Engine runs worse as throttle is increased. UPDATE!

[i386]

Chrysler 20HP 202HD

The engine is starting easily now. It idles pretty well in and out of gear. As I throttle up it runs worse and worse. Throttle back down, it smooths out again. I cannot tell by the sound of it what it "needs". Contrary to what my Seloc manual says about my Tillotson MD carb, the high speed jet is fixed and there's no high speed needle to adjust.

The carb is clean as a whistle (just rebuilt it).
Needle, seat, and float are working properly.
Fuel pump is working properly. Good firm bulb. (just rebuilt it)
Link and sync are set correctly.
Spark tester shows good spark on both cylinders.
Installed new plugs (L82C), made no difference.
Points are clean and gap is correct.
New fresh fuel.
No water in fuel.
Tank vent is open.
No leaks/air in fuel lines.
No rattles/vibrations.
High speed jet is correct for my altitude.



I'm about ready to turn this engine into fish habitat. Any idea what's wrong with it?

 

[i386]

Re: Engine runs worse as throttle is increased.

Re: Engine runs worse as throttle is increased.

There seems to be no rhyme or reason to this engine. I just took it down to the boat ramp for some WOT tests. Now like I said, it was starting easily. It started easily in the yard minutes earlier. But I get it down to the ramp, sob won't crank. I pulled it until I was wore out, and nothing. Thinking it may have flooded because it was tilted up, I pulled the top plug. To my surprise it was bone dry. I sprayed some premix in the carb and it fired up. I put it in gear and throttled up slowly and it runs like crap. Continue to throttle up and it will eventually die.

So apparantly I still have some weird intermittent fuel problem in conjunction with this new problem of running poorly at higher rpms.

 

[i386]

Re: Engine runs worse as throttle is increased.

Re: Engine runs worse as throttle is increased.

Guess everyone is as clueless as me on this one.


Since the last significant thing I did was rebuild the carb, I went back to that. I disassembled it again. I can probably do this blindfolded now. I wanted to inspect the high-speed nozzle and jet. Again, the carb was clean as a whistle. I check the float, needle, and seat while I had it apart. Still good. I removed the jet. It was clean and clear. I removed the high-speed nozzle. I noticed there are 2 small holes in it on the side. They are perpindicular to the screwdriver slot. My manual makes no mention of this fact. I reinstalled the nozzle and set the holes where they might line up with another small tube that's not mentioned in my manual. Reassembled. It started easily. I reved it up in neutral. Still good. I can't run it any faster w/o putting it in gear so I tilt up the engine, hook up the truck, and head to the ramp.

Just like last night, it tries to run, blows a little smoke and dies. After that it won't crank. Spray a little fuel in the carb and after a few tries it runs. I see a pattern. It has trouble starting after it's been tilted up.

Ok so it's running so I put it in gear and start to throttle up slowly. It runs a little better than yesterday, but still not good. I'm able to give it a little more throttle before it starts to break up.

Trying to figure out what it "needs" when it's breaking up, I spray in a little premix. It does not help.

If only I had some way to monitor the ignition while it's running to see what it's doing as the revs increase.

Anyone got any ideas?

 

[Jack Daniels]

Re: Engine runs worse as throttle is increased.

Re: Engine runs worse as throttle is increased.

Did you rebuild the fuel pump diaphram? I would take care of that also, it might help. Did you check your compression?

 

[eurolarva]

Re: Engine runs worse as throttle is increased.

Re: Engine runs worse as throttle is increased.

My manual (clymer) shows three different carbs for chrysler and none match the needle you posted on your other thread. In spite of the cleaning I think your carb is the problem. High speed running like crap tells me the needle is not releasing from the seat and the fuel bowl is not filling correctly. When you had the carb apart did you remove the welsh plug and clean the three tiny holes where the mixture screw goes into the carb? That is the area where your idle is coming from. When you tilt the motor up gravity takes over and your carb will drain however when you prime with the motor down it should fill the carb till the float hits the correct height and will shut off the fuel supply. When you are testing this in your driveway do you use muffs or a test tank? Also as mentioned by Jack Daniels the fuel pump should be rebuilt if you have not already done so. That might include replacing all three fuel check valves and gaskets.

 

[i386]

Re: Engine runs worse as throttle is increased.

Re: Engine runs worse as throttle is increased.

My manual (clymer) shows three different carbs for chrysler and none match the needle you posted on your other thread. In spite of the cleaning I think your carb is the problem. High speed running like crap tells me the needle is not releasing from the seat and the fuel bowl is not filling correctly. When you had the carb apart did you remove the welsh plug and clean the three tiny holes where the mixture screw goes into the carb? That is the area where your idle is coming from. When you tilt the motor up gravity takes over and your carb will drain however when you prime with the motor down it should fill the carb till the float hits the correct height and will shut off the fuel supply. When you are testing this in your driveway do you use muffs or a test tank? Also as mentioned by Jack Daniels the fuel pump should be rebuilt if you have not already done so. That might include replacing all three fuel check valves and gaskets.

Hmm. It's a Tillotson MD carb. It looks identical to the carb in my old factory Chrysler parts manual.

I believe the needle and seat are working correctly, but I was willing to test that theory. While I had it revved up (and it was running like crap) I sprayed a little premix into the carb. My thinking was if it was starved for fuel, spraying in a little more would smooth it out for a second or two. It didn't. Is this an acceptable test?

I never did remove the welch plug though I do have a new one in my kit. After you told me how to remove it, I still didn't. I'm concerned my hand drill is going to punch through and damage the carb. I don't have a drill press. I think that would be safer. But like we discussed before, the engine responds to my idle adjustments just fine.

When I squeeze the bulb I can hear fuel squirting into the bowl. The bulb gets firm and stays firm once the bowl is full. I can also remove the bowl and hold it level in my hand while I fill it. It fills right to the rim and stops when the float comes up, just like it's supposed to. I can continue to pump the bulb, but no more fuel comes in, just like it's supposed to. I can't see inside the bowl with it bolted up to the carb, but it "feels" right to me.

I use a big plastic trashcan for testing at home.

I rebuilt the fuel pump at the same time I did the carb. This one has the small round fuel pump. It contains 2 gaskets that sandwich the diaphragm, a diaphragm and another gasket. There are no check valves, but there are 2 small reed valves. I noticed that one of the reed valves does not tightly close over the hole like the other one does. It's close, but not tight like the other one. I did not dare try and bend it to correct the problem.

 

[eurolarva]

Re: Engine runs worse as throttle is increased.

Re: Engine runs worse as throttle is increased.

I have nothing that is helpful. You have tried and checked everything in the fuel system. I wish you luck. By the way thanks for the help in the tech forum. I deleted all them programs and have not had a problem. Good luck with your motor.

 

[i386]

Re: Engine runs worse as throttle is increased.

Re: Engine runs worse as throttle is increased.

I have nothing that is helpful. You have tried and checked everything in the fuel system. I wish you luck. By the way thanks for the help in the tech forum. I deleted all them programs and have not had a problem. Good luck with your motor.

You're welcome.

Yea this engine is a real booger. I'm enchanging a few emails with Franz about it. Maybe he'll come up with something.

Tonight I decided to give the starter rope a break since I have sprained both my wrist and elbow. Instead I took a closer look at the ignition system.

The points are a few years old, but they look fine to me.

The coils were replaced by the previous owner maybe 5 years ago. They still look pretty new. No cracks in the housing or anything like that. I thought it wouldn't hurt to test them though.

I can't get either coil to pass the secondary winding test. I have my meter set in the 1000ohm range. I've got one lead connected to the spark plug wire. The other lead I connect to either of the two small red wires on the same coil. I get nothing. In fact, I get nothing on either coil.

I'm having a hard time believing the readings, for several reasons:

2 coils failing at once isn't very likely.
It used to run before I started working on the fuel system.:redface:
I wouldn't think the engine would run at all if this reading was true.

 

[i386]

Re: Engine runs worse as throttle is increased. UPDATE!

Problem almost solved. Franz told me I could use a timing light to check for intermittent spark. That's what it was. With the light on the lower cylinder the pulse remains steady, even when the engine struggles. With the light on the top cylinder, you can definitely SEE the engine struggle.

I will never trust a spark tester again. The timing light will show you what's going on in real time. Maybe one of those inline spark testers will too, but I haven't tried that.

So thanks for all the help. I'm going to fix this intermittent spark condition and go from there.