Carb Rebuild!

[handsup]

Hi All,

A newbie to the forum and, well, repair in general.  Thanks in advance for any help or advice anyone is willing to offer!  I'm a recent college graduate who always loved vintage cars and always wanted to keep one up.  My dad grew up with these cars and always worked on them.  Unfortunately I hadn't had the chance to do this with him, so I'm taking to it while I've got the resources and time.  I've sort of dived in head first with a carb rebuild and I've come across a couple of issues that have me stumped.

The car is a 68 GT6 MK1 - US model.  For the carbs, it has this strange mixture of 150CDS emission controls (bypass valve, temp compensator) and fixed needle with adjustable jet (150CD style).  I'm getting some conflicting info as to whether this was spec for the veh, but it's changed hands a few times and my goal isn't to win shows, just learn and enjoy.

The disassembly/assembly was all pretty straightforward (so I think).  But I've got the carbs back on the car and I'm having a couple of issues:

First issue is that when trying to start the vehicle, the carb bores end up with an accumulation of fuel.  After a few seconds of cranking there's maybe 1/4 inch of gas pooled on either side of the air bridge where the air valve comes down.  The float chamber gasket is fully saturated with gas, so it looks like maybe the needle valves aren't working.  So I checked the needle valve for tightness and vacuum - all good - they hold vacuum for over 20 seconds.  I also checked that the floats are set to the correct height, that they float, and that they are free to move on the hinges - everything good there.  So I refitted the carbs and the problem persists.  The jets are positioned equal height with the bridge, then lowered three turns.  I am using replacement 6J needles, were just slightly longer, which was curious, but both had the same 6J markings, so I didn't worry about it - this may have been a mistake.  Other note, I did replace the mechanical fuel pump with the same type pump, but I don't see any apparent issues.

Additionally, I can't get the car to start.  Since the intake manifold has a slight uphill to it (ie the gas sitting in the carb bore), I'm not thinking that the engine is flooded or that it's so rich it won't start.  Does that sound right?  

I am getting good spark and did not change any of the ignition setup.  I have not yet checked timing, but I didn't alter anything since when I drove the car in, so I'm assuming it should still be alright.  The vehicle does have electronic ignition.  I don't have the vacuum lines connected yet, but my understanding is that this shouldn't prevent the car from starting, no?

Thanks for any insight you might be able to offer!!!!

Also, I have the original factory manual in binder (like what they gave to the dealerships) as well as Haynes manuals for the car as well as Strombergs/webers and SUs.  I'm happy to scan and email any diagrams or specs anyone needs (within reason  ;) )

[nang]

I'd check the "slightly longer" needles. Thought they should be the same as originals. Maybe the replacement fuel pump is giving too high a pressure. What was wrong with the original one ?
Cheers Tony.

[Falkon]

Are the float heights correctly adjusted.

[rotoflex]

Do you have a picture of the carbs?
Do you mean you have one of each?

The ones with the adjustable jet are beter in a few ways.  One example is the choke:  later ones use an assembly called a "starter box" for the choke which is simple & works very well, but unfortunately the apertures in the aluminum with age & deterioration become enlarged & they have no downward adjustability.

Someone mentioned once before that there was a run of repro mechanical pumps that produced too much fuel pressure.
The fuel pressure for the Strombergs should be 1.5 to 2.5 psi (0.106 to 0.176 kg/sq. cm)
It's possible that if there's too much fuel pressure, it's overcoming everything in the carbs & might lead to the pools of gas in the carbs.

If you check the fuel pressure & it's too high, you can get back on track with a Facet brand cube fuel pump, which can sometimes be found at local parts stores.  They make several; you want # 40163
http://www.facet-purolator.com/index.php?option=com_content&task=category&sectionid=7&id=16&Itemid=31

I think a 1968 Mk1 is a very late Mk1 moving into Mk2/GT6+ territory, so the last may have gotten the GT6+ emissions carbs, or yours may have come from a later car.  The GT6+ carbs are sort of rare, though, so it would likely have happened before the more prevalent carbs with the fixed jets became ubiquitous.

At any rate, adjusting the bimetallic temp compensator can be nerve wracking if it's been apart, or fruitless if the little pointy rubber stopper has deteriorated as most have.  There is a page on the internet someone made about re-calibrating them with hot water and a thermometer, but I who have gotten very impatient & lazy would just get new replacement temperature compensator units which are now available.

The bypass valves can also be troublesome, but mostly affect when the car is already running.  I have a friend who is a whiz at turning that screw to that one, exact place where it has to go, but I'm not so good at it.  On the other hand, the carbs work fine with the bypass valves blocked off, & lazy persons often fo that.  Some have cut a blockoff plate from a piece of an aluminum soda can to put on between the bypass valve & gasket, some have used gaskets alone that they've cut.

Neither of those things should cause the pools of gas that you spoke of - I mention them just because they're issues that often need to be dealt with.

If you're in the USA, a good source for parts & advice is Joe Curto.

Andrew Turner in England supplied me an excellent set of CDSE replacement carbs for my MK3, & he's another good resource.  I have a set of Webers that I used to alternate with the Strombergs when time came for rebuild or whatever so that the car did not become stationary, but I've grown less entranced with the Webers & with the new set of Strombergs can now just alternate them.

Do your carbs no longer have the little brass tags on them with numbers?  They were an identification to reference the car that the carbs originally went on. A possibility is that your Mk1 may have at one time blown its engine & a GT6+ engine was put in.  Looking at the head, are the tubes that the pushrods operate visible?

You've already got them together, but it would be interesting to see a picture of these differing carb needles side-by-side.

[handsup]

Thanks for the replies!

The original pump, which was leaking before the carb rebuild, stopped working after sitting for a few months.  Once I got the carbs "done" I tried to start the car and wasn't getting any fuel.  I had one on hand that I got from Spitbits, so I replaced it.  It is a repro, and I'll have to check the pressure on the fuel pump - thanks for posting the correct pressure!

Float height is good.  

I actually got the kits from Andrew Turner, who has definitely been helpful whenever I've asked.  Really nice guy I can't recommend him highly enough. I'll try Joe, maybe he's got an idea.

Unfortunately the carbs don't have the brass tags.  Both carbs are the same in that they both have the earlier adjustable jets and the later version temp compensator and bypass valve.  I can post photos of the carbs if you're interested, but the old needles got damaged in removal, so photos won't be too helpful for those (they were really set in the air valve).  They *should* be the same though - they are both marked 6J.  I'm going to try to get the correct length for the 6J needles and I'll post it so everyone can have it.

On the head you can see the tubes that the pushrods pass through.  I don't have the car or my manuals with me now to identify it, but I think the block # is from a GT6+.

I'll check the fuel pressure and we'll see if that's the issue.

Also, is it necessary to replace the float chamber gasket every time the bowl is taken off?  

[rotoflex]

If you can see the pushrod tubes, then it's a Mk1 head.

What do the plugs look like?  Are the electrodes coated with black fur?  If very rich, after afew semi-starts, the plugs foul badly & won't fire.

If you hold the end of the coil wire that usually goes in the center of the distributor cap near the head/block seam when cranking, do you see a spark jump?

Will it run briefly on starter fluid?  As in:  clean & re-gap the plugs, lift the carb pistons, spray some starter fluid in there, try to start, see if it runs briefly.

The float bowl gasket should be OK for re-use if it's not very old, not broken, & still compressible to seal.  If it's a new one that you've just put on for the rebuild, & are disassembling it to check problems, it should still be OK.