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WOT surge Johnson 150 Faststrike

L

luhrern

New member
I have a 150 Johnon Fasstrike with the following challenge:

At WOT & 5400 - 5500 RPM it runs ok for 15 seconds then surges to 3500 - 4000 RPM - I reduce the gas lever and it runs ok at 4500 RPM. Maximum stabil RPM = 5000 RPM.

The oil (VRO system) is not connected and I premix the fuel.

Boat - Fjordling 18' about 600 KG exclusive engine

Propeller Raker 14 3/4 x 22

When I get someone to pump the primer pump gently at 5500 RPM it runs ok.

Some of the components in my fuel system was not 3/8' but this is now rebuilt.

Vacum at WOT in the fuel line is 3 to maybe 4 HG.

I have a 1 m clear fuel line connected - formed as a vertical "ring" circle before the vaccummeter - there is small a air bubble on top of the ring - but no "stream" of air in the line.

The fuel pump "clicks" every 10 second at 1000 RPM.

Is there anyone that can suggest anything ?

Should I maybe consider to change to a premix pump P/N 5007422 ?
 
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Looks like its time for a new fuel pump...if you can pump the bulb and get the motor to run right that means you need a new pump...
 
I have now changed to VRO " premix version"P/N 5007422.

The problem is still there on WOT. When I go from 4800 - to 5300 - 5500 RPM the motor go ok for 5 - 10 seconds and then surge. I take back the throttle, and the engine picks up RPM again.

Running very satisfactory by 4600 - 4800 RPM about 75 % advance of the throttle, but when I advance to WOT - problem.

I have checked the fuel line again for air leaks by a clear 1 meter plastic hose formed as a circle in from of the engine intake, just at idle mode. During the first 1-3 minutes after start up, some air are coming from the engine side and are "trappped" on top ofthe "circle". I have removed the plastic pipe for fuel & oil intake in the lower cowling and put in a 10 mm staliness steel tube just to be sure.

New pump "cliks" still at at rate of 8 - 10 seconds at idle 800 - 1000 RPM.

However new problem observed. When running at low speed - aound 1000 RPM - or 5 knots it seems that the engine after a couple of minutes goes into S.L.O.W. mode. Before this I observe that the VRO pump get a higher and higher click "rate", an in the end it is like the pump (the new one) flicker.

Stops engine - S.L.O.W. resets - on sqeese on primer bulb and the engine fires.

All hoses and connections before the engine and the filter are changed. 3/8 size used all over.

Primer bulb maybe fitted too far from the engine rigth after the filter -and the hose length from the primer bulb to the engine ia 170 cm.


Does anyone have any suggestions ?

Carburators ?
 
If the year/model number of that engine is mentioned anywhere above, I'm constantly overlooking it. What is it?

In one of your statements, you say "When I get someone to pump the primer pump gently at 5500 RPM it runs ok."

That indicates a failing fuel pump which you've already corrected by installing another.

In another statement, you say " I take back the throttle, and the engine picks up RPM again."

Normally there is a full throttle butterfly stop on the carburetors to prevent having the butterfly travel past the horizontal full throttle position BUT check it to make sure that at the full throttle setting, that is neither butterfly is traveling past the horizontal position and is starting to close again.

Check the timer base under the flywheel. It should have traveled its full spark advance position long before the throttle lever has been pushed to its full throttle position. If this is as it should be, that would eliminate any timing problem as advancing the throttle further would not cause any further movement of the timer base. An exception to a timing problem would be if the full spark advance timing is not set properly in the first place.

If you haven't checked the full spark advance timing, do so if for no other reason, to eliminate that possibility.

Slow mode going into effect at a slow rpm indicates a failing water pump.

Year of that 150hp...... Model number?
 
Thankyou for the prompt reply.

Modelno: J150GLECD

1. I will check the travveling of the full throttle butterfly.
2. I think that I checked the full time advance settings when I changed to a new CDI powerpack / sensor last year. I thought the powerpack was the problem, but no same problem before & after. The engine has been reallly overheating before I bougth it, and the powerpack needed to be replaced anyhow. But I will check the timing.
3. S.L.O.W. - mode and failing water pump. The waterpressure reading at idle is around 5 psi.
 
I have checked the butterfly position at WOT. They are 99 % open.

The full spark advance timing is reached before the butterbly opens 99 %.

I have as well tested the boat with a small petrol tank very close to the engine.

Still problem at WOT. WOT ok in 15 seconds RPM reaching 5300, but then surge.

Running ok by 4800-4900 RPM - very stady and ok.

No more S.L.O.W. incidents this evening.

I will re-check WOT advance ignition tomorrow, using the procedure from CDI

http://www.cdielectronics.com/InstallSheet/113-6367K 1.pdf

However as the engine runs at WOT 15 seconds could there by anything regarding ignition ?

What about carburators- jets ?
 
1998 150hp Johnson. If the high speed jets (one to a cylinder) are somewhat fouled, that normally would cause the engine to die out when the throttle is applied. However, that is something worth looking at.
 
I have looked into the BRP exploded view in the part catalog for Carburator & Intake Manifold, see picture below:

convert


The gasket in position 69 are missing. P/N 0336821 Seal, AIR SILENCER. Could this be the problem i.e. that air is "leaking" in via the vacum that appear at WOT - after 10 - 15 second.

I will order 6 new gaskets and try.

0336821 SEAL, Air silencer. Included in Powerhead Gasket Set
 
Yes, the lack of having those gaskets in place results in a air leak of sorts.

When the V/6 loopers first came out, there was a time when I encountered a 225hp that would act similar to your problem. All was well EXCEPT the owner had removed the thick gasket within the carburetor face plate (air silencer). Replacing that gasket eliminated the problem.
 
The gasket (pos 69) o the exploded view above is installed.
Np change - still surging around 5000 - 5200 RPM. Very irritating.

Could my tachometer be wrong installed, and that I am really hitting the RPM limiter ?. This is an original OMC with option "5" & "6", where my is set to "5".
 
The tachometer operates off of the charging system's six (6) pulse setup. The tachometer should be set to #6..... (6 pulses).

At one point in your first post you stated:

"When I get someone to pump the primer pump gently at 5500 RPM it runs ok."

However, you had more than one problem apparently at that time. If this still holds true, and pumping the fuel primer bulb causes the engine to run okay at 5000 rpm or so, that might be due to a sticking anti siphon valve.

(Fuel Anti Siphon Valve)
(J. Reeves)

Many of the later OMC V/6 engines incorporate a fuel restriction warning via a vacuum device attached to the powerhead. If the engine overheats, or if you have a fuel restriction, the warning is the same.... a steady constant beep.

NOTE... Only the V/6 & V/8 engines have the above "Fuel Restriction Warning". The warning horn will not sound on the other models.

The fact that a engine is not overheating, but the warning horn sounds off with a constant steady beep, and that the rpms drop drastically would indicate that the engine is starving for fuel due to a fuel restriction. Check the built in fuel tank where the rubber fuel line attaches to the tank fitting. That fitting is in all probability a "Anti Siphon" valve which is notorious for sticking in a semi closed position. It will be aluminum, about 2" long, and the insides of it will consist of a spring, a ball, and a ball seat. If this valve exists, remove it, knock out those inner components which will convert it to a straight through fitting, then re-install it. Hopefully that cures the problem.

The above procedure will cure a restriction problem with the anti siphon valve as stated. BUT, it may also allow fuel to drain backwards to the fuel tank when the engine is not running (siphoning backwards) due to the fact that the carburetors/fuel pump etc are higher than the fuel tank. This condition is not an absolute as the valves in the fuel primer bulb usually prevent this backwards siphoning problem. However.... if this does take place, the cure would be to install a new anti siphon valve.
 
Regarding the Fuel Bracket, I have actually tested a fuel bracket from another engine ( I have two engines ). The problem is the same.

However one solution would be to rebuild the fulebracket with new gaskets and o-rings etc. and try this with my new VRO pump without oil pump.

Another issue has come up. It may be that the Tachometer has been not correct adjusted. This is an original OMC with red ligths showing oil - fuel restriction heat. The adjustment in the back of the tach is 5 and 6. I understand that this engine require 6 to show correct RPM. The adjustment screw is a bit loose, so it is not o to se if it is installed to 5 or 6.

I have experimented with the current position the surge comes at 6100 - 6200 RPM, as it is the RPM limiter that kick in.

However this is with a 22 pictch Raker and the speed should be higher than shown on the GPS 40 knots at 5500 RPM (4800 RPM at the other tach adjustment) - from there to WOT it is quick to 6100 - 6200 - before surging.

I have ordered a 24 pitch raker to see if this wil help. In addition I have as well an digital tacho ordered sp I can adjust my original tachometer.

However - any input on this theme is highly appreciated.
 
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I have noow changed the "float valve assy" in the vapour sepataror chamber.

The bota has not been in the water to test wether this will help on the WOT surge problem.

However, when I used the gasoline primer pump to fill the system up with gasoline, I had not connected the hoses to the vapor separator pump. Gasoline came out from the pulse hose connection in the small vapor separator pump (A on picutre) in addition to the smaller line that have a hose that are connected to the air intake (B on the picture).

Is it correct that the gasoline should come out of this pulse hose connection when I prime ?

When the vapor separator chamber had been filled up and the "float valve" was closed - the stream of gasoline stopped as well.
 

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