200 Johnson Venom planing issue

wbcook5

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Feb 6, 2014
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Hey all, this is my first forum post so bear with me. Also, I know this topic has been discussed in other threads, but I wanted to discuss the exact details of my situation. I have a late 90's 200 Johnson Venom behind a Sprint 297 Pro. The boat is 19' long. The engine starts and idles fine, but throttle response seems sluggish. It takes too long to plane off with just myself in the boat, but will not plane off with two people. When taking off, the engine will rev between 2600 and 2900 rpm and the boat will not get up. I don't expect the boat to be a hot rod, but I think it should perform better than it does currently. I am currently running a 10" manual jack plate with 2" spacer blocks and a 23p Raker prop. I took the boat to Lawrenceburg Marine in TN, and they told me that the rings were "carboned up" and that I needed to run some Yamaha Ring Free through it and switch to Quicksilver Premium Plus oil to hopefully resolve the issue. I followed their advice as well as changing sparks plugs and installing new fuel lines from the tank to the carbs. In an act of desperation, I also added a hydro-foil but to no avail. Any advice would be greatly appreciated. If I left out any pertinent information please ask.
 

racerone

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Dec 28, 2013
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They will sound / run very well on 5 of 6 cylinders.------Post compression numbers.------And does spark jump a gap of 7/16" on all 6 leads , yes or no ?
 

wbcook5

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Feb 6, 2014
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Thank you for the response.

Compression:

port side top Stbd side top

60 60

60 62

52. 52

Spark will jump a 7/16 gap on all six leads. I don’t know if this is relevant information but, there is a lot of soot around the vent ports near the base of the prop. Just an onservation.
 

racerone

Supreme Mariner
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Dec 28, 2013
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You have a bad compression testing gauge or a motor with serious problems.----Perhaps test with another gauge first.
 

jimmbo

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May 24, 2004
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When you checked the compression, did you remove all the plugs first, and kept cranking the engine(with a good Battery) until the gauge didn't go any higher?
 

wbcook5

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Feb 6, 2014
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When you checked the compression, did you remove all the plugs first, and kept cranking the engine(with a good Battery) until the gauge didn't go any higher?

Yes, I ran the engine up to temp, pulled all plugs and cranked on each cylinder until the gauge wouldn’t climb any higher.
 

flyingscott

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Apr 8, 2014
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I would get a different gauge because that is bad compression. If the second gauge reads the same time to pull the heads.
 

wbcook5

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Feb 6, 2014
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Update:

So I went through two compression testers that auto zone had on their tool rental and both of them were bad. Broke down and bought a brand new one. I tested compression with the engine both cold and hot for comparison.

Cold
95. 95
95. 95
95. 90

hot
98. 100
96. 105
90. 90
 

Faztbullet

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Mar 2, 2008
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15,920
Rakers are only even number so I'll bet you have a 24pitch. Is it vented???? Is the the exhaust ports buried when trimmed down?
 

havoc_squad

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Mar 5, 2011
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738
I would be curious about the following:

How much distance there is at the between the lowest point of the transom and the anti-cavitation plate?

Has anything changed since it last ran good, or is this a new to you boat?

I'm leaning towards missing on one or more cylinders, either most likely fuel or throttle sync issue if it responds decently til it hits your 2600 rpm wall.

When is the last time the carbs were serviced and what type of gas has been used previously? (Ethanol or Non-Ethanol)

If you have a spare prop with less pitch in good condition, you might want to test with that after ruling out all other possibilities.

I think you would get misfires with ignition, the increase in rpm would be poor and go up and down like a roller coaster.
 
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