I recently bought a '74 e9 with the triple Weber set up. This was set up in '02 along with a long stroke crank, I think I recall that made it a 3.2. Only have had the car a couple months & working out the bugs, just finished the brakes. So, now that it stops good, I need to get a "surging" out of the engine. It comes on when you hold the throttle steady around 2500 rpm no load. I'm rather sure it will be a carb issue & I've done lots of successful tuning, but this will be my first shot at Triple Webers so I figure any help would be a good place to start. Thanks in advance~
Three Webers
- Thread starter Rod Cole
- Start date
Belgiumbarry
Well-Known Member
please post a pic of the setup and what jetting ? idle,air ,main and emulsion tubes ?
I have yet to open it up, I got three rebuild kits knowing I had to get in there, and I will get the jet info for you tomorrow. I do have a photo of it~ Forgot to mention in the original post about the cam, I'll get that number also~
Are they synchronized?
Install a wide band O2 sensor so you can see you AFM in real time. This will tell you if you have a lean or rich condition.
You can add a throttle Position sensor cheaply to DCOE’s if you have a data collection capability.
You can add a throttle Position sensor cheaply to DCOE’s if you have a data collection capability.
jmackro
Well-Known Member
You can report on the current jet configuration, but it's doubtful someone over the internet can offer advice like: "just replace the 150 mains with 145's and everything will be hunky dory". Weber jetting depends on cams, compression, altitude, displacement, octane, and numerous other factors.
Your issue probably doesn't involve rebuilding the carbs; it involves re-jetting. Stevehose and bfeng's advice is good - make sure the carbs are synchronized, and then use an O2 sensor to figure out where it is running rich/lean. Play with the jets until the rich/lean issue is resolved.
Belgiumbarry
Well-Known Member
i fully agree with Jay , but when asking tune problems with webers that seems to me some basic info for members....just to have a idea.
Are they synchronized? 
So, what I found is Idle jet has a big 9 over a small 45, Main jet is 135, Air is 180, Emulsion tube is an F11. I found a bill from August 2009 where they put in new Idle & main jets to pass Emission tests. This looks like what's in it now~ I also have the bill from Feb. 2002 for a Schrick 282 cam, I'll need valve adjust numbers to check on how it's doing. I like the idea of an O2 sensor to get the tuning right, but feel I need a base line to be sure I'm even in the neighborhood. At some point this car was up in the Rocky Mountains, there's a bill for jetting for altitude. I live at about 700 ft. above sea level, so you can see my concern about carb jetting. The other note is fuel pressure 1.5-psi seems low to me.
Another thing I've read is the vacuum gauge adapter has an "internal restriction". I can make the adapters but would need to know the size of the restriction~
Another thing I've read is the vacuum gauge adapter has an "internal restriction". I can make the adapters but would need to know the size of the restriction~
jmackro
Well-Known Member
Yes, that is on the low side. DCOE's need low fuel pressure - say 2.5 to 3 psi - so you're right that 1.5 is at the low end of the range. What are you using as a fuel pump?
I didn't follow that at all. What does this "vacuum gauge adapter" connect to? What is it used for?
Ok so a 282 cam and triple webers most likely needs bigger jets. If they put smaller jets in to pass emmissions that tells me they did so in order to lean it out by choking the fuel supply. Your idle jet is a 45F9 which is smaller than usual for these engines (especially with bigger cam). Typically these need 50 or 55 idle jets (I run 60's) and 140 mains. It sounds like the idle circuit is running out of gas at 2500 rpm. Will it stop surging if you mash the throttle wide open when accelerating? But still, check that they are synchronized, chasing jetting issues without is futile.
Steve, yes when you stand on it it just takes off and howls, kind of dragster like (needs to be geared higher, it's like 3.65) I have a uni-syn around here somewhere, but wondering about following what this Weber book says relative to the use of vacuum gauges on each port?
Don't know what pump it is, just happen to see that it's a small cube near the diff. when I was looking at the brake pressure regulator~
restart
Well-Known Member
Far from an expert, any old timers here might say now there’s a guy who is to afraid to be wrong...
but sometimes it takes a couple of stupid ideas to expose the right ones
, to short circuit a couple of synapses...so......if the car accelerates fine but has surging at steady rpm, maybe th issue s a vacuum leak.? Have all the mounting bolts and all the screws around the top edge of the carb been checked. They like to loosen...Doesn’t the Weber manual say that most carb problems aren’t carb problems. .. I love that phrase... Linkage is so often the issue.
Last week I was trying to cure a hunting issue with an air cooled v dub and after taking the carbs linkage and ignition apart...it turned out to be a missing gasket at the base of the mechanical fuel pump.
Al
Belgiumbarry
Well-Known Member
those restrictors are just to "level" it out , so the gauges don't vibrate to much with the pulsating engine.
jmackro
Well-Known Member
Sounds like a Facet fuel pump. Does it look like:
There is nothing wrong with those, but assuming that fuel pressure is among your issues, that pump may be undersized for a 3.2L, triple Weber set-up (some versions of that configuration pump are only rated at 15 GPH). Or the pump may simply be failing.
I prefer the larger Facet pumps which can deliver up to 34 GPH. Just be sure to get a low pressure model.
Last edited:
Belgiumbarry
Well-Known Member
as far i know 2500 revs is typically the transition where the mains take over from the idle jets..... so yes, try bigger idle jets.
try bigger mains if to lean all the way
if only to lean in high revs , try smaller air
and yes, i found my best running jetting with webers on the "rich" side. Ok, it's safe but needs new plugs often….
try bigger mains if to lean all the way
if only to lean in high revs , try smaller air
and yes, i found my best running jetting with webers on the "rich" side. Ok, it's safe but needs new plugs often….
he can't fiddle with idle jets with any certainty without an AFR gauge, but the next size up idle jet may cure it. just won't really know whether it is too rich or not etc. Check fuel pump pressure as Jay says, but if it doesn't sputter when going WOT then it's likely not the fuel pump. If you can mash the throttle wide open with no stuttering etc then the mains are kicking in and the idles are out which points to idle jets too small. And yes, it is very difficult to do internet diagnosis of Weber issues. Since you have vacuum ports for each barrel you can get a device called the Carbmate which is an electronic vacuum gauge and works great. I've found that just hooking up a regular analog gauge is useless with the dial bouncing all over the place, even with a pulse smoother it's not as accurate as the Carbmate. You also have idle air bleed screws which will allow you to balance the barrels to each other in each carb.