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Engine wont start and backfires through carb


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05-27-10, 08:14 AM   #1  
Engine wont start and backfires through carb

Its a Briggs Model 31P777 Type 0296-E1. It wont start, backfires though the carb and the starter can barely turn it over. I have adjusted the valves to .005 on both intake and exhaust. The valves seem to be operating correctly in that the movement appears the same although I have not measured them. I have also put in a new plug. I am thinking bad cam. Are there any other tests I should be doing ?? The backfire is very loud and then whitish smoke comes out of the carb and spark plug hole after I remove the plug. The starter turns it over fine with the plug removed. I also checked the flywheel key and it is also fine.

 
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05-27-10, 01:11 PM   #2  
Check the flywheel key. If it is broken, the timing will be off causing the back fire thru the carb and no start or hard start.

 
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05-27-10, 09:42 PM   #3  
Sure sounds like a flywheel key to me too, or flooded cylinder. Double check that key.


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05-28-10, 04:54 AM   #4  
Indy and Cheese --- thank you for the responses. I was thinking flywheel key also however I double checked the key yesterday afternoon. I took the plastic fin ring off, removed the flywheel bolt (this engine has a bolt) and the key looked fine. Admittedly, I did not pull the flywheel because the key looked so good. I came to the conclusion that the cam needed to be replaced as the starter could not turn the engine past the compression stroke. Maybe I should have also adjusted the valves so that one of them would be open slightly at startup just to see if it would run ?????

 
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05-28-10, 05:40 AM   #5  
Posted By: jl66redcpe Indy and Cheese --- thank you for the responses. I was thinking flywheel key also however I double checked the key yesterday afternoon. I took the plastic fin ring off, removed the flywheel bolt (this engine has a bolt) and the key looked fine. Admittedly, I did not pull the flywheel because the key looked so good. I came to the conclusion that the cam needed to be replaced as the starter could not turn the engine past the compression stroke. Maybe I should have also adjusted the valves so that one of them would be open slightly at startup just to see if it would run ?????
try the intake valve down to .002 clearance

 
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08-17-10, 06:36 AM   #6  
This was a customer unit and the customer decided to purchase a new unit. I am in the process of trying to purchase it. If I can buy it and get it running, I will post the info.

 
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08-23-10, 05:42 AM   #7  
Well, I was able to purchase the unit. Have it here in the garage. I am going to try and remove the head this week if time allows. I have a feeling it is a sticking intake valve.

 
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08-28-10, 04:33 AM   #8  
Finally got to work on this unit. Removed the head and found a lot of carbon on both valves. I removed the carbon on the valves as well as the cylinder head and piston. Put it back together. Turning it by hand I dont hear the wheezing sound I used to and it seems to have much more compression. It had tested previously at 25 lbs. I didnt do a leak down test as I knew I was taking the head off. All I have to do is torque the cylinder head and I will try and start it this morning. On another note, the torque specs for the flywheel is 100 fr lbs. That is an awful lot of torgue. I dont remember torquing anything to 100 ft lbs. It is a cast iron flywheel.

 
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08-28-10, 07:17 AM   #9  
Torqued everything properly. Tried to start the engine. No luck -- Starter barely turns the engine over however there is no more backfire. I am beginning to think my original assessment was correct -- bad cam. Help and comments would be appreicated

 
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08-28-10, 09:05 AM   #10  
Posted By: jl66redcpe Indy and Cheese --- thank you for the responses. I was thinking flywheel key also however I double checked the key yesterday afternoon. I took the plastic fin ring off, removed the flywheel bolt (this engine has a bolt) and the key looked fine. Admittedly, I did not pull the flywheel because the key looked so good. I came to the conclusion that the cam needed to be replaced as the starter could not turn the engine past the compression stroke. Maybe I should have also adjusted the valves so that one of them would be open slightly at startup just to see if it would run ?????
You cannot "really" check the flywheel key by just removing the nut and looking down at the key, it can be very decieving, check the 2 pictures below to see what I mean, it drove me nuts. Have a good one. Geo
Look good here.

OOOOOPS:

 
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08-28-10, 09:33 AM   #11  
Geogrubb - thanks for the response. I will go pull the flywheel and report back.

 
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08-28-10, 10:50 AM   #12  
Ok -- I pulled the flywheel and checked the key. It was perfect. I put a new key in anyway and blew away all the dust etc under the flywheel around the magnets. Tried to start it -- same thing. The starter will not turn it past the compression stroke. As I had said before after I removed the head and valves it is not backfiring anymore -- it just turns over so hard like the compression release is not working.

Let me go over my procedure for adjusting the valves again -- I turn the engine clockwise and watch for the intake (bottom) valve to close. I then stick a screwdriver in the spark plug hole and check for the piston to be at its highest point then continue turning until the piston goes down 1/4 inch. That is where I adjust the valves -- Right ????

I also tried letting the intake open all the way and adjust the exhaust and then let the exhaust open all the way and adjust the intake -- right ??

I set them both at .005.

Please help

 
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08-28-10, 06:05 PM   #13  
try the intake at .003 or even .002

 
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08-29-10, 04:50 AM   #14  
38racing - I tried this based on your earlier suggestion. I even brought it down to zero clearance and had the same results.

 
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08-29-10, 08:49 PM   #15  
Is the spark plug electrode wet?


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08-30-10, 07:07 AM   #16  
cheese thanks for weighing in. I cant get the engine to turn over enough times to wet the spark plug - the compression is that much. Of course, if I take the plug out it turns over fine. I am using my 12v 650/1200 amp battery box for power. I have the leads directly connected to the battery cables - battery is out.

 
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08-30-10, 07:41 AM   #17  
Posted By: jl66redcpe cheese thanks for weighing in. I cant get the engine to turn over enough times to wet the spark plug - the compression is that much. Of course, if I take the plug out it turns over fine. I am using my 12v 650/1200 amp battery box for power. I have the leads directly connected to the battery cables - battery is out.
Put a battery in it and connect the charger to the battery. Think of the battery as a head tank and your charger as the fill hose...the charger doesn't have the electro pressure the battery will.

 
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08-30-10, 09:01 AM   #18  
BFH thanks for the response. I am going to buy a barnd new battery 360 cranking amps, install it and connect as you suggest. Just a note -- the battery box was actually one of those devices you use to jump start a car not a charger.

 
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08-30-10, 09:36 AM   #19  
Posted By: jl66redcpe BFH thanks for the response. I am going to buy a barnd new battery 360 cranking amps, install it and connect as you suggest. Just a note -- the battery box was actually one of those devices you use to jump start a car not a charger.
Understand, however, it is still just a bigger fill hose. I think even the instructions for the battery box will say to use in conjunction with a battery, not instead of.

 
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08-30-10, 06:37 PM   #20  
Ah, now I can make sense of the problem. I agree, put a battery on it. The jumper box most likely isn't sufficient.


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08-31-10, 06:00 AM   #21  
I purchased a new battery yesterday from tractor supply a Huskee 360. I left it on my charger overnight and installed it this morning. I checked the voltage on the battery after the charge and it read over 12V. The starter would not turn it past the compression stroke. I then added my "jump start" box and it still would not turn it past the compression stroke.

 
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08-31-10, 09:49 PM   #22  
Well shoot... I just knew it was going to be the jumper box. How hard is it to turn by hand? Do you think the starter is working as it should? The spark plug is not wet then I suppose? The reason I ask is because the spark plug can get wet without the engine turning at all. If it is, that may point to your problem. If the plug is dry, the valves are adjusted to zero clearance, and the battery is good, then there's not much it can be other than hydro-locking or a bad starter or poor connection. I really doubt a bad camshaft would keep it from turning past the compression stroke with the valves set to zero clearance and a 360 amp battery.


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09-01-10, 05:09 AM   #23  
Cheese - with the spark plug out, the starter turns it over fine. It is difficult to turn by hand with the spark plug in. It sure seems to me that the compression release is not working and doesnt that point to bad camshaft ??? The connections are all good, I cleaned and checked them.

 
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09-01-10, 09:54 AM   #24  
Sometimes a weak starter can turn an engine with no resistance (plug out) but not with the plug in. If you adjusted the valves to zero and put a 360 amp battery on it, it doesn't matter if the compression release is working or not.


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09-03-10, 02:53 PM   #25  
I have ordered a brand new Briggs starter -- not aftermarket. It shipped yesterday and should be here by middle of next week. I will install and report back.

 
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09-03-10, 10:15 PM   #26  
Hmm, I was thinking about this earlier today. I was going to ask you to estimate how many rpm the starter is turning the engine with the plug out. It should turn it several hundred rpm with a good battery and connections with the plug out. If it does not, then I would say put a starter on it. If it does turn it that fast, I'd think about it some more.


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09-04-10, 09:49 AM   #27  
Well Cheese - you were correct !! The mailperson delivered the new starter around lunchtime. I installed it and gave it a try and the new starter turned the engine over fine and the engine started. I got to tell you, I was a little bit skeptical re the starter but it no doubt was the starter. I was not looking forward to replacing the camshaft. Thank you very much.

 
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09-04-10, 11:16 PM   #28  
Great!! I was starting to wonder about this thing. I just couldn't believe it was the cam though. Glad you got it fixed!


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