Briggs based Model 08 Racer Project

[MotorbikeMike]

I have my old original Model 08 Racer that I had built in about 2006, long before anyone would have a category for it. We used to put them either in Vintage bikes, or Whizzer!
This bike has been driven by a 2005 NE5 and also a 49cc HuaSheng with Q-matic. I am now wanting to do a Briggs project, with a twist! Among the parts I have available are.

ENGINES

2hp upright Briggs, runs good, points model I think

3hp upright briggs, (8 cu in) ran good when parked, seems to have stuck intake valve, good spark, Magnetron Ignition setup.

3.5 hp (9 cu in) upright Briggs, ran good when parked, good compression, no spark, points model

Other unknown upright Briggs, (8 or 9cu in) ran good when parked.

ALL have the flap-type integrated tank carburetor.

I do have a few carb choices, but I'd like to hear what others are using on the venerable Briggs and Stratton, Made in USA powerplant

The drive will either be Pacesetter with chain rear, or Pacesetter with belt rear depending upon the wheels, and a Whim.

Color is pre-selected, and will be a "Barn Bike build, with added rust (are they still calling that carp "Patina"?).

WHEELS

I have Worksman, Husky, and my current favorite CT-90 wheels, tho I am in the mood for some 18" motorcycle wheels.

OK guys, some ideas here?

Mike

 

[butchl]

Mike: Good to see you back to building. You've done some cool things.

 

[MotorbikeMike]

Awww thanks Butchl, I really want to solve some of my concerns with the faster type of Motor bicycle. One of my concerns has always been the thin tires and weak brakes of MotorBicycle.

This time I want to embrace either Moped, or real Motorcycle tires and brakes, with an "Honest to Saint Peter" American Engine, the mistreated Briggs and Stratton Upright Stationary.

I am looking forward to a fun, solid bike, the Chassis (which I need to dig up pics) is a good solid Droploop, it was the prototype for the whole Racer line. It's been chopped 3 times, and bears some scars, BUT I am sure many of the Privateers bikes would have shown similar battle scars.


Mike

 

[Mr.B.]

Go big!

3.5er...

-Kirk

 

[chainmaker]

Glad to see you are building a bike. Are you going for a true racer or the look? I'm not a Briggs expert but there aren't many hop up parts for the under 5 hp Briggs sized motors. Dale is the guy go to guy for Briggs info. I will be finishing up my Briggs racer this winter if you want to get some ideas, you have to go past post 27 for Briggs stuff. http://motorbicycling.com/showthread.php?t=44393

 

[curtisfox]

I like the smaller engines one is that here you can only go 20 to 30 mph without getting in trouble. 50 cc max to be legal. When i was a kid i had 1 1/2 hp briggs and went 25-30 mph. Sure was fun. I am going to do another this winter with a 1hp,try to coppie what i did as a kid.
Can't waite to see what you do............Curt

 

[MotorbikeMike]

Hi all, yeah speed, well CA law is 30 mph, so I guess I will need to go easy on the throttle? I've been home sick today reading VERY much on wheels, tires, and a bit on the Briggs, so here is my (right as of now) plan.
I found a pic of the bike, from 2007, when it was just back from being chopped again (neck angle/rake problem). New tank, new rake, new BAD attitude.
ENGINE
I think I can pull the Magnetron out of the 3hp with stuck valve, and put in in the 3.5?
I will clean the paint off of the crankcase, because AM's almost always had Aluminum crankcases. Fins black, if possible head bare alum.
Clean up the ports a bit, larger carb, Tuned Straight Pipe (probably Whizzer style flex pipe with tip). I figger, that with a little porting, free-flow air cleaner on bigger carb, and the pipe I should pick up .5 hp easy. I am not looking to race this bike, so 4 hp should be respectable.

What else might I NEED to do to get reasonable performance?

CARBURETOR
Still completely up in the air on this one, I will use spring-back rotary throttle handle, NOT Vintage Whizzer Lawnmower type cables, BUT what carb to use?
Ideas anyone?

WHEELS
I really want a vintage looking tread pattern, whether similar to CT-90, or Triumph Flat track, or early Dual-sport, but certainly NOT Avon style. I really think I can use a motorcycle front, if I can find the right one, but I believe the rear would need to be laced. The booger in the whole deal, is the need for the rear freewheel, so I can truly maintain the pedals, and the easiest way I see is the Moped Hub. I have 2 rear Harley Davidson hubs, no drive sprocket mounts. I can belt drive, or chain drive, I prefer belts. I do already have both clutches around here somewhere.

 

[curtisfox]

Its easy to free up the stuck valve, just pop the head off use a little auto tranny flued and tap with hammer turning engine over as you work it free.
Yep the Magnetron will fit they are all the same up to 5 hp I am sure just check the flywheel diameter. Some of the bolt holes my be different as well as the bolts......Curt

 

[MotorbikeMike]

Hi Curtisfox, I have heard the stuck valve is probably a real easy fix, but are the head gaskets re-useable? The reason the white engine (with points) is attractive to me is it is 9cu in, 3.5 hp, and I was thinking, seeing that the bike is heavy, and I am 300+ that I might have a use for the extra hp. The Gray engine (with Magnetron) is 8cu in, 3.0 hp.

Mike

 

[curtisfox]

Yes you can reuse the head gasket if it don't tear. My last three engines had stuck valves and was able to reuse them,one was a briggs and didn't even have a gasket. So just used some high temp silicone untill i get a gasket. You can get gaskets from NAPA not bad in price............Curt

 

[chainmaker]

The Briggs small flo jets are a decent carb , http://outdoorpowerinfo.com/repairs/briggs_small_two-piece_flo-jet.asp.

 

[curtisfox]

Yes they are and they come in different size 3,5,8,and 10 hp also Tecumesh snow blower 5 or 7hp has the high and low jets. Kohler 7 hp Carter is another.

Of corse there is always Mikuni................Curt

 

[Gbrebes]

I am not a Briggs expert, but I use a 5hp briggs on my bike. I have run three different carbs. I used the briggs updraft carb with the float bowl, as has been mentioned previously. It worked and looked cool, but not amazing performance-wise.

I then used a tillotson diaphragm carb. Mine has the numbers HL 129E426 stamped on it. This one worked a lot better and they seem to be preferred by Gokart guys who still run the flatheads. This carb developed problems recently and I need to service it, but for now I am using a Mikuni vm22.

This carb works nicely as well, but you have to fiddle with different idle jets (currently using a15) to get it to accelerate off idle properly. You also need to fiddle with the main jet whenever changing altitude or even weather.

So I prefer the tillotson, just for ease of adjustment. It only takes a few minutes to adjust the high speed jet with a screwdriver, then a few seconds more to set the low speed jet.

Hope that helps,

Gilbert

 

[maniac57]

I always had great results on the 5hp flathead briggs with a small motorcycle carb, like the Honda XR 75 carbs. Not sure the specific model but they give MUCH better throttle response and power. Very seldom had to touch the jetting except on high power modified engines.
Simply fab a manifold and bolt it on for instant improvement over any stock briggs carb.

 

[Moisstink]

Hey MotorbikeMike, I am pretty new at this whole 4 stroke approach and have a Briggs and Stratton Model 6B S Type 901010 (I believe it is a 2hp engine) that I want to use on a boartracker type build on a 1940's cleveland welding cruiser frame. My question to you or anyone reading this is what is the basic parts list to get this thing going? I am going to fab my own engine mount and as many parts as possible on a cnc but I am wondering about what kinds of clutch or drive system would be good. I wanted to keep it chain driven not belt. and I was wondering what type of carb may work. The engine currently has a carb that is functioning but it is a suction type that is a little bulky and I wanted to go with a gas tank that is not attached to the engine. Thanks for all info.

 

[MotorbikeMike]

Hi I will use EZMotorbike Q-matic drive on mine, I know them well, and they work for me. Sorry this is so late, had E-Mail and health issues since the start of this thread. Am currently assembling 1953 Schwinn B-4 with 1947 H Motor.

Mike