new carb. worse off

And I did clean my anti siphon valve the other night. When I pulled it apart nothing was in there but I did hit it with carb cleaner and some air.

with my rush of getting on the water I didn't seat my fuel feed. So It was hard to tell since I had so much gas on the rags in the boat. I did correct the issue immediately but I did acquire a health dose of fuel in my bilge. What should I be checking? The smell of fuel out of the exhaust?

I'm sort of stuck between a whole new distributor, a new coil, and a new fuel pump. Only because those are the three things remaining that I haven't replaced.

the vent line to the fuel pump cannot be clogged or the fuel pump wont stroke. but its highly unlikely that you would have the same issue with a new carb.
are your timing weights advancing the distributor? set your base than wang on it and the timing mark to will advance...it should, inspect the weights under the rotor making sure no corrosion or broken springs.
at this point it really sounds like a spark isssue to me, A coil is cheap and without being able to test it, thats what i would go after next, it should be a resisted coil so you should see around 9ish volts on the positive side while running.
pull a plug and groung out watching the spark, it should be a nice blueish purple, not orange

def sounds like an ignition problem

peter1234 wrote: def sounds like an ignition problem

Grabbed the timing light and checked the timing still at 10 btc, so I loosened the distributor and set to 10 atc. It runs like a top in the driveway. Now to bring it out on the water and test it under load.................Please God be the cure or I'm going to .

What I'm noticing is that my advance takes a while to come back to the initial timing. Is this normal? also it seems like the timing changes a little every time the engine is started.    Now what causes this and where can I find information on the remedy?

76tique wrote: I'm having EXACTLY the same issue with the 302 in my Tique, after installing a new rebuilt Holley carb from National. I'm pretty sure my issue is spark advance related. Bolting on the new Mallory distributor tomorrow, we're going out on Monday and I am crossing my fingers that this cures it. Am thinking I probably should have sprung for a new coil as well. We'll see...

If you find the cure, please let me know.

Well my new distributor was not the answer. I am now 90% sure my issue is the accel pump. A couple of suggestions for you. #1 - if you were ok out of the hole with your old carb, swap the accel pump nozzle and cam from the old carb to the new one. I discovered my old carb had a more aggressive cam and larger pump nozzle than the new one. This improved my performance when I swapped them on today. My old carb was not great out the the hole either (main reason I got a new one.) I still think I need a much bigger accel pump shot, and more accel pump tuning. Reason why:

Test I did on the water that I think you may want to try - (requires 2 people) Open the motorbox. I let my buddy drive, while I played with the accel pump. My buddy hit the throttle hard(the boat is still dying if I don't throttle up slowly), while I pumped the accel pump by hand. The boat shot up to 3k rpm and blasted out of the hole like never before!! I think I have found my issue. I am going to go for a much larger pump nozzle and more aggressive cam and see what happens.

76tique wrote: Well my new distributor was not the answer. I am now 90% sure my issue is the accel pump. A couple of suggestions for you. #1 - if you were ok out of the hole with your old carb, swap the accel pump nozzle and cam from the old carb to the new one. I discovered my old carb had a more aggressive cam and larger pump nozzle than the new one. This improved my performance when I swapped them on today. My old carb was not great out the the hole either (main reason I got a new one.) I still think I need a much bigger accel pump shot, and more accel pump tuning. Reason why: Test I did on the water that I think you may want to try - (requires 2 people) Open the motorbox. I let my buddy drive, while I played with the accel pump. My buddy hit the throttle hard(the boat is still dying if I don't throttle up slowly), while I pumped the accel pump by hand. The boat shot up to 3k rpm and blasted out of the hole like never before!! I think I have found my issue. I am going to go for a much larger pump nozzle and more aggressive cam and see what happens.

What were the two sizes that you have? I'm not sure what's in mine.

Here's for choosing the proper size.

To properly size a power valve, take a vaccum reading at idle and if it is above 12" for a standard transmission a 6.5" will be safe to use. For automatic transmissions take a vaccume reading in gear at idle and if the vaccum is below 12" divide that in half for proper size. Example 9" of vaccume in gear at idle will require a 4.5" power valve.


If you were able to get it with your finger and the current valve, do you think that it might just be adjusting the timing of when it shoots? Or are you having to pump it more than once for it to shoot out of the hole.

I'm also curious if it could be because I'm using that square bore gasket in combo with the 4 bore gasket.

Can anyone chime in on what size accelerator pump nozzle and cam seem to be working for our engines. Between my two carbs I have a 25 and 31 nozzle and a white, and black cam.

To see the number on the pump just open your choke plate and at the bottom of it you'll see a number stamped on the nozzle. (the nozzle is held down by a single phillips head).

YooperSully wrote: Here's some pics maybe someone will notice something.

This isn't the type of carb most of you have?

The national carbs are Holley 4160's. Isn't that what almost everyone is running on these motors?

Just downloaded and read the PCM service manual holley carb section. Strangely, it lists the red cam as being appropriate but doesn't say anything about the shooter nozzle size (or pump capacity.) I assume everyone runs the stock 30cc pump.

I have a 21 nozzle on my old carb and a 25 nozzle was supplied with the new carb. I am going to go up to a 40 nozzle and may experiment with the 50cc pump, I have one on the way. I would love to know what others are running for nozzle size. The Holley carb tuning video says that lighter vehicles that build rpm quickly should use the 35-40 size shooters. Wouldn't this apply to our boats?

My pump seems to shoot immediately when the throttle is opened, but as I stated above, when I manually depressed the accel pump immediately and all the way under acceleration in the water, to try and supply more fuel sooner (simulate a larger nozzle size, I noticed a huge performance difference. Leads me to believe I need a larger nozzle for earlier fuel delivery. I was thinking about the larger pump size b/c right now my acceleration is great from 2200rpm up and I am not sure the current pump would do as well, with a larger nozzle using up all the fuel sooner. Thoughts anyone?

I was under the impression that the power valve affects high speed mixture and shouldn't have an effect on acceleration out of the hole. Is the power valve even relevant to our issue here?

I haven't done the idle mixture adjustment yet, other than to set them at baseline 1 1/2 turns out. I do have a vaccuum gauge, reason I haven't set yet is that I am under the impression (from reading on this site) that the mix should be set in gear at 650 rpm. Is this correct? I am not lucky enough to have a dock to tie the boat to and play with the mixture setting screws, unfortunately. Can I do it at home with the boat on the hose? Obviously can't put the boat in gear without her in the water, guessing that wouldn't be a good idea with a dry cutlass bearing.

set the idle mixture screws while your in the drive and in neutral, this will get you close enough that it won't cause issues, then once you have the time you can fine tune it and the idle while in gear later while your out on the water.

BTW I feel the 1 1/2 turn usually is on the lean side and that Holleys like to be slightly on the rich side, but I was never the type of guy to say it's this or that, because not all the parts are identical, ever, there is always variation in them and then when you start stacking up that variation it addes up quickly so what works for one carb is way off for the other carb.