Briggs 18 HP Hard to Start

TobyU

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Either start some gas or carb cleaner into the intake when it won't start or hold your hand over the intake after you remove air filter to block off all air going in.
If it starts up in 2-3 revolutions, you suspect choke not shutting all the way or not enough fuel on its own.
If choke is closing all the way then pop fuel line off at carb and crank to see if fuel pump is pumping fuel out. It should blub blub blub out as it cranks.
If good there, then the less likely things are fuel solenoid acting up or leaking fuel slightly or bowl leaking so as to lower level in carb bowl and it takes all that cranking for pump to fill the bowl back up enough to start
If it runs fine under load then it's unlikely to be a fuel pump or restricted fuel line or tank UNLESS it's intermittent as those can come and go.
 

TobyU

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Also, get out of the habit of suspecting and adjusting valves.
Just not that critical on these and unless you take rockers off and tighten rocker arm stud, all the wrenching will cause one to loosen up and then it will bend a pushrod and but run ...WAIT that's on the Single cyl ones
The twins are more forgiving a they have the nut adjuster at the pushrod tip of rocker and not in the middle on stud.
Regardless, when you first check a Briggs ohv valves (if you're the first in there) they will be REALLY out of spec.
Really loose.
Once you set them, they will move be that out again as they don't get out much in their own and most all the wear is from the early break in hours and slows to near nothing after that.
When the valves are needing adj esp on a single, it will be hard to spin over. Like a week batt or starter. Many batts and starters have been replaced because of this with no improvement.
It's like it starts to spin and then hits arl rubber wall and stops and bounces back a hair.
When this happens (singles esp) you HOPE to find the valves out and not a busted ACR. I am SO Happy when I see that valve "bump" back open.
 

VRR.DYNDNS>BIZ

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Briggs 350777 Replaced plugs, coils, adjusted valves. Have to turn it over for 20-30 seconds to get it to start. Once started runs fantastic. What am I missing? Some kind of fuel problem? Replaced fuel pump a couple of years ago.
search for about 4 replies about a hard to start that I replied the fuel solenoid will not retract under 12 volts when cranking.
 

Freddie21

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What weight oil are you running. 5w30 in that cold weather.
 

goodO1boydws

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Just a thought here, but have you tried checking for spark while its cranking? You might be surprised at what you find.

My rider was getting ornery and it was taking a long time cranking to get the engine to catch. I do regular maintenance, changing the oil and filter, checking fuel and air filters, and checking/cleaning the plugs much more often than usual, (because the engine is using oil). Did that all again-no difference.

Then i was checking for spark and noticed that when it wouldn't start there was no spark, but the spark was fine once itwas running.
So I checked the magneto's air gap, and it was a tiny bit off, so I adjusted that. Still no difference in starting, and the same pattern of no spark when cranking, but ok whem running. I picked up a "used but good" magneto and swapped that one in. Same thing was happening at cranking speed no spark, but fine once running . I figured the magneto was as bad as mine, returned it for another one. Same thing.
Hmmmmmm. What are the odds 3 magnetos are all bad in exactly this same way?
So I figured that it was most likely something else. But what to check next? I'd replaced the starter solenoid only a year previously, and the ignitionn switch at that same time. The power and ground wires were clean and tight and the battery was up to snuff too.

i didn't want to try the carburetor yet so that the starter as a possibility.

Since starters are available from sources other than Briggs now,(and their price has dropped like a rock) i ordered one. This is the third starter thar's been on the engine, along with a couple more starter gear changes. According to the engine parts list the first 2 were the correct starters for that engine in that application.

My engine is an 18.5 hp horizontal twin and I found out that there are 3 different length starters that COULD be used, one of which is at least a half inch longer than the original, so THIS time i ordered the longest one. Once installed the engine cranked over faster than it EVER had before-even when brand new. I was shocked at how much faster.
After installation of the longer starter it started very easily too- in a second or less, compared to 20-30 seconds or more of cranking before it was in..
This was without changing ANYTHING else besides what had already been done.

So, after doing some research, here's the poop.
On many Briggs engines, the magneto will not produce ANY spark below a certain cranking rpm.
Not just a WEAKER spark-none whatsoever.

Depending on the ambient temp, and other factors, such as battery strength, ENGINE OIL WEIGHT, and what starter is installed, its possible that an engine may be cranking over JUST SLIGHTLY below that needed for the magneto to fire (maybe only 25rpm too slowly)-until you're cranked it over long enough for the engine's internal friction to begin to decrease as it goes through more revolutions, after which it spins over just a LITTLE bit faster, but its enough to be above the rpm needed for the magneto to fire. It's also more liable to start quicker in warm weather-but many engines are-for any of several reasons.
 

Alton R

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Briggs 350777 Replaced plugs, coils, adjusted valves. Have to turn it over for 20-30 seconds to get it to start. Once started runs fantastic. What am I missing? Some kind of fuel problem? Replaced fuel pump a couple of years ago.
Just wondering if you have a vacuum leak. My mower is doing the same thing. I've already had one vacuum leak. I'm just wondering if your engine is a twen cylinder. You know a vacuum leak would memic the same symptoms as a choke not being fully closed. My engine is a 20 hp onan.

I have seen engines that the fuel tank cap was stopped up not letting it vent properly.
 

bk10s

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Just a thought here, but have you tried checking for spark while its cranking? You might be surprised at what you find.

My rider was getting ornery and it was taking a long time cranking to get the engine to catch. I do regular maintenance, changing the oil and filter, checking fuel and air filters, and checking/cleaning the plugs much more often than usual, (because the engine is using oil). Did that all again-no difference.

Then i was checking for spark and noticed that when it wouldn't start there was no spark, but the spark was fine once itwas running.
So I checked the magneto's air gap, and it was a tiny bit off, so I adjusted that. Still no difference in starting, and the same pattern of no spark when cranking, but ok whem running. I picked up a "used but good" magneto and swapped that one in. Same thing was happening at cranking speed no spark, but fine once running . I figured the magneto was as bad as mine, returned it for another one. Same thing.
Hmmmmmm. What are the odds 3 magnetos are all bad in exactly this same way?
So I figured that it was most likely something else. But what to check next? I'd replaced the starter solenoid only a year previously, and the ignitionn switch at that same time. The power and ground wires were clean and tight and the battery was up to snuff too.

i didn't want to try the carburetor yet so that the starter as a possibility.

Since starters are available from sources other than Briggs now,(and their price has dropped like a rock) i ordered one. This is the third starter thar's been on the engine, along with a couple more starter gear changes. According to the engine parts list the first 2 were the correct starters for that engine in that application.

My engine is an 18.5 hp horizontal twin and I found out that there are 3 different length starters that COULD be used, one of which is at least a half inch longer than the original, so THIS time i ordered the longest one. Once installed the engine cranked over faster than it EVER had before-even when brand new. I was shocked at how much faster.
After installation of the longer starter it started very easily too- in a second or less, compared to 20-30 seconds or more of cranking before it was in..
This was without changing ANYTHING else besides what had already been done.

So, after doing some research, here's the poop.
On many Briggs engines, the magneto will not produce ANY spark below a certain cranking rpm.
Not just a WEAKER spark-none whatsoever.

Depending on the ambient temp, and other factors, such as battery strength, ENGINE OIL WEIGHT, and what starter is installed, its possible that an engine may be cranking over JUST SLIGHTLY below that needed for the magneto to fire (maybe only 25rpm too slowly)-until you're cranked it over long enough for the engine's internal friction to begin to decrease as it goes through more revolutions, after which it spins over just a LITTLE bit faster, but its enough to be above the rpm needed for the magneto to fire. It's also more liable to start quicker in warm weather-but many engines are-for any of several reasons.
You may be on to something here. When I ran out of battery and hooked up my charger to try to start, the engine turned over faster and started quickly.
 

bk10s

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Just wondering if you have a vacuum leak. My mower is doing the same thing. I've already had one vacuum leak. I'm just wondering if your engine is a twen cylinder. You know a vacuum leak would memic the same symptoms as a choke not being fully closed. My engine is a 20 hp onan.

I have seen engines that the fuel tank cap was stopped up not letting it vent properly.
I have tried with the cap off. Where would I look for a vacuum leak? Valve cover gaskets, and possibly the pump not getting good vacuum?
 

Sherman Anderson

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Briggs 350777 Replaced plugs, coils, adjusted valves. Have to turn it over for 20-30 seconds to get it to start. Once started runs fantastic. What am I missing? Some kind of fuel problem? Replaced fuel pump a couple of years ago.
 

PLC

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ILENGINE has the right idea. I have a V twin that would crank and crank and crank. My repair guy told me that before I bring it in, I should check the cable adjustment to make sure it closes completely. When I checked the choke wasn't closing totally. There was a minimal adjustment needed to get it completely closed. Started immediately when I tried it after adjustment. I couldn't believe how little adjustment made such a difference.
 
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