merc 2.0l slower after carb change

[bryanwess2000]

I have a V135 and swaped the stock wmh8's for some wmh7's, no changes to anything else. I took it out today and noticed I could only hit about 5200rpm where I was getting 5400 with the wmh8's I was also ~2mph slower. I thought it was maybe due to being on the lower end of the rpm range so I dropped down to 2 less pitch same deal 200rpm less and 2mph less than the stock carb, 5600rpm vs. 5800.
Do I need to cut the heads to take advantage of the bigger carbs or is the tuner different too? I've got a good set of 2 piece heads from a 1985 mariner magnum I can use or I can cut the stock 1 piece heads. I really don't want to pull the tuner from the mariner because I plan to rebuild it later.

 

[Dukedog]

Re: merc 2.0l slower after carb change

Where did they come from? Did they come from a runnin' motor? Been sittin' up gatherin' dust n dirt? Taken apart, cleaned up?.............

 

[bryanwess2000]

Re: merc 2.0l slower after carb change

They were bought from ebay, completely disassembled soaked in a carb
cleaner,12hrs that contains methylene chloride, then sprayed with cheap carb
cleaner and blown out with compressed air. They were assembled with new
gaskets after inspection. Sync'd carbs then test run on drive way, then
taken out to lake. These carbs actually idle better and have better midrange
than my smaller wmh8s' they're just slower on top end.
I'm going to check compression today to make sure it hasn't changed. On
S&F I've read everything from just carbs to carbs, heads, tuner, and ports
being different between the 2.0 135hp and 150hp.
My manual confirms these as 150hp carbs they have .062 mains, my whm8s'
have .050 main jets. And the carb throat is bigger, same size as my wh29s'.
I'm definately getting more air and fuel but lacking something to use them.
This is on my 1991 V135, both carbs are listed for the 2.0 for this year.

 

[Dukedog]

Re: merc 2.0l slower after carb change

Tha 2.0 "fat" blocks are tha same. 135, 150 no different. As for tuner it can be different but shouldn't have any effect on tha top end of tha little motor. Sounds like ya got all tha bases covered with tha carbs. Might double check max timing and butterfly opening and lose tha idle and/or advance module if ya haven't already. Double check fuel lines and any filters. 'bout all I can think of right now. Maybe someone else has a good direct answer. Hope ya get it worked out.....

 

[bryanwess2000]

Re: merc 2.0l slower after carb change

I reset my wot to make sure the butterfly valves opened completely. I didn't
reset or recheck timing, I had set it at 21* about a month ago. I'm going to
go through the fuel system and replace the fuel pump and fuel line and primer
bulb. About the only thing I can think of is the fuel system may not be feeding
the carbs enough fuel and it just wasn't as evident on the smaller venturi
carbs since I was at about the max speed for my hull and the v135.
I already chunked the idle box.
Hopefully its just a fuel related issue, either delivery or restriction.
Thanks dukedog for clearing up the differences on the 135 and 150 for my
block.

 

[j_martin]

Re: merc 2.0l slower after carb change

At this point you need to do some full throttle cutoff and spark plug and piston reading runs. You may be a bit fat or lean on the mains.

Timing at 21 degrees with an advance module will go over top with 87 octane, should be OK with 92. It's a little slow without the module.

Based on experience, insufficient fuel delivery usually manifests as a sudden fall off of power at or near WOT. It's quite pronounced.

Sneak up on it. Don't grenade the power head before you get it tuned.

hope it helps
John

 

[bryanwess2000]

Re: merc 2.0l slower after carb change

UPDATE: I rebuilt the fuel pump, cleaned out the filter, and put a new fuel
hose on with a quicksilver primer bulb. Fired her up and she was idling ~300
rpm faster than before. I looked for fuel leaks, everything looked good.
Took her out to the lake and noticed hole shot and acceleration seemed
better. I hit 44.8-45mph both directions and about 5500rpm. With the
135 carbs I'd hit about 44.5mph down river and about 42mph upriver at ~5300
rpm. So I guess I solved my problem. I'm thinking it was the fuel pump.
Around 45mph seems to be a wall with this hull it started to wobble left and
right and pull the nose up for a few secs. then it'd fall some then pick it right
back up. It wasn't really porpoiseing it's hard to describe, it was like it was
trying to lift the whole hull out of water. I noticed my spray was coming out
at the last 2-3ft. of hull. I don't think I'll be trying to pass the 45mph mark,
it began to get scary and hard to control. SSchefer said this would be about
where it gets difficult to control.
Anyway I just wanted to post what I did and the results in case anyone
else experiences this problem. My conclusion is it was insufficient fuel supply
to the carbs resolved by 1 of the changes I made.
I'm still going to do as Jmartin suggested and read the plugs after some
WOT shutdowns, hopefully I'll be rich so I won't have to change the main jets

 

[bryanwess2000]

Re: merc 2.0l slower after carb change

Took the boat out and did a couple WOT shutdowns after running WOT
~1min,. 2 were golden brown, the others ranged from mostly golden brown
to ashy black. So I think the jetting is right to a little rich.
I took my wife and 2yo daughter and we hit 44mph. Then took out my spare
prop, tool box, socket set, extra battery, and anchor, and the boat hit
45.6mph. I had a full tank of gas and ~10 more gallons in a separate tank
plus my 8hp kicker motor so the boat may hit 46-47 with the extra weight
out and 1/2 tank of gas. The boat was much more stable with the extra
wieght out.

 

[sschefer]

Re: merc 2.0l slower after carb change

Bryan, check the jets on #3 carb. Later on they upped the juice to 6 on the 2.5's and maybe some shop read the manual wrong and put the wrong jets in them 7's of yours.... Yeah, the ones you stole from me early in the morning cuz you knew I wouldn't be biddin in my sleep... ROFLOL.... Have a good one.!!!

 

[j_martin]

Re: merc 2.0l slower after carb change

Took the boat out and did a couple WOT shutdowns after running WOT
~1min,. 2 were golden brown, the others ranged from mostly golden brown
to ashy black. So I think the jetting is right to a little rich.
I took my wife and 2yo daughter and we hit 44mph. Then took out my spare
prop, tool box, socket set, extra battery, and anchor, and the boat hit
45.6mph. I had a full tank of gas and ~10 more gallons in a separate tank
plus my 8hp kicker motor so the boat may hit 46-47 with the extra weight
out and 1/2 tank of gas. The boat was much more stable with the extra
wieght out.

If the jets are all the same size, I'd go back and detail the carbs related to the dark ones. If the floats are slightly high, then when fuel pressure is around 5 lbs at WOT, they might slightly flood.

Ain't it sweet when they run right?

John

 

[bryanwess2000]

Re: merc 2.0l slower after carb change

Thanks for the help and suggestions guys. It's good to have her pretty
much straightened out. SSchefer I owed you one for when you out bid
me on a stator and trigger back in Jan. While I was sleeping.

I remember reading somewhere that the V6 cranks were ground to where
2 of the cylinders would have more timing than the others and that going up
on the jets on those 2 would keep the cylinder temps cool and help prevent
knock. I can't remember which 2 it was though. These 7's have the same
main jets on all 3 .062's.