1987 johnson v4 110 cyl 4 not running

[lofud]

Hi.
1987 v4 110hp
Not totally sure of the model number as the sticker isnt there my best guess is J110TLCUR.
I'm at my ends with this motor.
I'd take it to a shop but they are 3 weeks booked up.
Cyl 4 not running.
Tested spark with a spark gap tester
Changed coils
Changed plugs
Changed leads
Changed cdi units
Checked and swapped reeds
Head gasket replaced
Checked timing
Tested the pickup and stator
Spark gap tested
Carbs cleaned and swapped
Cleaned and added extra earths
Sprayed some engine start around all the hoses and gaskets listening for any pitch change in the engine bit nothing happened.
Head gasket was replaced as I thought maybe water is leaking in, cleaned the head and block surface and checked it with a flat edge ruler and all came up to spec.
Compression tested all cyl around 100
Put compressed air into the crank and listed for leaks through the carbs (nothing)
Vro replaced with normal pump
Motor starts and will idle on muffs but won't in the water.
Cyl 4 has spark, fuel and air but doesn't appear to be doing anything (I can take cyl 4 lead off and on while the engine is running and it makes no difference to the engine pitch. As soon as I take off the lead i can see the spark coming from it to the plug.)
What else can I check ?

 

[racerone]

Sounds like there is an issue with crankcase compression or fuel pump diaphragm.-----Motor needs 4 things to run---Crankcase compression.---Correct amount of fuel.----Spark at the right time.---Compression in cylinder.----Is the replacement fuel pump ( 2 nipples ) mounted correctly on the intake manifold?----Pressure pulse port for VRO plugged ?----The orange wires going to the top coils have a blue stripe ??

 

[lofud]

Sounds like there is an issue with crankcase compression or fuel pump diaphragm.-----Motor needs 4 things to run---Crankcase compression.---Correct amount of fuel.----Spark at the right time.---Compression in cylinder.----Is the replacement fuel pump ( 2 nipples ) mounted correctly on the intake manifold?----Pressure pulse port for VRO plugged ?----The orange wires going to the top coils have a blue stripe ?

Thanks for th input.
what I should have said is that I replaced the vro while this was happening as I figured while I'm doing engine things I might aswell do that do, so it was doing this before and after.
and yes the blue wires are in top.
cyl 1,2,3 all run great and if you remove any of those leads it's makes a instant change to the engine running.
I did try putting compressed air into the crank case as a test to see if the reeds were leaking. I couldn't hear air coming from the carbs but it had to be going somewhere, I assume out the exhaust? It wasn't coming out fast enough to be able to actually hear where it's coming out from to be honest, I also used the air hose behind the throttle linkage to test this idea.

 

[racerone]

Post the outcome when you have this motor sorted out.----Where did you apply the pressure on cylinder #4 crankcase ?---There are 4 separate crankcases.----Was piston at bottom of travel ?----This issue should be easy to figure out I say.----High speed jet ( orifice plug ) for # 4 cylinder is confirmed clean ?

 

[ahicks]

I'm looking at the comment that it runs on muffs but not in the water. This leaves me wondering if it's a carb issue as well. Maybe carb sync?

 

[lofud]

Post the outcome when you have this motor sorted out.----Where did you apply the pressure on cylinder #4 crankcase ?---There are 4 separate crankcases.----Was piston at bottom of travel ?----This issue should be easy to figure out I say.----High speed jet ( orifice plug ) for # 4 cylinder is confirmed clean ?

Hi. I didn't think about there being 4 separate crank cases. (To used to 4 stroke world) so where I applied the pressure it wouldn't have got to cyl 4. I did that's to check for leaks from the reeds which I haven't now taken out checked,cleaned and swapped with cyl 3. But the problem still exists on cyl 4. Now this high speed jet you mean in the carbs? They have been pulled apart and cleaned the I also swapped the top and bottom carb with same results.

 

[lofud]

I'm looking at the comment that it runs on muffs but not in the water. This leaves me wondering if it's a carb issue as well. Maybe carb sync?

Hi, I have been through the link and sync procedure a few times with no success. Also tried swapping the carbs from top to bottom with no difference.

 

[racerone]

Facts-----Cylinder #4 needs 4 things to run----Correct amount of fuel.----Spark at the right time.------Compression in the #4 crankcase.-----Compression in the cylinder.------Should be easy to determine what is going on I think.----What sort of Fuel pump.-----If it has the regular ( 2 nipple ) fuel pump mounted on the intake manifold , then check the diaphragm.

 

[oldboat1]

If you measured spark with an open air tester, what did you get? Post results.

edit. 2 high speed jets in the float chamber of each carb? both need cleaning. Top of carb (cover and gasket needs to be removed, and idle passages cleaned individually).

 

[ahicks]

Idle passages, +1!

 

[lofud]

Facts-----Cylinder #4 needs 4 things to run----Correct amount of fuel.----Spark at the right time.------Compression in the #4 crankcase.-----Compression in the cylinder.------Should be easy to determine what is going on I think.----What sort of Fuel pump.-----If it has the regular ( 2 nipple ) fuel pump mounted on the intake manifold , then check the diaphragm.

I replaced the (working) vro pump with a standard pump while trying to figure out this problem. So it's a new pump but I had the same problem with both pumps. I have also pulled the new one apart as someone else suggested to check the diaphragm so I'm confident it's not that.
While doing a link and sync I also have checked timing and have also marked each cyl on the flywheel to check it's sparking at the correct time.
I have put a compression tester on all cylinders and all coming up with 100-105.
I also have swapped carbs around after cleaning them and the problem stayed in the same place making believe the carbs are ok and the problem isn't carb related.
Only thing I haven't checked for is compression in the crank case so that's tomorrow's job.

 

[lofud]

If you measured spark with an open air tester, what did you get? Post results.

edit. 2 high speed jets in the float chamber of each carb? both need cleaning. Top of carb (cover and gasket needs to be removed, and idle passages cleaned individually).

Yes I measured spark. I got out to 14mm or 15mm before it stopped working.

Both carbs have been taken off and completely apart and cleaned. Also I swapped the top carb with the bottom carb and the problem stayed in the same place so that leads me to believe it's not carb related.

 

[lofud]

I read on another forum (but now can't find it) about a seal or something along the lines of a rear/front main seal on the bottom of the motor that could leak and let air into cyl 4.
So the motor would need to come out for this.
Is this something it could be?

 

[racerone]

There is a seal on the bottom of the crankshaft.----Prevents crankcase compression from leaking out.----There are metal seal rings on the crankshaft ( 6 of them ). that prevent leakage between crankcases.----Sorry----I am not there to inspect.----I can only suggest what might need to be looked at.----It is up to the owner to use the information and run with it.

 

[ahicks]

Here's something to think about. If the crankcase pressures for this cylinder aren't up to par, the compression of the down coming piston couldn't pack the cylinder properly, and the result would be low(er) compression - especially as compared to the other cylinders. Point being, I'm thinking if the compressions match, I doubt seriously there's anything going on with the reed valves or crank seals.

Maybe time to recheck the compressions?

 

[racerone]

The crankcase compression has absolutely nothing to do with compression in the cylinder !!----One of the reasons for so much confusion on simple trouble shooting.----Crankcase compression puts fuel air into the cylinder.----It can not ---" pack "--- the cylinder since exhaust ports ( huge holes ) are OPEN during this scavenging process.

 

[ahicks]

The crankcase compression has absolutely nothing to do with compression in the cylinder !!----One of the reasons for so much confusion on simple trouble shooting.----Crankcase compression puts fuel air into the cylinder.----It can not ---" pack "--- the cylinder since exhaust ports ( huge holes ) are OPEN during this scavenging process.

Next time you get a chance, try to take a compression reading with a reed valve propped open..... see if that doesn't change your mind.

 

[racerone]

Throw the reed valves on the shop floor and do a compression test.

 

[lofud]

There is a seal on the bottom of the crankshaft.----Prevents crankcase compression from leaking out.----There are metal seal rings on the crankshaft ( 6 of them ). that prevent leakage between crankcases.----Sorry----I am not there to inspect.----I can only suggest what might need to be looked at.----It is up to the owner to use the information and run with it.

is there test i can do to check the crankshaft seal? or is it time to take out the motor?

 

[Crosbyman]

"I did try putting compressed air into the crank case as a test to see if the reeds were leaking. I couldn't hear air coming from the carbs but it had to be going somewhere, I assume out the exhaust?"

how did you pressurize the crankcase on #4 ?? if the piston is at TDC you should be able to send air via a plate/nipple made up to replace the #4 bypass cover . with reeds shut a bad seal should be noticeable

I have never done this but since the lack of sucking adequate quantities of fuel/air mix on the upstroke of the#4 piston seems to be the suspect here . a vacum meter could also show something

Either way alternating pressure (downstroke) or vacum (upstroke) should be producing some form of measurement ... or needle movement range you can compare with other crankcase cavities if you retest by moving your home made plate/nipple cover to another known good cyl.

little/low/ very different ..... needle movement should be indicative of a poorly sealed crankcase cavity.

just a suggestion....