9.8 Has Me Nearly Beaten

timmeraw

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Jun 10, 2008
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258
I have a 1980 Merc 9.8 with the Tolloston Carb that is giving me fits. It starts up ok....runs for a 10 secs or so and gets choked to death with fuel....as it takes it last breath it comes running out of the carb throat like hell.

What I have done so far:
* Replaced the engine side of the fuel line connector(activator pin got stuck in the corroded ball bearing or whatever in the line connector end and ruined the O-ring). Also replaced the fuel line connector) - No fix

* Took carb apart soaked everything with carb cleaner and cleaned it all. Drove 40 miles each way for an $8 inlet needle valve - No fix

* Interupted kind marine tech at work nearby and had him adjust the float level and set the idle screw to 1 1/4 turns out from seat - No Fix

* He recommended a new float if problem continued so I ordered and replaced the float with a new one - No Fix

That is where I am so far. Now when I said I soaked everything with Carb cleaner that included the old styrofoam-like float, and all of the various pieces/gaskets etc in the layers making up the fuel pump assembly. They appear to be still intact and in shape etc but could that
be the issue with the over loading of fuel?
Local Merc dealer wants $67 for a complete carb kit that includes all kinds of stuff besides just the gaskets and the stuff I have already replaced.

Any suggestions/help will be greatly appreciated thanks.
Tim
 

CN Spots

Lieutenant Commander
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1,612
Re: 9.8 Has Me Nearly Beaten

I'm on the second rebuild in the last two years for a friends 9.8. Most of his carb's problems resides in the fuel pump gaskets. You can buy just the fuel pump gaskets for between $9-20 depending where you look. Got mine for $16 at the local marine dealer.
 

timmeraw

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Re: 9.8 Has Me Nearly Beaten

Wow thanks for the quick responses guys. Laddies...#14 is listed as the Welch Plug (Body Channel). I assume that is referring to the plug on inside of bowl chamber that looks like the foil seal on top of a coffee can etc.? If so it is in and intact as far as I can tell.

As for the gaskets. In looking at that parts diagram it lists one gasket(#20) and one diaphram(#21) between the body of the fuel pump(#22) and the carb body. Looking at mine now tore apart it actually has the diaphram sandwiched between two gaskets?

In any case the gaskets seem fine as does the diaphram but I would gladly throw a new gasket kit at it if I could find one. Local marine shop only has the whole expensive rebuild kit. Could you perhaps provide me with a part# and supplier by chance?

How about this one?
http://buyboatmotorparts.com/Mercury-Carburetor-75-50HP-Gasket-Kit-18-7007-P665625.aspx

Thanks,
Tim
 

Laddies

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12,218
Re: 9.8 Has Me Nearly Beaten

Yes, that will work and that number is a Sierra part number it's available on tyhis site or from NAPA, CarQuest or most parts stores. The flooding can only be caused by a leaking inlet needle, improper float height 1/4" with the carb upside down from the bowl flange to the bottom of the float, leaking fuel pump diaphram as you have changed the float and that ruleds that out.
 

timmeraw

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Re: 9.8 Has Me Nearly Beaten

Ok I have ordered it from Napa and will be in first thing tomorrow. Hopefully this will solve the problem. I have adjusted the float and replaced the inlet needle so it has to be the diaphram/gasket issue. Fingers crossed.
 

ctoshack

Cadet
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Sep 9, 2009
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Re: 9.8 Has Me Nearly Beaten

Trade you my carb for your motor lol I can't get mine cooling properly
 

timmeraw

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Re: 9.8 Has Me Nearly Beaten

I am out of ideas.....today I replaced all of the gaskets and Diaphrams etc and verified that the the float is adjusted correctly and the slow speed idle mix is out 1.25 turns from lightly seated, and the new inlet needle valve does not appear to be sticking ...at least with carb and bowl off and turned upside down.....even if it was would just starve it not flood it right?

It is still pooring gas out of the throat and starts right up first time on re-install but within seconds bogs down and gets choked with fuel and dies. Once it is dead a bunch of fuel poors out.
Tank lines and connectors are fine as they work with my other Mercs, vacuum hose is connected to carb.

I am thinking it might be something clogging the inlet port. I squirted a bit of carb cleaner into the brass seat with the needle out upside down and it does not drain out as I assume it should. I inserted a small wire and it only goes in about 1/8 to 1/4 inch and hits something. Should it feed in deeper? I sprayed carb cleaner and compressed air into the hole but still no drain.

How does that brass seat come out? I assumed it is threaded but it is not moving and I am afraid to damage it.


What am I missing?

Good news is I am sure getting quick at removing and reinstalling the carb :)
 

timmeraw

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Re: 9.8 Has Me Nearly Beaten

FINALLY!!!!! I have is solved. Like the days when I used to fix computers, I did a couple of things and when it works I am not exactly sure which fixed it.

I cleaned out the inlet port really well with carb cleaner and compressed air but the major thing I did was..... I was always wondering why all of the parts pictures for this carb only showed two things between the fuel pump body and the body of the carb. First the plastic or composite looking diaphram and a gasket. Mine had first a rubber gasket/diaphram first, the diaphram and then a gasket making three. I removed the extra one.

It is now idling nicely and no flooding...and has all new gaskets, float, inlet needle etc so should be good for a long time now.

Thanks for all your assistance and I learned that such a simple little carb can really cause a lot or frustration, running around and for me, throwing a lot of parts at something to fix it.

Next up.....carb kit for an old classic Johnson 25 RD16. Stay tuned for more questions
 

timmeraw

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Re: 9.8 Has Me Nearly Beaten

NOT SO FAST..... elation to frustration overnight. It was running like a champ last night for at least 20 minutes as I played with the throttle, FWD/Rev, set idle etc. So confident I changed the lower unit oil and even gave the foot a good cleaning and a spanking new paint touchup.

This afternoon I hooked it back up to the hose just to convince myself that the nightmare was over and guess what...it isn't. Same thing...starts up right off....boggs up and quits.. fuel spitting out heavy again. I let it sit...pull the fuel line off...it starts and runs well until bowl empties.

Gotta be float and/or inlet needle not closing. I am baffled.

What the heck am I missing???? Besides a qualified mechanic :)
 

sschefer

Rear Admiral
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Nov 13, 2008
Messages
4,530
Re: 9.8 Has Me Nearly Beaten

Bad fuel bayonet, vent plugged, fuel tank pickup tube plugged, bad fuel tank fitting, pinched fuel hose, something stuck in the fuel hose. Just throwing out some ideas here, looks like you've covered everything else.

I lent out a gas tank once and the guy I lent it to put a rolled up piece of tape in the end of the hose to keep it from leaking. I never saw it and he never told me. I found it... out in the middle of the lake!

Guess who took a little swim the next time we went fishing together. He said, what tha heck did you do that for... I pulled out that little role of tape and all he could say was Oh...S...
 

timmeraw

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Re: 9.8 Has Me Nearly Beaten

Thanks for the ideas but most of them would cause starving not binging on fuel. Getting WAY too much. I wish I had a good picture of all of the gaskets and diamphrams etc that make up the fuel pump layers. I know that they only fit on one way but perhaps I am missing something or wrong order...my mind says no but? There is no rubber seat or anything on the inlet needle when it has that rubber tip on it and it should seat right into the brass ......seat...I guess I answered my own question.

My neck is sore from shaking my head...just tore it all apart again and cleaned and put everything back together....same thing.

Jeeeesh
 

CN Spots

Lieutenant Commander
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Oct 19, 2005
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1,612
Re: 9.8 Has Me Nearly Beaten

I posted the same questions about the gasket order on my 9.8 as well and had no takers. I know what you're talking about... one's thin rubber, the other looks like fine kevlar. Your's only shows using one in that diagram, mine uses both types. When I got the carb, one of the diaphram valves on the thin rubber gasket had been sucked into one of the inlet holes on the fuel pump. That causes mondo probs. Carefully take your pump apart and make sure this has not happened.
 

timmeraw

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Re: 9.8 Has Me Nearly Beaten

Common guys...someone must have some ideas here? Something is causing a fuel overload....recap...so far I have replaced float, inlet needle and all gaskets/diaphrams, cleaned and cleaned and blew out all ports etc.
I can keep it running by constantly pulling choke and then quickly returning it to open. It regains itself...revs to good idle and then bogs down to near death and I repeat. After a bit of this it will idle(and I use that term loosely) by itself with Choke 3/4 engaged.
 

timmeraw

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Re: 9.8 Has Me Nearly Beaten

Ok so I am a glutton for punishment. I am back at the process of pulling off the carb, farting around with it, and putting it back on. Waiting with baited breath as I fire it up only to see the old familiar .... start right up followed by a quick drop to stall...fuel spewing everywhere.

I have another 9.8(though a bit older 110) that runs well...so I pulled the carb and installed it. It ran pretty well though a bit fast. Therefore my problem is definately in the carb. I noticed that the 110 needle valve had a spring and was shorter than the newer one. So I tried it in my carb ...nope. Tried it in my carb with the other float....nope.

Tore both fuel pump bodies apart to ensure that I have gaskets and diaphrams in correct order etc. The only thing I have not removed/tried to clean is the high speed nozzle. I tried a bit to turn it out but it seems to be pretty tight so I stopped fearing to break something.

I am running out of ideas here and have replaced just about every carb part there is.

Help!!!!
 

Wingedwheel

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Jun 16, 2009
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1,071
Re: 9.8 Has Me Nearly Beaten

I know you said you replaced the float and re-built the carb, but did you replace the float needle and seat?. If not an easy way to re-seat the needle is to use valve lapping compound in the seat and spin the needle back and forth a few times until everything is nice and shiny. It may be that its not seated properly and allowing the bowl to continually flood. Just a thought.
 

timmeraw

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Jun 10, 2008
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Re: 9.8 Has Me Nearly Beaten

I replaced the idle needle but the seat is brass and punched into the carb. The needle has a rubber tip on it so greasing really is no option(the old one looked fine to me btw). It is getting/allowing too much fuel obviously but I cannot readily attribute it to the seat. I have played with adjusting the float many times and even set it past level to shut off early but still the same problem. Start easy....bog down immediately with too much fuel.

I am at my whits end. Argggggg.
 

timmeraw

Petty Officer 1st Class
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Jun 10, 2008
Messages
258
Re: 9.8 Has Me Nearly Beaten

OK I am getting closer I think. I read somewhere on here or another forum that on these 9.8 motors the reed valves are wrapped around the camshaft or something and someone suggested a fix to a problem with flooding is to pour isopropal alcohol into the head to clean the guck out of the reeds.

I thought it worth a try and poured a couple of ounces in and not being patient enough to wait like the guy suggested, put the carb back on and guess what. It started up and stayed running for a while. It did begin to bog down and as usual if I manually throttled it at a high rev all was well but when I put it back to idle the same thing started happening ...gas dripping and it bogged down.

Now my question.....Is there a way to try and clean those reeds thru the carb hole using either more alcohol or would something else work also? Kinda worried about using Carb cleaner etc. I dearly hope that the reeds are not hosed but the initial good running has me hopefull that they are just mucked up.

Ideas to try and clean. Getting at these I understand involves pulling the head and tearing down to cam etc which I hope not to do.

Thanks,
Tim
 
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