WOT only 3800 RPM

Check your spark plugs (clean and gap) or replace them. Next check your timing advance at 3000 RPM. If you do this at home don't hold the RPM that high any longer than necessary than it takes to get a reading. If you don't have a variable strobe delay timing light then get a timing tape label for your harmonic balancer. If you go this route make sure you get the right one for the diameter of the balancer. 3000 RPM with engine unloaded is not enough to get the secondaries to open.

I just saw this by GottaSki

Aim for 10 initial, 36 final
i like these numbers..I think its a little earlier than stock.
I run my boat light for slalom, you may want to be on the shy side of these numbers.
10 at 700
21 at 1500
30 at 2k
34 at 2500
36 by 3k

Now that I've got these numbers I'll look to see what mine does.

Still would like to know how to check the secondaries. Thanks.

Sounds like your choke isn't opening up all the way.

SNobsessed, Good thought on the choke. I went out and checked it right away and after a minute or two the choke plate was vertical. So I guess that one is off the list.

Yeah, when I had those needle valves all the way in and the engine was still running great I thought "this is odd behavior for a carburetor". I guess its the power valve or something in the metering body?

I've ordered the refresh kit and hope to rebuild it this weekend but it's been a while since I tackled that job. The last time I rebuilt a holley carb was 1978 and it was on my '68 Camero. Hope the instructions are good. I'll be posting any questions I have so stay tuned!

Tim

If the air mixture screws are not responding there's an issue with the carb for sure.
It's probably running on the transition slots and not the iddle circuit.
it seems like a good time for a carb rebuild.

I need some help here I'm running out of possible causes of the poor performance. Bit of a long post but wanted to provide you with the whole story.

After the carb rebuild the boat runs great in the driveway but this time it would not go over 3600 RPM?
Granted the water was a choppy with an occasional white cap and we had 6 people in the boat but still it should turn more than 3600.

I took a plug out when I got back and at least now no sign of it running rich, so that's good.

So far here is what I have done/checked

On the fuel side;
can of sea foam in the tank, ran it through
anti-siphon valve clean, spring compresses easily
new fuel-water filter
carb rebuilt

On the electrical side
checked timing
confirmed firing order (18456273)
new plugs
Last season replaced Pro Tech with Mallory (kit from SECC)


What I will check next...
Secondaries opening (best way to check by raising hatch and using mirror to see if they open?)
Poor Compression (will test that and report back)
Prop (previous prop had a ding, current prop was a remanufactured version of stock OJ, ordered new ACME prop which was needed anyway and will eliminate prop as cause of problem)



What else could be causing this poor performance?   

FYI, the original 351 HO was replaced by the previous owner with a Jasper long block. So I lost 40 or so HP due to that but even so shouldn't it still rev to 4400? I've wondered if the firing order stayed the same? I assume it did because the other version of firing order I've seen has 4 plugs in a different sequence. I assume there is if 4 plugs were firing out of order it would not run well at all.

Ideas on what else I should be checking?

Tim

Thanks Eric,

Yeah, its time for a compression test, it's raining right now but hopefully I can do it tomorrow morning.   I assume you do vacuum readings from the main port that runs to the PCV?

I assumed the boat is not soggy since it does not have wood, although I guess the foam could still be soggy though, had not thought about that. I'll re placing the carpet at the end of the season and could look for some worn fiberglass on the floor.

are you sure the secondaries are opening?

how old is your son? if not old enough to drive have someone else drive and hit the gas while you watch for the secondaries mechanism to open. If they dont, You could try to manually open them once you reach your limited wot to see if that gives you the lacking rpms.

First thing to check is the mechanism was correctly put together after the rebuild... then you should check the secondarie's diaphgram.

Check to make sure the shaft isnt frozen as well. You should be able to turn it by hand.

Thanks guys,

TRBenj, when I opwn the throttle all the way (engine off) I can lift the diaphragm linkage and the secondaries open easily.


Luchog,    There is a small vacuum opening next to one of the 4 screws that hold on the cover for the secondaries diaphragm. According to the exploded view a small "BB" goes in that general area. It's called the "diaphragm housing check ball" on the parts list. I put it in the small vacuum opening since it fit and I didn't see where else it would go. Should it go somewhere else?

Tim

I stand corrected, there's a checkball on the secondarie diaphgram too.

There's a nice carb rebuild procedure on the 302/351 service manual on the reference section. I think you want to check it.

Excel94 wrote: I have to wait to test it on the boat because the damper plate started making a racket now that I have the new prop in place. Should know somehting next week

have you checked if the problem is while at iddle? what's rpms while iddling around? I have found that these newer props with more surface area and less slip put some more load on the engine dropping the rpms while iddling. maybe you just need to bump up the iddle a little bit, mine's set at 750.

the problem is there indeed, but the urge to take it apart might depends on how much you need to bump your iddle to keep it silent.
How many rpms at iddle, and when iddling in gear?