1988 175HP yamaha rough idle....Please help!

[bell47]

I've got a 175 that idles rough, and dies in neutral. You have to advance the throttle to keep enough RPM's to keep it running as well as choke it every thirty seconds or so. When you have to choke it, it runs rough, poofs some blue smoke and then idles for about thirty seconds, then start the process again. if you pull the throttle back to neutral it dies. It has new spark plugs and also runs fine at cruise. Any advice or help you could share would be GREATLY appreciated. Thanks in advance!

 

[erniefish]

Re: 1988 175HP yamaha rough idle....Please help!

clean the carbs, i had a 89, same problems,

 

[bell47]

Re: 1988 175HP yamaha rough idle....Please help!

I didn't have time today to pull the carbs so I tried a quick fix. I took off the air intake cover and shot seafoam in the carbs as it was running about 2000 rpms. It actually idles a little better now, but still really rough. I looked into the carbs as it was running and could see fuel spray in the top right of the top carb, both barrels of the middle carb, and bottom right barrel of the bottom carb. So I'm not getting fuel to some cylinders I guess. Carbs are coming off tomorrow, for a real cleaning.

 

[bell47]

Re: 1988 175HP yamaha rough idle....Please help!

So I took the carbs off today and cleaned them really well. When I put them back on...Nothing! It still idles rough, and you have to choke it all the time. I can see gas spray in all the carbs now though, so they needed cleaning. I pulled the plugs(which are brand new) and they were really black with carbon, one was a little wet, but not much. Cleaned them and reinstalled, no change. So, thinking maybe my gas was bad, I ran the fuel line into a can with new gas....Nothing/no change. Then I mixed two pints of sea foam in about a gallon and a half of gas, and ran that through,......some smoke, but didn't change anything. Checked the timing at idle....right on. Gonna get new diaphrams and gaskets and replace these in the fuel pumps tomorrow. Now I'm out of ideas.............any advice? When I did the carbs I set them back exactly like they were before.

 

[99yam40]

Re: 1988 175HP yamaha rough idle....Please help!

You need to do the link and sync like the service manual states and adjust the carbs as the specs call for.
If carbs a cleaned properly the settings in the manual will allow for proper idling and running.
Setting them back like they were will not get it, as it was not running properly before and who knows if they were set properly at that time.
If there is trash, bad fuel, or water in the system then it will end up in the carbs after cleaning no matter how much additive you put in and run through, and require cleaning the carbs again and again

 

[bell47]

Re: 1988 175HP yamaha rough idle....Please help!

I replaced the diaphrams and gaskets in the fuel pumps.(Not really the problem, but I figured it couldn't hurt on 20 year old pumps.) I removed/cleaned again/ replaced the carbs, and did the link-n-sync like the manual calls for, but I still can't get it to idle smooth, although it's a little better, and I don't have to keep the throttle advanced as much. I've adjusted the mixtures like the manual said to get it as smooth as possible, but It still has a stumble or a cough, farts some blue smoke then either dies or if I can choke it, it will clear up and run for about 15 seconds before doing it again. When adjusting the mixtures I only turned them the width of the screw driver blade for each adjustment, until it was at it's smoothest point. When I cleaned the carbs the second time, I saw no visible problems in the carbs, should I clean them again and run gas staight from a clean can to see if the fuel is the issue? The boat has a fuel filter/water seperator on it. I changed the element before running it this time, and the filter on the side of the engine is spotless. It also has new fuel lines from the tank to the engine. I feel like I'm almost there, but missing something!

 

[livebaitdrifter]

Re: 1988 175HP yamaha rough idle....Please help!

Hey
I always test compression pretty quick in the equation. Old
Yammis werent famous for puking rings like the omc's did but it cant hurt.
Compression;
fuel
ignition.
Compression easy to test so why skip it.
I always change Racor filter as soon as motor idle gets strange.
Cleaning carbs can be tricky. Take bowl apart clean metering tubes,jets, i use a kit for cleaning spray guns forcleaning orifice holes, water causes bowl corrosion i think alcohol also causes corrosion, its an oxidizer, hook a pressurized flow of water or parts cleaner into intake hose barb, watch fluid flow thru needle seat, very common clog in lower carb,
ive used weak acid to clean but be careful.
Very common corrosion area on bottom of block causes water intrusion into combustion area, almost always on saltwater motors. Presents of water on plugs and huge missing problem at idle but motor mysteriously makes full power.
Good luck
the difter

 

[bell47]

Re: 1988 175HP yamaha rough idle....Please help!

Livebaitdrifter, can you PLEASE elaborate on the corrosion on the bottom of the block that you mentioned above. I've looked at the plugs a couple of times and they are not wet. But I'm still having issues. Please see my new post about old gas. Thanks.

 

[livebaitdrifter]

Re: 1988 175HP yamaha rough idle....Please help!

Livebaitdrifter, can you PLEASE elaborate on the corrosion on the bottom of the block that you mentioned above. I've looked at the plugs a couple of times and they are not wet. But I'm still having issues. Please see my new post about old gas. Thanks.

Theres a drainbac orifice pressed into bottom of block. I think it causes some electrolosis around it that leads to corrosion.
You sound like you have a lean idle sneeze. Clean the carbs again.learn all you can about what each part does. Sound like you ned to concentrate on idle circuit. Pay attention to metering tubes in bowl.
good luck, none said its easy.

 

[bell47]

Re: 1988 175HP yamaha rough idle....Please help!

I'm leaning towards the " lean idle sneeze" you mentioned! I found a video of this online, on an Evinrude, and it sounds like my problem! After reading some of the replies on my old gas thread, I don't feel that it's the problem, especially after seeing the video. The gas in the boat is old(about 2 months old) and will be run out but I think the carbs are the issue. I read somewhere about covering the carb intakes and when the problem carb was covered the engine would smooth out. I'm not sure how this would work because wouldn't you effectively be cutting out a cylinder? Any advice on this? THANKS EVERYONE FOR THE ADVICE!

 

[GrayBlue]

Re: 1988 175HP yamaha rough idle....Please help!

Have you checked the idle screws? What about the throttle screw? What RPM is it idling at? Does it smoke a lot or none at idle? Does it run fine at WOT?

 

[livebaitdrifter]

Re: 1988 175HP yamaha rough idle....Please help!

Put some 50:1 gas in a spray bottle and spray into each barrel, you should find the lean carb or b
arrel quickly.

 

[bell47]

Re: 1988 175HP yamaha rough idle....Please help!

Went out to the boat today. I first tried rag over the barrels of each carb to see if I could tell any difference in the idle, I thought as I covered the middle carb that it wound smooth out just a little. But honestly can't say for sure. I ran through the linc/sync procedure from scratch again. No change, I can't get it to idle right long enough to accurately adjust them. I also tried the alcohol/syringe method of testing the oil return valves, they all let it flow smoothly through, then locked up the syringe when pulled back. So, no luck with that. Finally I pulled the carbs off AGAIN and gave them a very VERY close inpection and cleaning. I found them to be spotless, but I cleaned them with solvent and compressed air anyway. I'll put them on tomorrow and go through the linc/sync. We'll see what happens. I think I'm gonna go have a steak and talk to Johnny Walker about it tonight.

 

[livebaitdrifter]

Re: 1988 175HP yamaha rough idle....Please help!

bell
You ask for advice then dont follow it.
You never checked compression. A 2 stroke with poor compression will not idle. Eliminating something is part of the process. Compression should be between 110 and 125.
You never sprayed gas in carb. Finding the lean carb would save work cleaning a carb that is working fine.
Some advice is poor advice , shoving a rag to richen a carb is not prudent, injesting rag fibers or a rag not good mechanics. Robbing a cyl of air is not going to give it more gas just less air.
good luck
ps dont forget to check fluid flo thru needle seat.
pss what kinda solvent, i use lacquer thinner or acetone.