1970 4hp Johnson low compression

[ugmold]

Hi folks,
I have 2, 1970 4hp Johnsons. One runs great. The other seems to have low compression. 25-30 each cylinder. I put some oil in the cylinders and it came up a tiny bit, 33. I am trying this with throttle wide open, choke off. I'm wondering if the rings might be stuck so I am spraying PB blaster in the cylinders every now and then and pulling it over.
Wondering if it might be a head gasket too, don't see any evidence of it blown.

Now I've had this running on the pond but it quits after 15 minutes or so. I guess I always thought it was a spark or carb issue.
-ugmold

 

[F_R]

That is practically no compression. Yes, very possibly a blown head gasket between cylinders. If not, then time for a major inspection.

 

[racerone]

Pull the head for inspection.-----Head is warped ( they all are ) , so refinish it on a piece of glass with emery paper before installing the new head gasket.

 

[ugmold]

Thanks, I'll dig into it.

 

[ct1762@gmail.com]

just remember these needed 25:1 oil mix with the bronze bearings. ive seen many of these with thrown rods from melted bearings due to improper fuel mix.

 

[ugmold]

just remember these needed 25:1 oil mix with the bronze bearings. ive seen many of these with thrown rods from melted bearings due to improper fuel mix.

Really, I thought it was 50:1?

 

[racerone]

Beginning in 1964 or so they all ran on 50:1 -------That may not be the best for those smaller motors 1.5 / 2 / 3 and 4 HP models that did not have needle bearings on the big end of the rods.------I have had many of the 6 HP models apart.-----Never an oiling issue on the bronze main bearings for the crank at 50:1 on them.

 

[ct1762@gmail.com]

Beginning in 1964 or so they all ran on 50:1 -------That may not be the best for those smaller motors 1.5 / 2 / 3 and 4 HP models that did not have needle bearings on the big end of the rods.------I have had many of the 6 HP models apart.-----Never an oiling issue on the bronze main bearings for the crank at 50:1 on them.

thats what I thought, but had 2 in a row that were under-lubricated. I guess by underlubricated it must have been a "zero oil" situation. I stand corrected.

 

[ugmold]

I took the head off today and found a passage between the 2 cylinders, everything else looked pretty good. Ordered up a head gasket.

 

[ugmold]

I'm going to try to get the head back on in the next few days, I searched around and found 60-84 inch lbs as the torque, is that like 5-7 ft lbs?

 

[racerone]

Correct.

 

[ugmold]

New gasket on, head clean, not warped, only came up to 50psi. My checker might not be the best. Cleaned carb, was clean. Set the points, they were good.
Took it out, sputter, sputter, then it slowly kicked in felt good for 10 seconds, died. I pulled off the fuel pump hose, nothing coming out. Must have ran on my squirting gas in. I think I "tried" to rebuild this pump once.
Anybody have luck with the cheap ones on ebay: https://www.ebay.com/itm/392818722793

 

[saltchuckmatt]

New gasket on, head clean, not warped, only came up to 50psi. My checker might not be the best. Cleaned carb, was clean. Set the points, they were good.
Took it out, sputter, sputter, then it slowly kicked in felt good for 10 seconds, died. I pulled off the fuel pump hose, nothing coming out. Must have ran on my squirting gas in. I think I "tried" to rebuild this pump once.
Anybody have luck with the cheap ones on ebay: https://www.ebay.com/itm/392818722793

Most people say junk. Better to rebuild....easy.

50 psi is not good. Check with another tester or test your tester on something else. It might be done.

 

[oldboat1]

No warpage if mating surface is equally shiny all aroundafter sanding process (above). I use 600 grit (+/-) on a steel table saw top, wet/dry paper used wet to provide smooth finish (and bottom sticks to saw top surface.) Use figure 8 pattern. Torque to specks -- two passes in circular pattern beginning in the middle. Final torque on second pass.

 

[ugmold]

Most people say junk. Better to rebuild....easy.

50 psi is not good. Check with another tester or test your tester on something else. It might be done.

The description says only if it has a 2 port pump, I only see one hole for this pump.
Only tester I had. My feeling is that it is the fuel pump, while it was running nothing came out. I tried a rebuild years ago, just took it apart. I don't have a parts layout to by, but things looked ok. I can blow thru it, but not suck.

 

[ugmold]

No warpage if mating surface is equally shiny all aroundafter sanding process (above). I use 600 grit (+/-) on a steel table saw top, wet/dry paper used wet to provide smooth finish (and bottom sticks to saw top surface.) Use figure 8 pattern. Torque to specks -- two passes in circular pattern beginning in the middle. Final torque on second pass.

Pretty much what I did. When the motor kicked in it actually felt pretty healthy, like my other good one.

 

[racerone]

Those little fuel pumps mount directly over the PRESSURE pulse port from the crankcase.-----And one visible port for fuel in and one visible port for fuel out.

 

[ugmold]

Those little fuel pumps mount directly over the PRESSURE pulse port from the crankcase.-----And one visible port for fuel in and one visible port for fuel out.

Does that mean it is 2 port?

 

[saltchuckmatt]

The description says only if it has a 2 port pump, I only see one hole for this pump.
Only tester I had. My feeling is that it is the fuel pump, while it was running nothing came out. I tried a rebuild years ago, just took it apart. I don't have a parts layout to by, but things looked ok. I can blow thru it, but not suck.

I mean the motor might be done. Fuel pump works off of the crankcase, with your low compression it may no longer work. Spit balling really.

 

[racerone]

There is very little that can go wrong with those pumps !!!------A new diaphragm fixes them in most cases.-----Yes the diaphragm is available all day long.