FS651V No High RPM

[Hayward51]

You don't want the actual throttle to go to full wide open; the engine will exceed the maximum safe RPM of 3600 RPM and blow itself apart.

I only want the rpm's up more than 3450 . 3600 would be good if I can get it there with adjustments.

 

[Auto Doc's]

Have you broken in the engine and changed the oil yet? The new rings have to wear in properly.

Next question is: Are you sure the cylinders are both firing properly? Put a spark gap type tester on each plug wire and confirm they are firing good all the way through the operating range. Ignition coils do breakdown with age.

V-twin engines do not shake or vibrate with a coil breakdown; they just lose power especially under load.

 

[Hayward51]

I have been mowing to break-in the rings and haven't got enough time (2 hrs) to change oil yet. I have checked the firing on both cylinders, though not under a load.

 

[Auto Doc's]

A quick method is with a spray bottle and shoot a stream of water on each exhaust outlet near the head to see if the water instantly burns off. If one side is slow, you have a weak combustion problem.

Check at idle, then at high RPM.

 

[Hayward51]

A quick method is with a spray bottle and shoot a stream of water on each exhaust outlet near the head to see if the water instantly burns off. If one side is slow, you have a weak combustion problem.

Check at idle, then at high RPM.

'a weak combustion problem' ? What does that mean ? I'm not new to this but that term is new.

 

[Auto Doc's]

Hello Hayward51

On these small single and V-twin engines, coils do not often totally fail totally open circuit, but the resin insulated windings rub together. When that happens, spark for combustion is not complete or consistent.

The next thing to check is to verify your valve lash adjustment is correct.

 

[txmowman]

fs651v-DS07-R I'm just trying to get a little more top end. It was showing 3600 on the machine's tach before I replaced wore out rings. Now it shows 3250 RPM. I can definitely tell the difference mowing.

The high idle spec for this engine is 3600 +/- 100. I am thinking that when you are adjusting the governor, you are using the throttle control lever to achieve WOT. Try this:
Loosen the black left-hand bolt in the center of the governor link
Have someone hold the throttle shaft in the WOT position.
With your right hand, gently lift the part of the governor link that is attached to the governor shaft until it won’t move any more. But, do not over force it.
Tighten the LH bolt back down.

 

[txmowman]

Have you adjusted the governor? There are some good videos online about how to do this properly. When you rebuilt it the sump gasket could have been thicker or thinner and that would affect the governor.

Also, there is a tension spring for the governor arm some models have multiple holes for the spring location and that dictates the top governor limit. Other models had a tab that the spring attached to, the tab could be bent slightly to increase or decrease the spring tension.

Do not exceed 3600 RPM or internal engine damage may result.

Exceeding 3600 rpm will not cause internal engine damage. You can run the engine without the governor and will float the valves at around 4200. Ask anyone racing lawnmowers. They modify the valve train and are running 6000-7000rpm easily with stock internal components. These engines are very tough. They fail mostly due to the very poor maintenance that they receive.

 

[Hayward51]

Hello Hayward51

On these small single and V-twin engines, coils do not often totally fail totally open circuit, but the resin insulated windings rub together. When that happens, spark for combustion is not complete or consistent.

The next thing to check is to verify your valve lash adjustment is correct.

I will check the valves and spray the exhaust today.

 

[Hayward51]

Exceeding 3600 rpm will not cause internal engine damage. You can run the engine without the governor and will float the valves at around 4200. Ask anyone racing lawnmowers. They modify the valve train and are running 6000-7000rpm easily with stock internal components. These engines are very tough. They fail mostly due to the very poor maintenance that they receive.

Thanks for that. I'm leaning toward me not getting the linkage right.