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Sport Jet 175 Carb Freeze in Cold Conditions

J

jdevries

New member
I have a 2006 Merc 175 Sportjet in my Jetcraft 1875 Whitewater. I am a hunting guide in Montana and run this boat year round. In the summer months the boat does not have any trouble. Recently it has started lose power on colder mornings.

Symptoms:

1. Boat will run fine at WOT and IDLE. If I drop off the throttle slowly from WOT the boat will die. Not a chug, chug chug die,... more like someone killed the key. If I put the boat back in neutral and turn the key the boat will start up immediately and idles fine. If I move the throttle up slowly it will die just like before. However, if I hammer it all the way to WOT the boat will "catch" and go WOT. Anytime I try to use midrange, the boat just completely dies.

2. This only happens after its been running for a 5-10 minutes. When I first leave the boat ramp in the morning the boat feels fine. Today's temperature was -1. After running for several miles, the rpms drop slowly from normal 5400 to about 4800. If I back off the throttle at all, dies again. However, if I let the boat sit for 45 minutes then go run it again, I will have full range of the rpms and works as normal. After 5 or 10 minutes, dies again when dropping of WOT.

3. Yesterday after running the WOT rpms would drop to 4800, (down from 5400 normal) then the boat would SURGE back and for the between 4800 and 5200. Seems like I am having problems with midrange and a little top end transitioning especially after the engine warms up.

I've read forums and tons of online info trying to figure this out.

Possible solutions people have offered:

1. Stator or electrical problem
2. Fuel pump diaphragm
3. Reeds
4. Jetting clog
5. Air intake cog
6. Water in the fuel
7. Water gas separator no functioning
8. Fuel filter

Has anyone else experienced this problem and can offer a fix?

Other observations:

1. Some water leaking between the motor seal and pump into the doghouse.
2. Visible ice/condensation on the carbs.
3. I use HEAT in my fuel all the time, always have.
4. I run TORCO full Synthetic snowmobile oil (for low smoke).
5. Engine really runs great! No loss of power etc.
6. I've never touched the carbs on this boat.
7. About 250hrs on the motor.
8. Cannot re-create the problem on the trailer.
9. I have another friend with a Sportjet 175 and he has experienced exact same problem.

Thanks.
 
Your correct as it sounds like carb icing,the leakage into compartment is the cold humidity that is freezing due to velocity thru carbs. Fix the leak an vent the compartment better and it should go away..
 
Airplane engines have had the problem for over a century. They cure it with exhaust heat. You might try insulating the cowling to keep more heat inside, or perhaps using an electrical block heater.

Jeff
 
If the leak is off the exhaust it will be warm water in bilge which will make it freeze up quicker....
 
Last edited:
...Hood then. Picky, picky......

It a SPORTJET!!!!! Its like a sterndrive setting inside the boat!!! Geesh......



sport.jpg
 
jdevries said:
I have a 2006 Merc 175 Sportjet in my Jetcraft 1875 Whitewater. I am a hunting guide in Montana and run this boat year round. In the summer months the boat does not have any trouble. Recently it has started lose power on colder mornings.

Symptoms:

1. Boat will run fine at WOT and IDLE. If I drop off the throttle slowly from WOT the boat will die. Not a chug, chug chug die,... more like someone killed the key. If I put the boat back in neutral and turn the key the boat will start up immediately and idles fine. If I move the throttle up slowly it will die just like before. However, if I hammer it all the way to WOT the boat will "catch" and go WOT. Anytime I try to use midrange, the boat just completely dies.

2. This only happens after its been running for a 5-10 minutes. When I first leave the boat ramp in the morning the boat feels fine. Today's temperature was -1. After running for several miles, the rpms drop slowly from normal 5400 to about 4800. If I back off the throttle at all, dies again. However, if I let the boat sit for 45 minutes then go run it again, I will have full range of the rpms and works as normal. After 5 or 10 minutes, dies again when dropping of WOT.

3. Yesterday after running the WOT rpms would drop to 4800, (down from 5400 normal) then the boat would SURGE back and for the between 4800 and 5200. Seems like I am having problems with midrange and a little top end transitioning especially after the engine warms up.

I've read forums and tons of online info trying to figure this out.

Possible solutions people have offered:

1. Stator or electrical problem
2. Fuel pump diaphragm
3. Reeds
4. Jetting clog
5. Air intake cog
6. Water in the fuel
7. Water gas separator no functioning
8. Fuel filter

Has anyone else experienced this problem and can offer a fix?

Other observations:

1. Some water leaking between the motor seal and pump into the doghouse.
2. Visible ice/condensation on the carbs.
3. I use HEAT in my fuel all the time, always have.
4. I run TORCO full Synthetic snowmobile oil (for low smoke).
5. Engine really runs great! No loss of power etc.
6. I've never touched the carbs on this boat.
7. About 250hrs on the motor.
8. Cannot re-create the problem on the trailer.
9. I have another friend with a Sportjet 175 and he has experienced exact same problem.

Thanks.
Click to expand...

Year #2, SAME PROBLEM.

Boat ran great all spring and summer. Not a single issue.

This morning it was -9 degrees when we left the boat ramp. I am a duck hunting guide in Montana. The boat ran great, no problems to start. The boat started easily on the trailer, and I had WOT, midrange, and could adjust throttle positions around corners while driving. The steering and throttle controls were VERY stiff due to the cold, but the engine seems perfect for the first 20-30 minutes of running.

After about 30 minutes of running (to get to our duck blind) this is when the problem returned. Literally the second I backed off the throttle to ease into the blind,..... the boat dies. Not chug chug chug,....but the second I pull back the throttle,.....kills the engine.

I started the engine back up,....and it would idle, so we limped it into the bank. We decide to hunt set up the decoys and work on the boat later as the ducks were flying. This is the weirdest part of this situation.

After letting the boat sit for about 30-40 minutes, I went back to check on it. The boat started right up, and ran through the full throttle range perfectly! However, after running the boat for about 20 minutes, the same problem would happen. If I backed off full throttle, the boat will die.

If I parked the boat, and let it sit for 30 minutes, it runs great????? The boat continued to do this all day. Run for about 20-30 minutes perfectly, but once hit gets kinda warmed up,......I can only go either WOT or IDLE. I did try running it the last time of the day with the doghouse completely open. No change. Still dies after prolonged running.

Also on the way home, it would not keep up with WOT the entire way, and was surging from 5400rpm, down to 5000 regularly.

suggetions?

I just can't figure this out!!
 
The air going into carb. needs to be warmed up some how to prevent icing, 70's GM cars had ducting coming of right side exhaust up to carb which was controlled by a vacuum operated door, Something to think about
 
johnnygjr said:
The air going into carb. needs to be warmed up some how to prevent icing, 70's GM cars had ducting coming of right side exhaust up to carb which was controlled by a vacuum operated door, Something to think about
Click to expand...

I had a mechanic today tell me they were planning to wrap the fuel pump/fuel line with a 12v heater of some sort with a switch to the control panel to try and heat the fuel as it enters the carbs. I though it was an interesting idea. Have you done this?
 
No i haven't, but on this site iv'e heard of the exact opposite condition,fuel evaporating in fuel components due to heat sink on hot summer days, Issue was cured by cooling fuel pump and lines.
 
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