Big ole 275 Johnson

**afr** · 10-29-2016, 09:55 AM

re-adjusted everything lets see how that does

https://www.youtube.com/watch?v=d2gIdMRwfuM

**afr** · 10-29-2016, 02:05 PM

ok pointer is straight dles at 500 600 ish in gear but 1100 out of gear
cant get that to come back down ?
to windy to go for a run yet this is at the dock

**Bodhi** · 10-29-2016, 04:04 PM

Not sure bout your idle problem, but I sure do like the video......you omc guys and your johnsons!!

**afr** · 10-29-2016, 05:42 PM

Originally Posted by Bodhi

Not sure bout your idle problem, but I sure do like the video......you omc guys and your johnsons!!

the book calls for 650 and 750 both seem low to me now it might drop some when i drop the rest of the motor in the water

wind is pose to lay down tomorrow

**Capt.Insane-o** · 10-29-2016, 06:01 PM

You can't set the idle on anything omc without it in the water and or under load.

**afr** · 10-29-2016, 08:27 PM

Originally Posted by Capt.Insane-o

You can't set the idle on anything omc without it in the water and or under load.

yea its in gear with a load on it

**lilabner** · 10-30-2016, 10:55 AM

The OMC Factory Reps used a Magnahelic gauge to set the idle. They worked great. There was a kit that came with them, but when I got mine there were no more kits. I had the parts made by a small parts maker. Expensive, but worked great. This was with the big 3.6 carbs on a 4.0 liter. A little time consuming but great results. You have to be in the water, and not on a trailer just backed in, and moving at idle. Really takes two people.

**frank jackson** · 10-30-2016, 02:10 PM

Originally Posted by lilabner

The OMC Factory Reps used a Magnahelic gauge to set the idle. They worked great. There was a kit that came with them, but when I got mine there were no more kits. I had the parts made by a small parts maker. Expensive, but worked great. This was with the big 3.6 carbs on a 4.0 liter. A little time consuming but great results. You have to be in the water, and not on a trailer just backed in, and moving at idle. Really takes two people.

Could you explain this further please ...........

**lilabner** · 10-30-2016, 06:03 PM

Originally Posted by frank jackson

Could you explain this further please ...........

I'll try, I haven't used my gauge in about 20 years, but I only needed to use it once. From then on I never had a problem unless I stuck a piston. But the carbs never changed. I scanned the instructions and took pictures also. You need smooth water and someone to drive the boat that follows your instructions.
I used the large 3.6 carbs on modified 4.0 engines. They have all fixed jets. You first remove all the air bleed jets, some call them intermediate jets. Mine were all 22's. Then screw them into the adapters, and screw the adapters into the jet hole. Put rubber vacuum plugs on each hose barb in the adapters. The gauge has to be vertical. Attach the vacuum hose to the low pressure fitting on the gauge and the other end to the hose barb on the adapter, one at a time. You gotta get your mind right for this. Have the engine idling in gear with the water level about half way up the exhaust housing. You can't bury the engines in the water. Get a reading on each carb. Write them down and find what looks like the average. The gauge measures the amount of vacuum in inches of water for each carb. On a fixed jet carb you change the idle jet to change the reading, richer or leaner. On adjustable idle jets you just screw the jet in or out until all the carbs are about the same.

**flabum1017** · 10-30-2016, 07:12 PM

Originally Posted by afr

ok pointer is straight dles at 500 600 ish in gear but 1100 out of gear
cant get that to come back down ?
to windy to go for a run yet this is at the dock

Like everyone says, it has to be in the water with the engine lowered to idle down in neutral. needs the back pressure on the exhaust. If you did the link and sync right, you'll be pretty close. Change the idle timing to get it to idle in gear at 650 - 700

**Bodhi** · 10-30-2016, 10:16 PM

Originally Posted by Capt.Insane-o

You can't set the idle on anything omc without it in the water and or under load.

100% correct....omc's need the back pressure of being in the water to properly set idle. My 90 johnson was all over the place at idle till I got it wet

**frank jackson** · 10-31-2016, 12:38 AM

Originally Posted by lilabner

I'll try, I haven't used my gauge in about 20 years, but I only needed to use it once. From then on I never had a problem unless I stuck a piston. But the carbs never changed. I scanned the instructions and took pictures also. You need smooth water and someone to drive the boat that follows your instructions.
I used the large 3.6 carbs on modified 4.0 engines. They have all fixed jets. You first remove all the air bleed jets, some call them intermediate jets. Mine were all 22's. Then screw them into the adapters, and screw the adapters into the jet hole. Put rubber vacuum plugs on each hose barb in the adapters. The gauge has to be vertical. Attach the vacuum hose to the low pressure fitting on the gauge and the other end to the hose barb on the adapter, one at a time. You gotta get your mind right for this. Have the engine idling in gear with the water level about half way up the exhaust housing. You can't bury the engines in the water. Get a reading on each carb. Write them down and find what looks like the average. The gauge measures the amount of vacuum in inches of water for each carb. On a fixed jet carb you change the idle jet to change the reading, richer or leaner. On adjustable idle jets you just screw the jet in or out until all the carbs are about the same.

thank you for the reply .... I have never seen one used , I have seen something similar they used on bikes . and similar but different the use on car carbs on the old multi single barrel set ups

**afr** · 10-31-2016, 07:02 AM

Originally Posted by lilabner

I'll try, I haven't used my gauge in about 20 years, but I only needed to use it once. From then on I never had a problem unless I stuck a piston. But the carbs never changed. I scanned the instructions and took pictures also. You need smooth water and someone to drive the boat that follows your instructions.
I used the large 3.6 carbs on modified 4.0 engines. They have all fixed jets. You first remove all the air bleed jets, some call them intermediate jets. Mine were all 22's. Then screw them into the adapters, and screw the adapters into the jet hole. Put rubber vacuum plugs on each hose barb in the adapters. The gauge has to be vertical. Attach the vacuum hose to the low pressure fitting on the gauge and the other end to the hose barb on the adapter, one at a time. You gotta get your mind right for this. Have the engine idling in gear with the water level about half way up the exhaust housing. You can't bury the engines in the water. Get a reading on each carb. Write them down and find what looks like the average. The gauge measures the amount of vacuum in inches of water for each carb. On a fixed jet carb you change the idle jet to change the reading, richer or leaner. On adjustable idle jets you just screw the jet in or out until all the carbs are about the same.

wow i just heard about this over the weekend using vacuum to tune these motors
seems you need to be a magician to tune one of these