MTD Tractor Starting problem

[lefty]

Well, this one has me stumped. New coil, tested spark with one of those that you can adjust the gap(not the inline ones with the light). Good spark. Even though I can see plenty of fuel in the venturi during starting, I went through the carb again. Tested the after fire solenoid and it's operating properly. Tried without the kill wire, same results. Did another leak down and it's perfect, no leaks and holding strong. Crank no start. A few squirts of carb cleaner into the carb and after some cranking, it starts up and runs perfectly. Just to recap, the fuel lines, filter and shut off are new. I also tried to run it off of my auxiliary fuel tank with the same results. I'm out of ideas. Am I missing something?

[bgsengine]

choke closing completely? testing with air cleaner base on or off? while it is running, spray carb cleaner around intake gaskets and manifold, etc look for air leaks...?

[lefty]

Choke operates. Testing air cleaner off and on. Intake leak sounds like a good bet now that you mention it. I'll check it out. Thank you. What am I looking for when spraying carb cleaner around the manifold? My guess is a change in RPM?

[bgsengine]

Yup

[Arkie]

Some of them have a plastic intake with O-rings as a seal.
I've heard of them plastic manifolds with hairline cracking but never seen such myself. I've seen manifold O rings that were flatten out but generally the engine won't idle really smooth a very low idle. Have you tried turning down the idle screw and listen to the engine at a really low idle?
Does it idle really good and smooth at very slow speed after it starts?
Are you sure that the after fire solenoid is fully retracting easily and not hanging slightly at first?
I've seen them after fire pintles not retract fully when 12v testing off the engine and I could push in on the pintle gently and the pintle would go in further and I could usually free them up for full retraction by testing with 12v on the workbench.

Keep a heads up when spraying the carb cleaner, most are flammable.
Oil in a squirt can is less hazardous but messy. WD40 is also flammable.

How does the engine act when it does start, does it have oil smoke or act like it might have been flooded or want to start at full throttle with no choke or????

Stay Safe when your are around that dog testing for air leak and people. It can get you from both sides.

[lefty]

I tried spraying the carb cleaner around where the manifold attaches to the head and at the end with the carb. No change in the engine. Funny you say that because I was super paranoid about doing it given the flammability. But everything worked out well. I was not able to spray under the manifold but will remove it and inspect it for cracks tomorrow morning. I'll also turn the idle down and test.

As far as how it runs, yes, it will run extremely smooth at idle. I have it turned down pretty low already.

I tested the solenoid in the circuit by removing it and grounding it to the engine. The retraction was complete and appears adequate. I have a new oring for the manifold that came with some parts I got with another machine with the same setup. Maybe I'll give it a try tomorrow.

An air leak seems like a likely cause I think. I had to spray a good amount of carb cleaner down the manifold through the carb to get it going, and I had to spray it deep. I can't help but think it's not drawing strongly through the venturi. I can see the fuel rising up into the venturi during cranking but it just seems to dance around in there and spit back out toward me. But who knows. There's not much left to try right? I have a new gas cap so the vent is good. But I already knew that because I got the same results with my auxiliary tank.

I'll point out as well that this has gone from a periodic problem to a chronic one. I don't know if that bit of info helps. It was sporadic under all conditions, cold, hot, whenever. No it's every time. I've had to charge the battery a few times trying to diagnose it.

And no smoke. When it runs, it runs awesome.

Thanks

[38racing]

My tractor dealership friend would suggest that you try removing the fuel cap and blowing into the tank. He had a newer mower trade in that required that before it would start. I witnessed it. Unfortunately he sent it to his shop for repair but never followed up on it.

[Arkie]

Give this a shot. You say you have to inject carb cleaner deep into the manifold.
Check the clearance on the intake valve again and take it too max tolerance or even just little more. I think the compression release on that engine is on the intake valve.
Reason I say this is right after your intake valve issue and you got it back together it operated Ok for awhile.

Reason I say this is:
This is too see if you might get a hint that the intake compression release is blowing the fuel back into the manifold too soon on the intake stroke, The tighter the valve lash tolerance the sooner the manifold fuel get blowed back.
Then if this changes anything think about worn cam wear or ?????
Before changing the intake valve lash see if it's the same lash as you adjusted it too few days before. If you loosen the lash too far the engine might not have any compression release and the starter not power through on the crank stroke, so try to find the max lash position that it still cranks ok when the engine is hot if it starts ok cold.

[lefty]

My tractor dealership friend would suggest that you try removing the fuel cap and blowing into the tank. He had a newer mower trade in that required that before it would start. I witnessed it. Unfortunately he sent it to his shop for repair but never followed up on it.

That's actually quite funny because I've tried that. I figured I'd make myself a human primer bulb. Worked once but when it didn't work again, I figured it was just a coincidence.

Arkie,
That seems like a logical next step. So you mean, for instance, if the intake is supposed to be 5-7 thousandths I should set it to 7 or 8? So that would put the compression release a little later in the compression stroke? Am I understanding that correctly?

[Arkie]

So that would put the compression release a little later in the compression stroke? Am I understanding that correctly?

YES:

First make sure the intake valve lash is at the same setting as when you set it when you got through lapping the valves and it started good for few times/days. think you mention on pg 2 it was testing starting good then. (sometihine has changed since then???????????

Increase the INTAKE valve lash as much as you can without the starter stalling on the comp stroke and then test.

When you get it set at max cold if the engine will start then you may have to re-test the crank stall when the engine is hot.
You are indicating that when you inject a primer deep into the manifold you get a start and you see ventura gas blowback, like the fuel in not being sucked into the engine when cranking.

If the problem gets little better starting, we can then suspect from the findings.?????????????