1988 Johnson GT 175 fuel starvation

[rammerjammer05]

I am having a fuel related problem with my Johnson 175 GT. At 1/2 - 3/4 throttle I'm having a fuel starvation and the motor will die out. I have replaced all fuel lines,VRO pump (mixing my own gas 50:1), primer bulb, checked for vacuum leaks, replaced all spark plugs, rebuilt carbs, new pulse limiter. Compression is 100psi on all cylinders. I can actually keep the motor running if I manually pump the bulb, I have a clear inline filter before and after the VRO pump. The filter before the pump stays full of gas but the filter coming out of the fuel pump to the carbs I can see gas being pumped into it but just seems like it's not enough especially at higher RPMs. Just all of a sudden started doing this about 3 weeks ago and I have checked or replaced everything I can think off. Am I'm missing something else.

 

[racerone]

Running with a 3/8" fuel line ?-----The fuel pump runs off crankcase PRESSURE pulses.-----There may be an issue there.-----My opinion is that your compression is not good.----Test with another gauge.

 

[rammerjammer05]

Yes 3/8 fuel line from tank to VRO. I have checked the compression with 2 different gages all range from 95-110 PSI. It's pumping fuel from the VRO I can see it it gets more fuel in the inline filter as I open the throttle up. But it's not enough to keep it running unless I manually pump the primer bulb

 

[racerone]

Test run with another tank ?----With compression numbers like that on my gauges , your motor would be coming apart !---Perhaps remove the bypass cover on the 95 PSI cylinder to look at piston and rings.

 

[rammerjammer05]

I just checked with my 2 neighbors compression guage. One gauge read 75 on all cylinders and the other guage read 70 on all cylinders. Guess my 2 cheapo gauges aren't very good. Is this too low for the compression. I was told that these were low compression motors or maybe some put a set of low compression head gaskets on it. I have ran it off a portable take with same problem. I did unhook the pule limiter from the crankcase and it sounds like a machine gun and my neighbor said he say flames coming from the nipple on the crankcase could thus be my problem.But I'll take the bypass covers off and give the pistons an inspection. Thanks

 

[rammerjammer05]

We did just find a small drip from the bottom carb and one of the flyheel magnets has came unglued. Hopefully the drip us causing it th such air

 

[racerone]

There should not be any flames coming from the crankcase !-----A loose flywheel magnet is indeed a problem.----Pull the flywheel with a puller using 3 bolts.

 

[rammerjammer05]

Is 75psi to low of compression I haven't got my manual in yet and I'm unable to find any info online. I was always told don't as long as all cylinders are within 10% of each other its OK but I don't know if the compression is to low overall. It's pumping enough gas at idle speed and fir about 1-2 min and 3/4 throttle but as I watch the fuel coming from the pump it's not a constant steady flow more like a pulse of gas every 2-3 seconds. At lower RPMs its a pulse every 4-5 seconds is this correct.

 

[rammerjammer05]

There should not be any flames coming from the crankcase !-----A loose flywheel magnet is indeed a problem.----Pull the flywheel with a puller using 3 bolts.

That's the next on my list before any more troubleshooting would that be causing the flame from the crankcase. Not really a flame of fire more like a really hot burst of exhaust kind of like a backfire

 

[racerone]

There is no way you would see exhaust or a flame there !!----You would be seeing fresh fuel / air mixture coming out of the pulse limiter.

 

[rammerjammer05]

There is no way you would see exhaust or a flame there !!----You would be seeing fresh fuel / air mixture coming out of the pulse limiter.

Yea that's what I ment. It's not coming from the pulse limiter only from the nipple on the crankcase the limiter is connected to but I see what your talking about.With everything connected back engine idles great .So could the flywheel magnet being loose and shifted over be causing this. I'm not to familiar with how the magnets work I just know they are glued to the flywheel and as the flywheel turns its creates a electrical field for charging around the stator didn't know they where for ignition spark also. So if a magnet has shifted over to where there is no gap in between 2 of them and a large gap between the other 2 it would throw the spark off on which ever cylinder in my case the #6 cylinder (same cylinder fuel pump gets its pulse from) and cause the fuel not to get burned at the correct time. Just trying g to get a better understanding before I start throwing money at it. Also 75PSI across all 6 cylinder too low for these motors.

 

[racerone]

Why of course those magnets have to do with making spark.----Stop trying to run this motor !!----Repair / replace the flywheel.

 

[rammerjammer05]

Thanks and since I've discovered the loose magnet this evening the motor hasn't been turned over. Just glad I found it before it destroyed something else. Can regular heat resistant epoxy be used or should I just order the OEM epoxy. I read the procedure and plan on cleaning it thoroughly before gluing it back and also gonna check the other 5 magnets while I have the flywheel off

 

[Faztbullet]

The loose magnet is not going to cure the fuel delivery problem, rebuild the VRO. Also make sure the cooling system is 100% as this is the big bore 175 with thin sleeves. The slighest overheat and you got a rebuild on yer hands....

 

[rammerjammer05]

The loose magnet is not going to cure the fuel delivery problem, rebuild the VRO. Also make sure the cooling system is 100% as this is the big bore 175 with thin sleeves. The slighest overheat and you got a rebuild on yer hands....

Thanks
The water pump is new I installed it about 3 months ago temperature buzzer has never altered me of an overheat. I also doubled checked to make sure the warning buzzer is working and it is. VRO pump is also new less than a month old. I have taken it apart and double checked to make sure it's working properly and it is per the testing procedures. The motor runs and idles great on muffs and in the water. In the water under load is were my problem is. It fires right up first try starting. I let it come to operating temp. Rev engine in natural and everything good. Once you put it in gear runs good to maybe 3/4 throttle about the time boat is coming up on plane and it will just bog and die out unless you manually pump it for gas. I've tried pushing the key in to add more fuel but doesn't help. I have replaced all the fuel lines even the smaller ones that go to the regulation valves.

 

[racerone]

Have your assistant drive the boat.----Remove airbox cover.----Shine a STRONG flashlight into carburetor bores.----See / compare amount of fuel coming up the main nozzles for all cylinders.------See if it is a fuel issue at 3/4 throttle.----Oh----It will rev up in neutral on 4 of 6 cylinders so that test means nothing !

 

[rammerjammer05]

I did notice yesterday will troubleshooting. With air cover off I placed my hand over each carb and can feel good amount of air being pulled in. I the placed my hand over each carb quickly and gas came out of the top and middle carb but hardly any from bottom carb. Could I have a stuck needle not allowing enough fuel to it

 

[racerone]

Inspect bottom carburetor.-----See post # 16 and test run.

 

[Faztbullet]

. I can actually keep the motor running if I manually pump the bulb,

Is the replacement VRO a OEM or knockoff

 

[rammerjammer05]

OEM