Merc carb help!!!!!!!!!!!

[fasteddie]

Running a Merc 245HP carb engine.
Engine has WHM non accelerator pump carbs.
Engine pulls good up to 8000RPM then seems to peter out.
I have been told this is due to the carbs float bowls being sucked dry.
Has anyone else seen or had this problem??
How did you solve it??

I have been told to increase the needle and seat size, but am having problems finding the parts to do this.

Thanks in advance,
Ed

[TTriton]

get a holley red or blue electric fuel pump and don't use the stock pump.. that is the easy fix if that is the problem.

[fasteddie]

The engine uses a red holley pump regulated to 5psi
It is a 245 high performance engine and has no vacuum pump.
Thanks anyhow,
Ed

[TTriton]

is this a new problem? Do you have a HIPO stator.. Fishing motor stators will peter out at higher RPMs but I don't think at 8000 RPM's...

[fasteddie]

No, It is not really a new problem, it is just a problem that was not a concern on the old boat. I was not trying to turn the motor quite as hard and still had the RPM limiter on it last year on the other rig.
Yes, it has a 9 amp hipo stator.
The enging is a factory 93and1/2 245 hipo carb.
It only has a total of 19 hrs run time.

[TTriton]

Maybe US1 or one of the other Merc Masters will think of something to try..

[Talon2.5]

i'm using an electric pump, that on it's own puts out 7 to 9 psi with no regulator, seems to be good, had another style pump that would not keep up and it was a 5 psi pump with no regulator and it would suck the bowls dry and the nose would drop a bit, i would let the pump catch up and fill the bowls and hammer down on it again and it would be fine for a little while than the nose would drop and i would go through the same thing again

the 7-9 stopped that from happening and i have no problems with the pressure blowing the needles off the seats or anything of that nature, it's a carbed 2.5 with the WMH carbs that had the pumpers removed

just some thoughts fer ya there on what i faced and did to stop it

oh.... been running it like that for 2 years now in the year round boating state of fla. and no probs ;)

[rob vaughn]

I run a little more than 5 psi., you might want to up it a pound or two.....

What size jets are you running?
US1 has said that the power gain drops off somewhere between 7200-7800.... I turn more than that, but have since stopped!

[Rickracer]

....another pound or two might cure it. Also make sure you don't have any flow bottlenecks. I.E. 90* brass fittings are not the most freeflowing, etc. Also, if you are using a separate regulator, you want it as near as possible to the carbs, not in the boat. :cool:

[fasteddie]

I am gonna go ahead and increase the pressure and give it another shot just to see if it will turn on up and stay rich enough. I had the pressure up before but could not keep the fuel from flooding past the seats.This in turned caused the motor to be real lazy on the bottom and stumble pretty bad.On advise from this board I was told that 4 to 5 psi would be more than sufficient, so I tried.Yeah, 4 to 5 psi solved the stumble and the flooding, but I feel myself that at the lower PSI combined with the small size of the needle and seats is the cause.I finally found a set of needle and seats that with a slight modification will work in these carbs and hopefully provide enough volume at the lower pressure. The hole in the factory seat is @.093." The seats that I found have a hole size of .145"

[bfly]

I have the same motor and what I've been told is that motor is only good to about 7500 rpm's . After that they start dropping power pretty fast.

[fasteddie]

I agree, that Mercury says the engine makes peak power @7500RPM.(STOCK)
I want more than 7500.
I feel that the fuel problem is all that is keeping it back, I just wanted to know if anyone else has had and cured the problem I am having.
I know the engine is going lean from reading the plugs.It is jetted rich (70) so I know it is not a jetting problem.

[ProComp]

Just curious, I just rebuilt mine and the motor came to me without thermostats just small washers with small holes in them and nothing in the poppet valve. Is this the same as yours?

Thanks

ProComp

[jmc]

I had a '92 2.5 carb that would hit the limiter with the right prop. Does that year still have the bottom guided rods? If so, beware of going past 8k. Im 300+ feet above sea level, my engine came with 76 mains swapped them for 72's after break in. I could hit the limiter with a 26" Hoss triton @ 8k. I bet you are chalking w/ 70 mains. Even though your engine is new check for leakdowns those rings were not that good in '93 even if they are t. nitrides.

[Rickracer]

I don't believe 70s is fat, it's probably lean. 76s or 74s might be fat. :cool:

[Reese]

how did you regulate the pump...hope it's not with one of those dreaded "dead head" regulators....:eek:

[bfly]

I'm curious as to what makes you think the jetting is rich enough. The best way to check your jetting is probably going to be reading your piston tops. Jay Smith wrote a good article on this about a month ago. I have the same motor and carbs running 74's. I realize that I'm probably a little rich but from what I've seen 70's are definately pushing it. You might try 72's in #2 and #5. Those are the ones that should lean out first

[rob vaughn]

I got 76's in two of my cylinders.....It'll turn 8700, with 7 lbs. of fuel pressure.....

[XTB21]

What carbs are you guys running? i have a 93 260 block with wh-1's with 68 mains 66 progression and it only turns 7800 with a 24 chopper on an Allison 2003 bassboat.


The hipo manual calls for 68 mains

p.s. i also run about 7psi of fuel

[fasteddie]

Reese
I adjust pressure by chaning the spring pressure on the pump relief.

Bfly
What carbs are you running?? If you are running accelerator pump carbs, yeah you will need the larger jets.Also, what compression are you running, that also will justify how you jet the engine.
My motor runs non acc pump wmh carbs and I run 145 lbs compression.
My motor really pretty rich as long as I prop the boat where it will turn under 8000 rpm.
The manual also states that the motor comes with 72 breakin jets and 68 for run jets, and usually the factyory is pretty conservative.

Rob

Same questions as I asked bfly.
There are a lot of variables that determine the jetting, and I have worked pretty hard to make sure it is jetted safely.

Thanks again for the input,
Ed

[rob vaughn]

Yes I run the accel. pumps with 170 lbs. compression...... There is also some more port work done to this motor, I JUST FOUND OUT ABOUT, since purchase......

Keep us informed, I just got my lower unit back together, and it is now ready TO RUMBLE!!!!!!!! :D With this weather, that may be the next NICE WEEKEND....

[bfly]

I'm sorry I'm coming in so late on this reply but I've been vacationing. I wanted to answer fast eddie's comments by saying I'm running whm's without accelerator pumps and only 120-125 psi compression. From what you guys are saying I must be way too rich.:rolleyes:

[WaterBoy]

I had a 94 245hp without accel pumps also. When I bought the boat it had 72's in 1 & 2 holes and the others were 70's. I ran it that way for 3 years ( with 26cc heads) until relocating pin came out. Broke it in with 72's ( and stock heads) and then went to all 70's but I was pushing it. I was also using 6 to 7 lbs of fuel pressure with a Blue holley. I had a bog on take off also. The screws on the top side of the carbs with the white plastic caps. I adjusted those 1/8 turn one way, bog got worse, so, 1/8 turn the other way, bog was gone. Just a thought?

Rpm's: Just after break in, with stock heads, turned only 8100 with 131 comp. in all cylinders. (sold it right after that)

Before break in, with 26cc heads, turned 9000

Maybe this'll help somewhat.

Waterboy