More compression, runs way fast?

[WheelHorse520H 708]

Okay, so while I am waiting to cough up the money to finish the transmission on my 607 I decided to up the power on the 6.5 hp Greyhound engine and I shaved the cylinder head about 0.030” to get a good amount of power for pulling trailers and pushing the heavy wet snow we get here on the south shore. Now I have to run the engine at idle with the choke almost fully on, otherwise it revs way way up. It seems to be acting like a vacuum leak but I have sprayed flammable carb cleaner near all the gaskets and seams to find a leak but I can’t seem to find anything. Did I do something wrong? I will post the engine model number and serial number later.

Thanks,

Andrew

[lynnmor 7,313]

Somehow you goofed up the governor.

[littleredrider 409]

Check for leaks, but could be now that makes more power need to rejet the carb…

[Handy Don 12,243]

5 hours ago, lynnmor said:

Somehow you goofed up the governor.

[WheelHorse520H 708]

5 hours ago, lynnmor said:

Somehow you goofed up the governor.

One of the springs was off and I found online where it goes but the problem persists. I will do more investigating on that.

 

5 hours ago, littleredrider said:

Check for leaks, but could be now that makes more power need to rejet the carb…

When I get the smooth idle with the choke on I get a heavy blue smoke and the spark plug fouls easily.

Edited October 8, 2021 by WheelHorse520H

[Handy Don 12,243]

Just now, WheelHorse520H said:

When I get the smooth idle with the choke on I get a heavy blue smoke and the spark plug fouls easily.

Blue smoke is oil burning.

With full choke, the intake pressure above the piston is lower than with the choke off. That likely is pulling oil into the combustion chamber, probably around the rings.

 

This is separate from it wanting to run fast--that is still likely that the governor isn't set properly (springs, linkages, adjustments all matter)

[WheelHorse520H 708]

1 minute ago, Handy Don said:

Blue smoke is oil burning.

I thought so but someone on another thread said it was gas and black was oil.

 

2 minutes ago, Handy Don said:

 

This is separate from it wanting to run fast--that is still likely that the governor isn't set properly (springs, linkages, adjustments all matter)

Ok, will check that out.

Thanks for the help everyone.

[Handy Don 12,243]

1 minute ago, WheelHorse520H said:

I thought so but someone on another thread said it was gas and black was oil.

 

Ok, will check that out.

Thanks for the help everyone.

Black is fuel. Oil is blue/white.

 

Take some pictures of the governor/throttle linkage setup.

First with the engine off and throttle lever set to IDLE.

Second the same but throttle lever set to FULL.

Then, with throttle lever set to IDLE and using the governor arm connected to the throttle butterfly plate on the carb, manually and gently move the arm and take a picture when it is at each end of its range of movement.

 

[WheelHorse520H 708]

Thanks @Handy Don, the governor arm is about 1/4” away from where it should be. How can I adjust this?

[WheelHorse520H 708]

SOLVED: the spring was too tight so I stretched it out a little and it ran fine. Still burning a little oil though.

[Handy Don 12,243]

46 minutes ago, WheelHorse520H said:

SOLVED: the spring was too tight so I stretched it out a little and it ran fine. Still burning a little oil though.

Yep. Good general rule on governors: tighten spring to increase the throttle.

 

Glad that's ok. The smoking, well, that's different kettle of fish. Hoping someone good with these will chip in!

[953 nut 55,325]

4 hours ago, WheelHorse520H said:

Still burning a little oil though.

 

11 hours ago, WheelHorse520H said:

I shaved the cylinder head about 0.030”

Higher compression also results in higher pressure and vacuum felt in the crank case.  May want to consider a larger vent to the intake  or atmosphere to reduce the crank case pressure.

[Handy Don 12,243]

3 minutes ago, 953 nut said:

Higher compression also results in higher pressure and vacuum felt in the crank case

Not sure how this can be affected if the stroke and bore have not changed.

[WheelHorse520H 708]

12 minutes ago, 953 nut said:

 

Higher compression also results in higher pressure and vacuum felt in the crank case.  May want to consider a larger vent to the intake  or atmosphere to reduce the crank case pressure.

Assuming the pressure does change against what Don believes, how would I do that? 

Edited October 9, 2021 by WheelHorse520H

[WheelHorse520H 708]

7 minutes ago, Handy Don said:

Not sure how this can be affected if the stroke and bore have not changed.

I am with you on this too. How would it change?

[Handy Don 12,243]

 

8 minutes ago, WheelHorse520H said:

I am with you on this too. How would it change?

I'm not really able to calculate the change in compression ratio that you've caused by "lowering the ceiling" of the combustion chamber and making it smaller.

 

You've introduced three changes, as I see it:

1. On intake, the cylinder will draw in the same amount of fuel/air mix as before (bore x stroke) but it will have less burned exhaust air remaining from the previous exhaust stroke. I don't see that this affects the pressure differential above and below the piston in any meaningful way compared to before your modification.

2. On compression, the cylinder will compress a slightly smaller initial volume (stroke x bore + combustion chamber) into a somewhat smaller volume (combustion chamber). Doing this puts a somewhat higher pressure on top of the piston but unless there is excessive blow-by on the rings, there is likely no significant change in the crankcase.

3. On ignition and power stroke, due to the now denser fuel/air mix, the pressure in the chamber and on top of the piston is higher--by how much I have no idea. But, with more power output and higher cylinder pressure, potentially, gases are going around the rings into the crankcase which could increase the crankcase pressure. Again, by how much I have no idea.

 

The smoking engine is some evidence that the rings (or bore, or both) are worn, increasing the possibility of #'s 2 and 3. However, if the pressure is moving gasses from above the piston to below, how is the oil going in the other direction? The only thing I can imagine is that the oil film on the cylinder walls is thicker given the poor rings and it's being burned off the cylinder sidewalls.

 

That's it for my guesswork.