Plug question: Champion or NGK, .030 or .040 gap....

Jet Wrench

Petty Officer 3rd Class
Joined
May 26, 2010
Messages
97
1975 Johnson 70. OK, got the beast running yesterday. Replaced the plugs, the parts store did not have the Champions (L77JC4), but had NGK (B7HS10). The manual says the gap should be .040, I see that posts showing it should be .030? Another question. If the fuel line to the engine, and the fuel line to the fuel pump is a larger inner diameter (ID) than the line from the fuel pump to the carbs, can this cause a "losing prime" issue? Thanks in advance.

Jet Wrench
 

Vic.S

Rear Admiral
Joined
May 4, 2004
Messages
4,690
Re: Plug question: Champion or NGK, .030 or .040 gap....

Champion L77JC4 or QL77JC4 are the recommended plugs, the latter having low resistance inductive interference suppression.

B7HS-10 are the nearest NGK equivalenet to L77JC4.

The equivalvent of QL77JC4 is BZ7HS-10. Do not be tempted to use the ordinary resistor plug, BR7HS 10, which is often given as an equivalent.

The gap change to 0.030"was recommended some years ago, in the 1990s ? Use 0.040"or 0.030" which ever seems to be the better. I could tell no difference.

I can see no reason for the larger bore fuel line to cause any problems ... within reason. What problems are you having.
 

F_R

Supreme Mariner
Joined
Jul 7, 2006
Messages
28,195
Re: Plug question: Champion or NGK, .030 or .040 gap....

Your fuel line issue seems normal. Reason: It is easier for the pump to push gas to the carburetor than it is to pull (lift) gas from the tank. It's a psi thing.
 

Jet Wrench

Petty Officer 3rd Class
Joined
May 26, 2010
Messages
97
Re: Plug question: Champion or NGK, .030 or .040 gap....

I re-worked the fuel line to be used on my Whaler. The new line is approximately 12' long. The fuel cell is placed just aft of mid ship under the pilot seat. At one point during my engine run yesterday, the engine starved for fuel and I needed to re-prime. It seemed OK after that. I did disassemble the fuel pump and clean it prior to the engine run. The bellows seemed OK, maybe a bit distended being as old as it is, but no perforations. I'm thinking I need to rebuild it to achieve max pressure (manual states 2.5 psi). I haven't put a fuel line pressure gauge in series to determine the actual pressure. I will just bite the bullet and rebuild it regardless. Thanks for your inputs!
 
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