HELP please! DCOE’s stumbling (leaning out) at ‘tip in’...

[Stevenc22]

Check your float level. I had very similar problems and fixing my float levels helped a ton. Pull the top of the carb and use a drill bit of the correct diameter to dry the first level.

 

 

[sam1904]

Thanks all, I’ve checked my float level and driven several times. I have plastic floats and each time I think I am bang on setting it at 12 mm at the center of the float. When I then measure fuel level with the carbs assembled it is around 29 mm and not 27 mm. I am assuming I should dial-in on the fuel level number even if it results in slightly less float gap?

[Son of Marty]

Do you have a fuel pressure regulator? Webers don't like to see over 3 psi, anything more you'll start to over power the floats

[Chris_B]

7 hours ago, sam1904 said:

Thanks all, I’ve checked my float level and driven several times. I have plastic floats and each time I think I am bang on setting it at 12 mm at the center of the float. When I then measure fuel level with the carbs assembled it is around 29 mm and not 27 mm. I am assuming I should dial-in on the fuel level number even if it results in slightly less float gap?

Float gap is irrelevant except to the fact that float adjustment determines fuel level. You should dial in the fuel level as measured in the main jet well, not the float level. Of course, the float level controls the fuel level. A bit of a conundrum.

[kbmb02]

Question: How many 'turns out' are your idle mixture* screws? (smooth, at idle speed, warmed-up engine)

 

[Hans]

I assume we're talking Spanish here with plastic floats. I saw one diagram that showed 12mm at the tip rather than the middle. Elsewhere, saw 14 recommended. Probably better to use bowl level as reference. 25mm as I recall, but there was some debate about 29.

 

As above, fuel pressure regulator? Mixture screws?.

 

 

 

 

[wegweiser]

Fatter idle jets have cured this issue on just about every DCOE equipped car I've ever set up (except the ones with comically oversized venturis!) . Don't be afraid to try bigger/ richer 65f8 idles... or (before spending the money on larger idle jets) try richening up the idle mixture by about 1/2 turn on each cylinder. If that solves the stutter at tip-in... larger idles may be your answer.

 

Edited May 10, 2021 by wegweiser

[Chris_B]

+1, Paul, as I suggested on Saturday. Of course, this will tend to fatten up the transition and folks with AFMs sometimes find that alarming (at least, I did). You have to learn to live with it.

[kbmb02]

17 hours ago, Chris_B said:

+1, Paul, as I suggested on Saturday. Of course, this will tend to fatten up the transition and folks with AFMs sometimes find that alarming (at least, I did). You have to learn to live with it.

 

And/or/consider: Tune the low-speed* circuit first (*aka idle circuit, though it's more than idle), then adjust the main circuit to improve transition and higher RPM's as necessary. -KB

[Hans]

https://www.apexspeed.com/forums/showthread.php?64306-Weber-40-45-DCOE-Experts-Proper-Float-Level&s=4fd5b72079b5f57038003d82d3f4d987

[Hans]

On 5/10/2021 at 4:16 PM, wegweiser said:

Fatter idle jets have cured this issue on just about every DCOE equipped car I've ever set up (except the ones with comically oversized venturis!) . Don't be afraid to try bigger/ richer 65f8 idles... or (before spending the money on larger idle jets) try richening up the idle mixture by about 1/2 turn on each cylinder. If that solves the stutter at tip-in... larger idles may be your answer.

 

Richen by turning them out?

[Stevenc22]

10 hours ago, Hans said:

Richen by turning them out?

Yes. And there is alot of confusion about how many turns are needed for 151's. Some people same 1.5 others say 3. Top End performance says 2.5 - 3.0 turns for 151's.

 

https://www.racetep.com/manufacturer/carbs-and-injection/weber/weber-carb-tuning-and-technical-info/jetting-and-tuning-downdraft-and-sidedraft-weber-carbs.html

[2002iii]

4 minutes ago, Stevenc22 said:

Yes. And there is alot of confusion about how many turns are needed for 151's. Some people same 1.5 others say 3. Top End performance says 2.5 - 3.0 turns for 151's.

 

https://www.racetep.com/manufacturer/carbs-and-injection/weber/weber-carb-tuning-and-technical-info/jetting-and-tuning-downdraft-and-sidedraft-weber-carbs.html

I believe its 1.5 turns for the old Italian made Weber's and 3 turns for the new Spanish made Weber's.

[Chris_B]

He has an AFM, right? This discussion of how many turns on the idle mixture screws is somewhat irrelevant. He should turn them out (counterclockwise) until he sees the desired AFR on his meter. I would  try ~12:1 just to see the effect on the lean spot.

[Stevenc22]

19 minutes ago, Chris_B said:

He has an AFM, right? This discussion of how many turns on the idle mixture screws is somewhat irrelevant. He should turn them out (counterclockwise) until he sees the desired AFR on his meter. I would  try ~12:1 just to see the effect on the lean spot.

 

Actually it is relevant. You want to hit the right AFR with the right number of turns as that then sets the rest of low speed driving. If you have too small an idle jet but set the right idle AFR with 4 turns, when you start driving you are going to go lean because you are already using some of the progression holes just to make IDLE and there wont be enough progression holes left to cover the rest of the low speed driving.