CARB REPLACEMENT DIDN'T WORK- I THINK I FOUND SOMETHING

[FreeBeeTony]

Re: CARB REPLACEMENT DIDN'T WORK- I THINK I FOUND SOMETHING

I don't think the rev limiter (if I even had one, it's Thunderbolt IV not V) would affect the vacuum.<br /><br />Nick, I really think you need to do the vacuum test........I think you problem is different....didn't you say you had gas in the oil? Maybe the gas is getting past the seat in the carb when it should be closed?

 

[KaGee]

Re: CARB REPLACEMENT DIDN'T WORK- I THINK I FOUND SOMETHING

Tony, read the post from Manipulator about his weekend ruined. Look at the outcome.

 

[FreeBeeTony]

Re: CARB REPLACEMENT DIDN'T WORK- I THINK I FOUND SOMETHING

KaGee.........I am making arrangements to have the boat taken out of the water so I can Pull the Drive. I will be able to tell right away what the condition of the bottom is.<br /><br />Would a dirty bottom affect the vacuum readings?

 

[Don S]

Re: CARB REPLACEMENT DIDN'T WORK- I THINK I FOUND SOMETHING

Would a dirty bottom affect the vacuum readings?

Just like a plugged exhaust..... Check bottom and the drive. Don't just assume the bottom looks dirty enough and end up doing the job twice.

 

[imported_scott_m]

Re: CARB REPLACEMENT DIDN'T WORK- I THINK I FOUND SOMETHING

Just a word on a dirty bottom...yes, I live in west central FL, so yes, the water temps are vastly different. I had both my boats painted in March of this year with Tropikote - supposedly pretty good stuff. I don't really know which paint is better than another. Anyway, have not been using the boat nearly as much as I'd like due to a new home and such, but about a month ago we went out on the cruiser and the bottom and props were so fouled I could not make more than 1200 RPM. Needless to say, a diver was needed to clean things up. Most of the fouling was on the props. So yeah, things can grow in 2 months, however, I'm with the rest on the exhaust blockage.

 

[tommays]

Re: CARB REPLACEMENT DIDN'T WORK- I THINK I FOUND SOMETHING

Turns out I had a half-inch of fresh water gunk attached to the hull. I should of known better but did not understand how that much crappiola could rob me of so much power. Anyway, he pulled it out, power washed it and supposedly we are back to normal

ya just cant make this stuff up i will be waiting to see if you bottom is clean<br /><br />tommays

 

[FreeBeeTony]

Re: CARB REPLACEMENT DIDN'T WORK- I THINK I FOUND SOMETHING

DonS.....can you explain why a dirty bottom would cause the engine to have low vacuum?<br /><br />I can see how a plugged exhaust would do it by not letting the engine breath properly. But I would think that the engine would be under an extreme load with a dirty bottom, but how could/would that affect the vacuum?

 

[Buttanic]

Re: CARB REPLACEMENT DIDN'T WORK- I THINK I FOUND SOMETHING

The vacuum decreases as more load (power production)is put on the engine. Do not confuse RPM with load or power, an engine that is under maximun load or power production at 1000 RPM would have very little if any vacuum. The amount of vacuum depends on the amount power being produced and the degree of throttle opening required to produce the power necessary. The dirty bottom makes the engine work harder so the vacuum is less. Think of it as though you were driving on the highway at 50 MPH and without taking your foot off the gas you stated putting on the brakes and at the same time giving it more gas to maintain 50 MPH. Even though you aren't going any faster the engine is producing more power to over come the brakes. The dirty bottom is a brake.

 

[FreeBeeTony]

Re: CARB REPLACEMENT DIDN'T WORK- I THINK I FOUND SOMETHING

So what would normal vacuum readings be at different RPM's?<br /><br />Someone stated that the readings at 3000RPM should be the same as what I read at idle.<br /><br />The readings I posted above were while I was underway......not in neutral.<br /><br />Does that make a difference........now I'm confused.......<br /><br />Will the readings be different at the same RPM's between neutral and underway?

 

[Mahoney]

Re: CARB REPLACEMENT DIDN'T WORK- I THINK I FOUND SOMETHING

This is a fairly simple example, but the more throttle you have on, the further your throttle plates are open, the more air flowing through the carb, hense the less difference in air pressure between outside air and the throttle body.<br /><br />While you can maintain 2000 RPM out of the water with very minimal throttle advance, this doesn't let air rush into the engine equalizing the pressure. Although the displacement of your cylinders still needs to be accounted for so it creates a vacuum.<br /><br />When in the water, you need much more throttle advance to reach 2000 RPM as you are now pushing against water. This is allowing more air to flow through the carb due to the throttle plates being open further, thus reducing the difference between ambiant air pressure and what is in the throttle body.

 

[Buttanic]

Re: CARB REPLACEMENT DIDN'T WORK- I THINK I FOUND SOMETHING

Yes it makes a difference. In neutral there is no load on the engine. Even at 3000 rpm, in neutral the trottle is barely cracked open and there is no load on the engine. The vacuum is caused by the suction of the pistons going down. The trottle plates control the amount of air the engine can suck in so when they are just cracked open the vacuum is high. As the trottle is opened and LOAD applied by pushing the boat through the water vacuum will start to drop until the point the trottle is wide open and the engine is producing maxium power. Remember an engine does not produce maxium power until maxium load is applied to it. You can have a 500 HP engine turing 5000 RPM in neutral but there is no load on it so it is only producing enough power to overcome it's own internal friction and power to turn the water pump, alternator, power steering, etc so the vacuum would be high 19 -21 inches. If it were pushing a boat through the water and it is proped right then at 5000 RPM it would be producing 500 HP, the trottle would be wide open and vacuum would be 1 or 2 inches.

 

[FreeBeeTony]

Re: CARB REPLACEMENT DIDN'T WORK- I THINK I FOUND SOMETHING

So then it seems like the readings I recorded while underway are normal?<br /><br />These are the vacum readings at different RPM's while underway:<br /><br />1) 600 @ idle: 19<br />2) 1000 (in gear) 16.5<br />3) 1500 17<br />4) 2000 15<br />5) 2500 13.5<br />6) 3000 11<br />7) 3200 9<br />8) when bog occured and I gave it more throttle the vacum went to 2<br /><br />Maybe I should retake the data in neutral?<br /><br />If so........now what?

 

[Buttanic]

Re: CARB REPLACEMENT DIDN'T WORK- I THINK I FOUND SOMETHING

The numbers from 2500 to 3200 look an inch or two low but on a heavy boat it could be normal. I would still be in favor of checking fuel pressure when the bog happens while underway. Also run the vacuum numbers in neutral, that would give you a better indication of an exhaust restriction.

 

[Limited-Time]

Re: CARB REPLACEMENT DIDN'T WORK- I THINK I FOUND SOMETHING

FBT<br /><br />Check out this thd http://www.iboats.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=24;t=012429#000010 Note final outcome

 

[FreeBeeTony]

Re: CARB REPLACEMENT DIDN'T WORK- I THINK I FOUND SOMETHING

So now I am down to a dirty bottom?

 

[Limited-Time]

Re: CARB REPLACEMENT DIDN'T WORK- I THINK I FOUND SOMETHING

Just poasted that link as an FYI, and to let ya know other iboaters are fighting the same type of issues.

 

[FreeBeeTony]

Re: CARB REPLACEMENT DIDN'T WORK- I THINK I FOUND SOMETHING

I feel like I am back to square one!

 

[tommays]

Re: CARB REPLACEMENT DIDN'T WORK- I THINK I FOUND SOMETHING

tony<br /><br />its not that cold mask fins and take a dive you will no if the bottoms clean or not in about 3 minutes<br /><br />tommays

 

[FreeBeeTony]

Re: CARB REPLACEMENT DIDN'T WORK- I THINK I FOUND SOMETHING

If the bottom is clean.........which I think it is.......then what?

 

[tommays]

Re: CARB REPLACEMENT DIDN'T WORK- I THINK I FOUND SOMETHING

tony <br /><br />would you rather do a short haul and rule out the bottom and the exaust issue or spend all summer at 3200 rpm wondering whats wrong<br /><br />tommays