Yet another rough running problem

[Robbie693]

Here we go again...

The Plus 2 has developed another reluctance to rev. Like before it only occurs when the engine is hot (after maybe 20 minutes driving), but this time I have a choking up and misfiring above 3500 rpm. It will rev cleanly and go past 3500rpm on light throttle openings but if I use more than about half throttle I get this choking up thing happening.

It does it both when under load and also if just revving it out of gear.

Would I be correct in assuming it is a carburation problem rather than ignition as it is throttle position dependant?

As ever, help appreciated

Robbie

[elansprint71]

What type of carbs?
Is your timing set correctly

[AHM]

Float levels set correctly?

[Robbie693]

Sorry - should have mentioned that bit . Car has Dellorto's. Float levels are correct, or were when I set them less than 500 miles ago, but will check again tomorrow. Timing set to 12 deg btdc, max advance about 28 deg... I haven't checked the points gap but I presumed if the timing hadn't moved then the the gap hadn't either(?). Has a 43d4 Distributor in too.

Cheers

Robbie

[toomspj]

Sounds like ignition to me - unlikely to be fuel based on your description.

Assuming you have a well charged battery, I would be looking to the coil, distributor cap or rotor arm. In that order. it is asbsolutely calssic that hese items start misbehaving once they warm up.

P

[toomspj]

Having re-read your post, if you still have points, then i wwould put the condenser high on my list of suspects.
Paul

[twincamman]

We have problems here with junk fuel.It doesn't matter what brand or octain rating we use. The race cars won't start after each session ,wthout new plugsthe ?lan needs New plugs every few starts .The plugs foul with a slight black soot and they are done .so you may have to carry spare plugs as we do here. I wonder if the really hot summer weather has caused the oil barons to fool with the formula

[Robbie693]

Thanks Paul,

After some more testing and cleaning all the jets/carb filters out I am coming to the conclusion that this is a development of the problem I had last year, documented in this marathon thread - http://www.lotuselan.net/forums/elan-f15/running-getting-worse-t22355.html.

I'm not expecting everyone to plough through all 5 pages but the conclusion I came to was, after replacing the condensor and points, that the coil was getting too hot. I ended up wrapping it in heat shielding tape as an experiment and the problem went away. For a bit.

When it returned I figured I had cooked the coil so I bought a new one a couple of months ago and made a heat shield to cover the bottom hose. Unfortunately this didn't work, neither did re-wrapping the new coil. I've put the old coil back (two old ones actually) but no joy there either.

I've just bought some BP7ES plugs to see if a cooler plug works (using BPR6ES up till now). Thoughts?

I am also wondering if the Lucas Sport coil(s) I have are too high an output and maybe I should try a standard one. Is this plausible or am I clutching at straws?

Ed - no chance of really hot summer weather here - it has P***ed down since March!

Cheers

Robbie

[George4th]

Robbie
My old +2 was set up and run really well on ......
Dellortos with 35 horizontal pump jets, rest as standard
Lucas Sports Coil in standard location
Timing 10 degrees BTDC
BP6ES Plugs
71 degree thermostat with modern Kenlowe fan switched (revotec) to come on at 78 degrees
Lumention ignition.

The only thing I use to notice is when the car did run slightly hot (85 to 90 so not that much hotter) , it did run slightly rougher , my trick was to keep the car running cool and it seemed to like it, so it could be a temperature thing?

George (4th)

[bast0n]

Robbie

When it returned I figured I had cooked the coil so I bought a new one a couple of months ago and made a heat shield to cover the bottom hose. Unfortunately this didn't work, neither did re-wrapping the new coil. I've put the old coil back (two old ones actually) but no joy there either.

I have had three coil failures over time and have sorted the problem - I think brought on by overheating - by mounting the coil above and to the right of my feet. Simple job of just extending all the leads.

Hope that this helps.

[Matt Elan]

Have you changed the plugs? apparently according to my motorcyling chums there are pattern NGKs out there which fail, and your issue sounds like plugs to me. Try using a different brand, or get some NGKs from a reputable source. That would be my first port of call with any missfire....

[gjz30075]

Does your distributor cap have the aluminum contacts? If so, they're likely causing part of the problem. Try to find one with the brass contacts or count of often replacing the aluminum contact ones.

Greg Z

[Robbie693]

Thanks chaps,

George - yes it does run on the warm side, 85-95 deg, but the fan always keeps it in check, sort of.

David - I have seen in a few other posts that you moved the coil, I am considering that as a test but I don't think I have a coil failure as such - the new one was exactly the same out of the box - but possibly a hot environment...

Matt - Yes I just bought some new plugs, Halfords only had NGK's unfortunately, but they are a cooler grade so will give them a go this weekend.

Greg - The distributor cap was my next port of call, it does indeed have aluminium contacts. I have read on here about some having problems with certain caps even brand new so am trying to find a supplier of good ones if anyone has any suggestions? Last one was from Paul Matty but I'd like to get one with brass contacts; hopefully they are not all made in the same Chinese factory! I have a 43D4 distributor by the way

Cheers all

Robbie

[George4th]

George - yes it does run on the warm side, 85-95 deg, but the fan always keeps it in check, sort of.

Why don't you wire a temporary manual override on the fan and switch it on early and see whether it runs better. I presume you are running a 74 degree theromostat?
I think some of these problems are because the standard otter switch switches on at about 92 degrees.
I don't beleive a twincam likes running hot at all. It will run but it doesn't run as cleanly as it does at 75 to 85 degrees

Good luck with the adjustments this weekend

George (4th)

[Andy8421]

Back when I was a young man, the only time you changed a rotor arm was when you trod on it.

At a recent track day, I went through 3 rotor arms, burning through from the rivet to the top of the distributor spindle. I have also suffered from a spate of distributor cap failures where the distributor cap became conductive at high temperature.

It seems that the pattern parts available for ignition systems are crap these days. Try replacing both cap and rotor arm, but don't assume that if it starts running rough again that the replacements haven't failed as well.

Good luck.