I have a 120 hp, 4 cyclinder, I/O Mercruiser that I just rebuilt the carb. Before rebuilding the carb there was a dead spot at mid range. The power valve was bad. I replaced that during the rebuild, and that is fine, but now there is no power or speed at full throttle.
Make (of engine): Mercruiser
Horsepower: 120 hp
Rebuilt carb, and now have this new problem.
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Were you getting power/rpms out of the engine except for the dead spot before the carb rebuild?
Yes, it was running good except for the dead spot in midrange. We could get past the dead spot and get up to full throttle and then it ran fine.
And not anymore correct?
That problem is corrected. I replaced the power value when I rebuilt the carb. Now it will smoothly throttle up to about 3/4, but then it dogs out like it's fuel starved (rpm's reduce) .
Now did anything else change except for you rebuilding the carb?
How much time as passed? Is this a case of you rebuilt the carb last year, but this is the first time your trying it this year?
1. How old is the fuel your burning now?
2. Have you checked the fuel pressure when running yet, to make sure it is not dropping?
3. What did you set the float height to when you put it all back together?
No, I only rebuilt the carb. Just rebuilt it two days ago and we've ran several tanks of gas in the boat this season so far. We did put seafoam in the tank two weeks ago to see if it would make a difference, but it didn't. That gas has all been used and replaced with fresh. I don't have a fuel pressure gauge to check the fuel pressure. The float height was set at the specification listed on the carb kit.
Merc used 2 different carbs on these engines. They used the Rochester 2GC and the Mercarb. They are very very close looking. Which one do you have?
It is the Mercarb.
Now you said you set the float to the spec in the repair kit. Can you tell me exactly how you set it and what it was?
Basically the problem here is the float is not set correctly, and I can give you the correct way to set it. Along with the measurements and where you measure it from.
Or, there is a lack of fuel/fuel pressure problem to the engine. And the carb is not getting the fuel it needs.
It is fuel delivery, it is just a question of where. Is it fuel delivery from the pump to the carb? Or fuel delivery from the carb to the engine.
You would need to pull off the steel line and temporarily rig up some rubber fuel line along with a T fitting and a fuel pressure gauge to check the pressure. 4 to 7 PSI at full throttle is where you need to be. Under 4 psi and you know it's fuel deliver to the carb, and the carb is not the immediate issue. Personally I would start with that first.
Now on to the carb, the float drop spec is 1-3/4 inches. To measure it. Your holding the top of the carb upside down. You need to have the gasket in place. An you are measuring from the face of the gasket to the toe of the float. Have a look at this picture.
That is where your issue lays. In 1 of those 2 spots. It is up to you if you want to check the fuel pressure first, or tear the carb open and double check that float first. As it takes equal amounts of time to do either.
Feel free to reply back with any questions
I see that you left me negative freedback. And need more help. What did you find out after following my above instructions?
I do work for tips, and my feedback is very important to me. So I want to make sure your up and running here. What's going on?
Unfortunately after tearing the carb apart again to check the float, nothing changed there. (It was set correctly) I'm sure the fuel pump is working fine, because it didn't have this issue until the carb was rebuilt. It has to be something with the rebuild, so I have pulled the boat from the lake and dropped it to the mechanic this morning.
I do believe there should be a neutral rating available that says something like "unable to solve problem - required hands on" or something like that that would not affect your rating.
Let me know if there is a different rating I can give for that outcome.
Thanks for getting back to me.
I agree as well. Justanswer changed the feedback system last week and it is just terrible now. We used to have a neutral rating, but no longer. Justanwer does not seem to understand that we can not see these engines with our own eyes and hands. And that not every single problem is solvable over the internet.
If you don't mind, rate this answer as "good service", that would be the closest we have to a neutral. Then if you like afterwards, after you rate, you can put in for a refund.
The way this crazy system works is like this. We (I/me) do no work for Justanswer, we are classified as "site users". When you ask your question you put down a deposit, so you were already charged.
If you rate a negative as you did, I get that thrown on my record, and Justanswer keeps your money unless you put in for a refund.
If you rate "good service" or higher. Justanswer credits me with a portion of your deposit for helping you.
If you rate the good service or higher, and then later put in for a refund. I do not get any monetary credit for helping you, but I will not have the negative feedback sitting on my profile either. The positive will overwrite the negative. And cancels it out. And the refund is the refund.
Crazy isn't it?
Either way. If you could do that I would be most appreaciative. I do feel that I did try, and that I did give you good service. I am just not there to see it, so it can be extremely hard to impossible to solve.
Feel free to post back if there is anything else
Thanks a bunch,
Degree in Marine Technology. Gas and diesel marine mechanic.
Here you go, I hope it overwrites the other. I have applied for a refund also, since we have to take it to the shop anyway. I do appreciate your fast responses on the weekend.
That does take care of the feedback and strikes it off my record, thanks. I appreciate you doing that. Some folks would not come back.
Justanswer handles the refunds (I personally have no control over that). But I suspect you would see it in a few days.
Good luck with the boat, and thanks again.
Your very welcome. And thank you!