Help with single SU on midget

[maddy]

I’ve installed a single SU HIF4 on the stock manifold of a 79 1500 midget. The fuel pump is from AutoZone rated at 2-4 psi. All smog has been disconnected. Can’t find any vacuum leaks. Installed vacuum advance as per Hap's suggestion.
I can start the car but it only runs for a second unless I pump gas to rev it to 4500 then she drops down to 2000 and will die unless I pump back up to 4500. It will not run steady at any rpm so I sit there going 4500-2000-4500-2000. Any advice? Please
Mark

 

[jlaird]

Did you check for air leaks between the manifold and the block?

 

[maddy]

I didn't take the manifolds off and she was running on the zenith carb. I don't think there are any leaks. I'll look again though.
Took the carb back out to check things one more time. Readjusted the needle valve (didn't have it right} now it will run at higher RPM's but bogs down as more gas is fed to it. I've messed with the mixture adjustment going rich and lean but not able to get the engine running good or at idle.

 

[bthompson]

It <span style="font-style: italic">sounds </span>like it's running lean--but most "carb problems" are electrical, so rule that out first. My first thought: have you put a timing light on it? The timing may be out; the centrifugal at 4500 may be enough to throw it <span style="font-style: italic">just </span>on time, but as the revs die the timing pulls in to the point that it won't run. If your timing's good, is the jet set rich enough? Are you sure your needle isn't too lean for a 1500? (All right, now I'm just shooting in the dark!)

 

[dklawson]

Before going too much further, can you tell us a little more? Was the car running OK with the ZS carb or did it have problems with that also?

I agree with Jack that if the car was running OK before the transplant, look for vacuum leaks. That said, I have never worked with HIF carbs so I don't know what critical initial adjustments are required for initial start up before tuning.

 

[maddy]

The car was running OK with the ZS. Main problem with the ZS was the choke. If the engine wasn't run to higher temp then shut off for a couple of minutes I could hardly get it started. Just don't want to mess with that ZS anymore. I was told by a couple of guys from this forum that a single SU is better than a down draft weber, so I want to give it a shot. So, here I am. I've only messed with the fuel system leaving everything else alone so I shouldn't need to trouble shoot anything else on the car.

 

[dklawson]

This is good news. Since you haven't altered anything else you can be pretty confident that the issue is with the fuel system.

As mentioned a couple of times above, it sure sounds like the car is running way lean and this could either be from a large vacuum leak or from the carb being way out of adjustment. Did you find out how to make the initial adjustments to the HIF and did you fit a needle that is appropriate for a 1500 engine?

 

[maddy]

I think I've got it figured out! I tried starting it again cold, no choke or gas. Started right up... hum could it be the choke? Took it back out again took the choke apart and found a little something in it. Well this time it wouldn't start without choking.. Good news. I don't get to work on it anymore cause the wifie is getting jealous. I'll let you know how it all comes out when I get back to it.

The kit came with instructioons for initial adjustments. Have no clue as to the proper needle for a stock 1500. I hope someone know and would let me know.

 

[blkcorvair]

A HIF with a 1500 is not something most would have a needle reccomendation for. The best way would be an air fuel gauge. Sounds alot like you have an air leak. Mine had these problems too until I re-shafted the throttle on the carb. Is it a used carb?

 

[maddy]

Yes it is used, but the shaft and body seems in good shape. I'll know by the end of the day.

 

[bigjones]

The kit came with instructioons for initial adjustments.

Maddy,

Is this a kit for converting from ZS to SU on a 1500 Midget?

As an aside, there is a school of thought, over in the MGB Forum , that the problem with the ZS is not the ZS but the constrictive exhaust. At least on the MGB. I wonder if the same applies to the Midget.

Good Luck,
Adrian

 

[maddy]

Not a kit, just had to modify the SU a bit so she fits the original MG manifold.

SU HIF4 success! Why go with a weber down draft?

Replaced the ZS carb with a single SU HIF4 and she runs so much better now. Feels like more power and idles smooth. Had to richen it up all the way but still bogs down a little on full throttle. I’m figuring that I need to get a larger needle assembly, am I correct? I can lean it out some which eliminates the bogging down, but as per John Twist’s YuoTube, when pushing up the plunger engine shouldn’t stutter or bog down.

Thanks for the help everyone. This forum really got me through!

Mark

 

[blkcorvair]

Mark got any pics of the finished product? I found if you take the needle out and put it in a drill press on low speed you can customize it very easily with a piece of sand paper and than polish it up.

 

[maddy]

No pix yet Scott. Way ashamed after seeing your awesome setup! I am about to pay a tribute to you though! Forgot to hook up the vacuum advance at my last post. This car now runs like I think it should. Squeeeeeels around corners... sounds hot(got to fix the exhaust)and absolutely goes! Anyone that goes with a weber does not know what they are doing! Thanks for your help!

IOU some pix though, I'll get them here or to you.

 

[blkcorvair]

Anyone that goes with a weber does not know what they are doing! Thanks for your help!

IOU some pix though, I'll get them here or to you.

SU is definatally the way. Im actually gonna replace my Single HS4 with an early manifold (Larger runners and an HS6 1 3/4" soon) working on that now.

 

[JPSmit]

Scott - when you say "early manifold" is this as in earlier 1500 Intake Manifold? Please enlighten

 

[billspit]

Scott - when you say "early manifold" is this as in earlier 1500 Intake Manifold? Please enlighten

Yea, please. I've read that the intake off a 1500 Toldeo or ???? is the ideal intake as it has the bigger runners. I've been looking for one over the internet, but can't find anything.

 

[blkcorvair]

Correct, you can find an earlier version of the 1500 manifold that does indeed have larger runners. Not sure what they came off but it is a noticeble difference that can be recognized by looking at it.

 

[bthompson]

So, to summarize...
<span style="font-style: italic"><span style="font-weight: bold">I</span></span> said:
<div class="ubbcode-block"><div class="ubbcode-header">Quote:] The timing may be out; the centrifugal at 4500 may be enough to throw it just on time, but as the revs die the timing pulls in to the point that it won't run. [/QUOTE]
And then <span style="font-style: italic"><span style="font-weight: bold">you </span></span>said:
<div class="ubbcode-block"><div class="ubbcode-header">Quote:] Forgot to hook up the vacuum advance at my last post. This car now runs like I think it should.[/QUOTE]
Zing!

<span style="color: #999999">(Yes, that IS the sound of my own horn tooting...) </span>:laugh:

 

[maddy]

Why didn't you say "check if ya hooked up vacuum advance stupid"? I'd have figured that that's what you meant. But oh no, had to go technical with a guy that isn't there.. Might be why my hand went against the loose hose, kind of a subliminal thing.

Bill you also deserve one of these....

But this is me...