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View Full Version : OT Small motor carbs, gravity feed vs pump?



vpt
10-08-2012, 10:16 PM
I am fixing up an old briggs 16hp single banger. I've already went threw the carb and now I am onto the lines and pump but a question arose. The fuel tank is a foot+ above the carb, the motor has a fuel pump on it originally but the motor is in a different chassis than original. Does the carb need the fuel to be pumped or would a gravity feed be ok? I see talk about different carbs for gravity feed but then I see some guys say most carbs can be gravity fed.

lakeside53
10-08-2012, 10:33 PM
Most can be gravity fed, but some pumped carbs will have a higher pop-off pressure on the float valve. Why not just leave the fuel pump in the fuel circuit?

firbikrhd1
10-08-2012, 10:34 PM
I am fixing up an old briggs 16hp single banger. I've already went threw the carb and now I am onto the lines and pump but a question arose. The fuel tank is a foot+ above the carb, the motor has a fuel pump on it originally but the motor is in a different chassis than original. Does the carb need the fuel to be pumped or would a gravity feed be ok? I see talk about different carbs for gravity feed but then I see some guys say most carbs can be gravity fed.

I don't know of any Briggs and Stratton carbs that can't be gravity fed, unless they don't have a float bowl. I do know that there are two types of fuel filters though, one for Briggs engines with fuel pumps and one for engines without. I noticed this at the local NAPA last time I replaced the filter on my 11HP horizontal shaft Briggs. I suspect the ones for engines with fuel pumps won't work well with gravity feed. At 1 foot above the carb you should have around .4 PSI (four tenths) approximately due to gravity maybe a tenth or so less.

vpt
10-08-2012, 10:45 PM
Most can be gravity fed, but some pumped carbs will have a higher pop-off pressure on the float valve. Why not just leave the fuel pump in the fuel circuit?

I haven't opened it up yet but I am suspecting being dry for 20 years may have ruined it. Not that I am cheap and don't want to buy one, the simpler the better to prevent breakdowns is more on my mind.




I don't know of any Briggs and Stratton carbs that can't be gravity fed, unless they don't have a float bowl. I do know that there are two types of fuel filters though, one for Briggs engines with fuel pumps and one for engines without. I noticed this at the local NAPA last time I replaced the filter on my 11HP horizontal shaft Briggs. I suspect the ones for engines with fuel pumps won't work well with gravity feed. At 1 foot above the carb you should have around .4 PSI (four tenths) approximately due to gravity maybe a tenth or so less.



Thanks much! I'll check for a filter tomorrow and set it up. I have to go pick up the hose a starter solenoid, and stuff anyhow.

sasquatch
10-08-2012, 10:50 PM
At 16 Hp and a single cyl. engine i,m guessing this is an older Briggs that came with the "Flow-Jet" carb.

Didn't know they came with a fuel pump.

The first two didgits of the model number are the cubic inches , check with a briggs dealer preferably an older one to get a positive I.D. on this engine.

flylo
10-08-2012, 11:40 PM
With out the fuel pump you may need a shut off?

wtrueman
10-09-2012, 12:01 AM
A bit off topic but: My 79 buick V6 in my model A is gravity fed. My .02, Wayne.

vpt
10-09-2012, 09:31 AM
At 16 Hp and a single cyl. engine i,m guessing this is an older Briggs that came with the "Flow-Jet" carb.

Didn't know they came with a fuel pump.

The first two didgits of the model number are the cubic inches , check with a briggs dealer preferably an older one to get a positive I.D. on this engine.

I found two stickers on the engine. One says 16hp briggs, and the other says synchro balanced. lol Its is old


With out the fuel pump you may need a shut off?


The carb does have a bowl with needle. The needle should stop and hold the fuel I would think. Even with the pump, the fuel tank above carb and fuel pump would be the same deal wouldn't it? From what I remember the fuel pump on these small motors can "flow threw" without the motor running.

justanengineer
10-09-2012, 09:50 AM
The carb does have a bowl with needle. The needle should stop and hold the fuel I would think. Even with the pump, the fuel tank above carb and fuel pump would be the same deal wouldn't it? From what I remember the fuel pump on these small motors can "flow threw" without the motor running.

Correct and correct. I wouldnt worry about the fuel pump unless youre running a filter. My old Cub Cadet has a Kohler, didnt come with a filter, Ive never added one, and its run fine for 40+ years. OTOH, Ive eliminated the fuel pump on several motorcycles (when they puked) and gone with a simply gravity feed system through a filter without issue.

sasquatch
10-09-2012, 10:18 AM
The model, type and serial number should be stamped in the fan shroud.

Sometimes it is small letters and hard to see, especially if it's been painted over a few times.

topct
10-09-2012, 10:49 AM
If that needle is on the bottom of the carburetor it is more likely the high speed jet adjustment.

The engine will run without the pump and I would install a shut off valve somewhere between the tank and carburetor. You can find small inline fuel filters at any lawnmower shop.

J. Randall
10-09-2012, 01:27 PM
If that needle is on the bottom of the carburetor it is more likely the high speed jet adjustment.

The engine will run without the pump and I would install a shut off valve somewhere between the tank and carburetor. You can find small inline fuel filters at any lawnmower shop.

It may have the high speed needle on the bottom, but he already stated he had been through the carb, and it has a float bowl and the needle should shut off the fuel flow.
James

topct
10-09-2012, 03:11 PM
It may have the high speed needle on the bottom, but he already stated he had been through the carb, and it has a float bowl and the needle should shut off the fuel flow.
James

It will shut off the high speed circuit. Fuel can still flow into the carb past the float needle. I think its best to be able to shut off the supply of fuel to the carb when the engine isn't in use. Should the float needle fail to shut, the fuel will overflow and those carbs do not have an overflow vent.

Willy
10-09-2012, 04:19 PM
I have to agree with topct as well about a fuel shutoff valve on any gravity fed fuel system.
Yes 99.9% of the time the needle and seat from the float system will shut off the fuel. But in the event that needle and seat fail to close fully you will end up with an engine full of fuel.
When an engine is stationary for long periods of time a very small piece of debris on the needle and seat will allow fuel into the float bowl and eventually into the engine.

The fuel shutoff valve for gravity fed systems is universal, just look at any non-fuel injected MC with an above engine fuel tank.
It's not if it's going to happen but when.

Bill736
10-09-2012, 06:00 PM
I agree with the idea of installing a shutoff valve between the gas tank and the carburetor. Parts for a lot of my older equipment are now only available as Chinese replacements. Fuel system parts are pathetically poor, and many of the Chinese needles and seats I've bought have leaked right out of the box, and never do seal well. I never had that problem with US made parts.

sasquatch
10-09-2012, 08:12 PM
If that is a "Flowjet" carb, the bottom needle is the high speed adjustment.
I have used those carbs,, all with a fuel shut off tap, BUT they will not run well or at all with a gravity fed inline fuel filter. There is just enough restriction in flow to kill them.
Even a large automotive inline filter wouldn't work.
Strange, as you would think enough fuel would seep through to keep it running.
Those are a very good reliable carb.

vpt
10-09-2012, 11:02 PM
I'll find and post a pic of the carb and motor I have below.

I got new tangent fuel line today, new gravity feed filter, starter relay, wire, some switches, and whatnot. Got everything together and got the motor to pop a few pops at a time and die, over and over again for an hour. I tried pressurizing the fuel tank a few times just to se if it was a fuel delivery issue and there was no change. I would adjust the lower main jet needle out some then all of a sudden the plug would be wet. I would turn the needle back in 1/4 turn and then the plug would be dry. Back and forth for hours this went on. Finally I got it to run continuously while playing with the choke and throttle plate. Still I couldn't find the sweet spot with the high speed needle. I would turn it out a tiny bit and get way to much fuel then not enough, back and forth it it never seemed to want to be consistent.

Finally I got it to run good enough to get out and drive it and kept playing with the high speed needle. By the time I ran a whole 1.5 gallons of gas threw the motor I had it pretty well dialed in. I think there may have been some junk or air or something somewhere that worked out because it did eventually be consistent with needle adjustments. Idled good, ran good at any constant throttle, but am having a bit of an issue yet with the rev up (rolling onto the throttle from idle). It will stumble some and sometimes have trouble reving up like it is not getting enough or to much fuel but when it gets up to speed it hold the rpm fine.

I have to disclaim some stuff yet, there was 1.25" of water in the bottom of the crank case for 20 years in this motor with its 2 quarts of oil on floating on the water. I have drained the oil, dumped in "clean" waste oil, ran the motor for a few minutes and drained it, and put in fresh good oil. One of the things the water did it seems is rust away the governor inside the crankcase since I can't feel or see it move ever when running. So I redid the the throttle direct to the carb. Now before you guys explain all the reasons not to do this I have to say the throttle is foot controlled exactly like a car gas peddle so I can control the engine rpm's constantly just like a car and not let it over rev. I believe I have been around enough of these motors to know what to high of rpms sounds like.

Can't find any pics apparently. I'll have to go out and take a few pics and post up in a minute.

vpt
10-09-2012, 11:16 PM
Ok, some pics.

http://imageshack.us/a/img803/6569/coot011.jpg

http://imageshack.us/a/img826/6017/coot012.jpg

http://imageshack.us/a/img90/4404/coot014.jpg

http://imageshack.us/a/img59/4809/coot015.jpg

vpt
10-09-2012, 11:18 PM
Oh yeah, Thanks for all the tips on the fuel shut off, I'll pick one up tomorrow and install it.

sasquatch
10-09-2012, 11:24 PM
That sure looks like the "Flow-jet" carb.

Those engines that i have had do stumble as you say, going from idle up to high rpm, at least all mine did.

Think they were mainly meant for either idle or steady rpm's.
What is this engine driving?

vpt
10-09-2012, 11:35 PM
The engine is driving a coot.

http://imageshack.us/a/img211/8274/coot016.jpg

http://imageshack.us/a/img69/6195/coot018.jpg

This one runs and performs much better than mine right now.
http://www.youtube.com/watch?v=3H0SPWfJ29w&feature=related

vpt
10-09-2012, 11:44 PM
These guys push this one a little better. They are amphibious, mine has the prop shaft option on the back.

http://www.youtube.com/watch?v=Isi4NGVCIKQ&feature=related

Black_Moons
10-09-2012, 11:58 PM
Best reason for fuel shutoff: Is that float WILL get stuck someday, and moreso then fill your engine up it will likey piss fuel all over. Nothing stupider then siting there as you leak a full tank of fuel everywhere wondering when it will stop.

Willy
10-10-2012, 12:55 AM
Idled good, ran good at any constant throttle, but am having a bit of an issue yet with the rev up (rolling onto the throttle from idle). It will stumble some and sometimes have trouble reving up like it is not getting enough or to much fuel but when it gets up to speed it hold the rpm fine.

Have you tried fattening up the idle mixture?
If you don't have a minor vacuum leak, a slightly fat idle mixture should serve as a transition between the idle jet downstream of the throttle butterfly and main jet located in the bottom of the fuel bowl which feeds into the main venturi.

A slightly lean idle mixture usually results in sluggish throttle response in these units, although with a proper main jet setting the engine is still able to function well under load at higher engine speeds.

vpt
10-10-2012, 01:07 AM
Thanks much Willy!

I didn't play with the idle jet much, I adjusted it till it idled fine without backfiring and left it. I will give the low jet some more adjustment tomorrow when I try it again.

Doing some searching and research on the coot and am thinking of rebuilding the whole thing. There isn't much there to rebuild (clean, reseal, new bushings and whatnot). After driving it a little today I think the clutches need to be gone threw as well. The drive clutch that I could see while driving wasn't closing all the way at WOT, it would start to close and work like it should and then stop about half-3/4 way to full engagement. I don't think anything has been cleaned or serviced in this thing much if at all. Seems stuff that broke was replaced or fixed and that was it, no maintenance.

J. Randall
10-10-2012, 09:20 PM
It will shut off the high speed circuit. Fuel can still flow into the carb past the float needle. I think its best to be able to shut off the supply of fuel to the carb when the engine isn't in use. Should the float needle fail to shut, the fuel will overflow and those carbs do not have an overflow vent.

Don't disagree with any of that, was just pointing out that Andy had already stated the needle he was talking about was in the carb as in needle and seat. I always put a shutoff in if there is not one there already.

J. Randall
10-10-2012, 09:24 PM
I'll find and post a pic of the carb and motor I have below.

I got new tangent fuel line today, new gravity feed filter, starter relay, wire, some switches, and whatnot. Got everything together and got the motor to pop a few pops at a time and die, over and over again for an hour. I tried pressurizing the fuel tank a few times just to se if it was a fuel delivery issue and there was no change. I would adjust the lower main jet needle out some then all of a sudden the plug would be wet. I would turn the needle back in 1/4 turn and then the plug would be dry. Back and forth for hours this went on. Finally I got it to run continuously while playing with the choke and throttle plate. Still I couldn't find the sweet spot with the high speed needle. I would turn it out a tiny bit and get way to much fuel then not enough, back and forth it it never seemed to want to be consistent.

Finally I got it to run good enough to get out and drive it and kept playing with the high speed needle. By the time I ran a whole 1.5 gallons of gas threw the motor I had it pretty well dialed in. I think there may have been some junk or air or something somewhere that worked out because it did eventually be consistent with needle adjustments. Idled good, ran good at any constant throttle, but am having a bit of an issue yet with the rev up (rolling onto the throttle from idle). It will stumble some and sometimes have trouble reving up like it is not getting enough or to much fuel but when it gets up to speed it hold the rpm fine.

I have to disclaim some stuff yet, there was 1.25" of water in the bottom of the crank case for 20 years in this motor with its 2 quarts of oil on floating on the water. I have drained the oil, dumped in "clean" waste oil, ran the motor for a few minutes and drained it, and put in fresh good oil. One of the things the water did it seems is rust away the governor inside the crankcase since I can't feel or see it move ever when running. So I redid the the throttle direct to the carb. Now before you guys explain all the reasons not to do this I have to say the throttle is foot controlled exactly like a car gas peddle so I can control the engine rpm's constantly just like a car and not let it over rev. I believe I have been around enough of these motors to know what to high of rpms sounds like.

Can't find any pics apparently. I'll have to go out and take a few pics and post up in a minute.

Assuming that carb has the removable main jet, did you take it out and make sure the tiny holes in it were clear? Symptoms sure sound like you might have had a slight blockage left there somewhere, tuning should not have been that touchy. Agree about fattening up the idle adjustment a little bit.
James

vpt
10-10-2012, 09:57 PM
Assuming that carb has the removable main jet, did you take it out and make sure the tiny holes in it were clear? Symptoms sure sound like you might have had a slight blockage left there somewhere, tuning should not have been that touchy. Agree about fattening up the idle adjustment a little bit.
James



Yes I pulled the whole carb apart (although it doesn't look clean and fresh in the pics) and went threw every port, hole, journal, and whatnot and made sure all were clean. The only thing I can think of that could have been left behind would be some paper towel fibers or cloth fibers from rags. Today I went out and gave the low speed needle a 1/8 of a turn and started the motor, still idles good and did seem to rev up easier, but I didn't run it long to warm it up.

I started in on some more fun today and have another question lol. Are greased bearings the same as oiled bearings? I found a couple pitted bearings and races in the gearbox today and actually found the 1" trailer bearings are identical in all dimensions. Just curious if something metal wise is different between greased and oiled bearings?

Found more milkshake today.

http://imageshack.us/a/img571/4648/coot1001.jpg

Pulled the trans apart and cleaned it all up.
http://imageshack.us/a/img255/4145/coot1002.jpg

Couldn't get the secondary clutch off the shaft So I had to do all the work with the clutch shaft on the main shaft.
http://imageshack.us/a/img571/1731/coot1007.jpg

Everything looks good except this idler gear. These few teeth must have dipped into the water in the bottom of the case over the last 20 years. Is there any repair options for these few teeth? I can't imagine it would be easy to find this gear. File test says its hard like most gears. Can the water craters be cleaned up and filled with tig fast without heating everything up? Or heat it, weld, cool with something, or welding is not a viable option at all? I have welded gear teeth before on less stressed gears and have about a 50% fail rate but normally welding in full teeth.
http://imageshack.us/a/img688/3253/coot1017.jpg

Willy
10-11-2012, 10:32 AM
No difference in bearing material for grease or oil lubed bearings. Grease is just a carrier for oil anyway and is used when oil is not a viable alternative for a particular application.

You should be able to verify that your Coot transmission bearings are in fact 1" trailer bearings by looking up the bearing numbers and doing a bearing number cross reference.

The gear in question does look like it should be sidelined before it does more damage to the corresponding gear that it meshes with. There are a number of options available, everything from a proper welding procedure and heat treatment to making a completely new gear.
I personally don't have much experience with gear repair so I won't comment on the process, perhaps someone else here will have that info.

Have you tried Richard's Relics for parts availability?
http://www.route6x6.com/howto/Coottrans/index.html

vpt
10-12-2012, 09:54 AM
Thanks Willy!

Yes I have been looking over (all 3, lol) places that have coot parts and info. The 6x6 place has the single gears in stock apparently but not the double gear. I am getting mixed opinions on fixing the gear, I may have to give it a try yet.

I did press in the new trailer bearing races last night and they are a perfect fit. At least I didn't have to spend hundreds on weird impossible to get bearings. The gearbox says apex gear company on it, I am going to try searching that a bit and see what I find.

I have welded quite allot of things in my life but it seems I am getting the most off the wall weird jobs lately.