Thermostat housing hole.

[Sea Rider]

Don't know if adjusting all 3 carbs to meet 15 mm setting it's a exact Mars science, there should be some small gap tolerance. That info should be stated in the Yam's 40 HP Service Manual which no one seems to have a copy to check that out. When the fuel pump delivers fuel will fill the carb's bowls under some pressure which should pass through the cleaned needle's seat passages nicely without effort.

Before assembling the carbs back on the motor, could check each carb individually. With carb siting on a flat surface connect a fuel hose direct on each carb's fuel entrance, prime the bulb till firm and check for fuel spills if any. On middle carb must close the other side of the T fuel connector for the test.

Positively sure that when priming the bulb till firm all the carb's needles will close nicely on their respective cleaned seat and previous fuel spills will be canceled forever. Fingers crossed!!

Happy Boating​

 

[Douglasdzaster]

Don't know if adjusting all 3 carbs to meet 15 mm setting it's a exact Mars science, there should be some small gap tolerance. That info should be stated in the Yam's 40 HP Service Manual which no one seems to have a copy to check that out. When the fuel pump delivers fuel will fill the carb's bowls under some pressure which should pass through the cleaned needle's seat passages nicely without effort.

Before assembling the carbs back on the motor, could check each carb individually. With carb siting on a flat surface connect a fuel hose direct on each carb's fuel entrance, prime the bulb till firm and check for fuel spills if any. On middle carb must close the other side of the T fuel connector for the test.

Positively sure that when priming the bulb till firm all the carb's needles will close nicely on their respective cleaned seat and previous fuel spills will be canceled forever. Fingers crossed!!

Happy Boating​

I figured it out. The orifice in #1 is messed up. It’s quite a bit bigger than the other two. I’ll have to take it to town and have it removed in order to replace it. See pics for comparison.

 

[Faztbullet]

Here ya go...

 

[Douglasdzaster]

Here ya go...
View attachment 332491View attachment 332492View attachment 332493View attachment 332494

Thanks but I think these specs are for 2 cylinder mine is a 3cylinder model 40 MSHQ 1992, and markings on carburetors don’t match any of these.

 

[Douglasdzaster]

I figured it out. The orifice in #1 is messed up. It’s quite a bit bigger than the other two. I’ll have to take it to town and have it removed in order to replace it. See pics for comparison. I have extra fuel line I can hook up a single hose to test each carburetor. Good idea. Another sour stomach moment when I figured out the seat was messed up. Air passes through the same with or without the needle and float. It opens completely. You can see how it’s out of shape.

 

[Douglasdzaster]

I figured it out. The orifice in #1 is messed up. It’s quite a bit bigger than the other two. I’ll have to take it to town and have it removed in order to replace it. See pics for comparison.

I have some extra fuel line I can hook up to test each carburetor. Good idea. You can see in the pictures how #1 seat is out of shape. It lets the same amount through with or without the float and needle when blowing through it. Another sour stomach moment.

 

[Faztbullet]

These are spec for 1990-91 Yamaha 3 cylinder.... Carbs may have a different number but all the Kehin set up the same...

 

[Sea Rider]

Gee, carb 1 still with hidden issues, luckily was detected on time before assembling back all 3 carbs in a row. What stated in the Carb Inspection Data has been plainly checked and fulfilled, you can save money by cleaning the pilot, main jet and nozzle instead than throwing them away if highly contaminated as suggested. The issue is will you go after such a long cleaning, polishing task or not and if money it's a must save or not ?

On 2 strokes motors running carb dry will avoid long carb soaks and small parts cleaning, polishing, whatever needs to be done. My carbs with 1 K run hours maintains all the parts factory delivered with with the sole exception of the bow's gasket, fuel pump diaphragms that were changed as a preventive maintenance as were somewhat screwed by E-8 fuels. After watching the parts scheme can hook a fuel hose direct at each carb's fuel connector entrance instead than doing so at each individual fuel line.

Happy Boating​

 

[Douglasdzaster]

Gee, carb 1 still with hidden issues, luckily was detected on time before assembling back all 3 carbs in a row. What stated in the Carb Inspection Data has been plainly checked and fulfilled, you can save money by cleaning the pilot, main jet and nozzle instead than throwing them away if highly contaminated as suggested. The issue is will you go after such a long cleaning, polishing task or not and if money it's a must save or not ?

On 2 strokes motors running carb dry will avoid long carb soaks and small parts cleaning, polishing, whatever needs to be done. My carbs with 1 K run hours maintains all the parts factory delivered with with the sole exception of the bow's gasket, fuel pump diaphragms that were changed as a preventive maintenance as were somewhat screwed by E-8 fuels. After watching the parts scheme can hook a fuel hose direct at each carb's fuel connector entrance instead than doing so at each individual fuel line.

Happy Boating​

I think everything else is good Pilot jets etc. have been changed before. And I’ve been cleaning everything for a week. What hasn’t been polished to new has been replaced. Nozzles are nla but I got them clean. The seats I’m sure are the original or at least close. I’m hoping by going ahead and getting all three removed and replacing those I’ll be starting fresh. Running non ethanol fuel, not letting fuel sit in them like you’re saying. I’ve already installed the water separator. Maybe I won’t have to open them up for awhile. Meanwhile I’ll be keeping my eye out for nozzles.

 

[Douglasdzaster]

These are spec for 1990-91 Yamaha 3 cylinder.... Carbs may have a different number but all the Kehin set up the same...
View attachment 332499

You’re right they are Keihin carburetors. Can’t find the nozzles anywhere. Think with so many of those carburetors out there it wouldn’t be so hard to get some of the parts. After I replied I noticed they were I recognized some of the specs and parts. My bad

 

[Sea Rider]

You said that been using a carbon remover product mixed with fuel since you bough the motor, what about previous owner ?. Those products are only good if constantly used on new out of the box motors. Won't do a thing on motors that have already carboned up, better save money. If wanting to go to the next high tech decarbonization level before assembling the large air silencer back on the carbs, turn it upside down on a flat surface and drill a 2 mm orifice side to side as seen. Order a can of CRC Engine Tuner....



Once the motor is running will go through a real fast decarbon process, day nigh difference compered to any other carbon remover product poured into the fuel tank if not used since day 1...


Seems all main nozzles are alike in length with variations on the number of orifices seen at left and at middle. Compare it against a Yam 40 nozzle and check how much differs...

Happy Boating​

 

[Faztbullet]

That is the emulsion jet tube. The holes before/after step controls the fuel transition from off idle to WOT. I change to larger holed ones these all the time on my Predator motors I build for my racing go-carts. Attached is pick on how it works..

 

[Douglasdzaster]

You’re right they are Keihin carburetors. Can’t find the nozzles anywhere. Think with so many of those carburetors out there it wouldn’t be so hard to get some of the parts. After I replied I noticed they were I recognized some of the specs and parts. My bad

You said that been using a carbon remover product mixed with fuel since you bough the motor, what about previous owner ?. Those products are only good if constantly used on new out of the box motors. Won't do a thing on motors that have already carboned up, better save money. If wanting to go to the next high tech decarbonization level before assembling the large air silencer back on the carbs, turn it upside down on a flat surface and drill a 2 mm orifice side to side as seen. Order a can of CRC Engine Tuner....

View attachment 332582

Once the motor is running will go through a real fast decarbon process, day nigh difference compered to any other carbon remover product poured into the fuel tank if not used since day 1...
View attachment 332593

Seems all main nozzles are alike in length with variations on the number of orifices seen at left and at middle. Compare it against a Yam 40 nozzle and check how much differs...

Happy Boating​

I was wondering if they were still made just a different part number for a different carburetor. I’m not where I can look at the silencer right now. Drill the holes and ta turns spray in them with the engine running? Is that better than directly in the carburetors with the silencer off? Will the CRC say for marine or just engine tuner. I think I’ve seen it in Walmart here. I’m going to start another thread about removing those frozen seat valves before bothering the guy in town again. His main business is building hot rod engines to restoration of antique cars. He didn’t even charge me last time and I felt bad for bothering him. I mentioned me wanting to clean the cooling passages and removing 14 bolts. I kind of got a look the way my wife looks at me sometimes. Lol

 

[Douglasdzaster]

That is the emulsion jet tube. The holes before/after step controls the fuel transition from off idle to WOT. I change to larger holed ones these all the time on my Predator motors I build for my racing go-carts. Attached is pick on how it works..
View attachment 332594
View attachment 332595

So maybe the tubes for a 50hp will work?

 

[Sea Rider]

If the noozles are clean and shinny no need to replace them. Was checking Keihin's web page, lots of carbs for motorcycles. Doesn't show outboards carbs but there's a contact form, check with them. The Yam 40 HP nozzles could be found in other carbs as well, the issue is to know precisely which HP motor and brand to look for.

Drilling 3 small orifices its much better than removing the whole air silencer and sprying CRC into each throat everytime will need/want to do so. The idea is to spray CRC shots inserting the red cannula in the orifices and voila. All my motors, my club's and my friends motors have drilled orifices, are beginning to love the wonders this gold canned product does for 2 strokes motors if applies regularly. If the orifices is what worries you, tape them over with a small round portion of Duct Tape, Duck Tape, 3M electric tape. Just order CRC Marine Tune-Up Decarbonizer.
​

Happy Boating

 

[Faztbullet]

You can also use the Seafoam spray

 

[Douglasdzaster]

If the noozles are clean and shinny no need to replace them. Was checking Keihin's web page, lots of carbs for motorcycles. Doesn't show outboards carbs but there's a contact form, check with them. The Yam 40 HP nozzles could be found in other carbs as well, the issue is to know precisely which HP motor and brand to look for.

Drilling 3 small orifices its much better than removing the whole air silencer and sprying CRC into each throat everytime will need/want to do so. The idea is to spray CRC shots inserting the red cannula in the orifices and voila. All my motors, my club's and my friends motors have drilled orifices, are beginning to love the wonders this gold canned product does for 2 strokes motors if applies regularly. If the orifices is what worries you, tape them over with a small round portion of Duct Tape, Duck Tape, 3M electric tape. Just order CRC Marine Tune-Up Decarbonizer.
​

Happy Boating

I bet it’s going to smoke like a train the first time at least. Will I need to change the plugs afterwards?

 

[Sea Rider]

Definitedly will smoke but not that heavy as when doing the decarbon process on a 2 stroke 2 cylinder one carb motor in which will need to squirt more product than on single independent carbed motors. The decarbon process should be done at terra firme soon after the motor run healthy at wot at open waters for some minutes.

If the spark plugs are new don't need to change them as will be cleaned during the decarbon process. Just check that are gaped tight to 1.0 mm, the plug when turned up side down must not fall from the filler gauge, if so, re gap as needed.

Happy Boating​

 

[Douglasdzaster]

Definitedly will smoke but not that heavy as when doing the decarbon process on a 2 stroke 2 cylinder one carb motor in which will need to squirt more product than on single independent carbed motors. The decarbon process should be done at terra firme soon after the motor run healthy at wot at open waters for some minutes.

If the spark plugs are new don't need to change them as will be cleaned during the decarbon process. Just check that are gaped tight to 1.0 mm, the plug when turned up side down must not fall from the filler gauge, if so, re gap as needed.

Happy Boating​

I haven’t gone anywhere. Almost done with the home repair then back to the boat soon. All parts are here. Had to order the CRC should be here just in time. I will post how it’s going. Meanwhile I’ve got a tachometer and ir gun to check on the temperature and a couple other toys. Lol

 

[Sea Rider]

Welcome back, home repairs specially the important ones can't wait that long or the Admiral will be mad at you. Which brand tach/model do you have, is it a dial or induction one ?

Happy Boating​