5hp Briggs and Stratton wont stay on

mapbike

Active Member
Mar 14, 2010
5,393
10
38
Central Texas
I've always said the same about spark plugs Rolls Royce or rotary mower, they don't know and they don't care. They just sit there sparking.
some spark plugs do out perform others though, I have experienced that first hand many times, some will actually not fire under compression and some raise or lower head temps and some fuel foul easier than others.
 

Ludwig II

Well-Known Member
Jul 17, 2012
5,070
639
113
UK
This why I used to buy plugs from boxes with different batch numbers on. If one plug from a production run fails, others might. Spreading the risk is sensible.
 

Jandir

New Member
Mar 28, 2014
7
0
0
California
Hey thanks for the advice everyone. I finally took some time out and worked on the engine. Luckily I did not have to re-jet the carb and got it to run very nicely. I started with adding a scour pad for an air filter and replaced the water bottle gas tank with a gas tank from a weed wacker. The engine ran great with this setup on choke but kept dying on run unless I gave it throttle. After a few minutes of adjusting the carb I got everything dialed in, and now it runs smooth on both choke and run. I did however notice that the engine likes to back fire and release a nice flame from the straight pipe exhaust. As much as I love the backfire and flame, I might have to put a muffle on it. Anyone have any ideas on what kind of pipe I can use for the exhaust? I am using a 3/4 inch conduit pipe right now, but do not have a bender to bend the exhaust downwards and away from the bike. If anyone has ideas on easy exhaust setups please post them. I will try and post a video on youtube and post the link here for you guys to see the engine running.
 

MEASURE TWICE

Well-Known Member
Jul 13, 2010
2,355
343
83
CA
Four Pictures of my exhaust using plumbing parts. They are heavy and I'd say use care that the pipes are held in place so they don't move. A length of pipe has a mechanical advantage prying the threads, or cracking the engine exhaust port you don't want to have happen.

I previously used flex pipe (that was water pipe with gaskets changed to copper ones I made), still too thin a metal and broke. There are flex pipe for exhaust but of the smaller diameter that would take a tighter radius bend, it is very expensive.

Now for what I am using, all the parts are from hardware store except the large low tone muffler that has the special spark arrestor screen that actually costs seperate from the muffler $25. Muffler $17. You need this screen for trail riding, OHV DMV approval sticker registration.

On the thread:

"How to make some serious bread"

Post #242

http://motorbicycling.com/showthread.php?p=592150#post592150
 

MEASURE TWICE

Well-Known Member
Jul 13, 2010
2,355
343
83
CA
I notice there is a hand clutch, was wondering where the parts are from?

Glad the carb new / engine is working well!
 

Jandir

New Member
Mar 28, 2014
7
0
0
California
MT- The clutch is all custom. I used the wire system from an old bike brake. And I used the pulley that acts as a clutch from the tiller I removed the engine from. Lastly I found an old spring to keep everything tensioned. The whole system had to be custom made.Here is a picture of it.
 

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silverbear

The Boy Who Never Grew Up
Jul 9, 2009
8,191
45
38
northeastern Minnesota
I like your hand clutch. I'm doing something very similar on a Villiars powered 1934 Elgin. Mine will use a brake lever. Yours, too? And congrats on getting your engine running well.
SB
 

Jandir

New Member
Mar 28, 2014
7
0
0
California
So here is an update. I did lots of more work to the bike and even rode it. It was really fun to riding it. But a few days after riding it I went to turn it on and the motor kept dying. I don't know whats wrong with it. I even took off the carb and cleaned it out, and still the motor wont stay on. Im not sure what to do at this point. The carb has an idle adjustment screw and an air screw. I tried all sorts of adjustments to those screws and still have had no success. Should I just get a an nt carb? I searched ebay for nt carbs and found simple carbs for around 10 bucks. Or is there a way I can make this workout. What should you look for when adjusting a carb of this sort? Also the copper exhaust pipe I made for it keeps falling off because the solder in it keeps melting, is it bad to run it without an exhaust as I have been doing so? How can I solder it so it stays on? Also sometimes gas and vapor comes out of the intake of the carb, and the carb goes through gas fairly quickly. So now should I order a filter for the current carb and try to work with it, or just buy a different carb?
Thanks, all feedback is greatly appreciated!

Here are links to me test riding it and the engine in its current state.
https://www.youtube.com/watch?v=avNgyRVb-us&feature=youtu.be
https://www.youtube.com/watch?v=WHCzMWYGki4
 

Tony01

Well-Known Member
Nov 28, 2012
1,370
753
113
sf bay area
Don't run without an exhaust pipe at least 8" long. You risk burning the exhaust valve. Best to make a header for it.

Check your valves make sure you have the correct amount of valve lash.

Check your float bowl, make sure it is allowing gas to fill the bowl. I'm thinking empty bowl. With the bowl off and the float valve removed make sure gas flows freely out of it when you turn your petcock on.

Put in a fresh spark plug, get it to run for at least 3mins and look at it. This is the best indicator of mixture.
 

Agreen

Member
Feb 10, 2013
791
10
18
Southeastern GA
I don't think you are quite grasping the carburetor concept yet.

That mikuni has a main jet and an idle circuit. The main jet is essentially a straw stuck down in the bowl. It's what feeds the engine the fuel when it's not idling. Inside the main jet is a needle. It comes from the top and is driven by the throttle slide. It is responsible for fuel mixture above idle, up to about 3/4 throttle. It essentially changes the size of the main jet for partial throttle mixture. It's adjustable via a little e-clip. Move the e-clip down, more rich. Up, more lean. The needle is important for throttle response. It may die off if its too far off. There is also an air bypass tube that you can see from the opening of the carb. That also has a little straw going in to the bowl, but the mixture is controlled by the screw. So you have an idle screw mixture screw and an idle speed screw. That's it. Do not over tighten the idle mixture screw! It's an itty bitty needle valve inside an aluminum bore. Damage the seat and your carb is done for.

So there are a few things that could go wrong. Also, the spark plug can tell you the story about how lean or rich it is. On a 4 stroke engine, lean will surge (the speed goes up, down, up, down) and rich will bog (engine sounds labored). On a 2 stroke, it's almost backwards. Rich will sputter like a machine gun (and sound about 1/2 speed) and lean will bog down.

If the spark plug is looking like you just drug it out of a coal mine, then lean it up some. If it's not getting a little soot, you need to fatten up the mix.

Start with a fresh plug, and try moving the slide needle before messing with the main jet.

I also just remembered about the float. If your bowl isn't level, you will have such a hard time with it. Does it dribble fuel out the inlet when the engine is off? On the flip side, maybe the float isn't letting enough fuel in the bowl and the jet can only suck air in?
 

silverbear

The Boy Who Never Grew Up
Jul 9, 2009
8,191
45
38
northeastern Minnesota
Soldering a copper exhaust pipe doesn't work as the heat is too great and melts the solder. Ask me how I know this... sigh. If you want to use copper then you need a mechanical connection somehow. On one of my bikes I have a copper exhaust which screws into the exhaust manifold and then sections are held together with bolts. Copper looks nice at first, but changes drastically from the heat where it is hottest.
SB