Guigario S4 Hybrid

[hotrod1000]

Some time ago I talked of modifying my 84 turbo after the engine let go when a valve broke. The final result was an SE bottom end with an S4 head with modification to the head outlet to match up with the cars water system. The other special bits are a spacer in the end of the crank for the citoren input shaft and the inlet manifold has been opened up to the size of the S4 ports. The installation has gone resonably well although taken some time but setting up is proving trying and any thoughts would be welcome.

Im running the original Dellorto 40s as mentioned with the manifold matched to the S4 ports. The carbs have had a full overhaul during the rebuild. The ignition is the original Lucas Constant Energy with no changes, both carbs and distributor were working well on the old engine. I set the idle timing a 12btdc, it does actually run faster with more advance but not through the revs as this take the advance way past 30. The only other modification is an SJ Sportcars stainless exhaust.

The carbs have been balanced with a morgan carbtune although trying to get anything meaningful on the mixture adjustment proved unsuccesful. I also tried a colourtune but this was no better. The car idles fine and sitting in the garage revs ok with a small stumble off idle. It appears to misfire slightly all the time through the revs, off and on like a lack of fuel intermittently. On the road its terrible, misfiring and then pulling and particularly bad on up hills. I adjusted the pressure regulator and got some improvement but not enough. The pressure regulator did spring a leak and has been sealed to sort intially. Any thoughts on a plan of action.

The old short LC motor is for sale in the classifieds.

[grk]

Steve,

I suggest you take the car down to Steve Greenald at Road and Track in Rainham - Steve specialises in dyno tuning work but previously ran the Lotus Servicentre in Essex - he is a former Brian Hart guy (the now defunct F1 engine builder), Steve has extensive experience with these engines and put SE ngines in Guigarios many years back. You can call him on 07774 773824.

GARRY

[Dr.Hess]

A dyno would certainly be the way to tune it. But, lacking that, I would:

Take the car for a drive, let it warm up and nail it so that it is running rough, then kill the ignition while still rolling and it is running rough. Coast to the side of the road, pull a plug or all and look at the color. Tune the carbs (re-jet) as necessary. Black is too rich, white is too lean. Tan is just right.

My guess is that you are going to have to go richer on the jets with the new head which likely flows better than the old one. I am not going to begin to guess which of the jets/emulsion tubes/chokes to start with, letting a Delorto expert guess there. Also wouldn't hurt to pick up a book on tuning Delortos. Seems like I ran across some de-structions on tuning Delortos somewhere on the net. Might have a google.

Dr.Hess

[hotrod1000]

Thanks. At the moment the the plugs are all black except number three.

Ill try and book it in for a rolling road, at the moment taking it too essex is out of the question Ill try locally to start with, maybe even the factory?

[lotusguy]

Hi,

As mentioned, a Dyno will get you spot on. The current plug color - black indicates it's running rich, which is far better than lean, but still not ideal. Is this with new plugs? Idling or general running on/off bosst?

As you know, turbocharged carb'd cars have to contend with a split personality engine (on/off boost) and Lotus uses the fuel pressure to increase fuel flow when on boost- 3.5PSI off-boost, 5.0PSI on-boost. The fact that your plugs are black is somewhat inconsistent with a malfunctioning regulator.

I'm more inclined to think it may be ignition related. The 9XX engine loves lots of advance but no more than 32 degrees total. Try advancing your timing 1 or two more degrees and check results.
Happy Motoring! ...Jim'85TE

[hotrod1000]

Jim it runs splightly lumpy or misfiring even at idle, more so when fully warm. The misfire gets worse through the rev range and out on the road the more load the worse it gets. The plugs are new NGKs with two electrodes. As for the timimg at idle it will actually run faster with more advance but then misfires higher up the revs, 12 deg at idle seemed to give the best all round result.

At this stage it does seem more like a component problem rather than the jetting or timimg. I say that because the problem is intermittent and is even evident at idle when the main jets are not in play.

[mikelr]

Steve,

Sounds alot like you have a bad set of high tension leads, I know you said that they worked fine on the old motor, but that was before you yanked them off.

It wouldn't hurt to put a new set on to see if it at least cures your misfire problem.

Cheers,
Mike

[Dr.Hess]

Your 3 black plugs and 1 not black plug concerns me. The plugs should all be the same, preferably not black, of course, but they should be the same. Something is different there in #3. You didn't say when you pulled the plugs, at idle or after a run and killing it during the misfire?

Dr.Hess

[lotusguy]

mikelr said:

Steve, Sounds alot like you have a bad set of high tension leads, I know you said that they worked fine on the old motor, but that was before you yanked them off. It wouldn't hurt to put a new set on to see if it at least cures your misfire problem. Cheers, Mike

Hi,

I agree with Mike. Given all the work you've done, a new set of High-Tension leads will be sure that everything operates in top tune.

You can check the old set by using a DMM and testing for resistance. While I don't know your specific wire specs, a good rule of thumb would be to look for about 3k Ohms/linear foot resistance. If your reading is say +/- 15%, I'd replace them no matter.
Happy Motoring! ...Jim '85TE

[lotusguy]

Dr.Hess said:

Your 3 black plugs and 1 not black plug concerns me. The plugs should all be the same, preferably not black, of course, but they should be the same. Something is different there in #3. You didn't say when you pulled the plugs, at idle or after a run and killing it during the misfire? Dr.Hess

Doc,

HNY!! I suspect he's got a couple issues compounding themselves. As mentioned I believe that the ignition is suspect.

He should replace the HT leads, check the coil and dizzy air gap (also for play in the dizzy bearing which could allow the air gap to widen/narrow at various RPMs)

I also agree that there is a carb setting which is off. The Morgan CarbtuneII is a very basic instrument. And on delorto's, you're not looking for a specific value, just that all columns are equal.

Quick Primer: This assumes that all float heights are properly set and a good needle valve/seat is present. Connect CarbtuneII to each of the 4 barrel ports. Screw down all 4 mixture screws until closed (take care not to graunch the needles). Open each mixture screw 3.5 turns. Start car. With a warm engine, adjust idle speed screw to 1,000 rpm. Now check all 4 levels in the CTII. Adjust each mixture screw until the highest reading is achievable for that barrel, then proceed until all barrels are done (You will now have 4 unequal columns). If at any time the idle speed moves from 1,000rpm, adjust idle speed screw to compensate.

Now, open the air balance screw on the stronger of the two barrels for each carb until it matches it's weaker mate (you now have 2 pairs of equal columns, but unequal with each other usually). Be sure to maintain constant idle. Now adjusting the balance mechanism between the 2 carbs, turn the screw(s) until the stronger of the 2 is weakened to equal the other (you now have 4 equal columns). Re-check idle speed.

Be sure to allow 5-10 sec. between adjustments so the CTII meter can reflect the changes. Be sure the Otter Switch doesn't turn on the fans during this procedure as the idle will be interupted (Use a fan to cool the radiator or disconnect the Otter switch-less desireable.)

I think if this is done, you'll see a large improvement.
Happy Motoring! ...Jim'85TE

PS- forget the multi-electrode plugs, this is just a marketing gimmick and could actually impair performance by increasing resistance and making the coil work harder. Also, try going to a cooler plug the NGK BP7ES is the next cooler plug, if switching, watch for fluffy soot, indicating the plugs are too cold.

>> Edited by lotusguy on Wednesday 26th January 17:47

[judson]

I had similar issues when I brought my 910/912/907 hybrid back to life in my Jensen-Healey.

I would highly recommend investing in a timing light. Although my initial timing was 10^BTDC, the NEW Lucas 45DM I installed had a loose mounting plate which gave me VERY erratic timing above idle.

I also found a vacuum leak which resulted in #4 running VERY lean while 1-3 were running rich.

Have confidence in doing the big stuff right...it's just the little things now that are keeping you off the road.