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1999 Yamaha 25HP twostroke 2cylinder running rough

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alabass

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"I recently got a 1999 25hp Ya

"I recently got a 1999 25hp Yamaha. The motor doesn't have many hours on it judging from the looks of it but it has a problem of running rough when first starting out. The motor starts on the first pull and idles fine but when taking off it bogs, cuts out, stumbles, coughs, however you want to describe it. It will do this for several minutes then clears up and runs perfect until the next trip. I have replaced the fuel line from the tank to the motor due to cracks in the old one, cleaned the fuel filter and put in a new set of plugs. Any other suggestions as to what might be the problem? Thanks"
 
Update. I pulled the carbs and

Update. I pulled the carbs and replaced all the rubber parts including the fuel pump diaphragm and the carbs are clean as new.

I took it for a test run and it started and idled fine but when trying to get up on plane it sputtered and cut out at about half throttle. I backed off and it seemed like one cyl. was not getting fuel. I pulled the choke for just an instant and the cyl. picked back up. At this point I could get it up on plane without it cutting out but when I slowed to idle one cyl. seemed to cut out again until I pulled the choke lever for just an instant. If I pulled it too long the motor would bog and die. I tweaked the linkage between the butterflies a little to synch the carbs which caused it to idle high so I adjusted the idle down. By this time the motor was good and warmed up and I had no more problems.

I guess I need to take it out cold one more time to see what happens. It just seems strange to me that it runs so bad to begin with and then runs like nothings wrong after a few minutes. BTW I always disconnect the fuel line when loading up and let it run until it dies and I always run Seafoam in my gas.
 
Suggestions please! Update to

Suggestions please! Update to previous problem. Whatever is wrong with my 25hp seems to be temperature related. All this summer I haven't had any trouble with the motor running fine but today it was cool this morning and I experience the same problem of it cutting out again until it gets warmed up. Any ideas where to look?
 
"I have an electronic copy - r

"I have an electronic copy - repair manual on CD. This is a two cylinder motor and one thing I've discovered about it, according to the Model number (25MSHX) it is a 1999, but looking at the parts break down on the CD, it appears it's really a 1998 model (same as 25MSHW). I'm basing this on the configuration of the carbs. Also, it doesn't have a thermo switch. The CD doesn't list a 25MSHX for 1998 and for 1999 it only lists the 25MSHX3 which I believe is a 3 cyl."
 
"That's right, it is a 2 c

"That's right, it is a 2 cyl. 25hp. It is a 25MSHX and I believe the manufacture date was in the fall of 98."
 
"Are you talking about the pla

"Are you talking about the plastic cover over the front of the carbs? If so, I've tried that, in fact when I got the motor it didn't even have the cover. Also, when I replaced the fuel pump diaphragm and the gaskets in the carbs I ran with the cowl and cover off while I adjusted the linkage between the carbs."
 
"First, I really appreciate th

"First, I really appreciate the trouble you are going to to help me diagnose this problem.

It appears to be a factory manual based on the following statement: "NOTICE
This manual has been prepared by the Yamaha Motor Company Ltd. primarily for use by
Yamaha dealers and their trained mechanics when performing maintenance procedures and
repairs to Yamaha equipment."

I don't find the sync/link process in it though. Maybe I'm not looking in the right place.

Can you give me the steps?"
 
"Nevermind, I did find the pro

"Nevermind, I did find the procedure. It's for a 3cyl. model but I should be able to figure it out."
 
just ask and i can point in th

just ask and i can point in the right direction
i think it might be under maintenance
 
"Still having problems. Pulli

"Still having problems. Pulling my hair out and don't have any to spare. The carbs have been rebuilt, sync/link and new plugs. When cold, the top cylinder wants to cut out under load. After it's warmed up it runs like brand new. I can disconnect the linkage between the carbs and can run it wot in gear without it cutting out but put the linkage back on and the top cylinder starts cutting out. Any suggestions? Could there be an electrical problem?"
 
"Actually, I had a mechanic do

"Actually, I had a mechanic do it. I don't have a factory manual, just a service manual on cd. The motor idles perfect, and runs perfect once it's warmed up, but with the cold weather now here it takes an awful long time for it to get warmed up enough to run correctly."
 
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