Dellorto 36 idle mixture screw not working?

[dubdubz]

Anyone a real dell expert/guru?

I need your help - I'm stumped

from a thread I have running over on vzi....

I have an issue and wondered what you would consider is causing it....

recap - Dell 36's on 1745.

Trying to set best idle, one of the adjuster screws doesn't do anything.
I have put 52 idles in and have set all the others but no.2 cyl won't stumble when screwing the adjuster screw in. It seems the adjuster does nothing???

I do remember I had this before and cleaned the carb ...took all the jets out and blew out with compressed air.


In fact I can screw it all the way in and the idle doesn't change.

I have the mains removed....[having them in doesn't change it as I'm only trying to set the idle]

not sure what to do with it, any suggestions.....wondered if I should move the mixture screw to another cylinder and see if the fault moves indicating a dodgy mixture screw?

many thanks

Darren

==================

then after suggestion of cleaning stuff out I posted

==================

I have had both carbs stripped down and blown everything out - or so I thought. The jets are new put in today, this cct was problematic before which makes me wonder about something else?

I'll try blowing it out anyway as a normal precaution, then I'll pull the mixture screws on that carb and compare

==============

so I put the carb back on today, and it is pretty much the same so I'm stumped

the screw still doesn't do much , it seems to have to be turned out further than the others and it doesn't seem as responsive.

for eg

800 revs, turn the no.4 mixture in 1/4 turn wait, 1/4 turn etc then the revs drop as expected slight stumble, turn back out..revs pickup. Also if the plug lead is pulled the engine noise obviously changes.

Now on 2 it seems that you have to turn out a couple or 3 more turns, and then the pickup/stumble is slight, also I have pulled the lead on 2 and the noise doesn't change as much or at all, until the idle mix is what I would consider much further than the rest?

So I think that I may still have a blocked passageway still on that idle, the only thing I haven't yet checked is the compression [ the top end is all new ]
I don't want to poke anything in there but what is the best way to flush the bottom hole out?

any suggestions? how or what is best to blow/poke out the idle passageway as I'm thinking this is blocked still?
I am also going to do a compression check just in case the deck height spacer could be allowing blowby?

 

[Trikky2]

It sounds to me more like you may have an air leak on the inlet manifold, either between the carb and manifold or between the manifold and the head, which is affecting No.2 cylinder.

However, before dismantling anything its wise to check the valve clearances and the spark to No.2 are correct. Then use a compression guage to check in case you have low compression in No.2 due to maybe a leaking/burnt valve.

 

[dubdubz]

thanks trikky for replying.

the heads are new and have a 3 angle valve job, they held petrol whilst I measured cc for cr calcs.

I can actually remove the spark plug from cyl2 and the engine doesn't noticeably change - although it doesn't sound like it's on 3 cylinder either oddly. there is a spark and quite fat one present. I have already swapped the idle mixture jets around, the idle jets and the spark plugs.

I have removed the carb again as I just want to torture myself . I'll make sure the idle cct passes the same air on both barrels [ nothing scientific just listening ]

I may try the compression test to double check, but again the only real way I'd have thought is the barrel/head/spacer [it's a stroker] might be leaking but I'd have thought I'd hear that.

I'm going to [ seeing as it's now off ]

recheck the carb and jets etc, recheck the fit of the dellorto gaskets again checking for any signs.
then I'm going to move the carb to the other side and see if the fault moves or not [this is assuming nothing is found on the prev stage]
I'll also [in the morning now] recheck the valves

Trikky would I see anything on a gasket if the air has been leaking in.........

 

[Slammed]

I had this problem, it was a leaky carb to manifold gasket

 

[dubdubz]

can't see if can be the jets - I now realise that the idle jet hole/seat is massive, there is no obstruction in the carb whatsoever.

both blow air the same and the idle mix screws feel the same when air passed through.

so I'm going to see if my compression gauge does fit as the heads I have have ngk thin but long reach plugs - there is only 2 sizes of plug thread isn't there???

I do hope it's not the compression - please let it not be the compression - wheres the pray for me smiley!!

wish me luck..............

 

[K@rlos]

I had this problem, it was a leaky carb to manifold gasket

These buggers caused me loads of headaches with my Webers :evil:

 

[dubdubz]

I had this problem, it was a leaky carb to manifold gasket

These buggers caused me loads of headaches with my Webers :evil:

mmm - going to double triple check the valve clearances tonight, as I may have got that wrong or perhaps too tight. I have ordered an adapter for my compression tester as the fancy smancy heads I have are 12mm spark plugs:roll:

I might order up some o rings anyway so pehaps should invest in some new gaskets, although they are gen dellorto and card, I do have the bakelite spacers too so I had better check that gasket aswell.....

just for my sanity- blowby on a head - you'd hear this surely???

I can see an engine removal in my future :lol:

 

[K@rlos]

I had this problem, it was a leaky carb to manifold gasket

These buggers caused me loads of headaches with my Webers :evil:

mmm - going to double triple check the valve clearances tonight, as I may have got that wrong or perhaps too tight. I have ordered an adapter for my compression tester as the fancy smancy heads I have are 12mm spark plugs:roll:

I might order up some o rings anyway so pehaps should invest in some new gaskets, although they are gen dellorto and card, I do have the bakelite spacers too so I had better check that gasket aswell.....

just for my sanity- blowby on a head - you'd hear this surely???

I can see an engine removal in my future :lol:

Yes you would hear it if it was blowing at the head, sounds like a leaky exhaust system but louder.

 

[Trikky2]

If the gasket under the carb or between the head and manifold leaks its not always easy to see though it can sometimes be detected by spaying wd40 on the joins to see if the engine speed changes or by listening with a stethoscope. (or a bit of tube in your ear :lol

Your right - swapping the carbs left to right will give you a definite answer as to whether the problem is in the carbs or not. (but its a lot of hassle, rather delicate and I would not recommend doing this unless you have exhausted all other possibilities)

Please let me know what you find.

ps. I'm not familiar with heads that use undersize sparkplugs - what heads are they?

 

[dubdubz]

ok this is the plan [possibly flawed]

I'm going to physically check TDC is that as the carb is off that side, and will be easy to do, just in case the static timing is out somehow. I intend to then check and set the valve clearances to be doubly sure.

The issue with swapping the carbs over dawned on me - I'd have to strip the throttle connections of the spindles and swap these to the other ends of the carbs, something which might induce further complications [has the potential to]

seriously I have looked into the carb and the holes that feed the mains and then onto the seat of the idle are quite big, as in the order of 3-4mm id I would say, so it just can't be that. The idle mix screws and the seats both look clear and nothing looks different from one barrel to the next.

Oddly that cylinder takes longer for the exhaust to get hot, noticeably so, and the plug is still quite sooty, the others are a bit dark but a definite different shade. I'm not sure this is relevant or not really?

I'm now also wondering that I may have set the deck height is a 'redneck' way and whilst can work ok, can lead to blowby and isn't really that way to do it. I have shims at both ends of the barrel to get the height. It's just not the best way - so I may aswell go through the engine again - rectifying that problem and checking the top end stuff whilst I go.

Of course if the valve timing is the reason, then I'll wait a while to rectify my deck height solution!

Trikky the heads are these
http://www.drdracingheads.com/catalog/product_info.php?cPath=33_34&products_id=162" onclick="window.open(this.href);return false;

slightly cleaned up and with reasonable size valves, so sort of super stock :lol:, they were loads cheaper than std 1600 tp head when I bought them.

 

[Trikky2]

Ah - interesting - I hadnt seen those heads before. Thanks.

The plug being more sooty would indicate the mixture is too rich. If this wont adjust out using the screw then you will have to check the idle jet itself. Either its too big or it might simply be loose in the carb body.

If the idle jet checks out ok then the next suspect would be float level - if its too high, due to incorrect adjustment or leaking needle valve (due to a fault or excessive fuel pressure) then the excess fuel will dribble out and overflow into the engine. A small amount of seepage like this will not be noticeable when the throttle is opened up a bit - like when your driving - but at tickover it will run way too rich and will negate your efforts to set the mixture screw.

 

[dubdubz]

if the float was wrong - wouldn't this affect both barrels on the carb?

I've checked the valves and there wasn't anything obvious - the only thing that looks a bit iffy is the gasket on the head to manifold - its starting to de laminate, accelerated by me taking it off to inspect it.

don't you see excess fuel when that happens?

I'll order some more gaskets - can't you use cereal packets?

 

[Trikky2]

Excess float level would affect both barrels if its a lot out but may affect only one if its only slightly high (due to the design and angle of the carb).

Your right, you would be able to see the excess fuel using a mirror and a bright light. Anothe clue is to use the "bit of tube in the ear trick" and listen to each carb throat at tickover. If one is running rich then you will hear it because it will sound "spitty" compared to the others.

Its hard to diagnose this kind of thing at a distance because, for instance, the sootyness of the plug you describe could be due to rich mixture or due to that cylinder not firing correctly and without seeing, touching and smelling the sparkplug its not possible to tell - but I'm doing my best for you

If you suspect the gasket then try spraying it with wd40 while its ticking over - if theres a leak the wd40 will get sucked in and will briefly change the way the engine runs.

You can use cereal packets yes - the area does not normally get hot enough to burn cardboard.

 

[dubdubz]

Excess float level would affect both barrels if its a lot out but may affect only one if its only slightly high (due to the design and angle of the carb).

Your right, you would be able to see the excess fuel using a mirror and a bright light. Anothe clue is to use the "bit of tube in the ear trick" and listen to each carb throat at tickover. If one is running rich then you will hear it because it will sound "spitty" compared to the others.

Its hard to diagnose this kind of thing at a distance because, for instance, the sootyness of the plug you describe could be due to rich mixture or due to that cylinder not firing correctly and without seeing, touching and smelling the sparkplug its not possible to tell - but I'm doing my best for you

If you suspect the gasket then try spraying it with wd40 while its ticking over - if theres a leak the wd40 will get sucked in and will briefly change the way the engine runs.

You can use cereal packets yes - the area does not normally get hot enough to burn cardboard.

I appreciate the 'sounding board' it does help put another slant on things as you can be too close sometimes.

I have reattached the carb to the original sides - I haven't yet swapped them over as the hassle of the throttle mechanisms is frankly putting me off.

I have reset the valves, nothing really amiss there and rechecked TDC - my only query on that is the fact no.1 has 2 tdc's - when no.3 is being fired,BUT if the line in the dizzy and the rotor meet and no.1 plug lead corresponds to that then thats right isn't it, no.1 was at tdc in this instance and also of course when the rotor was pointing to no.3 cap position as you would expect.

Now some extra info

the engine ran perfectly before - really sweet. I had to borrow the heads, so I basically installed the new heads, setting the deckheight again as they were slightly different.
I added the bakelite gaskets to the dells and then the engine did nothing for about a year until I put it in my import and the problems I am now having.

So I think it has to be carb removal related - ie gaskets, the shims used to set the deck height are blowing by on one cyl, I may have a stuck ring I suppose.??

anyway I've used a cornflake packet and slight smear of grease, cleaned plugs on that side, and will try it tonight.

if it still mis behaves then I'm in 2 minds to swap the carbs over [ when I'm 80% sure it's not carb related ] or strip the engine down. I suppose the carbs if swapped makes no difference , then they can remain on the new sides and I've only lost my spare time!

thanks again

 

[Slammed]

Am I right in thinking if you are getting piston blowby the case will be pressurised, forcing oil out of the bottom pulley? Might be worth a quick look...

 

[Trikky2]

Re the TDC - if it were on the wrong cylinder the engine would not start.

Its very unlikely to be timing if only one of the four cylinders is not firing correctly. It can only be the power of the spark/the plug lead/supressor cap or the plug itself and you say you have already checked all of those.

That only leaves a carb fault, a gasket fault or a compression problem.

A stuck ring or a blow on the barrel to head seal (which would be audible) would both show up on a compression test - and, if your reasonably sensitive, you could also detect it when turning the engine over by hand, since you would feel theres less compression and hear the air escape as the suspect cylinder went onto its compression stroke.

An incorrectly seated oil control ring would cause fouling/sooty plug and misfiring but only after a while - initially, with a clean plug, it would not cause a problem.

You say it ran fine before - was that with these same carbs? If so, why did you add the bakalite gaskets and could one of them be the cause maybe?

All that said - I thought i would mention that I have come across a few twin ports with these and weber carbs where one mixture screw is significantly less responsive than the other three in setting up - including my own IDF 40's. However, by taking the mix screw to max and min of engine speed variation and choosing the mid point, these engines run fine and smooth. Subsequent plug removal on servicing has shown the mix to be correct. So what I am saying is if the engine runs fine then it should be OK.

The worrying thing in your case is that you say taking the plug lead off that one cylinder does not have the same effect as removing one of the other three - thats the worrying part of this problem.

Looking forward to hear what you find on the next test.

 

[dubdubz]

Am I right in thinking if you are getting piston blowby the case will be pressurised, forcing oil out of the bottom pulley? Might be worth a quick look...

If the shim/spacer I incorrectly used to get the deck height correct [ I should have shimmed the barrel base only ] is leaking it's at the head end.
It could be the head of course, just finishing off a cuppa and I'll pop out and see where we are . I cannot remember buying the head/manifold gasket so it may be the original kit one - it is a dark grey fibre/card one. It was quite easily split along it's width into thinner slices, so maybe this had a way through?

Trikky the bakelite was just a fuel evaporation deal, also both sides have got them and it's only one cylinder that's allegedly got issues?
The spark seems quite healthy it is fairly fat and will jump 5mm easily, it is just a bit weird. The weird thing is it doesn't really sound like it is on 3 cylinders. I'm convinced it's something so silly and it'll be a massive laugh
I also think the plug colour may a red herring as the mixture has been set and reset, sure that idle wasn't seated at one point due to the o-ring so it would have been running rich.

I might swap the carbs over yet - it's the obvious thing to do but seems quite a lot of work.

Last thing can you run without rocker covers - it may be worth seeing the rocker travel is consistent with the other cylinder on that side?

 

[dubdubz]

mini update - which I'm sure is key?

if I block off the velocity stack on cyl 2 [dodgy one] the engine note doesn't really drop much - no where near as much as say no4. Also when I rev it now it sounds like it's on 3, it sounds a bit lumpy at idle but nothing drastic, at 1200rpm it def sounds like it's missing a bit.

So can I cornflake packet the carb to manifold, as I currently have
>manifold,thick almost fibre gasket, bakelite thingy, thick gasket and then carb.

I'm off to the shed to find some small hose to listen for a air leak, will it be that obvious?

 

[67panel]

if plugs fouled fit new as you wont get allthe carbon off and spark will track,had plug fouling prob with race beetle and was down to weak spark,but it looked ok when testing.

 

[dubdubz]

if plugs fouled fit new as you wont get allthe carbon off and spark will track,had plug fouling prob with race beetle and was down to weak spark,but it looked ok when testing.

these plugs are odd size so I do need to order some more in, but I'll clean these up for today - the plugs looked all the same today tbh

it doesn't appear to be compression related either [thankfully]

#1 150psi
#2 150psi
#3 150psi
#4 150psi

cutting cardboard gaskets - I'm opting for a light smear of gen purpose grease...

also Mucky mentioned flatting the manifolds, mine did need it, they are flat now.

Lunch then off to put the carbs back on