91 20hp carb question

[jim_in_day]

Help, I'm working on a 91 20hp merc 2 stroke carb. What is the correct height for the float measured from the carb flange? Thanks for the help in advance

 

[Laddies]

Re: 91 20hp carb question

From the bottom of the casting that the float bowl attachs to to the top of the float is 1"

 

[jim_in_day]

Re: 91 20hp carb question

Thanks, This motor is giving us fits, has great spart, but the bottom plug isn't firing, I think because it is getting too much fuel, the plug is washed clean from fuel.

 

[Laddies]

Re: 91 20hp carb question

If the oring seal on the top of the driveshaft is bad the engine can suck exhaust up the crankshaft spines and cause a problem like that. The center of the crank is drilled all the way thru into the crankcase.

 

[Moody Blue]

Re: 91 20hp carb question

"the plug is washed clean from fuel"<br /><br />Could it also be you have a water leak into the cyl and the plug is being steam cleaned?

 

[jim_in_day]

Re: 91 20hp carb question

ok, the carb float was way off, but that wasn't the problem. The exhause side plate gasket is new (done by another shop) so I assume that they tried to fix that. If i pull the flywheel, is the oring seal easy to get at?

 

[jim_in_day]

Re: 91 20hp carb question

bump

 

[Laddies]

Re: 91 20hp carb question

Jim the oring is on the driveshaft end of the crank

 

[jim_in_day]

Re: 91 20hp carb question

Does that mean pull the powerhead, or is the o-ring on the driveshaft itself?

 

[KIGuy52]

Re: 91 20hp carb question

I replaced the lower seal on a 20 HP that had the same problem as yours many years ago. I forgot the year, but the block said "Super Hurricane". Anyway, from what I remember, after removing the powerhead, I removed the intake manifold, then carefully pulled the crank/piston assembly out about an inch to replace the seal. That way I didn't mess up the seating on the piston rings. The whole job was pretty easy but sadly, it didn't fix the problem. Hope you have better luck.

 

[Laddies]

Re: 91 20hp carb question

Just drop the lower unit and change the oring on the shaft

 

[jim_in_day]

Re: 91 20hp carb question

Thanks Laddies, will do, I only am at the shop this week on Sat and Sun, but I will replace o-ring and see if it fixes it and post results here.

 

[Fastjeff]

Re: 91 20hp carb question

KIGuy52:<br /><br />Did you ever solve the problem and, if so, what was causing it?<br /><br />Jeff

 

[jim_in_day]

Re: 91 20hp carb question

Well, it's getting interesting anyways. This 91 20hp merc apparently has never had a thermostat in in since the day it left the factory (paint was still on bolts and gasket) Replace thermostat, still had problem. Pulled lower unit (it was getting its first water pump impellor since new at factory) and guess what ..... no o-ring . HMMMMM must have been built on friday. We didn't have an o-ring, and the waterpump kit didn't come with one (Funny, the evenrude kits do) so have to wait until next week for another part.

 

[TxShorty]

Re: 91 20hp carb question

"...but the bottom plug isn't firing, I think because it is getting too much fuel, the plug is washed clean from fuel." <br /><br />A bad fuel pump diaphragm can also cause this problem, but I'm not absolutely sure the pump pulses off the #2 cylinder on this motor.

 

[jim_in_day]

Re: 91 20hp carb question

ok laddies, the mercury dealer says no o-ring on drive shaft (it is certainly machined for one). They say that none show up on parts diagram. any other suggestions. We are stumped on this and not sure where to go next.

 

[orca]

Re: 91 20hp carb question

No, they dont have a o ring<br />Check the reed valves behind the carby, some of these motors would chip the reed valve if over reved, giving similar symptons.

 

[jim_in_day]

Re: 91 20hp carb question

Thanks whaley, will look closely, but a cursory look didn't show any problems with the reeds.

 

[Laddies]

Re: 91 20hp carb question

Jim, sorry I haven't been back, there are really 2 o/rings that seal that shaft 1 under the seal sleeve which normally doesn't have to be replaced, it is only available as a assm. with the sleeve part# 822445A1. The one that does need to be replaced every time the unit is down// Mercury Manual 90-43509 Pages 5B4+5, Picture 6, Paragraphs 1 and 2, is part number 25-86203. Whaley, you are right A little knowlege can be a dangerous thing. It's like giving a monkey a hand grenade. Get a manual and read it before giving advice--Bob

 

[jim_in_day]

Re: 91 20hp carb question

Thanks laddies i will forward that info to my partner and have him call the merc dealer for parts. We don't work on that many mercs, so we don't have all the manuals, this motor may actually force us to buy a merc manual (for the customer who is really upset with the merc dealer for not fixing it and charging 450 bucks). I will keep after this problem until we fix it and keep posting until then