Briggs 4.5hp - hard to start when hot

Status
Not open for further replies.
F

Finz

Joined
Jun 6, 2013
Messages
709
Location
Northeast
Read a post on here weeks ago (about generators?.) and the poster had the same symptoms and someone mentioned the cause but I'll be darned if I can find it again

Have a Yard Machine lawn vacuum with a 4.5hp briggs engine

Starts on 1st - 3rd pull when I roll it out of the shed.

Once hot, however, it refuses to catch ( like right now) so I have to take a break and wait for it to cool down.

Now there IS an interlock on the bag which can get finicky but I'm aware of this and it's not the cause for the inability to start.

Choke on... choke off... partial throttle... full throttle... has no impact

One issue that could be relevant: the gas cap allows gas to weep out of the Neck of the filler. Just replaced the cap and it still weeps.... pretty sure I picked up the proper replacement. Actually 95% sure I ordered the right replacement although not an OEM

Anyone have any thoughts as to why this happens...?

Thank you

--bob
 
Originally Posted By: Finz
Read a post on here weeks ago (about generators?.) and the poster had the same symptoms and someone mentioned the cause but I'll be darned if I can find it again

Have a Yard Machine lawn vacuum with a 4.5hp briggs engine

Starts on 1st - 3rd pull when I roll it out of the shed.

Once hot, however, it refuses to catch ( like right now) so I have to take a break and wait for it to cool down.

Now there IS an interlock on the bag which can get finicky but I'm aware of this and it's not the cause for the inability to start.

Choke on... choke off... partial throttle... full throttle... has no impact

One issue that could be relevant: the gas cap allows gas to weep out of the Neck of the filler. Just replaced the cap and it still weeps.... pretty sure I picked up the proper replacement. Actually 95% sure I ordered the right replacement although not an OEM

Anyone have any thoughts as to why this happens...?

Thank you

--bob


It is always great on a hot summer day to have a good reason for that next cold beer while you wait for it to cool off.
 
Last edited:
I wonder if the gas in the final stages of mixing in a hot intake evaporates and now you don't have the stuff (vacuum) to start the process. Just for grins check the carb/manifold/block screws
 
I'll check for spark... hadn't thought of that

I KNEW I was setting myself up for the "taking a break" comment
smile.gif


I'll take the carb off and reassemble... maybe just look into replacement as it's 15 years old. Be surprised if more than $20

Thanks all
 
ok. dad same problem with a a new mower and i have had this with honda and B&S. We mow ALOT... leave about 1 inch of air space in gas tank when filling up to mow. lube spray all throttle linkinge from handle to engine. I use schaeffer's NEUTRA in all our gas cans.... it cleans carbs,stabilizes gas, and is a fuel lubricator,,,GREAT STUFF. We also only use redline oil or amsoil oil,,0w30. It made a huge diff in our seven push mowers and 2 drivers.
When shut down hot, I think some of the mowers got a little flooded. but not anymore.
goodluck
 
If you haven't been keeping the cooling system clean, it could be overheating. Pull the air shroud and clean the cylinder fins etc.

This does sound a lot like a coil that stops working due to heat soak. Spark test would tell. You can disconnect any kill switches, oil sensors, etc from the coil kill wire to test only the coil.
 
Originally Posted By: Merkava_4
What are the engine numbers Finz ?


12H802-1777-D1 02092557
 
Originally Posted By: mk378
If you haven't been keeping the cooling system clean, it could be overheating. Pull the air shroud and clean the cylinder fins etc.

This does sound a lot like a coil that stops working due to heat soak. Spark test would tell. You can disconnect any kill switches, oil sensors, etc from the coil kill wire to test only the coil.


I hear what you're saying but I don't have the first clue as to how check that. Cleaning out fins... sure. Check for spark,...? Pull plug and pull cord with plug grounded against engine....?

But the rest? I'll try to find a YouTube or something

Thank you
 
Originally Posted By: hyperscion
ok. dad same problem with a a new mower and i have had this with honda and B&S. We mow ALOT... leave about 1 inch of air space in gas tank when filling up to mow. lube spray all throttle linkinge from handle to engine. I use schaeffer's NEUTRA in all our gas cans.... it cleans carbs,stabilizes gas, and is a fuel lubricator,,,GREAT STUFF. We also only use redline oil or amsoil oil,,0w30. It made a huge diff in our seven push mowers and 2 drivers.
When shut down hot, I think some of the mowers got a little flooded. but not anymore.
goodluck


Thank you... all gas is already treated with Stabil and a splash of MMO and" because of the stupid leaky gas caps, I fill the tank halfway or so

I'll check out Neutra.... never heard of it

After reading that Generator post - which was really a discussion about oil - I replaced the oil with Rotella T6. 5w-40
 
I'd guess it's electrics as mentioned in some of the above posts. Failing that, it could possibly be tight valves. When the engine heats to the point of metal expansion, the valves may not be closing sufficiently to create necessary compression. Thus reluctance to start.
 
Originally Posted By: Finz
12H802-1777-D1 02092557


Those last set of numbers, the code number, tells me you have a carburetor with an automatic choke. The thermostat is probably not pulling the choke off. With the choke still on and the engine hot, it's not going to start. Replace thermostat 790830 and exhaust gasket 691881.

You can verify by pulling the air cleaner off. If the choke plate is still closed when the engine is hot, that's your problem. That engine came with 3 different carburetors depending on the date code: Primer Carb, Manual Choke Carb, and Auto Choke Carb. The automatic choke carb was for date codes before 05091900.

Personally, I'd convert it over to a primer carb system.
 
Beat me to it and far more articulate - I absolutely hate auto chokes because of this exact reason
 
Thanks everyone

Wobbly... I'll retorque (16.5 lbs I think) and blow out the cooling fins

Bubbatime/Bora... hoping it's that simple. I'll play with gap to see if that has any impact. Is there a way to truly check the coil or would messing with gap on plug be the easiest way to confirm?

Merk... thank you. I saw the same thing about this pre-2005 unit havimg an auto choke But no question there's a manual choke. And it's a very "solid" choke. By that, I mean, it clicks into 4 seperate stages of closure. I've never seen one like this but I like it - the way the closure settings are so defined. I'll try to grab a number off of it when I pull it out of the shed again. Aside from this hit-start issue, the can runs very well. Louder than all get out but it is, after all, just a huge vacuum. By the way, those replacement carbs designated for this unit, albeit wrong with auto choke, were more the twice what I figured... $40 - $50 so I'm glad it's not in need of replacement

This vac sat for a year or 2. Pulled it back into service a week or 3 ago and was is shock that it started right up. Couldn't believe it. Was sure I'd be tinkering all day trying to get it running.

The one thing I don't like about this unit is I can't find an oil drain plug.... supposed to be beneath the deck and it may we'll be there but the entire housing or shroud for the vacuum would have to removed. 15 years of partial neglect - I, to going near those shroud-attachment bolts

Just tip it to side and drain from oil-fill neck. Hate doing it that way... never feel I get all the gunk out of the bottom but not much choice in the matter

Now... the search continues for a non-leaky gas cap. WAIT: If the cap is bad, could that effect flow? I mean, I know it can but maybe while running there's enough draw from the tank, but after stopping or interrupting that flow, that cap itself is disallowing file to the carb?
 
Valve clearance out of specs, providing your not losing spark.
 
Last edited:
Hit it with starter fluid. If it doesn't start with that its electrical. When I have problems with small motors this is first in my bag of tricks for many decades.
 
Originally Posted By: Al
Hit it with starter fluid. If it doesn't start with that its electrical. When I have problems with small motors this is first in my bag of tricks for many decades.

That doesn't work if it's flooded though. As you add even more fuel, it still won't fire, and you'll make a wrong conclusion. Better to hook the spark wire to a test plug and check for spark directly.
 
Status
Not open for further replies.

Similar threads

9
Briggs&Strattons yard machines no start
Replies
15
Views
832
hardcore302
Pablo
Briggs I/C 7HP Tiller Engine CHOKE! Help please.
Replies
17
Views
2K
Pablo
MolaKule
New 21" Craftsman Mower
Replies
14
Views
1K
Gyro Gearloose
9
Craftsman Push Mower Starts and Stalls
2
Replies
30
Views
2K
99Saturn
JHZR2
Is my flathead Briggs dead?
2
Replies
27
Views
3K
JHZR2
Back
Top