Vanguard 35hp no vacuum pulse from manifold

[Mlippmann]

I have a vanguard that about 2 years old, maybe 15hours on it that suddenly stopped giving me a vacuum pulse from the manifold. I’ve removed the tube, left it connected to the pump and by slightly blowing and sucking and produce fuel but when turning over the engine I can’t feel a thing. It was running and just died like it ran out of fuel. No crazy noises and doesn’t sound bad when turning over. Tested compression and getting 150psi and holding. Pulled the manifold off and all looks well. Not sure what to do from here.

 

[kencombs]

The pulse line should connect to the crankcase, not the manifold. Often the little like cracks on the ends. Just a tiny leak will cause a no pump problem. Connect a vacuum gauge to the crankcase and spin the engine, you should see a up and down movement.

A bad crankshaft seal will leak air into the engine killing the pulse.

 

[Mlippmann]

Thanks, on this model it connects at the top of the intake manifold. Tried a new rubber tube and had no change. Even if I put my finger over the barbed fitting on the manifold while turning it over I can’t feel anything. Will have to get my hands on a vacuum gauge though, that’s a good idea.

 

[kencombs]

Thanks, on this model it connects at the top of the intake manifold. Tried a new rubber tube and had no change. Even if I put my finger over the barbed fitting on the manifold while turning it over I can’t feel anything. Will have to get my hands on a vacuum gauge though, that’s a good idea.

I don't understand how a pulse pump would ever work off the intake manifold? There is no pulse there, ever. At least no engine I've ever worked on had anything but a constant vacuum, varies with speed and load but always a vacuum.

Just in case someone notices, yes I know turbos are different but Briggs doesn't do those, yet.

 

[used red MN]

There is no pulse there, ever. At least no engine I've ever worked on had anything but a constant vacuum,

That indication of no pulses is very dependent on the gauge dampening and ability of the needle to respond quickly to pressure changes in the manifold. Even the length and size of the hose connecting the gauge to the manifold effects this. Even 16 cylinder engines have pulses however the closer you are to the valve the more pronounced they are. If this wasn’t true intake port and exhaust header length tuning would be a bust.

 

[used red MN]

I’ve removed the tube, left it connected to the pump and by slightly blowing and sucking and produce fuel

I haven’t work on these types of engines much but my educated guess is that it is your fuel pump. Small engines that relied on some sort of diaphragm to pump fuel have, ever since the inception of that system, been plagued by diaphragms that get hard and stiff over time. Ken is correct in the fact that the intake pulses are likely not pronounced enough to feel with your finger. Your artificial humanly produced suck/blow signals are likely far more pronounced and much slower than those from that engine when it is running. So yes you can artificially make it pump fuel, but apparently the intake pulses will not do the job. That is my WAG we’ll say.

 

[Hobo,NC]

The pulse is very weak You probably will not feel it with a finger. The best I remember its 3 to 5” of vacuum and probably less than 3”. That’s enough the see a vacuum gauge wiggle. I usually use a longer tube and stick the other end to my tongue if I can feel it, I’m good to go on vacuum. The ones I have been into the port for the fuel pump use a reed valve on the crank case to check off pressure and allow vacuum to pass through.

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[T.R.K.]

I am aware that some Vanguard engines do connect the fuel pump to the manifold. I don't think you can measure the vacuum as it pulses each time the intake valve opens.

You can test your fuel pump with a hand vacuum pump. Connect your vacuum pump to the pulse port on the pump. Hold your finger over the vent (either a hole or the sintered brass area on the pump) and pump to about 7" vacuum. It should hold for about a minute. Then if your vacuum pump can also make pressure, pump to 7 psi and see if it can hold for a minute. Be aware if air is leaking past your finger, the pump can still be good but it will look like it failed your test.

I suggest make sure your pulse hose from the manifold is good and fits tight on both ends. Try another fuel pump.

P.S. I have been burned twice this year by Amazon/Ebay knockoff fuel pumps. They just don't deliver fuel like the Mikuni fuel pumps can. Make sure your fuel pump says Mikuni on it.

 

[Mlippmann]

Here’s how this one connects. I’ve tried a couple different fuel pumps but worth a shot with another cause everything else checks out.

 

[used red MN]

Another shot in the dark I’ll suggest is checking the valve lash. Since valve lash changes are usually gradual the fact that it suddenly died really doesn’t support my suggestion. Are you certain it is a fuel problem? Try running it with a temporary gravity feed tank over the engine. Hate to put all the eggs in the fuel basket when there is also a possibility of an ignition problem.

 

[cjunrau]

I would use a spray bottle into the intake to make sure the thing is not getting gas. If it runs on sprayed in gas then you know it could be the pump or related to gas. If it does not fire up then you have a spark issue.

 

[Duner Wi]

Hook up vacuum gauge to intake manifold where your pulse pump attaches. Start engine and observe fluctuation. Un dampened gauge will bounce as your engine is odd fire I believe.

 

[Mule Meat]

If the engine is carberated and not EFI?

You can buy an electric fuel pump for about the same price as a vacuum pump and be done with the headache.

 

[Russ from MN]

If the pump ever fails on our Husqvarna I plan on putting on an electric fuel pump, then you turn on the key, wait until it clicks, the carb is full, and it starts.

 

[Old560]

I have a vanguard that about 2 years old, maybe 15hours on it that suddenly stopped giving me a vacuum pulse from the manifold. I’ve removed the tube, left it connected to the pump and by slightly blowing and sucking and produce fuel but when turning over the engine I can’t feel a thing. It was running and just died like it ran out of fuel. No crazy noises and doesn’t sound bad when turning over. Tested compression and getting 150psi and holding. Pulled the manifold off and all looks well. Not sure what to do from here.

Someone suggested an electric fuel pump if you put an electric one on how much psi should it be able to put out? Is there an electric one that’ll shut off when it reaches a certain pressure if so, which one?

 

[Duner Wi]

Look at an E8016S. That is low pressure and should work good with carburetor.

 

[Mule Meat]

Someone suggested an electric fuel pump if you put an electric one on how much psi should it be able to put out? Is there an electric one that’ll shut off when it reaches a certain pressure if so, which one?

You normally want one in the 2 to 5 psi range. Flow rate doesn't matter. It will only pump fuel into the carb when the needle is open. They all should stop fuel flow to the carb when the needle is closed. The pump never does actually shuts off as long as it has power. Just the flow stops. You can hear the difference in the sound the pump makes when pumping fuel and when it's not.

A fuel filter should be placed between the pumps outlet and carb. Not between the fuel tank and pump inlet.

I like to pump a few ounces of 2 cycle oil through new electric fuel pumps to lubricate the bearings and seals before installing them on the machines. I do it because I never know how long a fuel pump has been sitting on a shelf. And I do not like putting gasoline through one with dry bearing and rubber seals.


Since most here believe that Amazon is the only place to buy products. Here a pump that will work on a mower engine.

Fuel pump for mowers.

 

[kencombs]

The pulse line should connect to the crankcase, not the manifold. Often the little like cracks on the ends. Just a tiny leak will cause a no pump problem. Connect a vacuum gauge to the crankcase and spin the engine, you should see a up and down movement.

A bad crankshaft seal will leak air into the engine killing the pulse.

Replying to my own post. I've had some Vanguards but all 16/18hp. I think they had the pump attached to the valve cover/crankcase vacuum/pulse.. I should have said that the airflow pulse in the intake may not be strong enough to drive the pump as I didn't realize the bigger ones were connected that way.

Knowing that is connected to the intake and once worked I'd have to agree with the poster that mentioned valve clearance. An intake opening and closing early or late could well interfere with the air pulse enough to do what you describe.

I'd still recommend a vacuum gauge to see what's really there.