I seem to have tracked down the hot starting problem I've been having on my '65 B18 w/SU's 122.

The car wouldn't start back up after reaching operating temperature and sitting for about five minutes. If I tried restarting immediately, OK. If I waited 15-30 minutes, also OK.

I had two filters on it, pre and post-pump. First removed the post-pump filter, no change. Second replaced the Grose Jet Valves with the old Viton-tipped valves and BINGO! Problem solved. Car still wants to have the throttle opened up at start after reaching temperature but starts with no fuss.

So I'll be buying new OEM float valves in place of the Grose Jets. They sure seem to be a good idea but mine don't seem to seal. Tested with vacuum gauge and they bleed down from 15" in about ten seconds.

I'm guessing that they were bleeding the residual fuel pressure into the carbs and flooding them, causing the restart problem.

Hopefully IPD will work with me concerning these valves, they really didn't perform for me.

Hope this helps someone out there.

-Mario E.

Portland, OR

I came to the same conclusion about Grose Jets and have gone back
to the OEM float valves in mine. Don't know if it is a quality problem
or what.

I used to have a hot start problem on my 164 but have not lately.
I think the last do on its HIF6s solved the problem. I don't remember
ever having the problem on a 122. Do you have aluminum or cast arn manifold?

--
George Downs Bartlesville, Oklahoma

George (and Mario): Of interest to me was Mario's reply that he didn't use the carb insulators in the system, which makes me wonder if the heat shield is also off of the car. I've been using Grose Jets on the SUs in my British iron for YEARS and have found them, without exception, a superior design and execution to the needle and seat set up fron the old Skinners Union. I've experienced no wear, nor any of the problems that others seem to have had, with one caveat...that the system isn't butchered or "home modified" for the sake of a little more show, or (hopefully) more go. Case in point: Modified 1800cc MGB engine for autocross...head, valves, header, pushrods and lifters...you get the idea, a good solid top end rebuild. Then, like a dope, ignored the advice of the rebuilder who's been doing this work with old Brit and Swede pushrod engines for the past 40+ years, and for the sake of a little more pizzaz in the engine compartment, cut and 'modified' the heat shield which insulates the carbs from the header...largely so people could be impressed with the work I'd done. Car ran like absolute crap...bucking, surging, backfiring, until the mechanic just silently handed me a new heat shield, didn't say "I told you so" and I installed it without so much as a hoo-ha. Problem solved! He patiently explained that the problem lies with the creepy design of these engines in placing the float bowls directly over the hot exhaust manifold. Without the shield, the radiant heat literally BOILS the fuel in the bowls and forces the vapor past the Grose jets or the needles, as the case may be. Hence, the poor running and the tough hot starts, until the fuel has a chance to cool sufficiently, as Mario describes it....either right away, while the fuel hasn't boiled out yet, or after enough time for the gas to cool. So the question is, heat shield installed properly? If not, look there first, before you question a carb set up that has worked well on literally hundreds of thousands of SU installations. If the shield is there, by chance, then look into the carb bowls. Absolute cleanliness is a must! No gook, rust, scale or dirt is permitted as this will decrease the amount of heat required to force fuel past what would turn out to be a less than ideal seal in the bowl and into the carb itself. Well I've prattled enough....How about it Mario, everything where it should be?

Brad

These carbs are freshly rebuilt Ztherapy HS6's. The heat shield is there as it should be. Although I have thought of rigging up a double shield with some sheet metal, SS hardware, and spacers attached to the bottom of the OEM-style shield. When I track down a spare shield I may give that a try.

In any case the car starts fine at temperature now and the only difference is the OEM valves over the Grose Jets.

The thing that makes me suspect the Grose is the bleed-down when testing with the handy Mighty-Vac. The OEM held vacuum.

I am not a stockholder in SU nor do I have any affiliation with same. I'll allow that my methods aren't super scientific, I'm basing this on observation and my curiousity is way down now that its starting when I want it to.

The info about the interior of the float bowls is intriguing. Even though these are rebuilt the inside of the bowls aren't perfect. I wasn't too concerned but maybe that had something to do with it.

In any case, the 122 has many more problems that need to be attended to. I'm way behind schedule and the taxman has unfortunately taketh away. Good thing sanding doesn't cost much.

The quest continues...

-Mario E.

Portland, OR

do seem like a good idea. Were OEM with the Z cars' SU Hitachi's. Probably track some down and install next time I have the carbs off.

To the best of my knowledge the standard heat shield on a B18/B20
is a sheet metal device. I have not seen one equipped with the
plastic separators between carbs and manifold, only the sheet steel
plate, with gaskets on both sides, which probably perform at least
some insulating function.

My problem with grose jets was as evident cold as hot, and could be
seen as almost the same as not having a float valve at all: gasoline
coming out the vent in the top of the float chamber. A friend who is
pretty expert with SUs told me they never wear out, and that soaking in
carburetor cleaner would remove the gum which he thought was causing the
problem. In some cases it helped some, but I still had flooding problems.
I changed back (after about a dozen years) and about 90% of the problem
disappeared. Still have problems at high revs on one carb, which I
attribute to vibration or resonance of the float. The engine revs pretty
high and has not been balanced.

When I first started using Grose Jets they worked pretty well but I suspect
that they are not now made to the quality that marked the early product.
Also the same vibration may have caused some abrasion. Anyway the neoprene
or viton tip seems to work better for me.
--
George Downs Bartlesville, Oklahoma

I have the aluminum intake, no phenolic insulators for the carbs.

FWIW, I try to keep track of all modifications or changes and maintenance I do to the cars. Invariably problems like this show up AFTER I change something or do something (like the several years I had problems with rising rate fuel pressure regulators from a Saab aftermarket supplier--they fixed the RRFPR both times and I learned to test for fuel pressure when driveability went to heck)....and I can then go back to the way it was before I hacked it up.

Now if I could only figure out the durability failures as easily.