Why is my Hydrostream Valero YT with a 235 Johnson so slow??

[Fullthrottleguy]

Hey guys,
I'm new to the forum although i've read some great information on here in the past. A few weeks ago I traded my good running Hydrostream Viper with a 140 Johnson X-flow for this nice Hydrostream Valero YT with what i was told was a seized 235. If both were in good shape and runing well the Valero would be worth twice that of the Viper so I thought it was a fair trade. That night I got home and discovered that the motor ran fine; it was the bottom end that was locked up (no oil) - this became more of a steal that a great trade . I've been over the boat top to bottom and it looks like a nice solid example, the motor starts well, the hull seems solid and looks good as does the trailer. The only thing is ITS SLOW!! My Viper would do 61 MPH on GPS two people turning 24 pitch raker ski prop @ 5300 RPM and the motor fairly deep in the water; this thing will only do 55 MPH.

I need some help getting it to scream....and i thought this would be the best place to get some pointers.

Let me start off by talking about what i've done so far...
The compression is 105 PSI in every cylinder, I took the head off breifly when i thought the motor was seized and observed that it has .030" over pistons and the cylinder bores look to be in good shape - A new headgasket was installed afterwards. I put new plugs in, confirmed that i get full throttle, dissasembled and inspected the carbs (one jet was plugged), checked the spark at each cylinder with a spark tester while the engine was running and observed a crisp and consistant spark. I've dissasembled and inspected the two diaphram pumps for tears and they look good, adjusted the timing under load to 30 degrees advance while underway (that was fun) - it was only at 27.

The motor vibrates a bit at idle, but seems fairly smooth once you get going. It just feels consistantly underpowered; i've never driven a 235 outboard before but thought it would lauch this boat; in my opinion this motor feels like its my old 140 bolted onto a slightly heavier boat. It tops out at 55 MPH @ 4900 RPM spinning a 26 pitch Merc Trophy plus ski prop. The motor is sitting pretty normal on the jackplate with the anticavitation plate .5" above the water line at full speed.

What is going on?

[Forkin' Crazy]

What year motor? You may get a few more Xflow guys opinions before you stay with 30 degrees. At 105 you may be OK, but I would check on it. Some set the timing while strapped to the trailer (really well I might add).

Have you checked the ignition spark? Its possible you may have a coil (or two) breaking down.

[Fullthrottleguy]

Hey,
Thanks for the response. The powerhead is an '81, I ran the numbers on the block and carbs to make sure it was indeed a 235 - I even confirmed the jets were for the right year/hp. 105 seemed low to me too; it was always my opinion that +125 was desired with a max of 10% difference between the cylinders. From what i've read these motors were low compression and your target should be around 100, but i could be wrong. I'm not sure if this is due to the weird piston shape on x-flow motors or what, but the '79 140 x-flow on my old boat was around 125 each.

Can anyone enlighten me as to what the compression test reading should be for this old beast?

I would think that this motor would still blast my little boat along pretty well; but it really does feel like it has half the horsepower that it should.

X-flow guys please pipe in with your wealth of knowladge .

P.S. Expect setup questions to follow as i try to set this baby up to fly!

[Fullthrottleguy]

Oh and Forkin, I set the timing to 30 degress as per the specs for this motor. When you say that I may want to get some x-flow guys' opinions before i stay @ 30 are you implying that it may be dangerous to do so or that its common to advance them past this point to get some more power? And yes i check all the coils while the engine was running with one of those spark gap testers - they all seem fine.

[ChrisCarsonMarine]

You definitely have something way wrong,even set up poorly you should see 70's,80's set up well.Was this a fresh or salt water motor?Something's governing it...exhaust restriction from tuner falling apart and blocking the exhaust in the lower unit?I would start by running wot and hand choke each carb barrel,see if the rpm drops as you choke off separate cylinders,you'll see if it's running on all 6 at speed.I would drop the timing to about 26, at least for now,it will effect acceleration,but not top speed...keep looking ,you will find something,chris

[wanagofass]

You definitely have something way wrong,even set up poorly you should see 70's,80's set up well.Was this a fresh or salt water motor?Something's governing it...exhaust restriction from tuner falling apart and blocking the exhaust in the lower unit?I would start by running wot and hand choke each carb barrel,see if the rpm drops as you choke off separate cylinders,you'll see if it's running on all 6 at speed.I would drop the timing to about 26, at least for now,it will effect acceleration,but not top speed...keep looking ,you will find something,chris

I agree completely, I've got an old glastron gt hull that's around 800lbs and runs 65mph gps w/a 150hp crossflow and a 25p merc tempest plus, something is bad wrong.

[Lockjaw]

Leakdown test?

[rockman69]

The '81 models have the better heads (638-639's) Comp. should be higher

I have an '80 150 with 235 heads, carbs and intake stuffers and pushed a 1700 lb. trihull to 52 with a 25 shooter.

Just rebuild it over the winter and have it ready and running right for next season!

[Da Bull]

I would never set timming any higher than 26 degrees @6,000 rpm on that motor. That being said have someone work the throttle back and forth to insure that the timming trigger is in fact moving to full advance. These systems tend to stick. If so it will require removeall of the flywheel for cleaning and lube. This will be a good time to check the flywheel key. They break and the flywheel may be out of place. This can be checked with a dial indicator for TDC on #1 cylinder and look at the timming pointer.

[bigbluechevy454]

Sounds like its not running on all 6 4900rmps is crap

[rev.ronnie]

I agree that it is not hitting on all 6. You say that it has a vibration or shake at idle..this is not right. Those motors are pretty smooth idling and real smooth at speed. Run it at idle and pull the plug wires with a plug wire pliers, one at a time and see if you can isolate it.

That thing should haul balls with a 235. My buddy's VKing ran in the 80s with one...pulled like a freight train too.

[Forkin' Crazy]

Oh and Forkin, I set the timing to 30 degress as per the specs for this motor. When you say that I may want to get some x-flow guys' opinions before i stay @ 30 are you implying that it may be dangerous to do so or that its common to advance them past this point to get some more power? And yes i check all the coils while the engine was running with one of those spark gap testers - they all seem fine.

What kind of tester? It needs to be set at 7/16" gap to simulate compression. It should be a nice strong spark also.

80/81 or so was right in there when they started having problems with the motors burning down because of the crappy gas. One fix was to add thicker head gaskets or maybe even change the heads. What part numbers are they?

I'm running stock '80 235 heads (325638 & 325639 what yours should be) and get right around 125psi with 26* timing, premium fuel only.

[terry taylor]

Hey,
Thanks for the response. The powerhead is an '81, I ran the numbers on the block and carbs to make sure it was indeed a 235 - I even confirmed the jets were for the right year/hp. 105 seemed low to me too; it was always my opinion that +125 was desired with a max of 10% difference between the cylinders. From what i've read these motors were low compression and your target should be around 100, but i could be wrong. I'm not sure if this is due to the weird piston shape on x-flow motors or what, but the '79 140 x-flow on my old boat was around 125 each.
I saw pics.
Can anyone enlighten me as to what the compression test reading should be for this old beast?

I would think that this motor would still blast my little boat along pretty well; but it really does feel like it has half the horsepower that it should.

X-flow guys please pipe in with your wealth of knowladge .

P. S. Expect setup questions to follow as i try to set this baby up to fly!

I saw this rig in an ad, The jack plate and engine are bottomed on transom and will need to be raised at some point. Sometimes one can heat stick an engine and when it cools might seem to run fine . After removing heads evidence can show mild to severe damage, scuffing on cylinders fom piston expansion. It could also show compression loss. Does this block have bubble exhaust chamber? it should thanks.

[perfmarine1]

Yes check those heads,this could be someone changed the heads to higher comp and then sold it with different heads and did not change the jets back to what they should be. I have run into this several times. you must check the jets and make sure they were not drilled,this will kill the power.You can not look at the size on the jets on a motor this old size must be checked,as too many were modded and all screwed up after sold. Too rich at idle will make it shake also,this is why I brought this up.Low compresson is your first red flag. Also pull off a by pass cover and check the porting,that will be your second red flag. Do a running DVA check on the ignition wires to coils first and make sure it is good. Good luck.

[Fullthrottleguy]

Hey Chris,
Yeah i was hoping to see 70's for now and 80's once a get a more agressive wheel on it next spring. As far as i know the motor has only ever seen fresh water... the ocean is more than a day's drive away from Toronto so i doubt its ever seen the salt. The exhaust restriction isn't a bad thought; when you say "tuner" are you talking about the aluminum piece with the rubber on each end that connects the exhaust passage from the mid to the lower unit? I ran the boat the other day at an idle and pulled each plug wire one at a time to confirm that all six were operational. The next time i have it out I'll run it at speed without the airbox cover and block off each cylinder as you suggested. Thanks for the pointers.