Leak from carbs

[Michael Oritt]

Judging by the results of a "piston lift" test both H6 carbs seemed a bit lean so I dropped the jets by about two flats of the adjusting nut and the mixture is now better. However I now have about a two-second fuel leak on both carbs, seemingly coming from above the nut and I am guessing that my dropping the jet allowed a worn or dried out gland/seal to crack and leak fuel.

It's been many years since my carbs have been gone through and though I see that Moss sells a couple of different rebuild kits is this more art than science--should I try to do it myself or am I best off sending the carbs off to Joe Curto or the like for a professional rebuild?

 

[Bob_Spidell]

I think some of the seals are cork, and may have just dried out, so you might wait a couple days and see if they 'heal themselves.' If not, I'd say do it yourself, unless something is seriously worn (like the throttle shafts/bushings). I've heard nothing but good about Curto, but he's likely backlogged and you may be without your car for a while. The costlier kits come with more parts, like jet needles which you may or may not need. And, be thankful Healey didn't use Holley 4000s:

 

[BoyRacer]

Michael,
I just rebuilt a pair of HD8's. They are a bit easier in that the throttle shaft seals are teflon and you can replace those yourself. With the H6's, if there is play in the throttle shafts it will be necessary to rebush the carburetor body and I think you need to have that professionally done. Otherwise, you can do everything yourself and I found it to be very satisfying. If you want them to look like new, media blast with glass beads. I opted for just a good cleaning and bought an ultra sonic cleaner from harbor Freight for around $70. Add a good cleaning product but not Simple Green - it will discolor the carbs.
I also watched a number of Youtube videos. I highly recommend doing that first. Also, be sure to watch the videos about the piston drop test out of the dashpot. You may find that your pistons are in the wrong dashpot.

 

[Michael Oritt]

Bob/Richard--

Thanks for the words of confidence and I especially like Bob's comment (prayer?) that the cork seals might "expand" into their new position and save me the job. Re the throttle shafts am I correct that the need to ream and rebush or not is usually determined by whether the idle stays smooth and constant as the engine warms up (It does)?

 

[BoyRacer]

Worn throttle shafts will allow air in when the butterflies are closed - at idle. This will create a lean mixture and make it difficult (sometimes impossible) to get a good idle.
Not sure what Bob is talking about. There are no cork seals on the throttle shafts.

 

[Michael Oritt]

Richard--


According to Moss there is a cork sealing ring and a cork gland washer, both of which are part of the jet bearing kit for the H4/6 carb.

i'm hoping Bob's possible scenario comes true--any port in a storm!

 

[John Turney]

.... Re the throttle shafts am I correct that the need to ream and rebush or not is usually determined by whether the idle stays smooth and constant as the engine warms up (It does)?

That's one indication that the throttle bushings are good. The other is to spray a small amount of some flammable liquid (carb cleaner, WD40, Prep-All, etc) on the bushing/shaft interface while idling. If no change in idle, buses are good.

 

[steveg]

That's one indication that the throttle bushings are good. The other is to spray a small amount of some flammable liquid (carb cleaner, WD40, Prep-All, etc) on the bushing/shaft interface while idling. If no change in idle, buses are good.

When mine leaked, even windex would make the idle change.

Before the teflon strips and previous cork glands - on the H-types SU used plain brass bushings which were a bad idea because brass-on-brass wears quickly.

 

[blueskies]

I had good luck rebuilding a set of H4 SU carbs using the complete kits, including installing new shafts and bushings. For details on how I did this, you can refer to this earlier thread on the topic: https://www.britishcarforum.com/bcf...ics-of-throttle-shaft-reaming&highlight=lathe

Back in 2016, testing confirmed that the 100-6 ran well after rebuilding the carburetors. Then the project sat for a few years with not a lot of progress. Finally, paint and final assembly happened over the fall and winter. Since spring arrived, the 100-6 has seen lots of use. After sorting out the jet adjustment nut, I can say that the car runs well. So, home rebuilds of SUs can be done.

 

[Michael Oritt]

Based on several encouraging posts I decided that, provided there did not appear to be any leaks at the throttle shaft, I would attempt the rebuild. So this morning I started the car in order to warm it up and then do the "WD40 spray test. Unfortunately whatever seals were leaking the other day have gone way further south and what was a 1-2 second leak has become a constant stream of fuel from both carbs dripping directly onto the exhaust header.

Not being able to safely run the engine I cannot determine whether or not the carbs need rebushing, so I guess they are going to have to come off and go to the carb shop. I have used Joe Curto before on another car with good results but if he is snowed under are there any other good SU repair guys around?

 

[steveg]

...I have used Joe Curto before on another car with good results but if he is snowed under are there any other good SU repair guys around?

Can't recommend Tom Bryant too highly:
https://thosbryant.wordpress.com/faqs/

 

[Bob_Spidell]

Apple Hydraulics does them:

https://www.applehydraulicsonline.com/collections/carburators

They re-bushed my HD8s, results were satisfactory.

 

[Michael Oritt]

Steve--

I took your advice...thanks for the referral.

 

[steveg]

Steve--

I took your advice...thanks for the referral.

You're welcome, Michael.