1990 90-hp bogging down after carb rebuild and re-rebuild!

[mitchbuck]

I have a 1990 90-hp Force that ran fine in both idle and wide open, but the cold starts became very difficult to the point of needing starting fluid. Last summer the boat would start with a flick of the key, but I had a bad fuel episode towards the end of the season. So I rebuilt my carbs last week by spraying them down with carb cleaner, then used compressed air to clean them out, and lastly installed new gaskets. I verified the floats were at the proper height and I had installed new jet needles last year. When I tested the boat the engine started and idled fine but bogged down when trying to get up on plane. So I disassembled/cleaned/reassembled them again thinking I had either assembled them incorrectly or had some debris that I missed. I retested the boat out last night and got the same results (couldn't get up on plane) so I am at a loss of what the problem is. I did an on-the-water link n synch by adjusting the air mixture screws and the throttle cam/tower/roller, but none of these helped (the throttle plates were horizontal at wide open). In addition, I primed the bulb (it was solid) while trying to get up on plane but it didn't help. To review, this what I have done so far:
1) Compression check last fall (passed)
2) New spark plugs
3) Carb rebuild (cleaned/new gaskets recently & new needles in 2013)
4) link n synch. Adjusted the throttle cam, tower, and roller as well as air mixture & idle screws.
5) New fuel lines from gas tank to carbs (last fall/this spring)
6) Fresh fuel (running off portable tank)
7) New fuel filters.

So I have no idea what could be causing the bogging especially since I have replaced/eliminated a number of variables. So I need some ideas of what to check or do next! I plan to recheck compression this weekend (even though i did it last fall).

 

[Jiggz]

Re: 1990 90-hp bogging down after carb rebuild and re-rebuild!

The fuel filter you are referring to is that the built in one in the fuel pump? Do you have a clear filter between the fuel pump and the carbs' inlet? You can just use the cheapo Fram G2 (depending on hose size connections) and a couple of hose clamps and this will help tremendously with your troubleshooting. If the clear fuel filters stays full or 3/4 full when motor bogs down, then you can assume the problem is with the carbs. On the otherhand if it stays empty or less than 1/2 full then the problem is upstream of the filter, i.e. fuel pump, hoses, primer bulbs, pick up tube, tank vent, etc. Try installing a clear filter first but if you already did what is its status when the motor bogs down?

 

[mitchbuck]

Re: 1990 90-hp bogging down after carb rebuild and re-rebuild!

Jiggz - I didn't use a clear one b/c I had purchased the filter before you suggested it. I am going to get a clear one now so I can test as you suggested. However I suspect that its downstream of the filter because I didn't have this problem before rebuilding the carbs last week. Also I have new fuel lines that are short to portable tank with fresh gas (though maybe its fuel pump?).

 

[Jiggz]

Re: 1990 90-hp bogging down after carb rebuild and re-rebuild!

The clear fuel filter will let us know where the source of the problem is. Your problem may not be a result of the carb rebuilding but more of a coincidence. Just for a wild guess, I would think it is upstream of the filter (clear filter placed between fuel pump and carbs inlet) either an air leak from the fuel hose or bad primer bulb. By chance you do not have a water separator or another fuel filter between the fuel tank and the fuel pump, do you?

 

[mitchbuck]

Re: 1990 90-hp bogging down after carb rebuild and re-rebuild!

I do but right now it is by-passed as I have a 12 gallon portable tank hooked right up to the engine via ~5ft of fuel line. I replaced primer bulb 2 years ago I hope it hasn't gone bad. I will get the clear filter and report back...

 

[mitchbuck]

The forum is finally operational again!!!!! And I have an update!

First I checked compression and got 109, 114, and 109 psi in cylinders 1, 2, and 3, respectively, and while the pressures are low they do check out (though note the compression gauge had a 12in hose attached to it which might lower those numbers).

Then I installed a clear fuel filter between the fuel pump and carbs as jiggz suggested. At wide open throttle the filter remained full and did not loose any fuel volume! So now know the issue is after the filter (i.e. Carbs or after). That's a cool diagnostic tool to have though, thanks Jiggz!

Finally, I attempted to do more tuning via the link n synch including adjusting the throttle cam, roller, throttle tie-bar, and then air mixture & idle screws when I got desperate; however, I could not get up on plane no matter what I did. What would happen is the engine would seemingly loose power/bog when trying to get up on plane, and on two occasions it cut out and sounded as if it backfired (can't confirm that's actually what it was though). Also, a couple times the engine would die or come close to dying when I would throttle back after my failed attempt to get up on plane.

So now I am at kind of a loss on what to do and check next. I wonder if it is worth tearing the carbs down yet again but this time soaking overnight in heavy duty cleaner (though I am aware some of you guys frown on this) as I only sprayed them down with carb cleaner followed by compressed air last time. I also wonder if I could have messed up something after the carbs such as the reeds? Any input is appreciated!

 

[Jiggz]

Before going back to the carbs, check the timing and if you happen to have a digital video inspection camera (borescope) check the integrity of the reed units. I have a feeling with the low compression, there is a very good chance the reed petals are bent or not seated within specs anymore. But please do the timing check first and if it checks out then check the reeds. If you do not have the borescope, then might as well dismount and check the carbs and then check the reeds at the same time.

 

[mitchbuck]

Before going back to the carbs, check the timing and if you happen to have a digital video inspection camera (borescope) check the integrity of the reed units. I have a feeling with the low compression, there is a very good chance the reed petals are bent or not seated within specs anymore. But please do the timing check first and if it checks out then check the reeds. If you do not have the borescope, then might as well dismount and check the carbs and then check the reeds at the same time.

Haha well I actually just took the carbs off again because I was getting stir crazy. Timing was checked last year but who knows it could of gotten out of wack. So what am I looking for with the reeds now that I have the carbs off? I can take some photos if need be....

 

[Jiggz]

If you look at the reed, they should be almost flat and sealing (although there is an allowance of 0.10 inch clearance), the notional reed should all be perfectly closed meaning if you shine a flashlight on one side you shouldn't see any light on the other side. Timing check is still warranted, it doesn't take much to shear a key on the shaft that could have shifted the timing hence the misfiring on high rpm. So you need to get that out of the way also. However, since you already dismounted the carbs, might as well check the reeds. Let us know of your findings.

 

[mitchbuck]

If you look at the reed, they should be almost flat and sealing (although there is an allowance of 0.10 inch clearance), the notional reed should all be perfectly closed meaning if you shine a flashlight on one side you shouldn't see any light on the other side. Timing check is still warranted, it doesn't take much to shear a key on the shaft that could have shifted the timing hence the misfiring on high rpm. So you need to get that out of the way also. However, since you already dismounted the carbs, might as well check the reeds. Let us know of your findings.

Can I check timing with the carbs removed?

I can see the reed plates but it appears that I can't really inspect them until I pull the reed plates from the engine, correct? And it appears on my engine I also have to remove both the intake manifold and reed plates in order to do that, correct? Here is the diagram:

 

[Jiggz]

That is correct! You need to remove the intake adapter which could require new gasket unless you can save the old one to pull out the v-block for the reed. Yes, you can check timing with the carbs off as long as you catch fuel from the fuel pump or better yet disconnect the fuel hose from the suction side. There is a video on the sticky post explaining how to do the timing. Or you can just do the timing when everything is back together.

 

[mitchbuck]

Thanks for sticking with me and walking me through this Jiggz! I've used that video sticky last year so it will give me something to do while I wait for the new gaskets and/or reeds to arrive!

 

[jerryjerry05]

Bad reeds won't affect the compression.
Your testing the integrity of the rings and the head gasket.
The reeds allow air in, once the piston goes past the ports in the cylinder the reeds stop to function or affect the air pressure in the cylinder.
The extra 12" of hose won't affect the compression.
You remove all the plugs?
You let the motor spin at least 6-8 times?
Or until the gauge stops going up?
If your gauge only reads 112 #average then the comp is low on all 3 (not likely) or the gauge is just reading low.
The important thing is all 3 are reading close to each other.
Get a better gauge.
I bought mine in 1986 and paid 160$ then.
Still works like a new one.
You have the choke or the enricher?
The valves in the pump could be stopping the flow?
I might have an extra pump?

 

[mitchbuck]

No Title

Update: I took the intake manifold off of the block last night to inspect the reeds. I was surprised to find metal reeds and they are look in great condition! (I can't seem to upload a photo though?). The reeds are not warped, bent, or torn as can be seen in the photos. However, the bolts holding the manifold on seemed to come out way to easy so I am wondering if maybe there was an air leak?

Jerry - I removed all the plugs and cranked the engine at least 4-5 times....maybe I need to let it go longer? My engine has the choke, not the enricher.

 

[Jiggz]

Great, reeds are in good condition so we can X'ed that off our troubleshooting. Since you already have the carbs off make sure the floats are working immaculately. If you are not sure how they are supposed to be set, ask and you shall received. But mainly the floats should be in full horizontal with the carbs inverted and should not be binding or touching the center post or the bowl. If there is spring in the hinge pin make sure it is properly preloaded to push down on the float to make sure it goes down when fuel is low. Improperly installing this spring can cause the float to stay up causing fuel starvation.

 

[mitchbuck]

Jiggz I shoulda listened to you sooner and checked that timing because it is waaaaaay off! At full throttle the 30 degree marks were 90 degrees clockwise from where they are supposed to be! So I assuming the the key is sheared b/c there is no way the marks could be that far off. So do you or anyone else know what the part # is for this fly wheel key on my engine? Is it part #60 on the following diagram ( H0906X90B), which isn't available?

http://www.**********/parts/search/Me...EAD/parts.html

 

[pnwboat]

Looks like it is available to me. Item #16.

http://www.crowleymarine.com/mercury-outboard/parts/1328_11.cfm

 

[mitchbuck]

Thanks pnwboat, you are a correct I was looking at the wrong schematic! Guess I will studying up the clymer & seloc manuals......

 

[Jiggz]

When you get a chance can you post a pic of the sheared key? It will be a good prop for others.

 

[mitchbuck]

Will do Jiggz, if there is anything left of it!