SU Carbs problems

[allenjdeg2]

My Jag mechanic rebuilt my series 2 4.2 liter engine carburetors. Initially he found that the needle valves were of different lengths allowing a lean condition on the back bank and a rich condition on the front bank. Apparently the SU Carbs are from a 1974 Damlier Jaguar and needed to be rebuilt. Following a back and forth discussion with a Jaguar carburetor expert it was determined what size needle valves were needed. Unfortunately, following the rebuild the engine will not surpass 32000RPM’S. My mechanic, following a large bill, declared that the engine was running at 95% and only needed to be slightly adjusted. The car stalls at revs in 2nd and 3rd gear and only can obtain a top speed of 50 mph in 4th.
The engine runs well at idle and low RPM’s. Any suggestions are welcomed . Thanks

[cactusman]

I presume you mean 3200 rpm not 32000....that would be impressive . Presuming the butterfly valves are opening fully, the needles are reasonably appropriate and fuel pressure and flow is sufficient to provide enough fuel it is hard to imagine how a car 95 percent right can only get to 3200 rpm with just mildly misadjusted carbudettors. SU carbs are really pretty simple devices and would have to be hopelessly misadjusted to a horrendous degree to limit engine speed so drastically in my view. If they were that bad I'd expect it to be a bugger to start at all. I do wonder if maybe the issue lies, at least in part, with the ignition being way out and maybe the vacuum advance not working...others will probably have sage suggestions but it would be wise to check the ignition....incidentally what do the plugs look like? Loads of soot is over rich but unlikely to stall. Glazed and possibly burned electrodes suggests either extremely lean or severely misadjusted ignition timing which might cause stall....

[mgcjag]

Hi Welcom to the forum...whats your name......first you say the carbs are from a daimler...can you post a photo just so we can see what you have.....you also mention needle valves......these are in the fuel float chamber..you also have needles in the main body on the bottom of the pistons......SU,s are not too complicated to set up....can you also let us know what fuel pump you have....Steve

[allenjdeg2]

Thank you for your responses. My name is Allen, residence: So. California. I bought this 1969 E type series 2 for my wife a few months ago and, as a long time Xk150 jag owner, was aware of the problems they can possess. The car has always run “rough” at idle and had a tendency to blacken the plugs. An electronic ignition was previously installed. I just wanted the engine to run smoother at idle and mid range because I was happy with high end performance. Unfortunately the rebuild of the SU’s has made it much worse. I understand the fuel pressure and possible restriction issues with fuel flow at high RPM’s but I’m perplexed that the engine cannot get over the 3200’s when it was fine before. I’m not a mechanic but I assume it must be the SU carbs? My jag expert went on vacation and won’t be back until the 19th.......I just thought I could get some really good answers from you guys.

[bitsobrits]

My first comment would be that if a "mechanic" charged you a bunch of money and returned the car running as you describe, I would recommend a new mechanic.

I see you have a very non standard carb installation, so troubleshooting assistance will be very difficult to provide, though there are many very knowledgeable people on this forum.

Nonetheless, if the car ran somewhat decently before, the most logical reason for the present situation is that the mechanic got something wrong either during the rebuild process, during the installation, or with the post install adjustment.

I would progress from checking the simple, moving progressively to the more complex.

Remove the air cleaner housing so you can see into the carb throats.

Check that the throttle linkage/cables are functioning correctly by having someone slowly press the accelerator pedal all the way down while you watch the throttle spindle movements (engine not running). The throttle blades should move should of course move at the same rate. With the pedal all the way down, the throttle blades should be fully open, which you can see/feel from the outside of the carbs, or by viewing though the carb throats with the pistons lifted.

Check the action of the choke cable to ensure it is fully released when in the off position. With the car running, put the choke full on very briefly, and the engine speed should significantly increase. Return the choke to off and turn off the engine.

Lift the carb pistons one at a time with your finger to ensure they move smoothly and completely to the their top of travel. With oil in the carbs, it will take moderate pressure to move the pistons up against the damper action of the oil, but the movement should be smooth all the way.

Release them to see if they drop immediately with a small "clink" back to fully down. If you feel any issues, remove and inspect the vacuum chamber/pistons for damage: dents, burrs, nicks, etc on the inner surfaces of the chamber (which should appear to be highly polished). If there is any drag, he may have accidentally mixed the vacuum chamber/piston pairs which are precision matched to each other.

Inspect the piston springs and make sure the two are identical.

Verify fuel pressure with a suitable gauge, and flow volume. Youtube has many videos on measuring fuel volume.

I'm sure others with come up with more ideas.

[MarkRado]

Hi Allen, nice looking Etype (in a wonderful surrounding!).
A pity it is let down by non orig carbs. I would not bother trying to get these carbs right (esp with non orig distance pieces), but buy a set of original equipment carbs together with manifold instead (triple SU HD8) and re- convert (quite easy). Also brings up the car's value if you ever decide to sell on.

[cactusman]

Having seen the carbs you have I would probably agree with Mark...get a triple HD8 set up. The ones you have look like 1.5 inch carbs. Similar ones were.fitted to e.g. MGB's. My MGB on twin inch and an half carbs will get to 110mph on a tuned 1840 cc engine. Not sure if yours came from a Daimler saloon though although someone will know. All that said I still suspect the problems may not be entirely down to the carbs....I guess the car did manage more than 50 mph before the rebuild? If the ignition is very retarded and the vacuum advance is not working the engine may idle reasonably well but will be very sluggish and possibly this may be a contributing factor? Hope you get to the bottom of the issue....probably find another mechanic!

[mgcjag]

Hi your carbs look like 2in hif SU.s as used on S2 XJ6 no reason why a competent Jag mechanic shouldn't get them running well...not an uncommon conversion from the usual US spec Strombergs on some Jags.. Can't really add much to help that hasn't been said above..Steve

[Gfhug]

Perhaps Peter Crespin could sell you his triple set:
viewtopic.php?f=7&t=15139

A decent price and he's a good man

Geoff

[christopher storey]

This is a terrible "lash up" from the photo. I'm not sure what the carbs are from, but I feel sure it's not a Daimler/420 because there are clearly manual "chokes" fitted - although there is no connecting bar and levers, so how they work is a mystery . Next, the air filter connectors look to be out of line with the carb air apertures, and it looks as though there is a bolt, top centre of each carb, plugged into one of the balance passages of the carb. Your mechanic, quite frankly, doesn't sound as though he knows much about these things, because the tale about the needle valves ( which are what admit fuel to the float chambers ) just does not make sense. Did he mean the piston needles? And on that subject, do you know what needles are fitted because this has a crucial effect on mixture strength, and with a non-standard setup can be way off the mark

You need help from someone who knows what they are doing

[mgcjag]

Yes these Hif carbs should have a seperate AED choke unit but not fitted on above setup.. photo shows correct setup on XJ6 with AED unit between carbs.....Steve

[Gfhug]

Would it be sensible, even if it's only a short term solution, to get the old Strombergs refitted?
At least they should work and your wife could use the car until you find someone who can do a proper job on the SUs.

Geoff

[golfnut324]

Allen,

I strongly suggest that you check in to the Jag-lovers forum

https://forums.jag-lovers.com/c/e-type

where you will find dozens of enthusiasts near you many of which are very willing to contribute their time and expertise to help out the less informed, like you and me. Likewise the good folk here though most are a tad far away!

Craig

[allenjdeg2]

Einstein once said “ if I had one hour to solve a problem I’d spend 55 minutes thinking about the problem and 5 minutes thinking about the solution “. Since I’m no Einstein, especially when it comes to old SU Carbs, I really appreciate your help with both the problem and the solution. My Jag mechanic has a good reputation and is respected in these parts. I still believe that he can help me. With that said, I believe the problem lies with the wrong needle once said “ if I had one hour to solve a problem I’d spend 55 minutes thinking about the problem and 5 minutes thinking about the solution “. Since I’m no Einstein, especially when it comes to old SU Carbs, I really appreciate your help with both the problem and the solution. My Jag mechanic has a good reputation and is respected in these parts. I still believe that he can help me. With that said, I believe the problem lies with the wrong piston needles and perhaps with the identification of the SU Carbs. I also understand the logic of examining the possible causes of fuel blockage issues, pressure variants, and timing issues. I agree with the idea of replacing the SU’s with the original carbs but I understand that the SU’s are simple and actually more reliable than the original? Last night I checked my spark plugs and noticed that all were clean with no apparent blacken-soot appearance. I plan to forward the suggestions and responses from you guys to my mechanic that is currently on a two week cruise in the Caribbean.

With the SU carbs how do you identify them? Apparently the stamped embossed number is incorrect.

[allenjdeg2]

I apologize for the duplicate script

[MarkRado]

The SU Burlen reference catalogue states the HIF 44 with man choke to be correct for the 1983 Daimler limousine (4.2 litre), with NZX 8022 BDX needles (be careful- the 3.4 engine also used HIF44, but with different needles). So if thats the type of carbs you have its worth trying to keep the current carbs for the moment- just check that the correct needles are installed.
In your photo your vac pipe port on the frt carb is open/ missing the connection to the distributor vac capsule. I am not going into detail with the types of distributor vacuum adjustment (advance or retard) and where the vac has to come from for each type- you can look that up on the forum.
For the moment just close the port on the carb, then check your static ignition timing (around 8 - 10 before TDC) and check that the didtributor centrifugal advance works. Next step would be to make sure you have no air leaks with the non original distance blocks between carbs and manifold. Finally adust the carbs as per SU manual.
PS the recommended and initially oe carbs are triple SU HD8, which are -in my humble opinion- super reliable and convenient to adjust

Edit: in my SU catalogue edition (p 88) there is a confusing array of different HIF carb specs, but even the HIF 7 uses the a.m. needle and AUD4398 piston spring. Whatever car your carbs came from, if they are 1,75 in or 44mm diameter and have the correct needle and spring, they should be working.

[christopher storey]

Mark : I think you have put your finger on the Daimler reference. Those do look smaller than 2" and therefore are almost certainly HIF44 i.e. the same as the earlier HD6 of 1 3/4" bore. They are therefore probably too small for a 4.2 in E type specification ( the XJ6 used twin HD8 2 inch instruments ) and certainly will strangle the top end . Also I have a feeling the jets are only .100 rather than .125 and thus choosing a suitable needle for the E type is likely to be problematic, and probably will require one a good deal richer than at first one might think. I also wonder whether the distributor is one of the vacuum retard type which unless properly adapted could well explain the fact that it won't rev beyond 3200 rpm ?

[PeterCrespin]

The HIF carbs are probably 1.75” as were the “Stranglebergs” originally fitted. They would not, in themselves, limit performance in the way Allen describes if correctly refurbed and installed. With the home-made spacers there may be a way of fitting them incorrectly with the bores not aligned but it seems the expert is either very far from being one, or his work was fine but installation by Allen or someone else is faulty. There’s not much more we can do remotely but even if the expert was not at fault I’d regard him as your first port of call (to use a sea cruise metaphor). It shouldn’t take him long to diagnose the problem. And if he installed the carbs he should ‘t charge you IMO.

And yes, if you’re stuck I could probably supply all the SU conversion

[johnetype]

Allen, the carbs you have are perfectly able to run your engine and run it well if they did come from a 1974 Jaguar. The best starting point would be to use the same needles as were originally used in the 1974 setup.

However, for your lack of revs problem I'd be checking that the carb butterflies open fully when you press on the accelerator pedal and check out the distributor and timing.

You do not appear to have vacuum advance fitted as the vacuum take off on the front carb (in the middle above the throttle butterfly) has been sealed off with caulk or glue. Whilst lack of vacuum advance won't be the only and direct cause of your lack off RPM, it will help the smooth and economical running of the engine.

[mgcjag]

Hi Allan...this will be a good resource for your mechanic once you have identified your carb model.....they can supply all parts through the SU range...Steve http://sucarb.co.uk/?SID=63nrbucav8fptu ... __store=su