and you can buy replacement jets for them... The other one (Lesser priced ones) are a hit and miss and very little back up parts available (AS I have been able to find)

But you really need a few extra jets to drill and experiment with.. UNLESS someone has the exact mm carb you have and will share their findings.. So you need to give the actual mm size, the hi and low speed jet size that in it stock and a name that might be on it...

As for timing we need to know what flywheel thats on the engine to determine a offset key number that would get you close.. Close is all we need to be in most cases... WE need to get up around 32-36 degree range...

Good Luck in your venture..
Click to expand...
thank you for your information.
The carb: im not sure which it is... the only writing on the carb is "Japan- T\A" and "mikuni" so I'm guessing its Japanese??
its a 26mm, idk what the low and high speed jet sizes are, it says "Mikuni" and "Japan- T\A" on the carb...
its a stock flywheel
 
Gravey39 said:
I know you’d get more performance out of it. I just never ran it in a race so I never cared about switching or fiddling with the timing. I’m not too versed with engines anyways. I just knew about the jets.
Click to expand...
it started\ran with just the jets??? did u gain any performance???
 
95 shaw said:
Methanol burns much slower than gasoline, therefore, the fire must be ignited sooner to gain the power benefit from using it.

Jetting will be somewhat influenced by the timing set.
More timing, more fuel.

Your overall strategy influences this.
Click to expand...
what timing key should I get?? (stock flywheel)
 
Are you running stock flathead? In all honesty if you have a trusted local builder there you may want to talk to them. They should be able to steer you on what you need
 
Colt sr said:
Are you running stock flathead? In all honesty if you have a trusted local builder there you may want to talk to them. They should be able to steer you on what you need
Click to expand...
pretty much besides an
ARC billet rod, slightly heavier springs, 28mm Mikuni style carb, and a exhaust... but I don't know of any local builders ​
 
noahsm1th said:
what timing key should I get?? (stock flywheel)
Click to expand...
I've never run keys.

A selection of offset keys are inexpensive.
A search on here will find you a table of in the hole measurements relating to timing.
Once you know the depth, you can determine which key you need for future reference.

Jimmy Glenn's book on this site is a good read to help you understand these things.
 
Use a 4* key.
Be sure it's set so the flywheel moves clockwise from the key way.
Otherwise it will be retarded by that amount .
You need twice the area of the current jet hole.
Goggle area
 
If you want to use the carb that you've got, it will need to be set-up for alcohol. It's a bit more involved than simply changing jets, but you could start with that. A 26 is a pretty big carb for stock valve size and lift. A 22 would be a better "fit," but you can use what you've got to have some "growing room" for when you upgrade the cam and valves.
4 or 5* timing key will get you close (enough for now.)



-----
?Thanks and God bless,
Brian Carlson
Carlson Racing Engines
Vector Cutz
www.CarlsonMotorsports.com
Carlson Motorsports on Facebook
30 years of service to the karting industry
Linden, IN
765-339-4407
bcarlson@CarlsonMotorsports.com
 
Base rule of thumb for methanol is as said above, increase timing to at least 32-36* (usually #4 or #5 offset key) and double your jet size to start. So pull your jets and get the size, order double that or make your own with a precision # drill set.
 
What about going the other way, switching from methanol to gas? I went with the #37 jet as the only change. Engine starts but is tricky to keep running and falls on its face when opening the throttle
 
amusall said:
What about going the other way, switching from methanol to gas? I went with the #37 jet as the only change. Engine starts but is tricky to keep running and falls on its face when opening the throttle
Click to expand...
if it has the stock style briggs carb, the metering holes were reamed larger, go smaller on the jet
 
amusall said:
What about going the other way, switching from methanol to gas? I went with the #37 jet as the only change. Engine starts but is tricky to keep running and falls on its face when opening the throttle
Click to expand...

What kind of carb are we talking about? The original Briggs carb?
If so, then you're close on the jet at .037." I generally suggest .038."
The needle is used to tune a flathead on gas moreso than you would with alcohol. Start @ 1 1/2 turns and adjust from there.
If it idles fine, then falls on it's face when you step on the throttle, then it's likely too lean.
You may also have something plugged up in the carb (small idle circuit, pick-up tube, etc.)
If you've loosened the flywheel to change the ignition timing, then make sure that it is torqued plenty tight -- they slip easily if the taper is not lapped properly.
Also, check your plug gap -- Most WKA/IKF flatheads will use a slapper cam that "lofts" the valves. The intake valve will tag the ground strap on the spark plug if it is not indexed correctly, and that will make the engine fall on it's face when applying the throttle from an idle as well.


-----
?Thanks and God bless,
Brian Carlson
Carlson Racing Engines
Vector Cutz
www.CarlsonMotorsports.com
Carlson Motorsports on Facebook
30 years of service to the karting industry
Linden, IN
765-339-4407
bcarlson@CarlsonMotorsports.com
 
You must log in or register to reply here.
Back
Top