5hp Briggs and Stratton wont stay on

Jandir

New Member
Mar 28, 2014
7
0
0
California
Hey everyone, this is my first post here on motorbicycling.com. So I have been working on my motorized bicycle/board track racer inspired build for almost a year now, and am nearing completion. I mounted a temporary gasoline tank and temporary exhaust pipe (as can be seen in pictures) to the 5 hp Briggs & Stratton engine. I had to order a clone Mikuni 22mm carburetor from ebay and build a manifold to mount it on, because the original carburetor setup would not work with the limited space I had on the frame of the bicycle. I tried to run the bike for a test with the temporary gas tank and exhaust setup so I could dial in the mechanical parts before moving further with the build, but the engine would not run when off of choke. It runs briefly when I take it off of choke and on occasion will run with some throttle but always dies before I can get the bike moving. I am really confused with what to do to the carb to make it run. Can someone please help me get the motor to run normal. I tried to adjust the carburetor by adjusting the screws on the side but I couldn't make much of a difference. Is it possible that I have to spray some carb cleaner in it, even though its a new carb? Any advice would be appreciated.
 

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MEASURE TWICE

Well-Known Member
Jul 13, 2010
2,355
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83
CA
I have not used that carb on my briggs, but I expect it should work. Others will chime in an have more info that know that carb.

I usually think a carb would work without the airfilter in place, being careful, as there can be no dust around as ruining cylinder/piston can happen. I did think though that richer mix when choke on may work, so then thinking it is running lean. Lean running as possibly since no airfilter, but I might be wrong?

If you have an airfilter, I would try again with it installed.

MT
 

silverbear

The Boy Who Never Grew Up
Jul 9, 2009
8,191
45
38
northeastern Minnesota
I don't know, but am interested in the problem since I'm just now in the process of making a copper manifold to connect a 22mm Mikuni to a 5 horse Tecumseh on a cantilever Schwinn frame (kindalikeawhizzer thread). I'm having to mount my engine on a forward tilt, so a custom manifold is needed. I'm a ways off from firing up the engine and hope to learn from your experience. Did you do a build thread?
SB
 

Ludwig II

Well-Known Member
Jul 17, 2012
5,070
639
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UK
It's not something simple like the carb needle dropping down, is it? I had it once, and we spent 90 minutes chasing round the electrics.
 

MEASURE TWICE

Well-Known Member
Jul 13, 2010
2,355
343
83
CA
If it can run at idle with choke on and any faster for just a short while, I'm just thinking that is gas starvation.

I tried to see the bottle that is used on the bikes seat that has the gas. It is hard to see the amount, level of gas inside.

If you have more gas then there is a bit more pressure. Also higher up more pressure. Any bends too tight in the line restricts.

If you have a way of knowing the float is working and the float valve provides enough gas that would be good.

The bottle repositioned, or a gas tank preferably and try have it closer and up higher.

The bottle I hope is OK for gas as if it is being deteriorated and gumming the garb, then cleaning and rebuilding the carb would have to be done.

Checking the float level adjustment to see if you can allow a higher level which also gets more pressure is a fine tuning of the carb. I have never needed to do that, but cleaning silt and gummy from inside the bowl and jets yes I have.

The new carb never used anywhere on another engine from factory may have debris in it, it is not tested as far as I know..... just what ever quality control they use.

Have another carb just to try, like the original for the briggs you still keep. I think I heard you say you got this for a better fit. So the engine with the original carb if it works still and runs up throttle and idles, then I have think I'd rule out ignition stuff.

Also the air filter back on as soon as you can. This just because I've seen the results on cylinder and piston. I have heard that snow blowers may not use airfilters, the reason is that the air is not dusty with snow cover and they are getting greater power, but otherwise it is a risk.
 
Last edited:

Jandir

New Member
Mar 28, 2014
7
0
0
California
MT-I don't have an air filter for it, since I just ordered the carb alone. Could I just buy one of those K&N looking filters from an auto parts store and put it on with clamps? Or should I make my own. A while back I used some blue foam and put it inside a tin can w/ holes; and used that as an air filter. I'm not sure if that is the right way to go about it but it worked for the lawnmower's 3hp engine. Perhaps you know of an air filter I can buy/build? Sorry about the picture, but the bottle is just a plain plastic crystal geyser water bottle. I did not take into account that the gas may eat away at the bottle and gum up the carb; as I was only using it temporarily and was really excited to get the engine to run. I just punched a hole in the capof the bottle, slipped the fuel tube through, and made another small hole up top with a needle for air to come in. I did not put a lot of gas in it though, maybe I should fill it 3/4 with gas and try that, as you mentioned the pressure plays a role. Should I continue with this bottle setup or use something else? The engine ran great with the original carbureator, both on choke and run, and on idle and with throttle.
Silverbear - Sorry I did not do a build thread yet. I was leaning towards finishing the build and then creating a thread showing the whole process. Best of luck with your build, hope the info on this thread will be of some use to you.

Ludwig II - It may be, I will take apart the float an see.

Thanks for the advice everyone, your advice is appreciated!
 

Jandir

New Member
Mar 28, 2014
7
0
0
California
If it can run at idle with choke on and any faster for just a short while, I'm just thinking that is gas starvation.

I tried to see the bottle that is used on the bikes seat that has the gas. It is hard to see the amount, level of gas inside.

If you have more gas then there is a bit more pressure. Also higher up more pressure. Any bends too tight in the line restricts.

If you have a way of knowing the float is working and the float valve provides enough gas that would be good.

The bottle repositioned, or a gas tank preferably and try have it closer and up higher.

The bottle I hope is OK for gas as if it is being deteriorated and gumming the garb, then cleaning and rebuilding the carb would have to be done.

Checking the float level adjustment to see if you can allow a higher level which also gets more pressure is a fine tuning of the carb. I have never needed to do that, but cleaning silt and gummy from inside the bowl and jets yes I have.

The new carb never used anywhere on another engine from factory may have debris in it, it is not tested as far as I know..... just what ever quality control they use.

Have another carb just to try, like the original for the briggs you still keep. I think I heard you say you got this for a better fit. So the engine with the original carb if it works still and runs up throttle and idles, then I have think I'd rule out ignition stuff.

Also the air filter back on as soon as you can. This just because I've seen the results on cylinder and piston. I have heard that snow blowers may not use airfilters, the reason is that the air is not dusty with snow cover and they are getting greater power, but otherwise it is a risk.
It's not something simple like the carb needle dropping down, is it? I had it once, and we spent 90 minutes chasing round the electrics.
I don't know, but am interested in the problem since I'm just now in the process of making a copper manifold to connect a 22mm Mikuni to a 5 horse Tecumseh on a cantilever Schwinn frame (kindalikeawhizzer thread). I'm having to mount my engine on a forward tilt, so a custom manifold is needed. I'm a ways off from firing up the engine and hope to learn from your experience. Did you do a build thread?
SB
MT-I don't have an air filter for it, since I just ordered the carb alone. Could I just buy one of those K&N looking filters from an auto parts store and put it on with clamps? Or should I make my own. A while back I used some blue foam and put it inside a tin can w/ holes; and used that as an air filter. I'm not sure if that is the right way to go about it but it worked for the lawnmower's 3hp engine. Perhaps you know of an air filter I can buy/build? Sorry about the picture, but the bottle is just a plain plastic crystal geyser water bottle. I did not take into account that the gas may eat away at the bottle and gum up the carb; as I was only using it temporarily and was really excited to get the engine to run. I just punched a hole in the capof the bottle, slipped the fuel tube through, and made another small hole up top with a needle for air to come in. I did not put a lot of gas in it though, maybe I should fill it 3/4 with gas and try that, as you mentioned the pressure plays a role. Should I continue with this bottle setup or use something else? The engine ran great with the original carbureator, both on choke and run, and on idle and with throttle.
Silverbear - Sorry I did not do a build thread yet. I was leaning towards finishing the build and then creating a thread showing the whole process. Best of luck with your build, hope the info on this thread will be of some use to you.

Ludwig II - It may be, I will take apart the float an see.

Thanks for the advice everyone, your advice is appreciated!
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ElGallo

Member
Jul 1, 2012
119
1
16
San Antonio, Texas
hello Jandir, welcome to the forum.

much like M T said the use of plastic that is not gas 'proof' can and will gum up things.

what has worked for me in the past when i can not figure out what is going on is to take everything apart (labor and time intensive but peace of mind), clean everything, and back together. but for your case you mentioned that it does run well for a short time and with choke on. look at the spark plug how does it look? this can tell you if lean or rich.
side note for a quick air filter i have used a scour pad and zip tie. i have been running this on my gx200 without a problem.
if the only thing that you have changed is the carb and the motor was running normal before, grab some carb cleaner or brake cleaner or some M.E.K.(my personal favorite) and dismantle the carb. take eveerything off it, and give it all a good bath. check that all holes and pathways are free and clear of all debris, oil, gunk or anything.

a friend of mine had a similar problem with his '13' briggs ended up that some carpet like thread got caught in the jet and wouldnt let the motor run.

i hope you find a cure to this problem and get to riding that bike soon.
 

maniac57

Old, Fat, and still faster than you
Oct 8, 2011
4,484
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memphis Tn
If it only runs with the choke on, check for air leaks in the intake, and clogged or dirty jets.

Be SURE the manifold is airtight and properly sealed to the block.
Clean the carb top to bottom.

Might be too big a carb for the briggs as well.
I use a stock china NT carb on my flatheads with excellent results..
 

ElGallo

Member
Jul 1, 2012
119
1
16
San Antonio, Texas
If it only runs with the choke on, check for air leaks in the intake, and clogged or dirty jets.

Be SURE the manifold is airtight and properly sealed to the block.
Clean the carb top to bottom.

Might be too big a carb for the briggs as well.
I use a stock china NT carb on my flatheads with excellent results..
i second what he said
 

Slogger

Member
Sep 8, 2014
545
4
18
nohio
I third what he said, too.

You know, a short rubber hose piece between the carb and manifold might calm down the gas in the bowl, float and needle from the vibes of those bangers. The carb wouldn't get as hot, either.
Something to try if all else fails, maybe.
Good luck with it!
 

mapbike

Active Member
Mar 14, 2010
5,393
10
38
Central Texas
way to much air going through that carb for a stock BS 5hp

An NT type carb has a very similar throat size as the stock Briggs carb.

You can up jet the 22mm carb and see if you an get it to run, but Im thinking the carb is a bit large for that engine possibly.
 

silverbear

The Boy Who Never Grew Up
Jul 9, 2009
8,191
45
38
northeastern Minnesota
I may well have a similar problem with a 5 horse 199cc Tecemsuh flat head.

http://motorbicycling.com/showthread.php?t=49177&page=37

I'm using a 22mm Mikuni carb and discovered the throat size on the Tecumseh was smaller than the Mikuni.
Beginning at post 365 in the above thread there is some discussion of the discrepancy with suggestions by forum members which might be of interest to you. I won't have an opportunity to start my engine until springtime in my part of the world around the end of April, but I suspect I may have experiences similar to yours. I am keen to see how things work out for you. Good luck!
SB
 

maniac57

Old, Fat, and still faster than you
Oct 8, 2011
4,484
16
0
memphis Tn
Just for information, I have a Tecumseh HS40 outside that fired right up and runs just fine with a bone stock NT carb bolted to the intake.
I've used the NT on several Briggs and other flathead motors with great results.
 

silverbear

The Boy Who Never Grew Up
Jul 9, 2009
8,191
45
38
northeastern Minnesota
Just for information, I have a Tecumseh HS40 outside that fired right up and runs just fine with a bone stock NT carb bolted to the intake.
I've used the NT on several Briggs and other flathead motors with great results.
That's good to know. Since I have already made up an intake manifold for the Mikuni I'm going to try it. If it doesn't work out then I'll try the China girl since I have a couple sitting around gathering dust. Sometimes I make the mistake of looking far off for exotic solutions to a problem when a simple one is right in front of me. I was thinking in terms of the engine's cc's and what was being suggested for Honda clone engines of around the same horsepower. The old flat heads are different critters it appears. I just want my engine to start easily and run smoothly and won't ever try to find out how fast it will go.
SB
 

headtrama

Member
Jul 8, 2010
886
0
16
california
If it's running with the choke on it sounds lean. Try a richer main jet, I'm running a 28 mm Mikuni on a Briggs flat head. A 22 should run fine on your motor.
 

mapbike

Active Member
Mar 14, 2010
5,393
10
38
Central Texas
If it's running with the choke on it sounds lean. Try a richer main jet, I'm running a 28 mm Mikuni on a Briggs flat head. A 22 should run fine on your motor.
Wow, if the 28mm works then I stand corrected and yes the 22mm should also work just fine with correct jetting.

Thanks for ringing in here on this, I'll remember this.

map
 

maniac57

Old, Fat, and still faster than you
Oct 8, 2011
4,484
16
0
memphis Tn
Main thing to remember is the engine has no idea what carb is on it. As long as it's jetted right, nearly anything will work.
I once saw a guy running a huge Holley Dominator and a tunnel ram on a 215 Buick v8.
Ran just fine and had great top end.
 

Ludwig II

Well-Known Member
Jul 17, 2012
5,070
639
113
UK
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.