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87MCProstar
07-07-2010, 02:05 PM
now I am having issues with WOT, ran great for 3 trips to the lake but yesterday afternoon we started seeing/feeling problems and again this morning. So I don't know if I screwed anything up by adjusting the fuel screws, didn't know if I could of messed plugs up or timing or something just seems really wierd.

Here is what exactly happens, idle through about 30 mph she is fine then starts to get worse when you lay the throttle down. When you hit WOT she only hits 40, where she normally hits 45-46, then backs right down to about 34. There is some feel of hesitation too once she backs down.

Any suggestions would be great.
Thanks

87MCProstar
07-08-2010, 09:43 AM
41 views and no help?

Skipper
07-08-2010, 09:46 AM
It has been a minute since I adjusted a carb, but I recall that you run the motor to operating temp. Then, one set screw at a time turn the screw clockwise until the motor starts to stumble. Next, back the screw out half a turn and rev the throttle to clear out the carb. Repeat on the other set screw. Yes, I know this is the idle adjustment, but you have to start here to get the carb adjusted properly. If that doesn't correct the problem, you probably have a problem with a power valve or intake leak. To check for intake leak run the motor and spray starting fluid through the straw at the base of the carb. If it sputters, it leaks.

thatsmrmastercraft
07-08-2010, 10:14 AM
What was the source of the fuel smell? Chances are that is a clue to this issue.

You may have fouled your spark plugs if you were running too rich.

thatsmrmastercraft
07-08-2010, 10:22 AM
It has been a minute since I adjusted a carb, but I recall that you run the motor to operating temp. Then, one set screw at a time turn the screw clockwise until the motor starts to stumble. Next, back the screw out half a turn and rev the throttle to clear out the carb. Repeat on the other set screw. Yes, I know this is the idle adjustment, but you have to start here to get the carb adjusted properly. If that doesn't correct the problem, you probably have a problem with a power valve or intake leak. To check for intake leak run the motor and spray starting fluid through the straw at the base of the carb. If it sputters, it leaks.

If you set the mixture screws in this manner you will be close, but a better way is to start out with your method, then gradually back the screws out to hit max RPM. You don't have to be too worried about clearing the engine by revving it up as these changes don't actually add or remove a large amount of fuel. Better to just let it idle for a minute to stabilize between adjustments.

Using this method you are going to the rich side of where the engine runs best. If you are more concerned with fuel economy than power, once you have reached max RPM, you could turn your mixture screws in 1/2 a turn.

However you go about making adjustments to your carb, make sure that you check your spark plugs a few times following to verify your adjustments are not too rich or lean.

87MCProstar
07-08-2010, 10:30 AM
thanks guys, and just to make sure I'm look @ the plugs the right way, they don't want to be black or white correct? more grayish

thatsmrmastercraft
07-08-2010, 10:33 AM
A light tan would be an ideal color. Just not too black.

87MCProstar
07-08-2010, 10:44 AM
thats what I thought, thanks TMM

thatsmrmastercraft
07-08-2010, 10:45 AM
No problem.

87MCProstar
07-08-2010, 03:49 PM
well pulled the plugs, they were either a white/gray to tan color on all of them so fuel was good. I replaced the plugs and ran the motor again through the rpm range for an extented period of time and it was fine...
except when at WOT, it would pop through the carb while doing about 44/45mph...i didn't have a timing gun handy so I'll have to go up another time to check timing...
but if the timing is where it needs to be what else would be making the engine pop through the carb?

thatsmrmastercraft
07-08-2010, 04:19 PM
Might be a vacuum secondary diaphragm with a small hole. Bad power valve might cause a similar problem. Could be a bad cam, lifter, or worn/bent pushrod too.

87MCProstar
07-08-2010, 04:31 PM
well I don't think its a bad power valve, becasue when I closed the idle screws the motor died. While @ WOT secondaries did open and fuel just rushes in, will that happen when there is a small hole? And I sure as $h!t don't want it to be the other two, thats way over my head mechanically and don't want to deal with that.

thatsmrmastercraft
07-08-2010, 04:36 PM
The power valve will not open at idle no matter what you do with the mixture screws. The only way to check it is to remove it from the carb and grab both ends and try to twist it. If it will turn the valve is shot. The backfiring through the carb is a sure way to blow the power valve. Holley changed the design at some point to eliminate this from happening, but I am reasonably certain it was a while after your carb was manufactured. They do make a simple kit that resolves this issue as well. I am thinking power valve.............but I have been wrong before.

If you saw the secondaries working you should be OK there.

87MCProstar
07-08-2010, 04:46 PM
do you have a picture of where that would be located on the carb? and for 20 bucks it would be worth just replacing anyways right?

I did see the secondaries open, but are they supposed to be wide open that the primaries?

87MCProstar
07-08-2010, 05:02 PM
is the part # i'm looking for 125-65?

thatsmrmastercraft
07-08-2010, 06:00 PM
is the part # i'm looking for 125-65?

Close, but no cigar. You want the 125-25. The last two numbers designates at what vacuum the power valve opens. You would be too rich with a power valve opening at 6.5" of vacuum.
This is what you want. http://www.summitracing.com/parts/HLY-125-25/

At WOT, your secondaries should be fully open. Are yours not opening all the way?

87MCProstar
07-08-2010, 06:10 PM
No the secondaries aren't opening the whole way. Is that the culprit? Bad vaccum.

thatsmrmastercraft
07-08-2010, 06:33 PM
If they aren't opening all the way, you won't get enough air into the engine. I don't think that would cause it to pop back through the carb. Sounds like you need to replace the secondary diaphragm. May as well pick up a power valve at the same time. Both parts are cheap.

87MCProstar
07-08-2010, 11:38 PM
well the inital timing was down to about 5* adjusted to ~12 * and the popping went away, but it gets bogged down at around 35-36mph. The secondaries still aren't opening up completely so to me looks like thats the issue. Plugs look within normal range

thatsmrmastercraft
07-09-2010, 12:28 AM
If your secondaries aren't fully opening up that will certainly be an issue, however, that is about the same time your power valve will be opening up. I would first manually open the secondary throttle blade (without the engine running) to make sure there isn't a mechanical restriction. Assuming that is OK, I would replace the secondary diaphragm.

87MCProstar
07-15-2010, 01:51 PM
Okay so I replaced the secondary diaphram, seems to have cleaned up one issue, I'm now gettin 45 mph again, but now after run @ wot for a little while to boat will slow down to an idle on its own. If I don't follow it to an idle with the throttle it will stall, if I do it will idle on its own. So I am taken it that the power valve is crapping out. How do u replace that, I ant find any info online. And is there only 1 or is there 2 (one in each fuel bowl)? Any info would be great. Thanks

thatsmrmastercraft
07-15-2010, 02:06 PM
One power valve inside the primary fuel bowl. You need to remove the 4 bowl screws and take the bowl off. Check the stamping on the existing power valve. Should be a 2.5 if my memory still works. Buy blue bowl gaskets - they are reusable and you won't have to spend twenty minutes cleaning all the old gasket off next time.

87MCProstar
07-15-2010, 02:33 PM
I've now got a dilema, I'm out ont the water and boat starts runs, were doing 25 mph then boat f'n stalls and now won't start

thatsmrmastercraft
07-15-2010, 02:40 PM
May be flooded. Have you tried opening the throttle most or all the way while you are cranking?

87MCProstar
07-15-2010, 02:49 PM
Yeah that's probably it, flooded. I'll give it awhile. Thank god for friends though, buddy had to drag me back to dock.

thatsmrmastercraft
07-15-2010, 02:55 PM
Glad to hear you got back to the dock. You might owe him an adult beverage.

hkallestad
07-15-2010, 05:08 PM
Correct me if I'm wrong, but doesn't the mixture screws only have an effect at idle???

87MCProstar
07-15-2010, 05:10 PM
yeah i do, the funny thing is we got back to the dock, let boat sit for 2 minutes, tried to start again and it f'n fired right up. ***? If its not the PV what else could be causing me issues like this? it doesn't make any sense.

Can I pick those gaskets up at a auto parts store or are they 'marine' specific?

thatsmrmastercraft
07-15-2010, 05:10 PM
At idle and in the transition to the main metering system. No correction needed.