View single post by Esprit2
 Posted: 02-21-2016 01:49 am
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Joined: 05-01-2005
Location: Minneapolis, Minnesota USA
Posts: 343
I know, I'm very late, but I just ran across this thread. Maybe this will be of use to the next guy.Bfitz241 wrote:
The fuel tank is in the back of my pickup and I'm running it on an outboard gas tank with an inline electric fuel pump.

I'd also like some opinions on whether those Dellortos are even worth it.

But I still need to get the oil off the points and inspect that distributor.

Which inline fuel pump are you using. More to the point, what is the fuel pressure at the carb inlets? It should be 1.5 to 2.5 psi. More will over-power the float/ inlet valve and result in a high fuel level and flooding. If the pressure is high, install an inline fuel pressure regulator, and set it to 2.0 psi.

The Dellortos are great all by themselves, once set they require minimal maintenance/ tuning, but they will only be as good as the guy who installed them.

They should be installed with soft mounts and Thackeray washers (coil springs) or rubber grommets. Do not tighten the mounting nuts down hard. There should be a 0.040-0.050" gap all around both sides of the soft mount. They should never be hard mounted.

The carbs must be balanced after installation. If they're not balanced, then the engine will run like crap. That's not the carb's fault, that's the installer's fault. All multi-carb set-ups are subject to balance, not just Dellortos. It's basic Carbs 101.

There should be no oil on the points, or in the distributor. Presence of oil indicates the distributor's seal is bad. Either replace it, or pay to have the distributor rebuilt. Advanced Distributors is good (they're about a half hour from me), and Jeff can make a decrepit old piece of crap distributor better than new for about $115.

Jeff is a little stubborn, and has his own ideas about how to set up a distributor. Just tell him you want stock J-H spec, and be diplomatic in your conversations. Cop an attitude, and you'll lose him in the first sentence. He has zero tolerance for bull or attitude, despite his own attitude. He's really a nice guy, just go easy until you know him.
Bfitz241 wrote:What type of cranking compression does a stock 907 generate? Maybe I can figure it out with a compression gauge.
7.58 - 8.96 bar (110 - 130 psi) COLD = Jensen-Healey spec
10.2 - 11.6 bar (150 - 170 psi) HOT = Lotus spec
Lotus specifies that the compression is to be tested HOT with the engine up to full operating temperature, throttle held fully open, and engine cranking at least 200 rpm (ie, battery fully charged). That's a little tough if you can't get the engine running in the first place. If you have the option, check the compression pressure hot. Failing that, a cold test is better than nothing.
Bfitz241 wrote:It starts advancing at 1200/1*, 1300/3*, 1600/4*, 1800/5*, 2000/6*, 2200/7*, 2400/9*, 2600/10*, 2800/12*, 3200/14*, 3600/15*, 4200/16*, 4600/17*, 5200/18, 7000/18.5* Point bounce began to set in around 5500-5700.Spec is 17 crank degrees all in by 2500 rpm. However, 16 to 18 is good, and a little bit more by redline is okay... well, good.
Jim Ketcham wrote:I do not know if I was clear in my earlier post, but you should NOT be using VACUUM RETARD on the Dellorto configuration. Even on the Stromberg configuration it does not offer any performance benefit. The Dellorto configuration came with the Lucas 23D distributor that does not have a vacuum module on it.True, the vacuum retard is an emissions setting incorporated into the Zenith-Stromberg emissions set-up, and not fully consistent with the Dellorto performance set-up. But the vacuum retard only comes into play at closed throttle idle, and has no real detrimental affect when used with Dellortos. Once the throttle is cracked open enough to break the vacuum, the retard goes away (it's all or nothing). For all driving above idle, vacuum retard is a non-issue. Don't bust a hump over it either way.

The one downside is that the initial off-idle throttle response can be a little sluggish while the vacuum capsule responds (a split second), but once you're launched, it's not a factor. For autocross or motorsports, delete the vacuum retard for optimal throttle response. For street driving it's not much of a factor, and the upside is that the retard produces a more benign idle.
Bfitz241 wrote:Water pump out, looked ok but I took it out so it's getting rebuilt.The J-H water pump has forward curved vanes on the impellor, and the vanes are small and few in number. The forward curved vanes result in cavitation at higher rpm, resulting loss of pumping efficiency, and a tendancy to run hot or over-heat. Later 'Lotus' 907 impellers have backward curved vanes that cure the cavitation problem, but are still small and few in number

The 910 Turbo impellor has a full compliment of long, backward curved vanes, and it's a huge improvement in coolant flow. The problem is that the 910 impellor's snout is longer, so it won't fit in a J-H pump housing. But take the new and old impellors to a machine shop, and have them shorten the 910's snout so the overall length matches the short J-H impellor. Once that's done, the new impellor assembles into the pump as before (follow the book). If you live in a hot climate, or if the engine tends to run hot, this is a good mod.

Somewhere along the way, Lotus 'metricated'. The early impellor has a 1/2" bore, and later ones have a 12mm bore. And there's a matching bearing/shaft for each. Either will fit in any pump housing, just buy a bearing that matches the impellor you have. 910 impellors came both ways, so either specify one with a 1/2" bore to match a standard J-H bearing, or get the 12mm if that's all that's available, and order the right bearing to match.

Tim Engel

Last edited on 02-23-2016 03:57 am by Esprit2