1978 85 hp Chrysler with 1991-1994 90 hp Carbs

[ryanweber_20]

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?

 

[ryanweber_20]

Here is some more information. I set the WOT timing to 32 degrees before TDC using a voltmeter method I found on YouTube.

Idles fine at first, but then starts to idle rough and the rpms go down as it idles.

The throat size of the carb on the intake side is 1.560" and the throat on the intake manifold is 1.600" in diameter and tapers down from there. Also, both carbs (WB-21 and WB-100) use the same carb to intake gasket.

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).

 

[Trophy83]

Im dealing with a similar problem. Mine runs great with the cover off (holds idle) but when i cover her up goes down and wont hold idle, some said exhaust leak under the cowl choking out air, Im drilling 4 1 inch holes in the cowl in about 1/2 an hour ill let you know how it works. Im not chasing an exhaust leak on a 37 year old engine. lol

 

[jerryjerry05]

The problem with drilling holes:
You can flood the motor and suck a lot of water into the lower carb.

 

[The Force power]

Have you read any of the sticky notes at the top of this forum, here's one;

https://forums.iboats.com/forum/eng...ler-outboards/616464-carb-and-timing-tutorial

 

[The Force power]

The problem with drilling holes:
You can flood the motor and suck a lot of water into the lower carb.

somebody is going to be shopping for a bottom cowl

 

[ryanweber_20]

Thanks for the suggestion of the sticky notes. I watched Frank's YouTube video and I didn't see any difference between his and mweverett (which is the instructional videos I used to set the timing and throttle linkages). Unfortunately, there wasn't anything in there that is going to help with my situation.

 

[The Force power]

How old are the fuel-lines & when was the the fuel pump rebuilt?
Are the carbs. properly cleaned?
Have you tried it with air/fuel mixture turn out a bit more?