Lotus Elan

Sorting the Strombergs

PostPost by: The Veg » Mon Dec 28, 2015 2:55 am

First off thanks to all who've answered my new-guy questions in other threads. Time for questions of consequence to start being asked.

As some of you know, the Elan is new to me and I have yet to drive it due to several issues needing sorting first. The Stromberg carbs are one such issue. First, some background:

The engine was rebuilt two owners ago (but the rebuild only has about 500 miles on it to date...long story), and the rebuild included modifying the head to big valves and milling to Sprint specs, and a Dave Bean 112 cam ('hot street,' high lift/duration), and .020" bore-over. Despite all that, the intake system was unmolested- the emissions setup was all still intact!

The engine will run, as I started it and ran it for a couple of minutes two days ago- but there are some carburetion problems.

The first is that there is a leak from the O-ring on the brass plug in the bottom of one of the bowls...I know what to do about that and will be ordering rebuild kits. May as well go through and make sure that all the perishable bits are fresh (interestingly, the diaphragms seem new in appearance an pliability).

The needles are B1G and they don't look so good. The needle in one is all green, so I suspect the jet is corroded- better to renew both needle and jet, I assume? The other needle is coated with hard, dark brown crud, the removal of which I assume risks damaging the needle. I saw in another thread that the B2AR needle is a popular choice- would it work well with the above-described engine characteristics?

Today I removed the preheater pipes as advised in other threads. I have read that finding a non-emissions manifold is ideal but blanking off the ports where the pipes went will do. Would I be correct to assume that a much shorter connection between the ports would serve no particular advantage over simply blanking them off? Am I also correct to assume that there is no reason to bother blanking the ports on the exhaust manifold?
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PostPost by: RogerFrench » Mon Dec 28, 2015 4:09 am

Yes, you can simply blank off the ports. You can leave the exhaust, though you'll get better results by replacing the manifold by a good tubular header.
You can also remove the secondary throttles from the inlet manifold as long as you plug the spindle holes.
Note that B2AR are not direct replacements for your B1G needles. B1G are fixed needles, B2AR are adjustable. Look at a parts list, Burlen in England have one on line, and get the bits you need.
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PostPost by: CBUEB1771 » Mon Dec 28, 2015 4:17 am

The Dave Bean 112 cam is not a very aggressive profile and changing to the B2AR needles and correct springs would make sense. My federal +2S had the big valve head with higher (Sprint) compression ratio. I changed to a complete non-emissions arrangement with the Strombergs, with balance tube, and the B2ARs worked pretty well. The balance tube needs to have an internal diameter of about 5/8" to be effective so there is nothing you can do with your existing inlet manifold to get the flow balancing effect. You might as well just put a blanking plate over the preheat ports as you suggest. You don't need to blank off the corresponding ports on the exhaust manifold. It sounds like you read my post from earlier today also about changing to B2AR needles so you know about the tools you will need to adjust these needles. I am very curious to know if during the engine rebuild the cam timing was set properly. By surfacing the head to increase compression ratio the cam timing will change. The people who did this work should have used offset dowels in the cams to get the lobe centers back to the 110 degrees specified for the Bean 112 cam. Changing to B2AR needles won't have as much effect as getting the cam timing right.
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PostPost by: The Veg » Mon Dec 28, 2015 5:01 am

RogerFrench wrote:Yes, you can simply blank off the ports. You can leave the exhaust, though you'll get better results by replacing the manifold by a good tubular header.


Of course, and that's another project for another time.
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PostPost by: The Veg » Mon Dec 28, 2015 5:13 am

CBUEB1771 wrote:The Dave Bean 112 cam is not a very aggressive profile and changing to the B2AR needles and correct springs would make sense. My federal +2S had the big valve head with higher (Sprint) compression ratio. I changed to a complete non-emissions arrangement with the Strombergs, with balance tube, and the B2ARs worked pretty well. The balance tube needs to have an internal diameter of about 5/8" to be effective so there is nothing you can do with your existing inlet manifold to get the flow balancing effect. You might as well just put a blanking plate over the preheat ports as you suggest. You don't need to blank off the corresponding ports on the exhaust manifold. It sounds like you read my post from earlier today also about changing to B2AR needles so you know about the tools you will need to adjust these needles. I am very curious to know if during the engine rebuild the cam timing was set properly. By surfacing the head to increase compression ratio the cam timing will change. The people who did this work should have used offset dowels in the cams to get the lobe centers back to the 110 degrees specified for the Bean 112 cam. Changing to B2AR needles won't have as much effect as getting the cam timing right.


Hi Russ,
Yes, I did read that post. Sounds like this is going to be a fairly straightforward project for the most part. The last carbs I dealt with before this were Bing CVs on a BMW motorcycle, which are a similar type of design to the Strombergs although certain basic design qualities of the Bings seem to be a step above the Stroms.

I hadn't thought of the issue you raise about the cam timing, but it certainly makes sense. Luckily I'm in touch with the PO who had the work done and he's very supportive and cooperative, so I'll ask about whether or not the cam got precisely timed. Keep fingers crossed!
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PostPost by: The Veg » Sat Jan 02, 2016 4:08 am

Follow-up:

Got the rebuilds done today, and the blanking off of the manifold parts is done too.

When I ordered everything I did not realise that the B2AR needles were not a direct replacement, and on top of that, one needle was stuck in its piston. Luckily the B1Gs did actually clean up well enough to press back into service as all the crud was superficial rather than any actual corrosion of the needles.

I'm guessing that I don't want to stick with the B1Gs given the rest of the engine's setup, right? Now I see that Bean (whose salesman did not warn me about the compatibility issue when I called in the order, despite some discussion of needles) have the parts to convert to the adjustable needle but they are crazy-expensive! Looks like about $240 for the piston-kit, and I assume that's for just one of two. Is this really worth pursuing, or should I just return the B2ARs and get a different non-adjustable type? I see that they have a non-adjustable B1Y that the catalog describes as 'mild power increase over B1G.' Would this one be a good choice, or should I really just bite the bullet and go adjustable? Why or why not?

Thanks for your patience with all my questions...learning this as I go, y'know?
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PostPost by: david.g.chapman » Sat Jan 02, 2016 12:10 pm

I have lived with "non adjustable" needles ever since I got my +2 back in 2001.

I just undo the 4 screws holding the top of the Stromberg on, take out the piston, note where the needle shoulder is (you can pull the needle out a bit if the shoulder is hidden in the piston), slacken off the securing grub screw and reposition the needle. Up to richen the mixture and down to lean out.

Small movements are the order of the day of course. Enough so you can see the difference but no more (10 thou?). Try with the needles in a variety of positions to get the best results. IMHO it doesn't take too long, and when finished you don't need to touch them again.

So I would keep it as it is.

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PostPost by: m750rider » Sat Jan 02, 2016 2:52 pm

I have the exact same setup on my 1969 S4 SE that you've described, including the 112 cams but I also have tubular headers. The secondary throttle plates have been removed and a blanking plate installed on the intake as you have done. I use B1Y needles and upgraded springs. There is no need to go to adjustable needles, as the fixed needles are adjustable as Dave Chapman has explained above.

It's easy to set the proper mixture - it just takes a little trial and error looking at spark plugs to know exactly where to set the shoulder of the needle relative to the holder, moving up or down in very small increments, .002 -.003" at a time.

I had my carburetors rebuilt by Dave Curto many years ago, and I also recommend him as an excellent resource to put the Strombergs in perfect condition.

Bob

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PostPost by: RogerFrench » Sun Jan 03, 2016 7:02 am

Joe Curto maybe, not Dave?
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PostPost by: m750rider » Sun Jan 03, 2016 1:39 pm

Yes, Joe Curto. Thanks for catching this. Must have had Dave Bean on my mind.
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PostPost by: The Veg » Sun Jan 03, 2016 9:38 pm

Thanks guys, sounds like encouraging advice.

Yesterday I got the carbs installed. I also removed the secondary throttle-shafts from the manifold and plugged those holes. Whatever mechanism was supposed to open and close the secondaries was gone and they were tightened in the full-open position, but I figured that gone altogether would be better.

After copious cranking I managed to get the engine running. While finer tuning will be needed, it ran well enough to idle for several minutes and even a short drive up and down my street. There are still of course small problems that need sorting, such as:

-Fuel lines. The short pieces clamped to the metal 'T' don't seem to seal very well. Off to the store for some fresh hose.

-Throttle closure/idle. On the bench after rebuild the throttles closed smartly with no problem and the return-springs seemed to be doing their job. Installed in the car, the throttles don't want to close fully and as a result the idle is quite high, a little above 2000. I can get the idle down by pulling the throttle shaft to the stops by hand, and behind the wheel I could *sometimes* get the idle down by pulling up on the pedal with a foot hooked under it. The cable has some play in it, so I wonder if the cable is suffering too much friction in its sleeve. I'll try a squirt of oil and see if that helps.

-Throttle bypass valves. The diaphragms in these are hard as a rock, so replacements will get ordered. I still don't know what they actually do, but I figure a hard diaphragm can't be good.

-Dieseling. The engine Dieseled for a good 45 seconds to a minute after shutting off the ignition, so something must not be quite right. I know that lead-deposits in the cylinders could make cars do that back in the old days (my dad's old '70 Plymouth was the grand-champion of Dieseling!), but that shouldn't be an issue here since the engine was bored-over during the rebuild and was run on unleaded for years prior to that anyway.

But I was still really chuffed that it ran, and it definitely feels like progress. At the risk of embarrassing myself, here's some video:

https://www.youtube.com/watch?v=S0jkqFk7b8U
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PostPost by: The Veg » Mon Jan 04, 2016 6:30 pm

CBUEB1771 wrote:I am very curious to know if during the engine rebuild the cam timing was set properly. By surfacing the head to increase compression ratio the cam timing will change. The people who did this work should have used offset dowels in the cams to get the lobe centers back to the 110 degrees specified for the Bean 112 cam.


Just to follow-up on this, I'm pretty sure the cam timing is OK. I'm told that the job was done by American Cylinder Head of Salt Lake City, and I've found their timing-worksheet among the car's documents.
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PostPost by: bill308 » Wed Jan 06, 2016 9:17 pm

Hi Veg.

Your high idle may be caused by a carb imbalance. One carb may be closed, but because of the interconnecting linkage adjustment, the other may be more open and feeding more air via the balance tube. Get the carb balance right and your high idle should go away.

A consequence of a high idle is often run on after switching off the ignition. So, get the balance right and you will likely get a better, more controllable idle and a clean shut off. Also, grunt at lower rpm's will be better with well balanced carbs.

I happened to be reading DBE's catalog last night concerning Strombergs. One interesting observation he made was that the needle and orifice/jet should not be installed perfectly concentric. One side of the needle should rub on the id of orifice/jet for best metering. If perfectly concentric, metering is somewhat erratic.The consequence is that over time, both the needle and orifice need to be renewed. DB did not speculate as to the physics involved.

Finally, remember that Strombergs were introduced for emission purposes. As such they were likely tuned on the lean side. Now, introduce 10% ethanol laced gas, and the mixture will likely be an additional 2-4% leaner. You should consider richer needles. DBE's catalog gives some guidance here but perhaps other specialists could offer even better guidance.

Bill
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