Only Backfires Through The Carb Regardless Of What I Do (1450)

giddyup306 · #1 09-25-2010, 05:34 PM

I got my engine back from the machine shop. Turns out my binding issue was two-fold. The crank needed to be polished .0005", and the aftermarket rod was doing some goofy binding.

Now that I have every single thing back together I can't get it to run. The official Kohler manual says the points should be set to .020". I read in the archive that .015" - .020" might work. Someone even said as much as .030". I found in the library where it said to go off of the S on the flywheel. I tried every technique and I still can get it to do more than backfire through the carb! Every once in a while it will run for a few seconds, but it's fighting the piston, and runs rough! Everyone's probably thinking that the timing is a tooth off. I checked that before I put everything back together. The "." on the cam lines up with the "-" on the crank.

I'm really at ends wit here. I tried setting the points from .012" - .030 in .oo2" increments, and it still wouldn't start! Everyone was right. I would have been a lot of time and money ahead if I would have bought something new with a warranty...

I'm really stumped on this one, and I'd appreciate some input...

If I can't figure it out can someone suggest where to get something like a K341? I'd also like to know if there is a conversion kit available for this for pointless ignition. I know for sure it will at least need a new flywheel...

Thanks!

Mike

EDIT:

I forgot to mention the carb is a brand new Walbro unit....

Matt G. · #2 09-25-2010, 05:45 PM

Try this to get the timing correct. Backfiring out of the carb means either the timing is too far advanced, or something is up with the valves or valve lash. If you've verified the crank/cam timing is correct, and you've verified the timing is correct with the above link I provided, then either the valve lash on the intake valve is too tight, or you didn't lube it enough and it's sticking open.

That brand new Walbro carb is non-adjustable and a POS, although that probably doesn't have much to do with this.

Yosemite Sam · #3 09-25-2010, 07:03 PM

Quote:

Originally Posted by giddyup306

Everyone was right. I would have been a lot of time and money ahead if I would have bought something new with a warranty...

First off, (you're about to get a scolding) I'm not sure who "everyone" is but the people who have told you to buy "new" don't know know "something" from apple butter. New will get you -$2000.00 and some junk to throw away in four or five years. Rebuilding a quality product (imho) is much better than buying tomorrows trash today. (scolding over)

The last time you had this engine apart did you check to see if the ACR was working? The exhaust valve should open a little each time the engine is turned over slowly. Once the engine starts then the exhaust valve opens and closes just as any other valve would.

The next question is: Did you replace either the Flywheel or Crank shaft in this engine and did you put in a new push rod in for the points and is there a groove worn in the cam shaft where that push rod "rides"?

Just to rule out possible causes, if it were mine I would probably pull the head and watch the parts as they move when you turn the engine over (by hand) paying close attention to the valves to make sure they open and close as they should.

Good luck and let us know what you find out. If you do take it the head off, pictures wouldn't hurt either.

One other thing you could try first is to take the plug wire off and see it it turns over as it should or if it still stops/pauses. If it does the same thing, then the problem isn't electrical.

giddyup306 · #4 09-25-2010, 07:06 PM

Quote:

Originally Posted by Matt G.

Try this to get the timing correct. Backfiring out of the carb means either the timing is too far advanced, or something is up with the valves or valve lash. If you've verified the crank/cam timing is correct, and you've verified the timing is correct with the above link I provided, then either the valve lash on the intake valve is too tight, or you didn't lube it enough and it's sticking open.

That brand new Walbro carb is non-adjustable and a POS, although that probably doesn't have much to do with this.

Unfortunately I saw that link yesterday, and I still had no luck.

The valves I didn't touch. The machine shop did that. I was fearing that it would be the valves mis-adjusted...

Getting too late to mess with it today. I guess I'll check the valves tomorrow... :/

giddyup306 · #5 09-25-2010, 07:14 PM

Quote:

Originally Posted by Yosemite Sam

First off, (your about to get a scolding) I'm not sure who "everyone" is but the people who have told you to buy "new" don't know know "something" from apple butter. New will get you -$2000.00 and some junk to throw away in four or five years. Rebuilding a quality product (imho) is much better than buying tomorrows trash today. (scolding over)

I didn't start this thread to argue with anyone... but I know for a fact that a new Kohler 7/8 hp engine with a new carb is $185, and comes with a 1 year warranty... I have more money than that in machine work alone.

Quote:

Originally Posted by Yosemite Sam

The last time you had this engine apart did you check to see if the ACR was working? The exhaust valve should open a little each time the engine is turned over slowly. Once the engine starts then the exhaust valve opens and closes just as any other valve would.

Yes, the ACR is working. The tang was broken, but I replaced that part.

Quote:

Originally Posted by Yosemite Sam

The next question is: Did you replace either the Flywheel or Crank shaft in this engine and did you put a new push rod in for the points and is there a groove worn in the cam shaft where that push rod "rides"?

I replaced neither the flywheel or crank. The pushrod for the points is a new steel unit.

Quote:

Originally Posted by Yosemite Sam

Just to rule out possible causes, if it were mine I would probably pull the head and watch the parts as they move when you turn the engine over (by hand) paying close attention to the valves to make sure they open and close as they should.

Did that yesterday. I didn't get out a dial indicator, but it seems to be functioning properly...

eastonct124 · #6 09-25-2010, 09:15 PM

You are getting a true "backfire". As matt already stated, there are only two causes....the intake valve is sticking, or timing...and if the intake valve seats nice, then your timing is 180 deg off.
If the timing is all correct, and the valve seats good.....then the cam is a tooth or alot of teeth off.
And you may not be able to actually see it seating with your eye.....do a compression test first...then try lapping compound on the valves (intake is the problem, but do both) and look at how it's really seating.

giddyup306 · #7 09-25-2010, 09:55 PM

Quote:

Originally Posted by eastonct124

and if the intake valve seats nice, then your timing is 180 deg off.

The machine shop put in new valves, and should have cut new seats. I didn't pull it apart and double check tho. I don't understand how it could be 180* tho. Is there more than one timing mark on there? Plus the last time it was at the machine shop the machinist timed it. I know he's built a few of these engines, so I'm sure he did it right (plus I double checked it before I put the pan on).

Quote:

Originally Posted by eastonct124

And you may not be able to actually see it seating with your eye.....do a compression test first...then try lapping compound on the valves (intake is the problem, but do both) and look at how it's really seating.

According to the Kohler manual, you can't do a compression test due to the ACR.

Matt G. · #8 09-25-2010, 10:23 PM

Eastonct124 didn't phrase parts of that very well...I think he means the intake valve may be sticking, which would definitely be a possibility if the guy assembling it didn't properly lubricate the valve stem and guide before assembly. I'm still thinking there's practically no valve lash on the intake valve. Thankfully, it's easy to check and correct if necessary.

There are two timing marks on the flywheel: "S" and "T". "T" is top dead center, and "S" is 20 degrees before top dead center, and that's the one that should be centered in the timing sight hole as the points begin to break.

giddyup306 · #9 09-25-2010, 10:56 PM

Quote:

Originally Posted by Matt G.

There are two timing marks on the flywheel: "S" and "T". "T" is top dead center, and "S" is 20 degrees before top dead center, and that's the one that should be centered in the timing sight hole as the points begin to break.

Oh, I meant the timing marks on the crank and cam gear itself.

eastonct124 · #10 09-26-2010, 09:47 AM

Thanks matt, I'm alittle illiterate when typing.

To rephrase things:
It pops back through the carb because the intake valve isn't seating completely, and when the fuel mix ignites....it naturally blows out through carb.
But, if the valve does seat well, then the (intake) valve must be open at the wrong time...therefore, the cam is off.....or the timing is too far advanced.
And, you're right, with the crv, a comp test can't be done....sometimes I think out loud and forget.
what 'm saying is, it can only be one of those two things....it's not rocket science.....just take your time, and double check the valves, and the timing (including the cam to crank timing).