Last week I installed a used 45 DCOE and RB Dual exhaust on my 85 GSL (stock 12A). I used a Weber pump, which claims factory set to 6 psi. I installed a holley reg and guage to lower the psi to 2.5 psi (or so).. I followed lean best idle procedures from scratch and she fired right up. It revs smooth and idles ok, but a little hesitation. I checked the pressure gauge and the damn Holley regulator was barely reading 1. I tried to increase the pressure- no change. I mean I really adjusted that damn screw, let her sit running for a while, no change....I road tested her and found acceleration was pretty good but cruising steady in any gear, at any speed I experience Fumblin, bumblin, stumbling..(Fuel Starvation???)..
I switched the regulator to a Malpassi Fuel/Filter King (which the guy I bought it from was running), used an old 60 psi gauge, and she was dead on at 2.5-3psi. I took the car out again, same damn thing..stumble and hesitation..I'm confused as hell. I checked the jets etc.. and I'm using the following:

F-11 E tube
F9-60 idle jet
175 Air correction jet
180 main jet
85 pump jet

Oh and another thing I noticed- the intake manifold is hot..really hot. I remember 10 years ago when I had a Mikuni carb set up that sucker was ICE cold... weird... Sorry about the book, but I'm confuzed???

 

well ... if nothing else, i would suspect a pressure problem first simply because i'm not sure about gauge accuracy.

it might be worth your while to look into getting an EGT or AFM gauge to assist in the tuning in order to take some of the guesswork out of it. the other thing would be to hunt down an accurate pressure gauge. i know there were a few threads here that had links to some industrial-grade gauges, so run a search and see if you can find one.

good luck.

 

Well i've got 2 guages at my disposal, the Holley and this older 60psi one (which is on loan from a mechanic friend). He swears it reads ***** to the wall accurate.
I was thinking about getting a bung welded for an o2 sensor and AFM but have read in some threads that their accuracy is questionable as well. I figured because this is a stock port 12A and just a simple 45 DCOE, that ear and butt tuning should get get me pretty damn close. I would definately add the AFM if I ported and added an IDA or something like that.
I'm going to take another look at my pump and lines and see if there is any binding going on..Maybe take a reading from the outlet side of the pump to see if it shows 6psi (factory settings) to check gauge accuracy.

Any one run the 45 DCOE with these jet settings? Any recommendations?

 

an air/fuel meter will *really* help you tune the carb rather quickly. worked wonders with my dellorto and 12a streetport/lake cities manifold.

sure, a wideband O2 sensor is much more sensative, and more costly. But the $25 O2 sensor at local parts store works good enough ladies and gentlemen.

 

Well, I cant check for you as I said in my PM since my car was stolen, but if I recal correctly, I was running:

F-11 E Tube
F9-65 Idle Jet
160 Air Correcto
170 Main Jet*
45 Pump Jet**

* I know I had a 170 main and wanted to try a 160 or 165. I know that 180 made my car run worse than the 170, but the next size down I had was a 145, and that was WAY too small.

**Im not sure on this, I just think thats what it was...

I do however know for a fact that my intake manifold got ice cold as you described. Ive actually had frost form on it before. As for my fuel pressure, 3 PSI seemed to work well for me. I tried 3.5 PSI, but it would overflow out of the float vent hole too often. I never really messed with the fuel PSI level, mostly because I knew the jetting still needed fine tuning. Anyway, I hope that helps. I wish I could offer more, but my car is MIA .

~T.J.

 

Yeah TJ- I hope you get her back.

 

I got a weber 45 on a stock port and I'm going to try tuning it as soon as I get the oil leak fixed. Which will be tomorrow. I'll write down my jet sizes and what not.
My manifold is really cold also, even when the engine is hot. That tells me that it's running rich, but I'm no tuning expert. Seems to me it should be warm, but not ice cold. I dunno, tho

 

Paul Yaw has got the art of fuel regulation tuning down to a science! If you want a *real* *****-to-the-wall accurate guage, and a write-up of why and how other guages are innaccurate, check these pages below.

First off, he's got a great writeup on why you need a good fuel regulation system, and what you need to do to get one:
http://personal.riverusers.com/~yawpower/fueldel.html

I like his title "Fuel Delivery - Get it Right or You're Screwed!".. it's pretty definitive

and the page where he has his prices listed, (again with some more info)
http://personal.riverusers.com/~yawpower/access.html

If you peruse his site you'll find that this guy really does know what he's talking about. He also modifies nikki carbs for different race classes and "all out performance" ones too, not that you need one now, but it's nice to know that he's got a flowbench and everything. That way you *know* he's got fuel delivery in his considerations.

Jon

 

The 60F9 is really small for your set up, go to a 65F9 and see what happens. I bet your air bleed screws are out 3 or more turns, are they??

Ryan

PS. your will have to re-tune the air bleed screws. Good luck

 

I have a 48 dcoe that does the exact same thing. I have yet to figure it out either. I have messed with all the jets and the fuel pressure. I am stumped.

 

Air bleeds are about 1 1/2 - 1 3/4 turns out.. I will try the 65F9 to see what happens. I also need to get under the car and check out the fuel pressure on the outlet side of the pump. My weber pump is a cylinder type like the stock one, albeit longer. I used the stock mounting points but fear the hoses may be binding.. This could be screwing me a bit too. Hopefully its reading 6psi which would be dialed down by the regulator. I could definately use a good gauge as well. I'm trying to contact YAW to get a hold of his gauge..

 

Good luck getting ahold of him, lol.

~T.J.

 

T.J.- How well did / does your Holley pressure reg and gauge work (I mean- did it hold a steady prressure, reading during idle and higher throttle?

 

It seemed to work ok...It would read the pressure faily well, and it would change according to the regulator being changed, but I have no idea how accurate it was.

~T.J.

 

look here

 

Hmmm. My first set up with the Holley reg and gauge showed little to no change during idle/acceleration, reading at like .5 - 1.0 psi..It only spiked up if I pinched the return fuel line...
My original thought is that a fuel line somewhere near the pump is pinched or binding, but that would cause my pressure to increase, right?? The volume would drop, but pressure would go opposite.. Man, I've gotta crawl under there soon..(Been busy at work). I'm also gonna order some spare jets and stuff to tinker..You folks recommend RotaryShack?

 

I'll go and check my jets when I'm next in the garage.

2 questions though, what chokes do you have? People put 40's in for top end, but that can cause problems low end.

Secondly at what RPM do the stumbles occur? I have a pretty good idea of what your problem is.

 

I have not measured the chokes yet.. The stumble/hesitation occurs when I cruise in any gear pretty much above 3,000rpm. I have not touched float level or any of the jets that came with the carb (which someone had installed on a stock 12A). The jet sizes are listed in my thread starter. Any suggestions are appreciated!!

 

We need choke size, as jetting recommendations are pointless without them.

When cruising on part throttle you are generally still on the idle circuit (mind you my idea of cruise is anything under 100mph, but thats british motorways for you :-)

I suspect that you are seeing the classic progression problem that occurs with Webers. If I have a few mins tonight I'll run through the basic checklist you need to follow to see if this is the case.

Bill

 

Couple of quick notes. Please excuse if you know all of this but I am assuming that you grew up with holleys not webers.

Most important is the butterfly position at idle. This should be so that the slightest movement uncovers the first progression drilling, This is easily eyeballed by taking the progression cover off. IF this is wrong adjust it first. If you have newer DCOEs then you have idle air screws on each body to balance the flow.

Once that is right you have to look at the progression. A stumble at idle says that either your idle circuit is cutting out too early or your main jets are coming in too late. With a friend looking down the progression holes (engine off) open the throttle until the last hole is uncovered. If this is less throttle than you cruise at, then you need to richen up the idle circuit. If it is less then you need to play with the main jets.

I reckon the F9 is too large and you should go down a size on the idle bleed, but could be wrong.

If it turns out to be main circuit related, then there are a number of things you can play with.

1. Smaller chokes.
2. Higher float level
3. F3 emulsions. These are identical to F11 but narrower, so require less vacuum to start pulling the fuel through. Convinced they are better for rotaries, but emulsions are expensive.
4. Bigger main jet.

As you can see it is easier if you can do it via the idle circuit. Webers are a hassle to get right, but when dialled in are great.

 

Actually never had a Holley carb. The only other performance carb I had was a Mikuni on a 13B SP Rx-7 10 years ago..
This is good info Bill- I appreciate it! F3 emulsion huh? My DCOE has F11's..

 

Everyone says use F11, but noone knows why. I have the drawings of all the jets so can work out which one does what to a degree (still some black magic)

I would still focus on the idles first though.

 

Well, I just ran a few tests to see if (one) of the problems is fuel delivery. I installed the Holley pressure gauge on the outlet side of the fuel pump ( 3" from the outlet pipe). Started her up and I'm getting a whopping 3 psi (according to the Holley guage) out of the pump. It's a weber pump that states factory setting at 6psi..

Secondly I took the guage, installed on the inlet side of the carb ( 3" from the inlet pipe on the carb), started it up, the gauge reads slightly less than 1.5 psi. There was no regulator in line...Just straight from the fuel line.

It seems the pump is definately inadequate or defective. Either way, I should be getting more than that from the pump??

There was another odd thing I noticed. I have seen a few of the Weber installs (like T.J's) and noticed none of them has a return fuel line. When I pinched off the return fuel line at the carb, the psi reading went up to just below 3 psi, almost matching the outlet pressure from the pump..Should I swap out the dual pipe feed for a single one? Thanks folks!

 

I've never used a return with webers. That could be messing up the regulator, but again I always use mechanical interruptor pumps for that authentic clacking sound.

1.5PSI is still in the ball park for a weber. If you can sustain high power then your flow is OK. If the stumbles get worse after hard acceleration then it is pointing to the float bowl not filling up quickly/high enough, which could be pressure related.

 

I'm going to try and cap off the return line tonite and see how she runs. Thanks again for your help, Bill!