Help with 1979 305

Hi all,

I have been a lurker in this forum for a few years and finally bought a boat. It is a 1979 Chris Craft 280 with the single 305.

I ran it up from Lake St. Clair, up the St Clair River and around Lake Huron to Bay City Michigan this weekend.

When I purchased it and took it for a test drive, the previous owner stated that it cruised about 17 and topped out at 20.

I have heard others talk about 20 plus cruise and higher WOT.

During my travels Saturday and Sunday, I cruised around 17 mph (GPS verified) at 4300 to 4500 rpm. This sounds VERY high to me. It also burned around 15 gal per hour.

I know others may have the 350 or 2 x 350's, but what should I expect performance wise? It seems under prop'd to me. I do not know what is on there now.


Secondly (and a more pressing problem) I took the boat out on yesterday (Memorial day Monday) and could not get the boat to even go 4000 rpm. My first two guesses are a plugged fuel filter or the throttle cable slipped a little. Any thoughts? I could not even see a fuel filter in the engine room yesterday afternoon (It was 95 out and warmer than that down below, I didn't look hard). If it is the filter, I plan on replacing it with a Racor waterseperating one.

Thoughts?

Thanks all

Specs show this at 7k lb. That's quite a bit of weight for a 5.0L single engine.
If this is a planing hull, I doubt that 17 mph is anywhere near planing attitude.
If you can't get on plane, you'll be waisting fuel.
Two efficient speeds:
1) Hull speed, and 2) planing + a tad bit more.
Anything in between is not efficient, IMO.

This boat may need more engine power via a good Q/E built 5.7L, or perhaps a Q/E built 383 cu in SBC.

.

Thanks for the response.

I believe the boat does plane at 17 mph (I guess I define planing as when the boat is going fast enough that the water at the stern does not collapse back on itself and that I can see the tops of the trim tabs). My ideal cruising speed is just past the speed necessary to plane. I was running a little faster Saturday and Sunday because of the long journey and because the PO claimed that the boat cruised at 17 mph.

The boat will still plane, it just will not go as fast as it did on Saturday or Sunday. Somehow, I've lost 500 or more rpm and a couple of mph. Even on Saturday or Sunday, I could never get to the 20 mph that the PO talked about.

I have no idea how old the gas was in the tank, or what condition it was in. The boat has the original 33 year old galvanized tank and I did run it down low Saturday around noon (not many gas stations along the upper St. Clair River). Also, Sunday afternoon, Saginaw Bay had 6-8 footers on it . I'm guessing that I may have sucked up some crud from the tank and the existing fuel filter may be plugging up. At least that is my hope. I looked at the existing filter last night and it is a disposable screw-on, no brand type. I ordered a 60 gph Racor filter / water seperator (10 micron) which should be here this weekend. I guess I will see if that improves anything.


The original 100 gal tank is in good condition, but I plan on cutting it out at some point and putting in twin poly tanks (about 50 gal each). For right now, I would just like the ability to have my meger mph's back.

Thanks

Beartooth,

Did you ever solve this problem? I also have a 79 cc 280 catalina with single 305. When I test drove the boat it went 27 mph on gps. I had it for about a month and can now barely get 20 mph out of it. I did add some equipment to the boat but the weight should be minimal. I first noticed the change when I went to the marina for fuel. The boat had maybe an eighth of a tank in it when I purchased it. I put 50 gallons in and noticed the change in speed. I originally thought that the weight of the fuel made the difference but the problem hasn't reversed itself as the fuel tank is being emptied. One other note, after I had purchased the boat I was trying to figure out which battery was #1 and #2 on the battery isolator switch. While turning the switch with the engine running, I accidentally turned the switch to the 0 or off position for a few seconds. I later read that this could do damage to the alternator. The alternator still seems to charge as far as I can tell (volt gauge is usually around 13) but this was the same time I noticed the performance drop. Is there any chance that I could have done some damage to the alternator and this is the problem with my top end decrease? I could originally get about 4500 rpm out of the engine. Now I can only get about 3300. I should try changing the fuel filter. I was just wondering if anyone knows if the alternator could cause this problem.

I have not solved my problem to date. I replaced the original POS fuel filter with a 60 gpm Racor unit. I took the fuel strainer screen off the fuel line input to the carb, I checked the anti-siphon valve on the top of the tank. I blew air back through the pick-up line to make sure there was nothing stuck on the end of the pick-up tube. Last weekend I could barely get it to 3000 RPM so I took a can of carb cleaner and sprayed it around the carb, looking to see if there was a leak. I then cleaned the carb out real good and got it back to 3900 rpm or so. I also tried reversing hard to clear anything that might be stuck on the prop. I'm going to dive this weekend and check the running gear. Maybe I caught a rope or something.
Really? You got to 27? I would love that. I would love your 20 mph. I can only get about 16 wot. I was just getting ready to be happy with 15 mph then I hear about your 27??? Now its going to cost me.


This winter I am going to investigat a different prob as well as sand off 33 years of bottom paint that has the texture of stucco and repaint it smooth.

I have also heard that switching to off can kill your alternator. In fact, somone wrote next to my switch in pencil not to do that..... Pull your belts off. Your alternator should spin very freely by hand. I don't know if you could disconnect the wires from the alternator and run the motor like that. It would be worth the internet check.

My next plan is to pull the plugs and check for fowling. I know I ran a couple of tanks of ethenal fuel through the boat when I was bringing it home. Who know if that had anythign to do with it. I may pull the original round tank out this winter and replace it with a couple of poly tanks.

Good luck. Keep me in the loop.

Thanks for the reply. I too plan on taking a dive under the boat this weekend to inspect things. As for the alternator, I was planning on changing it out to a 105 amp anyway. The 50 amp doesn't seem to cut it. Spot light and rear floodlights aren't as bright as they should be. I may have voltage loss through some of the old wiring powering the helm. Not looking forward to rewiring that bird's nest.

I took my helm off for a minute on Saturday and not only is it a birds nest, it is full of old mud-wasp nests too. It looks like someone packed it full of hard clay. BTW, above my windshield there is a teak trim board that really did have a birds nest.... Oh the fun

bottom paint like stucco - will kill your high speed performance and any fuel economy...so will a 'wet hull'.

the alternator's field lead needs to be removed to turn it 'off' - never have an alternator running and then throw a battery switch connected to it...

You may wanna try a separate outboard tank as a fuel source in lieu of the on board tank - quick and easy way to isolate fuel related issues.

One other item to check that will inhibit WOT - make sure the ignition system's timing advance mechanism works - the 'springs and weights' inside the distributor may be frozen...

Strange. I had a bird nest behind the same board. Refinished the board and rebuilt the cabinet above the helm that hangs from the hardtop.

Update: So I went for a dive under my boat yesterday to check out the prop. Everything was fine down there. I then got out the carb cleaner. Sprayed it down on the outside, then fired it up and sprayed down the carb while working the throttle. I got behind the wheel with the carb still exposed and started driving. It was still doggy but gained a couple hundred rpm. I opened the throttle all the way up and could reach the carb while driving so proceeded to spray carb cleaner down both open barrels. Something came unstuck because it was like somebody flipped a switch. I gained 1000 rpm so I'm back to 4500 wot. I first thought it was just burning the carb cleaner but I ran the boat all day and it runs fine now. I can reach 25 mph (and that is with all my junk in the boat). Have good power now all the way through the throttle. I guess all the trolling I was doing was gumming up the carb. I need to keep a can of that GUNK carb cleaner on board in case it acts up again.