Urgent Briggs Help

#1
Hey all,

I'm usually the one giving advise, but right now I really need somebody's opinion as I am wasting more and more money and this project is in the way.

I have a 1974 Briggs 5HP some people may remember from my build thread awhile back. This motor ran great for one weekend, until it just stopped. It began running very rough, not idling, not revving, just firing at high throttle and stopping. It was running the pulsa jet back then.

I have since swapped the carb to a 22mm mikuni copy, and have tried a tecumseh dellorto - non adjustable.

I have bought a genuine Briggs coil for 60 bucks, and swapped the flywheel from my 1990 5HP. I have pulled the head, checked the timing but have not been in the crankcase for a bit.

I have no idea what the problem is. It fires now but wont run. With the tecumseh carb, every pull-over results in a series of backfires. This leads me to believe the problem is at the valves. do I have a bent valve? how do I know? Compression is still great. :hammer:

I have swapped over half of this motor and still have no joy. Any help would be appreciated here. Do I pull the head or sump? last time I pulled the head everything looked good, maybe I should have checked more thoroughly on the valve side of things? Everything in the spring box area looks good, and both valves go up and down. :thumbsup:

Motor does not knock, only mod is a Billet rod.

I think the valve or valves are bent. What are your thoughts? :confused:

-Jack
 
#8
Thanks guys, key is not sheared, checked last night. Also worth mentioning that it's running a magnetron.

I have sheared the key about 4 times on this motor, too much free revving. But it is not sheared this time. Also, the cam teeth are in line because it stopped the same day I rode it.

By the way, I had been riding the bike for about 30 minutes. We got home and washed off all the mud. I washed the engine and the revvs slowed when I rinsed the block. I cannot accurately remember, but after that wash it never ran right again. What would I have done?
 
#11
That could be it, but,

when the motor turns over every second rotation or so, air blows out the carb and sucks through the exhuast :confused:

Crack the case, that sounds like cam is not indexed properly--especially if you sheared 4 keys. I had a hell of a time with my Tecumseh OH195. Are you running an air filter on the carb? Not running one will cause problems especially if the carb is not adjustable. Check, too, to see if you bent a valve. Send me a private message, if needed, I've been solving problems with a 3.5 hp Briggs.
 
#14
I took the crankcase off today. Bit surprised when I found no damage. The oil was like that in the video, a dark grey, with a metallic flake, but it looks like my motor had water in it, but I believe it would still run with a small amount of water in the oil. The cam was perfectly in time and in good condition.

One thing I noticed was that a small piece may be chipped out of the crankcase support (the strengthening casting on the inside).

I think that the metal filings in the oil are due to my new piston rings.

Also, is air meant to come out the inlet? Bit of a weird question but it does and I don't know how to fix it.
 
#16
I took the crankcase off today. Bit surprised when I found no damage. The oil was like that in the video, a dark grey, with a metallic flake, but it looks like my motor had water in it, but I believe it would still run with a small amount of water in the oil. The cam was perfectly in time and in good condition.

One thing I noticed was that a small piece may be chipped out of the crankcase support (the strengthening casting on the inside).

I think that the metal filings in the oil are due to my new piston rings.

Also, is air meant to come out the inlet? Bit of a weird question but it does and I don't know how to fix it.
Jack--by inlet, you mean the crankcase breather tube or something else? You will get "air" pushing out of the breather--releases pressure in crankcase. You'll also get "air" coming out of the carb intake when it's being cranked (pre-ignition)--usually it's pretty rich because the piston is not creating enough of a vacuum to pull all of the air/fuel into the cylinder--that's normal.

I don't think the rings are going to take much off the cylinder wall to make shavings. Sounds more like an endplay issue or the valves are floating. That chip may be an indication the crank is too loose. There is a thrust washer to fix that problem.

If it still won't fire, check your ignition...I am so ready to build Tecumsehs exclusively. Briggs are killing me.
 
#17
The crank gear is all rough on the side, and so it the flange part on the crankcase! I dont recall it having, well, any endplay, which is bad. I'm going to fit a white paper gasket and see how it goes.

By inlet, I meant to say carb :thumbsup:

I struggled a bit with my H35, I just got used to the Briggs over time and have only had one Tecumseh.
 
#18
The crank gear is all rough on the side, and so it the flange part on the crankcase! I dont recall it having, well, any endplay, which is bad. I'm going to fit a white paper gasket and see how it goes.

By inlet, I meant to say carb :thumbsup:

I struggled a bit with my H35, I just got used to the Briggs over time and have only had one Tecumseh.
The engine would have been "screeching" if the crank was too tight, that's why I was wondering about too much endplay. You may want to fit the original carb and tank just to see if it starts after you add the gasket.

I used to be a Briggs-only person, but I've grown to like the Tecumsehs since I tend to restore bikes.
 
#19
I have spent many hours trying to get this thing to run. The answer? was right in front of my face. The sparkplug.

I put the original champion back in and it now runs on choke. I believe the float bowl on the PZ22 copy needs adjustment. The motor dies if the choke is taken off. I cannot believe I didn't check this earlier :laugh:
 
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