Stromberg Rebuild

[SENC]

Thanks Roger, the disc was in the correct orientation.

Upon disassembly, I found the spindle to spindle bearing was a bit loose and the inside of the 2 disc sections had a little film/corrosion where they meet. I had an old spare and pulled it apart at the same time for comparison, then polished both with 1000-1200-1500-2000 on a flat surface, picked the best, reassembled, and reinstalled. No leaks and was able to get the initial timing set. Balancing next, and hopefully not too far from a ride.

Stromberg cold start valve

Stromberg cold start valve discs disassembled

Stromberg cold start valve polished and reassembled

[SENC]

Intended to note in the prior comment that I did reinstall with the gasket, with success.

Had some unexpected time this morning and was able to spend an hour balancing and tuning, achieving an acceptably smooth idle at a touch over 900 rpm so pleased with the carb rebuild so far. Timing advanced pretty much as expected up to 3k rpm, so looks like the dizzie is about right, too. Smoking and sputter much reduced from pre-rebuild, and temp stayed consistently mid-70s C with the fan running despite idling and revving where I previously had some overheating issues (more due to removing a clogged heater/water valve and tstat replacementioned I'm sure).

All in all, very pleased with current state. I'm awaiting a new airbox from SJ Sportscars, hopefully by 1st week of April, we'll see if I'm patient enough to wait on it before a road test.

[oldelanman]

Well done !

[SENC]

New stromberg airbox from SJSportscars

[SENC]

First road test today started OK but engine was stumbling under load at low rpm. Also found dwell angle a little high when back in the shop. Removed the distributor and tweaked the gaps, reinstalled and timed again. Also pulled the carb pistons to dump the damper oil, double checked the diaphragms and reset the adjustable needles to 1 turn below full rich. Warmed it up, balanced the carbs again, and adjusted, ultimately ending up about 2 turns below full rich.

2nd road test was much better - stumbling gone, solid acceleration and pulling strong. Maybe still a touch rich, will check the plugs tomorrow.

However, on the 2nd drive (about 15 miles - with the bonnet off so I could observe) I noted puffs of smoke out of the engine bay from time to time after heavy acceleration, like oil burning off the exhaust. At a stop where I turned to head back, I noticed some oil spray on the caps of the clutch and brake master cylinders then realized a mist was making it to the windscreen (exhaust side). I couldn't determine the source straightaway so will have to play detective tomorrow, too. Not quite sure what could have changed to cause an oil leak on this side - I've changed tstat and clutch master, but nothing that should have caused this that I can think of.

[mbell]

Oil blowing past the filler cap understand positive crankcase pressure?

I noticed some oil seepage from the cap area on mine. Find the cap could be lifted off the seal by hand. Some tweaks to the cap fasteners addressed it and the leak.

[SENC]

Thanks mbell, will check on that tomorrow. I did notice a bit of dampness around that, as well as a little weeping around one of the cam cover nuts, neither of which I remember from pre-rebuild of carbs and dizzy. The only other engine related change during this time was changing the crankcase breather from the metal tube to the airbox to an early style elbow with a fuel hose running to a water bottle in the wing. The hose has a smaller id than the original metal tube, could that be enough to increase pressure?

[mbell]

Yes, I'd suggest making sure the hose is at least as big as the pipe you removed. The standard setup can be a little marginal to start with.

I'd expect the airbox to be at let than atmosphere pressure, which would aid flow in the standard setup. So personally I like to keep the standard setup up on my car.

[SENC]

Well, I'd say it was definitely a contributing factor, at a minimum.

I couldn't find any obvious leak points, so wiped down all the parts of the cam cover, head and block I could easily get to then pulled out the fuel hose I was using as a crankcase breather tube and put in a piece of 1" id vinyl tubing (snug fit around the rubber elbow). Cleaned the plugs and adjusted the needles a bit leaner to address fouling, and went for a long ride, again without the bonnet. Did get a little bit of oil on the windshield, but very minimal despite a much longer and faster ride and on return no weeping from the cam cover nuts and only a very small singular drip from the oil cap, so the small id fuel hose was certainly causing some back pressure. On inspection of the engine bay, it was also obvious a little was coming from the dipstick tube (probably what was making it to the windshield), so will address that with an old plug cover.

Thanks again for your help.

[SENC]

Acquired some 1969 and 1970 Lotus Service Bulletins, and among them some good information on Strombergs I wanted to share for the good of the group. First up, jet height guidance on LSB 1969/8 dated June 18, 1969. Looks like the official is 0.120" recessed.

[SENC]

Next up, LSB 1970/5 issued on January 1, 1970 on converting to air valve assemblies with adjustable needles.

[SENC]

Finally, LSB 1970/24 issued July 1, 1970 with specs for identifying the different carb setups (specifically needles).

[69S4]

Thanks for posting those - some of them I haven't seen before and had to make my own guesses when I was replacing my jets a few years back. The one with the hammer is particularly interesting as it shows the tool + method of setting the jet height. I had to guess the height based on what the old ones (almost certainly the originals) were set at. That figure came out as 0.092" (2.33mm) which is what I used for the new ones (give or take a bit of hammering). The difference between that and the 0.120" given in the diagram means the needle needs to be moved up to compensate - which is where I find myself at the moment. Plus, the actual hole that the needle enters is slightly recessed from the top of the jet and from the diagram it looks like the 0.120" figure is from the top rather than the hole. The car is running ok at the moment but, armed with this new info, I may revisit this during the winter.