Upsur Vertical Starts, but dies within 20 seconds

[marcmeng59]

I am very new to engine building. I just finished an Upsur vertical pump engine ( my first IC engine), I have been trying to get it to run to no avail. It will start and run for about 20 seconds and die. I tried it on both gas and Coleman fuel no change. I tried using vapor carb and a fuel mixer no change. I have the ignition timed very slightly past TDC. I have good compression. Any ideas?

 

[Brian Rupnow]

That's a tough one. I suggest playing about with the height of the gas tank. If your gas tank is built into the frame of the machine, try using a second gas tank on which you can adjust the height. Ideally, the top of the tank should be about 1/2" below the center of the carburetor. Also be sure that the tank is vented to atmosphere so it doesn't suffer from "vacuum lock". I generally drill a 1 mm hole thru the gas cap. --You may need a lighter spring on the intake valve, if it is an atmospheric valve with no cam and lifter.---Brian

 

[marcmeng59]

Thanks for suggetions

 

[coulsea]

since you have tried both a vapor carb and a fuel mixer it would seem to rule out fuel problems so it may be worth looking at the ignition system failing when it heats up or possibly a valve sticking when hot.

 

[Peter Twissell]

I have had a similar issue with an old motorcycle engine, due to a valve sticking during the warm up phase.
Easily diagnosed by turning the engine to check compression immediately after it stops.
Rectified by increasing the valve stem to guide clearance.
Is the spark plug fouling? does the engine start again after cooling down, or do you need to do anything else before it will run again?

 

[Brian Rupnow]

If it only runs for 20 seconds and then dies, it isn't a heat related issue.

 

[deverett]

I am very new to engine building.
I have the ignition timed very slightly past TDC. I have good compression. Any ideas?

Generally speaking, engines run better with the ignition timing Before TDC.
Have you tried advancing the timing?

Dave
The Emerald Isle

 

[awake]

I'm very much a newbie, so I may be WAY off ... but I thought I had understood that ignition is usually set a few degrees before TDC, not after - ???

On edit - Dave got his response in while I was typing!

 

[Brian Rupnow]

If it is a hit and miss engine, it should be timed to fire exactly at top dead center or very slightly after top dead center. If it is not a hit and miss, but is a conventional four cycle engine with throttled carburetor, it should be timed about 10 degrees before top dead center.

 

[Peter Twissell]

In a small engine, 20 seconds is plenty. The exhaust valve will heat up very quickly, But the surrounding material will heat up much more slowly, creating the differential expansion which can cause the valve to stick.

 

[awake]

If it is a hit and miss engine, it should be timed to fire exactly at top dead center or very slightly after top dead center. If it is not a hit and miss, but is a conventional four cycle engine with throttled carburetor, it should be timed about 10 degrees before top dead center.

That's interesting - why does a hit-n-miss need to fire at TDC or after?

I confess that I have a sketchy understanding of ignition timing based on what I have read here and elsewhere, with no hands-on experience (yet), and definitely no understanding of the finer points. No pun intended ... really! You can believe me on that - I was just trying to condense my knowledge into a single sentence. Oh wait - no pun intended on that one, either. Honest. I don't know what sparked this line of thought ...

 

[Brian Rupnow]

On a conventional four cycle engine, the rpm range is much higher than on a hit and miss engine (which are categorised as "slow" running engines.) With a fast revving engine, physics of inertia come into play. So--the intake valve has to start opening before top dead center is reached, and the exhaust valve has to begin opening before the piston reaches bottom dead center on the power stroke. Likewise, the intake valve will stay open for about 20 to 30 degrees into the compression stroke, after the piston has passed bottom dead center, and the exhaust valve will stay open part way into the intake stroke after the piston has reached top dead center. The spark which ignites the charge of fuel vapour has to actually start the fuel burning before the piston reaches top dead center, so the timing on these engine is always advanced. On a slow running engine like a hit and miss, inertia is much less of a consideration. The valve timing and ignition timing events are much closer to the theoretical top and bottom dead center of the piston---thus, you set the ignition exactly at top dead center or very slightly after it.

 

[awake]

I was wondering if it had to do with the relative RPM's. So much to learn ... but that's the fun of it; that's what ignites my interest. Oh, wait, no pun intended on that one, either. Really.

 

[marcmeng59]

I have had a similar issue with an old motorcycle engine, due to a valve sticking during the warm up phase.
Easily diagnosed by turning the engine to check compression immediately after it stops.
Rectified by increasing the valve stem to guide clearance.
Is the spark plug fouling? does the engine start again after cooling down, or do you need to do anything else before it will run again?

 

[marcmeng59]

Thanks for all of the suggestions. I will do some more troubleshooting and get back with results.

 

[johwen]

I am very new to engine building. I just finished an Upsur vertical pump engine ( my first IC engine), I have been trying to get it to run to no avail. It will start and run for about 20 seconds and die. I tried it on both gas and Coleman fuel no change. I tried using vapor carb and a fuel mixer no change. I have the ignition timed very slightly past TDC. I have good compression. Any ideas?

My experiences tells me that your engine fuel is far too lean. I would suspect that when you start the engine you choke it which draws in a rich mixture and it take a few revs to burn this up as the mixture leans out and then dies from being lean. Fuel height in relation to the carburetor may be too great and a ball valve in the pick up pipe can help here if you do not have one installed. The other cause could be that the venture diameter is too large and after choking the air speed is too slow to draw in fuel so try a smaller venture and see what happens. I doubt very much whether ignition timing is causing your trouble.

Don't give up John Samphier from Ozz.

 

[marcmeng59]

Follow-up question: From all I have been checking on the engine I think it is a carb issue. What would be a good venture size vs. the inlet size?

 

[Art K]

I have the Upshur vertical single SIC issues 63-66 the carb is .187 and matches the intake & exhaust size. If your carb is to big it won't run well if you open the throttle to much, but should run just not to high an rpm. Mine was .198 acted like sort of a governor. I do know the fuel tank from the print should be 1/4-1/2 inch below the jet level on the carb. When I first got mine running It wouldn't run more than about 1000 rpm's the cam timing was advanced three teeth to far. You can check that with a degree wheel & an indicator and match it with the cam diagram in the prints. You can probably find a degree wheel on line and print it in a scale to match your flywheel and set 0 at tdc. It's not clear what vertical single you have here, but from all the suggestions you have enough stuff to check on and see if one or more of these will help you. Best of luck.
Art

 

[Longboy]

20 seconds and dies........your engine may be seeing something it doesn't like unrelated to fuel or timing. You may have a friction issue in the reciprocating or rotating assemblies. See if you can feel for it with the spark plug removed and rotating it thru.