View single post by Esprit2
 Posted: 09-09-2014 09:32 pm
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Joined: 05-01-2005
Location: Minneapolis, Minnesota USA
Posts: 289

Nice to meet you and your Jensen-Healey face-to-face this morning

A 20W-50 oil is recommended. The 907's lubrication system is designed for relatively low pressure, a high flow rate, and high viscosity oil. Thin oils result in low indicated oil pressure once the engine is up to temp. The normal hot pressures are:
5 psi minimum at 900 rpm idle (scares me, 30 psi hot idle is more normal).
40 psi at 3500 rpm
50 psi at 6500 rpm

Your engine was idling hot at 30 psi with 10W40 oil... that's pretty good, and bodes well for the condition of the bearings.

The oil I mentioned is Mobil 1 20W50 V-Twin Motorcycle oil (Harleys). It's the old Mobil 1 Lotus used to recommend, but it contains way more ZDDP anti-wear additive than is allowed in cat converter friendly engines these days. So it was simply rebranded as a motorcycle oil. Or, Mobil 1 0W50 Racing Oil helps with cold weather starts, contains a full compliment of street additives, and a lot of ZDDP.

Don't use the timing belt tension specified in the J-H manual, as it's lower than is desireable. Lotus built variations of the same engine for 20 years after Jensen closed it's doors, and learned a lot more about keeping it running well. You'd be wise to use the higher belt tension that came from further experience.

Lotus recommends the Borroughs gauge, but it's a little expensive for some people's taste. The small tension gauge I showed to you is the Krikit KR1, made by HMC International, and marketed by Gates Rubber. Any Gates dealer (belts & hoses) can order one for you if they don't already stock it. The NAPA warehouse in Golden Valley stocks them. Call your nearby NAPA store in the morning, and the gauge will be in the store with the afternoon parts run. Or just go to the warehouse... you're close. I have a NAPA receipt from my last purchase and the line-entry reads:
Qty . Part No . Line . Descrip . Price .. Net ..... Total ... Code
1 ..... KR-1 .... NBH . Gauge ... __ ... $10.89 . $10.89 . T6N

The Krikit is made in several sizes, you want the smallest, the KR1 (KR-1)... mine is model 91107. The KR1 is made in several versions with different units of measure, but each also contains a pounds scale. You can use any of the KR1 versions, just be certain to read the pounds scale, as follows:

44 Too loose. Don't drive it. Avoid going below Krikit 50.
50 Normal minimum, time to re-tension the belt.
52 Used belt – target for re-tensioning a used belt.
55 New belts – set a little tight the first time to allow for stretch.
58 Too tight

With the carb jets cleaned up, the engine ran quite well. There's some smoke (quite a bit at first), but the rings are probably corroded after sitting for so many years. Cross your fingers, they may bed in again with some running. Actually, the smoke abated quite a bit in the brief time we ran the engine.

I intended to bring my magnifying visor, but forgot it. My old eyes couldn't read the markings on the emulsion tube, but here are the jet sizes I found in your Weber 40DCOE-2 carbs:
.................... Stock ....... Your J-H
Model ........... DCOE-2 .... DCOE-2
Throat .......... 40 ............ 40
Choke .......... 33 ............ ?
Emulsion Tube F16 .......... ?
Main Jet ........ 115 .......... 130
Air Corrector.. 150 .......... 200
Idle jet .......... 50F9 ........ 50F9
Float Height ... 8.5 ........... 8.5
Float Droop ... 15 ............ 15

Pretty much stock DCOE-2, except the main jets and air correctors are larger. Each new iteration of the DCOE got a new dash number. Yours are -2, and current production 40 DCOEs are -151, so lots of water has gone under the bridge since yours were made.

The idle jet nomenclature, 50F9, refers to a two-piece assembly. The idle jet is 50, the idle air corrector is F9, and they are purchased separately if you need to do some tuning. The engine ran quite well once the jets were cleaned out, so the 50F9 might be about right.

Since your carbs are DCOE-2, it's a pretty safe bet that the emulsion tubes are F16 as stock, but I'd still like to find the marks. Old eyes... I'll make a point to bring my magnifier visor next time.

The carbs need soft mounts ! The best are the die-cast Lotus parts I showed to you, unfortunately, they're also the most expensive. JAE has them in stock at $25 each, and two are required per carb, four total. Lotus made them for both 40 & 45mm throat carbs, so be sure to specify that you have 40mm DCOEs. I just talked with Jay, so it's fresh in his mind if you don't wait too long.
JAE, Jay Makwana, (805) 967-5767, Goleta, CA

If you don't want to spend that much on soft mounts, then JAE, Delta Motorsports (Jensen Specialist) and a lot of other places sell versions with a plastic spacer plate at a 'much' lower price. That soft mount will have a straight bore without the funnel taper (Kamm anti-reversion lip). They work, but lack the reversion flow control.
Delta Motorsports, Michael Dilimpio, (602) 265-8026, Phoenix

Finally, most Weber/ Dellorto/ Jensen/ Lotus suppliers (including Delta) also sell a thin, stamped steel plate with an integrally molded O-ring. It also works, I currently have it in my Europa, but I don't like it as well as the O-ring/ spacer plate/ O-ring type above, either plastic or die-cast. The Lotus die-cast soft mounts I showed to you are going into the Europa soon.

Any of the above will work better than the solid mount and air leaks you have now.

All soft mounts also require some manner of spring between the Nyloc mounting nut/washer and the carb flange. The original is a steel coil spring called a Thackeray washer. An alternative is a molded rubber grommet (polymer spring) that seats in a stamped steel cup washer. Either provides compliance to the joint as long as you don't screw it all down tight. Properly tightened, there will be a 0.030" gap between the manifold flange and spacer plate, and between the spacer plate and carb flange. With no gaps, the O-rings will be crushed. I can help you install the soft mounts, if you wish.

Last edited on 09-11-2014 02:18 am by Esprit2