Dellorto Tick Over system.

[vincereynard]

No 1 cylinder is not firing at tick over. A Colourtune plugs shows a healthy spark but no "colour". Increase the revs and it appears.
Pulling No1 plug lead off has no effect.
Totally removing No1 mixture screw also has no effect.
Squirting "Easy Start" down the carb. trumpet has no effect! A squirt down the others causes it to stumble.

I am assuming there is a blockage somewhere? The mixture screw is an air bleed? Therefore where does the tick over mixture come from?

I compression tested No1 and got 200 PSI so I am discounting mechanical nastiness at the moment.

I know it can be done as it used to be "balance a coin on the cam cover" smooth!

The exhaust sounds like "hunting" with an occasional pop of a misfire.

[lotusfan]

Vince

Try a new set of plugs?

[john.p.clegg]

Blocked idle jet....they are TINY

take them all out and give them a good blow.

John

[john.p.clegg]

Edit
When I sold my Plus2 I spent about a week cleaning/re-fitting/tuning the Dellortos , learned a hell of a lot..never had I had the engine running as smooth , unfortunately all my notes/diagrams went with the car.

The fuel level is critical , but here's a help...

http://www.s262612653.websitehome.co.uk ... llorto.htm

John

[vincereynard]

Thanks for the replies. I've discounted fuel level as No2 is OK.

I'm wondering now if perhaps the spindle is a bit twisted? So No1 if fully closed and therefore has little suction. Some slight mechanical problem in the actual carb. 2 & 4 are similar in that No4 is the stronger.

Does that make sense? Open the throttle a touch and No1 springs to life (According to the Colourtune)
If I remove the idle jet and squirt carb cleaner down should it dribble out somewhere? (Check the drilling is clear.)

Time to honk them off (again!), put a light at the end and check the butterflies?

[JonB]

Vince

As you say, check the butterflies.

I have a copy of the Des Hammill carb book if you want to have a butcher's? I also have a flow meter...

Other thing about No. 1 is it feeds the vacuum system. If holed, you'd get a very weak mixture at tickover.

Jolly nice compression you have there!

[vincereynard]

Vince
As you say, check the butterflies.
I have a copy of the Des Hammill carb book if you want to have a butcher's? I also have a flow meter...
Other thing about No. 1 is it feeds the vacuum system. If holed, you'd get a very weak mixture at tickover.
Jolly nice compression you have there!

No cheapo vacuum light lifts on Toad thankfully.

Having said that it had worked loose and was only hand tight. That's why it refused to tick over under 1000 revs. Rather large air leak.

I have the book, thanks for the offer. I also have a Cartune (?) balancer, problem is with that with no separate
choke balancing air bleed on Cheapo Chunky carbs, it's a bit limited.

I've removed the carbs and I'm going to check No1 does actually suck! I cannot see how it can't, but .................

[JonB]

Now this will surprise you a bit, but I like the vacuum assisted pop-up headlights. Neat solution, even if they have drawbacks. I think I'm a bit lucky though, as my single pod looks like it's been replaced, and I have a good cross member that doesn't leak. I think they stay down for at least two days. Yeah, I know.. but they're part of the charm of the thing. Errm. Sort of!

Anyway, hope that sorts it - let us know how you get on! I'd suggest something like a fibre washer to help it seal and stay put, maybe with a smear of Wellseal?

[vincereynard]

Anyway, hope that sorts it - let us know how you get on! I'd suggest something like a fibre washer to help it seal and stay put, maybe with a smear of Wellseal?

It's a tapered plug, so no washers but there is wellseal on the threads.

It has only allowed the tickover to be lowered. Not cured the miss fire on No1.

[JonB]

Darn it. OK, butterfly next. Then idle jet?

[rgh0]

Checking both idle jet and butterfly position for no1 cylinder is a 5 minute job without removing the carbs i would do that first.

cheers
Rohan

[vincereynard]

Checking both idle jet and butterfly position for no1 cylinder is a 5 minute job without removing the carbs i would do that first.

cheers
Rohan

I've squirted carb cleaner down the side drilling in the idle jet hole and it came out of the idle mixture hole.
So I assume that is clear.

I've read about shining light down the barrels and comparing the light ring around the butterflies to check they are both equal? How do you check them without removing the cars?

They should just be covering the first of the progression holes?

[rgh0]

To check the butterfly position remove the plug above the butterfly to see the progression holes and the butterflies should be just covering the first hole and all should be even. Some Dellortos have a buttrefly bypass passage and adjusting screw that can be used to balance up slightly uneven butterfly positions but I dont think any of the original Dellortos on Elans or Plus 2 had this. At least my 73 +2 Plus did not but my 78 Esprit does.

To check the idle jets, remove the jets and check under a magnifying glass for blockages and fouling and look for any damage done by cleaning attempts in the past.

What you cant check readily externally is are the butterfly properly centered in the bores for this you need to remove the carbs and check. Shining a light down and looking for an even light ring around the closed butterfly is one way to do this. Using feeler gauges is another

cheers
Rohan

[William2]

Hi Vince, you may be interested to hear that a year or so back I had exactly this problem on my Dellorto DHLA40E carbs that I had totally stripped and rebuilt. Like you, it was on number 1 cylinder only with a good spark. I had to give in and take the car to Max over in Guildford. He spent 4 hours on it and came to the conclusion that there was a blockage somewhere in the idle jet galleries. I stripped the forward carb once again and blew compressed air down every orifice but still no joy.
Luckily on Ebay at that time a guy was advertising a fully rebuilt pair of 40s', ultrasonically cleaned, etc, etc. I bit the bullet, bought them and swapped all the jets over. Fitted them to the car and it ran like a watch with no issues at all.
The old carbs must of had a blockage somewhere in the idle circuit of no. 1 cylinder that just would not clear, even with an airline. It has certainly convinced me to drive the car throughout the year to keep fresh fuel running through the carbs to help prevent corrosion and other Ethanol related problems.

[vincereynard]

Rohan,

Thanks for that.

It would appear that the front carb, spindle is slightly bent as opening the throttle slightly exposes the No2 first progression but not No1. (Light shone down first progression holes.) 3 and 4 are OK.

Like you, it was on number 1 cylinder only with a good spark. I had to give in and take the car to Max over in Guildford. He spent 4 hours on it and came to the conclusion that there was a blockage somewhere in the idle jet galleries. I stripped the forward carb once again and blew compressed air down every orifice but still no joy.

I also spent some time blowing through the idle drillings (I hope). There is a small diagonal hole going off
the idle jet "tunnel" that connects to the adjustment screw. I stuck the thin carb. cleaner tube down the hole and it squirted out the other end. SO I hope it is clear! I can blow through the actual jet so that should be OK as well.

Tweak the spindle and fingers crossed!