Wont reach WOT range after tune up

[welch181]

Ok, after fixing my idling problem, using idle mix screws to keep boat running now I put it in the water and now I have a new problem. The boat idles great, runs great gets up on plane great, but now the max rpm at WOT is right at 4000 rpms. Before changing the plugs, plug wires, fuel filters, and adjusting the carb, the boat pulled 4400 rpms and 44 mph. Now it does 39 at 4000 rpms.

Any ideas on where to start to determine what caused this after doing maintenance on the boat??

Motor is 93 OMC 4.3liter with Holley 2300 2 barrel carb, OMC Cobra outdrive

Thanks in advance for any insight.

 

[kmadsen]

Re: Wont reach WOT range after tune up

Check the timing 1 degree BTC if using 87 octane / 6 degrees if using 89 on '93 4.3L OMC. ( I've got same engine '93 ChrisCraft 185). How was the boat loaded (same passengers and fuel) and did you try adjusting the trim to find a better RPM? Did you adjust idle mixture screws when engine RPM was 550-650? Manual says turn both adjust screws 5/8ths open (counterclockwise) from full closed (close very gently as not to damage head and seat of screw) as a starting point.Then slowly adjust one slowly(open or closed) till a smoother idle, then the other. You may find you have to readjust the idle speed screw to keep the RPM 550-650 rpm after you find the appropriate idle mixture screw settings. If all this checks, try checking the ignition side. Good alternator charge, good spark (coil), correct spark plugs 43RT. One last thing first check throttle cable adjustment. Make sure when your Throttle(lever) is wide open the Throttle on the carb is wide open.Sometimes my best RPM is just a tad before WOT depending on atmospheric conditions. Hope this helps . By the way Im running a 19 pitch 14.75 inch prop and getting 4300-4400 rpm and 37-38mph indicated depending on water/wind conditions. Good hole-shot performance.

 

[welch181]

Re: Wont reach WOT range after tune up

Good idea, I havent checked the timing. Yes the boat was loaded the same, yes used trim to no avail on getting over 4000. I adjusted the mixture screws to get the idle to come down to 650 in the water in gear. Did I need to adjust the idle screw instead to bring it down from 900 to 650? Does changing the idle mixture screws have any effect on the mix at WOT? New plugs were identical to the ones removed when it ran higher rpm even though plugs were shot. Alternator shows 14.5 volts charging. On the throttle cable, should the choke plate on the carb be wide open when you move the throttle to WOT? Even when the motor is not running? I noticed that there is very little movement in the position of the choke plate on the carb, but I have not looked at it with it running didnt know if that would change anything.

Thanks for the response

 

[kmadsen]

Re: Wont reach WOT range after tune up

You are correct that idle mixture screws should be adjusted while in gear, but you should first adjust the idle screw to attain 550-650 rpm, and then adjust mixture screws to attain the smoothest idle. (Again 5/8th turn open from full closed is the recommended start point). Throttle plates are closed during idle, and fully open at WOT. You can check without having engine running, and just move your throttle lever and watch throttle plate. As for the choke, if it sticks in the open position, the engine will be hard to start. The choke is controlled automatically, and closes when starting a cold engine to decrease airflow and enrich the mixture. I f it is sticking the engine would be running rough especially at lower rpms. I'll read up in my manual if there are any adjustments you can make.
By the way did you just fill the tank?? Possible bad fuel batch.
You may want to invest in a manual, best bucks i ever spent.

 

[welch181]

Re: Wont reach WOT range after tune up

Ok so timing is correct at 6 degrees. I attempted to use the idle screw to set the idle down to 650 but i can take the idle screw completely out or screw it in farther and the idle just increases. Using that screw adjustment only increases the idle and will not get it down that low. The only thing that changes the idle is adjusting the mixture screws. I can get it to go down that low, but the mixture is no where near where it should be I am sure, the mix screws are almost seated to get the idle down to 650.

The idle screw is the screw that moves down to the throttle control arm correct? That is the only screw other than the mixture screws that I have been able to locate on the carb.

Would that change the WOT if the idle mixture screws are not set correctly or does that just effect the idle?

As to the just fueling question, no it was not any different fuel, I did however add a can of sea foam to the fuel.

Another thing I noticed was after running at WOT at 4000 rpms (wont go higher than that now) and bringing back to neutral, it idles at around 1200-1500 rpms for 15-30 seconds before coming back down to its normal idle range.

Still searching for answers and getting frustrated as usual.

Thanks for all the help

 

[chiefalen]

Re: Wont reach WOT range after tune up

Time for a full carb rebuild.

 

[welch181]

Re: Wont reach WOT range after tune up

Would the carb needing rebuilt cause all of my symptoms? If so I will get the kit and rebuild the carb this week if I was pretty confident that is my problem

Thanks for the continued help

 

[chiefalen]

Re: Wont reach WOT range after tune up

You say it's sticking at 1200-1500 when you return the throttle to neutral before it idles at 650.

Rebuild the carb, check all the filters are CLEAN. Than run it on a external tank of gas for tuning and adjusting the carb.

Than run it on the water to make sure everything is running well on the external tank.

When all is well than switch back to the on board tank.

But before switching to the on board tank i would, suck all the crap out of the bottom of the tank.

This is what i would do if it were MY boat.

Good luck!

 

[mthieme]

Re: Wont reach WOT range after tune up

By chance, do you have the cheesy Chrylser points in your distributor?
If so, you're getting more rpm than I got with mine!
Finally replaced with Pertronix CDI module. What a difference!

 

[welch181]

Re: Wont reach WOT range after tune up

Yeah when return to idle it drops back to around 12-1500 rpms for a few seconds then gradually drops down to around 800, which is where the idle is in neutral to achieve the 650 in gear in the water. I have replaced the fuel filter twice to try and solve this, no water in either and just a little sand in filter the first time.

So it looks like a carb rebuild time, do local parts stores sell the rebuild kit for the Holley 2300 2 bar carb or do I have to order it from somewhere?

Thanks again

 

[chiefalen]

Re: Wont reach WOT range after tune up

There is a fuel filter in the fitting bye the carb, clean?

There may be on in the fuel pump, Clean?

There is a screen on the fuel pickup tube, clean?

 

[welch181]

Re: Wont reach WOT range after tune up

Have not pulled the pick up tube screen, or the carb inlet screen, figured that if it was running up to 4000 rpms and running high when back to neutral, that it getting fuel was not the problem.

The fuel pump doesnt have a filter in it I dont think, the water separator is just below the fuel pump and it appears to be sealed so I would not know where a screen would be on that one.

 

[welch181]

Re: Wont reach WOT range after tune up

Will try the WD 40 after the rain stops, the only vacuum line I have on the carb is the line going to the electric choke. Is there supposed to be any other on the Holley 2300? If so connected where and to where? Of course it has never had any other vacuum lines and it ran fine up until a month ago.

Thank you guys for all the input

 

[sarantis]

Re: Wont reach WOT range after tune up

i would suggest you did a compression test before rebuilding the carb whose results are not always granted.Especially if you had an overheating in the past or if you see any signs of rust round the head.Personally i was running for many time with slightly blown gasket at 3500-4000 rpm.

 

[welch181]

Re: Wont reach WOT range after tune up

I did a compression test before the tune up, when it first started having idle difficulty. All tested fine. No signs of rust around head at all and it has never overheated. The initial problem just started about a month ago, ran great til brought to idle, ran real rough at idle, figured it was plugs, tried plugs, wires, etc. and now I am where I am at the beginning of this post

 

[welch181]

Re: Wont reach WOT range after tune up

Is the carb rebuild kit sold at local auto stores or do I have to order it online for the Holley 2300 2 barrel?

Thanks for all the help so far guys