crysis

I'm starting to run out of (efficient) ideas that could be causing stumbles on my 6-port 13b with a dellorto 48 dhla

The car idles perfectly at 1k rpms (500rpms on startup, ~1000-1100rpms when warmed up). It drives well and pulls great up to 6k ... but then it stumbles/breaks up/jumps and skips to 7k rpms. Thinking its a fuel issue, I've changed the filter, the pump, and put in a new FPR. I've pulled the plugs and theyre looking good .. slightly rich but not much buildup and spots of mocha. Brushed off the plugs too.

I've tried playing with different pressure settings from 4psi to 6psi now and still getting stumbles. It will get to 7k, but its a coin toss whether or not it will stumble there. Sometimes, it makes it through with perhaps one stumble, sometimes it will take a few stumbles to get to 7k.

Any thoughts on what to do next? Spray carb cleaner?

LongDuck

You may be describing the reason why Racing Beat went with 51IDA throats for the 13b to increase airflow at peak flow rates. Take a look over on RB tuning articles and I'll bet you can find some tips on jets and such that might help you out. Worst case, you could call them and I bet someone would be happy to walk you through it.

crysis

What's interesting is that it was running well a couple of months ago. I can't remember exactly when but at one point, it did run to redline and feel like it goes past that easily

t_g_farrell

iTrader: (1)

You should only be running, maybe 3 psi, at the most. Anymore and it will run rich and stumble
at various rpms. I ran a Dell on my 12A for 20 years so this is experience talking.

The way to adjust the FPR is to have it warmed up and idling. Then adjust it down until it starts
to stumble. Then move it up until the rpms start increasing, usually around 2.5 to 3 psi, then
back off a bit. The Dell is very sensitive to the fuel pressure. Also the flow needs to be at least
40gph or greater or it will lean out at the top end.

What kind of FPR are you using? I hopes it not one of those Mr Gasket dial things, they are
junk. A good Holley should work as long as it doesn't have internal flow issues, some do.

Heres a website that may help you out as well www.gruntled.com/Dellorto.

crysis

Maybe I need a lower pressure regulator. I'm running the holley blue pump and regulator.

New symptom: I adjusted the fuel/air screws on both sides to lean it out half a turn. This causes the stumbling to occur at an earlier RPM range (~5600?) but the stumbles are much less violent/dramatic. Thoughts? Do I need to richen it?

t_g_farrell

iTrader: (1)

Yep you should be using the low pressure 1 - 4psi regulator. You can dead head it but you
may want to use a return to keep your pump cool.

The air screws control the idle mixture which is what you actually run on for idle and cruising.
Getting the transition right requires the right pressure and possibly jets for your 13B.

crysis

I had a lower pressure regulator on it before this weekend and was having the same symptoms

crysis

On this subject,though, the return line is the other "big" metal line next to the fuel send line? It looks like there are 4 hardlines -- two big in the middle, two smaller on the outsides). In regards to the hardlines on the driver's side along the firewall

crysis

Looks like I got lucky and that the only differences in the holley pressure regulators is the spring. I think I'll swap out those

crysis

put the lower pressure spring in and still feeling hesitation

t_g_farrell

iTrader: (1)

Did you read up on the gruntled site? It has some good advice there.

Also theres the weber/dellorto book online at the Foxed.ca site. Its at the bottom with the
miscellaneous manuals.

t_g_farrell

iTrader: (1)

I would guess that either your emulsion tubes or jetting are not right for the 13B. Also what are
you doing with the extra ports since its a 6 port? Hows that work out for a Dell?