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RH
05-08-2002, 09:41 PM
I have been looking through my Chris Craft Manual that I have for the engine that was installed in my Hornet. The engine is the 350FLV Chris Craft marinized version of the Corvette 350. It produces 320HP. After my first trial run last evening, When I hit 4500 RPM, the boat seemed to flood out. The manual states that the engine is rated at 320 hp at 5600 rpm, which leads me to believe that my carb may not be operating properly. I had a lot of throttle left and when I went to WOT, the engine would "flood out". Any causes to look for in the carbueration? I noticed a strong smell of gas and no leaks. The boat appeared to run rich as well. Any thoughts out there?

Rootsy
05-08-2002, 09:50 PM
what kind of carburator?

RH
05-08-2002, 09:58 PM
I beleive that the Carb is a Carter AFB four barrel. I am running a 21Pitch propeller on a 270 Volvo drive.

tailwind
05-08-2002, 10:06 PM
Hi RH:

From your detailed post. I too would assume that your carb is indeed running rich at this RPM. Having a 91 OMC King Cobra 350 w/4200-4800 RPM limitaiton, 270 hp, it at first glance sounds that you may well be "over carbed".

Realistically speaking, lets first assume that your engine however rated in a chris craft, may not be rated the same in a DONZI ! Further, let us assume that you wish max speed with longevity, and therefore set a max RPM. Lets say for arguments sake WOT 5000 RPM !

I forgot to ask how fast ? Now it is simply more or less a question of Prop versus RPM.
The choice is indeed yours here - So my question is "what prop are you running, and what rpm?

next question of importance: hole shot or max speed? DONZI's are phenomnal craft and indeed will amaze most any guesses in this particular category!

RH
05-08-2002, 11:00 PM
Tailwind, thanks for the questions. First of all, the engine is the original powerplant that came with the boat when it was built in 1972. Chris Craft marinized the engine and it was an option for Donzi back in 1972. It was the second Highest hp rating that you could buy at that time. Mercruiser offered an option of 325HP. The Speedometer was not registering, so I hav'nt a clue as to the honest speed that I was running at 4500rpm. I have grown up in boats and do have a good idea of how fast I am really going. The propeller is a 21 pitch left hand Volvo 270 in excellent condition. The numbers on the hub are 7089 if that helps. At the 4500 rpm, I would guess that I had to be running anywhere from 45-48 MPH realistically. The boat handles so well that and is so effortless to drive, that I may hve been pushing 50. I have run 3 Donzi classics, a 16,18 and the 22. The Hornet handles more like the 22. After talking with a friend this evening, he feels that the needle valve is most likely the culprit. I will try to remedy that and give it another run. I am very impressed with the boat and it's handling. It has non stock power steering unit from Mercruiser installed that provides and extremely solid, yet comfortable steering control. I will just need to get a GPS unit and take some notes next run out.

tailwind
05-08-2002, 11:07 PM
Having been going thru the same RH, I now even question Tach stability and speedo errors!

Given that these errors should be cummaltive, perhaps we disregarde them. In this case we have only trial and error left. Your prop data does however seem like you are in the ball park

RH
05-09-2002, 07:01 AM
I have never owned a true performance boat before, all of my stuff has been more on the family side and woody material excluding the Boston Whalers. I think that I will just enjoy working through the idiosyncracies that each boat possesses and have some fun. I must admit that seeing other members projects keeps me excited for making my boat the best that I can get it and afford!
RH

AVickers
05-09-2002, 11:00 AM
I've got two of these engines sitting in my garage right now...down for overhauls. (I had a corroded-through exhaust manifold on one side and got water in two cylinders. Pulled 'em both to redo the generator and wiring as well. They have Carter AFB carbs -- which are fairly easy to deal with once you figure them out.

When you say it is flooding, does it flood when idling and running around at low RPM? Or only when you are running flat out?

The problems I've had with the fuel systems on my engines have usually resulted from them not being run for a long period of time. Here's the list of problems and fixes that I've done over the years...

1) There is an accelerator pump non-return valve in the bottom of the float bowl that cruds up and causes the pump to not fill or to fill slowly. This will cause it to run lean when getting into the secondaries and when doing a progressive throttle movement -- running along at half-throttle and then goosing it. A good cleaning will fix this.

2) Another problem I've had was with fuel pressure regulation: one fuel pump -- also a Carter -- would deliver fuel at something like 15 psi. This would cause cause it to slowly flood out as it idled or ran at low throttle. When running faster, it would use the fuel fast enough to not flood. Replacing the pump took care of the problem. The gas detector would howl when this would happen and the smell of fuel in the bilge was heavy.

3) I've had to replace both fuel pumps... They were leaking raw fuel out of the top side of the diaphram when the engines were running. It was a fine spray -- none of that slow drip for me! Again, heavy small of fuel...

4) Because of the angle of the engines -- direct drive -- I've had difficulty setting the float/needle valves correctly. I have since installed angled manifold plates to get the carbs more level.

I really wish fuel injection had been invented before this boat was manufactured. My life would have been somewhat simpler over the past number of years...

RH
05-09-2002, 04:57 PM
Acts like number 2 as there is a heavier smell of fuel in the engine compartment. When I started the boat, I had the compartment open to ventilate for good measure and left it up while I check for any leaks. I cannot see any fuel leaking, but the odor is there. It seemed to run rich at idle, but did not seem to load up. It didn't miss a beat on the acceleration portion of the runs, no hesitation unil 4500rpms, and then it started to what I felt was flooding out. Strong odor of fuel after that as well. I think that I will have the carb cleaned and checked as the boat has not had alot of use and it was the first time out since August of 2001. Thanks for you help, this will give me some things to check out!
RH

AVickers
05-09-2002, 11:05 PM
While you have the carb off, hook a pressure gage to the end of the fuel line and crank the starter for a few seconds. If memory serves, your pressure shouldn't go over something like 3.5 to 4 PSI. (I'll check specs and let you know if it's different from this...)

If it does, you're probably in for a fuel pump replacement.

Also, another way to check is to look down the carb throat when it's idling. If the pressure is too great, fuel will well up in the primary venturi tubes and you'll see it dripping down onto the butterflies. It'll be coming out of the venturi holders, the pump outlet and/or the top of the carb around the accelerator pump shaft...