Ok. Got new motor 582 with much bigger heads than previous 555. Headed went from pro1 335cc to bbx380. Both cnc. Both motors ran well.

Since moving to this new motor I have a stumble when matting it to get on two step. Same carb APD 1150 on alky.

Went thru carb and rebuilt it few weeks ago. Car otherwise runs really well and repeats. I leave at near exact same temps every run at 180*. Watch racepak dash for water temps and trans temps. Car repeats get well.

I'm thinking it's the change in heads causing the stumble. If I bring up rpms it does it less, but still is sluggish. Every once in awhile.. Rare it comes up perfect. But many times it is sluggish.

I'm no carb expert so looking for ideas.

Thanks

Here’s my order of operations for this issue. Not an expert by any means.

I’m assuming you already have 50cc pumps.

1. Bigger squirted on primary. If it gets a little better, put a bigger one in the secondary also.

2. If it’s better but only because it moves the stumble a little later, then move to the next pump cam on the primary

3.if it’s a 3 circuit carb, and it’s really being stubborn, drop about 5 numbers on the intermediate airbleeds. Start with primary only. Consider taking a couple numbers out of the high speed airbleed if the smaller intermediate bleed solves the issue. Many will shy away from this. Most will say intermediate bleeds are useless, should be removed completely, or the carb converted to 2 circuit. I have found the intermediate bleed to be a very useful tuning tool myself.

For harmony of rhythm staging, you need it to reach the rev limit the same every time.

Is this methanol or gasoline?

He said alky. I think BJs put forth a very logical progression for the accelerator pumps.

quote:

Originally posted by Canted Valve:
He said alky. I think BJs put forth a very logical progression for the accelerator pumps.

I see it now thanks.

Typically a methanol stumble means it's lean off idle. Smaller idle air bleeds and turn the idle mixture screws out a turn and a half max.

First thing blow out all of the air bleeds with carb cleaner. They get clogged and will cause that stumble.

The air bleeds are all clear. I cleaned that all when I rebuilt it with no change.

I'll check the squirters as outlined here

Re check your ignition timing...a few degrees more advance before the two step could help if you have some programmable features.. Great Throttle response isn't usually the product of giant pumps shots..Fuel injection doesn't use accelerator pumps, it relies on the quality of the A/F mixture supporting the needs at idle..same thing with a properly calibrated carb supporting the needs of the engine it is on...The idle circuit probably needs work...make sure front and rear throttles are open the same amount uncovering the idle transfer slots the same amount to start...

Thanks on the timing

I thought about that and even changed the distributor as in thought in found a problem in my old hei cap... So I upgraded to a billet small cap. Prob at first seemed better then came back.

And in was big into fuel injection. FI does have that feature of called accelerator enrichment works of tps percent change. Does the same thing as carb but with injectors obviously. And to your point timing can be altered as well during event.

Put a smaller idle air bleed jet in it. Typically an intermittent stumble on the starting line with methanol, is a lean condition off idle.

You can burn a lot of fuel trying a lot of different things, a smaller idle air bleed to richen idle will typically fix this condition.

How much smaller?

quote:

Originally posted by ski_dwn_it:
How much smaller?

8 - 12 - 16

Get em all, they're inexpensive

Take precautions installing not to drop em down the throat, they're small kinda like the size of a bebe or a pellet.

This message has been edited. Last edited by: Mike Rietow,

Your carb build sheet from APD will tell you what you have now for Idle air bleeds. Subtract 8 - 12 - 16.

One of those sets will get you there.

Turn the idle mixture screws out one and a half turns max.

quote:

Originally posted by Mike Rietow:
Your carb build sheet from APD will tell you what you have now for Idle air bleeds. Subtract 8 - 12 - 16.

One of those sets will get you there.

Turn the idle mixture screws out one and a half turns max.

Thanks the idle screws are less than 1.5 turns. I was having idle issues along with this and I adjusted them the other weekend. Put them all the way in, out all 1.5 turns and then tweaked them in a little from there. Now idle is smooth and only changes about 2-300 when put in gear. Before it would almost stall.

This problems with it getting up on 2 step was prior and still exists. All started with new motor. Before everything was crisp.

I will double check the arms for the pumps too. Before they were all adjusted properly but I will reconfirm.

Odd thing is sometimes it will come right up. Most times it stumbles and is slow.

Remembered is had my APD sheet in my phone:

Jets 196 - 196
high side .024 .024
intermediate .029 .029
idle .040 .040

squirters .070

quote:

Originally posted by ski_dwn_it:

quote:

Originally posted by Mike Rietow:
Your carb build sheet from APD will tell you what you have now for Idle air bleeds. Subtract 8 - 12 - 16.

One of those sets will get you there.

Turn the idle mixture screws out one and a half turns max.

Thanks the idle screws are less than 1.5 turns. I was having idle issues along with this and I adjusted them the other weekend. Put them all the way in, out all 1.5 turns and then tweaked them in a little from there. Now idle is smooth and only changes about 2-300 when put in gear. Before it would almost stall.

This problems with it getting up on 2 step was prior and still exists. All started with new motor. Before everything was crisp.

I will double check the arms for the pumps too. Before they were all adjusted properly but I will reconfirm.

Odd thing is sometimes it will come right up. Most times it stumbles and is slow.

Sounds good, that's what you want 200-300 rpm difference in gear, or less. New engine makes better signal, So you're gonna richen it a hair, Which means most likely you'll be visiting the idle mixture screws and idle rpm screw again, so it's crisp on the deck. Keep us posted on progress.

quote:

Originally posted by ski_dwn_it:
Remembered is had my APD sheet in my phone:

Jets 196 - 196
high side .024 .024
intermediate .029 .029
idle .040 .040

squirters .070

Got delayed and cant find air bleeds around this area anywhere.

So in talking with a buddy he may be onto something. I normally bring up my RPMs a little while staging which is likely using up some of the pump shot. He suggested that I get my arms of carb timed where there is zero depression of the arms at staging RPMs. Then when I mat it is will have a little more shot. In other words I am using up some of it before I need it and while staging.

As such I am going to back these off as I know they are touching at idle now.

Might be just enough to overcome the stumble.

Thoughts.

Makes sense because the carb when I got it those arms were pretty loose and they said it was setup for a transbrake.

quote:

Originally posted by Mike Rietow:

quote:

Originally posted by ski_dwn_it:
Remembered is had my APD sheet in my phone:

Jets 196 - 196
high side .024 .024
intermediate .029 .029
idle .040 .040

squirters .070

Don't think that diagram is accurate on APD carbs. I cant remember which, but APD swaps a couple of the air bleed locations around compared to conventional Holley locations.

They swap Int and idle around.

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