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1978 85 hp Chrysler with 1991-1994 90 hp Carbs

ryanweber_20

New member
Without realizing it, I purchased a 1978 85 hp Chrysler outboard which has carbs from a 1991-1994 90 hp (carb models are WB-100 and should be WB-21). I am questioning the size of the jets. The main jet on the top carb is .076 and the other two are .074 while the 1978 carb should have had .072. All three idle jets are .036, although I don't believe the 1978 carbs had a separate idle jet. From my research, 1983-1984 85 hp motors had a .050 idle jet and 1984-1985 85 hp motors had a .054 idle jet. How much does the size of the jets effect the motor performance? Any advice on whether I can make this work or do I need to replace the jets? Currently, the motor starts good, but after it idles for a few minutes it floods and dies. The idle mixture screws are at 1-1/2 turns out from the closed position. I can increase the number of turns, but is that the best way to fix it long term?
 
The idle air jets don't affect anything but the way it runs at idle.

Floods and dies or runs out of gas?
Seems the smaller jets would restrict the intake???
What rpm's at idle, in gear, in the water?
Should be 800

How well does it idle? smooth? rough? misses?

In the 90's the factory put out a service bulletin that mandates the air/screw is set at 1 turn out and left there.

But some of the older models won't run at that setting.
One of my customers(early 80's85hp) needed to have his carbs set at 3 turns out??

Measure the throat size on the carbs and the intake manifold.
They need to be real close in size for slow speed running.

The bore/stroke/piston size is different between the years.

Don't know if I answered your questions??
Maybe try iboatsdotcom and find the Force forum.
 
It floods. After it died, I unhooked the gas line, started the motor and it ran for a minute or less. Before it ran out of gas, the motor smoothed out and the idle sped up.

The tach doesn't work, so I can't confirm the 800 rpms, but I believe it is close. So far I have only started it on muffs in my driveway, so it hasn't been in the water or in gear.

Idles smooth at first, but then gets rough. I set the WOT timing to 32 degrees before TDC using a voltmeter method I found on YouTube. There's an occasional miss, but nothing drastic.

I'll measure the throat size and reply back later.

Thanks for the reply.
 
The carb throat size on the intake manifold side is 1.560" and the intake manifold throat starts at 1.600" and tapers down from that diameter. Also, both carbs (WB-21 and WB-100) use the same carb to intake gasket.

Thanks for questioning if it is running rich or lean. I had it mixed up in my mind, but based off of the idle jet size it would make more sense that it would be running lean, but it is flooding at idle. Maybe the idle problem is not associated with the jets and is something else. I did set the floats a little to the lean side (when the carb is held upside down and seated on the needle there is some daylight between the float and the base, rather than being parallel).

I'll post this to iboats.com too. Thanks.
 
The float needs to be flat, no light.

Seems like the bigger the jet, you'd run rich?
I'm not a carb expert by any strech.:0
 
Setting the float like that was an attempt to get it to run leaner.

Yes, I believe a bigger idle jet would mean it'd run rich. Since the idle jet is smaller, it should run lean, but it's not. Although, I'm definitely no carb expert either.

Thanks for the replies.
 
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