• Hi Guest!
    You can help ensure that British Car Forum (BCF) continues to provide a great place to engage in the British car hobby! If you find BCF a beneficial community, please consider supporting our efforts with a subscription.
    There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Subscribers don't see this gawd-aweful banner
Tips
Tips

MGB Anyone still use HIF SU carbs?

Share this page

wkilleffer

wkilleffer

Jedi Knight
Country flag
Offline
Hey everyone,

My car's a 1974 MGB with an 18GK series engine. I wish I knew the story behind that, but I don't. At some point, the original HIF SU carbs were removed and a set of HS's were fitted in their place. Those carbs have always seemed a bit dodgy. I've had new bushings and shafts done, replaced floats and jets, aligned needles, cleaned, attempted to tune etc, and it's like they're never quite spot-on. I've checked valve clearances and ignition timing along with that. I can get the running to be pretty good, but maybe never quite great. I wonder what role the car's mongrelization may play in this.

Someone nearby is selling a rebuilt set of HIF's along with extra parts for $225 negotiable. I'm not an absolute stickler for originality or anything like that, but aren't those the "proper" carbs for my car's engine?

Does anyone still have these fitted to their car? I'd like to think about getting them, but that's also $ that could be spent on other things too, you know?

Any advice would be appreciated.

Thank you,
-William
 
Hey, William -

First, regarding your engine, in case you don't already have it, here's a chart which shows which ones were supplied by years:

https://www.zeke.ne.jp/~glitter/main/html/mgb/mgbdata/MGBdata2.html

There's a stamped "clock" on the right side of the engine block just above the oil pan which will give the build date of the block. If memory serves, it's read clockwise - month, day, year, starting at the lower left. Kind of a moot point, though, as the GK was only supplied in '71, according to the chart.

The HIF carbs were introduced along with the 18V in '72, I believe. If so, your GK engine should have had the HS's. I have HIF's on my '73 and have had no issues at all with them; no fiddling required so far. Many owners prefer the side mount float bowls on the HS's over the integrated bowls on the HIF's; I like the compact design of the HIF's. But if you have to get to the bowls for cleaning, etc. the carbs have to be removed. Not had the pleasure (!) yet, so I'm still happy with them.

Hope this helps.

:cheers:
Mickey
 
My advice is to stick with what you've got on it. Nothing wrong with any SU carburetor! One of the simplest and most durable carbs ever made! HIFs are a nice carb, but a bugger to work on the float valve while on the engine should it leak. SU carbs are miss understood by a lot of back yard mechanics trying to repair them and don't know what their doing. They cuss the SUs and then go buy one of those junk Weber down drafts and think that cures all. I can guarantee, they don't! Rebuild or have rebuilt your HS carbs, their a fine carburetor used world wide. PJ
 
William,
Our '74 B-GT now has the original HIF4 SU carbs back on after being rebuilt by Joe Curto in NY. This set works just fine with the rebuilt engine.
Harry
 
Don't worry, I'm firmly of the belief that if God had intended an MGB to have a Weber, it would have come with one from the factory. Not gonna happen in my garage...

I know they're simple and easy. More so than anything I've had on any other car. But I do think I could be dealing with carbs with mis-matched pistons and dashpots, soft springs in the dashpots, and other wear items. LIke they might have been put together with whatever parts were on-hand at the time. The shafts and bushings still feel pretty tight, but that was a good 10 years ago. Most of my mileage has actually come within the last four years, but one never knows. I've changed the jets a couple of times, along with the floats in the bowl and installation of grosse jets.

I'm not against the idea of sending them off for a rebuild, but Joe Curto's prices would require savings from a couple of paychecks... Is there anything I can do in the meantime to maybe freshen them up a bit? Like maybe new springs in the dashpots, or how does one tell when the proper piston is matched to the proper dashpot?

One more "just curious" question: Which MGB SUs came with the vacuum advance port molded into the carb?
 
Well, Christmas is just around the corner! Throw out a lot of hints, or have the carbs rebuilt and call it a Christmas present to yourself!:encouragement:! PJ
 
I bought my6 MG as a retirement present to myself with the intention of using it as a hobby. I have never done car repair myself before owning an MG but I have now completed quite a few jobs on the car including a carb service. I found University Motors on Youtube to be very helpful and there are a couple of videos just on carbs including how to match the piston with the carb body.
 
William -

More info on the HS/HIF debate - though it's geared toward modified engines, still may answer some of your questions (like the molded port... '68 AUD265):

https://www.mgbmga.com/tech/mgb19.htm

Mickey
 
Just got through watching John Twist's video on matching the piston to the carb body and doing that procedure with my own car. I have mine where they fall at the rate where one reaches bottom at about one second faster than the other. That's the closest these are going to get. Went ahead and did a carb service and think I got it all squared away. Taking it on a test run shortly.
 
Another thing: When I was getting the carbs ready to do that adjust and balance thing, the front carb seemed to be quite reluctant for its jet to move upward. I took a look at the both of them, and saw that the metal arm that comes down from the choke linkage area to fasten onto the jet itself was connected backwards. Nobody's fault but mine cause I'm the last one to fiddle about down there, but not sure how I managed that. Set it to rights, got everything adjusted more or less satisfactorily, and am debating a slightly wet weather test drive.
 
HIF's are great carbs. Got 'em on my '73, and they've worked fine for years of daily driving.
 
I still have the HIF4s on my 1974 MGB. Just had them rebuilt last year. The float pin on the rear carb was grooved (after 40 years) and was sticking open, flooding the carb > charcoal cannister.

DSCF1583.jpg
 
William, try changing the dampers from one carb to the other and see if it changes which carb falls faster or slower than before. Just screw them out and switch them. If it changes the drop, then the dampers are miss matched and a new pair of dampers could solve your problem. Some carbs use a damper with a small hole in the top, some don't depending if the dome is vented on the carb or not. The piston that is dropping slower might not be vented correctly. ?? PJ
 
Back
Top