Lotus Elan

Breaking up over 5500rpm

PostPost by: collins_dan » Mon Aug 24, 2009 2:26 pm

I was autocrossing this weekend and didn't do the marque proud. The weak link is the dummy behind the wheel. The only issue I had with the care was on a couple of passes where the rpms got over 5500-6500rpms, it started to break up and not ignite smoothly. The engine was a bit hot, but not too bad. I'm wondering if the coil got too hot. Any thoughts appreciated. Dan
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PostPost by: paddy » Mon Aug 24, 2009 2:50 pm

Is the timing too advanced?

Or is the dwell angle out of spec?

Also, are you sure it isn't fuel starvation?

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PostPost by: Frank Howard » Mon Aug 24, 2009 3:16 pm

Dan,

Do you have a limiter on your distributor rotor? If so, it could be adjustable as it uses two springs whose mounting points can be designated by you. Either that or the springs can be substituted with ones that have more or less tension. It's designed to cut out the ignition if the revs get too high.
Last edited by Frank Howard on Mon Aug 24, 2009 6:50 pm, edited 1 time in total.
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PostPost by: RotoFlexible » Mon Aug 24, 2009 3:46 pm

I don't recall if you have electronic ignition (or which kind), but the gentleman who reconditioned my distributor reported that my Pertronix was inconsistent over 3K rpm. My engine builder has seen similar problems with other Pertronix/Aldon units. I am now back to good old points, at least for the time being.
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PostPost by: collins_dan » Mon Aug 24, 2009 6:17 pm

I have Petronix ignitor and flamethrower coil, and am about to put in petronix's rev limiter. I've been over 5500 before and not had an issue. I've had the problem one other time, which was also when it was hot and engine compartment air circulation minimized to direct all air through radiator. Hot being around 190F. I have removed the blocking in front of the coil to improve air flow to coil. If this works, then I may cut hots in wheel well similar to the other side. I'm also wondering about timing being too advanced as the car gets hot at idle, which I seem to think others have suggested could be a function of too advanced timing. If the timing was too advanced, what other symptoms would I have? Thanks. Dan
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PostPost by: Frank Howard » Mon Aug 24, 2009 6:49 pm

Dan,

If you don't want to reveal whether or not you have a rev limiter on your distributor rotor, then I guess I can't help you.
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PostPost by: alaric » Mon Aug 24, 2009 9:12 pm

Hi. I would have thought too much ignition advance should lead to pinking at low revs under load, and power loss at high revs. Is that right?

I did wonder if fuel starvation might be the culprit if your thackary washers are too tight, or if your fuel pump is not keeping up with demand, poss due to spec / condition of the pump, an inline filter or inertial forces etc. I don't suppose that ties in with only seeing the problem at high temperatures though.

If the engine's always running hotter than it should, is your cooling system clear - the galleries inside the engine and in the rad?

All the best.

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PostPost by: collins_dan » Mon Aug 24, 2009 9:33 pm

I don't believe that there is a rev limiter on my distributor rotor, unless it was placed their prior to my ownership. What would I be looking for? I can tell you that I had the lumenition electronic ignition replaced with a petronix igniter and flamethrower coil when I bought the car 4 years ago as the lumenition didn't get along with the RVI tach. The petronix has never had any issues. I have a petronix digital rev limiter in a box on my workbench with the intention of installing it, but haven't installed it yet. I'm hoping that it will not have a problem with the RVI tach. Does anyone out there use a petronix digital rev limiter with a Smith's RVI tach?

I did have a fuel regulator installed when I had the engine rebuilt 2 years ago as the pump was operating at too high pressure for the strombergs, maybe that is set too low. What pressure should it be set at?

As to engine running hot, I think I've come to the conclusion that it is an inadequate fan, which I will be replacing with 2 tornado fans, like others have done.

Thanks, Dan
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PostPost by: Frank Howard » Tue Aug 25, 2009 12:24 am

[quote="collins_dan"]I don't believe that there is a rev limiter on my distributor rotor, unless it was placed their prior to my ownership. What would I be looking for?/quote]
Dan,

It's pretty obvious. If your rotor has any moving parts on it including the springs I mentioned, then you have a rev limiting rotor. If the rotor is one solid piece of plastic and brass with no moving parts, then you don't. You're going to have to take the cap off, pull the rotor out, and then take a look.
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PostPost by: collins_dan » Tue Aug 25, 2009 12:41 am

It's been awhile since I took it apart and I recall it being one simple piece, no springs..., but I'll check when I get back home.

I was reading some of the old posts on this subject and found this one: "The flame-thrower is a gimmick. Having more windings then necessary is dumb because the field collapses slower. This will cause a high rpm miss sooner then a lower voltage coil. The trick is have enough voltage to spark the flame kernal at the highest cylinder pressure but not so much that the coil can't recover and collaspe the field completely before it's energized again. A 25k coil is the perfect match for the stock twinkcam."

So it sounds like it could be coil related amongst other options. I will check to see if there is an old rev limiter on the rotor, check fuel pressure to ensure its between 1.25 and 2.5, check timing advance... a couple others that I've seen in the old posts: check spark plug leads and sparkplug gap (suggestion to use .020).

Thanks all, Dan
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PostPost by: paddy » Tue Aug 25, 2009 6:21 am

For what it's worth, I have a flamethrower and haven't had any problems with it.

Does the problem happen if you're stationary and try to rev the engine? Or only when you're accelerating hard? If you can make the problem occur when the engine isn't under load, I think that would rule out fuel starvation.

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PostPost by: collins_dan » Tue Aug 25, 2009 12:25 pm

I'll add that to my list of tests. Its happened twice on me, both times when the engine has been hot and under load. I don't think its anything with the Flamethrower either, other than as it is right now, it doesn't get much air, so when the engine gets hot, it gets hot. I'm seriously considering cutting holes in the right wheel well similar to the left side to introduce more air. Thanks, Dan
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PostPost by: miked » Tue Aug 25, 2009 12:32 pm

The Flame thrower coil voltage is above the rated SAE spec' of the old 23D4 Dizzy cap and rotor arm. It brokedown my caps and arms.

Perhaps you have a different dizzy with higher rated cap & arm insulation. Keith (type 26, I thinkl) posted lots on this subject.

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PostPost by: collins_dan » Tue Aug 25, 2009 3:30 pm

I saw the old posts about your troubles. I'm not sure what cap and rotor are on the car. They have been there since I've owned it and had no issues, so no reason to check. If you could remind me the kind of wear you were experiencing, I would appreciate it and will check for it. Thanks, Dan
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PostPost by: memini55 » Tue Aug 25, 2009 4:05 pm

Dan,

Since I replied to your other post and am autocrossing as well I will give you some thoughts also.
The rotor limiter is easy to spot as it is a different type of rotor and at the back end of the rotor there is a piece of metal which will have two springs attached and as the rotor speed reaches high rpm the metal swings out and grounds out the distributor cap. My guess is that is not the issue as they work at that speed all the time and most have been thrown out as they cost too much.

The fuel presure could be an issue but not likely if only when running hot. I run a 3-4 lbs electric pump and have a regulator up at the carbs. I am running webers which don't like too high of presure. I started with 1.5lbs and found that the webers would break up under hard load so raised to 2lbs and it seems to work well. One other thought if you are running webers you might consider the airflow also. I am using small foam shocks on each barrel and if I have too much oil on them the carbs will starve for air at high revs. The easy test for this is to do a short run with and without filter.

The last thought is to look at the coil as I too have heard of issues with the higher output coils with the lucas distributors.

One other thought would be to look at the type of spark plugs you are running. Hard runs at full throttle and high revs need a different plug than driving on the street. I am using NGK BR8ES if my memory is right. They tent to run a little cold until the engine is fully warmed up but work great at the time.

Hope something helps.
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