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kayjay

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"I have a problem with my Merc

"I have a problem with my Merc. When I increase the RPM's the motor will jump from 2K to 3k. When coming from the high end the same is true, it goes from 3k to 2k with nothing in-between. It has four carbs on it and it feels like two of them are cutting in. Other then that the motor runs perfect.
Has anyone had a simular problem and is there a fix for it?

Thanks

Ken"
 
"supposed to do that. bottom c

"supposed to do that. bottom carbs have no idle jets. check your accelerator pump adjustment, its there to ease transition when #3,4 carbs come on-line."
 
Thanks Scott! Really appreciat

Thanks Scott! Really appreciate your reply. I hope I'm not pushing the envelope when I ask how I would go about adjusting the accelerator pump.

Thanks again

Ken
 
"Ken,

I would disagree with

"Ken,

I would disagree with most of this so far. The lower carbs do have idle jets, but they are not adjustable.

The engine should not jump directly from 2K to 3K if everything is properly adjusted and functioning properly.

Tony"
 
"excuse me a moment Ken, while

"excuse me a moment Ken, while I clarify myself to the PROFFESIONAL MARINE MECHANIC. what I was refering to when I said "supposed to do that" is that the bottom carbs are off-line at idle. they cut in at around 1800 R.P.M.(2000?) the jets in the lower carbs supply fuel for lube, and cooling. NOT idle. therefore they're not technically idle jets, right? now to answer your question, at full throttle (W.O.T. in tech terms)engine not running. accell. pump plunger depressed, should have .030 clearance between cam, and plunger. seriously though, there are a lot of adjustments on these engines, if you're going to work on it yourself you should invest in a service manual. don't depend on advice from crotchety old, know nothing farts. I further recommend, before making any adjustment, wait for response from PROFFESIONAL MARINE MECHANIC to make sure I told you right. maybe He will offer a suggestion, instead of a criticism."
 
"oops, gonna have to update. a

"oops, gonna have to update. after last post, went back to work for a while. after finishing the job,(carb rebuild) went back into office to make sure I hadn't misinformed you. looked up and saw all these diploma lookin' things. took a closer look and saw my name on them. who'da thunk it. gonna hafta find a neat logo for future posts."
 
"Thanks guys! I just bought th

"Thanks guys! I just bought this boat and didn't know what to expect with a 2+2. From everything I've read, the surge I feel at 2K rpm is normal. What I don't know is can the engine be tune to give me perfomance between 2k and 3k? I've been in water where 2k was too slow and 3k I was up on plane and too fast.

Thank you for your responses!

Ken"
 
"Ken,

There is no question

"Ken,

There is no question that the engine can be tuned to perform between 2k and 3k. My partner has the exact same engine, and while it can be difficult to synchronize the fuel supply and timing, I can guarantee that it is possible.

The accelerator pump would not afffect the performance as the rpms are decreased, so I doubt that adjustments here would solve your problem.

I'm wondering if the engine is the problem. Is it possible that the engine is laboring between 2k and 3k because the bow is rising up, making it difficult for the engine to lift the boat out of the water and up on plane?

I would remind Scott that we are not here to argue about who is right. The idea is to post our opinions so that others might profit by them. If you take offense when people disagree with you, it is pointless to participate in a discussion.

Tony"
 
"Hi Tony
I believe the engine

"Hi Tony
I believe the engine is the problem because it reacts the same regardless of load AND it drops from 3k to 2k (from plane to non-plane) when backing down the speed no matter how slow I move the throttle. I can watch the tack and run it up to 2K, give more throttle and nothing happens. Give it a bit more then I can feel one cylinder / carb come on line followed a very short (0.5 sec) hesitation and the other comes to life. When backing down the tack reaches 3k it will go directly to 2k.
I want to thank you guys again. I'm a pretty good mechanic but this one has got me scratching my head.
Ken"
 
"Ken,

I would check the thr

"Ken,

I would check the throttle linkage and throttle plates. The plates must open evenly and close completely at idle. Look into the throttle bores and watch the plates open and close as you advance the throttle. Do this without running the engine, and with the shift cable not connected. The throttle pick-up may be out of adjustment, causing the plates to open too late or too soon. Make sure the timing advances and retards smoothly, and that there are no restrictions anywhere in the linkage.

Tony"
 
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