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Converting from dual SU to Weber and have some questions

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JonathanDespeaux Avatar
JonathanDespeaux Jonathan Despeaux
Mt Pleasant, South Carolina, USA   USA
1980 MG MGB
Hello all, I have a 1980 MGB LE and I currently have dual SU HIF 4s installed. I am converting to a Weber downdraft and have some questions, I have electronic ignition and do have a distributed vacuum advance. I know where the fuel line connects and I know where the distributed vacuum advance connects. But I am having trouble figuring out where the other hoses connect and/or what to do with them. Such as the hose that goes from the charcoal canister and over to the overflow pipe for the dual symbol carbs. I also do not know what to do with the vacuum like that comes from the front of the engine, then splits with a y piece and goes into the sides of each su carb. (Picture attached b/c I don't know what this one is called) The third and final one is the line from the anti run on valve to the intake manifold. I need to know where these three hoses go I greatly appreciate any and all help.

Thanks, Jonathan

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riley1489 Avatar
riley1489 Gold Member Bruce H
Great White North, QC, Canada   CAN
1953 Jaguar XK120
1959 Riley 1.5 "King George"
1973 MG MGB
I am not quite sure why one would do as you are doing.confused smiley

In any event, the charcoal canister is performing two functions. One it collects fuel vapors from the fuel tank and the HIF float chambers. This is known as the evaporative loss system.
The canister also does function to draw filtered air into the engine, (large hose from canister to rocker box pipe) to take blow by to the carburetors to be burned off during normal combustion. (the Y piece you show). This is known as the crankcase ventilation system.
Read up here,
http://www.mgexp.com/phorum/read.php?1,2372702

all you need to know about fitting this aftermarket carburetor to your MGB can be found in this essay!

I believe you omit the anti run on valve, as the float chamber of the down draught carburetor is open to ambient and the distributor is ported rather than manifold as you currently have. Ensure your distributor is set up for this type of vacuum signal, you may need to change the vacuum advance unit?

Good luck

B



Check your ego Amigo!



Edited 3 time(s). Last edit at 2017-07-17 02:57 PM by riley1489.

OldDuffer Avatar
OldDuffer Silver Member John S
Eugene, Oregon, USA   USA
1970 MG MGB
1979 MG MGB "Mae B *SOLD*"
I agree with Bruce. Why not get those HIF4's sorted. I see from your previous posts that you already converted from a single carb to the dual SU's and that you had some issues with overflowing so now you're going to a Weber? I'd encourage you to spend some time getting to know the HIF4's and make them right. The time spent undoing everything to go to a single downdraft Weber could be spent fixing the existing setup and then enjoying it. Just my 2 cents. Good luck.



I was addicted to the hokey pokey but I turned myself around.

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jjonns74 Avatar
jjonns74 Gold Member John Dailey
Indianapolis, Indiana, USA   USA
1974 MG MGB "Athena"
1974 MG MGB "Apollo"
In reply to # 3553701 by JonathanDespeaux Hello all, I have a 1980 MGB LE and I currently have dual SU HIF 4s installed. I am converting to a Weber downdraft and have some questions, I have electronic ignition and do have a distributed vacuum advance. I know where the fuel line connects and I know where the distributed vacuum advance connects. But I am having trouble figuring out where the other hoses connect and/or what to do with them. Such as the hose that goes from the charcoal canister and over to the overflow pipe for the dual symbol carbs. I also do not know what to do with the vacuum like that comes from the front of the engine, then splits with a y piece and goes into the sides of each su carb. (Picture attached b/c I don't know what this one is called) The third and final one is the line from the anti run on valve to the intake manifold. I need to know where these three hoses go I greatly appreciate any and all help.

Thanks, Jonathan

1. No overflow w/Weber, so cap off one port of the charcoal canister.
2. Only ! carb, so no Y -- single hose goes to fwd,outboard corner of Weber filter base plate (3/4" hole, you need a nylon elbow)
3. No Anti Run-On, so leave disconnected.
4. You need a different intake manifold - Pierce or Canon.


Unsolicited advice:

Don't do this to your engine. I'll be converting my Apollo (Weber) back to Hif-4s as soon as I get them refurbished.

My Athena (Hif-4) is Much more responsive & better mileage (once set up properly).


John

tampaguy Avatar
tampaguy Jack Shea
Elgin, Oregon, USA   USA
Dumb idea Jonathan !

simon1966 Avatar
simon1966 Silver Member Simon Griffin
.Madison County, Illinois, USA   USA
I'm going the other way, Weber off, SU's on. Should have the car back on the road next week.

Perambulator David D
Phoenix, Arizona, USA   USA
Possibly you have a lemon of a HF carb. These things have been around the block more than Phyllis Diller and the bodies are starting to wear out in a few instances. I myself am not a fan of the HF, prefer the HS.

Lot of my frustrations with SU carbs was that the float levels were never right when adjusted according to the manual. I would follow the instructions and the car ran like crap. Learned on this board to adjust by sight looking down the jet and then testing by blowing a puff of air down the jet and watching for the fuel to JJJUUuuussssttt dribble over the bridge. There is a write-up around somewhere with details.

The DGV will at least improve your odds of success by cutting the number of variables in half and not require you to balance the intake. Personal experience with three installs and they all worked fine out of the box.

Don't need the anti run on valve cap it

Get rid of the Y and run the single tappet chest line to the underside of the air filter, or get a PCV valve and run it into the manifold.

Don't need the evaporatory recovery feature, so cap the lines. Be forewarned that your garage will acquire a slight fuel smell if you do this.

Seem to recall that the return spring was a PITA to rig maybe the newer kits have this covered?

riley1489 Avatar
riley1489 Gold Member Bruce H
Great White North, QC, Canada   CAN
1953 Jaguar XK120
1959 Riley 1.5 "King George"
1973 MG MGB
Be aware if you do dispose of the evaporative loss system you will need to vent your fuel tank. Some simply drill a hole in the fuel cap?

B



Check your ego Amigo!

barry s Avatar
barry s Silver Member Barry Stoll
Alexandria, VA, USA   USA
1972 MG MGB GT
1974 MG MGB
1976 Triumph TR6
1980 MG MGB
As John S points out, you only installed these HIFs a month ago and experienced a fuel overflow problem. You received various suggestions to deal with the issue. IMHO it should require more than a month of frustration to dump a pair of SUs for a Weber. No matter what you may hear, a Weber is not an assured plug and play.

My '80B came to me with a Weber. I tried for a couple of months to get it to perform anywhere close to my other twin SU equipped Bs, to no avail. It now sports HIFs as do the other 2.

aeroshadow Alex B
Port Dover, Ontario, Canada   CAN
Hi Jonathan
I have a 1980 LE which has a Weber dgv installed by someone sometime in it's history. They used the cast iron ex.manifold and Pierce intake. The car runs REALLY well (after rebuilding the carb.... the accelerator pump diaphragm leaked and the throttle cable cam was installed wrong so the PO didn't drive it) Post #7 has most of the info you need to get by. No worries it'll work fine.
BTW the best driveability improvement was sending the distributor to Jeff at Advanced Distributor for rebuild ( just sayin')
Alex

MGBBob80 Avatar
MGBBob80 Gold Member Bob Finley
Bremerton, Washington, USA   USA
1978 Volkswagen Transporter (Bus) "Buddy"
1980 MG MGB "Magoo"
2005 Harley-Davidson Touring "Big Red"
Hi Jonathon,

I hope that you elect to stay with the HIFs, but I'd be interested in purchasing your HIFs and their associated pieces/parts if you elect to go with the Weber.



Cheers,
Bob Finley

GMB3 Avatar
GMB3 George Badger
Soquel, CA, USA   USA
1968 MG MGB "1QUICK B"
What is broken?

In other words, why replace the SU's with another system?

In reply to # 3553701 by JonathanDespeaux Hello all, I have a 1980 MGB LE and I currently have dual SU HIF 4s installed. I am converting to a Weber downdraft and have some questions, I have electronic ignition and do have a distributed vacuum advance. I know where the fuel line connects and I know where the distributed vacuum advance connects. But I am having trouble figuring out where the other hoses connect and/or what to do with them. Such as the hose that goes from the charcoal canister and over to the overflow pipe for the dual symbol carbs. I also do not know what to do with the vacuum like that comes from the front of the engine, then splits with a y piece and goes into the sides of each su carb. (Picture attached b/c I don't know what this one is called) The third and final one is the line from the anti run on valve to the intake manifold. I need to know where these three hoses go I greatly appreciate any and all help.

Thanks, Jonathan



---
GEO

spikemichael Avatar
spikemichael Platinum Member Michael Caputo
Aberdeen, WA, USA   USA
1973 MG MGB "Freebie"
1973 MG MGB
1974 MG MGB "Spike"
1979 MG MGB "MegaBeanie"    & more
In reply to # 3553766 by Perambulator Get rid of the Y and run the single tappet chest line to the underside of the air filter, or get a PCV valve and run it into the manifold.

Don't need the evaporatory recovery feature, so cap the lines.

Yeah, um... don't play with the PCV valve you are inviting issues you don't have.

The Evap recovery works great with the Weber, from the canister run one line to the tank line, the big one to the rocker cover and either cap the third or run the third to the underside of the air filter.



Michael J. Caputo
'79 RBB and '73 CBB owner with extensive experience in 12v Audio System design and installation.
Vendor of Regalia and Promotional Products. Forum Member with a warped sense of humor.


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JonathanDespeaux Avatar
JonathanDespeaux Jonathan Despeaux
Mt Pleasant, South Carolina, USA   USA
1980 MG MGB
Thanks for all the fast responses! Let me give a little more info on why it is I am considering doing this. When I got the MGB it had a zenith Stromberg on it which was crap and I think most of you will agree with that. I got a rebuilt pair of hif 4s and the matching intake and exhaust manifolds and the exhaust down pipe. For the most part I was pleased with the hifs but ever since I first put them on about 2 months ago it has been problem after problem. First I had a high idle and running really rough, got it to run smoother and then the carbs overflowed, took them apart and the rear float was cracked and filled with fuel. Replaced float and set float height correctly. Next time i drove the car the exact same problem happened to the same float and had to have the car towed home. This time I bought two higher quality floats and haven't had an overflow problem since. Ever since I put the carbs on I have had a high idle issue. It idles at around 1200 rpm with the idle screws fully backed out. It also seems to be fine when you rev it up in the driveway, but when I drive it it stumbles upon acceleration and engine braking and has idling trouble. I have checked for vacuum leaks countless times with starter fluid, carb cleaner etc, and there are none. The linkage is not overtighted, both throttle plates are closing the way they should, there is slack in the throttle cable, the mixture is correct and the airflow is balanced correctly using a unison. I have consulted many "car gurus" on this and they all are completely stumped on what is causing this. The guy who rebuilt and sold me the hifs is completely stumped as well and he gave me a Weber downdraft to try. I would really like to have the hifs and have them work properly but I have had two months of trying to make them work properly just about every day and just was to drive my B again! So I am putting on the Weber just to see what happens. If it runs well with it I might just elect to stick with the Weber, but if not then I guess I'll attempt to sort out the hifs.
Thanks for all the replies, Jonathan

Wray Avatar
Wray Gold Member Wray Lemke
., South Carolina, USA   USA
Jonathan, why don't you stop by and we'll take a look at it. Might be something obvious.

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