TheSamba.com :: View topic - Center mount, progressive, 2BBl carb on Type IV doesn't suck FAQ

Sat Jan 14, 2017 3:30 pm

I have a question for the proggy failthful. Well, actually two, but first, thanks for all the help provided here. We have a proggy on our 1800 t4 and just about have it dialed in.

The first question is what your top cruising speed is with the proggy. Second is did you suffer on the top end vs duals or fi?

I ask, because we would like to cruise at 65, but we can only get 62 max. The top speed in the manual is listed as 79, but I'm just wanting 65.

So, are there any tricks or tips to get a 65 cruise speed with the proggy or do I need to go to duals. (That's another fiesta)

Thanks...Tim

Sat Jan 14, 2017 3:41 pm

I regularly cruise at 65-75 and go higher easily enough on level ground with an 003 tranny. My present 1800 is a never rebuilt POS with a worn out cam so it doesn't run anywhere near as well as my old 1800 did. The old engine was just getting onto the torque curve at 60 mph in forth gear with an 091 box.

If you can't go over 65 then the carb probably isn't what is limiting you. What do you have your timing set to? How many miles are on your cam? Are you sure it is running on all four cylinders?

Sat Jan 14, 2017 4:34 pm

we used to get 140 - 150 mph out of a progressive on the Fiat 124 spider when racing. The top RPM on a 1600 was about 10,000 RPM. That engine is a cross flow engine with over head cams. The point being I don't think the engine not being responsive in your bus is the progressive carb. It is more likely the tuning of the carb, and the engine / engine condition. My 1971 dual port 1600 could sustain 70 - 75 with the single barrel 34-pict-3. With dual carbs I could sustain 80 and occasionally reach 85 - 90 although the bus gets really spooky at that kind of speed. It develops a mind of its own in a bad way.

Sat Jan 14, 2017 4:51 pm

I'm inclined to agree with Wildthings and SG. The carb is probably not the source of your speed limit issue. Adjust your valves, check your ignition components and timing, then change your fuel filter even if you recently changed it. With crappy old rusty tanks in these beasts, fuel starvation is quite common and even a visual check of the filter won't reveal clogged pores in the filter media. Filters are cheap and easy to change. If you don't have one immediately handy, you can back flush your existing one for a temporary fix. Good luck and please report back! Oh yeah, I just remembered. The last time I had such an issue, the center conductor in the distributor cap where it connects the coil to the top of the rotor had begun to disintegrate. Less than 8 k miles on the cap....

Sat Jan 14, 2017 5:50 pm

The same carb feeds the leaning tower of power in my F'nDodge van enough to get it up to 80 and there's still pedal left.
Look at the obvious things first like is the throttle cable adjusted so you can actually get full throttle?, then move on to compression tests and looking for a dead cylinder, 3 cylinder engines top out ~ 62 MPH if you try hard.

Sat Jan 14, 2017 9:14 pm

Wow, thanks guys! I didnt expect such a robust response so soon!

Here is a little background...

Our bus found us (yeah, they do find you) and needed some work. The 1700 it had was toast and a friend had an 1800 that we acquired to replace it. I went through the 1800 and reringed and hones the cylinders. It was installed and a progressive was used for the carb. It has run fair, but I believe it can do better. Mileage wasnt the best, but we kept working on it.

I had acquired some 40 IDF duals and tried them, but was unsuccessful in making them work well (after much jetting, syncing and such), so I decided to go back to the progressive. It ran well, but I still thought it could do better.

I had a 009 with electronic points for a distributor, but upgraded to a Pertronix SVDA. I set the timing to 30 deg BTDC with the vac hose off and the port plugged on the proggy. The valves are set to .006 and the oil is fresh. Here is what is in the progressive for jetting:

Mains 140/145
Idle 55/50
Air 165/160
Em F6/F50
squirt 55

The idle screw is at 2 1/4 turns from seat and idles great. The power isnt bad up to about 50-55 and then it falls off. Im considering going to 145/150 main jets.

I will also look at my linkage and adjust the throttle cable as tight as it will allow without affecting idle.

This is an AW 1800 stock with a 5 rib trans. 74 Sportsmobile.

Thanks again for all the great advice and replies!

Tim

Sat Jan 14, 2017 9:18 pm

I forgot to mention, that we removed the fuel tank, boiled it and then sealed it. The filter is new and I run an electric fuel pump with a Holley regulator set to 3psi.

thanks

Tim

Sun Jan 15, 2017 2:19 am

RedBaronofRedBud wrote: Here is what is in the progressive for jetting:

Mains 140/145
Idle 55/50
Air 165/160
Em F6/F50
squirt 55

The jetting of your secondary seems pretty lean. The secondary lacks the vacuum operated power valve which the primaiy has so if the two are jetted the same the secondary is not going to be feeding anywhere near as much fuel as the primary

Sun Jan 15, 2017 3:09 am

Wildthings wrote: RedBaronofRedBud wrote: Here is what is in the progressive for jetting:

Mains 140/145
Idle 55/50
Air 165/160
Em F6/F50
squirt 55

The jetting of your secondary seems pretty lean. The secondary lacks the vacuum operated power valve which the primaiy has so if the two are jetted the same the secondary is not going to be feeding anywhere near as much fuel as the primary

Thank you! I am looking to increase the jetting on the secondary to a 150. Would it be prudent to increase the primary to a 145 as well? Thanks for the assistance!

Tim

Sun Jan 15, 2017 4:05 am

The best way to jet your carb is to borrow or buy a wide band a/f meter, this will cut much of the guess work out of jetting a carb.

As I said the primary side of the carb has a vacuum operated power valve and thus doesn't need to have as large of a main jet as the secondary side. If you don't have a bog coming off idle you are probably already running way rich once the power valve opens so don't want to go any richer.

Why don't you bump the secondary up to 165 and see if that makes a big change in your full throttle power.

Sun Jan 15, 2017 5:36 am

An A/F meter is on my list of items to acquire. I'll jet up on the secondaries and check.my linkages for full stroke.

Thanks again!

Tim

Mon Jan 16, 2017 1:43 am

Once again, I want to thank you all for your input on this issue. Now an update.

As per Wildthings recommendation, I went up on the secondary jet to 165. I also double checked the throttle linkage, adjusted any slack (there wasnt much) and then readjusted the mechanical stop on the accelerator pedal. On the test ride, the power was good until I floored it. The engine noise increased and then it fell on its face until I lifted. It was if it was running out of fuel and was popping like a lean condition. I then opted to go up again on the secondary jetting to a 180 and to a 145 in the primary. The idles and airs remained the same and the result was very similar with the going lean, popping and falling on its face. Max speed in both trials was around 60.

So, I come once again, hat in hand, and ask for suggestions and options.

Thanks again

Tim

Mon Jan 16, 2017 2:31 am

Are you sure the carb is getting sufficient fuel?

Blow out the passageway between the secondary main jet (15) and the well (14) and also blow out the nozzle (9).

The secondary will also have a high speed enrichment system that needs to be clear. This is 31, 32, 33, & 34 in the drawing below.

The is a cutaway of the primary side but it shows the same passageway and nozzle as the secondary has:
http://s1180.photobucket.com/user/onovakind67/medi...1391897251

You could try a 195 secondary main jet, jets that large are used on some carbs. I don't have any books with me, but do believe I have the stock jetting for a Weber written down somewhere, I will check.

Mon Jan 16, 2017 6:21 am

RedBaronofRedBud wrote: I forgot to mention, that we removed the fuel tank, boiled it and then sealed it. The filter is new and I run an electric fuel pump with a Holley regulator set to 3psi.

thanks

Tim

Check your fuel pressure whilst underway. You can have appropriate pressure all day at idle but inadequate volume under demand. This could be dangerous if engine leans out under load.
Colin

Thu Jan 19, 2017 9:54 pm

Amskeptic wrote: RedBaronofRedBud wrote: I forgot to mention, that we removed the fuel tank, boiled it and then sealed it. The filter is new and I run an electric fuel pump with a Holley regulator set to 3psi.

thanks

Tim

Check your fuel pressure whilst underway. You can have appropriate pressure all day at idle but inadequate volume under demand. This could be dangerous if engine leans out under load.
Colin

That's what it feels like that it's leaning out under heavy load (WOT). Valves, timing, compression, etc. all are good. I will have a helper watch the gauge and see if the pressure drops. I use a Holley regulator and electric fuel pump.

Thanks...I'll report back my findings

Tim

Thu Jan 19, 2017 9:55 pm

Wildthings wrote: Are you sure the carb is getting sufficient fuel?

Blow out the passageway between the secondary main jet (15) and the well (14) and also blow out the nozzle (9).

The secondary will also have a high speed enrichment system that needs to be clear. This is 31, 32, 33, & 34 in the drawing below.

The is a cutaway of the primary side but it shows the same passageway and nozzle as the secondary has:
http://s1180.photobucket.com/user/onovakind67/medi...1391897251

You could try a 195 secondary main jet, jets that large are used on some carbs. I don't have any books with me, but do believe I have the stock jetting for a Weber written down somewhere, I will check.

I have a 200 that will try.

Fri Jan 20, 2017 8:23 am

If the progressive is jetted close to out of the box and it is leaning out and popping, you have fuel feed problems, changing jets will not change the problems.

I would also suggest you get a helper to watch the carburettor mechanism as you put your foot on the gas, as although the throttle cable may be tight, the progressive may need more travel than other carburettors - e.g. compared with a 34 PICT-3 the progressive needs about 20% more throttle cable travel to wide open.

As a thought - you may well be just hitting the well known second-barrel lean transition flat spot of the stock jetted progressive and staying there with a half-opened throttle.

I was just driving up hill at 65mph with a 1641T1 and a progressive on my bus, and 70+ on the flat on my way home from work. With pretty close to stock jetting it was showing a nice 12.5:1 AFR on the gauge.
Backing off the throttle a bit, it leans out a lot to 16:1 AFR. Still not excessive for low load.

Fri Jan 20, 2017 10:32 am

mikedjames wrote: If the progressive is jetted close to out of the box and it is leaning out and popping, you have fuel feed problems, changing jets will not change the problems.

I would also suggest you get a helper to watch the carburettor mechanism as you put your foot on the gas, as although the throttle cable may be tight, the progressive may need more travel than other carburettors - e.g. compared with a 34 PICT-3 the progressive needs about 20% more throttle cable travel to wide open.

As a thought - you may well be just hitting the well known second-barrel lean transition flat spot of the stock jetted progressive and staying there with a half-opened throttle.

I was just driving up hill at 65mph with a 1641T1 and a progressive on my bus, and 70+ on the flat on my way home from work. With pretty close to stock jetting it was showing a nice 12.5:1 AFR on the gauge.
Backing off the throttle a bit, it leans out a lot to 16:1 AFR. Still not excessive for low load.

Great ideas!! I have a few more things to check but we will get this nailed down. BTW, what is your jetting? Thanks!

Tim

Sun Jan 22, 2017 4:31 am

An update for the group. I believe we have found the issue with bogging out. The fuel pump that is installed is a "42S", which has 2-3.5 psi output. I had placed a holley regulator in line and adjusted to 3.5 psi. Apparently, this wasn't needed. I removed the regulator from the circuit, went back to stock jetting, and it ran ok. No leaning out and a slight bog on the top end. It hit 65, but I know it can do better, so we will change the secondary as we are pleased with the primary. Here is what we have now...

Main 137/140
Idle. 60/50
Air. 165/170
Em. F6/F50

I am going to change the air corr to a 175 and see if response on the top end increases. It was a 160 and a change to 170 made a difference.

Now, does anyone know what the air corrector jets and emulsion tubes affect? I've read much but this has been a mystery for me.

Thanks...we are close

Tim

Sun Jan 22, 2017 6:48 am

The air correction jets operate in an opposite manner to the main jets. Going larger will lean the mixture and going smaller will enrich the mixture. The effect of the air correction jets increases progressively as the air flow increases, so a change in AC jet size will have less effect when the throttle is barely opened and more effect at full throttle.

If you haven't done so you should get a Weber or Holley book that explains how all the systems of the carburetor work.