Do I have a manifold air leak?!

[Olly the Ozbus]

...and where do I start my search :mrgreen:

Ello folks,

Bus has been running sweet all year but on my last big trip the old boy developed the following symptoms:

1: wandering idle (and sometimes so low it cuts out- although unable to adjust with the bypass screw)
2: cutting out when coming to a stop from high speed
3: pinking when descending steep hills on zero throttle
4: revs return very slowly to idle after blipping throttle
5: no longer able to adjust idle properly with the bypass screw

Just wondering if these are the symptoms of an airleak in the inlet manifold system as I've had a spraw of wd40 on the usual places (carb/manifold gasket, twinport rubber seals and manifold/head area) to see if the revs rise but they don't seem to.............I do have a servo but the leak doesn't seem to be at the manifold end or the non-return valve although I haven't checked at the servo end yet.

I wondered if it could be a problem with air leaking in past the bypass screw if the threads are worn- is this poss? Everything else (tappets, timing, carb tuning) should be fine but are there other things i should be looking for- I've seen mention of problems with the idle circuit in solex carbs so would it be worth blasting it with some carb cleaner down the top?!"

Ultimately some dellorto 36's are on the list but I'd like to get to the bottom of this in the mean time, especially if it has the tendency to run lean

Blimey, that is some rambling! Blame the vino and a long week but thanks oracle and hopefully I'll be getting my hands dirty this weekend :mrgreen:

ttfn

Olly

 

[67panel]

sounds like servo leak,blank off the manafold pipe to test.

 

[Olly the Ozbus]

Cheers mate, I'll check that- do you think it would be most likely to be the connection with the vac line (or a split in the line) or the servo itself.........? Also, what's the best way to blank off the manifold offtake-just a blocked off bit of tube? Thanks for your help

 

[Tristan71]

What type of inlet manifold gaskets do you have I had a similar problem with the grey card gaskets one had blown itself apart feel the manifolds to see if one is much hotter than the other ( inlet manifolds ) lol also you could always try reving it with the air filter off and putting your hand over the carb that can help a few things


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[Olly the Ozbus]

What type of inlet manifold gaskets do you have I had a similar problem with the grey card gaskets one had blown itself apart feel the manifolds to see if one is much hotter than the other ( inlet manifolds ) lol also you could always try reving it with the air filter off and putting your hand over the carb that can help a few things

Cheers, I'll check this too 8)

 

[ozziedog]

Where the pipe attaches to the inlet manifold, just take it off,if it`s old and crumbling that could be your issue. Whatever you block it off with,make sure it`s impossible for it to slip inside, something round and perhaps conical and smooth, rubbery if possible :shock: The perfect thing I found,, was a piece of silicone mastic that had gone off (cured) in the nozzle. Do your checks (run engine) then replace, if you go out for a drive REMEMBER A. your brakes will be a lot harder than you are used too :shock: , and B. make sure the pipe is secured somewhere and not just flopping about :mrgreen:

Ozziedog,,,,,,,,,,,,, :mrgreen:

 

[Olly the Ozbus]

Cheers Ozz, sounds good :mrgreen: Hopefully I'll be able to get some way to diagnosing on the drive so I don't have to put my chicken calf-muscles through hell

 

[ozziedog]

:lol: :lol: :lol: ^^^ :lol: :lol: :lol:

Ozziedog,,,,,,,,,,,,,, :mrgreen:

 

[71Westy]

Whilst your symptoms do sound like an air leak, one very simple check before you do all that - whip out the idle pilot jet and make sure it is clean. I had similar symptoms and changing the idle jet has made all the difference.

Nick

 

[ZedBed]

^ Too much air/not enough petrol - same symptoms indeed. Old timers trick - Try covering the carb throat gradually with a piece of card. If you have to cover a lot before it ticks over that represents a massive air leak, so more likely to be petrol blockage as 71westy suggests.

 

[ozziedog]

OOoohhhh he`s dead good that man there ^^^^^ :mrgreen:

Ozziedog,,,,,,,,,,, :mrgreen:

 

[67panel]

and dont forget to check air corrector cos if thats blocked no air will get in idle circuit(only found that out the other week )so jet can be clean and it still wont pull fuel.

 

[Olly the Ozbus]

Thanks all, just off to get some petrol so I don't use the teaspoonful in there on the driveway and I'll have a play :mrgreen: Forgot to mention that the timing at idle is also quite unstable (should be bang on with 123 dizzy) which I thought might be air-leak related but I'll check fuel and thangs too and try and nail this beetch- of all the camper-related foibles i find idle-related issues the beiggest ball-ache:msn4:

TTfn

Olly

 

[Olly the Ozbus]

Just checked and only one of the heat risers is hot.........would this just mean it could be blocked or would a leak at this gasket cause problemos?

Sorry for bombarding you with questions- I'm off to get greasy and I'll try and report back later :idea:

 

[Tristan71]

Could be I've used a metal coat hanger in a drill before to unblock them make sure one of the riser gaskets has a small hole and the other has a big hole also are your inlet manifold a similar temp


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[Olly the Ozbus]

Well, had a fiddle this afternoon and 67panel was spot on with leaky servo so cheers fella- t'was the first thing i checked properly too as I was a bit scared of taking the carb to bits on the street so it makes a pleasant change! Blanked it off and idle was dead smooth, throttle blips quickly and timing at idle is stable.

Soooooooo, doesn't seem to be much servicable on the servos so a new one is on the cards- ATE german ones are damn expensive but have seen you can fit brazilian ones if you modify the mounting bracket to accomdate the different drillings, which are about a third of the price..............had anyone got any idea of the quality of these?

Cheers oracle :mrgreen:

PS Tristan, the manifolds are the same temp so I think all is oK on that front- unblocking the heat riser goes onto the list of things to do- after doing the heat exchanger cables I've been meaning to do for 3 1/2 years !

 

[Tristan71]

It's good to hear you've found your problem mate


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[Trikky2]

In case you havnt done this already - before lashing out on a new servo just make sure its not the pipes that are leaking.

You can check this by blanking off at the servo end as opposed to the manifold end.

 

[Olly the Ozbus]

Good idea Trikky, I'll check that tonight if I get a chance to sneak out into the darkness :msn4: Noone seems to have the German servos and it'll probably have to be a Brazilian one, so if I can save myself the faff (and cash!) I'll be pleased as punch!

Cheers

 

[Olly the Ozbus]

In the excitement of not have a backfiring, farting bus I forgot to say that Trikky was spot on and it was in fact one of the sections of vac hose which had perished- so all sorted for a few quid- suweeeeeeeeeet :mrgreen:

Cheers all, great advice as always 8)