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70hp Yamaha rough idle and dies

D

dennis_j

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"My 70 hp Yamaha coughs and di

"My 70 hp Yamaha coughs and dies under 1000 rpm. I've had a Yamaha dealer clean the carbs, replaced the plugs.
It runs smooth on any one of the three cylinders when I disconnect the coil wires.
I just noticed today that when it coughs I can feel it in the fuel line bulb because it must lose a bit of compression in the line.
Could my problem be in the fuel line.
I've also checked and cleaned the filter on the side of the engine and found no water just some crud.
Any help or advice would be greatly appreciated
Dennis J."
 
It was 3 or 4 weeks ago. I pr

It was 3 or 4 weeks ago. I probably should have taken it back right away but where I live it is a long trip to get it to the launch site and on the trailer again. I hoped I could run it and cure itself cause the carbs were so gunked up with the ethanol gas. He charged $100.00 for each of the carbs. Is there a idle screw valve that I could clean out without taking everything apart?
Do you have any suggestions or advice that an amature like myself could try. I've taken motors apart and fixed them but I've only got the tools and knowledge to work on the older models without all the sophistication.
 
"Take it back, they haven'

"Take it back, they haven't fixed it. Still sounds like a carb issue. Dealerships charge the highest labour rates..you should expect the best results. If they can't give it back to you in proper running condition why should you pay the big rates? Trust me they can afford to put a tech on it and try again. Just tell them you put it in the water for the first time after they worked on it and its not right. If you can't get the boat to them right away..call them and let them know about yhour grief..and ask what they are prepared to do."
 
"Thanks Rollie;

I've ju

"Thanks Rollie;

I've just e-mailed the dealer and explained the situation. I told him what I had been doing and he told me that I was adjusting the wrong screw to change the idle speed. I was adjusting only the top carb. He thinks if I increase the idle speed a little on all three carbs it will correct the problem. Actually I think it is idling too high now and it fluctuates too much. I'll try again when I get off work tonight and let you know the results.
Thanks, Dennis J."
 
Hi Rollie;

I found the corr

Hi Rollie;

I found the correct idle adjustment screw and started the engine. I moved the idle to 1050 rpm before it ran smooth and didn't die. It coughed a couple of times but it held that setting and continued running.
Isn't that too high though? Won't it put excessive wear on the gears shifting at that speed? The manual I have calls for 800 plus or minus 50rpms.

The squeze bulb doesn't seem to want to hold the pressure. I put soapy water on all the joints but couldn't find any leaks.

Any ideas or advice for my next move?

Thanks for your help. Dennis J.
 
"Dennis, yes the rpms should b

"Dennis, yes the rpms should be lower, my 200 runs at 700 rpm in neutral. Make sure primer bulb hangs with the engine end higher than the tank end. This allows the check valve to work properly. Sounds like you still running lean on the carbs. Check your manual for adjustments and factory setup on adjustable jets if that model has them. Also make sure the gas tank vents are clear of salt and allowing the fuel pump to draw fuel properly."
 
Dennis also check that the eng

Dennis also check that the engine is coming up to temp. If the t-stat is stuck open it won't warm up and will run rough at idle.
 
"Hi Rollie;

Just talked wit

"Hi Rollie;

Just talked with the dealer and he says that 1050rpms isn't bad. He says the 800 + or- 50 is the speed it should maintain in gear not in neutral. I said I'd check out the idle rpm's tonight when it's in gear.

Is that rubber squeze bulb supposed to stay fairly hard all the time? I can slowly squeze it all the way while the engine is running. Is it possible that even though I recently purcchased it from West Marine, that it could be defective.

Maybe I should clean out the permanent tank and try it again. If I keep stabilizer in it maybe it won't cause any more problems.

By the way, when the dealer worked on the motor he also found the t-stat frozen so he replaced it. Where is that item located. That looks like something that needs to be checked often.

Thanks again for your help, I'll let you know what I find tonight. Dennis J."
 
"Hi Rollie;

Just got finish

"Hi Rollie;

Just got finished with the motor. Anytime I adjust the idle below the 1050 mark it starts coughing. When I put it in gear it looses about 50 rpm's. I guess it's back to studying the manual. I bought a factory manual on line. Do you think a Clymers book would be better?

Thanks, Dennis J."
 
"Once your engine is up to tem

"Once your engine is up to temp it should idle at 700-800 rpm in nuetral and drop about 50 rpm's in gear. With the engine running you will be able to squeeze the bulb a bit, it shouldn't collapse right down. The t-stat is located on top of head."
 
"Hi Just in time;

Now you&#

"Hi Just in time;

Now you've got me really worried. Are you talking about the three carbs being out of sync? Wouldn't the dealer who removed and cleaned the carbs have syncronized them? Is this something that needs sophistigated tools and knowledge or something that I can do?
Are you suggesting I bring it back to the dealer and tell him I want the carbs sycronized? I'd appreciate an elaboration of what you're telling me. Thanks, Dennis J."
 
"Just talked with the dealer w

"Just talked with the dealer who says there are no adjustment screws on those carbs. He feels that he put the carbs back in position properly and the problem is probably a timing problem. Is the timing on these motors the same as timing the old cars. Can I use my 50 year old timing light or do I have to buy a new fangled one.

Any advice would be appreciated. I've got a 50th wedding anniversary coming soon with a lot of family & friends coming to visit. I'd like to have a good working boat for them to use.

Thanks, Dennis J."
 
"GREAT NEWS
The dealer has of

"GREAT NEWS
The dealer has offered to come to my house on Monday to see if he can fix it.

I'll let you know the results.
Thanks again to all, Dennis J."
 
The Yamaha dealer came out ear

The Yamaha dealer came out early this morning and found the carbs out of sync. After he put them all three in sync it idles real smooth at about 800 rpm. The man was extremely polite and courteous and refused any compensation for his trip and labors.

Thank you all for your help and advice helping me get this problem solved.
Dennis J.
 
"Good to hear, they obviously

"Good to hear, they obviously want you to do business with them in the future...and now you more than likely will."
 
"I am a little late on this, b

"I am a little late on this, but, If the dealer says there is no adjustment on these carbs, how did he go about sync'ing them? I ask because I am having the same problem. It has gone on long enough that I burned a hole in the top piston. I replaced the piston, but the rough Idle still exists. I have someone who can sync them, but how do you if there is no adjustment? Where did he put the gauges?

Thanks for any help!
beas"
 
"There is no adjustment on the

"There is no adjustment on the jets on the individual carbs, but you have to set up the linkage so that all carbs are in -sinc with each other. (throttle position)"
 
"Thanks Rollie. After I posted

"Thanks Rollie. After I posted this, I read somewhere else where to find it in the manual. I looked, and its there, under routine mainainance. You would think there would at least be a note under the carb rebuild section, wouldn't you?!

Thanks again, I'll try this tomorrow!
Jason"
 
"nope

it is under maintenan

"nope

it is under maintenance

should be done yearly

if you read the carb section, it states do a sync and link"
 
I couldn't see exactly wha

I couldn't see exactly what he did but he said he adjusted the linkage on the top cyclinder afterwhich the idle came down to 800- 850 with no coughing.
We were both pleased with the outcome especially after he would not take any money for coming out to my house. I will definitely take it back to him for annual check ups or other work.
 
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