Vacuum on carbs 1 & 2 a lot more than 3... What gives?

[honda460ex]

What could be some possible causes for this issue? It's an '83 115hp inline 6. Carbs have been cleaned three times. They are spotless. The motor starts to miss just after you start it. The idle screw for carb 3 doesn't really do anything much when adjusted in or out. And like I said, they have been cleaned three times and were spotless every time. All small holes within the carb were and are clean... So please don't tell me to clean them again, they ARE clean. My problem lies deeper than that. You can place your hand over carb 3 and the motor will keep on running for a little while before it will finally die down and start dripping fuel out of the front of the carb.. The carb IS getting fuel. I really believe the lack of vacuum though is causing it to not pull enough fuel and hence the miss at idle. Spark plug 5 is slightly wet. Not much, but some. Spark plug 6 barely has any fuel on it at all. Almost totally dry. Can reeds cause this problem? Or a seal between the case? All other gaskets and seals are replaced, literally, EVERYONE. Some in depth help please.

 

[honda460ex]

Re: Vacuum on carbs 1 & 2 a lot more than 3... What gives?

Oh yeah. It won't idle below 1,000, lucky if I can get it to idle around 1,200 on muffs. Did a lync and sync on it today with no luck. Timing is set correctly.

 

[honda460ex]

Re: Vacuum on carbs 1 & 2 a lot more than 3... What gives?

One more thing to avoid a further question. Yes I have checked compression and yes they are all within an operable range.

 

[jimmbo]

Re: Vacuum on carbs 1 & 2 a lot more than 3... What gives?

When you cleaned the carbs, did you replace the inlet needle and seat, and also adjust the float setting?

 

[honda460ex]

Re: Vacuum on carbs 1 & 2 a lot more than 3... What gives?

I'm sorry, but I do know the carbs are not the issue. I know this for a fact. The motor is not pulling enough vacuum through carb 3. Even spraying WD40 or anything flammable with an oil base into that carb has no bearing on how the motor operates at 1,200 rpms. The vacuum being pulled through carb 3 is at least half of that of carbs 1 and 2. Without the proper amount of vacuum it would be impossible for a carb to pull fuel through the idle needle. The lower the motor idles, the less vacuum it has, less vacuum it has the less fuel it pulls. With the little amount of vacuum I have as is an idle right now below 1,200 rpms is impossible. To answer your question though I did not change them out, only cleaned them. I changed them out last year. Like I said too, if you hold your hand over carb three gas will back flush out of the carb but will not affect the way the motor runs hardly at all. So I know the carb is getting fuel and by capping your hand over it it is creating a greater vacuum through the jets of the carb and then pulling fuel up to the throat of the carb, just not enough vacuum to pull it in the motor and through the reeds. I am getting to the point that I think the reeds are getting replaced and a recheck on all of my gaskets and seals. Something has got to be leaking vacuum somewhere. Thanks for the input, and I hope I didn't seem rude, I just know that's not the issue I'm having in this case.

 

[DamianJP]

Re: Vacuum on carbs 1 & 2 a lot more than 3... What gives?

Just throwing it out there and using process of elimination ,if you take the carbs out of the equation move to the next item. The next thing to look at would be intake reeds. Mabey they are bent , broken and/or worn.

Seems like there are 3 reed block assemblies, 1 for each 2 cylinders. Could it be possible that the reed block assemblie / reeds associated with the 5/6 cylinders is not working the right way? I think its a good place to start.

Like you said compression is good. When you tested compression did you just keep cranking till the needle stopped or did you crank each cylinder with the same number of cranks (Exp. 5 cranks)?


Just checking because you got good readings (with just air) but the motor cant suck in a air/fuel mixture because of the reed(s) area not working I think. I would think the reed(s) area not working right would give a weird reading too on the comp gauge.

Was just thinking mabey the crank till stop would mabey mask the reading, because you'll eventually get you max reading regardless of how the reed assembly/reeds are working. Then I was thinking mabey the 5 crank test would show that the bottom 2 cylinders are infact lower than the upper ones. Again Im unsure if a reed assembly/reed(s) that arent working the right way would even effect a comp reading. Im trying to help you and learn at the same time. But I think these reed assemblies/reed(s) is your culprit.




DamianJP

 

[honda460ex]

Re: Vacuum on carbs 1 & 2 a lot more than 3... What gives?

Well, this motor is likely to put me in the crazy house. Changed the reeds and redid the lower crankshaft seals again. Seems carb 3 is pulling slightly more vacuum but still won't really die when placing your hand over it. Have only had it on muffs and I can tell it still isn't right. Now I have a misfire here and there, which was there before too. The motor idles lower than it would but fluctuates from 700-1,100 now with the intermittent miss. Pulled all plugs after being on muffs. Plug 3 looked to have some mixture of gas/oil water on it. I replaced the water jacket cover again for the second time already too... So apparently the only thing I can think of is that something is warped, otherwise why would it keep leaking every time I put a new gasket on!?!? It's starting to infuriate me... Anyone have any similar experiences? The other thing I noticed as well is that after taking it off muffs and parking it in the garage I got a gas/oil water mix leaking from the lower unit around the prop. So the only logical thing I can think of again is that the lower crankshaft seals STILL are not sealing all the way. Thoughts? I am ready to take my .30-30 to this thing... Really and truly, I think it would make me feel better. Also, plugs 5 and 6 were not very wet at all suggesting to me they are not getting much fuel. All cylinders are getting very good fire also. And here is the kicker to make everyone cringe, I fired it off of muffs for a few seconds too. I know, horrible, but at this point I don't care. The results of that.... It idles GREAT with no miss.... Which to me suggest more and more that I STILL have a water intrusion problem mixed with a possible vacuum leak... Anyone ever have a similar problem? Please help me out...

 

[Chris1956]

Re: Vacuum on carbs 1 & 2 a lot more than 3... What gives?

Maybe the crankcase is leaking? Did you install the crankcase cover seal? I would smear it with grease to help it seal. Did you torque the crankcase bolts in sequence? Is the seal on the lower end cap good? Is the bottom carb base gasket good?

 

[Chris1956]

Re: Vacuum on carbs 1 & 2 a lot more than 3... What gives?

Is the lowest transfer cover well sealed?

 

[honda460ex]

Re: Vacuum on carbs 1 & 2 a lot more than 3... What gives?

I thought that possible too, but i replaced it when I replaced the reeds and put a thin bead of gasket maker on both sides all the way up and down both sides. And I did follow the manual on torquing them in three stages and crossing to each one it said to next. I replaced all of the carb base gaskets too. Any way the very end of the crank could be slightly warped you think to cause the vacuum leak? As far as #3 getting water in it I think I am just going to have to tear the water jacket cover off again and look for a possible hairline crack or something in the powerhead. That's about the only idea I can figure on that one.

 

[Chris1956]

Re: Vacuum on carbs 1 & 2 a lot more than 3... What gives?

Lower end caps can have as many as 3 seals in them. See if the crank has grooves worn into it by the seals. If so, change the location of the seals in the end cap. Lower end cap has an oring as well. Why did you replace the reed valves? Usually stock reeds last forever..

 

[honda460ex]

Re: Vacuum on carbs 1 & 2 a lot more than 3... What gives?

The first time I had the lower end cap off I put two new seals in it just the way they were before. When i put it back together I had major vacuum problems off of the lower carb. So pulled the powerhead again and sure enough, water gas/oil mixture milky white right under the lower end cap. Like you said, I didn't pay enough attention the first time to the position of the seal to the crank. The crank does have a wear spot that the upper seal fell into. So this last time around I pressed the upper seal in even further and then put a third seal in the top and flipped it upside down so the seal would not be in the groove. So it has three seals in it and I believe I still have a leak. I did replace that o-ring as well. I even used some gasket maker here and there sparingly in that area to help. I am going to pull the powerhead here in a couple of hours to find out. I replaced the reeds for a couple reasons. I wanted to be able to get my idle lower on the motor. Since I owned it early last year and it ran good then even, it did not like to idle lower than 1,000 rpms hardly. The other reason is I honed one of my cylinders slightly and put new rings on the piston. So considering I was that far into it, what the heck I thought. Process of elimination also, I wanted to make sure my vacuum issue on carb 3 wasn't associated with a bad reed.

Last night when i took it on the water it would start and idle at around 1,100-1,200 rpms. Any lower and the miss would develop. When trying to put it in gear it would want to fall on its face. Had to be quick with the throttle. It would idle fast, but not take fuel above that. Seemed like it had no power what so ever. You could click the electric choke and it would idle it down to a normal idle when in gear and sound a lot better. This motor has had more ailments in the last two months than anything I have ever seen.

 

[Chris1956]

Re: Vacuum on carbs 1 & 2 a lot more than 3... What gives?

Sounds like the idle mixture may be a bit too lean. That causes acceleration problems. Richen it up 1/8 turn at a time, top carb first, followed by mid carb and then bottom carb. Test after each adjustment.

 

[honda460ex]

Re: Vacuum on carbs 1 & 2 a lot more than 3... What gives?

Well, I pulled the powerhead once more today. I found the lower crankshaft seals are STILL leaking... Going to have to see if I can't refinish the end of crank or but a used one because obviously it must be grooved to much to far that three seals can not take care of the problem. So I am still losing some vacuum there. I went over all my electrical once more before tearing the motor down just to ensure it was not and electrical issue. Everything checked out perfectly there. Cylinders 2 and 3 had water on the plugs. Cylinder 1 looked like it possibly had a little. Read somewhere on here where some people have had problems with cracks in the powerhead causing water to get sucked nto the cylinder. So I have been looking and have found no cracks, BUT, what I did find was the water jacket cover is warped. Should have looked at that the first time I had it tore apart. One end of the cover sits at least a 1/16th of an inch higher than the other. So, opinions, think this would be my water leak? Seriously? This is my first in depth outboard experience so I don't know what kind of tolerances really are acceptable. Going to see if a local machine shop can level it out for me, but if not, I guess I am looking for another water jacket cover...

 

[Laddies]

Re: Vacuum on carbs 1 & 2 a lot more than 3... What gives?

Mercury supplies a ready sleeve to fix that problem

 

[Chris1956]

Re: Vacuum on carbs 1 & 2 a lot more than 3... What gives?

The Ready sleeve will fit the end of the crankshaft. If the machine shop cannot true up the exhaust water jacket cover, you will need to get another one. The one that is warped is the inner one, the baffle or the exterior cover?

 

[honda460ex]

Re: Vacuum on carbs 1 & 2 a lot more than 3... What gives?

Thanks for the info! The one that is warped is the inner one that has the water passages in and around the cylinder sleeves. Thinking I should have just ordered a new one. May be tomorrow before I even know if they think it's salvageable. Found brand new ones from $115-120.

 

[honda460ex]

Re: Vacuum on carbs 1 & 2 a lot more than 3... What gives?

Mercury supplies a ready sleeve to fix that problem

Know where online I might be able to get it? I am having trouble finding it...

 

[CharlieB]

Re: Vacuum on carbs 1 & 2 a lot more than 3... What gives?

Carb synch will greatly effect vacuum, as a 'leading' carb will load those cyls more such that the 'lagging' carb will not pull near the vacuum.

Pay very close attention to your carb linkage.

 

[honda460ex]

Re: Vacuum on carbs 1 & 2 a lot more than 3... What gives?

Hadn't really thought of that, don't know why, but that makes perfect sense. I will double check that when I put it back together. Thanks. I do know the lower seals are still leaking some though because I had water oil/gas mix directly under the crankshaft seals once more. I found the order catalog for speedi-sleeves, but I guess I need to take some measurements off of the crank to find out the sleeve I need first as I don't see any reference guides for them...