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1984 70 Evinrude Rebuild

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evin15

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"I just finished a complete re

"I just finished a complete rebuild of my 1984 70hp Evinrude which included boring each cylinder .030 over. Considering this increase in cylinder volume, what is the best recommendation to increase the fuel flow. Someone suggested that the main jet located in each of the bowls be "drilled out" or replaced with larger jets. Any assistance on this matter would be welcomed. Thanks."
 
Dont drill the HS jets as the

Dont drill the HS jets as the drill can upset the fuel flow and run leaner...replace them with 1 to 2 sizes bigger
 
why should the mixture or jets

why should the mixture or jets change at all?
Think about it!
Does a bigger engine which you really dont have require a different mixture?
Of course not!
A 10 HP and a 300 HP 2 stroke need the same mixture!
 
"Yes same air fuel ratio but t

"Yes same air fuel ratio but the bigger the engine the more fuel air it requires.

More fuel means cooler running temps in the combustion chamber, less likely to run lean, more lubrication."
 
"Does this mean that any rebor

"Does this mean that any rebore of allcylinders require re-jetting? I rebuilt my 1977 70HP bored 020 all bores, it appears to run well without changing the jets"
 
"No offense intended here to a

"No offense intended here to anyone, just my opinion perhaps.

I've overhauled/rebuild a few hundred powerheads no doubt in my 30 plus years experience, many times simply a one O/S piston replacement, other times it would be a O/S replacement of all pistons. But in any and all cases, never have I enlarged the jets, nor have I ever encountered a problem for not doing so.

The only time I have changed jets would be for a engine that is changing altitute locations. Going from sea lever to say a lake at 3000 feet would require that change.

Although larger oversize pistons are available, I personally kept my rebuilds down not to exceed using .044 O/S pistons with the majority of rebuilds using .030 O/S piston. OMC never advised a jet enlargement to my knowledge so I followed that advice...... never a problem encountered as the increased space is minimal.

Now, if you're going from a 3" bore to a 3.5" bore, that's another story."
 
My engine I working on is bore

My engine I working on is bored .30 on all cyls.
The jets ares still HS=62d stock (per manual) ..Note I am not the original owner ..Hope this helps ..
 
Same here Joe. I have never in

Same here Joe. I have never increased the jet size either. Never had a problem.

I know the rebuilders advise you to do this along with using 94 octane fuel that contains no alcohol.
 
I have a '85 Johnson 70 th

I have a '85 Johnson 70 that was rebuilt and bored .030 over. Ever since it acts like it is starving for gas when I try to accelerate. It currently has 52D hs jets. What size is 2 sizes bigger? I am not sure how the numbering scheme works.
 
"The 52D high speed jet(s&

"The 52D high speed jet(s) are the proper size for the 1985 70hp Johnson. A larger size will do nothing but cause the engine to run rich.

Did you have "all" of the carburetors dismantled, cleaned thoroughly, and rebuilt with complete carburetor kits during the rebuild process? This includes manually cleaning those high speed jets. If not, do so.

Hesitation on that model is caused by fouled carburetors, clogged/restricted high speed jets, having the throttle butterfly opening too soon (synchronization wrong), or a sticking timer base under the flywheel.

However, to answer your question, two sizes larger would be a 54D, part number 321407."
 
"ENGINE SPECS TO IMPROVE YOUR

"ENGINE SPECS TO IMPROVE YOUR REBUILD.here are some other thoughts--

1986 AND UP 70HP OMC increase main jet one size.

1989 AND UP 60HP OMC increase main jet one size.

V4 and V6 Crossflow OMC set ignition timing at 24 degrees instead of 28.

1985-92 V6 Looper OMC install #65 main jets in engine with #62 main jets.

All V6 Mercury, increase main jet by .002

All V6 Mercury, retard timing 2 degrees from original spec.

Mercury, 1987 and up 3 cylinder, 70-90HP, increase main jet by .002

Mercury, 1987 and up 47 cylinder, 100-125HP, increase main jet by .002

Mercury V6 EFI, verify fuel pressure. Minimum, of 39 psi

Chrysler/Force 3 and 4 cylinder engines, retard timing to 28 degrees instead of 32"
 
"more tips-> • Install .

"more tips-> • Install .002" larger jets in carburetors.
• Max timing MUST be retarded 2 degrees.
• Max timing MUST be set with engine running over 4500 RPM & under load. DO NOT STATIC SET MAX TIMING.
• Re-torque cylinder heads to specs.
• After 1 hour of break-in, allow engine to cool and retorque heads.
• On 3 Cylinder engines, replace water pump with new high pressure water pump.
• On 3 Cylinder engines, drill and relocate overboard sensors.
• On 3 Cylinder engines, check latest OMC service bulletins and jet carburetors accordingly. THIS IS VERY IMPORTANT.
• Use 92-94 octane premium fuel.
• Clean and refill oil tank with TCW-3 oil.
• Mark oil tank to verify oil comsumption during double oil usage of break-in period.
• Run double oil during the first 30 gallons of fuel.
• If running oil injection use 1 pint oil per 6 gallons gas.
• If no oil injection, use 1 quart oil per 6 gallons gas.
• OBR recommends installing water pressure gauge to monitor water flow.
• OBR suggests removal of oil injection system or updating to latest VRO pump.
• OBR recommends you replace water pump and gasket at time of powerhead replacement and every 2 years afterwards."
 
"Thank you Joe Reeves and jwbm

"Thank you Joe Reeves and jwbmarine. I think I now have all the info I need to finally cure this problem. When I checked my throttle adjustment I found that the butterflies were beginning to open before the line on the cam pointed to the center of the roller. I corrected that and just need to get a chance to test run the boat in the lake. Unfortunately the weather in Western NY has been horrible for fishing and boating lately. If this throttle adjustment doesn't cure the problem I will try the larger jets. They are not that expensive anyway. I have already thoroughly cleaned and rebuilt the carbs, checked the compression, checked all the fuel lines, made sure the little in line filter was clean etc. The timer base under the flywheel seems to be moving freely as well."
 
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