Engine Woes Continued........

[mark030358]

Gents,
forgot to add apart from the low oil pressure cylinders 1&2 are not firing. I have sparks at the plugs but do not appear to have any fuel what is common on the carb. Checked both idle jets and theyare clear and adjusting the mixture has no effect. Any suggestions?
thanks
Mark
tooo tired to carry on and feeling very depressed

[types26/36]

Mark,
At what rpm are you quoting the oil pressure readings?
When you say 1 & 2 are not getting fuel, again are you talking @ idle or they do not fire @ any engine speed? if that was the case the engine would run very rough. If it is only on idle have you balanced the airflow between the two carbs?
Brian.

[steveww]

About 40 psi cold (15W40) is what my twinc gives but this is a more used engine. The twincs have lower oil pressure which is why there is a special oil/water temp gauge that only goes up to 60psi for the Elan.

[mark030358]

Brian/Steve, thanks for the replies.

Firstly the carbs. Forgot to say thay are Dellortos which have been fully cleaned and overhauled.

As this was the first time the engine has ran the revs were kept below 3000rpm, mostly 1500 to 2500 with the odd excursion to 3000, and yes the engine is running very rough (shakes like hell). The miss fires appear to be all the way up the rev range. It appears as if there is no fuel coming out of the carbs. Idle jets, passages, mixture adjustment screw etc are all clean (I can blow air through them and watch the petrol bubble in the float chamber).

I am assuming that as the engine is under no load that the only jets being used are the idle/progression circuits?

The fuel level "looks" ok in the bowls and I compared it to the other carb which appears to be working fine (maybe a tad lower level in the faulty one). The float heights/gaps (when hung vertically with gasket appeared to be 11 to 12 mm on each carb I am not sure how I would get 14.5mm??) were almost identical on each carb.

The plugs are sparking so I dont believe thats the problem.

I did set up the synchronisation of the carbs but will do it again.

Any thoughts...
Cheers
Mark

[tdafforn]

Firstly, Oil pressure on my twinc is 40lbs..
Secondly, have you tried opening the cold start on the dellorto a little. If it smooths out the non-firing cylinder then that would confirm something up in the other parts of the carb at least.
Tim

[types26/36]

Mark,
I dont think you have to worry about the oil pressure at this stage, this 1 & 2 not working at all seems odd, ..............stupid question but you DO have the plug leads on the correct cylinders dont you?
Maybe a compression check is in order, you didn't bend any valves setting the cams timing?............just going to basics!
Brian.

[mark030358]

Gents,
HAd a little go toda about sorting the none firing cylinders. Reset all the linkages and thay are now as good as they will ever be. Started the engine after crankingit two or three times and it ran as sweet as a nut..........for about a minute. Then progressivley got worse with nos 1&2 cylinders not firing. So pulled the top of the carb off and yep fuel in the bowl. However, the float distance when measured from the vertical (with gasket) was about 11 to 12 mm not 14.5 to 15mm. So my questions are (having never adjusted float heights):-

Do I set the gap to 14/15mm and at the same time ensure that this closes the needle valve?

Would such a small difference in heights cause the mis fire on both cylinders?

Am I correct in thinking this increase in distance will give me LESS fuel in the bowl?

ANyway, all help well received and is there something else I'm missing

[john.p.clegg]

Try swapping plugs between 1 and 2 to 3 and 4(they could be fouled)
John

[matnrach]

Hi,
Is there a big difference in the plug colour/condition btween the pairs of cylinders?
This may tell you if there is a big difference in fuelling between them.

[types26/36]

I have never found that the float level is that critical although others insist it is, is the front carb flooding? if you suspect the float to be the problem try swapping the carb top from front carb to rear carb, they are interchangable.
Brian

[flyinggellyfish]

Just a thought regarding the misfire . Have you removed the vac take off for the headlamp vacum from the 'manifold' end ? If you remove this and tape over the brass union in the take off point on the 'manifold' and try . If the misfire goes you have a leak in the vacum pipe/vacum tank or vacum unit for the headlamps . If a large enough air leak is there this will cause a misfire . A very common problem which is overlooked . Same with the servo connection at no 3+4 but this is normally acompanied with large plummes of white smoke as it burns brake fluid from the servo !
Like Brian says go back to basics and check every thing , but sounds like a vac leak to me .

Rick

[mark030358]

Gents,
Some more information.

Swapped the carb tops and no change, misfire still apparent on both cylinders.

Blanked off Vac connections no change, misfire still apparent on both cylinders.

Timing spot on no change, misfire still apparent on both cylinders.

However, when I activate the choke on that carb the engine speed picks up and thouhts on this?

Going to buy a compression tester now will post feed back later, what should I expect for a new engine?

Any more things to check?

cheers Mark

[types26/36]

I would expect a compression reading of 150+psi with a cold engine, throttle full open.
Rick may have something with the vac leak, how are the "O rings" and alloy spacers (carb to manifold) those spacers tend to distort/crack.
With the engine idling I have sprayed "quick start" around the spacers to detect leaks, if the rpm changes you have a leak.
YES! I know its not the right thing to do! safety and all that blah! blah! blah! :
What ign system are you using, points, electronic?
I know you said you have spark but under compression pressure? have you checked the distributor cap, leads and plug caps for a high resistance?
Brian.

[matnrach]

Another question,
Does it run consistently clean for a short while when cold?

[mark030358]

Gents,
Some more stuff...........

Compression test showed all cylinders giving 200 psi with a compression test and no difference at all between them.

Plug leads check ok from dizzy cap to plug cap (5Kohms each)

Rotor arm contact xactly the same on each dizzy post.

Swapped plugs around no difference at all.

I thought it did run ok when cold but this morning it appeared not to (if it did what would you suspect?)

I am running an aldon ignitor system, sparks a nice blue colour when earthed.
(I am going to try points anyway to eliminate this)

I have tightened the mounting flanges and they have new o rings fitted, the metal flanges are not cracked or bent...still misfires

When the choke is applied the revs definatley increase and when the plugs of either cylinder are pulled off when the choke is applied then the revs definatley fall. Does this sound like the carb is U/S. I closed the mixture screws, removed the progression hole nut covers and blew down each hole with a pipe and got bubbles in the float chamber. Idle jets are clean and secure (size 50's) and there is no rubbish or grit in the fuel bowls.

Getting really frustrated with all this.....any more suggestions.

cheers
Mark